Ultragenyx Pharmaceutical Inc. announced new data from the Phase 1/2 study of GTX-102 for the treatment of Angelman syndrome. Patients in Expansion Cohorts A & B treated with a set dose and regimen of GTX-102 showed rapid and clinically meaningful improvement across multiple domains consistent with or exceeding Dose-escalation Cohorts 4-7 data at Day 170. Treatment of the Dose-escalation Cohort 4-7 showed long-term increasing and sustained clinical benefit far exceeding Natural History data at Day 758.

There were no unexpected serious adverse events. Three patients had serious adverse events (mild to moderate) of lower extremity weakness assessed as related to study treatment; one in Cohort 7, two in Cohorts A & B; none reported in Cohorts C-E to date. The Cohort 7 patient has also been re-dosed safely multiple times and is receiving maintenance treatment without recurrence.

The two patients in Cohorts A & B remain in study and are expected to continue dosing. The FDA and other regulatory agencies were notified of all safety events and raised no issues nor required additional actions. The foregoing safety information is current as of April 5, 2024.

The Phase 1/2, open-label, multiple-dose, dose-escalating study is evaluating the safety and tolerability of GTX-102 administered by intrathecal (IT) injection to pediatric patients with Angelman syndrome with a genetically confirmed diagnosis of full maternal UBE3A gene deletion.