A Study of Autism Spectrum Disorder and Sensory Impairment in Adults with Intellectual Disability

Autism spectrum disorder (ASD) and sensory impairment are common in people with intellectual disability (ID), but little is known about the relationship between them. The primary aim of this thesis was to explore the relationship between deafness, blindness and ASD. The secondary aim was to determine the prevalence of sensory impairment, ASD and other co-morbidities in adults with ID. This thesis comprised a comprehensive literature review followed by a 2-stage study. Stage 1 involved cross-sectional analysis of data on adults with ID on a population-based case register. Stage 2 involved investigating adults with congenital deafness and their controls (deaf subgroup), and congenital blindness and their controls (blind subgroup) using medical case file review and face-to-face interviews, including the Pervasive Developmental Disorder in Mental Retardation Scale to identify ASD. Data were analysed using chisquared tests, estimated probabilities (to explore interactions) and general linear, conditional and non-conditional logistic regression modelling. Stage 1 identified 3183 adults with ID, 634 (20%) of whom had sensory impairment (congenital and acquired), comprising partial (n=447), total (n=165), or dual/deaf-blindness (n=22). Both visual and hearing impairment were associated with degree of ID, age and having Down syndrome but only visual impairment was associated with epilepsy. Neither visual impairment nor hearing impairment was associated with ASD at this stage of the study. In stage 2, those with an acquired sensory impairment were excluded and only 60 congenitally blind cases, 21 congenitally deaf cases and their controls (matched on degree of ID and gender) were included. Congenital blindness, but not deafness, was associated with ASD (OR=3.03; 95% CI: 1.34–6.89; p<0.008) after adjustment for potential confounders. This thesis supports previous findings of high prevalence of sensory impairment among adults with ID. For the first time, an independent relationship was observed between congenital blindness and ASD in a cohort of adults with ID. The implications of these findings are discussed.