Ultragenyx Reports Phase 3 Aspire Trial Misses Primary Endpoint

What Happened

• On September 2, 2026, Ultragenyx Pharmaceutical Inc. announced results from the Phase 3 Aspire study of apazunersen (GTX-102) in Angelman syndrome. The trial did not achieve the primary endpoint (change from baseline in Bayley-4 cognitive raw score) and also missed the key secondary endpoint (net response in the Multidomain Responder Index, MDRI). Ultragenyx reported that randomized groups were comparable at baseline and consistent with Phase 2 patients; safety in Aspire was consistent with Phase 1/2.

Key Details

• Study: Phase 3 Aspire for apazunersen (GTX-102) in Angelman syndrome; announcement date September 2, 2026.
• Primary endpoint: change from Baseline in Bayley-4 cognitive raw score — not met.
• Key secondary endpoint: MDRI net response — not met; no differences between treated and control groups on MDRI components.
• Next steps: Company will evaluate the apazunersen program and decide on its disposition; Ultragenyx said it will assess planned operations to define and implement significant expense reductions while supporting its growing commercial business.

Why It Matters

• A failed Phase 3 readout is a major setback for Ultragenyx’s apazunersen program and could affect the company’s pipeline value and near-term strategic plans. The company explicitly said it will evaluate the program’s future and pursue significant expense reductions, which may influence budgets, resource allocation, and investor expectations. Safety signals were consistent with earlier phases, but lack of efficacy is the primary issue reported.