Fayuvi is a one-time, intravenous gene therapy using an adeno-associated virus serotype 9 (AAV9). The therapy enables cells to produce sulfamidase, the enzyme missing or deficient in MPS IIIA. Mucopolysaccharidosis type IIIA (MPS IIIA) is a rare inherited disease that progressively damages the brain and nervous system. MPS IIIA causes children to lose cognitive, language, and other developmental abilities over time.

Prior to this approval, treatment for MPS IIIA was limited to managing symptoms, with no FDA-approved therapy designed to change the underlying course of the disease. Clinical study participants were pediatric patients between the ages of 2 and 5 years. Treated patients maintained or improved cognitive function compared to an untreated historical control cohort.

Common adverse reactions included increases in liver enzymes (AST), nausea, vomiting, fever, and decreased appetite. Important safety warnings include the risk of thrombotic microangiopathy (TMA). There is a potential long-term risk that inserted genetic material could integrate into the genome and lead to tumor development. Patients receive corticosteroid treatment beginning one day before infusion and continuing for a minimum of eight weeks afterward.

Why It Matters

This approval introduces the first therapy intended to alter the progression of MPS IIIA rather than solely manage symptoms. The condition involves a deficiency of a lysosomal enzyme that results in incomplete breakdown of the heparan sulfate sugar chain, leading to progressive neurological damage.

Additional reporting indicated that in patients under 2 years or with earlier-stage disease, there was a 23.2-point cognitive benefit with Fayuvi. These patients also showed improvements in receptive and expressive language, fine motor skills and gross motor function.

Timeline

On September 17, 2026, the U.S. Food and Drug Administration approved Fayuvi (rebisufligene etisparvovec-hopf). On the same date, Fayuvi became the first treatment approved for pediatric patients with mucopolysaccharidosis type IIIA (MPS IIIA), also known as Sanfilippo syndrome type A. The Acting FDA Commissioner stated that "The approval of Fayuvi marks a historic moment for children and families living with MPS IIIA, which is a disease that has, until now, offered no approved treatment to alter its devastating course." Also on September 17, 2026, the Acting FDA Commissioner said, "The Trump Administration is committed to bringing safe and effective treatments to patients with the most urgent and unmet needs."

What's New

Later reporting confirmed that 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. Additional data showed that in patients under 2 years or with earlier-stage disease (n=17), there was a 23.2-point cognitive benefit (p<0.0001) with Fayuvi, as well as improvements in receptive and expressive language, fine motor skills and gross motor function. Background information noted that Sanfilippo syndrome is a mucopolysaccharidosis characterized by a deficiency of the lysosomal enzyme resulting in incomplete breakdown of the heparan sulfate sugar chain.