Ionis Pharma's drug becomes first FDA-approved treatment for rare brain disorder

In an April note, William Blair analysts projected the drug could generate peak annual sales of $295 million.

Zanvastro works by blocking the production of a protein, GFAP, which builds up abnormally in the brain due to a genetic mutation and contributes to the disease.

It is administered as an injection into the spinal canal every three months by a trained healthcare professional.

In an early-to-late-stage study, patients who got a 50 mg dose of Zanvastro showed a statistically significant improvement in gait speed as assessed by a 10-meter walk test at 61 weeks.

The U.S. FDA on Thursday approved Ionis Pharmaceuticals' IONS.O therapy to treat a rare disease that affects the brain's white matter, making it the first treatment to get the nod for the genetic disorder.

Ionis' injectable drug zilganersen, branded as Zanvastro, can be used to treat adults and pediatric patients with Alexander disease, a neurological disorder that damages brain cells and causes problems with movement, speech and swallowing, often starting in early childhood.

The condition affects fewer than 1,000 people in the U.S., according to the National Institutes of Health.

"Today's approval is a landmark moment for this community, offering the first therapy that addresses the underlying cause of this rare and serious disease," said Emily Freilich, director of the Food and Drug Administration's neurology division that reviews treatments for rare genetic and neuromuscular diseases.