Huntington disease (HD) is a autosomal dominant neurodegenerative disease caused by expansion of a trinucleotide repeat (cytosine, adenine, and guanine [CAG]) on the short arm of chromosome four. Average age of motor diagnosis is 39 years, and age at diagnosis is associated with the length of the CAG mutation. The prodrome of HD can be recognized 15 years prior to motor diagnosis and is characterized by subtle impairments in emotional recognition, smell identification, speed of processing, time estimation and production, and psychiatric abnormalities. HD shows particular vulnerability of the medium spiny neuron in the basal ganglia. Progressive brain dysfunction and neuron death lead to insidious loss of function in motor, cognitive, and behavioral control over 34 years (17 prodromal and 17 post-diagnosis). Treatment plans rely on genetic counseling, psychiatric symptom treatment as needed, physical therapy, and environmental modifications. There are two treatments for the reduction of chorea, but there are no disease-modifying therapies. Experimental therapeutics are rapidly emerging with multiple and various targets, however, and gene therapies to silence the mutant HD gene are currently ongoing. This chapter reviews clinical and neuropathological descriptions of HD and discusses potential underlying mechanisms and animal models, diagnostic and clinical assessments used to characterize and track the disease, treatment planning, and challenges for research to advance care.
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