Ultragenyx (NASDAQ: RARE) starts rolling BLA for DTX401 gene therapy

Rhea-AI Filing Summary

Ultragenyx Pharmaceutical Inc. reported that it has begun a rolling submission of a Biologics License Application to the U.S. FDA for DTX401, an AAV gene therapy for Glycogen Storage Disease Type Ia. The company has submitted the non-clinical and clinical modules and plans to complete the full application, including the chemistry, manufacturing and controls module, in the fourth quarter of 2025.

The BLA will include 96-week data from a Phase 3 trial showing patients had greater reductions in total daily cornstarch from baseline at their last visit, with a -60% reduction in the ongoing DTX401 group and -64% in the Crossover Placebo to DTX401 group compared to the 48-week data. Ultragenyx also plans to incorporate updates in the CMC section to proactively address FDA observations from the UX111 complete response letter and at its gene therapy manufacturing facilities.

Insights

Biotech regulatory and clinical development analyst

Ultragenyx advances DTX401 with a rolling BLA based on 96-week Phase 3 data while addressing prior FDA observations.

Ultragenyx is initiating a rolling Biologics License Application for DTX401, an AAV gene therapy for Glycogen Storage Disease Type Ia. A rolling BLA lets the company submit sections over time, and here the non-clinical and clinical modules are already filed, with the chemistry, manufacturing and controls module planned for the fourth quarter of 2025.

The BLA relies on 96-week Phase 3 data, where patients showed larger total daily cornstarch reductions from baseline at their last visit than at 48 weeks: -60% in the ongoing DTX401 arm and -64% in the Crossover Placebo to DTX401 group. These reductions support the clinical effect on disease management. The company also plans CMC updates to respond to FDA observations from the UX111 complete response letter and its manufacturing facilities, underscoring that approval prospects will depend on both data and successful resolution of prior regulatory concerns.

8-K Event Classification

Item 8.01 — Other Events

1 item

Item 8.01 Other Events Other

Voluntary disclosure of events the company deems important to shareholders but not covered by other items.

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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

Date of Report (Date of earliest event reported): August 18, 2025

Ultragenyx Pharmaceutical Inc.

(Exact name of Registrant as Specified in Its Charter)

Delaware			001-36276	27-2546083
(State or Other Jurisdiction of Incorporation)			(Commission File Number)	(IRS Employer Identification No.)
60 Leveroni Court
Novato, California				94949
(Address of Principal Executive Offices)				(Zip Code)

Registrant’s Telephone Number, Including Area Code: 415 483-8800

(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:

☐Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

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

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock, $0.001 par value		RARE		Nasdaq Global Select Market

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 August 18, 2025, Ultragenyx Pharmaceutical Inc. (the “Company”) issued a press release announcing the initiation of a rolling submission of a Biologics License Application (“BLA”) to the U.S. Food and Drug Administration (“FDA”) seeking approval for DTX401 AAV gene therapy as a treatment for Glycogen Storage Disease Type Ia (“GSDIa”). The Company has submitted the non-clinical and clinical modules to the FDA and plans to complete the full BLA including submission of the chemistry, manufacturing and controls (“CMC”) module in the fourth quarter of 2025.

The BLA for DTX401 includes the previously disclosed 96-week data from the randomized, placebo-controlled Phase 3 study that demonstrated patients had even greater reductions in total daily cornstarch at their last visit compared to baseline in both the ongoing DTX401 group (-60%) and the Crossover Placebo to DTX401 group (-64%) when compared to the 48-week data. It will also include updates to proactively respond to related FDA observations identified in the UX111 complete response letter in the CMC section and at the Company’s gene therapy manufacturing facilities.

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 future operating results and financial performance, business plans and objectives for DTX401, expectations regarding the tolerability and safety of DTX401, expectations regarding the adequacy of clinical data to support the marketing application and approval of DTX401, the Company’s intent to file, and potential timing and success of, the marketing application and other regulatory approvals for DTX401, expectations regarding timing of BLA submission and receiving potential approval of DTX401, expectations regarding the prevalence of patients of DTX401, future regulatory interactions, expectations regarding the Company’s ability to resolve with the FDA the observations in the complete response letter, and the value to be generated by DTX401, and future clinical and regulatory developments for DTX401. 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 DTX401, the Company’s ability to achieve its projected development goals in its expected timeframes, risks related to adverse side effects, risks related to reliance on third party partners to conduct certain activities on the Company’s behalf, the Company’s limited experience in operating its own manufacturing facility, the ability of the Company and its third party manufacturers to comply with regulatory requirements, 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 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 Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission (SEC) on August 6, 2025, and its subsequent periodic reports filed with the SEC.

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.

			Ultragenyx Pharmaceutical Inc.
Date:	August 18, 2025	By:	/s/ Howard Horn
			Howard Horn Executive Vice President, Chief Financial Officer, Corporate Strategy

FAQ

What did Ultragenyx (RARE) announce about DTX401 in this 8-K?

Ultragenyx announced it has initiated a rolling Biologics License Application to the U.S. FDA for DTX401, an AAV gene therapy for Glycogen Storage Disease Type Ia, and has already submitted the non-clinical and clinical modules.

What is DTX401 and which condition is it intended to treat for Ultragenyx (RARE)?

DTX401 is an AAV gene therapy candidate being developed by Ultragenyx as a treatment for Glycogen Storage Disease Type Ia (GSDIa).

What Phase 3 results for DTX401 does Ultragenyx include in the BLA?

The BLA includes 96-week randomized, placebo-controlled Phase 3 data showing greater reductions in total daily cornstarch from baseline at the last visit, with a -60% reduction in the ongoing DTX401 group and -64% in the Crossover Placebo to DTX401 group compared to the 48-week data.

When does Ultragenyx (RARE) plan to complete the DTX401 BLA submission?

Ultragenyx plans to complete the full BLA for DTX401, including submission of the chemistry, manufacturing and controls module, in the fourth quarter of 2025.

How is Ultragenyx addressing prior FDA observations in the DTX401 application?

The BLA for DTX401 will include updates in the chemistry, manufacturing and controls section and at Ultragenyx’s gene therapy manufacturing facilities to proactively respond to related FDA observations identified in the UX111 complete response letter.

What forward-looking risks does Ultragenyx highlight regarding DTX401?

Ultragenyx notes risks such as the uncertainty of clinical development and regulatory approvals, its ability to develop DTX401 on expected timelines, potential adverse side effects, reliance on third-party partners, manufacturing and regulatory compliance challenges, competition from other therapies, and market size and financial performance risks.