Sensory Abnormalities in Twins with ASD: Investigating Associations with IQ and Behavioural Features of ASD

Background: Increased rates of sensory abnormalities, such as hypo- and hyper-sensitivity to sound, light, touch, and taste, are consistently reported in studies of individuals with autism spectrum disorders (ASD) (e.g. Leekam et al., 2007, Rogers & Ozonoff, 2005). However, despite a recent increase in studies of sensory abnormalities in autism, it is still unclear why there is such variability in sensory responsivity in individuals with ASD and which behavioural and cognitive aspects of ASD predict high levels of sensory problems. Rogers, Hepburn, and Wehner (2003) examined the occurrence of sensory symptoms in toddlers with autism and other developmental disorders. Significant associations were found in the autism group with the ADOS restricted activities algorithm score, but not with IQ, ADI, or other ADOS scores. In addition to this, the autism group showed more sensory symptoms than the control group. Szatmari et al. (2006) examined the structure of the restricted, repetitive behaviours and interests domain in autism measured by the ADOS and the ADI. Using factor analysis, they found that this domain actually consists of 2 factors: 'insistence on sameness' (IS) and 'repetitive and sensory motor behaviours and interests' (RSMB). High RSMB scores were found to be associated with more autistic symptoms in the social reciprocity domain and lower cognitive functioning. However, their analysis of sibling data to assess familiality of the RSMB factor yielded no significant results.
Objectives: The aim of this study was to investigate potential associations between sensory symptoms, IQ, and other behavioural features of ASD in a sample of teenage twins, as well as to explore the role of genetic factors in contributing to individual differences in sensory abnormalities in ASD, to assess whether sensory sensitivities form part of a broader autism phenotype.
Methods: This study forms part of a large-scale longitudinal twin study (TEDS - Twins Early Development Study). Twins with ASD (autism, Asperger Syndrome, atypical autism) were recruited for the Social Relationship Study (SRS).  The sample for the present study includes 50 ASD twin pairs (at least one twin with ASD) and 50 control twin pairs, aged 12-14 years. Patterns of sensory abnormalities were assessed using the Short Sensory Profile completed by children and parents. The Autism Diagnostic Observation Schedule (ADOS) and Autism Diagnostic Interview-Revised (ADI-R) were carried out for each twin to evaluate severity of symptoms. Level of cognitive functioning was determined using the Wechsler Abbreviated Scale of Intelligence (WASI).
Results: Results show higher rates of sensory abnormalities in ASD twins as compared to controls. Furthermore, we find interesting results concerning the associations between the sensory sensitivity scores obtained from the Sensory Profile and the ADOS, ADI, and WASI scores. The twin correlations indicate the contribution of genetic and environmental effects to individual differences in sensory responsivity in individuals with autism.
Conclusions: Sensory abnormalities can be severely debilitating for individuals with autism. Understanding why sensory sensitivities affect some children more than others provides the first step to intervention.