A Dose Range Finding Study With Open-Label Extension to Evaluate the Safety of Oral LMI070/Branaplam in Early Manifest Huntington's Disease

This is the first study of branaplam in adults with Huntington's Disease (HD) to determine the correct dose required to lower mutant huntingtin protein (mHTT) levels in the cerebrospinal fluid (CSF) to a degree expected to be efficacious over longer periods of time.

This study was a randomized, double-blind, placebo-controlled study with a variable duration (between approximately 17 weeks to approximately 53 weeks) for the core period and a one-year open label extension (OLE) in early-stage manifest Huntington's disease (HD) participants. After screening period and baseline assessments, the following two Treatment Periods were planned: • The core period consisted of a 17-week double-blind, placebo-controlled, Dose Range Finding (DRF) portion of the study, followed by a blinded extension (BE) of variable duration (up to approximately 53 weeks). The DRF Period was to evaluate the safety, tolerability, pharmacokinetivs (PK) and pharmacodynamics (PD) of branaplam, as well as determine the optimal dose(s) to explore in further clinical evaluations. The core period was planned to consist of 3 treatment arms: * Cohort 1: Treatment Arm A: branaplam 56 mg oral solution or matching placebo, once weekly * Cohort 2: Treatment Arm B: branaplam 112 mg oral solution or matching placebo, once weekly * Cohort 3: Treatment Arm C: branaplam 154 mg oral solution or matching placebo, once weekly or Treatment Arm X: branaplam 84 mg oral solution or matching placebo, once weekly or Treatment Arm Y: branaplam 28 mg oral solution or matching placebo, once weekly • The OLE was a one-year open-label extension to assess both long-term safety and tolerability, as well as the efficacy of the recommended optimal dose(s) for branaplam. Due to safety concerns an urgent safety measure (USM) follow-up notification dated 06-Dec-2022 was issued to permanently discontinue the study treatment in all participants. At that point, only cohort 1 was enrolled. Therefore, only cohort 1 data is available for analysis (Treatment Arm A: branaplam 56 mg oral solution or matching placebo, once weekly). Participants who received active treatment (branaplam) were to remain in the study for follow-up for approximately one year following initial treatment discontinuation. The OLE part was not opened.