Pridopidine Phase 3 Study in Huntington's Disease

Inclusion Criteria: * Adult-onset HD (onset of signs and symptoms and a clinical diagnosis at ≥21 years of age). * A diagnosis based on clinical features and the presence of ≥40 CAG repeats in the huntingtin (HTT) gene confirmed by historical laboratory quanitified results or by a diagnostic test at Screening. * Diagnostic confidence level (DCL) of 4 (DCL=4 unequivocal motor signs, ≥99% confidence) on the standardized motor exam Total Motor Score (TMS). * Total Functional Capacity (TFC) score of ≥7 at Screening and Baseline. * Cytosine-Adenine-Guanine (CAG)-Age Product (CAP)100 score ≥95 at Screening. * Independence Scale (IS) score ≤90% at Screening. * Total Motor Score (TMS) of ≥20 at Screening and Baseline. * Not using ADMs (VMAT2i and neuroleptics/antipsychotics) for at least 6 months prior to Screening visit. Importantly, it is not encouraged to discontinue the participants' ADM treatment solely for enrollment in the current trial. Exclusion Criteria: * Clinically significant cardiovascular disease (e.g. QTcF \>450 msec \[males\] or \>470 msec \[females\], arrhythmias, uncontrolled atrial fibrillation, or congenital long QT syndrome), seizure history ≤5 years, significant neurological disorders (e.g. intracranial pathology or cerebrovascular events), active/recent malignancy (unless localized and resolved), or any serious or uncontrolled systemic disease (e.g. hepatic, renal, respiratory, endocrine, infectious \[HBV, HCV, HIV\], or psychiatric) that may pose safety risk or interfere with participation. * Severe hepatic or renal impairment. * Any mutant huntingtin (mHTT) lowering therapy in the past year. * Medications that prolong QT interval, taken within 4 weeks of the baseline visit. * Use of pridopidine within 6 weeks or 5 half-lives before the screening visit. * Previous participation in intracranial gene therapy study. * Laboratory values that fall outside of the central laboratory's reference range at Screening and are considered clinically significantly abnormal by the Investigator and affect the participant's suitability to participate in the study or put the participant at risk if he/she enters the study in the Investigator's opinion. * Female participants who are pregnant, planning to become pregnant or breastfeeding.