Ultragenyx Pharmaceutical Inc. (NASDAQ: RARE) announced the U.S. Food and Drug Administration has accepted for review its resubmitted Biologics License Application seeking accelerated approval for UX111, an AAV gene therapy designed to treat Sanfilippo syndrome Type A.

The FDA set a Prescription Drug User Fee Act action date of September 19, 2026. If approved, UX111 would become the first therapy for treating Sanfilippo syndrome Type A, a rare genetic disease that affects young children and leads to progressive neurodegeneration.

The resubmitted application includes updated long-term clinical data representing up to 8 years of follow-up. According to the company, the FDA previously acknowledged that the neurodevelopmental outcome data are robust and that biomarker data provide additional supportive evidence during its prior review.

Sanfilippo syndrome Type A is caused by a deficiency in the sulfamidase enzyme, leading to abnormal accumulation of heparan sulfate in the brain. The condition affects an estimated 3,000 to 5,000 patients in commercially accessible regions, with a median life expectancy of 15 years.

UX111 is administered as a one-time intravenous infusion using an AAV9 vector to deliver a functional copy of the SGSH gene to cells. The FDA granted the application Priority Review in February 2025.

If approved, the therapy will be manufactured in the United States at facilities in Columbus, Ohio and Bedford, Massachusetts. The product has received multiple regulatory designations including Regenerative Medicine Advanced Therapy, Fast Track, Rare Pediatric Disease, and Orphan Drug designations in the U.S.