A Study of Pridopidine (ACR16) for the Treatment of Participants With Huntington's Disease

Inclusion Criteria

• Able to provide written Informed Consent prior to any study related procedure, including consent to genotyping of the CYP2D6 gene.
• Clinical features of HD, and a positive family history and/or the presence of ≥ 36 CAG repeats in the Huntington gene.
• Male or female age ≥ 30 years.
• Willing and able to take oral medication and to comply with the study specific procedures.
• Ambulatory, being able to travel to the assessment center, and judged by the Investigator as likely to be able to continue to travel for the duration of the study.
• Availability of a caregiver or family member to accompany the participant to two visits.
• A sum of ≥ 10 points on the mMS at the screening visit.
• For participants taking allowed antidepressants or other psychotropic medication , the dosing of medication must have been kept constant for at least 6 weeks before baseline visit.

Exclusion Criteria

• Treatment with any antipsychotic medication (neuroleptics) within 8 weeks of baseline visit, or at any time point during the study period.
• Use of tetrabenazine within 12 weeks of baseline visit, or at any time during the study period.
• Treatment with any investigational product within 4 weeks of baseline visit.
• Use of tricyclic antidepressants or class I antiarrhythmics within 6 weeks of baseline visit, or at any time during the study period.
• Use of concomitant medication that may lower the seizure threshold within 6 weeks of baseline visit, or at any time during the study period .
• Use of metoclopramide within 12 weeks of baseline visit, or at any time during the study period.
• Participants currently receiving deep brain stimulation (DBS).
• Participants with a history of surgical procedures aiming to improve the symptoms of Huntington disease, such as neural transplantations, lesions of the central nervous system, infusions of neurotrophic agents or previous attempts of deep brain stimulation.
• Participants previously randomized into this study.
• A prolonged QTc interval at Screening Visit (defined as a QTc interval of > 450 milliseconds [msec] for males or > 470 msec for females), or other clinically significant heart conditions as judged by the investigator.
• Creatinine clearance <40 milliliters (mL)/minute (min) as measured at the screening visit.
• Any clinically significant, abnormal, baseline laboratory result which in the opinion of the Investigator, affects the participant' suitability for the study or puts the participant at risk if he/she enters the study.
• Clinically significant hepatic or renal impairment.
• Participants with a known history of epilepsy or a history of febrile seizure(s) or seizure(s) of unknown cause.
• Severe intercurrent illness, which, in the opinion of the Investigator, may put the participant at risk when participating in the trial or may influence the results of the trial or affect the subjects' ability to take part in the trial.
• Alcohol and/or drug abuse as defined by Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision (DSM IV-TR) criteria for Substance Abuse - this includes the illicit use of cannabis within the last 12 months prior to Screening Visit
• Participants with suicidal ideation as defined as a positive score on criteria for major depressive episode, item A9 on the DSM -IV-TR criteria for a Major Depressive Episode
• Females who are pregnant or lactating or who intend to become pregnant during the study period.
• Females who are of child bearing potential and not taking adequate contraceptive precautions are excluded from the trial. (Females of childbearing potential taking acceptable contraceptive precautions can be included)
• Known allergy to any ingredients of the trial medication or placebo
• Any previous participation in a clinical study with ACR16.