Ionis Pharmaceuticals has received US FDA approval for zilganersen (Zanvastro) to treat Alexander disease, a rare and progressive neurodegenerative disorder, marking the first approval of a disease-modifying therapy for the condition.

The antisense oligonucleotide is approved for both paediatric and adult patients with Alexander disease. Ionis plans to begin the US commercial rollout in the coming weeks.

The FDA’s decision was supported by data from the pivotal NCT04849741 study, in which zilganersen significantly stabilised walking speed, a measure of motor function, in patients aged five years and older compared with the control group at week 61. 

The therapy also showed supportive evidence of benefit in children aged two to four.

Alexander disease is a genetic disorder associated with abnormal expression of the GFAP gene with patients developing seizures, muscle weakness, impaired mobility and swallowing difficulties. The disease is estimated to affect roughly one in one to three million people worldwide.

Until now, treatment for Alexander disease has largely focused on managing symptoms rather than modifying the underlying disease process. 

Amy Waldman, paediatric neurologist and lead investigator of the pivotal study, said the shift toward targeting the underlying biology of Alexander disease could potentially “meaningfully improve outcomes” for patients.

Zanvastro will be Ionis’ first independently launched neurology medicine. 

The company said it will provide patients and caregivers with support for insurance approvals, affordability programmes and other resources as the therapy reaches the US market. Ionis has not yet disclosed the drug’s US price.