The FDA approved Zanvastro for Alexander disease, which strikes fewer than one in a million

Zanvastro, an antisense drug from Ionis Pharmaceuticals, is now the first treatment approved by the Food and Drug Administration for Alexander disease, a nervous-system disorder that affects fewer than one in a million people worldwide. It is given by injection into the spinal canal every three months, and the approval covers patients from infancy through adulthood.

The approval comes after roughly 30 years of work, in the words of the university’s release, that began when University of Wisconsin-Madison researchers engineered a mouse to overproduce one protein and found it developing deposits resembling those in patients. That same protein is now the drug’s target.

What Alexander disease does and how Zanvastro works

A University of Wisconsin-Madison release, republished by ScienceDaily on Oct. 12, describes symptoms that can include seizures, loss of previously gained developmental skills, worsening movement and walking, trouble speaking or swallowing, and dangerously high pressure in the brain. Onset can come in infancy, childhood or adulthood, and the course varies. Mutations in the gene for glial fibrillary acidic protein, or GFAP, cause it, and a blood test can now confirm the diagnosis without an invasive brain biopsy.

Zanvastro, generically zilganersen, is an antisense oligonucleotide: a short strand of genetic material designed to reduce production of GFAP so that the protein does not build up in brain cells and cause further damage. Because it must reach the central nervous system, it is injected into the spinal canal by a trained health professional. The FDA’s announcement confirms that schedule and says the disease affects fewer than 1 in a million people.

Albee Messing, professor emeritus of comparative biosciences at the university’s School of Veterinary Medicine and a former director of its Waisman Center, led much of the laboratory work. “This is a wonderful and long-awaited day for the Alexander disease community,” he said in the release. He recalled that the group had created, without intending to, a mouse producing the classic lesions, which pointed to GFAP as an obvious and specific target for therapy. Michael Brenner, professor emeritus of neurobiology at the University of Alabama at Birmingham, co-led the late-1990s work that tied mutations in the GFAP gene to the disease, and Tracy Hagemann of the Waisman Center helped create improved rodent models along the way.

The pivotal trial and what it showed

The Ionis-sponsored study ran at 13 sites and enrolled 54 patients, according to the university release. The AJMC report, which dates the approval to Sept. 3, 2026, says 49 of them aged 2 and older were randomized two to one to zilganersen or control, and that the participants ranged from 2 to 53 years old. The FDA describes the same randomized trial, NCT04849741, as multicenter and controlled, with an open-label substudy of four patients under age 2.

In patients aged 5 and older, the primary endpoint was stabilization of walking speed on the 10-Meter Walk Test at week 61. AJMC reports a least-squares mean difference of 33.3% versus control, with a p-value of 0.041, in the 50 mg group. The FDA states that older patients with baseline walking difficulty walked significantly faster at 61 weeks than untreated controls, and that treated children aged 2 to 4 improved on broader motor skills while controls declined.

Emily Freilich, director of a neurology division in the FDA’s drug center, said in the agency announcement: “Today’s approval is a landmark moment for this community.” She noted that families had no approved treatment options before. For children under 2, the agency relied on pharmacokinetic modeling and limited safety data, since trial evidence there was thin.

Safety, access and what is still unknown

The most common side effects named by the FDA are vomiting, back pain, cough, headache and post-lumbar-puncture syndrome, and aseptic meningitis has been reported, so patients are told to report meningitis-like symptoms. Ionis told trade press that most adverse events were mild or moderate, according to American Pharmaceutical Review, which also reports that the label carries a warning for aseptic meningitis.

Ionis plans a U.S. rollout in the coming weeks, according to Pharmaceutical Technology, which adds that the company has not disclosed a price but will offer help with insurance approval and affordability programs. Outside the United States, Recordati holds the rights under a licensing deal signed in June 2026 with a $30 million upfront payment, and European and Japanese filings are expected in 2027.

Ionis also received a Rare Pediatric Disease Priority Review Voucher with the approval, the trade publication notes, a regulatory incentive for drugs aimed at serious pediatric conditions. Several questions remain open. The trial was relatively short at just over a year, and the drug stabilized motor function in many patients rather than reversing the disease. Whether longer treatment changes survival or lets adults keep walking for years is not answered by the published figures, and the university release, which gives no dosage or exact trial endpoints, offers no effect sizes at all.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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