September 3, 2026 - FDA Approves First Drug to Treat Alexander Disease

The U.S. Food and Drug Administration has approved Zanvastro (zilganersen) injection for the treatment of Alexander disease in pediatric and adult patients. Zanvastro is the first FDA-approved treatment for Alexander disease and the first therapy to directly target the protein buildup that drives the disease.

"For patients with Alexander disease and their families, there have been no approved treatment options - only supportive care while the disease progresses," said Emily Freilich, M.D., Director of the Division of Neurology I in the FDA's Center for Drug Evaluation and Research. "Today's approval is a landmark moment for this community, offering the first therapy that addresses the underlying cause of this rare and serious disease."

Alexander disease is a rare, progressive neurological disorder caused by mutations in the gene that produces glial fibrillary acidic protein (GFAP). When this protein is abnormal, it accumulates in the brain's supportive cells, causing damage to the nervous system over time. The disease affects less than 1 in a million people and can cause a wide range of serious and potentially life-threatening problems, including seizures, loss of developmental milestones, difficulty walking, muscle weakness, and increased pressure in the brain.

Zanvastro is an antisense oligonucleotide - a type of medicine that works by reducing the production of the abnormal GFAP protein before it can accumulate and cause further damage. It is administered as an injection into the spinal canal every three months by a trained healthcare professional.

The efficacy and safety of Zanvastro were evaluated in a multicenter, randomized, controlled clinical study (NCT04849741) enrolling 49 pediatric and adult patients with Alexander disease 2 years of age and older, and in an open-label substudy of 4 patients less than 2 years of age. Because Alexander disease is so rare and can affect patients across a wide range of ages, the FDA evaluated the available evidence in support of an indication covering patients from infancy through adulthood.

In patients aged 5 years and older who had measurable difficulties with walking at baseline, those treated with Zanvastro showed significantly better walking speed at 61 weeks compared to those who received no treatment. In children aged 2 to 4 years, where walking speed is not a reliable measure of progress, a broader assessment of motor skills - including standing, walking, running, and jumping - was used instead. Children treated with Zanvastro showed improvement on this measure while those in the control group declined.

For patients under 2 years of age, direct clinical trial data were limited by the rarity of the disease and lack of concurrent control. Pharmacokinetic modeling confirmed that drug levels in this age group are expected to be similar to those seen in older children at the same dose. This observation was also supported by safety data from four patients under 2 years of age treated in the study, as well as the safety data observed in the older pediatric patients. This approach supported extending the indication to the youngest patients while maintaining the evidentiary standards required to support approval.

The most common side effects of Zanvastro are vomiting, back pain, cough, headache, and post-lumbar puncture syndrome. Patients and caregivers should inform their healthcare provider if symptoms consistent with meningitis develop, as aseptic meningitis has been reported in patients treated with Zanvastro. Patients and providers should carefully review the full prescribing information when making treatment decisions.

Zanvastro received Orphan Drug, Fast Track, Breakthrough Therapy, and Rare Pediatric Disease and Priority Review Voucher designations, reflecting the serious and rare nature of Alexander disease, and FDA's commitment to rare disease drug development.

The approval of Zanvastro for the treatment of Alexander disease was granted to Ionis Pharmaceuticals, Inc.

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