FDA Approves $4 Million Gene Therapy for Sanfilippo Syndrome

Ultragenyx received FDA approval in September for Fayuvi, a one-time gene therapy for Sanfilippo syndrome.

The approval follows a two-decade research effort that relied heavily on funding from patient families. The drug treats a rare inherited metabolic disorder where a faulty gene prevents the body from breaking down heparin sulfate. This buildup causes severe cognitive and physical decline.

Three factors drove the development of the treatment. First, researcher Haiyan Fu at Nationwide Children's Hospital began working on the therapy in mice in the late 1990s. She nearly quit in 2009 but continued after families of affected children offered financial support to keep the lab running. Second, the O'Neill family in Columbia, S.C., raised $2 million in the spring of 2014. They used a viral video created by filmmaker Benjamin Von Wong to fund the first human clinical trial, which began in May 2016. Third, Ultragenyx acquired the rights to the therapy in 2022 and submitted data to the FDA for review.

The disease progresses rapidly in early childhood. According to the Cure Sanfilippo Foundation, which the O'Neills founded, children with Sanfilippo lose the ability to speak and walk and often do not live past their teens. The therapy works by delivering a functional copy of the broken gene to cells using a modified virus.

Ultragenyx CEO Emil Kakkis noted that younger patients show better outcomes. He stated that treating children at six months of age yields better gene therapy results than treating them at age two or three. The company set the price for the one-time infusion at nearly $4 million. A drug price research firm named 46brooklyn identified this as the second most expensive gene therapy ever.

The O'Neill family's daughter, Eliza, was the first patient to receive the treatment in the 2016 trial. She was six years old at the time and had already lost her speech. She now communicates using picture cards and devices and attends school. Fu, who led the initial research, received a call from Eliza's mother, Cara O'Neill, shortly after the FDA announcement. Fu described the approval as mixed news, noting that the timeline for getting the therapy to patients was longer than ideal.

The therapy is available for patients who meet the diagnostic criteria. Ultragenyx stated it aims to remove logistical barriers so that location or state rules do not prevent patients from receiving treatment.