Intellectual functioning in Huntington's disease

This thesis examines selected aspects of intellectual functioning in Huntington’s Disease (HD) which is a rare, degenerative disease of the brain with onset in the presenium. It is viewed as a valuable ’model’ disease for the study of primary ’dementias'. Twenty adult patients with HD (HD Group) and twenty-two adult offspring "at- risk" (AR Group) were assessed twice over a 1-2 year interval on psychological measures from the Savage Cognitive Impairment Model (SCIM) and the Halstead-Reitan Approach (HR Approach) to the measurement of intellectual abilities, and on CT scans. The investigations examined: 1 . Level of Performance on the Psychological Measures 2. Changes over Time 3. Brain-Behaviour Relationships 4. The Structure of the Intellect in HD. 5. Psychological Measures for a Screening Battery. The results demonstrated that both the SCIM and the HR-Approach offer well standardised, valid and reliable measures of the intellectual abilities of patients with HD and of adult offspring 'at risk’ but with merits and demerits to each system. Patients with HD differed significantly from subjects ‘at risk’ and from normative standards in level of performance on almost all of the psychological measures. Over a 1-2 year interval there were qualitative and quantitative differences in group mean scores for the HD and AR groups. Atrophy/intellect relationships were examined using discriminant function analyses and the psychological measures predicted degree of general cortical atrophy and caudate nucleus atrophy at 97.3% and 86.4% accuracy levels respectively. SCIM measures predicted diagnostic group (HD or AR Group) at 97.2% accuracy whilst the Category Test and Sensory Perceptual Exam scores together, were 100% accurate. Factor analytic methods were used to examine structural aspects of the intellect and results lent strong support to the theories of Savage et al. (1973) regarding the nature and structure of the intellect in normal and clinical groups. The findings are evaluated against theories about the nature and etiology of intellectual impairment in HD and related disorders. Applications are discussed for clinical settings diagnosis, patient and family counselling