September 2026

Clinical Overview of Alexander Disease and the FDA Approval of Zanvastro

Alexander disease represents an ultra-rare, progressive, and frequently fatal neurological disorder estimated to impact approximately 300 individuals across the United States. The pathology of the condition extensively compromises motor, cognitive, autonomic, and gastrointestinal functions. Until recently, clinical management was strictly confined to supportive care and symptom mitigation.

A historic milestone was reached with the regulatory approval of Zanvastro (zilganersen), an antisense oligonucleotide (ASO) developed by Ionis Pharmaceuticals. Recognized as the first approved disease-modifying treatment for Alexander disease, Zanvastro alters the underlying biological trajectory of the disorder. Dr. Amy Waldman, a pediatric neurologist at the Children’s Hospital of Philadelphia, highlighted the transformative nature of this development:

“There’s tremendous excitement about the fact that we now have a disease-modifying therapy for Alexander disease, that Zanvastro gets to the underlying biology.”

The approval follows more than a decade of focused research built upon a natural history study initiated in 2016, with foundational investigations into the biology and clinical trajectories of Alexander disease tracing back to the 1980s.

Mechanism of Action and Administration Protocols

Zanvastro functions as an antisense oligonucleotide designed to directly target and reduce the pathological accumulation of glial fibrillary acidic protein (GFAP). In Alexander disease, excess GFAP forms toxic intracellular aggregates within astrocytes, known as Rosenthal fibers, which severely disrupt neurological function. Dr. Waldman explained this mechanism:

“As an antisense oligonucleotide (ASO), Zanvastro works by reducing glial fibrillary acidic protein (GFAP), a toxic accumulation of astrocytes in the brain that leads to the creation of the Rosenthal fibers that disrupt neurological function.”

The therapeutic regimen is approved as a 50 mg dose administered quarterly via intrathecal injection.

Global Clinical Trial Design and Efficacy Outcomes

The safety and efficacy of Zanvastro were evaluated in a global, randomized, double-blind, placebo-controlled study encompassing 53 participants aged 2 to 53 years. Patients were randomized in a 2:1 ratio into 25 mg Zanvastro, 50 mg Zanvastro, and control cohorts.

Gait Speed and Motor Function Outcomes

In participants aged 5 years and older, the therapy demonstrated significant stabilization of gait speed, evaluated via the 10-Meter Walk Test after 60 weeks of treatment.

• At baseline, the 50 mg treatment group ($n = 17$) presented with a mean gait speed of 1.2 meters per second, compared to 1.1 meters per second in the control group ($n = 13$).
• Following 61 weeks, the Zanvastro cohort demonstrated a least squares mean (LSM) percent change of –2.1% (95% CI; –23, 18.8).
• Conversely, the control group experienced a marked LSM percent change of –35.4% (95% CI; –59.3, –11.5), yielding an LSM difference of 33.3% (95% CI, 1.4–65.3).

Reflecting on the rapid clinical decline observed in the untreated group, Dr. Waldman noted:

“It was very humbling that in those just 15 months … there was a decline in patients who were relatively stable to begin with. The fact that patients continued to worsen in the control arm compared to the stability that was seen in Zanvastro was quite an achievement.”

Biomarker and Pediatric Subgroup Findings

Significant divergence between treatment and control arms was also documented in plasma glial fibrillary acidic protein (GFAP) levels from baseline at week 61, demonstrating targeted modulation of the disease’s underlying biology (LSM difference 33.6%, $P = .003$). Among younger participants aged 2 to 4 years, evaluations using the Gross Motor Function Measure-88 revealed significant differences at week 61 (LSM difference 22.9%, $P = .034$). Furthermore, researchers successfully incorporated an open-label evaluation involving four patients under the age of 2 years. Dr. Waldman emphasized the broad applicability of the trial:

“It’s a very heterogeneous disease, and we were very fortunate that this trial was for all ages, all disease phenotypes, so we could offer it to everyone. Even with such heterogeneity, that it met its statistical endpoints and had clinical meaningful benefits is really tremendous.”

Summary of Clinical Trial Findings and Trial Demographics

Safety Profile and Tolerability

Adverse reactions associated with Zanvastro were predominantly mild to moderate in severity. The most frequently reported events included:

• Vomiting
• Back pain
• Cough
• Headache
• Post-lumbar puncture syndrome

One isolated case of aseptic meningitis occurred during the trial; however, the patient successfully continued therapy and was re-dosed without lasting complications. Dr. Waldman summarized the safety profile:

“The drug was very well tolerated. There weren’t really any of those significant things that didn’t resolve with just some supportive care.”

Broader Scientific Implications and Future Horizons

Beyond Alexander disease, clinical investigators view the successful validation of Zanvastro as a vital proof-of-concept for addressing other neurological conditions involving gain-of-function pathologies and rare leukodystrophies. Dr. Waldman highlighted the expanding pharmacological toolkit:

“I think people are so focused right now on gene therapy or CRISPR-Cas9 or other things, and it’s just a reminder that we really do have a number of tools that can work for these incurable neurologic conditions.”

To facilitate safe and structured distribution, Ionis Pharmaceuticals announced plans to roll out Zanvastro across 12 designated leukodystrophy centers of excellence throughout the United States, while simultaneously establishing broader outreach channels to identify new patients. The therapy will launch at a list price of $285,000 per dose, accompanied by dedicated reimbursement and financial assistance programs to support patient access and continuity of care.

Expert Perspective: Clinical Realities and Societal Challenges

Albee Messing, VMD, PhD, Chair of the Scientific Advisory Committee for the End AxD Foundation, provided an expert clinical perspective on the approval, contextualizing its emotional and practical significance for affected families:

“There’s no question that it’s really a dream come true for the Alexander disease community in many ways. They’ve been waiting. I’ve been contacted by several parents whose children died decades ago.”

Dr. Messing noted the limitations of the current therapeutic iteration while emphasizing its foundational importance:

“It’s not a cure. It’s imperfect, but hopefully it provides the foundation for future improvements. There are various ways you can imagine improving it. I’m hoping Ionis is working on that. But at least this sets the ground rules for it. It’s got the FDA endorsement behind it as a strategy, and that’s terrific.”

Addressing the clinical expectations of disease stabilization versus slowing progression, Dr. Messing observed:

“The real hope is that it either stabilizes patients in their current state or they actually improve. But really the most obvious benefit right now is hope more than anything else. I think there is a possibility, which we’ve always known was a possibility, that it slows the progression. In some people, it’s still a progressive disease, but it doesn’t progress as fast. Some people may be happy about that. They have more time with their family. Some people may find that an agonizing experience, and it really all depends on the individual and their current state.”

Emphasizing the value of early intervention down to infancy, Dr. Messing added:

“I think there’s been the general notion, and certainly from the animal work, that the earlier you treat, the more effective it will be. That’s one of the reasons why I’m really happy that they approved it down through infancy. The way the trial was initially set up, it started at 2 years old, but a_l_o_t of kids start having problems before then. So, the earlier you can give the treatment, the better off you’re going to be.”

Regarding future optimizations, dosing schedules, and drug delivery modalities, Dr. Messing remarked:

“This is my personal opinion because the End AxD Foundation’s Scientific Advisory Committee has not really gathered to talk about this. For Zanvastro specifically, I would think the obvious thing to consider is doses, and whether, if they play around with the doses, they can get better results. For instance, a higher dose might give you more suppression and be more effective. There may be some people who can be weaned off the ASO after a while, and we don’t know that. The earlier treatment will be more effective, and they just need more patients and more experience with that, more data and longitudinal studies to see. I think there’s a lot that can be done with Zanvastro as it is. I think from the medical science side, biology side, there are the obvious things that we all want to see, such as improved means of delivery so you don’t have to do intrathecal administration – something that you can give via an intravenous route or something like that, or subcutaneously. There are people working on that, but I think the results are a long way off.”

Finally, Dr. Messing raised critical considerations regarding healthcare equity, administration infrastructure, and broader economic models associated with ultra-orphan therapeutics:

“It goes beyond the biology. I think the other really serious problem is the cost and equity and availability and how that will roll out. I think a lot of places can do intrathecal administration. That’s not such a huge deal. I think right now Ionis is trying to limit it to the places that have been part of the clinical trial. Intrathecal administration by itself is not such a limiting factor. Whatever they say about insurance coverage or adjustments, that’s all a black box, as far as we’re concerned. You have more and more of these kinds of very highly specialized treatments, not so personalized, but for an ultra-rare disorder, astronomical costs are attached to that. How that gets settled at a societal level is a major problem.”

Clinical Background and Pathophysiological Context

Hidradenitis suppurativa (HS) is a chronic, painful, and debilitating autoinflammatory skin disease characterized by deep-seated nodules, abscesses, draining sinus tracts, and extensive scarring, typically localized to intertriginous anatomical regions such as the axillae, groin, buttocks, and inframammary folds. In recent years, substantial clinical research has underscored an intimate epidemiological and immunologic link between HS and inflammatory bowel disease (IBD), encompassing both Crohn’s disease and ulcerative colitis. Patients presenting with HS inherently exhibit an elevated baseline vulnerability to developing gastrointestinal inflammation compared to the general population.

Concurrently, the therapeutic landscape for moderate-to-severe HS has evolved beyond conventional antibiotics and anti–tumor necrosis factor (anti-TNF) agents like adalimumab. Biologics targeting the interleukin-17 (IL-17) signaling cascade have emerged as core therapeutic options. Among the three targeted biologic therapies approved for HS, two function through IL-17 inhibition:

• Secukinumab (Cosentyx, Novartis): A selective human monoclonal antibody that neutralizes interleukin-17A (IL-17A), validated through pivotal clinical trials including the SUNSHINE and SUNRISE programs.
• Bimekizumab (Bimzelx, UCB): A humanized monoclonal antibody designed to selectively and simultaneously inhibit both interleukin-17A and interleukin-17F (IL-17A/F), which proved superior efficacy in the BE HEARD clinical trial program.

Despite the robust efficacy demonstrated across these large-scale phase 3 initiatives, the clinical application of IL-17 inhibitors has been met with vigilance and prescriber hesitancy. This caution stems from earlier findings across dermatological, rheumatological, and gastroenterological trials—particularly in psoriasis, ankylosing spondylitis, and failed trials of IL-17 blockers in active Crohn’s disease—where IL-17 blockade was linked to paradoxical flares of bowel disease or reports of de novo intestinal inflammation. Because the IL-17 cytokine family serves a dual role by driving cutaneous inflammation while simultaneously reinforcing the gut mucosal barrier, the clinical community has debated whether IL-17 targeted therapies impose an independent, additive risk of IBD onto a population already predisposed to gastrointestinal pathology.

Systematic Review and Meta-Analysis Architecture

To rigorously evaluate this safety concern, Marley Cutrona, BS, a medical student in the Department of Dermatology at the Icahn School of Medicine at Mount Sinai, along with colleagues, conducted a comprehensive systematic review and meta-analysis published in JAMA Dermatology (Cutrona M, et al. JAMA Dermatol. 2026; doi:10.1001/jamadermatol.2026.3373).

The investigators aggregated global evidence to quantify the exact frequency and relative risk of de novo IBD onset and underlying IBD flares among HS patients undergoing IL-17 pathway blockade. The analysis evaluated 24 studies comprising a total cohort of 3,015 patients receiving an IL-17 inhibitor:

• 10 Randomized Controlled Trials (RCTs)
• 11 Observational Cohort Studies
• 3 Case Series

The primary objective was to determine whether IL-17 inhibition imposes a tangible, drug-induced additive risk of IBD above the pre-existing baseline incidence associated with hidradenitis suppurativa.

Quantitative Findings and Risk Stratification

The investigation demonstrated that gastrointestinal adverse events culminating in verified IBD were remarkably infrequent across all therapeutic trials and real-world cohorts.

In the high-evidence tier of randomized controlled trials:

• Across the 10 evaluated RCTs, 2,572 HS patients received an IL-17 inhibitor.
• Within this substantial population, only six patients developed new-onset IBD.
• Through the primary randomized control period (week 16), new-onset IBD materialized in 0.23% of participants receiving an active IL-17 inhibitor, compared to 0% among those randomized to placebo.
• The risk difference between the active treatment arms and the placebo cohorts was calculated at 0.002 (95% CI, 0.003 to 0.007).

In nonrandomized real-world cohorts and observational investigations:

• Across 11 cohort studies capturing 469 patients treated with IL-17 inhibitors, seven instances of new-onset IBD were identified.
• This corresponded to a crude incidence rate of 1.49% and an estimated pooled incidence rate of 3.9% (95% CI, 2.3% to 6.5%).
• The comparatively higher event rates documented within observational datasets relative to RCTs likely reflect longer clinical follow-up periods, the inclusion of medically complex patients routinely excluded from phase 3 protocols, and confounding by indication.

Across all 24 evaluated clinical studies (comprising 3,015 patients), the researchers identified a cumulative total of:

• 17 cases of new-onset IBD
• 4 instances of pre-existing IBD flares

A critical temporal pattern was identified regarding the time-to-onset of gastrointestinal pathology: the documented adverse events manifested predominantly within the first 6 months following the initiation of IL-17 targeted therapy. This finding indicates that the period of maximal clinical vulnerability for either unmasking latent subclinical bowel inflammation or triggering new gastrointestinal pathology falls squarely within the earliest stages of biologic administration.

Comparative Data Synthesis

Pooled incidence: 3.9% (95% CI, 2.3% to 6.5%) | Not applicable (observational/non-placebo designs) |
| Total Evidence Base (RCTs + Cohorts + Case Series) | 3,015 patients across 24 studies | 17 new cases

4 disease flares | Events concentrated within the initial 6 months of therapy | Overall risk remains low and non-additive to underlying disease baseline |

Summary of Approved IL-17 Biologics in Hidradenitis Suppurativa

Author Conclusions and Clinical Guidance

Synthesizing their quantitative findings, Marley Cutrona and colleagues concluded that while hidradenitis suppurativa carries an undisputed intrinsic association with inflammatory bowel disease, the administration of IL-17 inhibitors does not superimpose an additive pharmacological risk:

“In this systematic review and meta-analysis, IBD events during IL-17 inhibitor therapy for HS were uncommon, with higher incidence rates in nonrandomized studies compared with RCTs, although events remained rare overall,” Marley Cutrona, BS, a medical student in the department of dermatology at Icahn School of Medicine at Mount Sinai, and colleagues wrote. “Although HS is associated with IBD, an additive risk with IL-17 inhibitor treatment was not observed.”

The investigative team reiterated that their conclusions support the overall therapeutic safety profile of this class of medications in managing HS, while highlighting the importance of clinical diligence:

“The findings of our study support a low risk of IBD in patients with HS treated with IL-17 inhibitors,” the researchers wrote. “However, current guidelines recommend avoiding IL-17 inhibitors in patients with concomitant active IBD. For patients with HS without known IBD, a thorough gastrointestinal history should be obtained before treatment with IL-17 inhibitors and patients should be monitored for gastrointestinal symptoms.”

Expert Perspective and Practical Implications

In an accompanying clinical perspective, Christopher J. Sayed, MD, of the University of North Carolina at Chapel Hill, emphasized that these data provide crucial clarity for practicing dermatologists who manage severe, recalcitrant HS:

“This is very reassuring news. The increased risk for IBD in patients with HS has generated some hesitancy in prescribing IL-17 inhibitors. This reinforces that, if the risk exists, it is exceptionally low and should not interfere with appropriate treatment in the absence of concerning gastrointestinal symptoms.”

Dr. Sayed’s commentary highlights that the theoretical hazard of drug-induced bowel inflammation should not become a therapeutic barrier preventing patients from accessing clinically efficacious biologics. Provided that patients are free of unmanaged or suspicious gastrointestinal symptoms—such as persistent hematochezia, unexplained chronic diarrhea, involuntary weight loss, or severe abdominal cramping—IL-17 blockade represents a sound therapeutic modality.

Disclosures and Industry Affiliations

The perspective author, Dr. Christopher J. Sayed, documented financial associations (encompassing research support, advisory roles, or consulting arrangements) with multiple biotechnology and pharmaceutical entities, including:

• AbbVie
• Alumis
• AstraZeneca
• Cantargia
• Elasmogen
• Incyte
• InflaRx
• MoonLake Immunotherapeutics
• Novartis
• Sandoz
• Sanofi
• Sonoma Biotherapeutics
• Takeda Pharmaceuticals
• UCB

Methodological Limitations and Investigative Nuances

While the conclusions offer strong reassurance for clinical practice, the authors identified several methodological caveats that warrant careful interpretation:

1. Statistical Power Constraints: Because true de novo IBD presentations and unmasked flares occurred at exceptionally low absolute numbers, the statistical power to uncover subtle differences between various IL-17 targeting molecules (e.g., selective IL-17A inhibition versus dual IL-17A/F blockade) remained constrained.
2. Endpoint Designations: Across the majority of the randomized controlled trials evaluated, inflammatory bowel disease was monitored solely as a treatment-emergent adverse event rather than an adjudicated primary or secondary study endpoint. Consequently, surveillance protocols, gastrointestinal screening questionnaires, and diagnostic confirmation methods lacked standardization across protocols.
3. Follow-Up Inconsistencies: The observation windows varied considerably among the pooled investigations. While randomized phases offered uniform, highly monitored 16-week intervals, real-world observational cohorts and open-label extensions exhibited widely disparate durations of follow-up, which may account for the discrepancy in reported crude incidence rates between RCTs (0.23%) and observational cohorts (3.9%).

Overall, this extensive systematic synthesis clarifies the clinical safety parameters of IL-17 pathway inhibition in hidradenitis suppurativa, indicating that the inherent risk profile of these therapeutics does not exacerbate the pre-existing risk of inflammatory bowel disease in this patient population. Baseline gastrointestinal risk assessments and early-phase clinical symptom surveillance remain prudent best practices.