Ultragenyx Resubmits BLA to FDA Seeking Accelerated Approval of UX111 AAV Gene Therapy for Sanfilippo Syndrome Type A

NOVATO, Calif., Jan. 30, 2026 (GLOBE NEWSWIRE) — Ultragenyx Pharmaceutical Inc. has officially resubmitted its Biologics License Application (BLA) to the U.S. Food and Drug Administration (FDA) seeking accelerated approval for UX111, an investigational AAV9 gene therapy. This AAV candidate, also known as rebisufligene etisparvovec, is designed as a one-time treatment for patients with Sanfilippo syndrome type A (MPS IIIA). By utilizing a self-complementary AAV9 vector, the therapy delivers a functional copy of the SGSH gene directly to cells, aiming to stop the relentless neurodegeneration associated with this fatal lysosomal storage disease.

The resubmission of this AAV program follows a Complete Response Letter issued in July 2025. The updated filing includes comprehensive responses to chemistry, manufacturing, and controls (CMC) observations regarding AAV production, alongside substantial longer-term clinical data. This AAV dataset demonstrates a durable treatment effect across multiple biomarkers, including a significant reduction in CSF heparan sulfate. The AAV9 vector’s ability to cross the blood-brain barrier is central to its design, allowing transduced cells to secrete functional enzymes that can be taken up by neighboring neurons through cross-correction.

Emil D. Kakkis, M.D., Ph.D., CEO and President of Ultragenyx, emphasized the high stakes for the Sanfilippo community, noting that there are currently no approved treatment options for MPS IIIA. The AAV clinical data presented in the BLA shows a continued separation from natural history, suggesting that the AAV9 intervention can preserve neurologic function in affected children. The AAV program has already been recognized by the FDA with Regenerative Medicine Advanced Therapy, Fast Track, Rare Pediatric Disease, and Orphan Drug designations.

The company expects a Prescription Drug User Fee Act (PDUFA) action date to be assigned within a month of this AAV resubmission, with a final decision anticipated in the third quarter of 2026. If the FDA grants approval, UX111 will become the first-ever approved therapy for Sanfilippo syndrome type A, marking a major milestone for AAV gene therapy in the treatment of rare pediatric brain disorders. Detailed updates on the AAV clinical progress will be shared at the upcoming WORLDSymposium™ 2026 in San Diego.