Ultragenyx's Angelman syndrome drug fails Phase 3 trial

Angelman syndrome is a rare genetic condition. It leaves children with severe developmental delays. For years, one drug looked like it might change that. On Sept. 2, Ultragenyx announced its Phase 3 trial results for that drug, called apazunersen. It didn't work. The drug failed to beat a placebo on the trial's main measure, a standard test of cognitive ability.

Investors had high hopes for this drug. Ultragenyx shares fell more than 40% within hours of the announcement. That wiped out a large share of the company's value in a single trading session. The trial tested two separate measures: a cognitive score and a broader 'responder' index tracking multiple symptoms. Apazunersen missed both. That's a tougher outcome than a near-miss on just one goal. It raises real doubt about whether the drug's underlying approach can work at all.

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Does this mean the end of the road for Angelman syndrome treatments? Not necessarily. Other researchers are still pursuing different approaches to the same condition, in earlier stages of testing. What this failure really tests is one specific idea: that boosting a particular gene's activity can reverse the condition's effects. Ultragenyx will likely share more detailed data in the coming months. Doctors and families will be watching closely for one thing. Did the drug help a smaller group of patients, even after missing the trial's main goals?