FDA Approves First Gene Therapy for Sanfilippo Syndrome Type A

The FDA has approved Fayuvi (rebisufligene etisparvovec) as the first treatment for mucopolysaccharidosis type IIIA, also known as Sanfilippo syndrome type A, according to an FDA press announcement. This is a genuine approval, not an advisory recommendation, and it applies to a specific pediatric population.

MPS IIIA is a rare inherited disease in which a missing enzyme, sulfamidase, allows heparan sulfate to build up in cells, progressively damaging the brain and nervous system. Fayuvi is given as a single intravenous infusion. It uses an AAV9 viral vector to deliver a working copy of the SGSH gene so the body can produce its own sulfamidase.

The approval rests on an open label, single arm study in children between 2 and 5 years old, comparing their cognitive scores to an untreated historical control group. Treated patients maintained or improved cognitive function rather than following the expected decline, according to the release. That is a meaningful signal, though the study design has real limitations compared to a randomized trial.

Reported side effects included liver enzyme changes, nausea, vomiting, fever, and drops in white blood cell and platelet counts. The FDA also flagged a risk of thrombotic microangiopathy and, as with other AAV based therapies, a theoretical long term risk tied to how the inserted gene integrates into the genome.

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