Huntington’s disease 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 follows. 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.
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. TheHuntingtin 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.
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