SEC Filing—Ultragenyx Pharmaceutical Inc.

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S-8

As filed with the Securities and Exchange Commission on November 7, 2017

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-8

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Ultragenyx Pharmaceutical Inc.

(Exact name of Registrant as specified in its charter)


Delaware		27-2546083
(State or other jurisdiction of incorporation or organization)		(I.R.S. Employer Identification Number)

60 Leveroni Court Novato, CA 94949
(Address of Principal Executive Offices, including Zip Code)

Dimension Therapeutics, Inc. 2015 Stock Option and Incentive Plan

Dimension Therapeutics, Inc. 2013 Stock Plan

(Full title of the plans)

Emil D. Kakkis, M.D., Ph.D.

President and Chief Executive Officer

Ultragenyx Pharmaceutical Inc.

60 Leveroni Court

Novato, CA 94949

(415) 483-8800

(Name, address and telephone number, including area code, of agent for service)

with copies to:

Karah Parschauer

Executive Vice President and General Counsel

Ultragenyx Pharmaceutical Inc.

60 Leveroni Court

Novato, CA 94949

Telephone: (415) 483-8800

Facsimile: (415) 483-8810

Ryan A. Murr, Esq.

Sean Sullivan, Esq.

Gibson, Dunn & Crutcher LLP

555 Mission Street, Suite 3000

San Francisco, CA 94105-0921

Telephone: (415) 393-8200

Facsimile: (415) 393-8306

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the Registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

CALCULATION OF REGISTRATION FEE



Title of securities to be registered	Amount to be registered (1)	Proposed maximum offering price per share (2)	Proposed maximum aggregate offering price	Amount of registration fee
Common Stock, $0.001 par value per share (“Common Stock”)	639,897	$27.97	$17,897,919.09	$2,228.29

(1)

Pursuant to Rule 416 under the Securities Act of 1933, as amended (the “Securities Act”), this registration statement shall also cover any additional shares of Common Stock that become issuable under the plans by reason of any stock dividend, stock split, recapitalization or any other similar transaction effected without the receipt of consideration which would result in an increase in the number of outstanding shares of Common Stock.

(2)	Pursuant to Securities Act Rule 457(h)(1), the filing fee is calculated with respect to outstanding options, based on the price at which the options may be exercised.

EXPLANATORY NOTE

This Registration Statement on Form S-8 is filed by Ultragenyx Pharmaceutical Inc. (the “Company” or the “Registrant”) and relates to shares of common stock, par value $0.001 per share, of the Registrant (the “Common Stock”) to be offered pursuant to the Company’s assumption of the Dimension Therapeutics, Inc. 2015 Stock Option and Incentive Plan and the Dimension Therapeutics, Inc. 2013 Stock Plan, as amended (together, the “Plans”), and the outstanding stock options thereunder.

PART I

INFORMATION REQUIRED IN THE 10(a) PROSPECTUS

The information called for in Part I of Form S-8 is not being filed with or included in this Form S-8 (by incorporation by reference or otherwise) in accordance with the rules and regulations of the Securities and Exchange Commission (the “Commission”).

PART II

INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference

The following documents filed with the Commission are incorporated by reference in this Registration Statement:

(a)	the Company’s Annual Report on Form 10-K for the year ended December 31, 2016, filed on February 17, 2017.

(b)	all other reports filed by the Company with the Commission pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934 (the “Exchange Act”) since December 31, 2016.

(c)

the description of the Company’s Common Stock, $0.001 par value per share, contained in the Company’s Registration Statement on Form 8-A, filed with the Commission pursuant to Section 12 of the Exchange Act, on January 24, 2014, and any other amendments or reports filed for the purpose of updating such description.

All documents subsequently filed by the Company pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, prior to the filing of a post-effective amendment which indicates that all securities offered have been sold or which deregisters all securities then remaining unsold, shall be deemed to be incorporated by reference in this Registration Statement and to be part of this Registration Statement from their respective dates of filing; except as to any portion of any current report furnished under Items 2.02 or 7.01 of Form 8-K, including any exhibits included with such Items, that is not deemed filed under such provisions.

Any statement contained in a document incorporated or deemed to be incorporated by reference in this Registration Statement is deemed to be modified or superseded for purposes of this Registration Statement to the extent that a statement contained in this Registration Statement or in any subsequently filed document which also is or is deemed to be incorporated by reference in this Registration Statement modifies or supersedes such statement. Any such statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this Registration Statement.

The Registrant’s Exchange Act file number with the Commission is 001-36276.

Item 4. Description of Securities

Not applicable.

Item 5. Interests of Named Experts and Counsel

Not applicable.

Item 6. Indemnification of Directors and Officers

Section 145(a) of the Delaware General Corporation Law provides, in general, that a corporation may indemnify any person who was or is a party or is threatened to be made a party to any threatened, pending or completed action, suit or proceeding, whether civil, criminal, administrative or investigative (other than an action by or in the right of the corporation), because he or she is or was a director, officer, employee or agent of the corporation, or is or was serving at the request of the corporation as a director, officer, employee or agent of another corporation, partnership, joint venture, trust or other enterprise, against expenses (including attorneys’ fees), judgments, fines and amounts paid in settlement actually and reasonably incurred by the person in connection with such action, suit or proceeding, if he or she acted in good faith and in a manner he or she reasonably believed to be in or not opposed to the best interests of the corporation and, with respect to any criminal action or proceeding, had no reasonable cause to believe his or her conduct was unlawful.

Section 145(b) of the Delaware General Corporation Law provides, in general, that a corporation may indemnify any person who was or is a party or is threatened to be made a party to any threatened, pending or completed action or suit by or in the right of the corporation to procure a judgment in its favor because the person is or was a director, officer, employee or agent of the corporation, or is or was serving at the request of the corporation as a director, officer, employee or agent of another corporation, partnership, joint venture, trust or other enterprise, against expenses (including attorneys’ fees) actually and reasonably incurred by the person in connection with the defense or settlement of such action or suit if he or she acted in good faith and in a manner he or she reasonably believed to be in or not opposed to the best interests of the corporation, except that no indemnification shall be made with respect to any claim, issue or matter as to which he or she shall have been adjudged to be liable to the corporation unless and only to the extent that the Court of Chancery or other adjudicating court determines that, despite the adjudication of liability but in view of all of the circumstances of the case, he or she is fairly and reasonably entitled to indemnity for such expenses which the Court of Chancery or other adjudicating court shall deem proper.

Section 145(g) of the Delaware General Corporation Law provides, in general, that a corporation may purchase and maintain insurance on behalf of any person who is or was a director, officer, employee or agent of the corporation, or is or was serving at the request of the corporation as a director, officer, employee or agent of another corporation, partnership, joint venture, trust or other enterprise against any liability asserted against such person and incurred by such person in any such capacity, or arising out of his or her status as such, whether or not the corporation would have the power to indemnify the person against such liability under Section 145 of the Delaware General Corporation Law.

Article VI of our amended and restated certificate of incorporation, or the Charter, provides that no director of our company shall be personally liable to us or our stockholders for monetary damages for any breach of fiduciary duty as a director, except for liability (1) for any breach of the director’s duty of loyalty to us or our stockholders, (2) for acts or omissions not in good faith or which involve intentional misconduct or a knowing violation of law, (3) in respect of unlawful dividend payments or stock redemptions or repurchases, or (4) for any transaction from which the director derived an improper personal benefit. In addition, our Charter provides that if the Delaware General Corporation Law is amended to authorize the further elimination or limitation of the liability of directors, then the liability of a director of our company shall be eliminated or limited to the fullest extent permitted by the Delaware General Corporation Law, as so amended.

Article VI of the Charter further provides that any repeal or modification of such article by our stockholders or amendment to the Delaware General Corporation Law will not adversely affect any right or protection existing at the time of such repeal or modification with respect to any acts or omissions occurring before such repeal or modification of a director serving at the time of such repeal or modification.

We have entered into indemnification agreements with each of our directors and our executive officers. These agreements provide that we will indemnify each of our directors and executive officers to the fullest extent permitted by law and the Charter.

We also maintain an insurance policy that covers certain liabilities of our directors and officers arising out of claims based on acts or omissions in their capacities as directors or officers.

Item 7. Exemption from Registration Claimed

Not applicable.

Item 8. Exhibits

See the Exhibit Index included in this registration statement, which is incorporated into this Item 8 herein by reference.

Item 9. Undertakings

(a)	The undersigned Registrant hereby undertakes:

(1) To file, during any period in which offers or sales are being made, a post-effective amendment to this registration statement:

(i) To include any prospectus required by Section 10(a)(3) of the Securities Act;

(ii) To reflect in the prospectus any facts or events arising after the effective date of the registration statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the registration statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of a prospectus filed with the Commission pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than a 20 percent change in the maximum aggregate offering price set forth in the “Calculation of Registration Fee” table in the effective registration statement; and

(iii) To include any material information with respect to the plan of distribution not previously disclosed in the registration statement or any material change to such information in the registration statement; provided, however, that paragraphs (a)(1)(i) and (a)(1)(ii) above shall not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the Commission by the Registrant pursuant to Section 13 or 15(d) of the Exchange Act that are incorporated by reference in the registration statement.

(2) That, for the purpose of determining any liability under the Securities Act, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(3) To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

(4) That, for the purpose of determining liability of the Registrant under the Securities Act to any purchaser in the initial distribution of the securities: the undersigned Registrant undertakes that in a primary offering of securities of the undersigned Registrant pursuant to this Registration Statement, regardless of the underwriting method used to sell the securities to the purchaser, if the securities are offered or sold to such purchaser by means of any of the following communications, the undersigned registrant will be a seller to the purchaser and will be considered to offer or sell such securities to such purchaser: (i) any preliminary prospectus or prospectus of the undersigned Registrant relating to the offering required to be filed pursuant to Rule 424; (ii) any free writing prospectus relating to the offering prepared by or on behalf of the undersigned Registrant or used or referred to by the undersigned Registrant; (iii) the portion of any other free writing prospectus relating to the offering containing material information about the undersigned Registrant or its securities provided by or on behalf of the undersigned Registrant; and (iv) any other communication that is an offer in the offering made by the undersigned Registrant to the purchaser.

(b)

The undersigned Registrant hereby undertakes that, for purposes of determining any liability under the Securities Act, each filing of the Registrant’s annual report pursuant to Section 13(a) or 15(d) of the Exchange Act (and, where applicable, each filing of an employee benefit plan’s annual report pursuant to Section 15(d) of the Exchange Act) that is incorporated by reference in the registration statement shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(c)

Insofar as indemnification for liabilities arising under the Securities Act may be permitted to directors, officers and controlling persons of the Registrant pursuant to the foregoing provisions, or otherwise, the Registrant has been advised that in the opinion of the Commission such indemnification is against public policy as expressed in the Securities Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the Registrant of expenses incurred or paid by a director, officer or controlling person of the Registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the Registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act and will be governed by the final adjudication of such issue.

Exhibit Index

Incorporated by Reference

Exhibit
Number

Exhibit Description

Form

Date

Number

Filed
Herewith

4.1

Amended and Restated Certificate of Incorporation of Ultragenyx Pharmaceutical Inc.

8-K

2/5/2014

3.1

4.2

Amended and Restated Bylaws of Ultragenyx Pharmaceutical Inc.

8-K

2/5/2014

3.2

4.3

Form of Common Stock Certificate

S-1

11/8/2013

4.2

4.4

2015 Stock Option and Incentive Plan and forms of award agreements thereunder

4.5

2013 Stock Plan, as amended, and forms of award agreements thereunder

5.1

Opinion of Gibson, Dunn & Crutcher LLP

23.1

Consent of Independent Registered Public Accounting Firm

23.2

Consent of Gibson, Dunn & Crutcher LLP (included in Exhibit 5.1)

24.1

Power of Attorney (included on the signature page to this registration statement)

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Novato, State of California, on November 7, 2017.


ULTRAGENYX PHARMACEUTICAL INC.

By:		/s/ Emil D. Kakkis
		Emil D. Kakkis, M.D., Ph.D.
		President and Chief Executive Officer

POWER OF ATTORNEY

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below hereby constitutes and appoints each of Emil D. Kakkis, M.D., Ph.D. and Shalini Sharp, and each of them acting individually, as his or her true and lawful attorneys-in-fact and agents, each with full power of substitution and resubstitution in each of them singly, for him or her and in his or her name, place and stead, and in any and all capacities, to sign any and all amendments (including post-effective amendments) to this registration statement on Form S-8 of Ultragenyx Pharmaceutical Inc., and to file the same, with all exhibits thereto and other documents in connection therewith, with the Securities and Exchange Commission, granting to the attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in or about the premises, as full to all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that the attorneys-in-fact and agents or any of each of them or their substitutes may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, as amended, this registration statement has been signed by the following persons in the capacities and on the dates indicated.


Signature	Title	Date

/s/ Emil D. Kakkis Emil D. Kakkis, M.D., Ph.D.	Director, President and Chief Executive Officer (Principal Executive Officer)	November 7, 2017

/s/ Shalini Sharp Shalini Sharp	Executive Vice President, Chief Financial Officer (Principal Financial Officer)	November 7, 2017

/s/ Theodore Huizenga Theodore Huizenga	Corporate Controller (Principal Accounting Officer)	November 7, 2017

/s/ Daniel G. Welch Daniel G. Welch	Chairman of the Board	November 7, 2017

/s/ William Aliski William Aliski	Director	November 7, 2017

/s/ Deborah Dunsire Deborah Dunsire, M.D.	Director	November 7, 2017

/s/ Lars Ekman Lars Ekman, M.D., Ph.D.	Director	November 7, 2017

/s/ Matthew Fust Matthew Fust	Director	November 7, 2017

/s/ Michael Narachi Michael Narachi	Director	November 7, 2017

/s/ Clay Siegall Clay Siegall, Ph.D.	Director	November 7, 2017

EX-4.4

Exhibit 4.4

DIMENSION THERAPEUTICS, INC.

2015 STOCK OPTION AND INCENTIVE PLAN

SECTION 1. GENERAL PURPOSE OF THE PLAN; DEFINITIONS

The name of the plan is the Dimension Therapeutics, Inc. 2015 Stock Option and Incentive Plan (the “Plan”). The purpose of the Plan is to encourage and enable the officers, employees, Non-Employee Directors and Consultants of Dimension Therapeutics, Inc. (the “Company”) and its Subsidiaries upon whose judgment, initiative and efforts the Company largely depends for the successful conduct of its business to acquire a proprietary interest in the Company. It is anticipated that providing such persons with a direct stake in the Company’s welfare will assure a closer identification of their interests with those of the Company and its stockholders, thereby stimulating their efforts on the Company’s behalf and strengthening their desire to remain with the Company.

The following terms shall be defined as set forth below:

“Act” means the Securities Act of 1933, as amended, and the rules and regulations thereunder.

“Administrator” means either the Board or the compensation committee of the Board or a similar committee performing the functions of the compensation committee and which is comprised of not less than two Non-Employee Directors who are independent.

“Award” or “Awards,” except where referring to a particular category of grant under the Plan, shall include Incentive Stock Options, Non-Qualified Stock Options, Stock Appreciation Rights, Restricted Stock Units, Restricted Stock Awards, Unrestricted Stock Awards, Cash-Based Awards, Performance Share Awards and Dividend Equivalent Rights.

“Award Certificate” means a written or electronic document setting forth the terms and provisions applicable to an Award granted under the Plan. Each Award Certificate is subject to the terms and conditions of the Plan.

“Board” means the Board of Directors of the Company.

“Cash-Based Award” means an Award entitling the recipient to receive a cash-denominated payment.

“Code” means the Internal Revenue Code of 1986, as amended, and any successor Code, and related rules, regulations and interpretations.

“Consultant” means any natural person that provides bona fide services to the Company, and such services are not in connection with the offer or sale of securities in a capital-raising transaction and do not directly or indirectly promote or maintain a market for the Company’s securities.

“Covered Employee” means an employee who is a “Covered Employee” within the meaning of Section 162(m) of the Code.

“Dividend Equivalent Right” means an Award entitling the grantee to receive credits based on cash dividends that would have been paid on the shares of Stock specified in the Dividend Equivalent Right (or other award to which it relates) if such shares had been issued to and held by the grantee.

“Effective Date” means the date on which the Plan becomes effective as set forth in Section 22.

“Exchange Act” means the Securities Exchange Act of 1934, as amended, and the rules and regulations thereunder.

“Fair Market Value” of the Stock on any given date means the fair market value of the Stock determined in good faith by the Administrator; provided, however, that if the Stock is admitted to quotation on the National Association of Securities Dealers Automated Quotation System (“NASDAQ”), NASDAQ Global Market or another national securities exchange, the determination shall be made by reference to market quotations. If there are no market quotations for such date, the determination shall be made by reference to the last date preceding such date for which there are market quotations; provided further, however, that if the date for which Fair Market Value is determined is the first day when trading prices for the Stock are reported on a national securities exchange, the Fair Market Value shall be the “Price to the Public” (or equivalent) set forth on the cover page for the final prospectus relating to the Company’s Initial Public Offering.

“Incentive Stock Option” means any Stock Option designated and qualified as an “incentive stock option” as defined in Section 422 of the Code.

“Initial Public Offering” means the first underwritten, firm commitment public offering pursuant to an effective registration statement under the Act covering the offer and sale by the Company of its equity securities, or such other event as a result of or following which the Stock shall be publicly held.

“Non-Employee Director” means a member of the Board who is not also an employee of the Company or any Subsidiary.

“Non-Qualified Stock Option” means any Stock Option that is not an Incentive Stock Option.

“Option” or “Stock Option” means any option to purchase shares of Stock granted pursuant to Section 6.

“Performance-Based Award” means any Restricted Stock Award, Restricted Stock Units, Performance Share Award or Cash-Based Award granted to a Covered Employee that is intended to qualify as “performance-based compensation” under Section 162(m) of the Code and the regulations promulgated thereunder.

“Performance Criteria” means the criteria that the Administrator selects for purposes of establishing the Performance Goal or Performance Goals for an individual for a Performance Cycle. The Performance Criteria (which shall be applicable to the organizational level specified by the Administrator, including, but not limited to, the Company or a unit, division, group, or Subsidiary of the Company) that will be used to establish Performance Goals are limited to the following: total shareholder return; earnings before interest, taxes, depreciation and amortization; net income (loss) (either before or after interest, taxes, depreciation and/or amortization); changes in the market price of the Stock; economic value-added; development, clinical, regulatory or commercial milestones; funds from operations or similar measure; sales or revenue; acquisitions or strategic transactions; operating income (loss); cash flow (including, but not limited to, operating cash flow and free cash flow); return on capital, assets, equity, or investment; return on sales; gross or net profit levels; productivity; expense; margins; operating efficiency; customer satisfaction; working capital; earnings (loss) per share of Stock; sales or market shares and number of customers, any of which may be measured either in absolute terms or as compared to any incremental increase or as compared to results of a peer group. The Committee may appropriately adjust any evaluation performance under a Performance Criterion to exclude any of the following events that occurs during a Performance Cycle: (i) asset write-downs or impairments, (ii) litigation or claim judgments or settlements, (iii) the effect of changes in tax law, accounting principles or other such laws or provisions affecting reporting results, (iv) accruals for reorganizations and restructuring programs, and (v) any item of an unusual nature or of a type that indicates infrequency of occurrence, or both, including those described in the Financial Accounting Standards Board’s authoritative guidance and/or in management’s discussion and analysis of financial condition of operations appearing the Company’s annual report to stockholders for the applicable year.

“Performance Cycle” means one or more periods of time, which may be of varying and overlapping durations, as the Administrator may select, over which the attainment of one or more Performance Criteria will be measured for the purpose of determining a grantee’s right to and the payment of a Restricted Stock Award, Restricted Stock Units, Performance Share Award or Cash-Based Award, the vesting and/or payment of which is subject to the attainment of one or more Performance Goals. Each such period shall not be less than 12 months.

“Performance Goals” means, for a Performance Cycle, the specific goals established in writing by the Administrator for a Performance Cycle based upon the Performance Criteria.

“Performance Share Award” means an Award entitling the recipient to acquire shares of Stock upon the attainment of specified performance goals.

“Restricted Shares” means the shares of Stock underlying a Restricted Stock Award that remain subject to a risk of forfeiture or the Company’s right of repurchase.

“Restricted Stock Award” means an Award of Restricted Shares subject to such restrictions and conditions as the Administrator may determine at the time of grant.

“Restricted Stock Units” means an Award of stock units subject to such restrictions and conditions as the Administrator may determine at the time of grant.

“Sale Event” means (i) the sale of all or substantially all of the assets of the Company on a consolidated basis to an unrelated person or entity, (ii) a merger, reorganization or consolidation pursuant to which the holders of the Company’s outstanding voting power and outstanding stock immediately prior to such transaction do not own a majority of the outstanding voting power and outstanding stock or other equity interests of the resulting or successor entity (or its ultimate parent, if applicable) immediately upon completion of such transaction, (iii) the sale of all of the Stock of the Company to an unrelated person, entity or group thereof acting in concert, or (iv) any other transaction in which the owners of the Company’s outstanding voting power immediately prior to such transaction do not own at least a majority of the outstanding voting power of the Company or any successor entity immediately upon completion of the transaction other than as a result of the acquisition of securities directly from the Company.

“Sale Price” means the value as determined by the Administrator of the consideration payable, or otherwise to be received by stockholders, per share of Stock pursuant to a Sale Event.

“Section 409A” means Section 409A of the Code and the regulations and other guidance promulgated thereunder.

“Stock” means the Common Stock, par value $0.0001 per share, of the Company, subject to adjustments pursuant to Section 3.

“Stock Appreciation Right” means an Award entitling the recipient to receive shares of Stock having a value equal to the excess of the Fair Market Value of the Stock on the date of exercise over the exercise price of the Stock Appreciation Right multiplied by the number of shares of Stock with respect to which the Stock Appreciation Right shall have been exercised.

“Subsidiary” means any corporation or other entity (other than the Company) in which the Company has at least a 50 percent interest, either directly or indirectly.

“Ten Percent Owner” means an employee who owns or is deemed to own (by reason of the attribution rules of Section 424(d) of the Code) more than 10 percent of the combined voting power of all classes of stock of the Company or any parent or subsidiary corporation.

“Unrestricted Stock Award” means an Award of shares of Stock free of any restrictions.

SECTION 2. ADMINISTRATION OF PLAN; ADMINISTRATOR AUTHORITY TO SELECT GRANTEES AND DETERMINE AWARDS

(a) Administration of Plan. The Plan shall be administered by the Administrator.

(b) Powers of Administrator. The Administrator shall have the power and authority to grant Awards consistent with the terms of the Plan, including the power and authority:

(i) to select the individuals to whom Awards may from time to time be granted;

(ii) to determine the time or times of grant, and the extent, if any, of Incentive Stock Options, Non-Qualified Stock Options, Stock Appreciation Rights, Restricted Stock Awards, Restricted Stock Units, Unrestricted Stock Awards, Cash-Based Awards, Performance Share Awards and Dividend Equivalent Rights, or any combination of the foregoing, granted to any one or more grantees;

(iii) to determine the number of shares of Stock to be covered by any Award;

(iv) to determine and modify from time to time the terms and conditions, including restrictions, not inconsistent with the terms of the Plan, of any Award, which terms and conditions may differ among individual Awards and grantees, and to approve the forms of Award Certificates;

(v) to accelerate at any time the exercisability or vesting of all or any portion of any Award;

(vi) subject to the provisions of Section 6(c), to extend at any time the period in which Stock Options may be exercised; and

(vii) at any time to adopt, alter and repeal such rules, guidelines and practices for administration of the Plan and for its own acts and proceedings as it shall deem advisable;

(viii) to interpret the terms and provisions of the Plan and any Award (including related written instruments);

(ix) to make all determinations it deems advisable for the administration of the Plan; to decide all disputes arising in connection with the Plan; and

(x) to otherwise supervise the administration of the Plan.

All decisions and interpretations of the Administrator shall be binding on all persons, including the Company and Plan grantees.

(c) Delegation of Authority to Grant Awards. Subject to applicable law, the Administrator, in its discretion, may delegate to the Chief Executive Officer of the Company all or part of the Administrator’s authority and duties with respect to the granting of Awards to individuals who are (i) not subject to the reporting and other provisions of Section 16 of the Exchange Act and (ii) not Covered Employees. Any such delegation by the Administrator shall include a limitation as to the amount of Stock underlying Awards that may be granted during the period of the delegation and shall contain guidelines as to the determination of the exercise price and the vesting criteria. The Administrator may revoke or amend the terms of a delegation at any time but such action shall not invalidate any prior actions of the Administrator’s delegate or delegates that were consistent with the terms of the Plan.

(d) Award Certificate. Awards under the Plan shall be evidenced by Award Certificates that set forth the terms, conditions and limitations for each Award which may include, without limitation, the term of an Award and the provisions applicable in the event employment or service terminates.

(e) Indemnification. Neither the Board nor the Administrator, nor any member of either or any delegate thereof, shall be liable for any act, omission, interpretation, construction or determination made in good faith in connection with the Plan, and the members of the Board and the Administrator (and any delegate thereof) shall be entitled in all cases to indemnification and reimbursement by the Company in respect of any claim, loss, damage or expense (including, without limitation, reasonable attorneys’ fees) arising or resulting therefrom to the fullest extent permitted by law and/or under the Company’s articles or bylaws or any directors’ and officers’ liability insurance coverage which may be in effect from time to time and/or any indemnification agreement between such individual and the Company.

(f) Foreign Award Recipients. Notwithstanding any provision of the Plan to the contrary, in order to comply with the laws in other countries in which the Company and its Subsidiaries operate or have employees or other individuals eligible for Awards, the Administrator, in its sole discretion, shall have the power and authority to: (i) determine which Subsidiaries shall be covered by the Plan; (ii) determine which individuals outside the United States are eligible to participate in the Plan; (iii) modify the terms and conditions of any Award granted to individuals outside the United States to comply with applicable foreign laws; (iv) establish subplans and modify exercise procedures and other terms and procedures, to the extent the Administrator determines such actions to be necessary or advisable (and such subplans and/or modifications shall be attached to this Plan as appendices); provided, however, that no such subplans and/or modifications shall increase the share limitations contained in Section 3(a) hereof; and (v) take any action, before or after an Award is made, that the Administrator determines to be necessary or advisable to obtain approval or comply with any local governmental regulatory exemptions or approvals. Notwithstanding the foregoing, the Administrator may not take any actions hereunder, and no Awards shall be granted, that would violate the Exchange Act or any other applicable United States securities law, the Code, or any other applicable United States governing statute or law.

SECTION 3. STOCK ISSUABLE UNDER THE PLAN; MERGERS; SUBSTITUTION

(a) Stock Issuable. The maximum number of shares of Stock reserved and available for issuance under the Plan shall be the sum of 1,368,376 shares outstanding plus the shares of Stock remaining available for issuance under the Dimension Therapeutics, Inc. 2013 Stock Plan (the “2013 Plan”) as of the Effective Date (the “Initial Limit”), subject to adjustment as provided in this Section 3, plus on January 1, 2016 and each January 1 thereafter through January 1 2020, the number of shares of Stock reserved and available for issuance under the Plan shall be cumulatively increased by 4.0% percent of the number of shares of Stock issued and outstanding on the immediately preceding December 31 or such lesser number of shares determined by the Administrator (the “Annual Increase”). For purposes of this limitation, the shares of Stock underlying any Awards that are forfeited, canceled, held back upon exercise of an Option or settlement of an Award to cover the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of Stock or otherwise terminated under this Plan or the 2013 Plan (other than by exercise) shall be added back to the shares of Stock available for issuance under the Plan. In the event the Company repurchases shares of Stock on the open market, such shares shall not be added to the shares of Stock available for issuance under the Plan. Subject to such overall limitation, (a) the maximum aggregate number of shares of Stock that may be issued in the form of Incentive Stock Options shall not exceed the Initial Limit cumulatively increased on January 1, 2016 and on each January 1 thereafter by the lesser of the Annual Increase for such year or 4,500,000 shares of Stock and (b) shares of Stock may be issued up to such maximum number pursuant to any type or types of Award; provided, however, that Stock Options or Stock Appreciation Rights with respect to no more than 4,000,000 shares of Stock may be granted to any one individual grantee during any one calendar year period. The shares available for issuance under the Plan may be authorized but unissued shares of Stock or shares of Stock reacquired by the Company.

(b) Changes in Stock. Subject to Section 3(c) hereof, if, as a result of any reorganization, recapitalization, reclassification, stock dividend, stock split, reverse stock split or other similar change in the Company’s capital stock, the outstanding shares of Stock are increased or decreased or are exchanged for a different number or kind of shares or other securities of the Company, or additional shares or new or different shares or other securities of the Company or other non-cash assets are distributed with respect to such shares of Stock or other securities, or, if, as a result of any merger or consolidation, sale of all or substantially all of the assets of the Company, the outstanding shares of Stock are converted into or exchanged for securities of the Company or any successor entity (or a parent or subsidiary thereof), the Administrator shall make an appropriate or proportionate adjustment in (i) the maximum number of shares reserved for issuance under the Plan, including the maximum number of shares that may be issued in the form of Incentive Stock Options, (ii) the number of Stock Options or Stock Appreciation Rights that can be granted to any one individual grantee and the maximum number of shares that may be granted under a Performance-Based Award, (iii) the number and kind of shares or other securities subject to any then outstanding Awards under the Plan, (iv) the repurchase price, if any, per share subject to each outstanding Restricted Stock Award, and (v) the exercise price for each share subject to any then outstanding Stock Options and Stock Appreciation Rights under the Plan, without changing the aggregate exercise price (i.e., the exercise price multiplied by the number of Stock Options and Stock Appreciation Rights) as to which such Stock Options and Stock Appreciation Rights remain exercisable. The Administrator shall also make equitable or proportionate adjustments in the number of shares subject to outstanding Awards and the exercise price and the terms of

outstanding Awards to take into consideration cash dividends paid other than in the ordinary course or any other extraordinary corporate event. The adjustment by the Administrator shall be final, binding and conclusive. No fractional shares of Stock shall be issued under the Plan resulting from any such adjustment, but the Administrator in its discretion may make a cash payment in lieu of fractional shares.

(c) Mergers and Other Transactions. In the case of and subject to the consummation of a Sale Event, the parties thereto may cause the assumption or continuation of Awards theretofore granted by the successor entity, or the substitution of such Awards with new Awards of the successor entity or parent thereof, with appropriate adjustment as to the number and kind of shares and, if appropriate, the per share exercise prices, as such parties shall agree. To the extent the parties to such Sale Event do not provide for the assumption, continuation or substitution of Awards, upon the effective time of the Sale Event, the Plan and all outstanding Awards granted hereunder shall terminate. In such case, except as may be otherwise provided in the relevant Award Certificate, all Options and Stock Appreciation Rights that are not exercisable immediately prior to the effective time of the Sale Event shall become fully exercisable as of the effective time of the Sale Event, all other Awards with time-based vesting, conditions or restrictions shall become fully vested and nonforfeitable as of the effective time of the Sale Event, and all Awards with conditions and restrictions relating to the attainment of performance goals may become vested and nonforfeitable in connection with a Sale Event in the Administrator’s discretion or to the extent specified in the relevant Award Certificate. In the event of such termination, (i) the Company shall have the option (in its sole discretion) to make or provide for a cash payment to the grantees holding Options and Stock Appreciation Rights, in exchange for the cancellation thereof, in an amount equal to the difference between (A) the Sale Price multiplied by the number of shares of Stock subject to outstanding Options and Stock Appreciation Rights (to the extent then exercisable at prices not in excess of the Sale Price) and (B) the aggregate exercise price of all such outstanding Options and Stock Appreciation Rights; or (ii) each grantee shall be permitted, within a specified period of time prior to the consummation of the Sale Event as determined by the Administrator, to exercise all outstanding Options and Stock Appreciation Rights (to the extent then exercisable) held by such grantee.

SECTION 4. MAXIMUM AWARDS TO NON-EMPLOYEE DIRECTORS

Notwithstanding anything to the contrary in this Plan, the value of all Awards awarded under this Plan and all other cash compensation paid by the Company to any Non-Employee Director in any calendar year shall not exceed $1,000,000. For the purpose of this limitation, the value of any Award shall be its grant date fair value, as determined in accordance with Financial Accounting Standards Board Accounting Standards Codification 718 but excluding the impact of estimated forfeitures related to service-based vesting provisions.

SECTION 5. ELIGIBILITY

Grantees under the Plan will be such full or part-time officers and other employees, Non-Employee Directors and Consultants of the Company and its Subsidiaries as are selected from time to time by the Administrator in its sole discretion.

SECTION 6. STOCK OPTIONS

(a) Award of Stock Options. The Administrator may grant Stock Options under the Plan. Any Stock Option granted under the Plan shall be in such form as the Administrator may from time to time approve.

Stock Options granted under the Plan may be either Incentive Stock Options or Non-Qualified Stock Options. Incentive Stock Options may be granted only to employees of the Company or any Subsidiary that is a “subsidiary corporation” within the meaning of Section 424(f) of the Code. To the extent that any Option does not qualify as an Incentive Stock Option, it shall be deemed a Non-Qualified Stock Option.

Stock Options granted pursuant to this Section 5 shall be subject to the following terms and conditions and shall contain such additional terms and conditions, not inconsistent with the terms of the Plan, as the Administrator shall deem desirable. If the Administrator so determines, Stock Options may be granted in lieu of cash compensation at the optionee’s election, subject to such terms and conditions as the Administrator may establish.

(b) Exercise Price. The exercise price per share for the Stock covered by a Stock Option granted pursuant to this Section 6 shall be determined by the Administrator at the time of grant but shall not be less than 100 percent of the Fair Market Value on the date of grant. In the case of an Incentive Stock Option that is granted to a Ten Percent Owner, the option price of such Incentive Stock Option shall be not less than 110 percent of the Fair Market Value on the grant date.

(c) Option Term. The term of each Stock Option shall be fixed by the Administrator, but no Stock Option shall be exercisable more than ten years after the date the Stock Option is granted. In the case of an Incentive Stock Option that is granted to a Ten Percent Owner, the term of such Stock Option shall be no more than five years from the date of grant.

(d) Exercisability; Rights of a Stockholder. Stock Options shall become exercisable at such time or times, whether or not in installments, as shall be determined by the Administrator at or after the grant date. The Administrator may at any time accelerate the exercisability of all or any portion of any Stock Option. An optionee shall have the rights of a stockholder only as to shares acquired upon the exercise of a Stock Option and not as to unexercised Stock Options.

(e) Method of Exercise. Stock Options may be exercised in whole or in part, by giving written or electronic notice of exercise to the Company, specifying the number of shares to be purchased. Payment of the purchase price may be made by one or more of the following methods except to the extent otherwise provided in the Option Award Certificate:

(i) In cash, by certified or bank check or other instrument acceptable to the Administrator;

(ii) Through the delivery (or attestation to the ownership following such procedures as the Company may prescribe) of shares of Stock that are not then subject to restrictions under any Company plan. Such surrendered shares shall be valued at Fair Market Value on the exercise date;

(iii) By the optionee delivering to the Company a properly executed exercise notice together with irrevocable instructions to a broker to promptly deliver to the Company cash or a check payable and acceptable to the Company for the purchase price; provided that in the event the optionee chooses to pay the purchase price as so provided, the optionee and the broker shall comply with such procedures and enter into such agreements of indemnity and other agreements as the Company shall prescribe as a condition of such payment procedure; or

(iv) With respect to Stock Options that are not Incentive Stock Options, by a “net exercise” arrangement pursuant to which the Company will reduce the number of shares of Stock issuable upon exercise by the largest whole number of shares with a Fair Market Value that does not exceed the aggregate exercise price.

Payment instruments will be received subject to collection. The transfer to the optionee on the records of the Company or of the transfer agent of the shares of Stock to be purchased pursuant to the exercise of a Stock Option will be contingent upon receipt from the optionee (or a purchaser acting in his stead in accordance with the provisions of the Stock Option) by the Company of the full purchase price for such shares and the fulfillment of any other requirements contained in the Option Award Certificate or applicable provisions of laws (including the satisfaction of any withholding taxes that the Company is obligated to withhold with respect to the optionee). In the event an optionee chooses to pay the purchase price by previously-owned shares of Stock through the attestation method, the number of shares of Stock transferred to the optionee upon the exercise of the Stock Option shall be net of the number of attested shares. In the event that the Company establishes, for itself or using the services of a third party, an automated system for the exercise of Stock Options, such as a system using an internet website or interactive voice response, then the paperless exercise of Stock Options may be permitted through the use of such an automated system.

(f) Annual Limit on Incentive Stock Options. To the extent required for “incentive stock option” treatment under Section 422 of the Code, the aggregate Fair Market Value (determined as of the time of grant) of the shares of Stock with respect to which Incentive Stock Options granted under this Plan and any other plan of the Company or its parent and subsidiary corporations become exercisable for the first time by an optionee during any calendar year shall not exceed $100,000. To the extent that any Stock Option exceeds this limit, it shall constitute a Non-Qualified Stock Option.

SECTION 7. STOCK APPRECIATION RIGHTS

(a) Award of Stock Appreciation Rights. The Administrator may grant Stock Appreciation Rights under the Plan. A Stock Appreciation Right is an Award entitling the recipient to receive shares of Stock having a value equal to the excess of the Fair Market Value of a share of Stock on the date of exercise over the exercise price of the Stock Appreciation Right multiplied by the number of shares of Stock with respect to which the Stock Appreciation Right shall have been exercised.

(b) Exercise Price of Stock Appreciation Rights. The exercise price of a Stock Appreciation Right shall not be less than 100 percent of the Fair Market Value of the Stock on the date of grant.

(c) Grant and Exercise of Stock Appreciation Rights. Stock Appreciation Rights may be granted by the Administrator independently of any Stock Option granted pursuant to Section 5 of the Plan.

(d) Terms and Conditions of Stock Appreciation Rights. Stock Appreciation Rights shall be subject to such terms and conditions as shall be determined from time to time by the Administrator. The term of a Stock Appreciation Right may not exceed ten years.

SECTION 8. RESTRICTED STOCK AWARDS

(a) Nature of Restricted Stock Awards. The Administrator may grant Restricted Stock Awards under the Plan. A Restricted Stock Award is any Award of Restricted Shares subject to such restrictions and conditions as the Administrator may determine at the time of grant. Conditions may be based on continuing employment (or other service relationship) and/or achievement of pre-established performance goals and objectives. The terms and conditions of each such Award shall be determined by the Administrator, and such terms and conditions may differ among individual Awards and grantees.

(b) Rights as a Stockholder. Upon the grant of the Restricted Stock Award and payment of any applicable purchase price, a grantee shall have the rights of a stockholder with respect to the voting of the Restricted Shares and receipt of dividends; provided that if the lapse of restrictions with respect to the Restricted Stock Award is tied to the attainment of performance goals, any dividends paid by the Company during the performance period shall accrue and shall not be paid to the grantee until and to the extent the performance goals are met with respect to the Restricted Stock Award. Unless the Administrator shall otherwise determine, (i) uncertificated Restricted Shares shall be accompanied by a notation on the records of the Company or the transfer agent to the effect that they are subject to forfeiture until such Restricted Shares are vested as provided in Section 8(d) below, and (ii) certificated Restricted Shares shall remain in the possession of the Company until such Restricted Shares are vested as provided in Section 8(d) below, and the grantee shall be required, as a condition of the grant, to deliver to the Company such instruments of transfer as the Administrator may prescribe.

(c) Restrictions. Restricted Shares may not be sold, assigned, transferred, pledged or otherwise encumbered or disposed of except as specifically provided herein or in the Restricted Stock Award Certificate. Except as may otherwise be provided by the Administrator either in the Award Certificate or, subject to Section 19 below, in writing after the Award is issued, if a grantee’s employment (or other service relationship) with the Company and its Subsidiaries terminates for any reason, any Restricted Shares that have not vested at the time of termination shall automatically and without any requirement of notice to such grantee from or other action by or on behalf of, the Company be deemed to have been reacquired by the Company at its original purchase price (if any) from such grantee or such grantee’s legal representative simultaneously with such termination of employment (or other service relationship), and thereafter shall cease to represent any ownership of the Company by the grantee or rights of the grantee as a stockholder. Following such deemed reacquisition of Restricted Shares that are represented by physical certificates, a grantee shall surrender such certificates to the Company upon request without consideration.

(d) Vesting of Restricted Shares. The Administrator at the time of grant shall specify the date or dates and/or the attainment of pre-established performance goals, objectives and other conditions on which the non-transferability of the Restricted Shares and the Company’s right of repurchase or forfeiture shall lapse. Subsequent to such date or dates and/or the attainment of such pre-established performance goals, objectives and other conditions, the shares on which all restrictions have lapsed shall no longer be Restricted Shares and shall be deemed “vested.”

SECTION 9. RESTRICTED STOCK UNITS

(a) Nature of Restricted Stock Units. The Administrator may grant Restricted Stock Units under the Plan. A Restricted Stock Unit is an Award of stock units that may be settled in shares of Stock upon the satisfaction of such restrictions and conditions at the time of grant. Conditions may be based on continuing employment (or other service relationship) and/or achievement of pre-established performance goals and objectives. The terms and conditions of each such Award shall be determined by the Administrator, and such terms and conditions may differ among individual Awards and grantees. Except in the case of Restricted Stock Units with a deferred settlement date that complies with Section 409A, at the end of the vesting period, the Restricted Stock Units, to the extent vested, shall be settled in the form of shares of Stock. Restricted Stock Units with deferred settlement dates are subject to Section 409A and shall contain such additional terms and conditions as the Administrator shall determine in its sole discretion in order to comply with the requirements of Section 409A.

(b) Election to Receive Restricted Stock Units in Lieu of Compensation. The Administrator may, in its sole discretion, permit a grantee to elect to receive a portion of future cash compensation otherwise due to such grantee in the form of an award of Restricted Stock Units. Any such election shall be made in writing and shall be delivered to the Company no later than the date specified by the Administrator and in accordance with Section 409A and such other rules and procedures established by the Administrator. Any such future cash compensation that the grantee elects to defer shall be converted to a fixed number of Restricted Stock Units based on the Fair Market Value of Stock on the date the compensation would otherwise have been paid to the grantee if such payment had not been deferred as provided herein. The Administrator shall have the sole right to determine whether and under what circumstances to permit such elections and to impose such limitations and other terms and conditions thereon as the Administrator deems appropriate. Any Restricted Stock Units that are elected to be received in lieu of cash compensation shall be fully vested, unless otherwise provided in the Award Certificate.

(c) Rights as a Stockholder. A grantee shall have the rights as a stockholder only as to shares of Stock acquired by the grantee upon settlement of Restricted Stock Units; provided, however, that the grantee may be credited with Dividend Equivalent Rights with respect to the stock units underlying his Restricted Stock Units, subject to the provisions of Section 14 and such terms and conditions as the Administrator may determine.

(d) Termination. Except as may otherwise be provided by the Administrator either in the Award Certificate or, subject to Section 19 below, in writing after the Award is issued, a grantee’s right in all Restricted Stock Units that have not vested shall automatically terminate upon the grantee’s termination of employment (or cessation of service relationship) with the Company and its Subsidiaries for any reason.

SECTION 10. UNRESTRICTED STOCK AWARDS

Grant or Sale of Unrestricted Stock. The Administrator may grant (or sell at par value or such higher purchase price determined by the Administrator) an Unrestricted Stock Award under the Plan. An Unrestricted Stock Award is an Award pursuant to which the grantee may receive shares of Stock free of any restrictions under the Plan. Unrestricted Stock Awards may be granted in respect of past services or other valid consideration, or in lieu of cash compensation due to such grantee.

SECTION 11. CASH-BASED AWARDS

Grant of Cash-Based Awards. The Administrator may grant Cash-Based Awards under the Plan. A Cash-Based Award is an Award that entitles the grantee to a payment in cash upon the attainment of specified Performance Goals. The Administrator shall determine the maximum duration of the Cash-Based Award, the amount of cash to which the Cash-Based Award pertains, the conditions upon which the Cash-Based Award shall

become vested or payable, and such other provisions as the Administrator shall determine. Each Cash-Based Award shall specify a cash-denominated payment amount, formula or payment ranges as determined by the Administrator. Payment, if any, with respect to a Cash-Based Award shall be made in accordance with the terms of the Award and may be made in cash.

SECTION 12. PERFORMANCE SHARE AWARDS

(a) Nature of Performance Share Awards. The Administrator may grant Performance Share Awards under the Plan. A Performance Share Award is an Award entitling the grantee to receive shares of Stock upon the attainment of performance goals. The Administrator shall determine whether and to whom Performance Share Awards shall be granted, the performance goals, the periods during which performance is to be measured, which may not be less than one year except in the case of a Sale Event, and such other limitations and conditions as the Administrator shall determine.

(b) Rights as a Stockholder. A grantee receiving a Performance Share Award shall have the rights of a stockholder only as to shares of Stock actually received by the grantee under the Plan and not with respect to shares subject to the Award but not actually received by the grantee. A grantee shall be entitled to receive shares of Stock under a Performance Share Award only upon satisfaction of all conditions specified in the Performance Share Award Certificate (or in a performance plan adopted by the Administrator).

(c) Termination. Except as may otherwise be provided by the Administrator either in the Award agreement or, subject to Section 19 below, in writing after the Award is issued, a grantee’s rights in all Performance Share Awards shall automatically terminate upon the grantee’s termination of employment (or cessation of service relationship) with the Company and its Subsidiaries for any reason.

SECTION 13. PERFORMANCE-BASED AWARDS TO COVERED EMPLOYEES

(a) Performance-Based Awards. The Administrator may grant one or more Performance-Based Awards in the form of a Restricted Stock Award, Restricted Stock Units, Performance Share Awards or Cash-Based Award payable upon the attainment of Performance Goals that are established by the Administrator and relate to one or more of the Performance Criteria, in each case on a specified date or dates or over any period or periods determined by the Administrator. The Administrator shall define in an objective fashion the manner of calculating the Performance Criteria it selects to use for any Performance Cycle. Depending on the Performance Criteria used to establish such Performance Goals, the Performance Goals may be expressed in terms of overall Company performance or the performance of a division, business unit, or an individual. Each Performance-Based Award shall comply with the provisions set forth below.

(b) Grant of Performance-Based Awards. With respect to each Performance-Based Award granted to a Covered Employee, the Administrator shall select, within the first 90 days of a Performance Cycle (or, if shorter, within the maximum period allowed under Section 162(m) of the Code) the Performance Criteria for such grant, and the Performance Goals with respect to each Performance Criterion (including a threshold level of performance below which no amount will become payable with respect to such Award). Each Performance-Based Award will specify the amount payable, or the formula for determining the amount payable, upon achievement of the various applicable performance targets. The Performance Criteria established by the Administrator may be (but need not be) different for each Performance Cycle and different Performance Goals may be applicable to Performance-Based Awards to different Covered Employees.

(c) Payment of Performance-Based Awards. Following the completion of a Performance Cycle, the Administrator shall meet to review and certify in writing whether, and to what extent, the Performance Goals for the Performance Cycle have been achieved and, if so, to also calculate and certify in writing the amount of the Performance-Based Awards earned for the Performance Cycle. The Administrator shall then determine the actual size of each Covered Employee’s Performance-Based Award.

(d) Maximum Award Payable. The maximum Performance-Based Award payable to any one Covered Employee under the Plan for a Performance Cycle is 4,000,000 shares of Stock (subject to adjustment as provided in Section 3(b) hereof) or $5,000,000 in the case of a Performance-Based Award that is a Cash-Based Award.

SECTION 14. DIVIDEND EQUIVALENT RIGHTS

(a) Dividend Equivalent Rights. The Administrator may grant Dividend Equivalent Rights under the Plan. A Dividend Equivalent Right is an Award entitling the grantee to receive credits based on cash dividends that would have been paid on the shares of Stock specified in the Dividend Equivalent Right (or other Award to which it relates) if such shares had been issued to the grantee. A Dividend Equivalent Right may be granted hereunder to any grantee as a component of an award of Restricted Stock Units or Performance Share Award or as a freestanding award. The terms and conditions of Dividend Equivalent Rights shall be specified in the Award Certificate. Dividend equivalents credited to the holder of a Dividend Equivalent Right may be paid currently or may be deemed to be reinvested in additional shares of Stock, which may thereafter accrue additional equivalents. Any such reinvestment shall be at Fair Market Value on the date of reinvestment or such other price as may then apply under a dividend reinvestment plan sponsored by the Company, if any. Dividend Equivalent Rights may be settled in cash or shares of Stock or a combination thereof, in a single installment or installments. A Dividend Equivalent Right granted as a component of an Award of Restricted Stock Units or Performance Share Award shall provide that such Dividend Equivalent Right shall be settled only upon settlement or payment of, or lapse of restrictions on, such other Award, and that such Dividend Equivalent Right shall expire or be forfeited or annulled under the same conditions as such other Award.

(b) Termination. Except as may otherwise be provided by the Administrator either in the Award Certificate or, subject to Section 19 below, in writing after the Award is issued, a grantee’s rights in all Dividend Equivalent Rights shall automatically terminate upon the grantee’s termination of employment (or cessation of service relationship) with the Company and its Subsidiaries for any reason.

SECTION 15. TRANSFERABILITY OF AWARDS

(a) Transferability. Except as provided in Section 15(b) below, during a grantee’s lifetime, his or her Awards shall be exercisable only by the grantee, or by the grantee’s legal representative or guardian in the event of the grantee’s incapacity. No Awards shall be sold, assigned, transferred or otherwise encumbered or disposed of by a grantee other than by will or by the laws of descent and distribution or pursuant to a domestic relations order. No Awards shall be subject, in whole or in part, to attachment, execution, or levy of any kind, and any purported transfer in violation hereof shall be null and void.

(b) Administrator Action. Notwithstanding Section 15(a), the Administrator, in its discretion, may provide either in the Award Certificate regarding a given Award or by subsequent written approval that the grantee (who is an employee or director) may transfer his or her Non-Qualified Stock Options to his or her immediate family members, to trusts for the benefit of such family members, or to partnerships in which such family members are the only partners, provided that the transferee agrees in writing with the Company to be bound by all of the terms and conditions of this Plan and the applicable Award. In no event may an Award be transferred by a grantee for value.

(c) Family Member. For purposes of Section 15(b), “family member” shall mean a grantee’s child, stepchild, grandchild, parent, stepparent, grandparent, spouse, former spouse, sibling, niece, nephew, mother-in-law, father-in-law, son-in-law, daughter-in-law, brother-in-law, or sister-in-law, including adoptive relationships, any person sharing the grantee’s household (other than a tenant of the grantee), a trust in which these persons (or the grantee) have more than 50 percent of the beneficial interest, a foundation in which these persons (or the grantee) control the management of assets, and any other entity in which these persons (or the grantee) own more than 50 percent of the voting interests.

(d) Designation of Beneficiary. To the extent permitted by the Company, each grantee to whom an Award has been made under the Plan may designate a beneficiary or beneficiaries to exercise any Award or receive any payment under any Award payable on or after the grantee’s death. Any such designation shall be on a form provided for that purpose by the Administrator and shall not be effective until received by the Administrator. If no beneficiary has been designated by a deceased grantee, or if the designated beneficiaries have predeceased the grantee, the beneficiary shall be the grantee’s estate.

SECTION 16. TAX WITHHOLDING

(a) Payment by Grantee. Each grantee shall, no later than the date as of which the value of an Award or of any Stock or other amounts received thereunder first becomes includable in the gross income of the grantee for Federal income tax purposes, pay to the Company, or make arrangements satisfactory to the Administrator regarding payment of, any Federal, state, or local taxes of any kind required by law to be withheld by the Company with respect to such income. The Company and its Subsidiaries shall, to the extent permitted by law, have the right to deduct any such taxes from any payment of any kind otherwise due to the grantee. The Company’s obligation to deliver evidence of book entry (or stock certificates) to any grantee is subject to and conditioned on tax withholding obligations being satisfied by the grantee.

(b) Payment in Stock. Subject to approval by the Administrator, a grantee may elect to have the Company’s minimum required tax withholding obligation satisfied, in whole or in part, by authorizing the Company to withhold from shares of Stock to be issued pursuant to any Award a number of shares with an aggregate Fair Market Value (as of the date the withholding is effected) that would satisfy the withholding amount due. The Administrator may also require Awards to be subject to mandatory share withholding up to the required withholding amount. For purposes of share withholding, the Fair Market Value of withheld shares shall be determined in the same manner as the value of Stock includible in income of the Participants.

SECTION 17. SECTION 409A AWARDS

To the extent that any Award is determined to constitute “nonqualified deferred compensation” within the meaning of Section 409A (a “409A Award”), the Award shall be subject to such additional rules and requirements as specified by the Administrator from time to time in order to comply with Section 409A. In this regard, if any amount under a 409A Award is payable upon a “separation from service” (within the meaning of Section 409A) to a grantee who is then considered a “specified employee” (within the meaning of Section 409A), then no such payment shall be made prior to the date that is the earlier of (i) six months and one day after the grantee’s separation from service, or (ii) the grantee’s death, but only to the extent such delay is necessary to prevent such payment from being subject to interest, penalties and/or additional tax imposed pursuant to Section 409A. Further, the settlement of any such Award may not be accelerated except to the extent permitted by Section 409A.

SECTION 18. TERMINATION OF EMPLOYMENT, TRANSFER, LEAVE OF ABSENCE, ETC.

(a) Termination of Employment. If the grantee’s employer ceases to be a Subsidiary, the grantee shall be deemed to have terminated employment for purposes of the Plan.

(b) For purposes of the Plan, the following events shall not be deemed a termination of employment:

(i) a transfer to the employment of the Company from a Subsidiary or from the Company to a Subsidiary, or from one Subsidiary to another; or

(ii) an approved leave of absence for military service or sickness, or for any other purpose approved by the Company, if the employee’s right to re-employment is guaranteed either by a statute or by contract or under the policy pursuant to which the leave of absence was granted or if the Administrator otherwise so provides in writing.

SECTION 19. AMENDMENTS AND TERMINATION

The Board may, at any time, amend or discontinue the Plan and the Administrator may, at any time, amend or cancel any outstanding Award for the purpose of satisfying changes in law or for any other lawful purpose, but no such action shall adversely affect rights under any outstanding Award without the holder’s consent. Except as provided in Section 3(b) or 3(c), without prior stockholder approval, in no event may the Administrator exercise its discretion to reduce the exercise price of outstanding Stock Options or Stock Appreciation Rights or effect repricing through cancellation and re-grants or cancellation of Stock Options or Stock Appreciation Rights in exchange for cash or other Awards. To the extent required under the rules of any securities exchange or market system on which

the Stock is listed, to the extent determined by the Administrator to be required by the Code to ensure that Incentive Stock Options granted under the Plan are qualified under Section 422 of the Code, or to ensure that compensation earned under Awards qualifies as performance-based compensation under Section 162(m) of the Code, Plan amendments shall be subject to approval by the Company stockholders entitled to vote at a meeting of stockholders. Nothing in this Section 19 shall limit the Administrator’s authority to take any action permitted pursuant to Section 3(b) or 3(c).

SECTION 20. STATUS OF PLAN

With respect to the portion of any Award that has not been exercised and any payments in cash, Stock or other consideration not received by a grantee, a grantee shall have no rights greater than those of a general creditor of the Company unless the Administrator shall otherwise expressly determine in connection with any Award or Awards. In its sole discretion, the Administrator may authorize the creation of trusts or other arrangements to meet the Company’s obligations to deliver Stock or make payments with respect to Awards hereunder, provided that the existence of such trusts or other arrangements is consistent with the foregoing sentence.

SECTION 21. GENERAL PROVISIONS

(a) No Distribution. The Administrator may require each person acquiring Stock pursuant to an Award to represent to and agree with the Company in writing that such person is acquiring the shares without a view to distribution thereof.

(b) Delivery of Stock Certificates. Stock certificates to grantees under this Plan shall be deemed delivered for all purposes when the Company or a stock transfer agent of the Company shall have mailed such certificates in the United States mail, addressed to the grantee, at the grantee’s last known address on file with the Company. Uncertificated Stock shall be deemed delivered for all purposes when the Company or a Stock transfer agent of the Company shall have given to the grantee by electronic mail (with proof of receipt) or by United States mail, addressed to the grantee, at the grantee’s last known address on file with the Company, notice of issuance and recorded the issuance in its records (which may include electronic “book entry” records). Notwithstanding anything herein to the contrary, the Company shall not be required to issue or deliver any certificates evidencing shares of Stock pursuant to the exercise of any Award, unless and until the Administrator has determined, with advice of counsel (to the extent the Administrator deems such advice necessary or advisable), that the issuance and delivery of such certificates is in compliance with all applicable laws, regulations of governmental authorities and, if applicable, the requirements of any exchange on which the shares of Stock are listed, quoted or traded. All Stock certificates delivered pursuant to the Plan shall be subject to any stop-transfer orders and other restrictions as the Administrator deems necessary or advisable to comply with federal, state or foreign jurisdiction, securities or other laws, rules and quotation system on which the Stock is listed, quoted or traded. The Administrator may place legends on any Stock certificate to reference restrictions applicable to the Stock. In addition to the terms and conditions provided herein, the Administrator may require that an individual make such reasonable covenants, agreements, and representations as the Administrator, in its discretion, deems necessary or advisable in order to comply with any such laws, regulations, or requirements. The Administrator shall have the right to require any individual to comply with any timing or other restrictions with respect to the settlement or exercise of any Award, including a window-period limitation, as may be imposed in the discretion of the Administrator.

(c) Stockholder Rights. Until Stock is deemed delivered in accordance with Section 21(b), no right to vote or receive dividends or any other rights of a stockholder will exist with respect to shares of Stock to be issued in connection with an Award, notwithstanding the exercise of a Stock Option or any other action by the grantee with respect to an Award.

(d) Other Compensation Arrangements; No Employment Rights. Nothing contained in this Plan shall prevent the Board from adopting other or additional compensation arrangements, including trusts, and such arrangements may be either generally applicable or applicable only in specific cases. The adoption of this Plan and the grant of Awards do not confer upon any employee any right to continued employment with the Company or any Subsidiary.

(e) Trading Policy Restrictions. Option exercises and other Awards under the Plan shall be subject to the Company’s insider trading policies and procedures, as in effect from time to time.

(f) Clawback Policy. Awards under the Plan shall be subject to the Company’s clawback policy, as in effect from time to time.

SECTION 22. EFFECTIVE DATE OF PLAN

This Plan shall become effective on the date immediately preceding the date of the Company’s Initial Public Offering following stockholder approval in accordance with applicable state law, the Company’s bylaws and articles of incorporation, and applicable stock exchange rules or pursuant to written consent. No grants of Stock Options and other Awards may be made hereunder after the tenth anniversary of the Effective Date and no grants of Incentive Stock Options may be made hereunder after the tenth anniversary of the date the Plan is approved by the Board.

SECTION 23. GOVERNING LAW

This Plan and all Awards and actions taken thereunder shall be governed by, and construed in accordance with, the laws of the State of Delaware, applied without regard to conflict of law principles.

DATE APPROVED BY BOARD OF DIRECTORS:

DATE APPROVED BY STOCKHOLDERS:

INCENTIVE STOCK OPTION AGREEMENT

UNDER THE DIMENSION THERAPEUTICS, INC.

2015 STOCK OPTION AND INCENTIVE PLAN

Name of Optionee:

No. of Option Shares:

Option Exercise Price per Share: $

Grant Date:

Expiration Date:

Pursuant to the Dimension Therapeutics, Inc. 2015 Stock Option and Incentive Plan as amended through the date hereof (the “Plan”), Dimension Therapeutics, Inc. (the “Company”) hereby grants to the Optionee named above an option (the “Stock Option”) to purchase on or prior to the Expiration Date specified above all or part of the number of shares of Common Stock, par value $0.0001 per share (the “Stock”), of the Company specified above at the Option Exercise Price per Share specified above subject to the terms and conditions set forth herein and in the Plan.

1. Exercisability Schedule. No portion of this Stock Option may be exercised until such portion shall have become exercisable. Except as set forth below, and subject to the discretion of the Administrator (as defined in Section 2 of the Plan) to accelerate the exercisability schedule hereunder, this Stock Option shall be exercisable with respect to the following number of Option Shares on the dates indicated so long as the Optionee remains an employee of the Company or a Subsidiary on such dates:


Incremental Number of Option Shares Exercisable*		Exercisability Date
( %)
( %)
( %)
( %)
( %)

*	Max. of $100,000 per yr.

Once exercisable, this Stock Option shall continue to be exercisable at any time or times prior to the close of business on the Expiration Date, subject to the provisions hereof and of the Plan.

2. Manner of Exercise.

(a) The Optionee may exercise this Stock Option only in the following manner: from time to time on or prior to the Expiration Date of this Stock Option, the Optionee may give written notice to the Administrator of his or her election to purchase some or all of the Option Shares purchasable at the time of such notice. This notice shall specify the number of Option Shares to be purchased.

broker to promptly deliver to the Company cash or a check payable and acceptable to the Company to pay the option purchase price, provided that in the event the Optionee chooses to pay the option purchase price as so provided, the Optionee and the broker shall comply with such procedures and enter into such agreements of indemnity and other agreements as the Administrator shall prescribe as a condition of such payment procedure; or (iv) a combination of (i), (ii) and (iii) above. Payment instruments will be received subject to collection.

The transfer to the Optionee on the records of the Company or of the transfer agent of the Option Shares will be contingent upon (i) the Company’s receipt from the Optionee of the full purchase price for the Option Shares, as set forth above, (ii) the fulfillment of any other requirements contained herein or in the Plan or in any other agreement or provision of laws, and (iii) the receipt by the Company of any agreement, statement or other evidence that the Company may require to satisfy itself that the issuance of Stock to be purchased pursuant to the exercise of Stock Options under the Plan and any subsequent resale of the shares of Stock will be in compliance with applicable laws and regulations. In the event the Optionee chooses to pay the purchase price by previously-owned shares of Stock through the attestation method, the number of shares of Stock transferred to the Optionee upon the exercise of the Stock Option shall be net of the shares attested to.

(b) The shares of Stock purchased upon exercise of this Stock Option shall be transferred to the Optionee on the records of the Company or of the transfer agent upon compliance to the satisfaction of the Administrator with all requirements under applicable laws or regulations in connection with such transfer and with the requirements hereof and of the Plan. The determination of the Administrator as to such compliance shall be final and binding on the Optionee. The Optionee shall not be deemed to be the holder of, or to have any of the rights of a holder with respect to, any shares of Stock subject to this Stock Option unless and until this Stock Option shall have been exercised pursuant to the terms hereof, the Company or the transfer agent shall have transferred the shares to the Optionee, and the Optionee’s name shall have been entered as the stockholder of record on the books of the Company. Thereupon, the Optionee shall have full voting, dividend and other ownership rights with respect to such shares of Stock.

(c) The minimum number of shares with respect to which this Stock Option may be exercised at any one time shall be 100 shares, unless the number of shares with respect to which this Stock Option is being exercised is the total number of shares subject to exercise under this Stock Option at the time.

(d) Notwithstanding any other provision hereof or of the Plan, no portion of this Stock Option shall be exercisable after the Expiration Date hereof.

3. Termination of Employment. If the Optionee’s employment by the Company or a Subsidiary (as defined in the Plan) is terminated, the period within which to exercise the Stock Option may be subject to earlier termination as set forth below.

(a) Termination Due to Death. If the Optionee’s employment terminates by reason of the Optionee’s death, any portion of this Stock Option outstanding on such date, to the extent exercisable on the date of death, may thereafter be exercised by the Optionee’s legal representative or legatee for a period of 12 months from the date of death or until the Expiration Date, if earlier. Any portion of this Stock Option that is not exercisable on the date of death shall terminate immediately and be of no further force or effect.

(b) Termination Due to Disability. If the Optionee’s employment terminates by reason of the Optionee’s disability (as determined by the Administrator), any portion of this Stock Option outstanding on such date, to the extent exercisable on the date of such termination of employment, may thereafter be exercised by the Optionee for a period of 12 months from the date of disability or until the Expiration Date, if earlier. Any portion of this Stock Option that is not exercisable on the date of disability shall terminate immediately and be of no further force or effect.

(c) Termination for Cause. If the Optionee’s employment terminates for Cause, any portion of this Stock Option outstanding on such date shall terminate immediately and be of no further force and effect. For purposes hereof, “Cause” shall mean, unless otherwise provided in an employment agreement between the Company and the Optionee, a determination by the Administrator that the Optionee shall be dismissed as a result of (i) any material breach by the Optionee of any agreement between the Optionee and the Company; (ii) the conviction of, indictment for or plea of nolo contendere by the Optionee to a felony or a crime involving moral turpitude; or (iii) any material misconduct or willful and deliberate non-performance (other than by reason of disability) by the Optionee of the Optionee’s duties to the Company.

(d) Other Termination. If the Optionee’s employment terminates for any reason other than the Optionee’s death, the Optionee’s disability, or Cause, and unless otherwise determined by the Administrator, any portion of this Stock Option outstanding on such date may be exercised, to the extent exercisable on the date of termination, for a period of three months from the date of termination or until the Expiration Date, if earlier. Any portion of this Stock Option that is not exercisable on the date of termination shall terminate immediately and be of no further force or effect.

The Administrator’s determination of the reason for termination of the Optionee’s employment shall be conclusive and binding on the Optionee and his or her representatives or legatees.

4. Incorporation of Plan. Notwithstanding anything herein to the contrary, this Stock Option shall be subject to and governed by all the terms and conditions of the Plan, including the powers of the Administrator set forth in Section 2(b) of the Plan. Capitalized terms in this Agreement shall have the meaning specified in the Plan, unless a different meaning is specified herein.

5. Transferability. This Agreement is personal to the Optionee, is non-assignable and is not transferable in any manner, by operation of law or otherwise, other than by will or the laws of descent and distribution. This Stock Option is exercisable, during the Optionee’s lifetime, only by the Optionee, and thereafter, only by the Optionee’s legal representative or legatee.

6. Status of the Stock Option. This Stock Option is intended to qualify as an “incentive stock option” under Section 422 of the Internal Revenue Code of 1986, as amended (the “Code”), but the Company does not represent or warrant that this Stock Option qualifies as such. The Optionee should consult with his or her own tax advisors regarding the tax effects of this Stock Option and the requirements necessary to obtain favorable income tax treatment under Section 422 of the Code, including, but not limited to, holding period requirements. To the extent any portion of this Stock Option does not so qualify as an “incentive stock option,” such portion shall be deemed to be a non-qualified stock option. If the Optionee intends to dispose or does dispose (whether by sale, gift, transfer or otherwise) of any Option Shares within the one-year period beginning on the date after the transfer of such shares to him or her, or within the two-year period beginning on the day after the grant of this Stock Option, he or she will so notify the Company within 30 days after such disposition.

7. Tax Withholding. The Optionee shall, not later than the date as of which the exercise of this Stock Option becomes a taxable event for Federal income tax purposes, pay to the Company or make arrangements satisfactory to the Administrator for payment of any Federal, state, and local taxes required by law to be withheld on account of such taxable event. The Company shall have the authority to cause the minimum required tax withholding obligation to be satisfied, in whole or in part, by withholding from shares of Stock to be issued to the Optionee a number of shares of Stock with an aggregate Fair Market Value that would satisfy the minimum withholding amount due.

8. No Obligation to Continue Employment. Neither the Company nor any Subsidiary is obligated by or as a result of the Plan or this Agreement to continue the Optionee in employment and neither the Plan nor this Agreement shall interfere in any way with the right of the Company or any Subsidiary to terminate the employment of the Optionee at any time.

9. Integration. This Agreement constitutes the entire agreement between the parties with respect to this Stock Option and supersedes all prior agreements and discussions between the parties concerning such subject matter.

By entering into this Agreement, the Optionee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all Relevant Information; (ii) waives any privacy rights the Optionee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and (iv) authorizes the transfer of the Relevant Information to any jurisdiction in which the Relevant Companies consider appropriate. The Optionee shall have access to, and the right to change, the Relevant Information. Relevant Information will only be used in accordance with applicable law.

11. Notices. Notices hereunder shall be mailed or delivered to the Company at its principal place of business and shall be mailed or delivered to the Optionee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing.


DIMENSION THERAPEUTICS, INC.



By:
		Title:

The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned. Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Optionee (including through an online acceptance process) is acceptable.


Dated:
						Optionee’s Signature

						Optionee’s name and address:

NON-QUALIFIED STOCK OPTION AGREEMENT

FOR COMPANY EMPLOYEES

UNDER THE DIMENSION THERAPEUTICS, INC.

2015 STOCK OPTION AND INCENTIVE PLAN

Name of Optionee:

No. of Option Shares:

Option Exercise Price per Share: $

Grant Date:

Expiration Date:

1. Exercisability Schedule. No portion of this Stock Option may be exercised until such portion shall have become exercisable. Except as set forth below, and subject to the discretion of the Administrator (as defined in Section 2 of the Plan) to accelerate the exercisability schedule hereunder, this Stock Option shall be exercisable with respect to the following number of Option Shares on the dates indicated so long as Optionee remains an employee of the Company or a Subsidiary on such dates:


Incremental Number of Option Shares Exercisable		Exercisability Date
( %)
( %)
( %)
( %)
( %)

Once exercisable, this Stock Option shall continue to be exercisable at any time or times prior to the close of business on the Expiration Date, subject to the provisions hereof and of the Plan.

2. Manner of Exercise.

Payment of the purchase price for the Option Shares may be made by one or more of the following methods: (i) in cash, by certified or bank check or other instrument acceptable to the Administrator; (ii) through the delivery (or attestation to the ownership) of shares of Stock that have been purchased by the Optionee on the open market or that are beneficially owned by the Optionee and are not then subject to any restrictions under any Company plan and that otherwise satisfy any holding periods as may be required by the Administrator; (iii) by the Optionee delivering to the Company a properly executed exercise notice together with irrevocable instructions to a broker to promptly deliver to the Company cash or a check payable and acceptable to the Company to pay the option purchase price, provided that in the event the Optionee chooses to pay the option purchase price as so provided, the Optionee and the broker shall comply with such procedures and enter into such agreements of indemnity and other

agreements as the Administrator shall prescribe as a condition of such payment procedure; (iv) by a “net exercise” arrangement pursuant to which the Company will reduce the number of shares of Stock issuable upon exercise by the largest whole number of shares with a Fair Market Value that does not exceed the aggregate exercise price; or (v) a combination of (i), (ii), (iii) and (iv) above. Payment instruments will be received subject to collection.

(d) Notwithstanding any other provision hereof or of the Plan, no portion of this Stock Option shall be exercisable after the Expiration Date hereof.

(d) Other Termination. If the Optionee’s employment terminates for any reason other than the Optionee’s death, the Optionee’s disability or Cause, and unless otherwise determined by the Administrator, any portion of this Stock Option outstanding on such date may be exercised, to the extent exercisable on the date of termination, for a period of three months from the date of termination or until the Expiration Date, if earlier. Any portion of this Stock Option that is not exercisable on the date of termination shall terminate immediately and be of no further force or effect.

The Administrator’s determination of the reason for termination of the Optionee’s employment shall be conclusive and binding on the Optionee and his or her representatives or legatees.

6. Tax Withholding. The Optionee shall, not later than the date as of which the exercise of this Stock Option becomes a taxable event for Federal income tax purposes, pay to the Company or make arrangements satisfactory to the Administrator for payment of any Federal, state, and local taxes required by law to be withheld on account of such taxable event. The Company shall have the authority to cause the minimum required tax withholding obligation to be satisfied, in whole or in part, by withholding from shares of Stock to be issued to the Optionee a number of shares of Stock with an aggregate Fair Market Value that would satisfy the minimum withholding amount due.

7. No Obligation to Continue Employment. Neither the Company nor any Subsidiary is obligated by or as a result of the Plan or this Agreement to continue the Optionee in employment and neither the Plan nor this Agreement shall interfere in any way with the right of the Company or any Subsidiary to terminate the employment of the Optionee at any time.

8. Integration. This Agreement constitutes the entire agreement between the parties with respect to this Stock Option and supersedes all prior agreements and discussions between the parties concerning such subject matter.

9. Data Privacy Consent. In order to administer the Plan and this Agreement and to implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant Companies”) may process any and all personal or professional data, including but not limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or desirable for the administration of the Plan and/or this Agreement (the “Relevant Information”). By entering into this Agreement, the Optionee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all Relevant Information; (ii) waives any privacy rights the Optionee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and (iv) authorizes the transfer of the Relevant Information to any jurisdiction in which the Relevant Companies consider appropriate. The Optionee shall have access to, and the right to change, the Relevant Information. Relevant Information will only be used in accordance with applicable law.

10. Notices. Notices hereunder shall be mailed or delivered to the Company at its principal place of business and shall be mailed or delivered to the Optionee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing.


DIMENSION THERAPEUTICS, INC.



By:
		Title:


Dated:
						Optionee’s Signature

						Optionee’s name and address:

NON-QUALIFIED STOCK OPTION AGREEMENT

FOR NON-EMPLOYEE DIRECTORS

UNDER THE DIMENSION THERAPEUTICS, INC.

2015 STOCK OPTION AND INCENTIVE PLAN

Name of Optionee:

No. of Option Shares:

Option Exercise Price per Share: $

Grant Date:

Expiration Date:

Pursuant to the Dimension Therapeutics, Inc. 2015 Stock Option and Incentive Plan as amended through the date hereof (the “Plan”), Dimension Therapeutics, Inc. (the “Company”) hereby grants to the Optionee named above, who is a member of the Board (a “Director”) but is not an employee of the Company, an option (the “Stock Option”) to purchase on or prior to the Expiration Date specified above all or part of the number of shares of Common Stock, par value $0.0001 per share (the “Stock”), of the Company specified above at the Option Exercise Price per Share specified above subject to the terms and conditions set forth herein and in the Plan. This Stock Option is not intended to be an “incentive stock option” under Section 422 of the Internal Revenue Code of 1986, as amended.


Incremental Number of Option Shares Exercisable		Exercisability Date
( %)
( %)
( %)
( %)
( %)

Once exercisable, this Stock Option shall continue to be exercisable at any time or times prior to the close of business on the Expiration Date, subject to the provisions hereof and of the Plan.

2. Manner of Exercise.

Optionee and the broker shall comply with such procedures and enter into such agreements of indemnity and other agreements as the Administrator shall prescribe as a condition of such payment procedure; (iv) by a “net exercise” arrangement pursuant to which the Company will reduce the number of shares of Stock issuable upon exercise by the largest whole number of shares with a Fair Market Value that does not exceed the aggregate exercise price; or (v) a combination of (i), (ii), (iii) and (iv) above. Payment instruments will be received subject to collection.

(d) Notwithstanding any other provision hereof or of the Plan, no portion of this Stock Option shall be exercisable after the Expiration Date hereof.

3. Termination as Director. If the Optionee ceases to be a Director of the Company, the period within which to exercise the Stock Option may be subject to earlier termination as set forth below.

(a) Termination Due to Death. If the Optionee’s service as a Director terminates by reason of the Optionee’s death, any portion of this Stock Option outstanding on such date, to the extent exercisable on the date of death, may thereafter be exercised by the Optionee’s legal representative or legatee for a period of 12 months from the date of death or until the Expiration Date, if earlier. Any portion of this Stock Option that is not exercisable on the date of death shall terminate immediately and be of no further force or effect.

(b) Other Termination. If the Optionee ceases to be a Director for any reason other than the Optionee’s death, any portion of this Stock Option outstanding on such date may be exercised, to the extent exercisable on the date the Optionee ceased to be a Director, for a period of six months from the date the Optionee ceased to be a Director or until the Expiration Date, if earlier. Any portion of this Stock Option that is not exercisable on the date the Optionee ceases to be a Director shall terminate immediately and be of no further force or effect.

6. No Obligation to Continue as a Director. Neither the Plan nor this Stock Option confers upon the Optionee any rights with respect to continuance as a Director.

7. Integration. This Agreement constitutes the entire agreement between the parties with respect to this Stock Option and supersedes all prior agreements and discussions between the parties concerning such subject matter.

8. Data Privacy Consent. In order to administer the Plan and this Agreement and to implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant Companies”) may process any and all personal or professional data, including but not limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or desirable for the administration of the Plan and/or this Agreement (the “Relevant Information”). By entering into this Agreement, the Optionee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all Relevant Information; (ii) waives any privacy rights the Optionee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and (iv) authorizes the transfer of the Relevant Information to any jurisdiction in which the Relevant Companies consider appropriate. The Optionee shall have access to, and the right to change, the Relevant Information. Relevant Information will only be used in accordance with applicable law.

9. Notices. Notices hereunder shall be mailed or delivered to the Company at its principal place of business and shall be mailed or delivered to the Optionee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing.


DIMENSION THERAPEUTICS, INC.



By:
		Title:


Dated:
						Optionee’s Signature

						Optionee’s name and address:

RESTRICTED STOCK AWARD AGREEMENT

UNDER THE DIMENSION THERAPEUTICS, INC.

2015 STOCK OPTION AND INCENTIVE PLAN

Name of Grantee:

No. of Shares:

Grant Date:

Pursuant to the Dimension Therapeutics, Inc. 2015 Stock Option and Incentive Plan (the “Plan”) as amended through the date hereof, Dimension Therapeutics, Inc. (the “Company”) hereby grants a Restricted Stock Award (an “Award”) to the Grantee named above. Upon acceptance of this Award, the Grantee shall receive the number of shares of Common Stock, par value $0.0001 per share (the “Stock”), of the Company specified above, subject to the restrictions and conditions set forth herein and in the Plan. The Company acknowledges the receipt from the Grantee of consideration with respect to the par value of the Stock in the form of cash, past or future services rendered to the Company by the Grantee or such other form of consideration as is acceptable to the Administrator.

1. Award. The shares of Restricted Stock awarded hereunder shall be issued and held by the Company’s transfer agent in book entry form, and the Grantee’s name shall be entered as the stockholder of record on the books of the Company. Thereupon, the Grantee shall have all the rights of a stockholder with respect to such shares, including voting and dividend rights, subject, however, to the restrictions and conditions specified in Paragraph 2 below. The Grantee shall (i) sign and deliver to the Company a copy of this Award Agreement and (ii) deliver to the Company a stock power endorsed in blank.

2. Restrictions and Conditions.

(a) Any book entries for the shares of Restricted Stock granted herein shall bear an appropriate legend, as determined by the Administrator in its sole discretion, to the effect that such shares are subject to restrictions as set forth herein and in the Plan.

(b) Shares of Restricted Stock granted herein may not be sold, assigned, transferred, pledged or otherwise encumbered or disposed of by the Grantee prior to vesting.

(c) If the Grantee’s employment with the Company and its Subsidiaries is voluntarily or involuntarily terminated for any reason (including death) prior to vesting of shares of Restricted Stock granted herein, all shares of Restricted Stock shall immediately and automatically be forfeited and returned to the Company.

3. Vesting of Restricted Stock. The restrictions and conditions in Paragraph 2 of this Agreement shall lapse on the Vesting Date or Dates specified in the following schedule so long as the Grantee remains an employee of the Company or a Subsidiary on such Dates. If a series of Vesting Dates is specified, then the restrictions and conditions in Paragraph 2 shall lapse only with respect to the number of shares of Restricted Stock specified as vested on such date.


Incremental Number of Shares Vested		Vesting Date
( %)
( %)
( %)
( %)
( %)

Subsequent to such Vesting Date or Dates, the shares of Stock on which all restrictions and conditions have lapsed shall no longer be deemed Restricted Stock. The Administrator may at any time accelerate the vesting schedule specified in this Paragraph 3.

4. Dividends. Dividends on shares of Restricted Stock shall be paid currently to the Grantee.

5. Incorporation of Plan. Notwithstanding anything herein to the contrary, this Award shall be subject to and governed by all the terms and conditions of the Plan, including the powers of the Administrator set forth in Section 2(b) of the Plan. Capitalized terms in this Agreement shall have the meaning specified in the Plan, unless a different meaning is specified herein.

6. Transferability. This Agreement is personal to the Grantee, is non-assignable and is not transferable in any manner, by operation of law or otherwise, other than by will or the laws of descent and distribution.

7. Tax Withholding. The Grantee shall, not later than the date as of which the receipt of this Award becomes a taxable event for Federal income tax purposes, pay to the Company or make arrangements satisfactory to the Administrator for payment of any Federal, state, and local taxes required by law to be withheld on account of such taxable event. Except in the case where an election is made pursuant to Paragraph 8 below, the Company shall have the authority to cause the required minimum tax withholding obligation to be satisfied, in whole or in part, by withholding from shares of Stock to be issued or released by the transfer agent a number of shares of Stock with an aggregate Fair Market Value that would satisfy the minimum withholding amount due.

8. Election Under Section 83(b). The Grantee and the Company hereby agree that the Grantee may, within 30 days following the Grant Date of this Award, file with the Internal Revenue Service and the Company an election under Section 83(b) of the Internal Revenue Code. In the event the Grantee makes such an election, he or she agrees to provide a copy of the election to the Company. The Grantee acknowledges that he or she is responsible for obtaining the advice of his or her tax advisors with regard to the Section 83(b) election and that he or she is relying solely on such advisors and not on any statements or representations of the Company or any of its agents with regard to such election.

9. No Obligation to Continue Employment. Neither the Company nor any Subsidiary is obligated by or as a result of the Plan or this Agreement to continue the Grantee in employment and neither the Plan nor this Agreement shall interfere in any way with the right of the Company or any Subsidiary to terminate the employment of the Grantee at any time.

10. Integration. This Agreement constitutes the entire agreement between the parties with respect to this Award and supersedes all prior agreements and discussions between the parties concerning such subject matter.

11. Data Privacy Consent. In order to administer the Plan and this Agreement and to implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant Companies”) may process any and all personal or professional data, including but not limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or desirable for the administration of the Plan and/or this Agreement (the “Relevant Information”). By entering into this Agreement, the Grantee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all Relevant Information; (ii) waives any privacy rights the Grantee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and (iv) authorizes the transfer of the Relevant Information to any jurisdiction in which the Relevant Companies consider appropriate. The Grantee shall have access to, and the right to change, the Relevant Information. Relevant Information will only be used in accordance with applicable law.

12. Notices. Notices hereunder shall be mailed or delivered to the Company at its principal place of business and shall be mailed or delivered to the Grantee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing.


DIMENSION THERAPEUTICS, INC.



By:
		Title:

The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned. Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Grantee (including through an online acceptance process) is acceptable.


Dated:
						Grantee’s Signature

						Grantee’s name and address:

RESTRICTED STOCK UNIT AWARD AGREEMENT

FOR COMPANY EMPLOYEES

UNDER THE DIMENSION THERAPEUTICS, INC.

2015 STOCK OPTION AND INCENTIVE PLAN

Name of Grantee:

No. of Restricted Stock Units:

Grant Date:

Pursuant to the Dimension Therapeutics, Inc. 2015 Stock Option and Incentive Plan as amended through the date hereof (the “Plan”), Dimension Therapeutics, Inc. (the “Company”) hereby grants an award of the number of Restricted Stock Units listed above (an “Award”) to the Grantee named above. Each Restricted Stock Unit shall relate to one share of Common Stock, par value $0.0001 per share (the “Stock”), of the Company.

1. Restrictions on Transfer of Award. This Award may not be sold, transferred, pledged, assigned or otherwise encumbered or disposed of by the Grantee, and any shares of Stock issuable with respect to the Award may not be sold, transferred, pledged, assigned or otherwise encumbered or disposed of until (i) the Restricted Stock Units have vested as provided in Paragraph 2 of this Agreement and (ii) shares of Stock have been issued to the Grantee in accordance with the terms of the Plan and this Agreement.

2. Vesting of Restricted Stock Units. The restrictions and conditions of Paragraph 1 of this Agreement shall lapse on the Vesting Date or Dates specified in the following schedule so long as the Grantee remains an employee of the Company or a Subsidiary on such Dates. If a series of Vesting Dates is specified, then the restrictions and conditions in Paragraph 1 shall lapse only with respect to the number of Restricted Stock Units specified as vested on such date.


Incremental Number of Restricted Stock Units Vested		Vesting Date
( %)
( %)
( %)
( %)
( %)

The Administrator may at any time accelerate the vesting schedule specified in this Paragraph 2.

3. Termination of Employment. If the Grantee’s employment with the Company and its Subsidiaries terminates for any reason (including death or disability) prior to the satisfaction of the vesting conditions set forth in Paragraph 2 above, any Restricted Stock Units that have not vested as of such date shall automatically and without notice terminate and be forfeited, and neither the Grantee nor any of his or her successors, heirs, assigns, or personal representatives will thereafter have any further rights or interests in such unvested Restricted Stock Units.

4. Issuance of Shares of Stock. As soon as practicable following each Vesting Date (but in no event later than two and one-half months after the end of the year in which the Vesting Date occurs), the Company shall issue to the Grantee the number of shares of Stock equal to the aggregate number of Restricted Stock Units that have vested pursuant to Paragraph 2 of this Agreement on such date and the Grantee shall thereafter have all the rights of a stockholder of the Company with respect to such shares.

5. Incorporation of Plan. Notwithstanding anything herein to the contrary, this Agreement shall be subject to and governed by all the terms and conditions of the Plan, including the powers of the Administrator set forth in Section 2(b) of the Plan. Capitalized terms in this Agreement shall have the meaning specified in the Plan, unless a different meaning is specified herein.

6. Tax Withholding. The Grantee shall, not later than the date as of which the receipt of this Award becomes a taxable event for Federal income tax purposes, pay to the Company or make arrangements satisfactory to the Administrator for payment of any Federal, state, and local taxes required by law to be withheld on account of such taxable event. The Company shall have the authority to cause the required minimum tax withholding obligation to be satisfied, in whole or in part, by withholding from shares of Stock to be issued to the Grantee a number of shares of Stock with an aggregate Fair Market Value that would satisfy the withholding amount due.

7. Section 409A of the Code. This Agreement shall be interpreted in such a manner that all provisions relating to the settlement of the Award are exempt from the requirements of Section 409A of the Code as “short-term deferrals” as described in Section 409A of the Code.

8. No Obligation to Continue Employment. Neither the Company nor any Subsidiary is obligated by or as a result of the Plan or this Agreement to continue the Grantee in employment and neither the Plan nor this Agreement shall interfere in any way with the right of the Company or any Subsidiary to terminate the employment of the Grantee at any time.

9. Integration. This Agreement constitutes the entire agreement between the parties with respect to this Award and supersedes all prior agreements and discussions between the parties concerning such subject matter.

10. Data Privacy Consent. In order to administer the Plan and this Agreement and to implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant Companies”) may process any and all personal or professional data, including but not limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or desirable for the administration of the Plan and/or this Agreement (the “Relevant Information”). By entering into this Agreement, the Grantee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all Relevant Information; (ii) waives any privacy rights the Grantee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and (iv) authorizes the transfer of the Relevant Information to any jurisdiction in which the Relevant Companies consider appropriate. The Grantee shall have access to, and the right to change, the Relevant Information. Relevant Information will only be used in accordance with applicable law.

11. Notices. Notices hereunder shall be mailed or delivered to the Company at its principal place of business and shall be mailed or delivered to the Grantee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing.


DIMENSION THERAPEUTICS, INC.



By:
		Title:

The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned. Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Grantee (including through an online acceptance process) is acceptable.


Dated:
						Grantee’s Signature

						Grantee’s name and address:

RESTRICTED STOCK UNIT AWARD AGREEMENT

FOR NON-EMPLOYEE DIRECTORS

UNDER THE DIMENSION THERAPEUTICS, INC.

2015 STOCK OPTION AND INCENTIVE PLAN

Name of Grantee:

No. of Restricted Stock Units:

Grant Date:

Pursuant to the Dimension Therapeutics, Inc. 2015 Stock Option and Incentive Plan as amended through the date hereof (the “Plan”), Dimension Therapeutics, Inc. (the “Company”) hereby grants an award of the number of Restricted Stock Units listed above (an “Award”) to the Grantee named above. Each Restricted Stock Unit shall relate to one share of Common Stock, par value $0.0001 per share (the “Stock”), of the Company.

2. Vesting of Restricted Stock Units. The restrictions and conditions of Paragraph 1 of this Agreement shall lapse on the Vesting Date or Dates specified in the following schedule so long as the Grantee remains in service as a member of the Board on such Dates. If a series of Vesting Dates is specified, then the restrictions and conditions in Paragraph 1 shall lapse only with respect to the number of Restricted Stock Units specified as vested on such date.


Incremental Number of Restricted Stock Units Vested		Vesting Date
( %)
( %)
( %)
( %)
( %)

The Administrator may at any time accelerate the vesting schedule specified in this Paragraph 2.

3. Termination of Service. If the Grantee’s service as a member of the Board terminates for any reason (including death or disability) prior to the satisfaction of the vesting conditions set forth in Paragraph 2 above, any Restricted Stock Units that have not vested as of such date shall automatically and without notice terminate and be forfeited, and neither the Grantee nor any of his or her successors, heirs, assigns, or personal representatives will thereafter have any further rights or interests in such unvested Restricted Stock Units.

6. Section 409A of the Code. This Agreement shall be interpreted in such a manner that all provisions relating to the settlement of the Award are exempt from the requirements of Section 409A of the Code as “short-term deferrals” as described in Section 409A of the Code.

7. No Obligation to Continue as a Director. Neither the Plan nor this Award confers upon the Grantee any rights with respect to continuance as a member of the Board.

8. Integration. This Agreement constitutes the entire agreement between the parties with respect to this Award and supersedes all prior agreements and discussions between the parties concerning such subject matter.

9. Data Privacy Consent. In order to administer the Plan and this Agreement and to implement or structure future equity grants, the Company, its subsidiaries and affiliates and certain agents thereof (together, the “Relevant Companies”) may process any and all personal or professional data, including but not limited to Social Security or other identification number, home address and telephone number, date of birth and other information that is necessary or desirable for the administration of the Plan and/or this Agreement (the “Relevant Information”). By entering into this Agreement, the Grantee (i) authorizes the Company to collect, process, register and transfer to the Relevant Companies all Relevant Information; (ii) waives any privacy rights the Grantee may have with respect to the Relevant Information; (iii) authorizes the Relevant Companies to store and transmit such information in electronic form; and (iv) authorizes the transfer of the Relevant Information to any jurisdiction in which the Relevant Companies consider appropriate. The Grantee shall have access to, and the right to change, the Relevant Information. Relevant Information will only be used in accordance with applicable law.

10. Notices. Notices hereunder shall be mailed or delivered to the Company at its principal place of business and shall be mailed or delivered to the Grantee at the address on file with the Company or, in either case, at such other address as one party may subsequently furnish to the other party in writing.


DIMENSION THERAPEUTICS, INC.



By:
		Title:

The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby agreed to by the undersigned. Electronic acceptance of this Agreement pursuant to the Company’s instructions to the Grantee (including through an online acceptance process) is acceptable.


Dated:
						Grantee’s Signature

						Grantee’s name and address:

EX-4.5

Exhibit 4.5

DIMENSION THERAPEUTICS, INC.

2013 STOCK PLAN

ADOPTED ON OCTOBER 29, 2013

TABLE OF CONTENTS


			Page

SECTION 1.	ESTABLISHMENT AND PURPOSE			1

SECTION 2.	ADMINISTRATION			1

	(a)	Committees of the Board of Directors		1
	(b)	Authority of the Board of Directors		1

SECTION 3.	ELIGIBILITY			1

	(a)	General Rule		1
	(b)	Ten-Percent Stockholders		1

SECTION 4.	STOCK SUBJECT TO PLAN			2

	(a)	Basic Limitation		2
	(b)	Additional Shares		2

SECTION 5.	TERMS AND CONDITIONS OF AWARDS OR SALES			2

	(a)	Stock Grant or Purchase Agreement		2
	(b)	Duration of Offers and Nontransferability of Rights		2
	(c)	Purchase Price		3

SECTION 6.	TERMS AND CONDITIONS OF OPTIONS			3

	(a)	Stock Option Agreement		3
	(b)	Number of Shares		3
	(c)	Exercise Price		3
	(d)	Exercisability		3
	(e)	Basic Term		3
	(f)	Termination of Service (Except by Death)		3
	(g)	Leaves of Absence		4
	(h)	Death of Optionee		4
	(i)	Restrictions on Transfer of Options		4
	(j)	No Rights as a Stockholder		5
	(k)	Modification, Extension and Assumption of Options		5
	(l)	Company’s Right to Cancel Certain Options		5

SECTION 7.	PAYMENT FOR SHARES			5

	(a)	General Rule		5
	(b)	Services Rendered		5
	(c)	Promissory Note		5
	(d)	Surrender of Stock		6
	(e)	Exercise/Sale		6
	(f)	Net Exercise		6
	(g)	Other Forms of Payment		6

SECTION 8.	ADJUSTMENT OF SHARES			6


			Page

	(a)	General		6
	(b)	Corporate Transactions		7
	(c)	Reservation of Rights		8

SECTION 9.	MISCELLANEOUS PROVISIONS			8

	(a)	Securities Law Requirements		8
	(b)	No Retention Rights		8
	(c)	Treatment as Compensation		8
	(d)	Governing Law		9
	(e)	Conditions and Restrictions on Shares		9
	(f)	Tax Matters		9

SECTION 10.	DURATION AND AMENDMENTS; STOCKHOLDER APPROVAL			10

	(a)	Term of the Plan		10
	(b)	Right to Amend or Terminate the Plan		10
	(c)	Effect of Amendment or Termination		10
	(d)	Stockholder Approval		10

SECTION 11.	DEFINITIONS			10

DIMENSION THERAPEUTICS, INC. 2013 STOCK PLAN

SECTION 1.

ESTABLISHMENT AND PURPOSE.

The purpose of this Plan is to offer persons selected by the Company an opportunity to acquire a proprietary interest in the success of the Company, or to increase such interest, by acquiring Shares of the Company’s Stock. The Plan provides both for the direct award or sale of Shares and for the grant of Options to purchase Shares. Options granted under the Plan may be ISOs intended to qualify under Code Section 422 or NSOs which are not intended to so qualify.

Capitalized terms are defined in Section 11.

SECTION 2.

ADMINISTRATION.

(a) Committees of the Board of Directors. The Plan may be administered by one or more Committees. Each Committee shall consist, as required by applicable law, of one or more members of the Board of Directors who have been appointed by the Board of Directors. Each Committee shall have such authority and be responsible for such functions as the Board of Directors has assigned to it. If no Committee has been appointed, the entire Board of Directors shall administer the Plan. Any reference to the Board of Directors in the Plan shall be construed as a reference to the Committee (if any) to whom the Board of Directors has assigned a particular function.

(b) Authority of the Board of Directors. Subject to the provisions of the Plan, the Board of Directors shall have full authority and discretion to take any actions it deems necessary or advisable for the administration of the Plan. Notwithstanding anything to the contrary in the Plan, with respect to the terms and conditions of awards granted to Participants outside the United States, the Board of Directors may vary from the provisions of the Plan to the extent it determines it necessary and appropriate to do so; provided that it may not vary from those Plan terms requiring stockholder approval pursuant to Section 10(d) below. All decisions, interpretations and other actions of the Board of Directors shall be final and binding on all Purchasers, all Optionees and all persons deriving their rights from a Purchaser or Optionee.

SECTION 3.

ELIGIBILITY.

(a) General Rule. Only Employees, Outside Directors and Consultants shall be eligible for the grant of NSOs or the direct award or sale of Shares¹. Only Employees shall be eligible for the grant of ISOs.

(b) Ten-Percent Stockholders. A person who owns more than 10% of the total combined voting power of all classes of outstanding stock of the Company, its Parent or any of its Subsidiaries shall not be eligible for the grant of an ISO unless (i) the Exercise Price is

¹	Note that special considerations apply if the Company proposes to grant awards to an Employee or Consultant of a Parent company.

at least 110% of the Fair Market Value of a Share on the Date of Grant and (ii) such ISO by its terms is not exercisable after the expiration of five years from the Date of Grant. For purposes of this Subsection (b), in determining stock ownership, the attribution rules of Code Section 424(d) shall be applied.

SECTION 4.

STOCK SUBJECT TO PLAN.

(a) Basic Limitation. Not more than 10,000,000 Shares may be issued under the Plan, subject to Subsection (b) below and Section 8(a).² All of these Shares may be issued upon the exercise of ISOs. The number of Shares that are subject to Options or other rights outstanding at any time under the Plan may not exceed the number of Shares that then remain available for issuance under the Plan. The Company, during the term of the Plan, shall at all times reserve and keep available sufficient Shares to satisfy the requirements of the Plan. Shares offered under the Plan may be authorized but unissued Shares or treasury Shares.

(b) Additional Shares. In the event that Shares previously issued under the Plan are reacquired by the Company, such Shares shall be added to the number of Shares then available for issuance under the Plan. In the event that Shares that otherwise would have been issuable under the Plan are withheld by the Company in payment of the Purchase Price, Exercise Price or withholding taxes, such Shares shall remain available for issuance under the Plan. In the event that an outstanding Option or other right for any reason expires or is canceled, the Shares allocable to the unexercised portion of such Option or other right shall be added to the number of Shares then available for issuance under the Plan.

SECTION 5.

TERMS AND CONDITIONS OF AWARDS OR SALES.

(a) Stock Grant or Purchase Agreement. Each award of Shares under the Plan shall be evidenced by a Stock Grant Agreement between the Grantee and the Company. Each sale of Shares under the Plan (other than upon exercise of an Option) shall be evidenced by a Stock Purchase Agreement between the Purchaser and the Company. Such award or sale shall be subject to all applicable terms and conditions of the Plan and may be subject to any other terms and conditions which are not inconsistent with the Plan and which the Board of Directors deems appropriate for inclusion in a Stock Grant Agreement or Stock Purchase Agreement. The provisions of the various Stock Grant Agreements and Stock Purchase Agreements entered into under the Plan need not be identical.

(b) Duration of Offers and Nontransferability of Rights. Any right to purchase Shares under the Plan (other than an Option) shall automatically expire if not exercised by the Purchaser within 30 days (or such other period as may be specified in the Award Agreement) after the grant of such right was communicated to the Purchaser by the Company. Such right is not transferable and may be exercised only by the Purchaser to whom such right was granted.

²	Please refer to Exhibit A for a schedule of the initial share reserve and any subsequent increases in the reserve.

(c) Purchase Price. The Board of Directors shall determine the Purchase Price of Shares to be offered under the Plan at its sole discretion. The Purchase Price shall be payable in a form described in Section 7.

SECTION 6.

TERMS AND CONDITIONS OF OPTIONS.

(a) Stock Option Agreement. Each grant of an Option under the Plan shall be evidenced by a Stock Option Agreement between the Optionee and the Company. The Option shall be subject to all applicable terms and conditions of the Plan and may be subject to any other terms and conditions that are not inconsistent with the Plan and that the Board of Directors deems appropriate for inclusion in a Stock Option Agreement. The provisions of the various Stock Option Agreements entered into under the Plan need not be identical.

(b) Number of Shares. Each Stock Option Agreement shall specify the number of Shares that are subject to the Option and shall provide for the adjustment of such number in accordance with Section 8. The Stock Option Agreement shall also specify whether the Option is an ISO or an NSO.

(c) Exercise Price. Each Stock Option Agreement shall specify the Exercise Price. The Exercise Price of an Option shall not be less than 100% of the Fair Market Value of a Share on the Date of Grant, and in the case of an ISO a higher percentage may be required by Section 3(b). Subject to the preceding sentence, the Exercise Price shall be determined by the Board of Directors at its sole discretion. The Exercise Price shall be payable in a form described in Section 7. This Subsection (c) shall not apply to an Option granted pursuant to an assumption of, or substitution for, another option in a manner that complies with Code Section 424(a) (whether or not the Option is an ISO).

(d) Exercisability. Each Stock Option Agreement shall specify the date when all or any installment of the Option is to become exercisable. No Option shall be exercisable unless the Optionee (i) has delivered an executed copy of the Stock Option Agreement to the Company or (ii) otherwise agrees to be bound by the terms of the Stock Option Agreement. The Board of Directors shall determine the exercisability provisions of the Stock Option Agreement at its sole discretion.

(e) Basic Term. The Stock Option Agreement shall specify the term of the Option. The term shall not exceed 10 years from the Date of Grant, and in the case of an ISO, a shorter term may be required by Section 3(b). Subject to the preceding sentence, the Board of Directors at its sole discretion shall determine when an Option is to expire.

(f) Termination of Service (Except by Death). If an Optionee’s Service terminates for any reason other than the Optionee’s death, then the Optionee’s Options shall expire on the earliest of the following dates:

(i) The expiration date determined pursuant to Subsection (e) above;

(ii) The date three months after the termination of the Optionee’s Service for any reason other than Disability, or such earlier or later date as the Board of Directors may determine (but in no event earlier than 30 days after the termination of the Optionee’s Service); or

(iii) The date six months after the termination of the Optionee’s Service by reason of Disability, or such later date as the Board of Directors may determine.

The Optionee may exercise all or part of the Optionee’s Options at any time before the expiration of such Options under the preceding sentence, but only to the extent that such Options had become exercisable before the Optionee’s Service terminated (or became exercisable as a result of the termination) and the underlying Shares had vested before the Optionee’s Service terminated (or vested as a result of the termination). The balance of such Options shall lapse when the Optionee’s Service terminates. In the event that the Optionee dies after the termination of the Optionee’s Service but before the expiration of the Optionee’s Options, all or part of such Options may be exercised (prior to expiration) by the executors or administrators of the Optionee’s estate or by any person who has acquired such Options directly from the Optionee by beneficiary designation, bequest or inheritance, but only to the extent that such Options had become exercisable before the Optionee’s Service terminated (or became exercisable as a result of the termination) and the underlying Shares had vested before the Optionee’s Service terminated (or vested as a result of the termination).

(g) Leaves of Absence. For purposes of Subsection (f) above, Service shall be deemed to continue while the Optionee is on a bona fide leave of absence, if such leave was approved by the Company in writing and if continued crediting of Service for this purpose is expressly required by the terms of such leave or by applicable law (as determined by the Company).

(h) Death of Optionee. If an Optionee dies while the Optionee is in Service, then the Optionee’s Options shall expire on the earlier of the following dates:

(i) The expiration date determined pursuant to Subsection (e) above; or

(ii) The date 12 months after the Optionee’s death, or such earlier or later date as the Board of Directors may determine (but in no event earlier than six months after the Optionee’s death).

All or part of the Optionee’s Options may be exercised at any time before the expiration of such Options under the preceding sentence by the executors or administrators of the Optionee’s estate or by any person who has acquired such Options directly from the Optionee by beneficiary designation, bequest or inheritance, but only to the extent that such Options had become exercisable before the Optionee’s death (or became exercisable as a result of the death) and the underlying Shares had vested before the Optionee’s death (or vested as a result of the Optionee’s death). The balance of such Options shall lapse when the Optionee dies.

(i) Restrictions on Transfer of Options. An Option shall be transferable by the Optionee only by (i) a beneficiary designation, (ii) a will or (iii) the laws of descent and distribution, except as provided in the next sentence. If the applicable Stock Option Agreement so provides, an NSO shall also be transferable by gift or domestic relations order to a Family Member of the Optionee. An ISO may be exercised during the lifetime of the Optionee only by the Optionee or by the Optionee’s guardian or legal representative.

(j) No Rights as a Stockholder. An Optionee, or a transferee of an Optionee, shall have no rights as a stockholder with respect to any Shares covered by the Optionee’s Option until such person files a notice of exercise, pays the Exercise Price and satisfies all applicable withholding taxes pursuant to the terms of such Option.

(k) Modification, Extension and Assumption of Options. Within the limitations of the Plan, the Board of Directors may modify, extend or assume outstanding Options or may accept the cancellation of outstanding Options (whether granted by the Company or another issuer) in return for the grant of new Options or a different type of award for the same or a different number of Shares and at the same or a different Exercise Price (if applicable). The foregoing notwithstanding, no modification of an Option shall, without the consent of the Optionee, impair the Optionee’s rights or increase the Optionee’s obligations under such Option.

(l) Company’s Right to Cancel Certain Options. Any other provision of the Plan or a Stock Option Agreement notwithstanding, the Company shall have the right at any time to cancel an Option that was not granted in compliance with Rule 701 under the Securities Act. Prior to canceling such Option, the Company shall give the Optionee not less than 30 days’ notice in writing. If the Company elects to cancel such Option, it shall deliver to the Optionee consideration with an aggregate Fair Market Value equal to the excess of (i) the Fair Market Value of the Shares subject to such Option as of the time of the cancellation over (ii) the Exercise Price of such Option. The consideration may be delivered in the form of cash or cash equivalents, in the form of Shares, or a combination of both. If the consideration would be a negative amount, such Option may be cancelled without the delivery of any consideration.

SECTION 7.

PAYMENT FOR SHARES.

(a) General Rule. The entire Purchase Price or Exercise Price of Shares issued under the Plan shall be payable in cash or cash equivalents at the time when such Shares are purchased, except as otherwise provided in this Section 7. In addition, the Board of Directors in its sole discretion may also permit payment through any of the methods described in (b) through (g) below.

(b) Services Rendered. Shares may be awarded under the Plan in consideration of services rendered to the Company, a Parent or a Subsidiary prior to the award.

(c) Promissory Note. All or a portion of the Purchase Price or Exercise Price (as the case may be) of Shares issued under the Plan may be paid with a full-recourse promissory note. The Shares shall be pledged as security for payment of the principal amount of the promissory note and interest thereon. The interest rate payable under the terms of the promissory note shall not be less than the minimum rate (if any) required to avoid the imputation of additional interest under the Code. Subject to the foregoing, the Board of Directors (at its sole discretion) shall specify the term, interest rate, amortization requirements (if any) and other provisions of such note.

(d) Surrender of Stock. All or any part of the Exercise Price may be paid by surrendering, or attesting to the ownership of, Shares that are already owned by the Optionee. Such Shares shall be surrendered to the Company in good form for transfer and shall be valued at their Fair Market Value as of the date when the Option is exercised.

(e) Exercise/Sale. If the Stock is publicly traded, all or part of the Exercise Price and any withholding taxes may be paid by the delivery (on a form prescribed by the Company) of an irrevocable direction to a securities broker approved by the Company to sell Shares and to deliver all or part of the sales proceeds to the Company.

(f) Net Exercise. An Option may permit exercise through a “net exercise” arrangement pursuant to which the Company will reduce the number of Shares issued upon exercise by the largest whole number of Shares having an aggregate Fair Market Value (determined by the Board of Directors as of the exercise date) that does not exceed the aggregate Exercise Price or the sum of the aggregate Exercise Price plus all or a portion of the minimum amount required to be withheld under applicable tax law (with the Company accepting from the Optionee payment of cash or cash equivalents to satisfy any remaining balance of the aggregate Exercise Price and, if applicable, any additional withholding obligation not satisfied through such reduction in Shares); provided that to the extent Shares subject to an Option are withheld in this manner, the number of Shares subject to the Option following the net exercise will be reduced by the sum of the number of Shares withheld and the number of Shares delivered to the Optionee as a result of the exercise.

(g) Other Forms of Payment. To the extent that an Award Agreement so provides, the Purchase Price or Exercise Price of Shares issued under the Plan may be paid in any other form permitted by the Delaware General Corporation Law, as amended.

SECTION 8.

ADJUSTMENT OF SHARES.

(a) General. In the event of a subdivision of the outstanding Stock, a declaration of a dividend payable in Shares, a combination or consolidation of the outstanding Stock into a lesser number of Shares, a reclassification, or any other increase or decrease in the number of issued shares of Stock effected without receipt of consideration by the Company, proportionate adjustments shall automatically be made in each of (i) the number and kind of Shares available for future grants under Section 4, (ii) the number and kind of Shares covered by each outstanding Option and any outstanding and unexercised right to purchase Shares that has not yet expired pursuant to Section 5(b), (iii) the Exercise Price under each outstanding Option and the Purchase Price applicable to any unexercised stock purchase right described in clause (ii) above, and (iv) any repurchase price that applies to Shares granted under the Plan pursuant to the terms of a Company repurchase right under the applicable Award Agreement. In the event of a declaration of an extraordinary dividend payable in a form other than Shares in an amount that has a material effect on the Fair Market Value of the Stock, a recapitalization, a spin-off, or a similar occurrence, the Board of Directors at its sole discretion may make appropriate adjustments in one or more of the items listed in clauses (i) through (iv) above; provided, however, that the Board of Directors shall in any event make such adjustments as may be required by Section 25102(o) of the California Corporations Code. No fractional Shares shall be issued under the Plan as a result of an adjustment under this Section 8(a), although the Board of Directors in its sole discretion may make a cash payment in lieu of fractional Shares.

(b) Corporate Transactions. In the event that the Company is a party to a merger or consolidation, or in the event of a sale of all or substantially all of the Company’s stock or assets, all Shares acquired under the Plan and all Options and other Plan awards outstanding on the effective date of the transaction shall be treated in the manner described in the definitive transaction agreement (or, in the event the transaction does not entail a definitive agreement to which the Company is party, in the manner determined by the Board of Directors in its capacity as administrator of the Plan, with such determination having final and binding effect on all parties), which agreement or determination need not treat all Options and awards (or all portions of an Option or an award) in an identical manner. The treatment specified in the transaction agreement or as determined by the Board of Directors may include (without limitation) one or more of the following with respect to each outstanding Option or award:

(i) Continuation of the Option or award by the Company (if the Company is the surviving corporation).

(ii) Assumption of the Option by the surviving corporation or its parent in a manner that complies with Code Section 424(a) (whether or not the Option is an ISO).

(iii) Substitution by the surviving corporation or its parent of a new option for the Option in a manner that complies with Code Section 424(a) (whether or not the Option is an ISO).

(iv) Cancellation of the Option and a payment to the Optionee with respect to each Share subject to the portion of the Option that is vested as of the transaction date equal to the excess of (A) the value, as determined by the Board of Directors in its absolute discretion, of the property (including cash) received by the holder of a share of Stock as a result of the transaction, over (B) the per-Share Exercise Price of the Option (such excess, the “Spread”). Such payment shall be made in the form of cash, cash equivalents, or securities of the surviving corporation or its parent having a value equal to the Spread. In addition, any escrow, holdback, earn-out or similar provisions in the transaction agreement may apply to such payment to the same extent and in the same manner as such provisions apply to the holders of Stock. If the Spread applicable to an Option is zero or a negative number, then the Option may be cancelled without making a payment to the Optionee.

(v) Cancellation of the Option without the payment of any consideration; provided that the Optionee shall be notified of such treatment and given an opportunity to exercise the Option (to the extent the Option is vested or becomes vested as of the effective date of the transaction) during a period of not less than five (5) business days preceding the effective date of the transaction, unless (A) a shorter period is required to permit a timely closing of the transaction and (B) such shorter period still offers the Optionee a reasonable opportunity to exercise the Option. Any exercise of the Option during such period may be contingent upon the closing of the transaction.

(vi) Suspension of the Optionee’s right to exercise the Option during a limited period of time preceding the closing of the transaction if such suspension is administratively necessary to permit the closing of the transaction.

(vii) Termination of any right the Optionee has to exercise the Option prior to vesting in the Shares subject to the Option (i.e., “early exercise”), such that following the closing of the transaction the Option may only be exercised to the extent it is vested.

For the avoidance of doubt, the Board of Directors has discretion to accelerate, in whole or part, the vesting and exercisability of an Option or other Plan award in connection with a corporate transaction covered by this Section 8(b).

(c) Reservation of Rights. Except as provided in this Section 8, a Participant shall have no rights by reason of (i) any subdivision or consolidation of shares of stock of any class, (ii) the payment of any dividend or (iii) any other increase or decrease in the number of shares of stock of any class. Any issuance by the Company of shares of stock of any class, or securities convertible into shares of stock of any class, shall not affect, and no adjustment by reason thereof shall be made with respect to, the number or Exercise Price of Shares subject to an Option. The grant of an Option pursuant to the Plan shall not affect in any way the right or power of the Company to make adjustments, reclassifications, reorganizations or changes of its capital or business structure, to merge or consolidate or to dissolve, liquidate, sell or transfer all or any part of its business or assets.

SECTION 9.

MISCELLANEOUS PROVISIONS.

(a) Securities Law Requirements. Shares shall not be issued under the Plan unless, in the opinion of counsel acceptable to the Board of Directors, the issuance and delivery of such Shares comply with (or are exempt from) all applicable requirements of law, including (without limitation) the Securities Act, the rules and regulations promulgated thereunder, state securities laws and regulations, and the regulations of any stock exchange or other securities market on which the Company’s securities may then be traded. The Company shall not be liable for a failure to issue Shares as a result of such requirements.

(b) No Retention Rights. Nothing in the Plan or in any right or Option granted under the Plan shall confer upon the Participant any right to continue in Service for any period of specific duration or interfere with or otherwise restrict in any way the rights of the Company (or any Parent or Subsidiary employing or retaining the Participant) or of the Participant, which rights are hereby expressly reserved by each, to terminate his or her Service at any time and for any reason, with or without cause.

(c) Treatment as Compensation. Any compensation that an individual earns or is deemed to earn under this Plan shall not be considered a part of his or her compensation for purposes of calculating contributions, accruals or benefits under any other plan or program that is maintained or funded by the Company, a Parent or a Subsidiary.

(d) Governing Law. The Plan and all awards, sales and grants under the Plan shall be governed by, and construed in accordance with, the laws of the State of Delaware, as such laws are applied to contracts entered into and performed in such State.

(e) Conditions and Restrictions on Shares. Shares issued under the Plan shall be subject to such forfeiture conditions, rights of repurchase, rights of first refusal, other transfer restrictions and such other terms and conditions as the Board of Directors may determine. Such conditions and restrictions shall be set forth in the applicable Award Agreement and shall apply in addition to any restrictions that may apply to holders of Shares generally. In addition, Shares issued under the Plan shall be subject to conditions and restrictions imposed either by applicable law or by Company policy, as adopted from time to time, designed to ensure compliance with applicable law or laws with which the Company determines in its sole discretion to comply including in order to maintain any statutory, regulatory or tax advantage.

(f) Tax Matters.

(i) As a condition to the award, grant, issuance, vesting, purchase, exercise or transfer of any award, or Shares issued pursuant to any award, granted under this Plan, the Participant shall make such arrangements as the Board of Directors may require or permit for the satisfaction of any federal, state, local or foreign withholding tax obligations that may arise in connection with such event.

(ii) Unless otherwise expressly set forth in an Award Agreement, it is intended that awards granted under the Plan shall be exempt from Code Section 409A, and any ambiguity in the terms of an Award Agreement and the Plan shall be interpreted consistently with this intent. To the extent an award is not exempt from Code Section 409A (any such award, a “409A Award”), any ambiguity in the terms of such award and the Plan shall be interpreted in a manner that to the maximum extent permissible supports the award’s compliance with the requirements of that statute. Notwithstanding anything to the contrary permitted under the Plan, in no event shall a modification of an Award not already subject to Code Section 409A be given effect if such modification would cause the Award to become subject to Code Section 409A unless the parties explicitly acknowledge and consent to the modification as one having that effect. A 409A Award shall be subject to such additional rules and requirements as specified by the Board of Directors from time to time in order for it to comply with the requirements of Code Section 409A. In this regard, if any amount under a 409A Award is payable upon a “separation from service” to an individual who is considered a “specified employee” (as each term is defined under Code Section 409A), then no such payment shall be made prior to the date that is the earlier of (i) six months and one day after the Participant’s separation from service or (ii) the Participant’s death, but only to the extent such delay is necessary to prevent such payment from being subject to Section 409A(a)(1). In addition, if a transaction subject to Section 8(b) constitutes a payment event with respect to any 409A Award, then the transaction with respect to such award must also constitute a “change in control event” as defined in Treasury Regulation Section 1.409A-3(i)(5) to the extent required by Code Section 409A.

(iii) Neither the Company nor any member of the Board of Directors shall have any liability to a Participant in the event an award held by the Participant fails to achieve its intended characterization under applicable tax law.

SECTION 10.

DURATION AND AMENDMENTS; STOCKHOLDER APPROVAL.

(a) Term of the Plan. The Plan, as set forth herein, shall become effective on the date of its adoption by the Board of Directors, subject to approval of the Company’s stockholders under Subsection (d) below. The Plan shall terminate automatically 10 years after the later of (i) the date when the Board of Directors adopted the Plan or (ii) the date when the Board of Directors approved the most recent increase in the number of Shares reserved under Section 4 that was also approved by the Company’s stockholders. The Plan may be terminated on any earlier date pursuant to Subsection (b) below.

(b) Right to Amend or Terminate the Plan. Subject to Subsection (d) below, the Board of Directors may amend, suspend or terminate the Plan at any time and for any reason.

(c) Effect of Amendment or Termination. No Shares shall be issued or sold and no Option granted under the Plan after the termination thereof, except upon exercise of an Option (or any other right to purchase Shares) granted under the Plan prior to such termination. The termination of the Plan, or any amendment thereof, shall not affect any Share previously issued or any Option previously granted under the Plan.

(d) Stockholder Approval. To the extent required by applicable law, the Plan will be subject to approval of the Company’s stockholders within 12 months of its adoption date. To the extent required by applicable law, any amendment of the Plan will be subject to the approval of the Company’s stockholders within 12 months of the amendment date if it (i) increases the number of Shares available for issuance under the Plan (except as provided in Section 8), or (ii) materially changes the class of persons who are eligible for the grant of ISOs. In addition, an amendment effecting any other material change to the Plan terms will be subject to approval of the Company’s stockholder only if required by applicable law. Stockholder approval shall not be required for any other amendment of the Plan.

SECTION 11. DEFINITIONS.

(a) “Award Agreement” means a Stock Grant Agreement, Stock Option Agreement or Stock Purchase Agreement.

(b) “Board of Directors” means the Board of Directors of the Company, as constituted from time to time.

(d) “Committee” means a committee of the Board of Directors, as described in Section 2(a).

(e) “Company” means Dimension Therapeutics, Inc., a Delaware corporation.

(f) “Consultant” means a person, excluding Employees and Outside Directors, who performs bona fide services for the Company, a Parent³ or a Subsidiary as a consultant or advisor and who qualifies as a consultant or advisor under Rule 701(c)(1) of the Securities Act or under Instruction A.1.(a)(1) of Form S-8 under the Securities Act.

(g) “Date of Grant” means the date of grant specified in the applicable Stock Option Agreement, which date shall be the later of (i) the date on which the Board of Directors resolved to grant the Option or (ii) the first day of the Optionee’s Service.

(h) “Disability” means that the Optionee is unable to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment.

(i) “Employee” means any individual who is a common-law employee of the Company, a Parent⁴ or a Subsidiary.

(j) “Exchange Act” means the Securities Exchange Act of 1934, as amended.

(k) “Exercise Price” means the amount for which one Share may be purchased upon exercise of an Option, as specified by the Board of Directors in the applicable Stock Option Agreement.

(l) “Fair Market Value” means the fair market value of a Share, as determined by the Board of Directors in good faith. Such determination shall be conclusive and binding on all persons.

(m) “Family Member” means (i) any child, stepchild, grandchild, parent, stepparent, grandparent, spouse, former spouse, sibling, niece, nephew, mother-in-law, father-in-law, son-in-law, daughter-in-law, brother-in-law or sister-in-law, including adoptive relationships, (ii) any person sharing the Optionee’s household (other than a tenant or employee), (iii) a trust in which persons described in Clause (i) or (ii) have more than 50% of the beneficial interest, (iv) a foundation in which persons described in Clause (i) or (ii) or the Optionee control the management of assets and (v) any other entity in which persons described in Clause (i) or (ii) or the Optionee own more than 50% of the voting interests.

(n) “Grantee” means a person to whom the Board of Directors has awarded Shares under the Plan.

(o) “ISO” means an Option that qualifies as an incentive stock option as described in Code Section 422(b). Notwithstanding its designation as an ISO, an Option that does not qualify as an ISO under applicable law shall be treated for all purposes as an NSO.

³	Note that special considerations apply if the Company proposes to grant awards to consultant or advisor of a Parent company.

⁴	Note that special considerations apply if the Company proposes to grant awards to Employee of a Parent company.

(p) “NSO” means an Option that does not qualify as an incentive stock option as described in Code Section 422(b) or 423(b).

(q) “Option” means an ISO or NSO granted under the Plan and entitling the holder to purchase Shares.

(r) “Optionee” means a person who holds an Option.

(s) “Outside Director” means a member of the Board of Directors who is not an Employee.

(t) “Parent” means any corporation (other than the Company) in an unbroken chain of corporations ending with the Company, if each of the corporations other than the Company owns stock possessing 50% or more of the total combined voting power of all classes of stock in one of the other corporations in such chain. A corporation that attains the status of a Parent on a date after the adoption of the Plan shall be considered a Parent commencing as of such date.

(u) “Participant” means a Grantee, Optionee or Purchaser.

(v) “Plan” means this Dimension Therapeutics, Inc. 2013 Stock Plan.

(w) “Purchase Price” means the consideration for which one Share may be acquired under the Plan (other than upon exercise of an Option), as specified by the Board of Directors.

(x) “Purchaser” means a person to whom the Board of Directors has offered the right to purchase Shares under the Plan (other than upon exercise of an Option).

(y) “Securities Act” means the Securities Act of 1933, as amended.

(z) “Service” means service as an Employee, Outside Director or Consultant.

(aa) “Share” means one share of Stock, as adjusted in accordance with Section 8 (if applicable).

(bb) “Stock” means the Common Stock of the Company.

(cc) “Stock Grant Agreement” means the agreement between the Company and a Grantee who is awarded Shares under the Plan that contains the terms, conditions and restrictions pertaining to the award of such Shares.

(dd) “Stock Option Agreement” means the agreement between the Company and an Optionee that contains the terms, conditions and restrictions pertaining to the Optionee’s Option.

(ee) “Stock Purchase Agreement” means the agreement between the Company and a Purchaser who purchases Shares under the Plan that contains the terms, conditions and restrictions pertaining to the purchase of such Shares.

(ff) “Subsidiary” means any corporation (other than the Company) in an unbroken chain of corporations beginning with the Company, if each of the corporations other than the last

corporation in the unbroken chain owns stock possessing 50% or more of the total combined voting power of all classes of stock in one of the other corporations in such chain. A corporation that attains the status of a Subsidiary on a date after the adoption of the Plan shall be considered a Subsidiary commencing as of such date.

EXHIBIT A

SCHEDULE OF SHARES RESERVED FOR ISSUANCE UNDER THE PLAN


Date of Board Approval	Date of Stockholder Approval	Number of Shares Added		Cumulative Number of Shares
10/29/2013	10/29/2013		Not Applicable	10,000,000
02/18/2014	02/18/2014		-5,500,000	4,500,000
12/16/2014	01/30/2015		900,000	5,400,000
04/20/2015	04/20/2015		4,390,122	9,790,122
06/03/2015	06/03/2015		500,000	10,290,122

SUMMARY OF MODIFICATIONS AND AMENDMENTS TO THE PLAN

The following is a summary of material modifications made to the Plan (including any material deviations from the Gunderson Dettmer precedent form used to create the Plan):

DIMENSION THERAPEUTICS, INC. 2013 STOCK PLAN

NOTICE OF STOCK OPTION GRANT (EARLY EXERCISE)

The Optionee has been granted the following option to purchase shares of the Common Stock of Dimension Therapeutics, Inc.:


Name of Optionee:		«Name»

Total Number of Shares:		«TotalShares»

Type of Option:		«ISO» Incentive Stock Option (ISO)

		«NSO» Nonstatutory Stock Option (NSO)

Exercise Price per Share:		$«PricePerShare»

Date of Grant:		«DateGrant»

Date Exercisable:		This option may be exercised at any time after the Date of Grant for all or any part of the Shares subject to this option.

Vesting Commencement Date:		«VestComDate»

Vesting Schedule:		The Right of Repurchase shall lapse with respect to the first «Percent»% of the Shares subject to this option when the Optionee completes «CliffPeriod» months of continuous Service beginning with the Vesting Commencement Date set forth above. The


		Right of Repurchase shall lapse with respect to an additional «Fraction»% of the Shares subject to this option when the Optionee completes each month of continuous Service thereafter.

Expiration Date:		«ExpDate». This option expires earlier if the Optionee’s Service terminates earlier, as provided in Section 6 of the Stock Option Agreement, or if the Company engages in certain corporate transactions, as provided in Section 8(b) of the Plan.

By signing below, the Optionee and the Company agree that this option is granted under, and governed by the terms and conditions of, the 2013 Stock Plan and the Stock Option Agreement. Both of these documents are attached to, and made a part of, this Notice of Stock Option Grant. Section 14 of the Stock Option Agreement includes important acknowledgements of the Optionee.


OPTIONEE:		DIMENSION THERAPEUTICS, INC.

THE OPTION GRANTED PURSUANT TO THIS AGREEMENT AND THE SHARES ISSUABLE UPON THE EXERCISE THEREOF HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE SOLD, PLEDGED, OR OTHERWISE TRANSFERRED WITHOUT AN EFFECTIVE REGISTRATION THEREOF UNDER SUCH ACT OR AN OPINION OF COUNSEL, SATISFACTORY TO THE COMPANY AND ITS COUNSEL, THAT SUCH REGISTRATION IS NOT REQUIRED.

DIMENSION THERAPEUTICS, INC. 2013 STOCK PLAN:

STOCK OPTION AGREEMENT (EARLY EXERCISE)

SECTION 1.

GRANT OF OPTION.

(a) Option. On the terms and conditions set forth in the Notice of Stock Option Grant and this Agreement, the Company grants to the Optionee on the Date of Grant the option to purchase at the Exercise Price the number of Shares set forth in the Notice of Stock Option Grant. The Exercise Price is agreed to be at least 100% of the Fair Market Value per Share on the Date of Grant (110% of Fair Market Value if this option is designated as an ISO in the Notice of Stock Option Grant and Section 3(b) of the Plan applies). This option is intended to be an ISO or an NSO, as provided in the Notice of Stock Option Grant.

(b) $100,000 Limitation. Even if this option is designated as an ISO in the Notice of Stock Option Grant, it shall be deemed to be an NSO to the extent (and only to the extent) required by the $100,000 annual limitation under Section 422(d) of the Code.

(c) Stock Plan and Defined Terms. This option is granted pursuant to the Plan, a copy of which the Optionee acknowledges having received. The provisions of the Plan are incorporated into this Agreement by this reference. Except as otherwise defined in this Agreement (including without limitation Section 15 hereof), capitalized terms shall have the meaning ascribed to such terms in the Plan.

SECTION 2.

RIGHT TO EXERCISE.

(a) Exercisability. Subject to Subsection (b) below and the other conditions set forth in this Agreement, all or part of this option may be exercised prior to its expiration at the time or times set forth in the Notice of Stock Option Grant. Shares purchased by exercising this option may be subject to the Right of Repurchase under Section 7.

(b) Stockholder Approval. Any other provision of this Agreement notwithstanding, no portion of this option shall be exercisable at any time prior to the approval of the Plan by the Company’s stockholders.

SECTION 3.

NO TRANSFER OR ASSIGNMENT OF OPTION.

Except as otherwise provided in this Agreement, this option and the rights and privileges conferred hereby shall not be sold, pledged or otherwise transferred (whether by operation of law or otherwise) and shall not be subject to sale under execution, attachment, levy or similar process.

SECTION 4.

SECTION 4. EXERCISE PROCEDURES.

(a) Notice of Exercise. The Optionee or the Optionee’s representative may exercise this option by: (i) signing and delivering written notice to the Company pursuant to Section 13(c) specifying the election to exercise this option, the number of Shares for which it is being exercised and the form of payment and (ii) delivering payment, in a form permissible under Section 5, for the full amount of the Purchase Price (together with any applicable withholding taxes under Subsection (b)). In the event that this option is being exercised by the representative of the Optionee, the notice shall be accompanied by proof (satisfactory to the Company) of the representative’s right to exercise this option. In the event of a partial exercise of this option, Shares shall be deemed to have been purchased in the order in which they vest in accordance with the Notice of Stock Option Grant.

(b) Withholding Taxes. In the event that the Company determines that it is required to withhold any tax (including without limitation any income tax, social insurance contributions, payroll tax, payment on account or other tax-related items arising in connection with the Optionee’s participation in the Plan and legally applicable to the Optionee (the “Tax-Related Items”)) as a result of the grant, vesting or exercise of this option, or as a result of the vesting or transfer of shares acquired upon exercise of this option, the Optionee, as a condition of this option, shall make arrangements satisfactory to the Company to enable it to satisfy all Tax-

Related Items. The Optionee acknowledges that the responsibility for all Tax-Related Items is the Optionee’s and may exceed the amount actually withheld by the Company (or its affiliate or agent).

(c) Issuance of Shares. After satisfying all requirements for exercise of this option, the Company shall cause to be issued one or more certificates evidencing the Shares for which this option has been exercised. Such Shares shall be registered (i) in the name of the person exercising this option, (ii) in the names of such person and his or her spouse as community property or as joint tenants with the right of survivorship or (iii) with the Company’s consent, in the name of a revocable trust. Until the issuance of the Shares has been entered into the books and records of the Company or a duly authorized transfer agent of the Company, no right to vote, receive dividends or any other right as a stockholder will exist with respect to such Shares. In the case of Restricted Shares, the Company shall cause such certificates to be deposited in escrow under Section 7(c). In the case of other Shares, the Company shall cause such certificates to be delivered to or upon the order of the person exercising this option.

SECTION 5.

PAYMENT FOR STOCK.

(a) Cash. All or part of the Purchase Price may be paid in cash or cash equivalents.

(b) Surrender of Stock. At the discretion of the Board of Directors, all or any part of the Purchase Price may be paid by surrendering, or attesting to the ownership of, Shares that are already owned by the Optionee. Such Shares shall be surrendered to the Company in good form for transfer and shall be valued at their Fair Market Value as of the date when this option is exercised.

(c) Exercise/Sale. All or part of the Purchase Price and any withholding taxes may be paid by the delivery (on a form prescribed by the Company) of an irrevocable direction to a securities broker approved by the Company to sell Shares and to deliver all or part of the sales proceeds to the Company. However, payment pursuant to this Subsection (c) shall be permitted only if (i) Stock then is publicly traded and (ii) such payment does not violate applicable law.

SECTION 6.

TERM AND EXPIRATION.

(a) Basic Term. This option shall in any event expire on the expiration date set forth in the Notice of Stock Option Grant, which date is 10 years after the Date of Grant (five years after the Date of Grant if this option is designated as an ISO in the Notice of Stock Option Grant and Section 3(b) of the Plan applies).

(b) Termination of Service (Except by Death). If the Optionee’s Service terminates for any reason other than death, then this option shall expire on the earliest of the following occasions:

(i) The expiration date determined pursuant to Subsection (a) above;

(ii) The date three months after the termination of the Optionee’s Service for any reason other than Disability; or

(iii) The date six months after the termination of the Optionee’s Service by reason of Disability.

The Optionee may exercise all or part of this option at any time before its expiration under the preceding sentence, but only to the extent that this option is exercisable for vested Shares on or before the date when the Optionee’s Service terminates. When the Optionee’s Service terminates, this option shall expire immediately with respect to the number of Shares for which this option is not yet exercisable and with respect to any Restricted Shares. In the event that the Optionee dies after termination of Service but before the expiration of this option, all or part of this option may be exercised (prior to expiration) by the executors or administrators of the Optionee’s estate or by any person who has acquired this option directly from the Optionee by beneficiary designation, bequest or inheritance, but only to the extent that this option was exercisable for vested Shares on or before the date when the Optionee’s Service terminated. Once this option (or portion thereof) has terminated, the Optionee shall have no further rights with respect to the option (or portion thereof) or to the underlying Shares.

(c) Death of the Optionee. If the Optionee dies while in Service, then this option shall expire on the earlier of the following dates:

(i) The expiration date determined pursuant to Subsection (a) above; or

(ii) The date 12 months after the Optionee’s death.

All or part of this option may be exercised at any time before its expiration under the preceding sentence by the executors or administrators of the Optionee’s estate or by any person who has acquired this option directly from the Optionee by beneficiary designation, bequest or inheritance, but only to the extent that this option is exercisable for vested Shares on or before the date of the Optionee’s death. When the Optionee dies, this option shall expire immediately with respect to the number of Shares for which this option is not yet exercisable and with respect to any Restricted Shares. Once this option (or portion thereof) has terminated, the Optionee shall have no further rights with respect to the option (or portion thereof) or to the underlying Shares.

(d) Extension of Post-Termination Exercise Periods. Following the date on which the Company’s Stock is first listed for trading on an established securities market, if during any part of the exercise period described in Subsections (b)(ii) or (iii) or Subsection (c)(ii) above the exercise of this option would be prohibited solely because the issuance of Shares upon such exercise would violate the registration requirements under the Securities Act or a similar provision of other applicable law, then instead of terminating at the end of such prescribed period, the then-vested portion of this option will instead remain outstanding and not expire until the earlier of (i) the expiration date determined pursuant to Section 6(a) above or (ii) the date on which the then-vested portion of this option has been exercisable without violation of applicable law for the aggregate period (which need not be consecutive) after termination of the Optionee’s Service specified in the applicable Subsection above.

(e) Part-Time Employment and Leaves of Absence. If the Optionee commences working on a part-time basis, then the Company may adjust the vesting schedule set forth in the Notice of Stock Option Grant. If the Optionee goes on a leave of absence, then the Company may adjust the vesting schedule set forth in the Notice of Stock Option Grant in accordance with the Company’s leave of absence policy or the terms of such leave. Except as provided in the preceding sentence, Service shall be deemed to continue for any purpose under this Agreement while the Optionee is on a bona fide leave of absence, if (i) such leave was approved by the Company in writing and (ii) continued crediting of Service for such purpose is expressly required by the terms of such leave or by applicable law (as determined by the Company). Service shall be deemed to terminate when such leave ends, unless the Optionee immediately returns to active work.

(f) Notice Concerning ISO Treatment. Even if this option is designated as an ISO in the Notice of Stock Option Grant, it ceases to qualify for favorable tax treatment as an ISO to the extent that it is exercised:

(i) More than three months after the date when the Optionee ceases to be an Employee for any reason other than death or permanent and total disability (as defined in Section 22(e)(3) of the Code);

(ii) More than 12 months after the date when the Optionee ceases to be an Employee by reason of permanent and total disability (as defined in Section 22(e)(3) of the Code); or

(iii) More than three months after the date when the Optionee has been on a leave of absence for three months, unless the Optionee’s reemployment rights following such leave were guaranteed by statute or by contract.

SECTION 7.

RIGHT OF REPURCHASE.

(a) Scope of Repurchase Right. Until they vest in accordance with the Notice of Stock Option Grant and Subsection (b) below, the Shares acquired under this Agreement shall be Restricted Shares and shall be subject to the Company’s Right of Repurchase. The Company, however, may decline to exercise its Right of Repurchase or may exercise its Right of Repurchase only with respect to a portion of the Restricted Shares. The Company may exercise its Right of Repurchase only during the Repurchase Period following the termination of the Optionee’s Service, but the Right of Repurchase may be exercised automatically under Subsection (d) below. If the Right of Repurchase is exercised, the Company shall pay the Optionee an amount equal to the lower of (i) the Exercise Price of each Restricted Share being repurchased or (ii) the Fair Market Value of such Restricted Share at the time the Right of Repurchase is exercised.

(b) Lapse of Repurchase Right. The Right of Repurchase shall lapse with respect to the Restricted Shares in accordance with the vesting schedule set forth in the Notice of Stock Option Grant.

(c) Escrow. Upon issuance, the certificate(s) for Restricted Shares shall be deposited in escrow with the Company to be held in accordance with the provisions of this

Agreement. Any additional or exchanged securities or other property described in Subsection (f) below shall immediately be delivered to the Company to be held in escrow. All ordinary cash dividends on Restricted Shares (or on other securities held in escrow) shall be paid directly to the Optionee and shall not be held in escrow. Restricted Shares, together with any other assets held in escrow under this Agreement, shall be (i) surrendered to the Company for repurchase upon exercise of the Right of Repurchase or the Right of First Refusal or (ii) released to the Optionee upon his or her request to the extent that the Shares have ceased to be Restricted Shares (but not more frequently than once every six months). In any event, all Shares that have ceased to be Restricted Shares, together with any other vested assets held in escrow under this Agreement, shall be released within 90 days after the earlier of (i) the termination of the Optionee’s Service or (ii) the lapse of the Right of First Refusal.

(d) Exercise of Repurchase Right. The Company shall be deemed to have exercised its Right of Repurchase automatically for all Restricted Shares as of the commencement of the Repurchase Period, unless the Company during the Repurchase Period notifies the holder of the Restricted Shares pursuant to Section 13(c) that it will not exercise its Right of Repurchase for some or all of the Restricted Shares. The Company shall pay to the holder of the Restricted Shares the purchase price determined under Subsection (a) above for the Restricted Shares being repurchased. Payment shall be made in cash or cash equivalents and/or by canceling indebtedness to the Company incurred by the Optionee in the purchase of the Restricted Shares. The certificate(s) representing the Restricted Shares being repurchased shall be delivered to the Company.

(e) Termination of Rights as Stockholder. If the Right of Repurchase is exercised in accordance with this Section 7 and the Company makes available the consideration for the Restricted Shares being repurchased, then the person from whom the Restricted Shares are repurchased shall no longer have any rights as a holder of the Restricted Shares (other than the right to receive payment of such consideration). Such Restricted Shares shall be deemed to have been repurchased pursuant to this Section 7, whether or not the certificate(s) for such Restricted Shares have been delivered to the Company or the consideration for such Restricted Shares has been accepted.

(f) Additional or Exchanged Securities and Property. In the event of a merger or consolidation of the Company, a sale of all or substantially all of the Company’s stock or assets, any other corporate reorganization, a stock split, the declaration of a stock dividend, the declaration of an extraordinary dividend payable in a form other than stock, a spin-off, an adjustment in conversion ratio, a recapitalization or a similar transaction affecting the Company’s outstanding securities, any securities or other property (including cash or cash equivalents) that are by reason of such transaction exchanged for, or distributed with respect to, any Restricted Shares shall immediately be subject to the Right of Repurchase. Appropriate adjustments to reflect the exchange or distribution of such securities or property shall be made to the number and/or class of the Restricted Shares. Appropriate adjustments shall also be made to the price per share to be paid upon the exercise of the Right of Repurchase, provided that the aggregate purchase price payable for the Restricted Shares shall remain the same. In the event of any transaction described in Section 8(b) of the Plan or any other corporate reorganization, the Right of Repurchase may be exercised by the Company’s successor.

(g) Transfer of Restricted Shares. The Optionee shall not transfer, assign, encumber or otherwise dispose of any Restricted Shares without the Company’s written consent, except as provided in the following sentence. The Optionee may transfer Restricted Shares to one or more members of the Optionee’s Immediate Family or to a trust established by the Optionee for the benefit of the Optionee and/or one or more members of the Optionee’s Immediate Family, provided in either case that the Transferee agrees in writing on a form prescribed by the Company to be bound by all provisions of this Agreement. If the Optionee transfers any Restricted Shares, then this Agreement shall apply to the Transferee to the same extent as to the Optionee.

(h) Assignment of Repurchase Right. The Board of Directors may freely assign the Company’s Right of Repurchase, in whole or in part. Any person who accepts an assignment of the Right of Repurchase from the Company shall assume all of the Company’s rights and obligations under this Section 7.

SECTION 8.

RIGHT OF FIRST REFUSAL.

(a) Right of First Refusal. In the event that the Optionee proposes to sell, pledge or otherwise transfer to a third party any Shares acquired under this Agreement, or any interest in such Shares, the Company shall have the Right of First Refusal with respect to all (and not less than all) of such Shares. If the Optionee desires to transfer Shares acquired under this Agreement, the Optionee shall give a written Transfer Notice to the Company describing fully the proposed transfer, including the number of Shares proposed to be transferred, the proposed transfer price, the name and address of the proposed Transferee and proof satisfactory to the Company that the proposed sale or transfer will not violate any applicable federal, State or foreign securities laws. The Transfer Notice shall be signed both by the Optionee and by the proposed Transferee and must constitute a binding commitment of both parties to the transfer of the Shares. The Company shall have the right to purchase all, and not less than all, of the Shares on the terms of the proposal described in the Transfer Notice (subject, however, to any change in such terms permitted under Subsection (b) below) by delivery of a notice of exercise of the Right of First Refusal within 30 days after the date when the Transfer Notice was received by the Company.

(b) Transfer of Shares. If the Company fails to exercise its Right of First Refusal within 30 days after the date when it received the Transfer Notice, the Optionee may, not later than 90 days following receipt of the Transfer Notice by the Company, conclude a transfer of the Shares subject to the Transfer Notice on the terms and conditions described in the Transfer Notice, provided that any such sale is made in compliance with applicable federal, State and foreign securities laws and not in violation of any other contractual restrictions to which the Optionee is bound. Any proposed transfer on terms and conditions different from those described in the Transfer Notice, as well as any subsequent proposed transfer by the Optionee, shall again be subject to the Right of First Refusal and shall require compliance with the procedure described in Subsection (a) above. If the Company exercises its Right of First Refusal, the parties shall consummate the sale of the Shares on the terms set forth in the Transfer Notice within 60 days after the date when the Company received the Transfer Notice (or within such longer period as may have been specified in the Transfer Notice); provided, however, that in the event the Transfer Notice provided that payment for the Shares was to be made in a form

other than cash or cash equivalents paid at the time of transfer, the Company shall have the option of paying for the Shares with cash or cash equivalents equal to the present value of the consideration described in the Transfer Notice.

(c) Additional or Exchanged Securities and Property. In the event of a merger or consolidation of the Company, a sale of all or substantially all of the Company’s stock or assets, any other corporate reorganization, a stock split, the declaration of a stock dividend, the declaration of an extraordinary dividend payable in a form other than stock, a spin-off, an adjustment in conversion ratio, a recapitalization or a similar transaction affecting the Company’s outstanding securities, any securities or other property (including cash or cash equivalents) that are by reason of such transaction exchanged for, or distributed with respect to, any Shares subject to this Section 8 shall immediately be subject to the Right of First Refusal. Appropriate adjustments to reflect the exchange or distribution of such securities or property shall be made to the number and/or class of the Shares subject to this Section 8.

(d) Termination of Right of First Refusal. Any other provision of this Section 8 notwithstanding, in the event that the Stock is readily tradable on an established securities market when the Optionee desires to transfer Shares, the Company shall have no Right of First Refusal, and the Optionee shall have no obligation to comply with the procedures prescribed by Subsections (a) and (b) above.

(e) Permitted Transfers. This Section 8 shall not apply to (i) a transfer by beneficiary designation, will or intestate succession or (ii) a transfer to one or more members of the Optionee’s Immediate Family or to a trust established by the Optionee for the benefit of the Optionee and/or one or more members of the Optionee’s Immediate Family, provided in either case that the Transferee agrees in writing on a form prescribed by the Company to be bound by all provisions of this Agreement. If the Optionee transfers any Shares acquired under this Agreement, either under this Subsection (e) or after the Company has failed to exercise the Right of First Refusal, then this Agreement shall apply to the Transferee to the same extent as to the Optionee.

(f) Termination of Rights as Stockholder. If the Company makes available, at the time and place and in the amount and form provided in this Agreement, the consideration for the Shares to be purchased in accordance with this Section 8, then after such time the person from whom such Shares are to be purchased shall no longer have any rights as a holder of such Shares (other than the right to receive payment of such consideration in accordance with this Agreement). Such Shares shall be deemed to have been purchased in accordance with the applicable provisions hereof, whether or not the certificate(s) therefor have been delivered as required by this Agreement.

(g) Assignment of Right of First Refusal. The Board of Directors may freely assign the Company’s Right of First Refusal, in whole or in part. Any person who accepts an assignment of the Right of First Refusal from the Company shall assume all of the Company’s rights and obligations under this Section 8.

SECTION 9.

LEGALITY OF INITIAL ISSUANCE.

No Shares shall be issued upon the exercise of this option unless and until the Company has determined that:

(a) It and the Optionee have taken any actions required to register the Shares under the Securities Act or to perfect an exemption from the registration requirements thereof;

(b) Any applicable listing requirement of any stock exchange or other securities market on which Stock is listed has been satisfied; and

SECTION 10.

NO REGISTRATION RIGHTS.

The Company may, but shall not be obligated to, register or qualify the sale of Shares under the Securities Act or any other applicable law. The Company shall not be obligated to take any affirmative action in order to cause the sale of Shares under this Agreement to comply with any law.

SECTION 11.

RESTRICTIONS ON TRANSFER OF SHARES.

(a) Securities Law Restrictions. Regardless of whether the offer and sale of Shares under the Plan have been registered under the Securities Act or have been registered or qualified under the securities laws of any State or other relevant jurisdiction, the Company at its discretion may impose restrictions upon the sale, pledge or other transfer of such Shares (including the placement of appropriate legends on the stock certificates (or electronic equivalent) or the imposition of stop-transfer instructions) and may refuse to transfer Shares acquired hereunder (or Shares proposed to be transferred in a subsequent transfer) if, in the judgment of the Company, such restrictions, legends or refusal are necessary or appropriate to achieve compliance with the Securities Act or other relevant securities or other laws, including without limitation under Regulation S of the Securities Act or pursuant to another available exemption from registration.

or other distribution of research reports or (ii) analyst recommendations and opinions, including (without limitation) the restrictions set forth in Rule 2711(f)(4) of the National Association of Securities Dealers and Rule 472(f)(4) of the New York Stock Exchange, as amended, or any similar successor rules. The Market Stand-Off shall in any event terminate two years after the date of the Company’s initial public offering. In the event of the declaration of a stock dividend, a spin-off, a stock split, an adjustment in conversion ratio, a recapitalization or a similar transaction affecting the Company’s outstanding securities without receipt of consideration, any new, substituted or additional securities which are by reason of such transaction distributed with respect to any Shares subject to the Market Stand-Off, or into which such Shares thereby become convertible, shall immediately be subject to the Market Stand-Off. In order to enforce the Market Stand-Off, the Company may impose stop-transfer instructions with respect to the Shares acquired under this Agreement until the end of the applicable stand-off period. The Company’s underwriters shall be beneficiaries of the agreement set forth in this Subsection (b). This Subsection (b) shall not apply to Shares registered in the public offering under the Securities Act.

(c) Investment Intent at Grant. The Optionee represents and agrees that the Shares to be acquired upon exercising this option will be acquired for investment, and not with a view to the sale or distribution thereof.

(d) Investment Intent at Exercise. In the event that the sale of Shares under the Plan is not registered under the Securities Act but an exemption is available that requires an investment representation or other representation, the Optionee shall represent and agree at the time of exercise that the Shares being acquired upon exercising this option are being acquired for investment, and not with a view to the sale or distribution thereof, and shall make such other representations as are deemed necessary or appropriate by the Company and its counsel, including (if applicable) that as of the date of exercise the Optionee is (i) not a U.S. Person; (ii) not acquiring the Shares on behalf, or for the account or benefit, of a U.S. Person; and (iii) is not exercising the option in the United States.

(e) Legends. All certificates evidencing Shares purchased under this Agreement shall bear the following legend:

“THE SHARES REPRESENTED HEREBY MAY NOT BE SOLD, ASSIGNED, TRANSFERRED, ENCUMBERED OR IN ANY MANNER DISPOSED OF, EXCEPT IN COMPLIANCE WITH THE TERMS OF A WRITTEN AGREEMENT BETWEEN THE COMPANY AND THE REGISTERED HOLDER OF THE SHARES (OR THE PREDECESSOR IN INTEREST TO THE SHARES). SUCH AGREEMENT GRANTS TO THE COMPANY CERTAIN RIGHTS OF FIRST REFUSAL UPON AN ATTEMPTED TRANSFER OF THE SHARES AND CERTAIN REPURCHASE RIGHTS UPON TERMINATION OF SERVICE WITH THE COMPANY. IN ADDITION, THE SHARES ARE SUBJECT TO RESTRICTIONS ON TRANSFER FOR A LIMITED PERIOD FOLLOWING THE EFFECTIVE DATE OF THE UNDERWRITTEN PUBLIC OFFERING OF THE COMPANY’S SECURITIES AND MAY NOT BE SOLD OR OTHERWISE DISPOSED OF BY THE HOLDER WITHOUT THE CONSENT OF THE COMPANY OR THE MANAGING UNDERWRITER. THE SECRETARY OF THE COMPANY WILL UPON WRITTEN REQUEST FURNISH A COPY OF SUCH AGREEMENT TO THE HOLDER HEREOF WITHOUT CHARGE.”

All certificates evidencing Shares purchased under this Agreement in an unregistered transaction shall bear the following legend (and such other restrictive legends as are required or deemed advisable under the provisions of any applicable law):

“THE SHARES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”) OR ANY SECURITIES LAWS OF ANY U.S. STATE, AND MAY NOT BE SOLD, REOFFERED, PLEDGED, ASSIGNED, ENCUMBERED OR OTHERWISE TRANSFERRED OR DISPOSED WITHOUT AN EFFECTIVE REGISTRATION THEREOF UNDER SUCH ACT OR AN OPINION OF COUNSEL, SATISFACTORY TO THE COMPANY AND ITS COUNSEL, THAT SUCH REGISTRATION IS NOT REQUIRED. IN THE ABSENCE OF REGISTRATION OR THE AVAILABILITY (CONFIRMED BY OPINION OF COUNSEL) OF AN ALTERNATIVE EXEMPTION FROM REGISTRATION UNDER THE ACT, THESE SHARES MAY NOT BE SOLD, REOFFERED, PLEDGED, ASSIGNED, ENCUMBERED OR OTHERWISE TRANSFERRED OR DISPOSED OF EXCEPT IN ACCORDANCE WITH REGULATION S (RULES 901 THROUGH 905 AND PRELIMINARY NOTES) OF THE ACT. HEDGING TRANSACTIONS INVOLVING THESE SHARES MAY NOT BE CONDUCTED UNLESS IN COMPLIANCE WITH THE ACT.”

(f) Removal of Legends. If, in the opinion of the Company and its counsel, any legend placed on a stock certificate representing Shares sold under this Agreement is no longer required, the holder of such certificate shall be entitled to exchange such certificate for a certificate representing the same number of Shares but without such legend.

(g) Administration. Any determination by the Company and its counsel in connection with any of the matters set forth in this Section 11 shall be conclusive and binding on the Optionee and all other persons.

SECTION 12.

ADJUSTMENT OF SHARES.

In the event of any transaction described in Section 8(a) of the Plan, the terms of this option (including, without limitation, the number and kind of Shares subject to this option and the Exercise Price) shall be adjusted as set forth in Section 8(a) of the Plan. In the event that the Company is a party to a merger or consolidation or in the event of a sale of all or substantially all of the Company’s stock or assets, this option shall be subject to the treatment provided by the Board of Directors in its sole discretion, as provided in Section 8(b) of the Plan.

SECTION 13.

MISCELLANEOUS PROVISIONS.

(a) Rights as a Stockholder. Neither the Optionee nor the Optionee’s representative shall have any rights as a stockholder with respect to any Shares subject to this option until the Optionee or the Optionee’s representative becomes entitled to receive such Shares by filing a notice of exercise and paying the Purchase Price pursuant to Sections 4 and 5.

(b) No Retention Rights. Nothing in this option or in the Plan shall confer upon the Optionee any right to continue in Service for any period of specific duration or interfere with or otherwise restrict in any way the rights of the Company (or any Parent or Subsidiary employing or retaining the Optionee) or of the Optionee, which rights are hereby expressly reserved by each, to terminate his or her Service at any time and for any reason, with or without cause.

(c) Notice. Any notice required by the terms of this Agreement shall be given in writing. It shall be deemed effective upon (i) personal delivery, (ii) deposit with the United States Postal Service, by registered or certified mail, with postage and fees prepaid, (iii) deposit with Federal Express Corporation, with shipping charges prepaid or (iv) deposit with any internationally recognized express mail courier service. Notice shall be addressed to the Company at its principal executive office and to the Optionee at the address that he or she most recently provided to the Company in accordance with this Subsection (c).

(d) Modifications and Waivers. No provision of this Agreement shall be modified, waived or discharged unless the modification, waiver or discharge is agreed to in writing and signed by the Optionee and by an authorized officer of the Company (other than the Optionee). No waiver by either party of any breach of, or of compliance with, any condition or provision of this Agreement by the other party shall be considered a waiver of any other condition or provision or of the same condition or provision at another time.

(e) Entire Agreement. The Notice of Stock Option Grant, this Agreement and the Plan constitute the entire contract between the parties hereto with regard to the subject matter hereof. They supersede any other agreements, representations or understandings (whether oral or written and whether express or implied) that relate to the subject matter hereof.

(f) Choice of Law. This Agreement shall be governed by, and construed in accordance with, the laws of the State of Delaware, as such laws are applied to contracts entered into and performed in such State.

SECTION 14.

ACKNOWLEDGEMENTS OF THE OPTIONEE.

In addition to the other terms, conditions and restrictions imposed on this option and the Shares issuable under this option pursuant to this Agreement and the Plan, the Optionee expressly acknowledges being subject to Sections 7 (Right of Repurchase), 8 (Right of First Refusal), 9 (Legality of Initial Issuance) and 11 (Restrictions on Transfer of Shares, including without limitation the Market Stand-Off), as well as the following provisions:

(a) Tax Consequences. The Optionee agrees that the Company does not have a duty to design or administer the Plan or its other compensation programs in a manner that minimizes the Optionee’s tax liabilities. The Optionee shall not make any claim against the Company or its Board of Directors, officers or employees related to tax liabilities arising from this option or the Optionee’s other compensation. In particular, any Optionee subject to U.S. taxation acknowledges that this option is exempt from Section 409A of the Code only if the Exercise Price is at least equal to the Fair Market Value per Share on the Date of Grant. Since

Shares are not traded on an established securities market, the determination of their Fair Market Value is made by the Board of Directors or by an independent valuation firm retained by the Company. The Optionee acknowledges that there is no guarantee in either case that the Internal Revenue Service will agree with the valuation, and the Optionee shall not make any claim against the Company or its Board of Directors, officers or employees in the event that the Internal Revenue Service asserts that the valuation was too low.

(b) Electronic Delivery of Documents. The Optionee agrees to accept by email all documents relating to the Company, the Plan or this option and all other documents that the Company is required to deliver to its security holders (including, without limitation, disclosures that may be required by the Securities and Exchange Commission). The Optionee also agrees that the Company may deliver these documents by posting them on a website maintained by the Company or by a third party under contract with the Company. If the Company posts these documents on a website, it shall notify the Optionee by email of their availability. The Optionee acknowledges that he or she may incur costs in connection with electronic delivery, including the cost of accessing the internet and printing fees, and that an interruption of internet access may interfere with his or her ability to access the documents. This consent shall remain in effect until this option expires or until the Optionee gives the Company written notice that it should deliver paper documents.

(c) No Notice of Expiration Date. The Optionee agrees that the Company and its officers, employees, attorneys and agents do not have any obligation to notify him or her prior to the expiration of this option pursuant to Section 6, regardless of whether this option will expire at the end of its full term or on an earlier date related to the termination of the Optionee’s Service. The Optionee further agrees that he or she has the sole responsibility for monitoring the expiration of this option and for exercising this option, if at all, before it expires. This Subsection (c) shall supersede any contrary representation that may have been made, orally or in writing, by the Company or by an officer, employee, attorney or agent of the Company.

(d) Waiver of Statutory Information Rights. The Optionee acknowledges and agrees that, upon exercise of this option and until the first sale of the Company’s Stock to the general public pursuant to a registration statement filed under the Securities Act, he or she will be deemed to have waived any rights the Optionee might otherwise have had under Section 220 of the Delaware General Corporation Law to inspect for any proper purpose and to make copies and extracts from the Company’s stock ledger, a list of its stockholders and its other books and records or the books and records of any subsidiary. This waiver applies only in the Optionee’s capacity as a stockholder and does not affect any other inspection rights the Optionee may have under other law or pursuant to a written agreement with the Company.

(e) Plan Discretionary. The Optionee understands and acknowledges that (i) the Plan is entirely discretionary, (ii) the Company and the Optionee’s employer have reserved the right to amend, suspend or terminate the Plan at any time, (iii) the grant of an option does not in any way create any contractual or other right to receive additional grants of options (or benefits in lieu of options) at any time or in any amount and (iv) all determinations with respect to any additional grants, including (without limitation) the times when options will be granted, the number of Shares offered, the Exercise Price and the vesting schedule, will be at the sole discretion of the Company.

(f) Termination of Service. The Optionee understands and acknowledges that participation in the Plan ceases upon termination of his or her Service for any reason, except as may explicitly be provided otherwise in the Plan or this Agreement.

(g) Extraordinary Compensation. The value of this option shall be an extraordinary item of compensation outside the scope of the Optionee’s employment contract, if any, and shall not be considered a part of his or her normal or expected compensation for purposes of calculating severance, resignation, redundancy or end-of-service payments, bonuses, long-service awards, pension or retirement benefits or similar payments.

(h) Authorization to Disclose. The Optionee hereby authorizes and directs the Optionee’s employer to disclose to the Company or any Subsidiary any information regarding the Optionee’s employment, the nature and amount of the Optionee’s compensation and the fact and conditions of the Optionee’s participation in the Plan, as the Optionee’s employer deems necessary or appropriate to facilitate the administration of the Plan.

(i) Personal Data Authorization. The Optionee consents to the collection, use and transfer of personal data as described in this Subsection (i). The Optionee understands and acknowledges that the Company, the Optionee’s employer and the Company’s other Subsidiaries hold certain personal information regarding the Optionee for the purpose of managing and administering the Plan, including (without limitation) the Optionee’s name, home address, telephone number, date of birth, social insurance number, salary, nationality, job title, any Shares or directorships held in the Company and details of all options or any other entitlements to Shares awarded, canceled, exercised, vested, unvested or outstanding in the Optionee’s favor (the “Data”). The Optionee further understands and acknowledges that the Company and/or its Subsidiaries will transfer Data among themselves as necessary for the purpose of implementation, administration and management of the Optionee’s participation in the Plan and that the Company and/or any Subsidiary may each further transfer Data to any third party assisting the Company in the implementation, administration and management of the Plan. The Optionee understands and acknowledges that the recipients of Data may be located in the United States or elsewhere. The Optionee authorizes such recipients to receive, possess, use, retain and transfer Data, in electronic or other form, for the purpose of administering the Optionee’s participation in the Plan, including a transfer to any broker or other third party with whom the Optionee elects to deposit Shares acquired under the Plan of such Data as may be required for the administration of the Plan and/or the subsequent holding of Shares on the Optionee’s behalf. The Optionee may, at any time, view the Data, require any necessary modifications of Data or withdraw the consents set forth in this Subsection (i) by contacting the Company in writing.

SECTION 15.

DEFINITIONS.

(a) “Agreement” shall mean this Stock Option Agreement.

(b) “Board of Directors” shall mean the Board of Directors of the Company, as constituted from time to time or, if a Committee has been appointed, such Committee.

(d) “Immediate Family” shall mean any child, stepchild, grandchild, parent, stepparent, grandparent, spouse, sibling, mother-in-law, father-in-law, son-in-law, daughter-in-law, brother-in-law or sister-in-law and shall include adoptive relationships.

(e) “Optionee” shall mean the person named in the Notice of Stock Option Grant.

(f) “Plan” shall mean the Dimension Therapeutics, Inc. 2013 Stock Plan, as in effect on the Date of Grant.

(g) “Purchase Price” shall mean the Exercise Price multiplied by the number of Shares with respect to which this option is being exercised.

(h) “Repurchase Period” shall mean a period of 90 consecutive days commencing on the date when the Optionee’s Service terminates for any reason, including (without limitation) death or disability.

(i) “Restricted Share” shall mean a Share that is subject to the Right of Repurchase.

(j) “Right of First Refusal” shall mean the Company’s right of first refusal described in Section 8.

(k) “Right of Repurchase” shall mean the Company’s right of repurchase described in Section 7.

(l) “Service” means service as an Employee, Outside Director or Consultant.

(m) “Transferee” shall mean any person to whom the Optionee has directly or indirectly transferred any Share acquired under this Agreement.

(n) “Transfer Notice” shall mean the notice of a proposed transfer of Shares described in Section 8.

(o) “U.S. Person” shall mean a person described in Rule 902(k) of Regulation S of the Securities Act (or any successor rule or provision), which generally defines a U.S. person as any natural person resident in the United States, any estate of which any executor or administrator is a U.S. Person, or any trust of which of any trustee is a U.S. Person.

DIMENSION THERAPEUTICS, INC. 2013 STOCK PLAN

NOTICE OF STOCK OPTION GRANT (INSTALLMENT EXERCISE)

The Optionee has been granted the following option to purchase shares of the Common Stock of Dimension Therapeutics, Inc.:



Name of Optionee:		«Name»

Total Number of Shares:		«TotalShares»

Type of Option:		«ISO» Incentive Stock Option (ISO)

		«NSO» Nonstatutory Stock Option (NSO)

Exercise Price per Share:		$«PricePerShare»

Date of Grant:		«DateGrant»

Date Exercisable:		This option may be exercised with respect to the first «Percent»% of the Shares subject to this option when the Optionee completes «CliffPeriod» months of continuous Service beginning with the Vesting Commencement Date set forth below. This option may be exercised with respect to an additional «Fraction»% of the Shares subject to this option when the Optionee completes each month of continuous Service thereafter. This option may become exercisable on an accelerated basis under Section 2(a) of the Stock Option Agreement.

Vesting Commencement Date:		«VestComDate»

Expiration Date:		«ExpDate». This option expires earlier if the Optionee’s Service terminates earlier, as provided in Section 6 of the Stock Option Agreement, or if the Company engages in certain corporate transactions, as provided in Section 8(b) of the Plan.

Section 13 of the Stock Option Agreement includes important acknowledgements of the Optionee.


OPTIONEE:		DIMENSION THERAPEUTICS, INC.

DIMENSION THERAPEUTICS, INC. 2013 STOCK PLAN:

STOCK OPTION AGREEMENT (INSTALLMENT EXERCISE)

SECTION 1.

GRANT OF OPTION.

(c) Stock Plan and Defined Terms. This option is granted pursuant to the Plan, a copy of which the Optionee acknowledges having received. The provisions of the Plan are incorporated into this Agreement by this reference. Except as otherwise defined in this Agreement (including without limitation Section 14 hereof), capitalized terms shall have the meaning ascribed to such terms in the Plan.

SECTION 2.

RIGHT TO EXERCISE.

(a) Exercisability. Subject to Subsection (b) below and the other conditions set forth in this Agreement, all or part of this option may be exercised prior to its expiration at the time or times set forth in the Notice of Stock Option Grant. In addition, if the Optionee is subject to an Involuntary Termination within 12 months following a Change in Control, [100]%of the shares subject to this option shall immediately vest and become exercisable.

SECTION 3.

NO TRANSFER OR ASSIGNMENT OF OPTION.

SECTION 4.

EXERCISE PROCEDURES.

(a) Notice of Exercise. The Optionee or the Optionee’s representative may exercise this option by: (i) signing and delivering written notice to the Company pursuant to Section 12(c) specifying the election to exercise this option, the number of Shares for which it is being exercised and the form of payment and (ii) delivering payment, in a form permissible under Section 5, for the full amount of the Purchase Price (together with any applicable withholding taxes under Subsection (b)). In the event that this option is being exercised by the representative of the Optionee, the notice shall be accompanied by proof (satisfactory to the Company) of the representative’s right to exercise this option.

(b) Withholding Taxes. In the event that the Company determines that it is required to withhold any tax (including without limitation any income tax, social insurance contributions, payroll tax, payment on account or other tax-related items arising in connection with the Optionee’s participation in the Plan and legally applicable to the Optionee (the “Tax-Related Items”)) as a result of the grant, vesting or exercise of this option, or as a result of the transfer of shares acquired upon exercise of this option, the Optionee, as a condition of this option, shall make arrangements satisfactory to the Company to enable it to satisfy all Tax-Related Items. The Optionee acknowledges that the responsibility for all Tax-Related Items is the Optionee’s and may exceed the amount actually withheld by the Company (or its affiliate or agent).

(c) Issuance of Shares. After satisfying all requirements for exercise of this option, the Company shall cause to be issued one or more certificates evidencing the Shares for which this option has been exercised. Such Shares shall be registered (i) in the name of the person exercising this option, (ii) in the names of such person and his or her spouse as community property or as joint tenants with the right of survivorship or (iii) with the Company’s consent, in the name of a revocable trust. Until the issuance of the Shares has been entered into the books and records of the Company or a duly authorized transfer agent of the Company, no right to vote, receive dividends or any other right as a stockholder will exist with respect to such Shares. The Company shall cause such certificates to be delivered to or upon the order of the person exercising this option.

SECTION 5.

PAYMENT FOR STOCK.

(a) Cash. All or part of the Purchase Price may be paid in cash or cash equivalents.

SECTION 6.

TERM AND EXPIRATION.

(b) Termination of Service (Except by Death). If the Optionee’s Service terminates for any reason other than death, then this option shall expire on the earliest of the following occasions:

(i) The expiration date determined pursuant to Subsection (a) above;

(ii) The date three months after the termination of the Optionee’s Service for any reason other than Disability; or

(iii) The date six months after the termination of the Optionee’s Service by reason of Disability.

The Optionee may exercise all or part of this option at any time before its expiration under the preceding sentence, but only to the extent that this option had become exercisable before the Optionee’s Service terminated. When the Optionee’s Service terminates, this option shall expire immediately with respect to the number of Shares for which this option is not yet exercisable. In the event that the Optionee dies after termination of Service but before the expiration of this option, all or part of this option may be exercised (prior to expiration) by the executors or administrators of the Optionee’s estate or by any person who has acquired this option directly from the Optionee by beneficiary designation, bequest or inheritance, but only to the extent that this option had become exercisable before the Optionee’s Service terminated. Once this option (or portion thereof) has terminated, the Optionee shall have no further rights with respect to the option (or portion thereof) or to the underlying Shares.

(c) Death of the Optionee. If the Optionee dies while in Service, then this option shall expire on the earlier of the following dates:

(i) The expiration date determined pursuant to Subsection (a) above; or

(ii) The date 12 months after the Optionee’s death.

All or part of this option may be exercised at any time before its expiration under the preceding sentence by the executors or administrators of the Optionee’s estate or by any person who has acquired this option directly from the Optionee by beneficiary designation, bequest or inheritance, but only to the extent that this option had become exercisable before the Optionee’s death. When the Optionee dies, this option shall expire immediately with respect to the number of Shares for which this option is not yet exercisable. Once this option (or portion thereof) has terminated, the Optionee shall have no further rights with respect to the option (or portion thereof) or to the underlying Shares.

(e) Part-Time Employment and Leaves of Absence. If the Optionee commences working on a part-time basis, then the Company may adjust the vesting schedule set forth in the Notice of Stock Option Grant. If the Optionee goes on a leave of absence, then the Company may adjust the vesting schedule set forth in the Notice of Stock Option Grant in accordance with the Company’s leave of absence policy or the terms of such leave. Except as provided in the preceding sentence, Service shall be deemed to continue for any purpose under this Agreement while the Optionee is on a bona fide leave of absence, if (i) such leave was approved by the Company in writing and (ii) continued crediting of Service for such purpose is expressly required by the terms of such leave or by applicable law (as determined by the Company). Service shall be deemed to terminate when such leave ends, unless the Optionee immediately returns to active work.

(i) More than three months after the date when the Optionee ceases to be an Employee for any reason other than death or permanent and total disability (as defined in Section 22(e)(3) of the Code);

(ii) More than 12 months after the date when the Optionee ceases to be an Employee by reason of permanent and total disability (as defined in Section 22(e)(3) of the Code); or

SECTION 7.

RIGHT OF FIRST REFUSAL.

(c) Additional or Exchanged Securities and Property. In the event of a merger or consolidation of the Company, a sale of all or substantially all of the Company’s stock or assets, any other corporate reorganization, a stock split, the declaration of a stock dividend, the declaration of an extraordinary dividend payable in a form other than stock, a spin-off, an adjustment in conversion ratio, a recapitalization or a similar transaction affecting the Company’s outstanding securities, any securities or other property (including cash or cash equivalents) that are by reason of such transaction exchanged for, or distributed with respect to, any Shares subject to this Section 7 shall immediately be subject to the Right of First Refusal. Appropriate adjustments to reflect the exchange or distribution of such securities or property shall be made to the number and/or class of the Shares subject to this Section 7.

(d) Termination of Right of First Refusal. Any other provision of this Section 7 notwithstanding, in the event that the Stock is readily tradable on an established securities market when the Optionee desires to transfer Shares, the Company shall have no Right of First Refusal, and the Optionee shall have no obligation to comply with the procedures prescribed by Subsections (a) and (b) above.

(e) Permitted Transfers. This Section 7 shall not apply to (i) a transfer by beneficiary designation, will or intestate succession or (ii) a transfer to one or more members of the Optionee’s Immediate Family or to a trust established by the Optionee for the benefit of the Optionee and/or one or more members of the Optionee’s Immediate Family, provided in either case that the Transferee agrees in writing on a form prescribed by the Company to be bound by all provisions of this Agreement. If the Optionee transfers any Shares acquired under this Agreement, either under this Subsection (e) or after the Company has failed to exercise the Right of First Refusal, then this Agreement shall apply to the Transferee to the same extent as to the Optionee.

(f) Termination of Rights as Stockholder. If the Company makes available, at the time and place and in the amount and form provided in this Agreement, the consideration for the Shares to be purchased in accordance with this Section 7, then after such time the person from whom such Shares are to be purchased shall no longer have any rights as a holder of such Shares (other than the right to receive payment of such consideration in accordance with this Agreement). Such Shares shall be deemed to have been purchased in accordance with the applicable provisions hereof, whether or not the certificate(s) therefor have been delivered as required by this Agreement.

SECTION 8.

LEGALITY OF INITIAL ISSUANCE.

No Shares shall be issued upon the exercise of this option unless and until the Company has determined that:

(a) It and the Optionee have taken any actions required to register the Shares under the Securities Act or to perfect an exemption from the registration requirements thereof;

(b) Any applicable listing requirement of any stock exchange or other securities market on which Stock is listed has been satisfied; and

SECTION 9.

NO REGISTRATION RIGHTS.

SECTION 10.

RESTRICTIONS ON TRANSFER OF SHARES.

two years after the date of the Company’s initial public offering. In the event of the declaration of a stock dividend, a spin-off, a stock split, an adjustment in conversion ratio, a recapitalization or a similar transaction affecting the Company’s outstanding securities without receipt of consideration, any new, substituted or additional securities which are by reason of such transaction distributed with respect to any Shares subject to the Market Stand-Off, or into which such Shares thereby become convertible, shall immediately be subject to the Market Stand-Off. In order to enforce the Market Stand-Off, the Company may impose stop-transfer instructions with respect to the Shares acquired under this Agreement until the end of the applicable stand-off period. The Company’s underwriters shall be beneficiaries of the agreement set forth in this Subsection (b). This Subsection (b) shall not apply to Shares registered in the public offering under the Securities Act.

(e) Legends. All certificates evidencing Shares purchased under this Agreement shall bear the following legend:

“THE SHARES REPRESENTED HEREBY MAY NOT BE SOLD, ASSIGNED, TRANSFERRED, ENCUMBERED OR IN ANY MANNER DISPOSED OF, EXCEPT IN COMPLIANCE WITH THE TERMS OF A WRITTEN AGREEMENT BETWEEN THE COMPANY AND THE REGISTERED HOLDER OF THE SHARES (OR THE PREDECESSOR IN INTEREST TO THE SHARES). SUCH AGREEMENT GRANTS TO THE COMPANY CERTAIN RIGHTS OF FIRST REFUSAL UPON AN ATTEMPTED TRANSFER OF THE SHARES. IN ADDITION, THE SHARES ARE SUBJECT TO RESTRICTIONS ON TRANSFER FOR A LIMITED PERIOD FOLLOWING THE EFFECTIVE DATE OF THE UNDERWRITTEN PUBLIC OFFERING OF THE COMPANY’S SECURITIES AND MAY NOT BE SOLD OR OTHERWISE DISPOSED OF BY THE HOLDER WITHOUT THE CONSENT OF THE COMPANY OR THE MANAGING UNDERWRITER. THE SECRETARY OF THE COMPANY WILL UPON WRITTEN REQUEST FURNISH A COPY OF SUCH AGREEMENT TO THE HOLDER HEREOF WITHOUT CHARGE.”

(g) Administration. Any determination by the Company and its counsel in connection with any of the matters set forth in this Section 10 shall be conclusive and binding on the Optionee and all other persons.

SECTION 11.

ADJUSTMENT OF SHARES.

SECTION 12.

MISCELLANEOUS PROVISIONS.

(b) No Retention Rights. Nothing in this option or in the Plan shall confer upon the Optionee any right to continue in Service for any period of specific duration or

interfere with or otherwise restrict in any way the rights of the Company (or any Parent or Subsidiary employing or retaining the Optionee) or of the Optionee, which rights are hereby expressly reserved by each, to terminate his or her Service at any time and for any reason, with or without cause.

SECTION 13. ACKNOWLEDGEMENTS OF THE OPTIONEE.

In addition to the other terms, conditions and restrictions imposed on this option and the Shares issuable under this option pursuant to this Agreement and the Plan, the Optionee expressly acknowledges being subject to Sections 7 (Right of First Refusal), 8 (Legality of Initial Issuance) and 10 (Restrictions on Transfer of Shares, including without limitation the Market Stand-Off), as well as the following provisions:

valuation firm retained by the Company. The Optionee acknowledges that there is no guarantee in either case that the Internal Revenue Service will agree with the valuation, and the Optionee shall not make any claim against the Company or its Board of Directors, officers or employees in the event that the Internal Revenue Service asserts that the valuation was too low.

SECTION 14.

DEFINITIONS.

(a) “Agreement” shall mean this Stock Option Agreement.

(b) “Board of Directors” shall mean the Board of Directors of the Company, as constituted from time to time or, if a Committee has been appointed, such Committee.

(c) “Cause” shall mean (i) Optionee’s unauthorized use or disclosure of the Company’s confidential information or trade secrets, which use or disclosure causes material harm to the Company; (ii) Optionee’s material breach of any agreement between Optionee and the Company; (iii) Optionee’s material failure to comply with the Company’s written policies or rules; (iv) Optionee’s conviction of, or Optionee’s plea of “guilty” or “no contest” to, a felony under the laws of the United States or any State; (v) Optionee’s gross negligence or willful misconduct; (vi) Optionee’s continuing failure to perform assigned duties after receiving written notification of such failure from the Company’s Board of Directors or (vii) Optionee’s failure to cooperate in good faith with a governmental or internal investigation of the Company or its directors, officers or employees, if the Company has requested Optionee’s cooperation.

(d) “Change in Control” shall mean (i) the consummation of a merger or consolidation of the Company with or into another entity or (ii) the dissolution, liquidation or winding up of the Company. The foregoing notwithstanding, a merger or consolidation of the Company does not constitute a “Change in Control” if immediately after the merger or consolidation a majority of the voting power of the capital stock of the continuing or surviving entity, or any direct or indirect parent corporation of the continuing or surviving entity, will be owned by the persons who were the Company’s stockholders immediately prior to the merger or consolidation in substantially the same proportions as their ownership of the voting power of the Company’s capital stock immediately prior to the merger or consolidation.

(e) “Code” shall mean the Internal Revenue Code of 1986, as amended.

(f) “Committee” shall mean a committee of the Board of Directors, as described in Section 2 of the Plan.

(g) “Company” shall mean Dimension Therapeutics, Inc., a Delaware corporation.

(h) “Consultant” shall mean a person who performs bona fide services for the Company, a Parent or a Subsidiary as a consultant or advisor, excluding Employees and Outside Directors.

(i) “Date of Grant” shall mean the date of grant specified in the Notice of Stock Option Grant, which date shall be the later of (i) the date on which the Board of Directors resolved to grant this option or (ii) the first day of the Optionee’s Service.

(j) “Disability” shall mean that the Optionee is unable to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment which can be expected to result in death or which has lasted, or can be expected to last, for a continuous period of not less than 12 months.

(k) “Employee” shall mean any individual who is a common-law employee of the Company, a Parent or a Subsidiary.

(l) “Exercise Price” shall mean the amount for which one Share may be purchased upon exercise of this option, as specified in the Notice of Stock Option Grant.

(m) “Fair Market Value” shall mean the fair market value of a Share, as determined by the Board of Directors in good faith. Such determination shall be conclusive and binding on all persons.

(n) “Good Reason” means that Optionee resigns within 12 months after one of the following conditions has come into existence without Optionee’s consent:

(i) A reduction in Optionee’s base salary by more than 10%;

(ii) A material diminution of Optionee’s authority, duties or responsibilities; or

(iii) A relocation of Optionee’s principal workplace by more than 30 miles.

A condition will not be considered “Good Reason” unless Optionee gives the Company written notice of the condition within 90 days after the condition comes into existence and the Company fails to remedy the condition within 30 days after receiving Optionee’s written notice.

(o) “Immediate Family” shall mean any child, stepchild, grandchild, parent, stepparent, grandparent, spouse, sibling, mother-in-law, father-in-law, son-in-law, daughter-in-law, brother-in-law or sister-in-law and shall include adoptive relationships.

(p) “Involuntary Termination” shall mean a Separation resulting from either (i) Optionee’s involuntary discharge by the Company for reasons other than Cause or (ii) Optionee’s voluntary resignation for Good Reason.

(q) “ISO” shall mean an employee incentive stock option described in Section 422(b) of the Code.

(r) “Notice of Stock Option Grant” shall mean the document so entitled to which this Agreement is attached.

(s) “NSO” shall mean a stock option not described in Sections 422(b) or 423(b) of the Code.

(t) “Optionee” shall mean the person named in the Notice of Stock Option Grant.

(u) “Outside Director” shall mean a member of the Board of Directors who is not an Employee.

(v) “Parent” shall mean any corporation (other than the Company) in an unbroken chain of corporations ending with the Company, if each of the corporations other than the Company owns stock possessing 50% or more of the total combined voting power of all classes of stock in one of the other corporations in such chain.

(w) “Plan” shall mean the EiQ Networks, Inc. 2008 Stock Plan, as in effect on the Date of Grant.

(x) “Purchase Price” shall mean the Exercise Price multiplied by the number of Shares with respect to which this option is being exercised.

(y) “Right of First Refusal” shall mean the Company’s right of first refusal described in Section 7.

(z) “Securities Act” shall mean the Securities Act of 1933, as amended.

(aa) “Separation” shall mean a “separation from service,” as defined in the regulations under Section 409A of the Code.

(bb) “Service” shall mean service as an Employee, Outside Director or Consultant.

(cc) “Share” shall mean one share of Stock, as adjusted in accordance with Section 8 of the Plan (if applicable).

(dd) “Stock” shall mean the Common Stock of the Company.

(ee) “Subsidiary” shall mean any corporation (other than the Company) in an unbroken chain of corporations beginning with the Company, if each of the corporations other than the last corporation in the unbroken chain owns stock possessing 50% or more of the total combined voting power of all classes of stock in one of the other corporations in such chain.

(ff) “Transferee” shall mean any person to whom the Optionee has directly or indirectly transferred any Share.

(gg) “Transfer Notice” shall mean the notice of a proposed transfer of Shares described in Section 7.

DIMENSION THERAPEUTICS, INC. 2013 STOCK PLAN

NOTICE OF STOCK OPTION GRANT (INSTALLMENT EXERCISE)

The Optionee has been granted the following option to purchase shares of the Common Stock of Dimension Therapeutics, Inc.:


Name of Optionee:		«Name»

Total Number of Shares:		«TotalShares»

Type of Option:		«ISO» Incentive Stock Option (ISO)

		«NSO» Nonstatutory Stock Option (NSO)

Exercise Price per Share:		$«PricePerShare»

Date of Grant:		«DateGrant»

Date Exercisable:		This option may be exercised with respect to the first «Percent»% of the Shares subject to this option when the Optionee completes «CliffPeriod» months of continuous Service beginning with the Vesting Commencement Date set forth below. This option may be exercised with respect to an additional «Fraction»% of the Shares subject to this option when the Optionee completes each month of continuous Service thereafter.

Vesting Commencement Date:		«VestComDate»

Expiration Date:		«ExpDate». This option expires earlier if the Optionee’s Service terminates earlier, as provided in Section 6 of the Stock Option Agreement, or if the Company engages in certain corporate transactions, as provided in Section 8(b) of the Plan.

By signing below, the Optionee and the Company agree that this option is granted under, and governed by the terms and conditions of, the 2013 Stock Plan and the Stock Option Agreement. Both of these documents are attached to, and made a part of, this Notice of Stock Option Grant. Section 13 of the Stock Option Agreement includes important acknowledgements of the Optionee.


OPTIONEE:		DIMENSION THERAPEUTICS, INC.

DIMENSION THERAPEUTICS, INC. 2013 STOCK PLAN:

STOCK OPTION AGREEMENT (INSTALLMENT EXERCISE)

SECTION 1.

GRANT OF OPTION.

(b) $100,000 Limitation. Even if this option is designated as an ISO in the Notice of Stock Option Grant, it shall be deemed to be an NSO to the extent (and only to the extent) required by the $100,000 annual limitation under Section 422(d) of the Code.

(c) Stock Plan and Defined Terms. This option is granted pursuant to the Plan, a copy of which the Optionee acknowledges having received. The provisions of the Plan are incorporated into this Agreement by this reference. Except as otherwise defined in this Agreement (including without limitation Section 14 hereof), capitalized terms shall have the meaning ascribed to such terms in the Plan.

SECTION 2.

RIGHT TO EXERCISE.

SECTION 3.

NO TRANSFER OR ASSIGNMENT OF OPTION.

SECTION 4.

EXERCISE PROCEDURES.

withholding taxes under Subsection (b)). In the event that this option is being exercised by the representative of the Optionee, the notice shall be accompanied by proof (satisfactory to the Company) of the representative’s right to exercise this option.

(b) Withholding Taxes. In the event that the Company determines that it is required to withhold any tax (including without limitation any income tax, social insurance contributions, payroll tax, payment on account or other tax-related items arising in connection with the Optionee’s participation in the Plan and legally applicable to the Optionee (the “Tax-Related Items”)) as a result of the grant, vesting or exercise of this option, or as a result of the transfer of shares acquired upon exercise of this option, the Optionee, as a condition of this option, shall make arrangements satisfactory to the Company to enable it to satisfy all Tax-Related Items. The Optionee acknowledges that the responsibility for all Tax-Related Items is the Optionee’s and may exceed the amount actually withheld by the Company (or its affiliate or agent).

(c) Issuance of Shares. After satisfying all requirements for exercise of this option, the Company shall cause to be issued one or more certificates evidencing the Shares for which this option has been exercised. Such Shares shall be registered (i) in the name of the person exercising this option, (ii) in the names of such person and his or her spouse as community property or as joint tenants with the right of survivorship or (iii) with the Company’s consent, in the name of a revocable trust. Until the issuance of the Shares has been entered into the books and records of the Company or a duly authorized transfer agent of the Company, no right to vote, receive dividends or any other right as a stockholder will exist with respect to such Shares. The Company shall cause such certificates to be delivered to or upon the order of the person exercising this option.

SECTION 5.

PAYMENT FOR STOCK.

(a) Cash. All or part of the Purchase Price may be paid in cash or cash equivalents.

SECTION 6.

TERM AND EXPIRATION.

(b) Termination of Service (Except by Death). If the Optionee’s Service terminates for any reason other than death, then this option shall expire on the earliest of the following occasions:

(i) The expiration date determined pursuant to Subsection (a) above;

(ii) The date three months after the termination of the Optionee’s Service for any reason other than Disability; or

(iii) The date six months after the termination of the Optionee’s Service by reason of Disability.

(c) Death of the Optionee. If the Optionee dies while in Service, then this option shall expire on the earlier of the following dates:

(i) The expiration date determined pursuant to Subsection (a) above; or

(ii) The date 12 months after the Optionee’s death.

All or part of this option may be exercised at any time before its expiration under the preceding sentence by the executors or administrators of the Optionee’s estate or by any person who has acquired this option directly from the Optionee by beneficiary designation, bequest or inheritance, but only to the extent that this option had become exercisable before the Optionee’s death. When the Optionee dies, this option shall expire immediately with respect to the number of Shares for which this option is not yet exercisable. Once this option (or portion thereof) has terminated, the Optionee shall have no further rights with respect to the option (or portion thereof) or to the underlying Shares.

(c)(ii) above the exercise of this option would be prohibited solely because the issuance of Shares upon such exercise would violate the registration requirements under the Securities Act or a similar provision of other applicable law, then instead of terminating at the end of such prescribed period, the then-vested portion of this option will instead remain outstanding and not expire until the earlier of (i) the expiration date determined pursuant to Section 6(a) above or (ii) the date on which the then-vested portion of this option has been exercisable without violation of applicable law for the aggregate period (which need not be consecutive) after termination of the Optionee’s Service specified in the applicable Subsection above.

(e) Part-Time Employment and Leaves of Absence. If the Optionee commences working on a part-time basis, then the Company may adjust the vesting schedule set forth in the Notice of Stock Option Grant. If the Optionee goes on a leave of absence, then the Company may adjust the vesting schedule set forth in the Notice of Stock Option Grant in accordance with the Company’s leave of absence policy or the terms of such leave. Except as provided in the preceding sentence, Service shall be deemed to continue for any purpose under this Agreement while the Optionee is on a bona fide leave of absence, if (i) such leave was approved by the Company in writing and (ii) continued crediting of Service for such purpose is expressly required by the terms of such leave or by applicable law (as determined by the Company). Service shall be deemed to terminate when such leave ends, unless the Optionee immediately returns to active work.

(i) More than three months after the date when the Optionee ceases to be an Employee for any reason other than death or permanent and total disability (as defined in Section 22(e)(3) of the Code);

(ii) More than 12 months after the date when the Optionee ceases to be an Employee by reason of permanent and total disability (as defined in Section 22(e)(3) of the Code); or

SECTION 7.

RIGHT OF FIRST REFUSAL.

foreign securities laws. The Transfer Notice shall be signed both by the Optionee and by the proposed Transferee and must constitute a binding commitment of both parties to the transfer of the Shares. The Company shall have the right to purchase all, and not less than all, of the Shares on the terms of the proposal described in the Transfer Notice (subject, however, to any change in such terms permitted under Subsection (b) below) by delivery of a notice of exercise of the Right of First Refusal within 30 days after the date when the Transfer Notice was received by the Company.

(c) Additional or Exchanged Securities and Property. In the event of a merger or consolidation of the Company, a sale of all or substantially all of the Company’s stock or assets, any other corporate reorganization, a stock split, the declaration of a stock dividend, the declaration of an extraordinary dividend payable in a form other than stock, a spin-off, an adjustment in conversion ratio, a recapitalization or a similar transaction affecting the Company’s outstanding securities, any securities or other property (including cash or cash equivalents) that are by reason of such transaction exchanged for, or distributed with respect to, any Shares subject to this Section 7 shall immediately be subject to the Right of First Refusal. Appropriate adjustments to reflect the exchange or distribution of such securities or property shall be made to the number and/or class of the Shares subject to this Section 7.

either case that the Transferee agrees in writing on a form prescribed by the Company to be bound by all provisions of this Agreement. If the Optionee transfers any Shares acquired under this Agreement, either under this Subsection (e) or after the Company has failed to exercise the Right of First Refusal, then this Agreement shall apply to the Transferee to the same extent as to the Optionee.

(f) Termination of Rights as Stockholder. If the Company makes available, at the time and place and in the amount and form provided in this Agreement, the consideration for the Shares to be purchased in accordance with this Section 7, then after such time the person from whom such Shares are to be purchased shall no longer have any rights as a holder of such Shares (other than the right to receive payment of such consideration in accordance with this Agreement). Such Shares shall be deemed to have been purchased in accordance with the applicable provisions hereof, whether or not the certificate(s) therefor have been delivered as required by this Agreement.

SECTION 8.

LEGALITY OF INITIAL ISSUANCE.

No Shares shall be issued upon the exercise of this option unless and until the Company has determined that:

(a) It and the Optionee have taken any actions required to register the Shares under the Securities Act or to perfect an exemption from the registration requirements thereof;

(b) Any applicable listing requirement of any stock exchange or other securities market on which Stock is listed has been satisfied; and

SECTION 9.

NO REGISTRATION RIGHTS.

SECTION 10.

RESTRICTIONS ON TRANSFER OF SHARES.

Shares (including the placement of appropriate legends on the stock certificates (or electronic equivalent) or the imposition of stop-transfer instructions) and may refuse to transfer Shares acquired hereunder (or Shares proposed to be transferred in a subsequent transfer) if, in the judgment of the Company, such restrictions, legends or refusal are necessary or appropriate to achieve compliance with the Securities Act or other relevant securities or other laws, including without limitation under Regulation S of the Securities Act or pursuant to another available exemption from registration.

(b) Market Stand-Off. In connection with any underwritten public offering by the Company of its equity securities pursuant to an effective registration statement filed under the Securities Act, including the Company’s initial public offering, the Optionee or a Transferee shall not directly or indirectly sell, make any short sale of, loan, hypothecate, pledge, offer, grant or sell any option or other contract for the purchase of, purchase any option or other contract for the sale of, or otherwise dispose of or transfer, or agree to engage in any of the foregoing transactions with respect to, any Shares acquired under this Agreement without the prior written consent of the Company or its managing underwriter. Such restriction (the “Market Stand-Off”) shall be in effect for such period of time following the date of the final prospectus for the offering as may be requested by the Company or such underwriter. In no event, however, shall such period exceed 180 days plus such additional period as may reasonably be requested by the Company or such underwriter to accommodate regulatory restrictions on (i) the publication or other distribution of research reports or (ii) analyst recommendations and opinions, including (without limitation) the restrictions set forth in Rule 2711(f)(4) of the National Association of Securities Dealers and Rule 472(f)(4) of the New York Stock Exchange, as amended, or any similar successor rules. The Market Stand-Off shall in any event terminate two years after the date of the Company’s initial public offering. In the event of the declaration of a stock dividend, a spin-off, a stock split, an adjustment in conversion ratio, a recapitalization or a similar transaction affecting the Company’s outstanding securities without receipt of consideration, any new, substituted or additional securities which are by reason of such transaction distributed with respect to any Shares subject to the Market Stand-Off, or into which such Shares thereby become convertible, shall immediately be subject to the Market Stand-Off. In order to enforce the Market Stand-Off, the Company may impose stop-transfer instructions with respect to the Shares acquired under this Agreement until the end of the applicable stand-off period. The Company’s underwriters shall be beneficiaries of the agreement set forth in this Subsection (b). This Subsection (b) shall not apply to Shares registered in the public offering under the Securities Act.

(e) Legends. All certificates evidencing Shares purchased under this Agreement shall bear the following legend:

“THE SHARES REPRESENTED HEREBY MAY NOT BE SOLD, ASSIGNED, TRANSFERRED, ENCUMBERED OR IN ANY MANNER DISPOSED OF, EXCEPT IN COMPLIANCE WITH THE TERMS OF A WRITTEN AGREEMENT BETWEEN THE COMPANY AND THE REGISTERED HOLDER OF THE SHARES (OR THE PREDECESSOR IN INTEREST TO THE SHARES). SUCH AGREEMENT GRANTS TO THE COMPANY CERTAIN RIGHTS OF FIRST REFUSAL UPON AN ATTEMPTED TRANSFER OF THE SHARES. IN ADDITION, THE SHARES ARE SUBJECT TO RESTRICTIONS ON TRANSFER FOR A LIMITED PERIOD FOLLOWING THE EFFECTIVE DATE OF THE UNDERWRITTEN PUBLIC OFFERING OF THE COMPANY’S SECURITIES AND MAY NOT BE SOLD OR OTHERWISE DISPOSED OF BY THE HOLDER WITHOUT THE CONSENT OF THE COMPANY OR THE MANAGING UNDERWRITER. THE SECRETARY OF THE COMPANY WILL UPON WRITTEN REQUEST FURNISH A COPY OF SUCH AGREEMENT TO THE HOLDER HEREOF WITHOUT CHARGE.”

SECTION 11.

ADJUSTMENT OF SHARES.

SECTION 12.

MISCELLANEOUS PROVISIONS.

SECTION 13.

ACKNOWLEDGEMENTS OF THE OPTIONEE.

In addition to the other terms, conditions and restrictions imposed on this option and the Shares issuable under this option pursuant to this Agreement and the Plan, the Optionee expressly acknowledges being subject to Sections 7 (Right of First Refusal), 8 (Legality of Initial Issuance) and 10 (Restrictions on Transfer of Shares, including without limitation the Market Stand-Off), as well as the following provisions:

(a) Tax Consequences (No Liability for Discounted Options). The Optionee agrees that the Company does not have a duty to design or administer the Plan or its other compensation programs in a manner that minimizes the Optionee’s tax liabilities. The Optionee shall not make any claim against the Company or its Board of Directors, officers or employees related to tax liabilities arising from this option or the Optionee’s other compensation. In particular, any Optionee subject to U.S. taxation acknowledges that this option is exempt from Section 409A of the Code only if the Exercise Price is at least equal to the Fair Market Value per Share on the Date of Grant. Since Shares are not traded on an established securities market, the determination of their Fair Market Value is made by the Board of Directors or by an independent valuation firm retained by the Company. The Optionee acknowledges that there is no guarantee in either case that the Internal Revenue Service will agree with the valuation, and the Optionee shall not make any claim against the Company or its Board of Directors, officers or employees in the event that the Internal Revenue Service asserts that the valuation was too low.

monitoring the expiration of this option and for exercising this option, if at all, before it expires. This Subsection (c) shall supersede any contrary representation that may have been made, orally or in writing, by the Company or by an officer, employee, attorney or agent of the Company.

entitlements to Shares awarded, canceled, exercised, vested, unvested or outstanding in the Optionee’s favor (the “Data”). The Optionee further understands and acknowledges that the Company and/or its Subsidiaries will transfer Data among themselves as necessary for the purpose of implementation, administration and management of the Optionee’s participation in the Plan and that the Company and/or any Subsidiary may each further transfer Data to any third party assisting the Company in the implementation, administration and management of the Plan. The Optionee understands and acknowledges that the recipients of Data may be located in the United States or elsewhere. The Optionee authorizes such recipients to receive, possess, use, retain and transfer Data, in electronic or other form, for the purpose of administering the Optionee’s participation in the Plan, including a transfer to any broker or other third party with whom the Optionee elects to deposit Shares acquired under the Plan of such Data as may be required for the administration of the Plan and/or the subsequent holding of Shares on the Optionee’s behalf. The Optionee may, at any time, view the Data, require any necessary modifications of Data or withdraw the consents set forth in this Subsection (i) by contacting the Company in writing.

SECTION 14.

DEFINITIONS.

(a) “Agreement” shall mean this Stock Option Agreement.

(b) “Board of Directors” shall mean the Board of Directors of the Company, as constituted from time to time or, if a Committee has been appointed, such Committee.

(e) “Optionee” shall mean the person named in the Notice of Stock Option Grant.

(f) “Plan” shall mean the Dimension Therapeutics, Inc. 2013 Stock Plan, as in effect on the Date of Grant.

(g) “Purchase Price” shall mean the Exercise Price multiplied by the number of Shares with respect to which this option is being exercised.

(h) “Right of First Refusal” shall mean the Company’s right of first refusal described in Section 7.

(i) “Transferee” shall mean any person to whom the Optionee has directly or indirectly transferred any Share acquired under this Agreement.

(j) “Transfer Notice” shall mean the notice of a proposed transfer of Shares described in Section 7.

(k) “U.S. Person” shall mean a person described in Rule 902(k) of Regulation S of the Securities Act (or any successor rule or provision), which generally defines a U.S. person as any natural person resident in the United States, any estate of which any executor or administrator is a U.S. Person, or any trust of which of any trustee is a U.S. Person.

DIMENSION THERAPEUTICS, INC. 2013 STOCK PLAN:

SUMMARY OF STOCK GRANT (FOR SERVICES)

The Transferee is acquiring shares of the Common Stock of Dimension Therapeutics, Inc. on the following terms:


Name of Transferee:		«Name»

Total Number of Transferred Shares:		«TotalShares»

Date of Transfer:		«DateTransfer»

Vesting Commencement Date:		«VestComDate»

Vesting Schedule:		The Forfeiture Condition shall lapse with respect to the first «Percent»% of the Transferred Shares when the Transferee completes «CliffPeriod» months of continuous Service beginning with the Vesting Commencement Date set forth above. The Forfeiture Condition shall lapse with respect to an additional «Fraction»% of the Transferred Shares when the Transferee completes each month of continuous Service thereafter.

By signing below, the Transferee and the Company agree that the acquisition of the Transferred Shares is governed by the terms and conditions of the 2013 Stock Plan and the Stock Grant Agreement. Both of these documents are attached to, and made a part of, this Summary of Stock Grant. The Transferee agrees to accept by email all documents relating to the Company, the Plan or this grant and all other documents that the Company is required to deliver to its security holders (including, without limitation, disclosures that may be required by the Securities and Exchange Commission). The Transferee also agrees that the Company may deliver these documents by posting them on a website maintained by the Company or by a third party under contract with the Company. If the Company posts these documents on a website, it shall notify the Transferee by email of their availability. The Transferee acknowledges that he or she may incur costs in connection with electronic delivery, including the cost of accessing the internet and printing fees, and that an interruption of internet access may interfere with his or her ability to access the documents. This consent shall remain in effect until the Transferee gives the Company written notice that it should deliver paper documents.


TRANSFEREE:		DIMENSION THERAPEUTICS, INC.



				By:

Address for Mailing Stock Certificate:				Title:

DIMENSION THERAPEUTICS, INC. 2013 STOCK PLAN:

STOCK GRANT AGREEMENT (FOR SERVICES)

SECTION 1.

ACQUISITION OF SHARES.

(a) Transfer. On the terms and conditions set forth in the Summary of Stock Grant and this Agreement, the Company agrees to transfer to the Transferee the number of Shares set forth in the Summary of Stock Grant. The transfer shall occur at the offices of the Company on the date of transfer set forth in the Summary of Stock Grant or at such other place and time as the parties may agree.

(b) Consideration. The Transferee and the Company agree that the Transferred Shares are being issued to the Transferee as consideration for a portion of the services performed by the Transferee for the Company. The value of such portion is agreed to be not less than 100% of the Fair Market Value of the Transferred Shares.

(c) Stock Plan and Defined Terms. The transfer of the Transferred Shares is subject to the Plan, a copy of which the Transferee acknowledges having received. The provisions of the Plan are incorporated into this Agreement by this reference. Except as otherwise defined in this Agreement (including without limitation Section 11 hereof), capitalized terms shall have the meaning ascribed to such terms in the Plan.

SECTION 2.

FORFEITURE CONDITION.

(a) Scope of Forfeiture Condition. All Transferred Shares initially shall be Restricted Shares and shall be subject to forfeiture to the Company. The Transferee shall not transfer, assign, encumber or otherwise dispose of any Restricted Shares without the Company’s written consent, except as provided in the following sentence. The Transferee may transfer Restricted Shares to one or more members of the Transferee’s Immediate Family or to a trust established by the Transferee for the benefit of the Transferee and/or one or more members of the Transferee’s Immediate Family, provided in either case that the Transferee agrees in writing on a form prescribed by the Company to be bound by all provisions of this Agreement. If the Transferee transfers any Restricted Shares, then this Agreement shall apply to the Subsequent Transferee to the same extent as to the Transferee.

(b) Vesting. The Forfeiture Condition shall lapse and the Restricted Shares shall become vested in accordance with the vesting schedule set forth in the Summary of Stock Grant.

(c) Execution of Forfeiture. The Forfeiture Condition shall be applicable only if the Transferee’s Service terminates for any reason, with or without cause, including (without limitation) death or disability, before all Restricted Shares have become vested. In the event that the Transferee’s Service terminates for any reason, the certificate(s) representing any remaining Restricted Shares shall be delivered to the Company. The Company shall make no payment for Restricted Shares that are forfeited.

(d) Additional or Exchanged Securities and Property. In the event of a merger or consolidation of the Company, a sale of all or substantially all of the Company’s stock or assets, any other corporate reorganization, the declaration of a stock dividend, the declaration of an extraordinary dividend payable in a form other than stock, a spin-off, a stock split, an adjustment in conversion ratio, a recapitalization or a similar transaction affecting the Company’s outstanding securities, any securities or other property (including cash or cash equivalents) that are by reason of such transaction exchanged for, or distributed with respect to, any Restricted Shares or into which such Restricted Shares thereby become convertible shall immediately be subject to the Forfeiture Condition. Appropriate adjustments to reflect the exchange or distribution of such securities or property shall be made to the number and/or class of the Restricted Shares.

(e) Termination of Rights as Stockholder. If Restricted Shares are forfeited in accordance with this Section 2, then the person who is to forfeit such Restricted Shares shall no longer have any rights as a holder of such Restricted Shares. Such Restricted Shares shall be deemed to have been forfeited in accordance with the applicable provisions hereof, whether or not the certificate(s) therefor have been delivered as required by this Agreement.

(f) Escrow. Upon issuance, the certificates for Restricted Shares shall be deposited in escrow with the Company to be held in accordance with the provisions of this Agreement. Any new, substituted or additional securities or other property described in Subsection (d) above shall immediately be delivered to the Company to be held in escrow, but only to the extent the Transferred Shares are at the time Restricted Shares. All regular cash dividends on Restricted Shares (or other securities at the time held in escrow) shall be paid directly to the Transferee and shall not be held in escrow. Restricted Shares, together with any other assets or securities held in escrow hereunder, shall be (i) surrendered to the Company for forfeiture and cancellation in the event that the Forfeiture Condition or Right of First Refusal applies or (ii) released to the Transferee upon the Transferee’s request to the extent the Transferred Shares are no longer Restricted Shares (but not more frequently than once every six months). In any event, all Transferred Shares that have vested (and any other vested assets and securities attributable thereto) shall be released within 60 days after the earlier of (i) the termination of the Transferee’s Service or (ii) the lapse of the Right of First Refusal.

(g) Part-Time Employment and Leaves of Absence. If the Transferee commences working on a part-time basis, then the Company may adjust the vesting schedule set forth in the Summary of Stock Grant. If the Transferee goes on a leave of absence, then the Company may adjust the vesting schedule set forth in the Summary of Stock Grant in accordance with the Company’s leave of absence policy or the terms of such leave. Except as provided in the preceding sentence, Service shall be deemed to continue while the Transferee is on a bona fide leave of absence, if (i) such leave was approved by the Company in writing and (ii) continued crediting of Service is expressly required by the terms of such leave or by applicable law (as determined by the Company). Service shall be deemed to terminate when such leave ends, unless the Transferee immediately returns to active work.

SECTION 3.

RIGHT OF FIRST REFUSAL.

(a) Right of First Refusal. In the event that the Transferee proposes to sell, pledge or otherwise transfer to a third party any Transferred Shares, or any interest in Transferred Shares, the Company shall have the Right of First Refusal with respect to all (and not less than all) of such Transferred Shares. If the Transferee desires to transfer Transferred Shares, the Transferee shall give a written Transfer Notice to the Company describing fully the proposed transfer, including the number of Transferred Shares proposed to be transferred, the proposed transfer price, the name and address of the proposed Subsequent Transferee and proof satisfactory to the Company that the proposed sale or transfer will not violate any applicable federal, State or foreign securities laws. The Transfer Notice shall be signed both by the Transferee and by the proposed Subsequent Transferee and must constitute a binding commitment of both parties to the transfer of the Transferred Shares. The Company shall have the right to purchase all, and not less than all, of the Transferred Shares on the terms of the proposal described in the Transfer Notice (subject, however, to any change in such terms permitted under Subsection (b) below) by delivery of a notice of exercise of the Right of First Refusal within 30 days after the date when the Transfer Notice was received by the Company.

(b) Transfer of Shares. If the Company fails to exercise its Right of First Refusal within 30 days after receiving the Transfer Notice, the Transferee may, not later than 90 days after the Company received the Transfer Notice, conclude a transfer of the Transferred Shares subject to the Transfer Notice on the terms and conditions described in the Transfer Notice, provided that any such sale is made in compliance with applicable federal, State and foreign securities laws and not in violation of any other contractual restrictions to which the Transferee is bound. Any proposed transfer on terms and conditions different from those described in the Transfer Notice, as well as any subsequent proposed transfer by the Transferee, shall again be subject to the Right of First Refusal and shall require compliance with the procedure described in Subsection (a) above. If the Company exercises its Right of First Refusal, the parties shall consummate the sale of the Transferred Shares on the terms set forth in the Transfer Notice within 60 days after the Company received the Transfer Notice (or within such longer period as may have been specified in the Transfer Notice); provided, however, that in the event the Transfer Notice provided that payment for the Transferred Shares was to be made in a form other than cash or cash equivalents paid at the time of transfer, the Company shall have the option of paying for the Transferred Shares with cash or cash equivalents equal to the present value of the consideration described in the Transfer Notice.

(c) Additional or Exchanged Securities and Property. In the event of a merger or consolidation of the Company, a sale of all or substantially all of the Company’s stock or assets, any other corporate reorganization, a stock split, the declaration of a stock dividend, the declaration of an extraordinary dividend payable in a form other than stock, a spin-off, an adjustment in conversion ratio, a recapitalization or a similar transaction affecting the Company’s outstanding securities, any securities or other property (including cash or cash equivalents) that are by reason of such transaction exchanged for, or distributed with respect to, any Transferred Shares subject to this Section 3 shall immediately be subject to the Right of First Refusal. Appropriate adjustments to reflect the exchange or distribution of such securities or property shall be made to the number and/or class of the Transferred Shares subject to this Section 3.

(d) Termination of Right of First Refusal. Any other provision of this Section 3 notwithstanding, in the event that the Stock is readily tradable on an established securities market when the Transferee desires to transfer Transferred Shares, the Company shall have no Right of First Refusal, and the Transferee shall have no obligation to comply with the procedures prescribed by Subsections (a) and (b) above.

(e) Permitted Transfers. This Section 3 shall not apply to (i) a transfer by beneficiary designation, will or intestate succession or (ii) a transfer to one or more members of the Transferee’s Immediate Family or to a trust established by the Transferee for the benefit of the Transferee and/or one or more members of the Transferee’s Immediate Family, provided in either case that the Transferee agrees in writing on a form prescribed by the Company to be bound by all provisions of this Agreement. If the Transferee transfers any Transferred Shares, either under this Subsection (e) or after the Company has failed to exercise the Right of First Refusal, then this Agreement shall apply to the Subsequent Transferee to the same extent as to the Transferee.

(f) Termination of Rights as Stockholder. If the Company makes available, at the time and place and in the amount and form provided in this Agreement, the consideration for the Shares to be purchased in accordance with this Section 3, then after such time the person from whom such Shares are to be purchased shall no longer have any rights as a holder of such Shares (other than the right to receive payment of such consideration in accordance with this Agreement). Such Shares shall be deemed to have been purchased in accordance with the applicable provisions hereof, whether or not the certificate(s) therefor have been delivered as required by this Agreement.

SECTION 4.

OTHER RESTRICTIONS ON TRANSFER.

(a) Transferee Representations. In connection with the issuance and acquisition of Shares under this Agreement, the Transferee hereby represents and warrants to the Company as follows:

(i) The Transferee is acquiring and will hold the Transferred Shares for investment for his or her account only and not with a view to, or for resale in connection with, any “distribution” thereof within the meaning of the Securities Act.

(ii) The Transferee understands that the Transferred Shares have not been registered under the Securities Act by reason of a specific exemption therefrom and that the Transferred Shares must be held indefinitely, unless their sale or other transfer is subsequently registered under the Securities Act or the Transferee obtains an opinion of counsel, in form and substance satisfactory to the Company and its counsel, that such registration is not required. The Transferee further acknowledges and understands that the Company is under no obligation to register the Transferred Shares.

(iii) The Transferee is aware of Rule 144 under the Securities Act, which permits limited public resales of securities acquired in a non-public offering, subject to the satisfaction of certain conditions. These conditions may include (without limitation) that certain current public information about the issuer be available, that the resale occur only after a holding period required by Rule 144 has been satisfied, that the sale occur through an unsolicited “broker’s transaction,” and that the amount of securities being sold during any three-month period not exceed specified limitations. The Transferee acknowledges and understands that the conditions for resale set forth in Rule 144 have not been satisfied as of the Date of Transfer and that the Company is not required to take action to satisfy any such conditions.

(iv) The Transferee will not sell, transfer or otherwise dispose of the Transferred Shares in violation of the Securities Act, the Securities Exchange Act of 1934, or the rules promulgated thereunder, including Rule 144 under the Securities Act. The Transferee agrees that he or she will not dispose of the Transferred Shares unless and until he or she has complied with all requirements of this Agreement applicable to the disposition of Transferred Shares and he or she has provided the Company with written assurances, in substance and form satisfactory to the Company, that (A) the proposed disposition does not require registration of the Transferred Shares under the Securities Act or all appropriate action necessary for compliance with the registration requirements of the Securities Act or with any exemption from registration available under the Securities Act (including Rule 144) has been taken and (B) the proposed disposition will not result in the contravention of any transfer restrictions applicable to the Transferred Shares under applicable state law.

(v) The Transferee has received and has had access to such information as he or she considers necessary or appropriate for deciding whether to invest in the Transferred Shares, and the Transferee has had an opportunity to ask questions and receive answers from the Company regarding the terms and conditions of the issuance of the Transferred Shares.

(vi) The Transferee is aware that his or her investment in the Company is a speculative investment that has limited liquidity and is subject to the risk of complete loss. The Transferee is able, without impairing his or her financial condition, to hold the Transferred Shares for an indefinite period and to suffer a complete loss of his or her investment in the Transferred Shares.

(b) Securities Law Restrictions. Regardless of whether the offer and sale of Shares under the Plan have been registered under the Securities Act or have been registered or qualified under the securities laws of any State or other relevant jurisdiction, the Company at its discretion may impose restrictions upon the sale, pledge or other transfer of the Transferred Shares (including the placement of appropriate legends on the stock certificates (or electronic equivalent) or the imposition of stop-transfer instructions) and may refuse to transfer Shares acquired hereunder (or Shares proposed to be transferred in a subsequent transfer) if, in the judgment of the Company, such restrictions, legends or refusal are necessary or appropriate to achieve compliance with the Securities Act or other relevant securities or other laws, including without limitation under Regulation S of the Securities Act or pursuant to another available exemption from registration.

(c) Market Stand-Off. In connection with any underwritten public offering by the Company of its equity securities pursuant to an effective registration statement filed under the Securities Act, including the Company’s initial public offering, the Transferee or a Subsequent Transferee shall not directly or indirectly sell, make any short sale of, loan, hypothecate, pledge, offer, grant or sell any option or other contract for the purchase of, purchase any option or other contract for the sale of, or otherwise dispose of or transfer, or agree to engage in any of the foregoing transactions with respect to, any Transferred Shares without the prior written consent of the Company or its managing underwriter. Such restriction (the “Market Stand-Off”) shall be in effect for such period of time following the date of the final prospectus for the offering as may be requested by the Company or such underwriter. In no event, however, shall such period exceed 180 days plus such additional period as may reasonably be requested by the Company or such underwriter to accommodate regulatory restrictions on (i) the publication or other distribution of research reports or (ii) analyst recommendations and opinions, including (without limitation) the restrictions set forth in Rule 2711(f)(4) of the National Association of Securities Dealers and Rule 472(f)(4) of the New York Stock Exchange, as amended, or any similar successor rules. The Market Stand-Off shall in any event terminate two years after the date of the Company’s initial public offering. In the event of the declaration of a stock dividend, a spin-off, a stock split, an adjustment in conversion ratio, a recapitalization or a similar transaction affecting the Company’s outstanding securities without receipt of consideration, any new, substituted or additional securities which are by reason of such transaction distributed with respect to any Shares subject to the Market Stand-Off, or into which such Shares thereby become convertible, shall immediately be subject to the Market Stand-Off. In order to enforce the Market Stand-Off, the Company may impose stop-transfer instructions with respect to the Transferred Shares until the end of the applicable stand-off period. The Company’s underwriters shall be beneficiaries of the agreement set forth in this Subsection (c). This Subsection (c) shall not apply to Shares registered in the public offering under the Securities Act.

(d) Rights of the Company. The Company shall not be required to (i) transfer on its books any Transferred Shares that have been sold or transferred in contravention of this Agreement or (ii) treat as the owner of Transferred Shares, or otherwise to accord voting, dividend or liquidation rights to, any Subsequent Transferee to whom Transferred Shares have been transferred in contravention of this Agreement.

SECTION 5.

SUCCESSORS AND ASSIGNS.

Except as otherwise expressly provided to the contrary, the provisions of this Agreement shall inure to the benefit of, and be binding upon, the Company and its successors and assigns and be binding upon the Transferee and the Transferee’s legal representatives, heirs, legatees, distributees, assigns and transferees by operation of law, whether or not any such person has become a party to this Agreement or has agreed in writing to join herein and to be bound by the terms, conditions and restrictions hereof.

SECTION 6.

NO RETENTION RIGHTS.

Nothing in this Agreement or in the Plan shall confer upon the Transferee any right to continue providing services to the Company for any period of specific duration or interfere with or otherwise restrict in any way the rights of the Company (or any Parent or Subsidiary employing or retaining the Transferee) or of the Transferee, which rights are hereby expressly reserved by each, to terminate his or her Service at any time and for any reason, with or without cause.

SECTION 7.

TAX ELECTION.

The acquisition of the Transferred Shares may result in adverse tax consequences that may be avoided or mitigated by filing an election under Code Section 83(b). Such election may be filed only within 30 days after the date of transfer set forth in the Summary of Stock Grant. The form for making the Code Section 83(b) election is attached to this Agreement as an Exhibit. The Transferee should consult with his or her tax advisor to determine the tax consequences of acquiring the Transferred Shares and the advantages and disadvantages of filing the Code Section 83(b) election. The Transferee acknowledges that it is his or her sole responsibility, and not the Company’s, to file a timely election under Code Section 83(b), even if the Transferee requests the Company or its representatives to make this filing on his or her behalf.

SECTION 8.

LEGENDS.

All certificates evidencing Transferred Shares shall bear the following legends:

“THE SHARES REPRESENTED HEREBY MAY NOT BE SOLD, ASSIGNED, TRANSFERRED, ENCUMBERED OR IN ANY MANNER DISPOSED OF, EXCEPT IN COMPLIANCE WITH THE TERMS OF A WRITTEN AGREEMENT BETWEEN THE COMPANY AND THE REGISTERED HOLDER OF THE SHARES (OR THE PREDECESSOR IN INTEREST TO THE SHARES). SUCH AGREEMENT GRANTS TO THE COMPANY CERTAIN RIGHTS OF FIRST REFUSAL UPON AN ATTEMPTED TRANSFER OF THE SHARES AND IMPOSES CERTAIN FORFEITURE CONDITIONS UPON TERMINATION OF SERVICE WITH THE COMPANY. IN ADDITION, THE SHARES ARE SUBJECT TO RESTRICTIONS ON TRANSFER FOR A LIMITED PERIOD FOLLOWING THE EFFECTIVE DATE OF THE UNDERWRITTEN PUBLIC OFFERING OF THE COMPANY’S SECURITIES AND MAY NOT BE SOLD OR OTHERWISE DISPOSED OF BY THE HOLDER WITHOUT THE CONSENT OF THE COMPANY OR THE MANAGING UNDERWRITER. THE SECRETARY OF THE COMPANY WILL UPON WRITTEN REQUEST FURNISH A COPY OF SUCH AGREEMENT TO THE HOLDER HEREOF WITHOUT CHARGE.”

All certificates evidencing the Transferred Shares acquired under this Agreement in an unregistered transaction shall bear the following legend (and such other restrictive legends as are required or deemed advisable under the provisions of any applicable law):

If required by the authorities of any State in connection with the issuance of the Transferred Shares, the legend or legends required by such State authorities shall also be endorsed on all such certificates.

SECTION 9.

MISCELLANEOUS PROVISIONS.

(a) Choice of Law. This Agreement shall be governed by, and construed in accordance with, the laws of the State of Delaware, as such laws are applied to contracts entered into and performed in such State.

(b) Notice. Any notice required by the terms of this Agreement shall be given in writing. It shall be deemed effective upon (i) personal delivery, (ii) deposit with the United States Postal Service, by registered or certified mail, with postage and fees prepaid, (iii) deposit with Federal Express Corporation, with shipping charges prepaid or (iv) deposit with any internationally recognized express mail courier service. Notice shall be addressed to the Company at its principal executive office and to the Transferee at the address that he or she most recently provided to the Company in accordance with this Subsection (c).

(c) Entire Agreement. The Summary of Stock Grant, this Agreement and the Plan constitute the entire contract between the parties hereto with regard to the subject matter hereof. They supersede any other agreements, representations or understandings (whether oral or written and whether express or implied) that relate to the subject matter hereof.

SECTION 10.

ACKNOWLEDGEMENTS OF THE TRANSFEREE.

In addition to the other terms, conditions and restrictions imposed on the Shares acquired pursuant to this Agreement, the Transferee expressly acknowledges being subject to Sections 2 (Forfeiture Condition), 3 (Right of First Refusal) and 4 (Other Restrictions on Transfer, including without limitation the Market Stand-Off), as well as the following provisions:

(a) Waiver of Statutory Information Rights. The Transferee acknowledges and agrees that, until the first sale of the Company’s Stock to the general public pursuant to a registration statement filed under the Securities Act, he or she will be deemed to have waived any rights the Transferee might otherwise have had under Section 220 of the Delaware General Corporation Law to inspect for any proper purpose and to make copies and extracts from the Company’s stock ledger, a list of its stockholders and its other books and records or the books and records of any subsidiary. This waiver applies only in the Transferee’s capacity as a stockholder and does not affect any other inspection rights the Transferee may have under other law or pursuant to a written agreement with the Company.

(b) Plan Discretionary. The Transferee understands and acknowledges that (i) the Plan is entirely discretionary, (ii) the Company and the Transferee’s employer have reserved the right to amend, suspend or terminate the Plan at any time, (iii) the transfer of the Transferred Shares does not in any way create any contractual or other right to receive additional awards under the Plan at any time or in any amount and (iv) all determinations with respect to any additional awards, including (without limitation) the times when awards will be granted, the number of Shares offered and the vesting schedule, will be at the sole discretion of the Company.

(c) Termination of Service. The Transferee understands and acknowledges that participation in the Plan ceases upon termination of his or her Service for any reason, except as may explicitly be provided otherwise in the Plan or this Agreement.

(d) Extraordinary Compensation. The value of the Transferred Shares shall be an extraordinary item of compensation outside the scope of the Transferee’s employment contract, if any, and shall not be considered a part of his or her normal or expected compensation for purposes of calculating severance, resignation, redundancy or end-of-service payments, bonuses, long-service awards, pension or retirement benefits or similar payments.

(e) Authorization to Disclose. The Transferee hereby authorizes and directs the Transferee’s employer to disclose to the Company or any Subsidiary any information regarding the Transferee’s employment, the nature and amount of the Transferee’s compensation and the fact and conditions of the Transferee’s participation in the Plan, as the Transferee’s employer deems necessary or appropriate to facilitate the administration of the Plan.

(f) Personal Data Authorization. The Transferee consents to the collection, use and transfer of personal data as described in this Subsection (f). The Transferee understands and acknowledges that the Company, the Transferee’s employer and the Company’s other Subsidiaries hold certain personal information regarding the Transferee for the purpose of managing and administering the Plan, including (without limitation) the Transferee’s name, home address, telephone number, date of birth, social insurance number, salary, nationality, job title, any Shares or directorships held in the Company and details of all options or any other entitlements to Shares awarded, canceled, exercised, vested, unvested or outstanding in the Transferee’s favor (the “Data”). The Transferee further understands and acknowledges that the Company and/or its Subsidiaries will transfer Data among themselves as necessary for the purpose of implementation, administration and management of the Transferee’s participation in the Plan and that the Company and/or any Subsidiary may each further transfer Data to any third party assisting the Company in the implementation, administration and management of the Plan.

The Transferee understands and acknowledges that the recipients of Data may be located in the United States or elsewhere. The Transferee authorizes such recipients to receive, possess, use, retain and transfer Data, in electronic or other form, for the purpose of administering the Transferee’s participation in the Plan, including a transfer to any broker or other third party with whom the Transferee elects to deposit Shares acquired under the Plan of such Data as may be required for the administration of the Plan and/or the subsequent holding of Shares on the Transferee’s behalf. The Transferee may, at any time, view the Data, require any necessary modifications of Data or withdraw the consents set forth in this Subsection (f) by contacting the Company in writing.

SECTION 11.

DEFINITIONS.

(a) “Agreement” shall mean this Stock Grant Agreement.

(b) “Board of Directors” shall mean the Board of Directors of the Company, as constituted from time to time or, if a Committee has been appointed, such Committee.

(d) “Forfeiture Condition” shall mean the forfeiture condition described in Section 2.

(e) “Immediate Family” shall mean any child, stepchild, grandchild, parent, stepparent, grandparent, spouse, sibling, mother-in-law, father-in-law, son-in-law, daughter-in-law, brother-in-law or sister-in-law and shall include adoptive relationships.

(f) “Plan” shall mean the Dimension Therapeutics, Inc. 2013 Stock Plan, as amended.

(g) “Restricted Share” shall mean a Transferred Share that is subject to the Forfeiture Condition.

(h) “Right of First Refusal” shall mean the Company’s right of first refusal described in Section 3.

(i) “Subsequent Transferee” shall mean any person to whom the Transferee has directly or indirectly transferred any Transferred Shares.

(j) “Transferee” shall mean the individual named in the Summary of Stock Grant.

(k) “Transfer Notice” shall mean the notice of a proposed transfer of Transferred Shares described in Section 3.

(l) “Transferred Shares” shall mean the Shares acquired by the Transferee pursuant to this Agreement.

EXHIBIT I

SECTION 83(b) ELECTION

The undersigned taxpayer hereby elects, pursuant to Section 83(b) of the Internal Revenue Code of 1986, as amended, and pursuant to Treasury Regulations Section 1.83-2, to include in gross income as compensation for services the fair market value of the shares described below.

(1)

The taxpayer who performed the services is:

Name:

Address:

Social Security No.:

(2)

The property with respect to which the election is made is shares of the common stock of Dimension Therapeutics, Inc.

(3)

The property was transferred to the taxpayer on , .

(4)

The taxable year for which the election is made is the calendar year .

(5)

The property is subject to forfeiture if for any reason taxpayer’s service with the issuer terminates. The forfeiture condition lapses in a series of installments over a -year period ending on , .

(6)

The fair market value of such property at the time of transfer (determined without regard to any restriction other than a restriction that by its terms will never lapse) is $ per share x shares = $ .

(7)

No amount was paid for such property.

(8)

The amount to include in gross income is $ . [The amount in Line 6.]

(9)

A copy of this statement was furnished to Dimension Therapeutics, Inc., for whom taxpayer rendered the services underlying the transfer of such property.

(10)

This statement is executed on , .



Spouse (if any)		Taxpayer

Within 30 days after the date of transfer of the property, this election must be filed with the Internal Revenue Service office where the taxpayer files his or her annual federal income tax return. The filing should be made by registered or certified mail, return receipt requested. The taxpayer must (a) include a copy of the completed form with his or her federal income tax return for the taxable year in which the property is transferred and (b) deliver an additional copy to the Company.

EX-5.1

Exhibit 5.1

Gibson, Dunn & Crutcher LLP

2029 Century Park East

Los Angeles, CA-90067-3026

Tel 310.552.8500

www.gibsondunn.com

November 7, 2017

Ultragenyx Pharmaceutical Inc.

60 Leveroni Court

Novato, CA 94949

Re: Ultragenyx Pharmaceutical Inc. Registration Statement on Form S-8

Ladies and Gentlemen:

We have examined the Registration Statement on Form S-8 (the “Registration Statement”), of Ultragenyx Pharmaceutical Inc., a Delaware corporation (the “Company”) filed with the Securities and Exchange Commission (the “Commission”) pursuant to the Securities Act of 1933, as amended (the “Securities Act”), in connection with the offering by the Company of up to 639,897 shares of the Company’s common stock, par value $0.001 per share (the “Common Stock”). The Common Stock subject to the Registration Statement are to be issued under the Dimension Therapeutics, Inc. 2015 Stock Option and Incentive Plan and the Dimension Therapeutics, Inc. 2013 Stock Plan (collectively, the “Plans”).

We have examined the Plans and the originals, or photostatic or certified copies, of such records of the Company and certificates of officers of the Company and of public officials and such other documents as we have deemed relevant and necessary as the basis for the opinions set forth below. We have also made such other investigations as we have deemed relevant and necessary or appropriate in connection with the opinion hereinafter set forth. In our examination, we have assumed the genuineness of all signatures, the legal capacity and competency of all natural persons, the authenticity of all documents submitted to us as originals and the conformity to original documents of all documents submitted to us as copies. We have also assumed that there are no agreements or understandings between or among the Company and any participants in the Plans that would expand, modify or otherwise affect the terms of the Plans or the respective rights or obligations of the participants thereunder. Finally, we have assumed the accuracy of all other information provided to us by the Company during the course of our investigations, on which we have relied in issuing the opinion expressed below.

Based upon the foregoing examination and in reliance thereon, and subject to the assumptions stated and in reliance on statements of fact contained in the documents that we have examined, we are of the opinion that the shares of Common Stock issuable under the Plans, when issued and sold in accordance with the terms of the respective Plans and against payment therefor, and when the Registration Statement has become effective under the Securities Act, will be validly issued, fully paid and non-assessable.

We render no opinion herein as to matters involving the laws of any jurisdiction other than the Delaware General Corporation Law (the “DGCL”). We are not admitted to practice in the State of Delaware; however, we are generally familiar with the DGCL as currently in effect and have made such inquiries as we consider necessary to render the opinions above. This opinion is limited to the effect of the current state of the law of the DGCL and the facts as they currently exist. We assume no obligation to revise or supplement this opinion in the event of future changes in such law or the interpretations thereof or such facts.

Beijing • Brussels • Century City • Dallas • Denver • Dubai • Frankfurt • Hong Kong • London • Los Angeles • Munich

New York • Orange County • Palo Alto • Paris • San Francisco • São Paulo • Singapore • Washington D.C.

LOGO

We consent to the filing of this opinion as an exhibit to the Registration Statement. In giving this consent, we do not thereby admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act or the Rules and Regulations of the Commission.

Very truly yours,

/s/ Gibson, Dunn & Crutcher LLP

Gibson, Dunn & Crutcher LLP

EX-23.1

Exhibit 23.1

Consent of Independent Registered Public Accounting Firm

We consent to the incorporation by reference in the Registration Statement (Form S-8) pertaining to the Dimension Therapeutics, Inc. 2015 Stock Option and Incentive Plan and the Dimension Therapeutics, Inc. 2013 Stock Plan, both as assumed by Ultragenyx Pharmaceutical Inc., of our reports dated February 16, 2017, with respect to the consolidated financial statements of Ultragenyx Pharmaceutical Inc. and the effectiveness of internal control over financial reporting of Ultragenyx Pharmaceutical Inc. included in its Annual Report (Form 10-K) for the year ended December 31, 2016, filed with the Securities and Exchange Commission.

/s/ Ernst & Young LLP

San Jose, California

November 2, 2017