Ultragenyx disclosed that its Phase 3 trial Aspire in Angelman syndrome failed to meet the study’s primary and key secondary endpoints for apazunersen. The company reported that Bayley-4 Cognitive raw score change did not show the needed improvement versus control, and net response in a Multidomain Responder Index also missed. The result intensifies the debate around endpoint selection and treatment positioning in rare neurological disorders, especially for mechanisms intended to modulate core biology rather than symptoms. Ultragenyx indicated it would assess significant next steps with the program and examine costs, reflecting a typical consequence of late-stage failure. The pipeline setback also carries read-through risk for similar Angelman development strategies, while other programs with related biology may now face renewed scientific and commercial scrutiny.