Ultragenyx said its Phase 3 study in Angelman syndrome failed to meet both primary and key secondary goals for apazunersen (GTX-102). The result sharply escalates uncertainty around the program’s endpoint strategy and its readthrough potential to other antisense candidates in development. The trial, branded Aspire, did not achieve change from baseline in the Bayley-4 Cognitive raw score at the primary endpoint and also missed net upside in the Multidomain Responder Index as a key secondary endpoint. The company said safety aligned with earlier phase data. Ultragenyx indicated it will assess next steps and pursue cost actions. The Phase 3 failure also revives scrutiny of how confirmatory trials in rare neurodevelopmental disorders are structured and interpreted after encouraging early signals.