For the first time, people with Alexander disease have an approved medicine. The US Food and Drug Administration (FDA) approved Zanvastro (generic name zilganersen), made by Ionis Pharmaceuticals, as the first treatment for this rare, progressive brain disorder1. The decision came on September 3, 2026, ahead of a September 22 target date2. Wider coverage in late October described it as the end of a research effort lasting about 30 years3.
Until now, care for Alexander disease focused only on managing symptoms3. Zanvastro is the first approved therapy designed to address the biological cause of the disease, a buildup of an abnormal protein called GFAP1. The approval covers patients of all ages, from infants to adults31.
What Alexander disease does
Alexander disease affects fewer than one in a million people1. One patient resource notes that about 500 cases have been reported since 19492. It is caused by a fault in the gene that makes glial fibrillary acidic protein, or GFAP3. The faulty protein clumps into tangles called Rosenthal fibers. These stress astrocytes, the star-shaped helper cells of the brain, which then become damaged along with myelin, the fatty insulation around nerve fibers3.
Symptoms can include seizures, loss of developmental milestones, trouble walking, muscle weakness and increased pressure in the brain1. Most children show symptoms by age four, and earlier onset usually means more severe disease4. The disease usually leads to death within 14 to 25 years after symptoms begin54.
What the trial measured
Zanvastro is an antisense oligonucleotide, a short, man-made strand of genetic material that tells cells to make less of a specific protein, in this case GFAP31. A health professional injects it into the spinal canal once every three months1.
The main study, registered as NCT04849741 and sponsored by Ionis, started in June 2021 and enrolled 54 people6. It was randomized and double-blind: patients were assigned by chance, two to one, to the drug or a dummy treatment, and neither they nor their doctors knew which they got during a 60-week period54. It ran at 13 sites in eight countries5. The main goal was the change in walking speed on a 10-meter walk test at week 616.
The sources describe the group slightly differently. The trial registry and one report count 54 participants aged 1.5 to 5346. The FDA’s summary, as reported by Global Genes, describes 49 patients aged 2 and older in the controlled trial plus four children younger than 2 in a separate open-label part where everyone got the drug1.
According to the FDA, as reported by Global Genes:
- Among patients aged 5 and older who had measurable walking problems at the start, those on Zanvastro had significantly better walking speed at 61 weeks than untreated patients1.
- In children aged 2 to 4, walking speed was not a reliable measure, so researchers used a broader test of standing, walking, running and jumping. Treated children improved on it, while children in the control group declined1.
Sources frame the walking result in different ways. A report from the Oligonucleotide Therapeutics Society said patients on the higher of two doses had a mean 33% improvement in walking speed from the start of the study4. ScienceAlert and Trial Friend described older participants’ walking speed as holding steady while untreated patients declined32.
Side effects
Most side effects were mild or moderate, and serious ones were less common in treated patients than in the control group3. The most common were vomiting, back pain, cough, headache and pain or headache after the spinal injection31. The FDA also warned that some patients developed aseptic meningitis, an inflammation of the lining around the brain and spinal cord, and advised patients and caregivers to tell a health care provider if symptoms like this appear31.
What it does not show yet
The drug is not a cure. It does not reverse the condition or make it disappear3. Ionis said in 2024 that the goal was to slow or stabilize disease progression5.
Evidence in the youngest patients is thin. Direct trial evidence in children younger than 2 was limited because the disease is so rare and there was no comparison group1. The FDA instead relied on computer modeling suggesting drug levels in those infants should be similar to levels in older children, backed by safety data from the four infants treated and from older children1.
The controlled part of the study lasted about 60 weeks5, so long-term effects are not yet known. Participants were set to continue on the drug in a longer open-label phase, where everyone knows they are getting it5. The trial registry lists the study as active but not recruiting and shows no results posted yet6. None of the sources available here describe a peer-reviewed journal publication of the full results.
Who is behind it
Ionis Pharmaceuticals developed the drug and sponsored the trial36. The company specializes in RNA-targeted medicines and said in 2024 that it had five marketed medicines5. It also made an earlier antisense drug for spinal muscular atrophy7.
Along the way, the drug picked up several FDA designations meant to encourage and speed development for rare diseases: Orphan Drug, Fast Track, Breakthrough Therapy and Rare Pediatric Disease1. With the approval, Ionis also received a priority review voucher12, a reward the FDA gives for some rare pediatric drugs. Orphan status, which the FDA granted in 2020, brings incentives including seven years of market exclusivity after approval7.
“[The] approval of Zanvastro begins a new chapter for people living with Alexander disease and their families, who have long faced this relentlessly progressive and often fatal disease with no treatment options,” said Brett Monia, CEO of Ionis3.
A long road from mouse research
The groundwork came from academic labs. Neuropathologist Albee Messing of the University of Wisconsin-Madison has studied the condition for more than 30 years3. With colleagues including neurobiologist Michael Brenner of the University of Alabama at Birmingham, he bred mice to make too much GFAP. The researchers were surprised to find the mice developed the classic brain lesions of Alexander disease3.
“This provided an obvious and specific strategy for therapy – the GFAP protein,” said Messing3.
The team first looked at whether any existing approved drugs might help, before deciding to design a custom drug to lower GFAP production3. It was tested in animals before human trials began in 20213.
“This is a wonderful and long-awaited day for the Alexander disease community,” Messing said3.
Families also played a part. Messing credited “the support and participation from the patient and family community”3. One mother, describing her daughter’s response to treatment, said: “The fog’s being lifted on her brain, and her personality gets a chance to come out more and more.”3 That is one family’s account, not a trial measurement.
What to watch next
Longer follow-up from the trial’s open-label phase should show whether the effects hold beyond the first year or so5. Patient groups also point out that getting an approved rare-disease drug often takes weeks of specialty pharmacy setup and insurance review2.
Research on the disease continues. A long-running natural history study at Children’s Hospital of Philadelphia, which follows patients without giving treatment, is still recruiting. It aims to enroll about 200 people and measure motor skills, speech, swallowing and GFAP levels in spinal fluid and blood, with data collection planned to run until 20308. Other approaches being explored include RNA interference, another way to turn down GFAP production2.
