Risperidone for the Treatment of Huntington's Disease Involuntary Movements

Inclusion Criteria: * Manifest HD (Diagnostic Confidence Level 4 + CAG repeat ≥ 37 or family history of HD) * UHDRS Total Maximal Chorea (TMC) ≥ 8 * UHDRS Total Functional Capacity ≥ 5 * Subject willing and able to provide written informed consent OR legally authorized representative provides written informed consent and subject provides assent\* * Between 18 and 65 years of age Exclusion Criteria: * Use of antipsychotic, levodopa, dopamine agonist, monoamine oxidase inhibitor or other disallowed medication in the 30 days prior to the baseline visit (see Section 4.2.5)\* * Prior non-response to risperidone or intolerability to risperidone (in the investigator's opinion) * Allergy or hypersensitivity to risperidone * Dysphagia that in the investigator's opinion would preclude participation in the study * Active suicidal ideation or psychiatric condition that in the investigator's opinion would preclude study participation * QTc \> 460 msec for women and QTc \> 450 msec for men on 12-lead EKG * History of cardiac arrhythmia or congenital long QT syndrome * Significant renal impairment (creatinine clearance \< 30 mL/min as estimated by the Cockgroft-Gault formula) or hepatic impairment (AST or ALT \> 2.5 times upper limit of normal OR alkaline phosphatase or total bilirubin \> 2 times upper limit of normal) * Active drug or alcohol abuse or dependence * Pregnant or breast-feeding * Any contraindication to MRI (e.g. pacemakers, aneurysm clips, metallic prostheses, shrapnel fra…