UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Ultragenyx Pharmaceutical Inc.

(Exact name of Registrant as Specified in Its Charter)

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☐

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 13(a) of the Exchange Act. ☐

Item 8.01 Other Events.

On April 15, 2024, Ultragenyx Pharmaceutical Inc. (the “Company”) announced new data from the Phase 1/2 study of GTX-102 for the treatment of Angelman syndrome. Patients in Expansion Cohorts A & B treated with a set dose and regimen of GTX-102 showed rapid and clinically meaningful improvement across multiple domains consistent with or exceeding Dose-escalation Cohorts 4-7 data at Day 170. Treatment of the Dose-escalation Cohorts 4-7 showed long-term increasing and sustained clinical benefit far exceeding Natural History data at Day 758. These data will be discussed in more detail in a corporate presentation being hosted by the Company on April 15, 2024 at 8:00 a.m. ET and will also be presented by Kemi Olugemo, M.D., FAAN at the 76th Annual American Academy of Neurology Meeting (“AAN”) in Denver on Tuesday, April 16, 2024.

New Expansion Cohorts A & B data include Day 170 results on 24 patients, and long-term Dose-escalation Cohorts 4–7 data include up to Day 758 results on 15 patients.

Expansion Cohorts at Day 170:

Dose-escalation Cohorts up to Day 758:

There were no unexpected serious adverse events. Three patients had serious adverse events (mild to moderate) of lower extremity weakness assessed as related to study treatment; one in Cohort 7, two in Cohorts A & B; none reported in Cohorts C–E to date. All resolved rapidly without sequelae and remain in the study without ongoing safety concerns. The five original patients affected by lower extremity weakness from Cohorts 1–3 have been re-dosed safely multiple times and are receiving maintenance treatment without recurrence. The Cohort 7 patient has also been re-dosed safely multiple times and is receiving maintenance treatment without recurrence. The two patients in Cohorts A & B remain in study and are expected to continue dosing. The FDA and other regulatory agencies were notified of all safety events and raised no issues nor required additional actions. The foregoing safety information is current as of April 5, 2024

Data comparisons of GTX-102 data to data from the Angelman Syndrome Natural History Study (Natural History Data) are illustrative only. The Angelman Syndrome Natural History Study is a multisite, prospective, observational study. The study data are combined with clinic and registry data and stored in the Linking Angelman and Dup15q Data for Expanded Research (LADDER) database platform, which is managed by Boston Children’s Hospital and spans different Angelman syndrome cohorts. The Natural History study populations analyzed for comparative purposes to GTX-102 are a subset of the larger populations, and only include 4- to 17-year-old gene deletion patients. Differences exist between study designs, subject characteristics and geographical regions and caution should be exercised when comparing data across studies. Natural history data are not available for the ASA assessments.

Cautionary Note Regarding Forward-Looking Statements

This Current Report on Form 8-K contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. These statements may be identified by the use of words such as, but not limited to, “anticipates,” “continue,” “will,” or other similar terms or expressions that concern the Company’s expectations, plans and intentions. Forward-looking statements include, without limitation, statements regarding the clinical benefit, tolerability and safety of GTX-102 and the corresponding impact on patients, the anticipated dosing of the Phase 2 study for GTX-102, and the timing for initiation of a Phase 3 study for GTX-102 and associated regulatory meetings. Such forward-looking statements involve substantial risks and uncertainties that could cause the Company’s clinical development programs, collaboration with third parties, future results, performance or achievements to differ significantly from those expressed or implied by the forward-looking statements. Such risks and uncertainties include, among others, the uncertainty of clinical drug development and unpredictability and lengthy process for obtaining regulatory approvals, the ability of the Company to successfully develop GTX-102, the Company’s ability to achieve its projected development goals in its expected timeframes, the risk that results from earlier studies may not be predictive of future study results, risks related to adverse side effects, risks related to reliance on third party partners to conduct certain activities on the Company’s behalf, smaller than anticipated market opportunities for the Company’s products and product candidates, manufacturing risks, competition from other therapies or products, and other matters that could affect the sufficiency of existing cash, cash equivalents and short-term investments to fund operations, the Company’s future operating results and financial performance, the timing of clinical trial activities and reporting results from same, and the availability or commercial potential of the Company’s products and drug candidates. The Company undertakes no obligation to update or revise any forward-looking statements. For a further description of the risks and uncertainties that could cause actual results to differ from those expressed in these forward-looking statements, as well as risks relating to the business of the Company in general, see the Company's Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on February 21, 2024, and its subsequent periodic reports filed with the SEC.

Item 9.01 Financial Statements and Exhibits.

(d)Exhibits

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.