Longitudinal cognitive and motor changes among presymptomatic Huntington disease gene carriers.

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Abstract
HUNTINGTON disease (HD) is an autosomal-dominant, neurodegenerative disorder characterized neuropathologically by the loss of medium-sized spiny neurons in the neostriatum and clinically by a triad of progressive motor, cognitive, and emotional symptoms. The HD phenotype is caused by an increased number of triplet (CAG) repeats in the 5‘-translated region of the HD gene on chromosome 4.1 Typically, individuals with HD have 38 or more CAG repeats. A negative correlation between the number of CAG repeats and age at onset of HD has been found, with individuals with juvenile HD having the largest number of repeats (>55).1,2 The clinical implication of an allele with 32 to 37 repeats is ambiguous. These repeat sizes are often considered intermediate alleles with variable penetrance.