FDA approves Fayuvi, first treatment for Sanfilippo syndrome type A

The US Food and Drug Administration on September 17, 2026, approved Fayuvi (rebisufligene etisparvovec-hopf), a gene therapy from Ultragenyx, for pediatric patients with mucopolysaccharidosis type IIIA, also known as Sanfilippo syndrome type A. It is the first FDA-approved treatment for the disease, according to CGTLive and Contemporary Pediatrics.

"The approval of Fayuvi marks a historic moment for children and families living with MPS IIIA," FDA Acting Commissioner Kyle Diamantas said, as quoted by Contemporary Pediatrics.

The disease

Nationwide Children's Hospital, where the therapy was developed, describes Sanfilippo syndrome type A as an ultrarare lysosomal storage disease affecting 1 in 70,000 live births. It is caused by mutations in the SGSH gene, which lead to an enzyme deficiency and a buildup of complex sugars in cells. Children appear to develop normally at birth, but then experience "severe, progressive developmental delays and neurological disorders, leading to early mortality," the hospital said. Contemporary Pediatrics reported that historical data put the mean age at death at about 15 years.

"For families living with Sanfilippo syndrome type A, the trajectory of this disease is heartbreaking," said Karim Mikhail of the FDA's Center for Biologics Evaluation and Research, according to CGTLive.

How the therapy works and what the study showed

Fayuvi is an AAV9 gene-replacement therapy delivered by intravenous infusion, designed to provide a working copy of the gene. The approval was based on an open-label, single-arm, multicenter study known as Transpher A, CGTLive reported. Most participants were between 2 and 5 years old, and follow-up extended to 8.5 years, with a median of 4.8 years, according to Contemporary Pediatrics.

Patients treated with Fayuvi maintained or improved cognitive function compared with an untreated historical control group, CGTLive reported. Because the study had no randomized control arm, the comparison was made against data from untreated patients rather than a concurrent placebo group.

Megha Kaushal, an FDA acting deputy director, said: "Achieving meaningful neurodevelopmental benefit through a single intravenous administration represents a significant scientific milestone."

Safety

According to CGTLive, the most common adverse reactions, seen in more than 5% of patients, included elevated liver enzymes, nausea and vomiting, fever, decreased appetite, decreased white blood cells and platelets, and increased amylase. The product carries a boxed warning for the risk of thrombotic microangiopathy, and there is a potential long-term risk of genomic integration and tumor development. All patients receive corticosteroids for at least eight weeks after the infusion.

A long road to approval

The therapy was co-invented by Douglas McCarty and Haiyan Fu at the Jerry R. Mendell Center for Gene Therapy at Nationwide Children's. Abeona Therapeutics licensed the program in 2013, and it moved to Ultragenyx in 2022. The first study participant was treated in 2016, the hospital said. CGTLive reported that the FDA issued a complete response letter in July 2025, and the company resubmitted with additional neurologic and biomarker data in January 2026.

"This approval is particularly gratifying because we are finally able to provide a meaningful gene therapy to families affected by such a devastating childhood disease," said Dr. Kevin Flanigan of Nationwide Children's.

Why it matters

Until now, families of children with Sanfilippo syndrome type A had no approved treatment. Fayuvi is the fourth gene therapy originating at Nationwide Children's to win FDA approval, the hospital said.

Sources

This article was drafted with AI assistance and checked against the sources above. Company claims are reported as claims. Cover image is AI-generated.