Study of Memantine to Treat Huntington's Disease

Inclusion Criteria:

• Men or women aged 18 or older.
• Diagnosis of HD with current complaints of memory or concentration difficulties.
• Dementia Rating Scale score of <129, to ensure that patients have sufficient cognitive impairment.
• Adequate visual and auditory acuity to allow neuropsychological testing.
• Good general health with no additional diseases expected to interfere with the study.
• Patient is not institutionalized.
• Sufficient English skills to complete all testing without assistance of an English language interpreter.
• Availability of a responsible caregiver who agrees to supervise administration of study drug, monitor the patient's compliance and adverse events, and accompany the patient to all clinic visits.

Exclusion Criteria:

• 1. Any significant neurologic disease other than HD.
• Severe psychotic features or other severe psychiatric problems within the last three months which could lead to difficulty complying with the protocol.
• History of alcohol or substance abuse within the past two years (DSM IV criteria).
• Any significant systemic illness or unstable medical condition which could lead to difficulty complying with the protocol.
• History of MI in the past year or head trauma with loss of consciousness greater than 20 minutes.
• Insulin-requiring diabetes.
• Use of any FDA approved cognitive enhancing prescription medications or investigational drugs within 30 days.
• Use of ginkgo biloba or DHEA within four weeks prior to baseline.
• Use of narcotic analgesics within 4 weeks prior to baseline.
• Patients who, in the investigator's opinion, would not comply with study procedures.