RARE: Ultragenyx Stock Crashes 45% After Rare Disease Drug Fails Trial

Ultragenyx Pharmaceutical's (RARE) stock plummeted by 45% in aftermarket trading on Wednesday after its experimental drug apazunersen failed to meet its targets in a Phase 3 clinical trial for Angelman syndrome.

The Aspire trial, which tested whether apazunersen could improve cognitive and developmental outcomes in young children with the condition, missed both the primary endpoint and key secondary endpoint. The safety profile was consistent with earlier studies, but this offered little comfort to investors.

CEO Emil Kakkis called the result 'disappointing' for patients and families who had invested hope in the drug. Apazunersen had held several FDA designations, including Breakthrough Therapy and Orphan Drug status.

The failure also raises questions about a related study called Aurora, which is testing apazunerness in Angelman syndrome patients with different genetic subtypes. Analyst Sami Corwin noted that even if Aurora hits its primary endpoint, commercialization would be difficult due to the small addressable patient population.