This study is a randomized, double-blind, placebo-controlled study which will be conducted in approximately 75 early manifest HD participants.~After screening and baseline assessments are completed, participants will enter the Core Treatment Period which is double-blinded and placebo-controlled. The Core Treatment Period includes a Dose Range Finding (DRF) period of 17 weeks, followed by a Blinded Extension period of up to 53 weeks. Three cohorts will be enrolled in the Core Treatment Period, and data from each cohort will be evaluated for efficacy and safety before proceeding to a new cohort with a higher dose. The Core Treatment Period will serve to evaluate the safety, tolerability, pharmacokinetic(s) (PK) and pharmacodynamic(s) (PD) and to find the best dose(s) to use in future studies.~After the dose(s) is determined at the end of the Core Treatment Period, participants will roll over into the Open Label Extension (OLE) and will be given branaplam for approximately 1 year and attend clinic visits every 4 weeks. At the end of the OLE, the study may be amended to provide open-label branaplam beyond 1 year or a separate extension study may be initiated.
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.