Ionis Pharmaceuticals, Inc. (Nasdaq: IONS) announced the pivotal Phase 3 study design following successful alignment with the U.S. Food and Drug Administration (FDA) on ION582, an investigational medicine for the treatment of people living with Angelman syndrome (AS). AS typically presents in infancy and is characterized by profound intellectual disability, impaired verbal abilities and severe motor impairment.

"Following positive results for ION582 in the Phase 2 HALOS trial, we are pleased to have alignment with the FDA on the design of our Phase 3 REVEAL trial, which will address clinical endpoints that reflect the most pressing and meaningful outcomes for people living with AS and their caregivers," said Brett Monia, Ph.D., chief executive officer of Ionis. "We will enroll a broad group of individuals living with AS in the global pivotal Phase 3 trial, planned to begin in the first half of 2025. We look forward to working with the community to advance a potential new treatment targeting the underlying cause of disease in this debilitating neurological condition that has no approved medicines."

The planned global, randomized, placebo-controlled Phase 3 study will enroll approximately 200 children and adults with AS that have a maternal UBE3A gene deletion or mutation. The primary analysis will occur after approximately one year of treatment, followed by all patients transitioning into an open-label long-term extension (LTE) phase of the study. Patients will be randomized 2:1 to active therapy or placebo, and ION582 will be evaluated at two dose levels which will be dosed quarterly without a loading regimen. The primary endpoint will be improvement in expressive communication as assessed by the Bayley Scales for Infant and Toddler Development-4 (Bayley-4), an objective and direct clinician-administered assessment of clinical functioning. Deficits in expressive communication are reported to be the symptoms most challenging to caregivers of people with AS. The study will evaluate several secondary endpoints including overall disease severity, cognition, communication, sleep, motor functioning and daily living skills, in addition to other exploratory endpoints.

The End of Phase 2 meeting was supported by data from the Phase 2 open-label HALOS study. In the recently completed multiple ascending dose (MAD) portion of the study, ION582 treatment provided strong evidence of clinically meaningful improvement on all functional domains including communication, cognition and motor function. Overall, 97% of people in the medium and high dose groups assessed in the study saw an improvement in overall AS symptoms as measured by the Angelman Syndrome Clinical Global Improvement Change (SAS-CGI-C) scale, which evaluates clinicians' impressions. ION582 showed favorable safety and tolerability at all dose levels in the study.

At the FAST Global Science Summit this weekend (November 8-9), Ionis will provide an update to the community on the Phase 3 program and review data from the MAD portion of the HALOS trial.