Positive topline results have been announced from a pivotal study of zilganersen, an investigational medicine developed by Ionis Pharmaceuticals, Inc., for the treatment of Alexander disease (AxD). for the treatment of Alexander disease (AxD). This rare, progressive, and often fatal neurological condition currently has no approved disease-modifying treatments. The study, which included both children and adults, demonstrated that zilganersen achieved a statistically significant and clinically meaningful stabilization in gait speed, as measured by the 10-Meter Walk Test, compared to a control group after 61 weeks. This represents a substantial 33.3% mean difference, making zilganersen the first medicine to show a positive disease-modifying impact on AxD. In addition to the primary endpoint, the drug also showed consistent favorable trends across key secondary endpoints, including improvements in patients' self-reported symptoms and clinician-assessed global impression scores, suggesting a slowing of the disease's progression.

The safety and tolerability of zilganersen were favorable, with most adverse events being mild to moderate. Notably, the incidence of serious adverse events was lower in the group receiving zilganersen compared to the control group. Following these encouraging results, Ionis plans to submit a new drug application to the U.S. Food and Drug Administration in the first quarter of 2026. The company is also considering an Expanded Access Program to make the treatment available to patients in urgent need.

Zilganersen is an antisense oligonucleotide medicine designed to target the underlying genetic cause of AxD by stopping the production of excess glial fibrillary acidic protein (GFAP), which accumulates in the brains of affected individuals.

This groundbreaking development offers significant hope for patients and their families living with AxD, a condition that most commonly begins in early childhood and progressively leads to the loss of fundamental functions like walking, speaking, and swallowing. This new data reinforces Ionis’s legacy of developing transformational RNA-targeted medicines for severe neurological diseases.