FDA Approves Ionis Zanvastro (Zilganersen) as First-Ever Disease-Modifying Therapy for Alexander Disease; Approval Lands 19 Days Ahead of Sept 22 PDUFA With Rare Pediatric Disease Priority Review Voucher
Ionis Pharmaceuticals (NASDAQ: IONS) announced Thursday September 3, 2026 FDA approval of Zanvastro (zilganersen, an intrathecally-administered antisense oligonucleotide designed to reduce glial fibrillary acidic protein / GFAP production) for the treatment of Alexander disease in pediatric and adult patients. The approval is the first-ever disease-modifying therapy for Alexander disease, an ultra-rare autosomal dominant neurodegenerative disorder caused by GFAP gene mutations that presents in infancy through adulthood with progressive motor and cognitive decline. Approval landed 19 days ahead of the September 22, 2026 PDUFA target action date. In the registrational trial, walking speed stayed stable in Zanvastro-treated patients while control patients saw a 33% decline. FDA granted Ionis a Rare Pediatric Disease Priority Review Voucher (PRV) alongside the approval; PRVs have historically sold for $150-350 million on secondary markets. Zanvastro follows Ionis's Wainua (eplontersen) commercial franchise for hereditary transthyretin amyloid polyneuropathy and lands after the August 28 CARDIO-TTRansform ATTR-CM Phase 3 primary endpoint miss for the same molecule.