Ionis Pharmaceuticals has reported positive topline results from a pivotal study of its experimental drug zilganersen in patients with Alexander disease, a rare, progressive and often fatal neurological disorder. In a trial involving 54 participants, those who received a 50 mg dose of zilganersen showed statistically significant improvement in walking speed, as measured by a 10-metre walk test at 61 weeks.

Alexander disease causes abnormal accumulation of the protein GFAP in the brain due to a genetic mutation, leading to damage in brain cells and symptoms such as impaired movement, speech and swallowing; it currently has no approved disease-modifying treatments. Zilganersen works by blocking production of GFAP, thereby addressing a root cause of the disease.

The trial also showed favourable safety and tolerability, with most adverse events being mild or moderate in severity. Alongside the primary result, there were beneficial trends in secondary endpoints including patient-reported symptom severity, clinician and patient global impressions of change, which indicate slowed disease progression or stabilisation.

Ionis plans to submit a marketing application to the United States Food and Drug Administration in the first quarter of 2026. The full data from the study will be presented at an upcoming medical conference.