ARTICLE
7 October 2026

Ultragenyx’s FAYUVI Becomes First FDA-Approved Treatment for Sanfilippo Syndrome Type A

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Goodwin Procter LLP

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Ultragenyx Pharmaceutical has received FDA approval for FAYUVI, a groundbreaking one-time gene therapy designed to halt or slow the progression of mucopolysaccharidosis type IIIA (MPS IIIA), also known as Sanfilippo syndrome type A. This marks the first-ever treatment capable of addressing the underlying cause of this ultra-rare, fatal neurodegenerative disorder that has previously had no disease-modifying therapeutic options.
United States Food, Drugs, Healthcare, Life Sciences

Ultragenyx Pharmaceutical, Inc. has announced FDA approval for FAYUVI (rebisufligene etisparvovec-hopf), a first-ever treatment to stop or slow the progression of mucopolysaccharidosis type IIIA (MPS IIIA), also known as Sanfilippo syndrome type A. MPS IIIA is an ultra-rare inherited lysosomal storage disorder caused by deficiency of the sulfamidase (SGSH) enzyme, leading to progressive neurodegeneration. Children typically develop normally in their earliest years before then experiencing severe and irreversible cognitive, behavioral, and motor decline. Previous therapies focused on managing symptoms, and were unable to change the underlying course of the disease.

FAYUVI is a one-time, intravenous AAV9-based gene therapy that delivers a functional copy of the SGSH gene, enabling the body to produce sulfamidase and reduce harmful heparan sulfate buildup in the brain and body. The approval was based on an open-label, single-arm, multicenter study in patients aged 2 to 5 years, in which FAYUVI-treated patients maintained or improved cognitive function compared to an untreated historical control cohort. FAYUVI received Orphan Drug, Fast Track, and Breakthrough Therapy designations.

“The approval of FAYUVI reflects years of research from scientists and developers, as well as unwavering support from so many families and patient organizations in the face of a devastating, universally fatal disease with no treatment options. This is a historic milestone for a community that has waited far too long, but has never given up hope,” said Emil D. Kakkis, M.D., Ph.D., chief executive officer and president of Ultragenyx.

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