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Huntington's disease (HD) is a neurodegenerative genetic disorder that affects muscle coordination and leads to mental decline and behavioral symptoms. Symptoms of the disease can vary between individuals and affected members of the same family, but usually progress predictably. The earliest symptoms are often subtle problems with mood or cognition. A general lack of coordination and an unsteady gait often follow. As the disease advances, uncoordinated, jerky body movements become more apparent, along with a decline in mental abilities and behavioral symptoms.〔 Physical abilities gradually worsen until coordinated movement becomes difficult. Mental abilities generally decline into dementia. Complications such as pneumonia, heart disease, and physical injury from falls reduce life expectancy to around twenty years from the point at which symptoms begin. Physical symptoms can begin at any age from infancy to old age, but usually begin between 35 and 44 years of age. 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. 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. This means a child of an affected person typically has a 50% chance of inheriting the disease. 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 form of the protein, which gradually damages cells in the brain, through mechanisms that are not fully understood. Genetic testing can be performed at any stage of development, even before the onset of symptoms. This fact raises several ethical debates: the age at which an individual is considered mature enough to choose testing; whether parents have the right to have their children tested; and managing confidentiality and disclosure of test results. Genetic counseling has developed to inform and aid individuals considering genetic testing and has become a model for other genetically dominant diseases. There is no cure for HD, and full-time care is required in the later stages of the disease. Existing pharmaceutical and non-drug treatments can relieve many of its symptoms. 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 genetic basis of HD was discovered in 1993 by an international collaborative effort spearheaded by the Hereditary Disease Foundation. Research and support organizations, first founded in the 1960s and increasing in number, work to increase public awareness, to provide support for individuals and their families, and to promote and facilitate research. Current research directions include determining the exact mechanism of the disease, improving animal models to expedite research, clinical trials of pharmaceuticals to treat symptoms or slow the progression of the disease, and studying procedures such as stem cell therapy with the goal of repairing damage caused by the disease. ==Signs and symptoms== Symptoms of Huntington's disease commonly become noticeable between the ages of 35 and 44 years, but they can begin at any age from infancy to old age. In the early stages, there are subtle changes in personality, cognition, and physical skills.〔 The physical symptoms are usually the first to be noticed, as cognitive and behavioral symptoms〔 are generally not severe enough to be recognized on their own at the earlier stages.〔 Almost everyone with Huntington's disease eventually exhibits similar physical symptoms, but the onset, progression and extent of cognitive and behavioral symptoms vary significantly between individuals. The most characteristic initial physical symptoms are jerky, random, and uncontrollable movements called chorea.〔 Chorea may be initially exhibited as general restlessness, small unintentionally initiated or uncompleted motions, lack of coordination, or slowed saccadic eye movements.〔 These minor motor abnormalities usually precede more obvious signs of motor dysfunction by at least three years.〔 The clear appearance of symptoms such as rigidity, writhing motions or abnormal posturing appear as the disorder progresses. These are signs that the system in the brain that is responsible for movement has been affected. Psychomotor functions become increasingly impaired, such that any action that requires muscle control is affected. Common consequences are physical instability, abnormal facial expression, and difficulties chewing, swallowing, and speaking.〔 Eating difficulties commonly cause weight loss and may lead to malnutrition. Sleep disturbances are also associated symptoms. Juvenile HD differs from these symptoms in that it generally progresses faster and chorea is exhibited briefly, if at all, with rigidity being the dominant symptom. Seizures are also a common symptom of this form of HD.〔 Cognitive abilities are progressively impaired.〔 Especially affected are executive functions which include planning, cognitive flexibility, abstract thinking, rule acquisition, initiation of appropriate actions, and inhibition of inappropriate actions.〔 As the disease progresses, memory deficits tend to appear. Reported impairments range from short-term memory deficits to long-term memory difficulties, including deficits in episodic (memory of one's life), procedural (memory of the body of how to perform an activity) and working memory.〔 Cognitive problems tend to worsen over time, ultimately leading to dementia.〔 This pattern of deficits has been called a subcortical dementia syndrome to distinguish it from the typical effects of cortical dementias e.g. Alzheimer's disease.〔 Reported neuropsychiatric manifestations are anxiety, depression, a reduced display of emotions (blunted affect), egocentrism, aggression, and compulsive behavior, the latter of which can cause or worsen addictions, including alcoholism, gambling, and hypersexuality. Difficulties in recognizing other people's negative expressions have also been observed.〔 The prevalence of these symptoms is highly variable between studies, with estimated rates for lifetime prevalence of psychiatric disorders between 33% and 76%.〔 For many sufferers and their families, these symptoms are among the most distressing aspects of the disease, often affecting daily functioning and constituting reason for institutionalization.〔 Suicidal thoughts and suicide attempts are more common than in the general population.〔 Often individuals have reduced awareness of chorea, cognitive and emotional impairments. Mutant Huntingtin is expressed throughout the body and associated with abnormalities in peripheral tissues that are directly caused by such expression outside the brain. These abnormalities include muscle atrophy, cardiac failure, impaired glucose tolerance, weight loss, osteoporosis, and testicular atrophy. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Huntington's disease」の詳細全文を読む スポンサード リンク
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