Ionis Pharmaceuticals (IONS) said late Thursday the US Food and Drug Administration approved zanvastrotm, or zilganersen, to treat Alexander disease in pediatric and adult patients.

The treatment will be available in the US in the coming weeks, according to the company.

A zanvastrotm trial met its primary endpoint in individuals aged at least five years, with the 50-milligram dose showing "statistically significant and clinically meaningful" stabilization of gait speed, compared with control at week 61, Ionis said.

Alexander disease is an ultra-rare, progressive and often fatal neurological disorder that can affect motor, cognitive, autonomic and gastrointestinal function.

The company's shares were up 1.5% in premarket activity Friday.