Ultragenyx says apazunersen missed both main goals in Phase 3 Angelman syndrome trial

Ultragenyx Pharmaceutical Inc. reported on September 2, 2026 that its Phase 3 Aspire study of apazunersen (GTX-102) in Angelman syndrome fell short on its key goals. The company announced results from the Phase 3 Aspire study for apazunersen, which did not meet its primary endpoint, a change from baseline in Bayley-4 cognitive raw score, or the key secondary endpoint, measuring net response on the Multidomain Responder Index, or MDRI.¹

On the safety side, the profile seen in Aspire matched what had been observed in the earlier Phase 1/2 study.¹

Looking more closely at the data, the randomized treatment and control groups were comparable at baseline and aligned with the population studied in Phase 2.¹ However, the trial showed no separation between the two groups on the Bayley cognitive raw scores, and none on the MDRI whether measured by net response or by average changes across its five component endpoints.¹

In response to the readout, Ultragenyx said it will review the apazunersen program and decide on its future.¹ The company also said it plans to review its operations with an eye toward cutting expenses significantly, while continuing to support its expanding commercial business.¹

The 8-K was signed by Howard Horn, the company's Executive Vice President and Chief Financial Officer, Corporate Strategy.