IQ in Children with Autism Spectrum Disorders : Data from the SNAP Project

Background: Autism spectrum disorder (ASD) was once considered to be highly associated with intellectual disability and to show a characteristic IQ profile; with strengths in Performance over Verbal abilities and a distinctive pattern of ‘peaks’ and ‘troughs’ at the subtest level. However, there is little data from epidemiological studies. Method: Comprehensive clinical assessments were conducted with 156 ten-to-fourteen-yearold children (mean (SD)=11.7 (0.9)) seen as part of an epidemiological study (81 childhood autism, 75 other ASD). A sample weighting procedure enabled us to estimate characteristics of the total ASD population. Results: 55% of children with ASD had an intellectual disability (IQ<70) but only 16% had moderate to severe intellectual disability (IQ<50). 28% of children with ASD had average intelligence (115>IQ>85) but only a minority (3%) were of above average intelligence (IQ>115). There was some evidence for a clinically significant PIQ/VIQ discrepancy but discrepant verbal versus performance skills were not associated with a particular pattern of symptoms, as has been previously reported. There was mixed evidence of a characteristic subtest profile: Whilst some previously reported patterns were supported (e.g. poor Comprehension); others were not (e.g. no ‘peak’ in Block Design). Adaptive skills were significantly lower than IQ and were associated with severity of early social impairment as well as IQ. Conclusions: In this epidemiological sample, ASD was less strongly associated with intellectual disability than traditionally held and there was only limited evidence of a distinctive IQ profile. Adaptive outcome was significantly impaired even for those children of average intelligence.