Three-year extension data from the phase 3 IB1001-301 trial show levacetylleucine slowed disease progression in both adults and children with Niemann-Pick disease type C.
Long-term follow-up from the phase 3 trial of levacetylleucine (Aqneursa) found that adults and children with Niemann-Pick disease type C (NPC) who stayed on treatment for 36 months continued to show less disease progression than would be expected based on the condition's natural course. Investigators presented the findings at the 2026 Child Neurology Society (CNS) Annual Meeting in Montreal, Quebec, Canada.1
The analysis was led by Marc C. Patterson, MD, FRACP, FAAN, FANA, professor of neurology, pediatrics, and medical genetics at
The data come from the ongoing Extension Phase (EP) of IB1001-301, a phase 3, double-blind, placebo-controlled crossover trial that also included a separate Parent Study. The EP follow-up analysis evaluated outcomes in participants ages 18 and older and those younger than 18 separately, using the modified 5-domain NPC Clinical Severity Scale (5-D-NPC-CSS) as the primary endpoint.
Additionally, the 15-domain and 4-domain NPC-CSS and the Scale for the Assessment and Rating of Ataxia served as exploratory endpoints. Results were compared with the expected annual trajectory of decline modeled from published natural history data on untreated NPC.
Thirty-nine participants, 22 adults and 17 children, completed the 36-month EP visit. Their mean baseline 5-D-NPC-CSS score was 10.38 (SD 4.46). After 36 months, the full cohort's mean change from baseline was -0.28 (SD 2.76) with levacetylleucine, compared with an expected worsening of +4.50 (SD 9.48) in the historical comparator, a mean difference of -4.78 points (95% CI, -7.96 to -1.61; P =.0037).
Adults had a mean change of -0.18 (SD 2.32), and pediatric participants had a mean change of -0.41 (SD 3.32); exploratory endpoint findings were described as supportive of the primary result. Levacetylleucine was reported as well tolerated, with no serious adverse events.1
These extension data build on IB1001-301's randomized, double-blind, placebo-controlled Parent Study, which enrolled 60 patients with NPC ages 4 and older and found a treatment difference of -0.4 points (95% CI, -0.7 to -0.2; P <.001) on the functional Scale for the Assessment and Rating of Ataxia (fSARA) versus placebo, with benefits apparent within 12 weeks. Based on those results, the FDA approved levacetylleucine in September 2024 for neurological manifestations of NPC in adults and pediatric patients weighing at least 15 kg, making it the first FDA-approved stand-alone therapy for the disease.2,3
A separate 12-month open-label extension analysis, published in 2025, similarly reported disease stabilization on the 5-D-NPC-CSS relative to the natural history comparator, consistent with the longer-term data now reported at 36 months.4
Levacetylleucine's use has since broadened beyond NPC. In September 2026, the
