FDA Approves Fayuvi Gene Therapy for Pediatric Sanfilippo Syndrome Type A

The FDA approved Fayuvi (rebisufligene etisparvovec-hopf) for pediatric patients with mucopolysaccharidosis type IIIA (MPS IIIA), or Sanfilippo syndrome type A, a rare inherited disease causing progressive neurodevelopmental decline. The one-time intravenous therapy uses an adeno-associated virus serotype 9 vector to deliver a functional SGSH gene, enabling production of sulfamidase to reduce heparan sulfate accumulation. Approval was granted to Ultragenyx Pharmaceutical, Inc.

Effectiveness was evaluated in an open-label, single-arm, multicenter pediatric study measuring mean changes in cognitive scores in children aged 2–5 years. According to the FDA announcement, treated patients maintained or improved cognitive function compared with an untreated historical control cohort. The announcement did not report sample size, numerical cognitive outcomes, follow-up duration or statistical uncertainty. The nonrandomized design and historical comparison limit interpretation of the reported benefit.

Adverse reactions reported in more than 5% of patients included increased AST, nausea and vomiting, fever, decreased appetite, decreased white blood cell and platelet counts, and increased amylase. Warnings include thrombotic microangiopathy and a potential long-term risk of tumor development from integration of genetic material into the genome.

Fayuvi must be administered in a healthcare setting equipped to manage infusion reactions. Corticosteroids begin one day before infusion and continue for at least eight weeks afterward. The approval provides a treatment option where care previously focused on symptom management, although the announcement alone does not establish the magnitude or durability of cognitive benefit.