Cognitive deficits in Huntington's disease
This thesis presents and discusses the pattern of neuropsychological deficits in subjects affected by Huntington's Disease. Dysfunction is assessed in the area of general intelligence, as measured by the WAIS-R, in mnestic tasks, in visuospatial and motoric tasks and in skills associated with frontal lobe pathology. Affected subjects are compared with controls, individually matched for age, sex and years of education. Cognitive deficits in the at-risk population are also discussed and a comparison made between at-risk gene carriers and their non affected siblings. Findings from the WAIS-R demonstrated severe intellectual impairment, with affected subjects achieving significantly lower scores than their individually matched controls on all three IQ measures. The assessment of premorbid intelligence demonstrated that NART performance in Huntington's Disease declines. It is suggested that demographic variables may provide a more suitable method for predicting premorbid ability in this subject group. Investigation of mnestic skills in affected subjects indicated impairment on a wide range of tasks, including those assessing memory for verbal, numerical, spatial and pictorial information. The thesis also considers implicit memory systems in Huntington's Disease and a dissociation is noted, with intact implicit memory for verbal material and impairment of skill learning. The presence of cognitive deficits resembling those seen in frontal lobe damaged patients is also apparent. Affected subjects demonstrate severe impairment on the Modified Wisconsin Card Sorting Test, assessment of Verbal Fluency and the Cognitive Estimation Task, all tasks which rely on Supervisory Attentional System integrity. Visuospatial and motor functioning are shown to be severely compromised in Huntington's Disease and high correlations between tests of voluntary movement and assessment of cognitive ability are presented. The Comparison of at-risk gene carriers and non gene carriers indicated that although overall at-risk gene carriers performed more poorly than non gene carriers no one cognitive test significantly reflected this difference.