Ionis Pharmaceuticals has secured an approval from the US Food and Drug Administration (FDA) for its therapy, zilganersen, in the rare neurodegenerative disorder Alexander disease – marking the first time a disease-modifying therapy has debuted in this indication.

Following the FDA’s go-ahead, the antisense oligonucleotide, which Ionis will market as Zanvastro in the US, is now indicated for use in both paediatric and adult patients with Alexander disease.

This genetic condition is primarily driven by the abnormal expression a specific skeleton gene called GFAP, which forms toxic clumps in specific brain cells called astrocytes. Because of this buildup, patients often experience seizures and muscle weakness, while progressively losing their functional mobility and their ability to swallow. Researchers currently estimate that Alexander disease impacts around one in one-to-three million globally,

The FDA opted to greenlight Zanvastro based on the positive outcome of a pivotal study on the therapy (NCT04849741), in which it significantly stabilised walking speed – a common measure of motor function – in treated patients over five years of age compared with the control group at week 61. The drug also demonstrated similar potential in patients aged between two and four during this trial.

Expanding treatment horizons in Alexander disease

Zanvastro’s approval will represent a notable step forward for patients and caregivers alike, as previously the only treatment options revolved around symptom management, rather than tackling the disease at its core.

According to Zanvastro’s pivotal study lead investigator and paediatric neurologist, Amy Waldman, the shift away from managing individual manifestations of Alexander disease to focus on addressing its underlying biology could hold the potential to “meaningfully improve outcomes” for patients.

Now, with an approval in the bag, Ionis plans to roll out Zanvastro across the US “in the coming weeks.” To encourage a smooth transition to market, the California-based pharma company will offer patients and caregivers resources and assistance with insurance approval, as well as details on affordability programmes. Ionis is yet to publicly disclose how much the drug will cost.

While Zanvastro – Ionis’ first independently launched neurology drug – will soon become available to American patients, it is yet to be seen when the drug may make its debut further afield. Currently, Recordati owns the ex-US rights to Zanvastro, as it previously inked a $30m upfront licensing deal with Ionis for the drug in June 2026. Through this agreement, Recordati assumed responsibility for regulatory filings and commercial operations around Zanvastro outside of the US.