This is a Phase 3, randomized, double-blind, placebo-controlled study to evaluate the efficacy, safety, and tolerability of valbenazine in subjects with Huntington's Disease (HD). The study includes a 4-week screening period, an 8-week dose-adjustment period, a 4-week maintenance period, and a final study visit 2 weeks following the final dose of study drug. Approximately 120 adult male and female subjects with motor manifest HD (a type of HD that causes uncontrolled movements and balance issues) and a genetic diagnosis of HD will be enrolled.
Study drug will be self-administered (in the presence of the subject's caregiver, if applicable) once daily (qd), preferably in the morning but before 1800 hours, beginning on Day 1. Study drug should be administered at approximately the same time each day during the study. Valbenazine will be supplied as orally administered capsules containing 20 or 40 mg of valbenazine. Subjects must swallow the capsules with approximately 4 ounces of water or other liquid, with or without food.