   huntington's disease (hd) is a neurodegenerative genetic disorder that affects muscle coordination and leads to cognitive decline and behavioral symptoms. 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. it is much more common in people of western european descent than in those of asian or african ancestry. the disease can affect both men and women. 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 hd can begin at any age from infancy to old age, but usually begin between 35 and 44 years of age. through genetic anticipation, the disease may develop earlier in life in each successive generation. 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. the huntingtin gene provides the genetic information for a protein that is also called "huntingtin". expansion of a cag (cytosine-adenine-guanine) triplet repeat stretch within the huntingtin gene results in a different (mutant) form of the protein, which gradually damages cells in the brain, through mechanisms that are not fully understood. the genetic basi
Autosomal_dominant_disorders Extrapyramidal_and_movement_disorders Genetic_disorders Huntington\'s_disease Systemic_atrophies_primarily_affecting_the_central_nervous_system Trinucleotide_repeat_disorders