For Immediate Release: September 17, 2026
The U.S. Food and Drug Administration today approved Fayuvi (rebisufligene etisparvovec-hopf), the first treatment for pediatric patients with mucopolysaccharidosis type IIIA (MPS IIIA), also known as Sanfilippo syndrome type A. This rare inherited disease progressively damages the brain and nervous system, causing children to lose cognitive, language, and other developmental abilities over time. Until today, no FDA-approved therapy existed to alter the underlying course of the disease.
"The approval of Fayuvi marks a historic moment for children and families living with MPS IIIA," said Acting FDA Commissioner Kyle Diamantas. "Gene therapy holds tremendous promise for rare diseases like Sanfilippo syndrome type A."
How It Works
Fayuvi is a one-time intravenous gene therapy that uses a modified AAV9 vector to deliver a working copy of the SGSH gene into the patient's cells. This enables production of sulfamidase, the enzyme deficient in MPS IIIA, allowing proper breakdown of heparan sulfate and reducing its harmful buildup in the body and brain.
Clinical Evidence
The safety and effectiveness of Fayuvi were evaluated in an open-label, single-arm, multicenter clinical study in pediatric patients aged 2 to 5 years. Treated patients maintained or improved cognitive function compared to an untreated historical control cohort, a meaningful divergence from the expected natural disease course of plateau and decline during this critical developmental window.
"Achieving meaningful neurodevelopmental benefit through a single intravenous administration represents a significant scientific milestone," said Dr. Megha Kaushal, Acting Deputy Director of the Office of Therapeutic Products.
Safety Profile
The most common adverse reactions reported in more than 5% of patients included elevated liver enzymes, nausea and vomiting, fever, decreased appetite, decreased white blood cell and platelet counts, and increased amylase. Important safety warnings include risk of thrombotic microangiopathy (TMA). As with other AAV-based gene therapies, there is a potential long-term risk of tumor development.
Fayuvi is administered in a healthcare setting equipped to manage infusion reactions. All patients receive corticosteroid treatment starting one day before infusion and continuing for at least eight weeks afterward.
Regulatory Designations
Fayuvi received Orphan Drug, Fast Track, and Breakthrough Therapy designations. The approval was granted to Ultragenyx Pharmaceutical, Inc.
