FDA Approves Ionis' Zanvastro (zilganersen) as First Disease-Modifying Therapy 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 milestone marks the approval of the first and only disease-modifying therapy for AxD, an ultra-rare, progressive, and often fatal neurological disorder that typically leads to death within 14 to 25 years of symptom onset.
Underlying Mechanism and Clinical Evidence
Alexander disease is caused by mutations in the glial fibrillary acidic protein (GFAP) gene, leading to the toxic accumulation and overproduction of GFAP in astrocytes, which subsequently damages neurons and myelin. Zanvastro is an RNA-targeted antisense oligonucleotide designed to reduce GFAP production. It is administered quarterly as a 50 mg intrathecal injection.
The FDA's decision was supported by positive results from a pivotal global Phase 1-3 study (NCT04849741) enrolling 54 participants aged 1.5 to 53 years:
- Primary Endpoint Met: In patients aged 5 and older, Zanvastro demonstrated a statistically significant and clinically meaningful stabilization of gait speed, as measured by the 10-Meter Walk Test (10MWT) compared to control at Week 61 (least square mean difference of 33.3%, p=0.041).
- Pediatric Benefit: In younger patients aged 2 to 4 years, Zanvastro demonstrated motor function improvements on the Gross Motor Function Measure-88 (GMFM-88) relative to control at Week 61.
- Safety: The drug exhibited a favorable safety profile, with most adverse events being mild or moderate in severity.
Upon approval, the FDA awarded Ionis a Rare Pediatric Disease Priority Review Voucher (PRV).
Global Commercialization Plans
Under a June 2026 licensing agreement, Recordati holds exclusive rights to commercialize zilganersen outside the United States. Ionis is working with Recordati to prepare regulatory submissions in Europe and Japan, which are expected in 2027.
"Today’s approval of ZANVASTRO begins a new chapter for people living with Alexander disease and their families, who have long faced this relentlessly progressive and often fatal disease with no treatment options... This transformative approval also marks our first independent launch from our industry-leading neurology pipeline and underscores the power of our RNA-targeted technology to address serious neurological diseases without adequate treatment options." — Brett P. Monia, Ph.D., Chief Executive Officer of Ionis
"For decades, care for people living with Alexander disease has focused primarily on managing symptoms, without an option to modify the underlying cause of disease... The approval of ZANVASTRO for the treatment of Alexander disease represents a significant advancement in care and opens new possibilities for patients and their families." — Amy Waldman, M.D., M.S.C.E., pediatric neurologist and lead investigator at Children’s Hospital of Philadelphia