FDA clears Ultragenyx gene therapy FAYUVI

On September 17, 2026, the U.S. Food and Drug Administration approved FAYUVI (rebisufligene etisparvovec-hopf; UX111), a gene therapy developed by Ultragenyx Pharmaceutical (RARE). The therapy is approved for the treatment of the neurologic manifestations of mucopolysaccharidosis type IIIA (MPS IIIA), also known as Sanfilippo syndrome Type A, in pediatric patients who have preserved neurodevelopmental function.

This approval provides the first FDA-authorized treatment option targeting the neurologic aspects of MPS IIIA in this pediatric population. The decision reflects the agency’s assessment of clinical data demonstrating functional benefits for treated children when compared with untreated or historical control groups.

FAYUVI is a single-dose, intravenous adeno-associated virus serotype 9 (AAV9) gene therapy. It is designed to deliver a functional copy of the SGSH gene, which encodes the enzyme sulfamidase. By enabling production of sulfamidase, the therapy aims to address the underlying enzyme deficiency associated with MPS IIIA and its neurologic manifestations.

Administration as a one-time IV infusion is intended to achieve systemic delivery, including to the central nervous system. The design of the therapy reflects a strategy to potentially offer durable benefit from a single treatment rather than ongoing chronic dosing.

The FDA approval is supported by clinical evidence from the pivotal Transpher A program and its long-term follow-up. In these studies, children treated with FAYUVI maintained or showed improvements in cognitive and developmental function compared with untreated or historical control cohorts.

The data set provided regulators with evidence that intervention with the gene therapy could alter the trajectory of neurodevelopmental decline associated with MPS IIIA. This comparative performance against historical controls was a central element in the risk–benefit assessment leading to full approval.

Ultragenyx expects commercial supply of FAYUVI to be available for shipment to a network of U.S. Qualified Treatment Centers within 30–60 days of approval. This planned rollout is intended to support access for eligible pediatric patients across specialized centers equipped to deliver gene therapy.

With the approval, Ultragenyx also received a Priority Review Voucher. This voucher can be used to obtain priority review for a future marketing application, reflecting the designation of MPS IIIA as a serious condition with unmet medical need and the significance of bringing a new gene therapy option to market.