The U.S. FDA has approved Ionis Pharmaceuticals’ antisense therapy Zanvastro (zilganersen) for Alexander disease in both pediatric and adult patients, establishing the first and only disease-modifying treatment for the ultra-rare, progressive neurodegenerative disorder. The clearance was based on pivotal trial findings showing statistical and clinical stabilization on gait speed and supportive motor-function outcomes in key subgroups. Zanvastro is administered intrathecally at 50 mg every quarter and is designed to reduce production of glial fibrillary acidic protein (GFAP), the protein implicated in Alexander disease pathophysiology. Ionis said the FDA also granted a rare pediatric disease priority review voucher, and the company expects availability in the coming weeks while preparing access and support programs for patients and caregivers. The approval tightens the competitive landscape for antisense and RNA-targeted programs in CNS diseases by demonstrating a regulator-backed pathway for therapeutics that address underlying biology rather than symptomatic care. For clinicians, the decision also clarifies expectations around monitoring and long-term disease control using a functional endpoint package that includes performance-based measures and patient-reported outcomes.