Huntington's disease (HD), also known as Huntington's chorea, is an inherited disorder that results in the death of brain cells. The earliest symptoms are often subtle problems with mood or mental abilities. A general lack of coordination and an unsteady gait often follow. As the disease advances, uncoordinated, jerky body movements become more apparent. Physical abilities gradually worsen until coordinated movement becomes difficult and the person is unable to talk. Mental abilities generally decline into dementia. The specific symptoms vary somewhat between people. Symptoms usually begin between 30 and 50 years of age but can start at any age. The disease may develop earlier in life in each successive generation. About eight percent of cases start before the age of 20 years and typically present with symptoms more like Parkinson's disease. People with HD often underestimate the degree of their problems.

HD is typically inherited, although up to 10% of cases are due to a new mutation. 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 CAG (cytosine-adenine-guanine) triplet repeats in the gene coding for the huntingtin protein results in an abnormal protein, which gradually damages cells in the brain through mechanisms that are not yet fully understood. Diagnosis is by genetic testing, which can be carried out at any time, regardless of whether or not symptoms are present. 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.

There is no cure for HD. Full-time care is required in the later stages of the disease. Treatments can relieve some symptoms and, in some, improve quality of life. The best evidence for treatment of the movement problems is with tetrabenazine. HD affects about 4 to 15 in 100,000 people of European descent. It is rare among Japanese, while the occurrence rate in Africa is unknown. The disease affects men and women equally. Complications such as pneumonia, heart disease, and physical injury from falls reduce life expectancy. Suicide is the cause of death in about 9% of cases. Death typically occurs 15–20 years from when the disease was first detected.

The first likely description of the disease was in 1841 by American physician Charles Oscar Waters. The condition was described in further detail in 1872 by American physician George Huntington. The genetic basis was discovered in 1993 by an international collaborative effort led by the Hereditary Disease Foundation. Research and support organizations began forming in the late 1960s to increase public awareness, provide support for individuals and their families and promote research. Current research directions include determining the exact mechanism of the disease, improving animal models to aid with research, testing of medications 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

Reported rates of behavioral symptoms in Huntington's disease

Symptoms of HD most 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 HD 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.

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Journal of Brain Research