Ultragenyx announced today that it has officially resubmitted its application to the U.S. FDA seeking accelerated approval of UX111, an AAV9 gene therapy for children living with Sanfilippo syndrome type A. With this resubmission, the FDA’s six month priority review clock has now begun and a decision date is anticipated in the third quarter of 2026. Read the company’s press release.
The Biologics License Application (BLA) was originally filed early in 2025 but received a Complete Response Letter (CRL) in July 2025, declining to approve the application at that time. Since then, Ultragenyx has been addressing the manufacturing observations noted by the FDA and working to provide updated long-term clinical data in the resubmission.
UX111 has been in clinical trials for nearly 10 years now and Cure Sanfilippo Foundation is proud to have contributed funding support that helped advance this therapy into clinical trial. With strong safety and efficacy data supporting this treatment, we are hopeful that FDA’s review will enable this transformative treatment to reach children living with Sanfilippo syndrome type A as rapidly as possible.
Learn more about what “Accelerated Approval” means, listen to Dr. Heather Lau from Ultragenyx speak about this topic during the Cure Sanfilippo Foundation’s ADVANCE 2024 conference:
A first approval under the accelerated pathway using spinal fluid heparan sulfate as a biomarker would stimulate drug development and open the door to faster approvals across the subtypes of Sanfilippo syndrome.
Cure Sanfilippo Foundation remains deeply committed to advocating for regulatory flexibility, speed, and the broadest label indication so that this and other treatments aren’t narrowly restricted by age or other factors unrelated to safety. We will continue to monitor this review closely and keep you updated as the process moves ahead.
Learn more about the UX111 therapy and trial history.
Update:
Ultragenyx announced on Feb. 3, 2026, new long‑term data from clinical studies evaluating UX111 (rebisufligene etisparvovec), an investigational AAV9 gene therapy for Sanfilippo syndrome Type A (MPS IIIA), a fatal neurodegenerative lysosomal storage disorder. The results demonstrate substantial and durable biomarker improvements and meaningful functional benefits compared with natural history, with consistent and highly statistically significant results across age and disease severity. UX111 was well-tolerated and the safety profile remains favorable. Read the complete statement from Ultragenyx.