Cognitive manifestations of Huntington disease in relation to genetic structure and clinical onset

Objective: To examine the cognitive manifestations of Huntington disease (HD) with respect to age, clinical onset, progression, and genetic analyses. Design: Case series of people with HD or at risk (AR) for HD. Setting: Movement disorders and medical genetics clinics. Participants: Volunteer sample of 50 patients with HD and 127 AR adults. Measures: Neuropsychological evaluation was conducted with multiple measures of cognitive function (intelligence, memory, attention, executive, spatial, language), strength, manual speed/dexterity, somatosensory function, and mood. Quantitative molecular genetic analysis by means of polymerase chain reaction was conducted on 31 patients with HD and 86 AR subjects. Results: In clinical HD, cognitive impairment correlated with number of years affected but not age at onset. The linear regression had a negative intercept, suggesting impaired cognitive function by the time of onset. In AR gene carriers, lower cognitive performance correlated with more trinucleotide repeats. In clinical HD, trinucleotide repeats interacted with disease chronicity such that more repeats were associated with worse performance over time; the overall effect of this was small compared with the effect of disease chronicity alone. Except for one AR Subject, mood state was not associated with cognitive performance in either patients with HD or AR subjects. Conclusions: Cognitive decline appears to start before clinical onset of HD and is correlated with the number of trinucleotide repeats. Subsequent cognitive decline is primarily a function of number of years affected, although there is evidence that the presence of more trinucleotide repeats is associated with faster deterioration.