Ultragenyx Announces Successful End-of-Phase 2 Meeting with FDA for GTX-102 Angelman Syndrome Program

Alignment with FDA on Phase 3 study primary endpoint of Bayley-4 cognition and key secondary endpoint of Multi-Domain Responder Index (MDRI)

Phase 3 study on track to initiate by the end of this year

Excerpt from the Press Release:

NOVATO, Calif., July 17, 2024 (GLOBE NEWSWIRE) — Ultragenyx Pharmaceutical Inc. (NASDAQ: RARE) today announced the successful completion of an end-of-Phase 2 (EoP2) meeting with the U.S. Food and Drug Administration (FDA), supporting its Phase 3 study plans for GTX-102, an antisense oligonucleotide for Angelman syndrome.

“FDA alignment on our Phase 3 study design for GTX-102 allows for rapid initiation of a global double-blind sham-controlled pivotal study by the end of this year,” said Eric Crombez, M.D., chief medical officer at Ultragenyx. “In addition to this pivotal study in patients with a full UBE3A gene deletion, we are working to initiate a study to evaluate GTX-102 in patients with other mutations. This will allow for the potential treatment of more children and adults impacted by this devastating disease.”

Phase 3 design and next steps
The EoP2 meeting focused on discussion of the Company’s interim Phase 1/2 data and resulted in alignment with the FDA on the Phase 3 study design and endpoints. The pivotal Phase 3, will be a global, randomized, double-blind, sham-controlled trial and will include a 48-week primary efficacy analysis period enrolling approximately 120 patients with Angelman syndrome with a genetically confirmed diagnosis of full maternal UBE3A gene deletion. The primary endpoint will be improvement in cognition assessed by Bayley-4 cognitive raw score. Control patients completing the study will be eligible to roll over onto treatment after the double-blind period is over.

Previously disclosed results from the Phase 1/2 study showed that UBE3A gene deletion patients treated with GTX-102 experienced rapid, progressive and clinically significant improvement in cognition, as assessed by Bayley-4, that was far greater than the minimal change observed in Natural History data¹ in deletion patients. UBE3A gene deletion patients are at the severe end of the clinical spectrum, with lower Bayley scores at baseline, and demonstrate a much slower rate of skill attainment compared to, for example, UBE3A missense mutation patients, who demonstrate higher Bayley cognition improvement in Natural History data.² In the Phase 1/2 study, GTX-102 treated patients also demonstrated meaningful improvements in other domains of communication, motor function, sleep problems, and behavior.

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