Huntington's disease (HD): Everything You Need To Know

Huntington's disease (HD), also known as Huntington's chorea, is a neurodegenerative disease that is mostly inherited.[7] The earliest symptoms are often subtle problems with mood or mental abilities.[1] A general lack of coordination and an unsteady gait often follow.[2] It is also a basal ganglia disease causing a hyperkinetic movement disorder known as chorea.[8][9] As the disease advances, uncoordinated, involuntary body movements of chorea become more apparent.[1] Physical abilities gradually worsen until coordinated movement becomes difficult and the person is unable to talk.[1][2] Mental abilities generally decline into dementia.[3] The specific symptoms vary somewhat between people.[1] Symptoms usually begin between 30 and 50 years of age but can start at any age.[3][4] The disease may develop earlier in each successive generation.[1] About eight percent of cases start before the age of 20 years, and are known as juvenile HD, which typically present with the slow movement symptoms of Parkinson's disease rather than those of chorea.[3]

HD is typically inherited from an affected parent, who carries a mutation in the huntingtin gene (HTT).[4] However, up to 10% of cases are due to a new mutation.[1] The huntingtin gene provides the genetic information for huntingtin protein (Htt).[1] Expansion of CAG repeats of cytosine-adenine-guanine (known as a trinucleotide repeat expansion) in the gene coding for the huntingtin protein results in an abnormal mutant protein (mHtt), which gradually damages brain cells through a number of possible mechanisms.[7][10] Diagnosis is by genetic testing, which can be carried out at any time, regardless of whether or not symptoms are present.[5] 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.[2]

No cure for HD is known, and full-time care is required in the later stages.[2] Treatments can relieve some symptoms, and in some, improve quality of life.[3] The best evidence for treatment of the movement problems is with tetrabenazine.[3] HD affects about 4 to 15 in 100,000 people of European descent.[1][3] It is rare among Japanese, while the occurrence rate in Africa is unknown.[3] The disease affects men and women equally.[3] Complications such as pneumonia, heart disease, and physical injury from falls reduce life expectancy.[3] Suicide is the cause of death in about 9% of cases.[3] Death typically occurs 15–20 years from when the disease was first detected.[4]

The earliest known description of the disease was in 1841 by American physician Charles Oscar Waters.[11] The condition was described in further detail in 1872 by American physician George Huntington.[11] The genetic basis was discovered in 1993 by an international collaborative effort led by the Hereditary Disease Foundation.[12][13] Research and support organizations began forming in the late 1960s to increase public awareness, provide support for individuals and their families and promote research.[13][14] Research directions include determining the exact mechanism of the disease, improving animal models to aid with research, testing of medications and their delivery to treat symptoms or slow the progression of the disease, and studying procedures such as stem-cell therapy with the goal of replacing damaged or lost neurons.[12]
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