O'Neill family funding led to FDA approval of Sanfilippo gene therapy

The O'Neill family raised $2 million in a matter of weeks in the spring of 2014, breaking GoFundMe's record at the time. That funding jump-started the first human clinical trial for a gene therapy targeting Sanfilippo syndrome, a rare inherited disorder. The Food and Drug Administration approved the resulting treatment, Fayuvi, in September 2025.

Eliza O'Neill was diagnosed with Sanfilippo syndrome in 2013 after her mother, pediatrician Cara O'Neill, noticed developmental delays in her daughter. The disease is caused by a faulty gene that prevents the body from breaking down heparin sulfate. The buildup of this molecule leads to severe complications, including seizures and the loss of speech and mobility. According to the Cure Sanfilippo Foundation, which the family established, children with the condition typically do not live past their teens.

Haiyan Fu, a researcher at Nationwide Children's Hospital in Columbus, Ohio, had been developing a gene therapy for Sanfilippo in mice since the late 1990s. The therapy uses a modified virus to deliver a working copy of the defective gene to patient cells. Fu nearly abandoned the project in 2009 due to lack of funding. She continued only after families with affected children, including the O'Neills, pledged financial support to keep the research alive.

In 2014, Glenn O'Neill, Eliza's father, contacted filmmaker Benjamin Von Wong to create a video for a crowdfunding campaign. The resulting video, titled Saving Eliza, generated enough interest to fund the initial clinical trial. That trial began in May 2016 with Eliza as the first participant. She was six years old at the time of treatment. By then, she had already lost her ability to speak, though she maintains communication through picture cards and devices.

The biotech company Ultragenyx acquired the rights to the gene therapy in 2022 and continued its study. The company submitted data to the FDA for review, leading to the approval of Fayuvi in September 2025. Ultragenyx CEO Emil Kakkis stated that the treatment is most effective when administered to younger children because more brain tissue remains intact. The company has treated infants as young as six months with favorable results.

Ultragenyx set the price for the one-time infusion at nearly $4 million. According to drug price research firm 46brooklyn, this price ties Fayuvi for the second most expensive gene therapy ever. Kakkis said the company is committed to treating every patient regardless of cost or location. "There should be no logistical location, site or state or other kind of rule that stops us from getting the patient treated," he said.

Fu received a call from Cara O'Neill moments after the FDA announced the approval. Other families who had funded the research also sent messages, some noting that they had lost children during the years of development. Fu described the approval as good news but expressed mixed emotions, stating, "It shouldn't take this long." Eliza is now almost 17. This summer, she swam and learned to float on a pool noodle.

Cara O'Neill recalled the initial diagnosis as a moment of dread. "When they said the word, it all kind of came rushing back," she said. "And it was just this bale of dread, like, oh, my goodness, this is horrific." Glenn O'Neill said the diagnosis prompted the family to act immediately. "It wasn't really until I got home that I realized how quickly the degeneration happened," he said. "And that was really the point where we said, 'Gosh. Whatever we need to do, we need to do it now.'"