FDA cleared Ionis Pharmaceuticals’ antisense therapy Zanvastro (zilganersen) for Alexander disease in pediatric and adult patients, marking the first and only disease-modifying treatment for the ultra-rare, progressive disorder. The approval establishes a new regulatory foothold for RNA-targeting rare-disease programs and shifts treatment expectations from symptom management toward underlying biology. Ionis previously reported that Zanvastro met a pivotal trial primary endpoint, with statistically significant stabilization of gait speed on the 10-Meter Walk Test at week 61 in patients ages 5 and older versus control. The therapy is administered intrathecally at a 50 mg dose on a quarterly schedule, and Ionis indicated the drug would be available in the coming weeks. The FDA also granted Ionis a rare pediatric disease priority review voucher, underscoring the agency’s focus on accelerating therapies for small patient populations. Ionis is now positioned to expand its neurology portfolio with a wholly owned commercialization model.