Autism and intellectual disability: new findings

New research by The Open University, King’s College London, the University of Cambridge and Birkbeck College suggests that the causes of autism and intellectual disability are mostly distinct.

The researchers found that behavioural and personality characteristics related to autism (also called ‘autistic traits’) are strongly genetic. Most importantly, they found that the genetic influences on autistic traits were largely distinct from the genetic influences on intellectual difficulties. This fits with the finding that although autism runs in families, relatives of children with autism do not tend to have intellectual disability.

“Autism and intellectual disability often occur together, and this has made many researchers think that the conditions must share the same genetic causes. Our research challenges this assumption,” says Dr Rosa Hoekstra, Lecturer in Psychology at The Open University, who led the study.

Autism can be diagnosed in people with all types of intellectual ability: some have profound learning difficulties, but others are extremely intelligent. The findings indicate that the characteristics of autism and intellectual disability are largely independent of each other. This contrasts with figures from clinics, which suggest that intellectual disability is common in people with an autism diagnosis. This may be because autism in very able children is going undetected.

Hoekstra, Rosa A.; Happé, Francesca; Baron-Cohen, Simon and Ronald, Angelica (2010). Limited genetic covariance between autistic traits and intelligence: Findings from a longitudinal twin study. American Journal of Medical Genetics Part B: Neuropsychiatric Genetics (In Press).