FDA Approves ZANVASTRO for Rare Alexander Disease

The U.S. Food and Drug Administration (FDA) has approved Ionis Pharmaceuticals’ ZANVASTRO™ (zilganersen) for the treatment of Alexander disease (AxD) in pediatric and adult patients.

ZANVASTRO is the first disease-modifying treatment approved for Alexander disease, an ultra-rare and progressive neurological disorder that can affect movement, thinking, and other important body functions. Until now, treatment has mainly focused on managing symptoms.

The approval marks a major development for patients with Alexander disease, which affects an estimated one in 1 million to 3 million people worldwide. Symptoms can begin at different stages of life, from infancy through adulthood, and often become more severe as the disease progresses.

Alexander disease is caused by changes in the GFAP gene. These changes lead to excessive production and buildup of glial fibrillary acidic protein (GFAP) in astrocytes, cells that support and protect neurons. Over time, this buildup can damage the nervous system and contribute to the symptoms of the disease.

ZANVASTRO is an RNA-targeted medicine designed to address the underlying cause of Alexander disease by reducing the production of GFAP. The treatment is administered as a 50 mg intrathecal injection once every three months.

The FDA’s decision was supported by positive results from a pivotal clinical study. In patients aged five years and older, ZANVASTRO achieved its primary endpoint, showing a statistically significant and clinically meaningful stabilization of walking speed compared with the control group at Week 61.

The study used the 10-Meter Walk Test to measure changes in gross motor function. ZANVASTRO also showed improvements in gross motor function among children aged two to four years, based on results from the Gross Motor Function Measure-88.

Patient, caregiver, and clinician assessments also generally favored ZANVASTRO. The treatment showed a favorable safety profile, with most adverse events reported as mild or moderate. Serious treatment-emergent adverse events occurred less often in patients receiving ZANVASTRO than in the control group.

Brett P. Monia, PhD, CEO of Ionis Pharmaceuticals, said the approval represents an important step for people living with Alexander disease and their families. He also said the approval demonstrates the potential of RNA-targeted medicines to address serious neurological diseases with limited treatment options.

The company plans to make ZANVASTRO available in the US in the coming weeks. Ionis will provide patient support through its Ionis Every Step program, including education, insurance assistance, affordability information, and other resources for patients and caregivers.

The FDA also granted Ionis a Rare Pediatric Disease Priority Review Voucher following the approval. The program is designed to encourage the development of treatments for serious and life-threatening rare diseases affecting children.

Ionis is also preparing for international expansion of zilganersen. In June 2026, the company signed a licensing agreement with Italy-based Recordati, giving the pharmaceutical company exclusive rights to develop and commercialize zilganersen outside the US. Regulatory submissions in Europe and Japan are expected in 2027.

With the FDA approval of ZANVASTRO, Alexander disease patients now have a treatment designed to target the underlying disease mechanism rather than only manage its symptoms.