FDA approves the first gene therapy for Sanfilippo syndrome type A

The US Food and Drug Administration approved Fayuvi (rebisufligene etisparvovec-hopf) on 17 September 2026, the first treatment cleared for Sanfilippo syndrome type A. It is a single-dose intravenous AAV9 gene therapy from Ultragenyx that delivers a working copy of the sulfamidase gene.

Children born with mucopolysaccharidosis type IIIA cannot break down heparan sulfate, which accumulates in the brain. Development stalls, then reverses: cognition, language and motor function are lost in turn. Median life expectancy is 15 years.

The approval rests on Transpher A, an open-label single-arm study. Ultragenyx reports that 17 treated patients scored 23.5 points higher on the Bayley-III cognitive raw scale than 27 untreated children drawn from a natural-history cohort, with follow-up running to nearly eight years.

That design is worth naming plainly. There was no randomised control group; the comparison is against children observed separately, and the FDA’s own summary describes the result as treated patients maintaining or improving cognitive function relative to that historical cohort. Ultragenyx expects to ship to qualified treatment centres within 30 to 60 days.