A Multicenter, Multinational, Randomized, Double Blind, Placebo Controlled, Parallel Group Study to Evaluate the Efficacy and Safety of Laquinimod (0.5, 1.0 and 1.5 mg/day) as Treatment in Patients with Huntington's Disease

Patients may be included in the study if they meet all of the following criteria: ;a. Documentation of prior positive genetic testing for HD, or a clinical diagnosis of symptomatic HD (Diagnostic Confidence Level 4).;b. Presence of 36-49 CAG repeats, inclusive, in the huntington gene based on centralized CAG testing during screening;c. Male or female between 21-55 years of age, inclusive, with an onset of HD at or after 18 years of age;d. Women of child-bearing potential (women who are not post menopausal or who have undergone surgical sterilization) must practice an acceptable method of birth control for 30 days before taking the study treatment, and 2 acceptable methods of birth control during all study duration and until 30 days after the last dose of treatment was administered. Acceptable methods of birth control in this study include: Intrauterine device, barrier method (condom or diaphragm with spermicide) and hormonal methods of birth control (e.g., oral contraceptive, contraceptive patch, long-acting injectable contraceptive) ;e. A sum of > 5 points on the UHDRS TMS at the screening visit;f. UHDRS- TFC >= 8 at the screening visit;g. Able and willing to provide written informed consent prior to any study related procedure being performed at the screening visit. Patients with a legal guardian should be consented according to local requirements;h. Willing to provide a blood sample for genomic CAG analysis at the screening visit;i. Willing and able to take oral medication and able to comply with the study specific procedures ;j. Ambulatory, being able to travel to the study centre, and judged by the investigator as likely to be able to continue to travel for the duration of the study ;k. Availability and willingness of a caregiver, informant, or family member to provide input at study visits assessing CIBIC Plus, CDR-SB, PBA-s,and HD QoL. A caregiver is recommended to be someone who attends to the patient at least 2 to 3 times per week for at least 3 hours per occasion, and the suitability of the caregiver should be judged by the investigator;l. For patients taking allowed antidepressant medication, the dosing of medication must have been kept constant for at least 30 days before baseline and must be kept constant during the study

Patients are excluded from participating in this study if 1 or more of the following criteria are met: ;a. Use of immunosuppressive agents, or cytotoxic agents, including cyclophosphamide and azathioprine within 12 months prior to screening;b. Previous use of laquinimod;c. Use of moderate/strong inhibitors of cytochrome P450 (CYP)3A4 within 2 weeks prior to randomization;d. Use of inducers of CYP3A4 within 2 weeks prior to randomization;e. Pregnant or breastfeeding;f. Serum levels >=2x upper limit of the normal range (ULN) of either alanine aminotransferase (ALT) or aspartate aminotransferase (AST) at screening ;g. Serum direct bilirubin which is >=1.5xULN at screening ;h. Estimated creatinine clearance < 60 mL/min at screening, calculated using the Cockcroft Gault equation: (140 - age) × mass (kg) × [0.85 if female] / 72 × serum creatinine (mg/dL) ;i. Subjects with a clinically significant or unstable medical or surgical condition that may put the patient at risk when participating in the study or may influence the results of the study or affect the patient's ability to take part in the study, as determined by medical history, physical examinations, ECG, or laboratory tests. Such conditions may include: ;1. A major cardiovascular event (e.g. myocardial infarction, acute coronary syndrome, de-compensated congestive heart failure, pulmonary embolism, coronary revascularization, angina) that occurred prior to randomization ;2. Significant cardiovascular risk factors (such as, but not limited to, uncontrolled hypertension, uncontrolled diabetes), per investigator discretion.;3. Any acute pulmonary disorder ;4. A central nervous system (CNS) disorder other than HD that may jeopardize the subject's participation in the study, including such disorders that are demonstrated on the baseline magnetic resonance imaging (MRI) (based on local read) ;5. A gastrointestinal disorder that may affect the absorption of study medication ;6. Acute or chronic renal disease including acute kidney injury (AKI).;7. Any form of acute or chronic liver disease.;8. Known human immunodeficiency virus (HIV) positive status. Patients will undergo an HIV test at screening per local requirements, if applicable ;9. Any malignancies, excluding basal cell carcinoma, in the 5 years prior to randomization ;j. Any clinically significant, abnormal, screening laboratory result which in the opinion of the investigator, affects the patients* suitability for the study or puts the patient at risk if he/she enters the study;k. Unsuitable for MRI (e.g., claustrophobia, metal implants);l. Alcohol and/or drug abuse within the 12 months prior to screening, as defined by Diagnostic and Statistical Manual of Mental Disorders - Fourth Edition Text Revision (DSM IV TR) criteria for substance abuse. For former alcohol and/or drug abusers, the abstinence should be confirmed by laboratory tests (drug testing and/or carbohydrate deficient transferrin (CDT) level in blood).;m. Patients with active suicidal ideation during the past month as measured by a most severe suicide ideation score of 4 (Active Suicidal Ideation with Some Intent to Act, without Specific Plan) or 5 (Active Suicidal Ideation with Specific Plan and Intent) on the baseline screening Columbia-Suicide Severity Rating Scale (C-SSRS) or subjects who answer *Yes* on any of the 5 C-SSRS Suicidal Behavior Items (actual attempt, interrupted attempt, aborted attempt, preparatory acts, or behavior) if the attempt or acts were performed within 1 year of screening, or subjects who, in the opinion of the investigator, present a serious risk of suicide;n. Patients with known intracranial neoplasms, vascular malformations, or intracranial hemorrhage;o. Known drug hypersensitivity that would preclude administration of laquinimod or placebo, such as hypersensitivity to mannitol, meglumine or sodium stearyl fumarate;p. Swallowing difficulties that would preclude administration of laquinimod or placebo capsules;q. Treatment with any investigational product within 30 days of screening or patients planning to participate in another clinical study assessing any investigational product during the study. Patients in non-interventional and/or observational studies will not be excluded from participating in this study;r. Treatment with tetrabenazine within 30 days of the study baseline visit;s. Treatment with antipsychotic medication within 30 days of the study baseline visit