FDA approves first drug to treat Alexander disease, offering a targeted therapy for the ultra-rare, progressive neurodegenerative disorder in children

The U.S. Food and Drug Administration approved Zanvastro (zilganersen) injection on September 3, 2026, as the first drug to treat Alexander disease in pediatric and adult patients, officials said. The RNA-targeted antisense therapy works by directly targeting the abnormal buildup of glial fibrillary acidic protein (GFAP) in astrocytes, which drives the ultra-rare, progressive neurodegenerative disorder.

The FDA approved Zanvastro nearly three weeks ahead of the scheduled September 22, 2026, target action date, granting the drug Priority Review status, according to the agency’s announcement. Zanvastro (zilganersen), developed by Ionis Pharmaceuticals, is the first FDA-approved treatment for Alexander disease, an ultra-rare neurodegenerative disorder that affects both pediatric and adult patients. Ionis officials confirmed the approval in a September 3 press release, describing Zanvastro as the “first and only disease-modifying treatment” for Alexander disease.

Clinical trial data cited by Ionis and independent analyses showed that patients treated with Zanvastro experienced stabilization of walking speed, while untreated patients exhibited a 33% decline in gait speed, a key endpoint for neurological disorders.

Zanvastro is an RNA-targeted antisense therapy designed to reduce the abnormal buildup of glial fibrillary acidic protein (GFAP) in astrocytes, a hallmark of Alexander disease pathology. The drug is administered by intrathecal injection into the cerebrospinal fluid, typically on a quarterly schedule, according to clinical trial reports and company materials. While not a cure, the therapy aims to slow or stabilize disease progression, particularly motor and functional decline, officials said.

In children aged 2 to 4, treated patients demonstrated motor improvements, with those aged 5 and older showing stabilization of gait speed, sources confirmed. These results represent the first evidence of disease-modifying impact in Alexander disease and were pivotal to the FDA’s approval decision.

The FDA approval covers both pediatric and adult patients, providing the first authorized therapy for children with Alexander disease, which is often diagnosed in early childhood. Advocacy groups noted that prior to Zanvastro, treatment options were limited to symptomatic management, such as seizure control and spasticity relief. The broad label encompassing all ages was highlighted by external experts as significant given the disease’s early onset and progressive nature.

Alexander disease is an ultra-rare leukodystrophy caused by pathogenic variants in the GFAP gene, leading to toxic protein accumulation and widespread central nervous system dysfunction. The disorder affects motor, cognitive, autonomic, and gastrointestinal functions and has historically been fatal without approved treatments. Records from the FDA’s rare disease approvals list include Zanvastro under the 2026 rare disease drug approvals, confirming its status as the first drug approved for this condition.

Ionis Pharmaceuticals announced that Zanvastro would be available to U.S. patients “in the coming weeks” following the approval. The company set the price at $285,000 per dose, consistent with costs typical of ultra-rare disease therapies, Reuters reported. Ionis also launched a patient support program called Ionis Every Step to assist families with education, insurance navigation, and affordability resources as the drug becomes commercially available.

The FDA granted Ionis a Rare Pediatric Disease Priority Review Voucher in conjunction with the approval, a regulatory incentive aimed at encouraging development of therapies for rare pediatric conditions. Ionis retains U.S. commercialization rights, while Recordati holds rights outside the United States, according to industry sources.

FDA officials emphasized that Zanvastro is the first therapy to directly target the protein buildup that drives Alexander disease, marking a scientific advance for this pediatric and adult indication. Ionis’ CEO described the drug as establishing a new pillar in the company’s rare disease pipeline. Rare disease advocacy organizations characterized the approval as a historic milestone for families affected by Alexander disease, enabling access to the first disease-modifying therapy despite the drug not being curative.

Alexander disease was first genetically characterized nearly 30 years ago, but until Zanvastro’s approval, no FDA-approved treatments existed. Care had been limited to managing symptoms such as seizures, spasticity, and feeding difficulties. The approval represents a significant development for a disorder that has been historically neglected in pediatric neurodegenerative research and drug development.