Ultragenyx gets priority review tag, August PDUFA date for Sanfilippo syndrome AAV gene therapy

The U.S. FDA has accepted Ultragenyx Pharmaceutical’s BLA seeking accelerated approval for its AAV gene therapy as a treatment for patients with Sanfilippo syndrome type A, granting it priority review and assigning a PDUFA action date of August 18, 2025.

The FDA also informed the company that the agency is not currently planning to hold an advisory committee meeting to discuss the application.

Ultragenyx’s UX111 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 that primarily affects the brain and currently has no approved treatment. 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. Ultragenyx picked up the therapy in 2022, through an exclusive licensing agreement with its developer, Abeona Therapeutics.

The BLA submission for UX111 is supported by 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 in cerebrospinal fluid 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 group compared to natural history data from untreated patients.