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news.Ionis Pharmaceuticals has secured breakthrough therapy designation from the US Food and Drug Administration (FDA) for ION582, an investigational antisense medicine designed to treat Angelman syndrome (AS).
Ionis has a clinical-stage portfolio including 13 investigational medicines. Credit: Hans Reniers on Unsplash.
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AS, a rare neurological disorder often diagnosed in infancy, affects approximately one in 21,000 individuals worldwide and is caused by the loss of function of the maternal UBE3A gene.
The disorder is marked by severe intellectual disability, communication difficulties, motor impairments, and seizures.
Ionis said the designation is based on results from the Phase I/II HALOS study, which demonstrated consistent and promising clinical improvement across all AS functional domains including communication, cognition, and motor function.
Additionally, the study reported favourable safety and tolerability for ION582. The breakthrough therapy designation aims to accelerate the development and review of drugs that treat serious or life-threatening conditions and show potential for significant improvement over existing therapies.
Earlier in 2025, Ionis started the worldwide Phase III REVEAL study of ION582. The trial is expected to include children and adults with AS that have a maternal UBE3A gene deletion or mutation.
ION582 is an RNA-targeted medicine designed to inhibit the expression of the UBE3A antisense transcript and increase production of the UBE3A protein. It has received orphan drug designation from both the FDA and the European Medicines Agency, as well as fast track and rare pediatric designations from the FDA.
Ionis senior vice president of neurology Holly Kordasiewicz said: “With no approved disease-modifying treatments available for people living with Angelman syndrome, receiving this Breakthrough Therapy designation for ION582 underscores both the severity of this disease and the significant unmet need for treatment.
“This recognition also highlights the potential of ION582 to deliver meaningful benefits for individuals with Angelman syndrome. We are deeply grateful to the Angelman syndrome community and investigators who have made this progress possible, and we remain committed to advancing ION582 as quickly as possible to bring this potential treatment to those in need.”
Ionis has a clinical-stage portfolio including 13 investigational medicines, with eight wholly owned by the company. Their work spans a range of conditions from rare diseases like AS to more common ones such as Alzheimer’s disease.
