FDA Grants Priority Review to Levacetylleucine for Ataxia-Telangiectasia, Potentially Positioning First Approved Therapy

The FDA has accepted a IntraBio’s supplemental new drug application (sNDA) for levacetylleucine (AQNEURSA) for the treatment of ataxia-telangiectasia (A-T) in adult and pediatric patients. The administration has also granted the application Priority Review, assigning a Prescription Drug User Fee Act (PDUFA) target action date of September 19, 2026.¹

If approved, levacetylleucine would become the first FDA-approved therapy specifically indicated for A-T, a rare inherited neurodegenerative condition characterized by progressive cerebellar dysfunction, immunodeficiency, and increased malignancy risk.²

“Today’s announcement represents a step forward — not just for IntraBio, but for the thousands of patients and families living with Ataxia-Telangiectasia who have waited far too long for a treatment option,” said Mallory Factor, president and chief executive officer at IntraBio in Austin Texas. “The FDA’s Priority Review designation reflects the urgency of this unmet need, and we are fully committed to working with the agency to make AQNEURSA the first approved therapy for A-T as swiftly as possible.”¹

The regulatory milestone follows earlier reporting that IntraBio had submitted an sNDA supported by findings from the pivotal phase 3 IB1001-303 trial (NCT06673056), which evaluated AQNEURSA in pediatric and adult patients with A-T.³ According to the company, the study met its primary endpoint and all key secondary endpoints, demonstrating statistically significant improvements in neurologic signs, symptoms, and patient functioning.¹ Full peer-reviewed efficacy and safety results from the trial have not yet been published, limiting independent evaluation of the magnitude and durability of treatment benefit.

Supportive Data for Levacetylleucine

The FDA’s Priority Review designation shortens the standard review timeline for therapies that may provide meaningful advances in treatment for serious diseases with unmet medical need. The designation does not indicate likely approval but reflects the agency’s assessment of potential clinical significance.

As noted, the current application is supported by data from the randomized, double-blind, placebo-controlled crossover phase 3 IB1001-303 trial. Findings from the study indicated that treatment with the agent was associated with statistically significant improvement on the change in Scale for the Assessment and Rating of Ataxia (SARA) score, the primary end point, compared with placebo (−1.92 vs −0.14; between-group difference, −1.88; P <.001).³

Levacetylleucine-treated patients also demonstrated statistically significant improvements on the International Cooperative Ataxia Rating Scale (mean change, −4.22 vs −1.69; P = .003) and the Investigator’s Clinical Global Impression of Improvement (mean change, −0.6 vs −0.2; P = .02) compared with placebo, meeting the trial’s secondary endpoint.

In addition to meeting both primary and secondary endpoints, the study revealed that treatment with levacetylleucine led to improvements across measures assessing neurologic function and disease-related impairment in A-T.³ Furthermore, Levacetylleucine was reported to be generally well tolerated, with no treatment-related serious adverse events observed during the study period.¹ Longer-term safety outcomes remain uncertain.

Additional context supporting the phase 3 evaluation of levacetylleucine comes from late-breaking findings presented at the 2025 International Congress of Parkinson’s Disease and Movement Disorders (MDS), held October 5–9 in Honolulu, Hawaii. The data were derived from an extension of the phase 2 IB1001-203 trial (NCT03759678), which enrolled patients aged 6 years and older with ataxia-telangiectasia (A-T).⁴ Patients who completed the parent study were eligible to continue into an extension phase, with 12 participants aged 6 to 36 years remaining on levacetylleucine treatment.

The primary endpoint of the extension study assessed change in SARA scores from baseline through the first year of treatment, while exploratory analyses evaluated changes during a treatment washout period and outcomes after a second year of continued therapy.

At 12 months, patients experienced a mean reduction of 2.25 points in SARA score from baseline (SD, 3.16; 95% CI, −4.25 to −0.25; P = .031), suggesting improvement in ataxia-related symptoms. During the subsequent washout period, participants (n = 11) showed a mean increase of 1.36 points in SARA score (SD, 2.04; 95% CI, 0–2.73; P = .25), indicating potential worsening after treatment discontinuation. Among the 7 patients who completed an additional year of therapy following washout, the mean SARA score change was −0.33 points relative to the beginning of the extension phase.⁴

Drug Background: Existing Approval in Niemann-Pick Disease Type C

Levacetylleucine is already marketed in the United States as AQNEURSA following FDA approval in 2024 for treatment of neurologic manifestations associated with Niemann-Pick disease type C (NPC) in adults and pediatric patients weighing at least 15 kg.⁷ Previous coverage characterized the approval as the first stand-alone therapy specifically approved for NPC.⁸

The prior approval provides regulators with an established safety database that may inform review of the pending A-T indication expansion. Levacetylleucine is believed to modulate neuronal metabolism and cerebellar function, although its precise mechanism of action remains incompletely understood. Known adverse reactions in the approved NPC indication include abdominal pain, vomiting, dysphagia, and upper respiratory tract infections.⁷

READ MORE: FDA Approves Stand-Alone Therapy Levacetylleucine for Niemann-Pick Disease Type C

Unmet Need in Ataxia-Telangiectasia

A-T is an autosomal recessive disorder caused by pathogenic variants in the ATM gene and is estimated to affect approximately 1 in 40,000 to 100,000 individuals worldwide.² Neurologic manifestations typically emerge in early childhood and progressively worsen over time, leading to gait impairment, dysarthria, abnormal eye movements, and eventual loss of ambulation.

Beyond neurologic decline, patients often experience recurrent respiratory infections, pulmonary complications, immune dysfunction, and markedly elevated lifetime cancer risk.² Management currently relies on supportive interventions, rehabilitation strategies, and treatment of complications, as no FDA-approved pharmacologic therapies exist specifically for A-T.^2,6

The absence of approved treatments has left a substantial unmet need, making even symptomatic improvements clinically relevant if durable and reproducible across disease stages.

Limitations and Next Steps

Available evidence supporting the application remains largely derived from sponsor communications and secondary reporting rather than peer-reviewed publication.^1,6 Consequently, independent assessment of efficacy and safety is limited.

The FDA is expected to complete review by September 19, 2026.¹ Approval would establish AQNEURSA as the first therapy specifically indicated for ataxia-telangiectasia in the United States.

References
1. IntraBio Inc. FDA accepts sNDA and grants Priority Review to AQNEURSA for Ataxia-Telangiectasia. News release. Published May 2026. Accessed May 20, 2026. https://www.businesswire.com/news/home/
2. Rothblum-Oviatt C, Wright J, Lefton-Greif MA, et al. Ataxia telangiectasia: a review. Orphanet J Rare Dis. 2016;11:159. https://ojrd.biomedcentral.com/articles/10.1186/s13023-016-0543-7
3. IntraBio Announces Positive Pivotal Trial Results of Levacetylleucine for the Treatment of Ataxia-Telangiectasia. News release. IntraBio. January 21, 2026. Accessed March 20, 2026. https://www.businesswire.com/news/home/20260121091020/en/IntraBio-Announces-Positive-Pivotal-Trial-Results-of-Levacetylleucine-for-the-Treatment-of-Ataxia-Telangiectasia
4. Patterson M, Zanrucha B, Raymond J, et al. N-acetyl-L-leucine: Findings from the Extension Phase of a Phase II Clinical Trial in Ataxia-Telangiectasia. Presented at: 2025 MDS Congress; October 5-9; Honolulu, Hawaii. LBA-4.
5. FDA. Priority Review. Accessed May 20, 2026. https://www.fda.gov/patients/fast-track-breakthrough-therapy-accelerated-approval-priority-review/priority-review
6. [GeneReviews] Ataxia-Telangiectasia. Updated 2023. Accessed May 20, 2026. https://www.ncbi.nlm.nih.gov/books/NBK26468/
7. FDA approves new drug to treat Niemann-Pick disease type C. FDA news release. Published September 24, 2024. Accessed May 20, 2026. https://www.fda.gov/news-events/press-announcements/fda-approves-new-drug-treat-niemann-pick-disease-type-c
8. FDA approves stand-alone therapy levacetylleucine for Niemann-Pick disease type C. NeurologyLive. Accessed May 20, 2026. https://www.neurologylive.com/view/fda-approves-stand-alone-thearpy-levacetylleucine-niemann-pick-disease-type-c