Ultragenyx UX111 (Rebisufligene Etisparvovec) FDA PDUFA Action Date Sits 5 Days Out on September 19 for Sanfilippo Syndrome Type A Gene Therapy; If Approved, First-Ever MPS IIIA Treatment
The Ultragenyx (NASDAQ: RARE) UX111 (rebisufligene etisparvovec, AAV9-delivered gene therapy for the SGSH gene) FDA PDUFA action date for Sanfilippo Syndrome Type A (mucopolysaccharidosis type IIIA, or MPS IIIA — a rare autosomal recessive lysosomal storage disorder causing progressive irreversible neurodegeneration in young children with a median life expectancy in the mid-teens) is set for Saturday September 19, 2026 (weekend PDUFA date; the FDA typically issues weekend action-date decisions on the adjacent Friday or the following Monday), five days from the September 14 opening of Morgan Stanley conference week. The resubmitted Biologics License Application under Accelerated Approval was accepted by the FDA in April 2026 following a July 2025 complete response letter that identified chemistry, manufacturing, and controls (CMC) plus manufacturing-site inspection issues. The clinical package includes up to 8 years of follow-up in treated children, with sustained cerebrospinal fluid heparan sulfate (the accumulated substrate) reduction plus preserved developmental trajectories relative to untreated natural history. If approved, UX111 would become the first-ever therapy for MPS IIIA anywhere in the world; the drug would also confer a Rare Pediatric Disease Priority Review Voucher on Ultragenyx (historically valued $150-350 million on the secondary market). Manufacturing runs domestically at Andelyn Biosciences in Columbus, Ohio and Ultragenyx's own Bedford, Massachusetts facility.