FDA Approves Fayuvi for Pediatric Sanfilippo Syndrome Type A

The FDA approved rebisufligene etisparvovec-hopf (Fayuvi, Ultragenyx Pharmaceutical), the first treatment for pediatric patients with mucopolysaccharidosis type IIIA (MPS IIIA), also known as Sanfilippo syndrome type A. Previously, treatment was limited to symptom management, with no FDA-approved therapy designed to alter the disease’s underlying course.

Fayuvi is a one-time intravenous gene therapy that uses a modified, noninfectious adeno-associated virus serotype 9 vector to deliver a working copy of the SGSH gene into patients’ cells. This enables production of sulfamidase, the enzyme missing or deficient in MPS IIIA, allowing heparan sulfate to be broken down in lysosomes and reducing its accumulation in the body and brain.

The approval was supported by an open-label, single-arm, multicenter study in pediatric patients with MPS IIIA. The study assessed mean changes in cognitive scores among patients aged 2 to 5 years. According to the FDA, Fayuvi-treated patients maintained or improved cognitive function compared with an untreated historical control cohort, diverging from the expected plateau and decline during that developmental period.

Safety was evaluated in pediatric patients who received a single intravenous infusion across clinical studies. Adverse reactions reported in more than 5% of patients included increased liver enzymes (AST), nausea, vomiting, fever, decreased appetite, reduced white blood cell and platelet counts, and increased amylase. Important warnings include thrombotic microangiopathy. The FDA also noted a potential long-term risk of tumor development if the inserted genetic material integrates into the genome.

Fayuvi is to be administered in a healthcare setting equipped to manage infusion reactions. Patients receive corticosteroids beginning one day before infusion and continuing for at least 8 weeks afterward. The therapy received Orphan Drug, Fast Track, and Breakthrough Therapy designations, and the FDA granted approval to Ultragenyx Pharmaceutical.

Source: US Food and Drug Administration. FDA approves first gene therapy for pediatric patients with Sanfilippo syndrome type A. Press release. US Food and Drug Administration; September 17, 2026. Accessed September 17, 2026.