RARE Ultragenyx Pharmaceutical Inc

Ultragenyx Pharmaceutical Inc. (NASDAQ: RARE) today announced the U.S. Food and Drug Administration (FDA or the Agency) has accepted for review the Biologics License Application (BLA) seeking accelerated approval for UX111 (ABO-102) AAV gene therapy as a treatment for patients with Sanfilippo syndrome type A (MPS IIIA). The FDA granted the BLA Priority Review with a Prescription Drug User Fee Act (PDUFA) action date of August 18, 2025. The FDA also informed the company that they are not currently planning to hold an advisory committee meeting to discuss this application.

“Acceptance of the UX111 BLA brings us closer to being able to provide a first-ever treatment for Sanfilippo syndrome type A and, if our application is successful, we’re prepared to launch this therapy for patients and their families,” said Emil D. Kakkis, M.D., Ph.D., chief executive officer and president of Ultragenyx. “By reaching alignment with the Agency on a path forward for accelerated approval in neuronopathic MPS diseases, our UX111 program could serve as a step towards advancing drug development across multiple metabolic diseases of the brain.”

The BLA submission for UX111 is supported by available data, including the latest data from the ongoing pivotal Transpher A and long-term follow-up studies presented at WORLDSymposium™ 2025, demonstrating treatment with UX111 resulted in rapid and sustained decreased levels of heparan sulfate (HS) in cerebrospinal fluid (CSF) in patients with Sanfilippo syndrome type A irrespective of age or stage of disease progression at the time of treatment. The data showed a statistically significant improvement in the Bayley-III raw scores for the subdomains of cognition, receptive communication and expressive communication in the modified intent-to-treat (mITT) group compared to natural history data from untreated patients. These clinical endpoints were correlated with substantial and sustained reduction in levels of CSF-HS. The most frequently reported treatment-related adverse events to date were elevations in liver enzymes, and the majority of these events were mild (Grade 1) or moderate (Grade 2) in severity and all resolved.

About UX111UX111 is a novel in vivo gene therapy in Phase 1/2/3 development for Sanfilippo syndrome type A (MPS IIIA), a rare fatal lysosomal storage disease with no approved treatment that primarily affects the brain. The therapy is designed to address the underlying SGSH enzyme deficiency responsible for abnormal accumulation of heparan sulfate, a glycosaminoglycan, in the brain that results in progressive cell damage and neurodegeneration. UX111 is dosed in a one-time intravenous infusion using a self-complementary AAV9 vector to deliver a functional copy of the SGSH gene to cells. These transduced cells then produce the enzyme and secrete it to be taken up by other brain cells, cross-correcting the enzyme deficiency. The product was originally developed by Abeona Therapeutics and transferred to Ultragenyx to complete development. The UX111 program has received Regenerative Medicine Advanced Therapy, Fast Track, Rare Pediatric Disease, and Orphan Drug designations in the U.S., and PRIME and Orphan medicinal product designations in the EU. If approved, the product will be commercialized with Ultragenyx’s existing metabolic disease team seeing the same biochemical genetics doctors.

About Sanfilippo Syndrome Type A (MPS IIIA)Sanfilippo syndrome type A (MPS IIIA) is a rare, fatal lysosomal storage disease with no approved treatment that primarily affects the brain and is characterized by rapid neurodegeneration, with onset in early childhood. Children with MPS IIIA present with global developmental delay which eventually leads to progressive cognitive, language and motor decline, behavioral abnormalities and early death. MPS IIIA is estimated to affect approximately 3,000 to 5,000 patients in commercially accessible geographies with a median life expectancy of 15 years. MPS IIIA is caused by biallelic pathogenic variants in the SGSH gene that lead to a deficiency in the sulfamidase (SGSH) enzyme responsible for breaking down heparan sulfate, a glycosaminoglycans, which accumulate in cells throughout the body resulting in the observed rapid neurodegeneration that is associated with the disorder.

About UltragenyxUltragenyx is a biopharmaceutical company committed to bringing novel therapies to patients for the treatment of serious rare and ultrarare genetic diseases. The company has built a diverse portfolio of approved medicines and treatment candidates aimed at addressing diseases with high unmet medical need and clear biology, for which there are typically no approved therapies treating the underlying disease.

The company is led by a management team experienced in the development and commercialization of rare disease therapeutics. Ultragenyx’s strategy is predicated upon time- and cost-efficient drug development, with the goal of delivering safe and effective therapies to patients with the utmost urgency.

For more information on Ultragenyx, please visit the company's website at: www.ultragenyx.com.

Forward-Looking Statements and Use of Digital Media Except for the historical information contained herein, the matters set forth in this press release, including statements related to Ultragenyx's expectations and projections regarding its future operating results and financial performance, business plans and objectives for UX111, expectations regarding the tolerability and safety of UX111, and future clinical and regulatory developments for UX111 are forward-looking statements within the meaning of the "safe harbor" provisions of the Private Securities Litigation Reform Act of 1995. Such forward-looking statements involve substantial risks and uncertainties that could cause our 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 UX111, 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, 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 Ultragenyx’s products and drug candidates. Ultragenyx 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 Ultragenyx in general, see Ultragenyx's Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission (SEC) on November 6, 2024, and its subsequent periodic reports filed with the SEC.

In addition to its SEC filings, press releases and public conference calls, Ultragenyx uses its investor relations website and social media outlets to publish important information about the company, including information that may be deemed material to investors, and to comply with its disclosure obligations under Regulation FD. Financial and other information about Ultragenyx is routinely posted and is accessible on Ultragenyx’s Investor Relations website (https://ir.ultragenyx.com/) and LinkedIn website (https://www.linkedin.com/company/ultragenyx-pharmaceutical-inc-/mycompany/).

ContactsUltragenyx Pharmaceutical Inc.

InvestorsJoshua Higa+1-415-475-6370ir@ultragenyx.com

MediaCarolyn Wang+1-415-225-5050media@ultragenyx.com