The FDA has approved zilganersen (Zanvastro, Ionis Pharmaceuticals) as the first disease-modifying therapy for Alexander disease — a rare, progressive neurological disorder caused by mutations in the GFAP gene that leads to toxic protein accumulation in brain cells. The drug is an antisense oligonucleotide (ASO) that targets GFAP RNA, triggering its breakdown and reducing harmful protein buildup before it causes further neurological damage. It is administered as an intrathecal injection every three months and is approved for patients from infancy through adulthood.

The approval was based on a phase 3 trial enrolling 49 patients aged 2 and older. In patients aged 5+, zilganersen significantly stabilized gait speed compared to controls, who declined by 35.4% over 61 weeks. Children aged 2–4 showed improved gross motor skills while controls declined. Approval for infants under 2 was supported by pharmacokinetic modeling and safety data. The drug was generally well tolerated, with the most common side effects being vomiting, back pain, headache, and post-lumbar puncture syndrome.

Key Takeaways:

• Zilganersen is the first ASO approved for any leukodystrophy, offering proof of concept for targeting glial cells rather than neurons
• Clinicians should monitor patients for disease-related symptoms (e.g., vomiting, elevated intracranial pressure) that may be mistaken for drug side effects
• Stability — not just improvement — is a meaningful treatment goal given existing brain atrophy in many patients
• No eligibility cutoff based on age or disease progression; the broad indication covers all phenotypes

Why it matters: For a community that had only supportive care before, this approval is a landmark moment. Beyond Alexander disease, experts say it opens the door for ASO-based therapies across a range of rare neurological conditions where protein levels need to be modulated.