What is Fayuvi, the first treatment for Sanfilippo syndrome?

The FDA granted full approval on Sept. 17 to Fayuvi (UX111), a one-time gene therapy for Sanfilippo syndrome type A — a fatal childhood neurodegenerative disease that previously had no treatment at all. In trials, treated children maintained or improved cognitive function compared with the historical pattern of steady decline. It’s priced at $3.95 million per patient, among the world’s most expensive drugs — a reminder that gene therapies’ biggest hurdle after approval is often who can actually get them. This is a real approval for a specific rare disease, not a general cure.