Overview
Disease Pattern and Mechanism
Huntington disease (HD) is an autosomal dominant neurodegenerative disorder caused by expansion of a CAG trinucleotide repeat in the HTT gene on chromosome 4p16.3.
CNPLE
CNPLE
Huntington disease (HD) is an autosomal dominant neurodegenerative disorder caused by expansion of a CAG trinucleotide repeat in the HTT gene on chromosome 4p16.3. The expansion lengthens a polyglutamine tract in mutant huntingtin, making the protein prone to abnormal folding and aggregation. Neurons are progressively damaged, particularly in the striatum—the caudate nucleus and putamen—so basal ganglia circuits lose their ability to regulate movement smoothly. The clinical picture is classically a combination of motor impairment, cognitive decline, and psychiatric disturbance. Chorea is the most recognizable motor feature: irregular, flowing, involuntary movements that may initially look like restlessness or poor coordination. As striatal injury progresses, the patient may develop dystonia, impaired postural control, rigidity, bradykinesia, and akinesia. Cognitive changes affect judgement, planning, attention, and the ability to manage daily tasks. Depression, irritability, impulsivity, anxiety, psychosis, and suicidal thinking may occur before or after obvious motor symptoms. CAG-repeat length helps estimate penetrance and likely age of onset: - 26 or fewer repeats: normal range. - 27–35 repeats: intermediate allele. The individual is not expected to develop HD from this allele, but it may...
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