FDA Approves Zanvastro as First Alexander Disease Treatment

Key Takeaways

• Zanvastro (zilganersen) is the first FDA-approved treatment for Alexander disease, approved for pediatric and adult patients.
• Among patients 5 years and older with measurable walking difficulty at baseline, walking speed at 61 weeks was significantly better with Zanvastro than in controls.
• In children aged 2 to 4, motor skills improved with treatment while declining in controls.
• Infants younger than 2 were included without a concurrent control group, based on pharmacokinetic modeling and limited safety data.
• Aseptic meningitis has been reported in patients treated with Zanvastro.

Alexander disease is a rare, progressive neurological disorder caused by mutations in the gene for glial fibrillary acidic protein (GFAP). The abnormal protein accumulates in the brain’s supportive cells and damages the nervous system over time, causing problems that include seizures, loss of developmental milestones, difficulty walking, and muscle weakness. Until now, care has been supportive only.

Zilganersen is an antisense oligonucleotide that reduces production of the abnormal GFAP protein before it can build up. A trained healthcare professional administers it by injection into the spinal canal every three months.

The FDA based its approval on a multicenter, randomized, controlled study (NCT04849741) of 49 patients aged 2 and older, along with an open-label substudy of 4 patients younger than 2. Because the disease is so rare and affects people across a wide age range, the agency evaluated the evidence for an indication spanning infancy through adulthood.

Walking speed was the key measure in patients aged 5 and older who had measurable walking difficulty at baseline. At 61 weeks, those treated with Zanvastro walked significantly faster than controls. In children aged 2 to 4, walking speed is not a reliable gauge of progress, so investigators used a broader motor assessment covering standing, walking, running, and jumping. Treated children improved on that measure, while controls declined.

For patients younger than 2, direct trial data were limited by the rarity of the disease and the lack of a concurrent control group. Pharmacokinetic modeling indicated that drug levels in this age group should be similar to those in older children at the same dose. Safety data from the four infants in the substudy, and from older pediatric patients, supported extending the indication to the youngest patients. Efficacy in infants rests on this modeling and safety evidence rather than on a controlled comparison.

The most common side effects are vomiting, back pain, cough, headache, and post-lumbar puncture syndrome. Aseptic meningitis has also been reported, and patients and caregivers should tell their healthcare provider if symptoms consistent with meningitis develop. The FDA approved Zanvastro on September 3, 2026, granting the approval to Ionis Pharmaceuticals. The drug received Orphan Drug, Fast Track, Breakthrough Therapy, and Rare Pediatric Disease designations, along with a Priority Review Voucher.