Ionis Pharmaceuticals Receives FDA Approval for ZANVASTRO, First Disease-Modifying Treatment for Alexander Disease
Ionis Pharmaceuticals, Inc. (Nasdaq: IONS) has announced that the U.S. Food and Drug Administration (FDA) has approved ZANVASTRO™ (zilganersen) for the treatment of pediatric and adult patients living with Alexander disease (AxD). The approval represents a major milestone for the rare neurological disease community, as ZANVASTRO becomes the first and only disease-modifying treatment approved for Alexander disease.
Alexander disease is an ultra-rare, progressive, and often fatal neurological disorder that can affect multiple aspects of a person’s health and daily functioning. These can include motor abilities, cognitive development, autonomic function, and gastrointestinal function. Until the approval of ZANVASTRO, medical care for people with AxD was largely focused on managing individual symptoms and complications rather than addressing the underlying biological mechanism responsible for disease progression.
ZANVASTRO is an RNA-targeted medicine designed to address the underlying cause of Alexander disease by reducing the production of glial fibrillary acidic protein (GFAP). The medicine is administered as a 50 mg intrathecal injection once every three months, providing a quarterly treatment schedule for patients.
For Ionis, the FDA decision also represents an important achievement in the company’s broader neurology strategy. ZANVASTRO is the company’s first independently launched medicine from its neurology pipeline, demonstrating the potential of its RNA-targeted drug development platform to generate therapies for serious neurological disorders where treatment options have historically been limited.
A New Treatment Approach for Alexander Disease
Alexander disease affects approximately one in one to three million people worldwide. Although rare, the condition can have a profound impact on patients and their families.
The disease can emerge at different stages of life, with initial signs appearing from infancy through adulthood. The specific symptoms and their severity can vary depending on the age at which the disease begins.
As Alexander disease progresses, patients may experience worsening motor and cognitive dysfunction. The condition can gradually affect independence and interfere with fundamental activities such as swallowing, airway protection, and purposeful movement.
The disease is associated with changes in the GFAP gene, which result in excessive production and accumulation of GFAP within astrocytes. Astrocytes are specialized cells in the central nervous system that play important roles in maintaining the health and function of neurons.
When excessive GFAP accumulates, astrocyte function can become impaired. Over time, this dysfunction can contribute to damage involving neurons and myelin, ultimately producing many of the neurological manifestations associated with Alexander disease.
ZANVASTRO has been designed to target this underlying mechanism. By reducing GFAP production, the therapy aims to address the biological process driving disease progression rather than simply treating individual symptoms.
Pivotal Study Supports FDA Approval
The FDA approval was supported by positive results from a pivotal clinical study evaluating ZANVASTRO in people living with Alexander disease.
The pivotal study achieved its primary endpoint in participants aged five years and older. Patients receiving ZANVASTRO 50 mg demonstrated statistically significant and clinically meaningful stabilization of gait speed compared with the control group at Week 61.
Gait speed was assessed using the 10-Meter Walk Test (10MWT), a commonly used clinical measure of gross motor function in neurological disorders. The least-square mean difference between the ZANVASTRO and control groups was 33.3%, with a p-value of 0.041.
The results suggest that treatment with ZANVASTRO may help preserve motor function in patients with Alexander disease, an important consideration for a progressive neurological condition in which loss of mobility and independence can become increasingly debilitating.
The therapy also demonstrated evidence of benefit in younger children. Among patients between two and four years of age, ZANVASTRO improved gross motor function as measured by the Gross Motor Function Measure-88 (GMFM-88) compared with control at Week 61.
The GMFM-88 is an established clinical tool used to assess gross motor abilities and changes in motor function, particularly in pediatric neurological conditions.
In addition to the primary motor endpoint, secondary and exploratory assessments provided further supportive evidence. Patient- and caregiver-reported outcomes, as well as clinician-reported measures, consistently favored ZANVASTRO.
Together, the findings provided the clinical foundation for the FDA’s approval and support the potential of ZANVASTRO to modify the progression of Alexander disease.
Potential Shift From Symptom Management to Disease Modification
For decades, treatment for Alexander disease has primarily centered on symptom management. Physicians and caregivers have addressed individual manifestations of the disease, but there has been no approved therapy specifically designed to target the underlying disease biology.
The approval of ZANVASTRO changes that treatment landscape.
Amy Waldman, M.D., M.S.C.E., a pediatric neurologist at Children’s Hospital of Philadelphia and lead investigator for the ZANVASTRO study, described the FDA decision as a significant advancement for the AxD community.
“For decades, care for people living with Alexander disease has focused primarily on managing symptoms, without an option to modify the underlying cause of disease,” Waldman said.
She noted that ZANVASTRO provides an opportunity to move beyond managing individual symptoms and instead address the biological mechanism underlying the disorder.
The significance of this change extends beyond the availability of a new medicine. For patients and families, the approval creates the possibility of intervening in a disease process that previously had no disease-modifying treatment.
Safety and Tolerability Profile
In addition to demonstrating efficacy, ZANVASTRO showed a favorable safety and tolerability profile in the pivotal clinical program.
Most adverse events reported during treatment were mild or moderate in severity. Importantly, serious treatment-emergent adverse events occurred less frequently among patients receiving ZANVASTRO than among those in the control group.
The safety findings will remain an important component of the medicine’s ongoing clinical use, particularly because Alexander disease can affect children as well as adults and ZANVASTRO is intended for long-term disease management.
The quarterly administration schedule may also provide a practical treatment framework for patients and caregivers, although administration by intrathecal injection requires treatment in an appropriate clinical setting.
Families and Patient Advocacy at the Center
The approval has particular significance for families who have spent years managing Alexander disease without an approved therapy directed at its underlying cause.
Emily Petty, president of End Alexander Disease and a parent of a child living with the condition, described the approval as a fundamental change for the community.
“As a mom to a young boy living with Alexander disease and an advocate for this community, I have seen firsthand the profound impact this disease has on individuals and their families,” Petty said.
She described the approval as a shift in the conversation from managing the disease to actively considering how it can be treated.
For families affected by ultra-rare disorders, regulatory approval can represent more than the availability of a new medicine. It can also provide greater recognition of the disease and create new possibilities for patients who previously had limited therapeutic options.
Ionis Every Step Program to Support Patients
Ionis has announced that it will provide a comprehensive suite of support services for patients prescribed ZANVASTRO through its Ionis Every Step™ program.
The initiative is designed to help patients and caregivers navigate different aspects of the treatment journey. Available resources will include disease-state and product education, access to a dedicated Patient Education Manager, assistance with insurance approval, information about affordability programs, and additional ongoing support.
Such services can be particularly important for people living with rare diseases, where treatment pathways may involve specialized healthcare providers, insurance considerations, and unfamiliar clinical processes.
Ionis has established the support program as part of its effort to help eligible patients access the medicine following the FDA approval.
ZANVASTRO is expected to become available in the United States in the coming weeks.
Rare Pediatric Disease Priority Review Voucher
Along with the approval, the FDA granted Ionis a Rare Pediatric Disease Priority Review Voucher (PRV).
The Rare Pediatric Disease Priority Review Voucher program is designed to encourage the development of therapies for serious or life-threatening diseases affecting children. A PRV can provide a mechanism for potentially accelerating FDA review of a future regulatory application, adding another strategic benefit associated with the development of therapies for rare pediatric conditions.
The award highlights the broader significance of ZANVASTRO’s development program and its focus on a disease that can affect children early in life.
International Development Continues
While the FDA approval establishes ZANVASTRO’s regulatory pathway in the United States, Ionis is also preparing for potential availability in international markets.
In June 2026, Ionis entered into a licensing agreement with Recordati, a global pharmaceutical company headquartered in Italy and focused on specialty and rare diseases. Under the agreement, Recordati received exclusive rights to develop and commercialize zilganersen in countries outside the United States.
Ionis and Recordati are working together on regulatory preparations for Europe and Japan. Regulatory submissions in those markets are expected in 2027.
The agreement gives Recordati responsibility for the development and commercialization of ZANVASTRO outside the U.S., while Ionis retains its U.S. commercialization efforts.
A Major Milestone for Ionis’ Neurology Pipeline
For Ionis, the FDA approval of ZANVASTRO represents a significant milestone in the company’s evolution from a developer of RNA-targeted medicines to a company capable of independently bringing a neurology therapy to patients.
Brett P. Monia, Ph.D., Chief Executive Officer of Ionis, said the approval begins a new chapter for people affected by Alexander disease and their families.
He also highlighted the significance of ZANVASTRO as Ionis’ first independent launch from its neurology pipeline and as an example of how RNA-targeted technology can be applied to serious neurological diseases with limited treatment options.
The company’s approach reflects the growing role of RNA-targeted therapies in drug development. By selectively influencing the production of disease-associated proteins, RNA medicines can potentially address biological mechanisms that are difficult to target using conventional therapeutic approaches.
The FDA approval of ZANVASTRO marks a turning point in the treatment of Alexander disease. With the first approved disease-modifying therapy now available, patients and physicians have a treatment option specifically designed to address the underlying biology of the disorder.
Clinical evidence supporting the approval demonstrated stabilization of gait speed in patients aged five and older, improvements in gross motor function among younger children, and consistent positive trends across patient-, caregiver-, and clinician-reported outcomes. The therapy also showed a favorable safety and tolerability profile, with most adverse events characterized as mild or moderate.
For a disease that has historically been managed primarily through supportive and symptomatic care, the availability of an RNA-targeted treatment represents a significant therapeutic advance.
The next phase will focus on bringing ZANVASTRO to eligible patients in the United States, supporting families through the treatment process, and continuing international regulatory development. With Recordati preparing submissions in Europe and Japan and Ionis beginning U.S. commercialization, the potential reach of zilganersen could expand considerably over the coming years.
For the Alexander disease community, the approval offers a new therapeutic possibility where none previously existed. For Ionis, it demonstrates the company’s ability to translate RNA science into an independently launched neurological medicine and reinforces its broader commitment to developing treatments for serious diseases with substantial unmet medical needs.
About the ZANVASTRO Study
The global, multicenter, randomized, double-blind, controlled, multiple-ascending dose (MAD) Phase 1-3 study (NCT04849741) enrolled 54 participants with Alexander disease (AxD) between the ages of 1.5 and 53 years across 13 sites in eight countries. Most participants in the study were children, reflecting the early onset and severe progression of AxD in pediatric populations. Participants were randomized in a 2:1 ratio to receive ZANVASTRO or control for a 60-week double-blind treatment period.
The study included two dose cohorts, 25 mg and 50 mg, with the 50 mg dose cohort analyzed as the pivotal dose cohort, with dosing every 12 weeks. At week 60, eligible participants entered a 60-week open-label treatment period, followed by a 120-week open-label long-term extension period. During the long-term extension, participants in the 25 mg dose cohort transitioned to the 50 mg dose cohort.
Participants in countries where zilganersen has not been or is not commercially available can continue to receive zilganersen treatment through a 240-week extended long-term extension period, which includes 20 additional doses, followed by a 28-week post-treatment follow-up period. The primary endpoint was percent change from baseline in gait speed as assessed by the 10-Meter Walk Test (10MWT), an assessment of functional mobility, at the end of the double-blind treatment period.
Key secondary endpoints include patients’ self-identified Most Bothersome Symptom (MBS) Score, change from baseline in Patient Global Impression of Severity (PGIS) Score and Patient Global Impression of Change (PGIC) Score and Clinician Global Impression of Change (CGIC) Score at the end of the double-blind treatment period.
About Alexander Disease (AxD)
AxD is an ultra-rare, progressive and often fatal neurological disease that occurs in approximately 1 per 1 to 3 million people worldwide and affects a type of cell in the brain called astrocytes. Astrocytes have multiple roles in the brain including support of neurons and oligodendrocytes, which maintain the myelin sheath around nerve fibers. AxD is caused by disease-causing variants in the glial fibrillary acidic protein (GFAP) gene and is generally characterized by progressive neurological deterioration resulting in loss of functional mobility, loss of independence and the inability to control muscles for large movements, swallowing and airway protection, though symptoms can vary depending on age of onset. AxD usually leads to death within 14 – 25 years after symptom onset.
About ZANVASTROTM (zilganersen)
ZANVASTROTM (zilganersen)is approved by the U.S. Food and Drug Administration (FDA) for the treatment of Alexander disease (AxD) in pediatric and adult patients. ZANVASTRO is an RNA-targeted therapy designed to inhibit production of excess glial fibrillary acidic protein (GFAP) that accumulates as a result of pathogenic variants in the GFAP gene. For more information about ZANVASTRO, visit ZANVASTRO.com.
About Ionis Neurology
Ionis has been at the forefront of discovering and developing leading neurological disease medicines, including ZANVASTROTM (zilganersen), the only approved treatment for Alexander disease, SPINRAZA® (nusinersen), the first approved treatment for spinal muscular atrophy, WAINUA® (eplontersen), a medicine to treat hereditary transthyretin-mediated amyloid polyneuropathy (ATTRv-PN), and QALSODY® (tofersen) for SOD1-ALS.
The clinical-stage portfolio includes 12 investigational medicines, of which seven are wholly owned by Ionis. Ionis’ investigational portfolio includes medicines for which there are few or no disease modifying treatments, such as rare diseases including Angelman syndrome, prion disease and multiple system atrophy, as well as more common conditions like Alzheimer’s disease.
About Ionis Pharmaceuticals, Inc.
For more than three decades, Ionis has invented medicines that bring better futures to people with serious diseases. Ionis currently has marketed medicines and a leading pipeline in neurology, cardiometabolic disease and select areas of high patient need. As the pioneer in RNA-targeted medicines, Ionis continues to drive innovation in RNA therapies in addition to advancing new approaches in gene editing. A deep understanding of disease biology and industry-leading technology propels our work, coupled with a passion and urgency to deliver life-changing advances for patients. To learn more about Ionis, visit Ionis.com and follow us on X (Twitter), LinkedIn and Instagram.