The US Food and Drug Administration has approved zilganersen, marketed in the United States as Zanvastro, for paediatric and adult patients with Alexander disease.
The decision is important because Alexander disease previously had no FDA-approved treatment. The disorder is caused by disease-causing changes in the gene encoding glial fibrillary acidic protein, or GFAP, which leads to abnormal accumulation of the protein in astrocytes — support cells that are essential to the function and maintenance of the central nervous system.
Zilganersen is designed to reduce production of GFAP rather than only treating symptoms.
What Alexander disease is
Alexander disease is a rare neurological disorder classified among the leukodystrophies, conditions that damage the brain's white matter.
It is associated with toxic accumulation of abnormal GFAP in astrocytes. Those cells help regulate the environment around neurons, support the blood-brain barrier and contribute to many aspects of brain homeostasis.
As GFAP accumulates, astrocyte function becomes abnormal and characteristic protein aggregates known as Rosenthal fibres can form. The disease can cause developmental problems, weakness, spasticity, swallowing difficulty, seizures, problems with balance and other neurological symptoms. Severity and age of onset vary widely.
How the drug works
Zilganersen is an antisense oligonucleotide.
Antisense medicines are short synthetic strands of nucleic acid designed to bind a specific RNA sequence. By binding the messenger RNA that carries instructions for making GFAP, zilganersen reduces production of the protein.
That is a fundamentally different strategy from treating downstream symptoms. It targets the molecular process that drives the disease.
The FDA describes the medicine as the first therapy to directly target the protein buildup responsible for Alexander disease.
Why this type of treatment is possible
Genetic diseases caused by excessive production of a harmful protein are particularly attractive targets for antisense technology because the RNA instruction can be intercepted before the protein is made.
The same general therapeutic principle is already used in several neurological and rare diseases, although each antisense drug is sequence-specific and must be developed for its particular target.
In Alexander disease, lowering GFAP has a strong mechanistic rationale because GFAP accumulation is central to the disease biology.
What approval does and does not establish
FDA approval means the agency determined that the available evidence supported a favourable benefit-risk balance for the approved population and use.
It does not mean the medicine reverses all established neurological damage or that every patient will respond in the same way.
Rare-disease trials also face practical limitations: patient populations are small, phenotypes can vary substantially and long-term outcomes may take years to characterize.
Post-approval follow-up will therefore remain important for understanding durability of benefit, long-term safety and how outcomes differ across ages and disease stages.
Why the approval matters beyond one disease
Alexander disease is exceptionally rare, but the regulatory milestone illustrates a broader change in neurological drug development.
Diseases once treated mainly by managing symptoms can increasingly be approached at the level of RNA or gene expression when a clear molecular driver is known.
That does not make development easy. Delivering medicines into the central nervous system, establishing meaningful clinical endpoints and treating patients early enough to preserve function remain difficult problems.
But the first approved therapy changes the clinical landscape from supportive care alone to disease-directed treatment.
What to watch next
The most useful evidence after approval will include longer follow-up of treated patients, data across different disease-onset groups and evidence on whether earlier treatment preserves neurological function more effectively than treatment after substantial damage has accumulated.
Because Alexander disease can progress differently between individuals, real-world evidence may become especially important in defining which patients benefit most.
Primary source
- US Food and Drug Administration. FDA Approves First Drug to Treat Alexander Disease. 4 September 2026. https://www.fda.gov/news-events/press-announcements/fda-approves-first-drug-treat-alexander-disease