Ultragenyx Announces Positive Interim Phase 1/2 Data in Patients with Angelman Syndrome After Treatment with GTX-102

Expansion Cohorts showed rapid, clinically meaningful improvement across multiple domains; improvements consistent or exceeding Dose-escalation Cohorts data at Day 170

Additional long-term data in Dose-escalation Cohorts showed increasing and sustained clinical benefit through Day 758

Company will host investor call at 8:00 a.m. ET

NOVATO, Calif., April 15, 2024 (GLOBE NEWSWIRE) -- Ultragenyx Pharmaceutical Inc. (NASDAQ: RARE) today 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 Cohorts 4-7 showed long-term increasing and sustained clinical benefit far exceeding Natural History data at Day 758. These data will be discussed in more detail in a corporate presentation being hosted by the company today at 8:00 a.m. ET and will also be presented by Kemi Olugemo, M.D., FAAN at the 76th Annual American Academy of Neurology Meeting (AAN) in Denver on Tuesday, April 16.

“There is currently no approved disease modifying treatment for Angelman syndrome, which results in profound impairment in individuals living with this disease,” said Erick Sell, M.D., director of the Angelman clinic at the Children’s Hospital of Eastern Ontario, and a principal investigator on the Phase 1/2 study. “The multidomain improvement in the Bayley-4 and ASA measures are significant and in line with the clinically meaningful change observed by patient families. These kids have continued to make functional gains over time, which may ultimately lead to more independence.”

New Expansion Cohorts A & B data include Day 170 results on 24 patients, and long-term Dose-escalation Cohorts 4–7 data include up to Day 758 results on 15 patients.

Expansion Cohorts at Day 170:

• Cognition assessed by Bayley-4 showed rapid and clinically significant improvement compared with Natural History data. Day 170 data were consistent with the treatment benefit observed in the Dose-escalation Cohorts at a similar timepoint.
• Behavior assessed by the Angelman Severity Assessment (ASA) showed rapid improvement exceeding the treatment benefit observed in the Dose-escalation Cohorts at Day 170.
• Hyperactivity and noncompliance assessed by the Aberrant Behavior Checklist-Community (ABC-C) showed rapid and clinically significant improvement at Day 170 compared with Natural History data, providing further insight into one of the most commonly reported behavioral issues.
• Sleep assessed by ASA showed rapid and clinically meaningful improvement exceeding treatment benefit observed in the Dose-escalation Cohorts at Day 170.
• Receptive communication assessed by Bayley-4 showed rapid improvement compared with Natural History data. Day 170 data were consistent with the treatment benefit observed in the Dose-escalation Cohorts at a similar timepoint.
• Gross Motor function assessed by ASA showed rapid improvement exceeding the treatment benefit observed in the Dose-escalation Cohorts at Day 170. Gross motor assessments as measured by Bayley-4 were not performed at Day 170 in the Expansion Cohorts to reduce patient testing burden and are not included in this analysis at this timepoint.
• Multi-domain Responder Index (MDRI) analysis across the four domains of Cognition, Receptive Communication, Behavior and Sleep resulted in a total net response of +2.0 (p-value <0.0001). The majority of patients had already achieved a total net response of +2 to +4 domains, demonstrating improvement exceeding the minimally important difference (MID) threshold in several domains even at this early Day 170 timepoint.