Safety and efficacy of levacetylleucine in ataxia-telangiectasia: a phase 3, randomised, double-blind, placebo-controlled crossover trial

BACKGROUND: Ataxia-telangiectasia is a rare, autosomal recessive neurodegenerative disorder. Levacetylleucine (N-acetyl-L-leucine) has been shown to be efficacious for the treatment of neurological manifestations and to have a disease-modifying effect in lysosomal storage disorders such as Niemann-Pick disease type C. We aimed to assess the safety and efficacy of levacetylleucine for paediatric and adult patients with ataxia-telangiectasia. METHODS: In this phase 3, randomised, double-blind, placebo-controlled crossover trial, participants were enrolled across ten research hospitals in Germany, Slovakia, Spain, Switzerland, the UK, and the USA. Eligible patients aged 4 years or older with genetically confirmed ataxia-telangiectasia were randomly assigned (1:1) using interactive response technology to receive two or three times daily orally administered levacetylleucine or a matching placebo over two consecutive 12-week treatment periods (patients weighing 35 kg or more received 4 g per day of orally administered levacetylleucine or a matching placebo three times per day and patients weighing less than 35 kg received weight-tiered doses two or three times per day based on approximately 0·1 g/kg per day). All participants, investigators, and assessors were blinded to group assignment. The primary outcome was the mean change on the Scale for the Assessment and Rating of Ataxia (SARA), assessed at baseline and at the end of each 12-week treatment period of levacetylleucine or placebo. Safety and efficacy analyses were done in all randomly assigned patients who received at least one dose of study medication, and a linear mixed-effects model was used to account for data missing at random. The trial is registered with ClinicalTrials.gov, NCT06673056, and CTIS, 2024-517706-29; the open-label extension phase is ongoing. FINDINGS: Between March 18, 2025 and June 30, 2025, 77 participants with a genetically confirmed diagnosis of ataxia-telangiectasia were screened for inclusion. Four patients were excluded (not meeting inclusion criteria) and 73 were enrolled and randomly assigned (36 to levacetylleucine followed by placebo and 37 to placebo followed by levacetylleucine. 73 patients were included in the primary analysis and safety sets. 38 (52%) of 73 patients were female and 35 (48%) were male; 55 (75%) of 73 patients were White. 47 (64%) of 73 were younger than 18 years and 26 (36%) were aged 18 years or older. The mean change in the SARA total score with levacetylleucine was -1·92 (SD 2·81) versus -0·14 (2·38) with placebo (linear mixed model treatment effect -1·88 SD 0·41, 95% CI -2·70 to -1·06; p<0·0001). 54 adverse events occurred in 29 patients receiving levacetylleucine versus 75 events in 25 patients receiving placebo. No treatment-related serious adverse events or deaths occurred. INTERPRETATION: Levacetylleucine showed a significant and clinically meaningful improvement in functioning and was safe and well-tolerated, providing a favourable benefit-risk profile for the treatment of ataxia-telangiectasia. An ongoing open-label extension phase of this trial will investigate potential long-term, neuroprotective and disease-modifying effects. FUNDING: IntraBio.