HD - Huntington's Disease

Huntington’s disease (HD) is characterized by choreiform movements, progressive dementia and psychiatric manifestations (depression, psychosis, etc.). Choreiform movements consist of involuntary, rapid, irregular, jerky motor actions including facial twitching or writhing and twitching of distal extremities, and later more generalized forms that may impair gait.

HD is an autosomal dominant inherited disease meaning that the child of an affected patient has a 50% chance of developing the disease. The causative gene is present on chromosome 4 and encodes a protein known as huntingtin. Gradually, this protein accumulates within brain cells causing damage and cell death in certain areas of the brain, namely the basal ganglia and the neocortex. The rate of huntingtin accumulation is associated with the number of repeats of a specific sequence of three nucleic acids (CAG repeats). A greater number of repeats is associated with an earlier disease onset (Imarisio et al., 2008).

HD is encountered throughout the world and in all ethnic groups. Global prevalence of HD is estimated to be four to five per one million people. In western countries it is estimated to be eight to ten per 100,000 people. There is no gender predominance. HD usually begins between the ages of 30 to 50 and leads to death 15 to 20 years after onset of neurological impairment. An early-onset variant exists (juvenile HD or Westphal variant) and typically begins in adolescence and with motor features, predominantly slowness of movement (bradykinesia) and increased muscular tone (rigidity type). It presents a more severe course with an average survival time of five to ten years. No effective cure for HD exists.