Ultragenyx Shares Rise 10% on FDA Approval of Gene Therapy for Sanfilippo Syndrome

Ultragenyx Pharmaceutical (NASDAQ:RARE) shares surged by 10% on Friday following the U.S. Food and Drug Administration's approval of Fayuvi, its gene therapy for mucopolysaccharidosis type IIIA (MPS IIIA). The decision marks a significant milestone, as Fayuvi is the first-ever approved treatment for the rare pediatric disease, also known as Sanfilippo syndrome type A.

Landmark Approval for Rare Disease

The FDA's approval addresses a critical unmet need for pediatric patients with MPS IIIA, a rare inherited disorder that causes progressive and severe damage to the brain and nervous system. Prior to this decision, no therapy existed to alter the course of the disease.

Fayuvi's path to approval was expedited through several key FDA programs, receiving Orphan Drug, Fast Track, and Breakthrough Therapy designations. These programs are intended to facilitate the development and review of drugs that treat serious conditions and fill an unmet medical need.

Mechanism of Action

Fayuvi is administered as a one-time intravenous gene therapy. According to the FDA, it uses a modified adeno-associated virus (AAV9) to deliver a functional copy of the SGSH gene into a patient's cells.

Ad

This process enables the cells to produce sulfamidase, an essential enzyme that is deficient or missing in individuals with MPS IIIA. By addressing the underlying genetic cause, the therapy aims to slow or halt the disease's progression.

Clinical Data and Safety Profile

The regulator's decision was based on data from an open-label, single-arm clinical study in pediatric patients aged 2 to 5 years. The FDA stated that patients treated with Fayuvi maintained or improved their cognitive function compared to an untreated historical control group.

However, the therapy is associated with certain risks. Adverse reactions reported in more than 5% of patients included elevated liver enzymes, nausea, vomiting, fever, and decreased white blood cell and platelet counts. The FDA also noted a risk of thrombotic microangiopathy and a potential long-term risk of tumor development associated with the therapy. Patients must receive corticosteroid treatment before and after the infusion, which must be administered in a qualified healthcare setting.