The FDA has approved Fayuvi (rebisufligene etisparvovec-hopf, Ultragenyx), marking the first-ever gene therapy for children with mucopolysaccharidosis type IIIA (MPS IIIA), also known as Sanfilippo syndrome type A. This rare and severe condition causes children — who develop normally in their earliest years — to progressively lose cognitive, language, and other developmental abilities due to a deficiency of the enzyme sulfamidase, leading to toxic heparan sulfate accumulation in the body and brain.

Fayuvi works by using an adeno-associated virus (AAV9) to deliver a functional copy of the SGSH gene directly to patients' cells, enabling the body to produce sulfamidase on its own. It is administered as a single intravenous infusion in a clinical setting, accompanied by corticosteroid treatment starting the day before and continuing for at least 8 weeks post-infusion. Prior to approval, the FDA had granted Fayuvi Orphan Drug, Fast Track, and Breakthrough Therapy designations.

By the Numbers:

• Sanfilippo syndrome type A accounts for more than half of all Sanfilippo syndrome cases
• The disease affects approximately 1 in 50,000–200,000 people
• Symptoms in Type A appear between ages 1 and 4; life expectancy is just 11–19 years
• Clinical trial enrolled children aged 2 to 5 years

Why it matters: Until now, treatment for Sanfilippo syndrome type A only managed symptoms without altering disease progression. Fayuvi is the first therapy to address the underlying genetic cause, offering real hope for preserving cognitive function in affected children during a critical developmental window.