Huntington’s disease (HD) is a neurodegenerative genetic disorder that affects muscle coordination and leads to cognitive decline and psychiatric problems. It typically becomes noticeable in mid-adult life. HD is the most common genetic cause of abnormal involuntary writhing movements called chorea, which is why the disease used to be called Huntington’s chorea. The disease is caused by an autosomal dominant mutation in either of an individual’s two copies of a gene called Huntingtin, which means any child of an affected person typically has a 50% chance of inheriting the disease. 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.