Date of Award

2009

Document type

Thesis

Degree Name

PhD (Doctor of Philosophy)

First Supervisor

Professor Kieran Murphy

Keywords

Mental Retardation, Chromosome Deletion

Abstract

Background: 22q11.2 deletion syndrome (22qDS) is a common microdeletion disorder arising from a deletion on the long (q) arm of chromosome 22. It is associated with a complex and variably expressed phenotype, which includes a range of neuroanatomical and cognitive abnormalities. The effect of general intellectual disability on the neurocognitive profile of 22qDS and the development of cognitive abilities across developmental stages requires further research. Aims: The current study aims to investigate the extent to which the neurocognitive profile of 22qDS is mediated by general intellectual impairment and to construct cross-sectional developmental trajectories of executive functions and memory abilities in children, adolescents and adults with 22qDS. Methods: Standardised cognitive test batteries were employed to assess the key areas of visual-motor function, executive function and memory in children, adolescents and adults with 22qDS. The effects of IQ were assessed using an IQ-matched control group and a statistical method for testing for differential deficits in cognitive functioning. Cross-sectional developmental trajectories were constructed to examine changes in cognitive profiles across age ranges. Results: Each age group displayed cognitive profiles characterised by preserved verbal/auditory processing and selective deficits in visual and spatial perception. Compared to IQ-matched controls, the child/adolescent group exhibited differential deficits in fine motor speed and visuospatial memory but they did not differ from IQ-matched controls on any measure of executive function. The adult group did not display any cognitive deficit in excess of their overall intellectual impairment. Visuospatial and pattern recognition memory were observed to improve significantly across the age range. Executive functions, with the exception of verbal working memory, displayed no significant improvement across the age range. Conclusions: These findings suggest that the impact of general intellectual disability on the neurocognitive phenotype of 22qDS was mediated by the developmental stage of the study participants. Fine motor ability and visuospatial recall may exhibit developmental delay relative to other cognitive abilities and pre-frontally mediated executive functions appear to exhibit atypical developmental trajectories.

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Comments

PhD thesis : a thesis submitted to the Royal College of Surgeons in Ireland for the degree of Doctor of Philosophy from the National University of Ireland in 2009.