Ultragenyx Says Phase 3 Study on Rare Neurogenetic Disorder Missed Primary, Secondary Endpoints; Shares Fall After-Hours

05:20 PM EDT, 09/02/2026 (MT Newswires) -- Ultragenyx Pharmaceutical (RARE) said late Wednesday the phase 3 Aspire study of apazunersen in Angelman syndrome, a rare, neurogenetic disorder, did not achieve its primary endpoint or its key secondary endpoint. The late-stage study did not reach the primary endpoint of change from Baseline in Bayley-4 cognitive raw score nor the key secondary endpoint of net response in Multidomain Responder Index, according to a statement. The safety profile for the phase 3 trial remained consistent with phase 1 and phase 2, the company said. Ultragenyx said it will assess the apazunersen program following this outcome and make a decision on its disposition. Shares of Ultragenyx were down about 45% in after-hours trading.