High Quality Content by WIKIPEDIA articles! Huntington`s disease, chorea, or disorder (HD), is a neurodegenerative genetic disorder that affects muscle coordination and leads to cognitive decline and dementia. It typically becomes noticeable in middle age. HD is the most common genetic cause of abnormal involuntary writhing movements called chorea. It is much more common in people of Western European descent than in those of Asian or African ancestry. The disease is caused by an autosomal dominant mutation on either of an individual`s two copies of a gene called Huntingtin, which means any child of an affected parent has a 50% risk of inheriting the disease. In the rare situations where both parents have an affected copy, the risk increases to 75%, and when either parent has two affected copies, the risk is 100% (all children will be affected). Physical symptoms of Huntington`s disease can begin at any age from infancy to old age, but usually begin between 35 and 44 years of age. About 6% of cases start before the age of 21 years with an akinetic-rigid syndrome; they progress faster and vary slightly. The variant is classified as juvenile, akinetic-rigid or Westphal variant HD.