FDA Approves First Gene Therapy for Sanfilippo Syndrome Type A

Silver Spring, Md., Sept. 17, 2026 /CourierPR/ -- The U.S. Food and Drug Administration (FDA) has approved Fayuvi (rebisufligene etisparvovec-hopf), the first gene therapy for pediatric patients with Sanfilippo syndrome type A (MPS IIIA). This approval marks a significant milestone in the treatment of a rare and debilitating disease that has long left families with few options.

Sanfilippo syndrome type A is a rare inherited disorder that progressively damages the brain and nervous system, causing children to lose cognitive, language, and other developmental abilities over time. Until now, treatment was limited to managing symptoms, with no FDA-approved therapy designed to alter the disease's course. The approval of Fayuvi represents a breakthrough for children and families facing this devastating condition.

Fayuvi is a one-time, intravenous gene therapy that uses a modified, non-infectious virus called an adeno-associated virus serotype 9 (AAV9) to deliver a working copy of the SGSH gene into the patient's cells. This enables the body’s cells to produce sulfamidase, the enzyme that is missing or deficient in MPS IIIA, allowing heparan sulfate to be properly broken down in lysosomes and reducing its harmful buildup throughout the body and brain.

The safety and effectiveness of Fayuvi were evaluated in an open-label, single-arm, multicenter clinical study in pediatric patients with MPS IIIA. The study measured mean changes in cognitive scores in patients between the ages of 2 and 5 years. Fayuvi-treated patients maintained or improved cognitive function compared to an untreated historical control cohort, a meaningful divergence from the expected natural disease course of plateau and decline during this critical developmental window.

The FDA approval underscores the agency's commitment to bringing safe and effective treatments to patients with urgent and unmet needs. Acting FDA Commissioner Kyle Diamantas, J.D., stated, "The Trump Administration is committed to bringing safe and effective treatments to patients with the most urgent and unmet needs. The approval of Fayuvi marks a historic moment for children and families living with MPS IIIA, which is a disease that has, until now, offered no approved treatment to alter its devastating course."

For families living with Sanfilippo syndrome type A, the trajectory of this disease is heartbreaking. Children who develop normally in their earliest years face a relentless regression with no approved treatment to slow it. Parents and clinicians have been waiting far too long for an option. Today's approval of Fayuvi is a meaningful step forward, not only for these children and their families but for the promise of gene therapy to address rare and devastating diseases where the need for safe and effective treatment is the most urgent.

The safety of Fayuvi was evaluated in pediatric patients who received a single intravenous infusion across clinical studies. The most commonly reported adverse reactions included increases in liver enzymes (AST), nausea and vomiting, fever, decreased appetite, decreased white blood cell and platelet counts, and increased amylase. Important safety warnings include the risk of thrombotic microangiopathy (TMA). As with other AAV-based gene therapies, there is a potential long-term risk that the inserted genetic material could integrate into the genome and potentially lead to tumor development.

Fayuvi is administered in a healthcare setting equipped to manage infusion reactions. All patients receive corticosteroid treatment beginning one day before the infusion and continuing for a minimum of eight weeks afterward.

Ultragenyx Pharmaceutical, Inc., the company behind Fayuvi, received orphan drug and fast track, and breakthrough therapy designations. The FDA granted Fayuvi approval to Ultragenyx Pharmaceutical, Inc.