a1 Centre for Research in Autism and Education, Institute of Education, London, UK
a2 Division of Epidemiology and Health Sciences, University of Manchester, UK
a3 Institute of Psychiatry, King's College London, UK
a4 School of Psychology and Clinical Language Sciences, University of Reading, UK
a5 Guy's and St Thomas' NHS Foundation Trust, London, UK
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 are few data from epidemiological studies.
Method Comprehensive clinical assessments were conducted with 156 children aged 10–14 years [mean (s.d.)=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 Of the 75 children with ASD, 55% had an intellectual disability (IQ<70) but only 16% had moderate to severe intellectual disability (IQ<50); 28% had average intelligence (115>IQ>85) but only 3% were of above average intelligence (IQ>115). There was some evidence for a clinically significant Performance/Verbal IQ (PIQ/VIQ) discrepancy but discrepant verbal versus performance skills were not associated with a particular pattern of symptoms, as has been reported previously. There was mixed evidence of a characteristic subtest profile: whereas 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 and also 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.
(Received October 02 2009)
(Revised April 06 2010)
(Accepted April 09 2010)
(Online publication May 19 2010)
c1 Address for correspondence: Professor T. Charman, Chair in Autism Education, Centre for Research in Autism and Education, Department of Psychology and Human Development, Institute of Education, 25 Woburn Square, London WC1H 0AA, UK. (Email: firstname.lastname@example.org)