FDA Approves Ionis' Zanvastro (zilganersen) as First Disease-Modifying Treatment for Alexander Disease
On September 3, 2026, the U.S. Food and Drug Administration (FDA) approved Ionis Pharmaceuticals' Zanvastro (zilganersen) for the treatment of Alexander disease (AxD) in pediatric and adult patients. This marks the first and only disease-modifying treatment for AxD, an ultra-rare, progressive, and often fatal neurological disorder that leads to progressive motor and cognitive decline.
Zanvastro is an antisense oligonucleotide (ASO) administered quarterly via intrathecal (IT) injection. It is designed to reduce the production of glial fibrillary acidic protein (GFAP), addressing the toxic overproduction and accumulation of GFAP in astrocytes that drives the pathology of AxD.
The approval was supported by positive results from a global Phase 1-3 study (NCT04849741) of 54 participants. In individuals aged 5 years and older, Zanvastro 50 mg demonstrated statistically significant and clinically meaningful stabilization of gait speed compared to control at Week 61 (a difference of 33.3%, p=0.041). It also showed improvements in gross motor function in younger pediatric patients (ages 2 to 4) on the GMFM-88 scale.
In conjunction with the approval, the FDA awarded Ionis a Rare Pediatric Disease Priority Review Voucher (PRV). Ionis plans to launch the drug in the U.S. in the coming weeks, pricing it at $285,000 per dose ($1.14 million annually for quarterly dosing). Recordati holds the exclusive rights to commercialize the therapy outside the U.S.