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Brains of children with autism are hyperconnected. Image credit: Cell Reports, Keown et al

A link between autism and higher intelligence

Genes linked with a greater risk of developing autism may also be associated with higher intelligence. Researchers found new evidence linking genes associated with Autism Spectrum Disorder (ASD) and Attention-Deficit Hyperactivity Disorder (ADHD) with higher intelligence.

The relationship between autism and intelligence is unclear as there isn't consistent evidence comparing the two. The aim of this study was to examine the multi-gene overlap between ASD/ADHD as compared to the overall cognitive ability of a large general population.

Although up to 70 per cent of individuals with autism have an intellectual disability, some people with the disorder have relatively well-preserved, or even higher than average, non-verbal intelligence.

Professor Nick Martin, of the Queensland Institute for Medical Research adds: "Links between autism and better cognitive function have been suspected and are widely implied by the well-known "Silicon Valley syndrome" and films such as "Rain Man" as well as in popular literature. This study suggests genes for autism may actually confer a small intellectual advantage in those who carry them, provided they are not [severly] affected by autism."

Autism is a brain developmental disability that can cause significant language and speech difficulties. Non-verbal intelligence, though, can also enable some affected people with an ability to solve complex problems using visual and hands-on reasoning skills - while having little or no use of spoken language.

Researchers at the Universities of Edinburgh and Queensland analysed almost 10,000 people recruited from the general population of Scotland, to test for cognitive ability while also screening their DNA for evidence of autism associated genes.

Even among people who never develop autism, carrying genetic traits associated with the disorder is linked on average to scoring slightly better on cognitive tests.

When researchers carried out the same tests on 921 adolescents who were part of the Brisbane Adolescent Twin Study, they found more evidence of a link between autism-associated genes and intelligence. They published their results in the journal Molecular Psychiatry.

"Our findings show genetic variation that increases risk for autism is associated with better cognitive ability in non-autistic individuals. As we begin to understand how genetic variations associated with autism impact brain function, we may begin to further understand the nature of autistic intelligence."

Dr Toni-Kim Clarke, University of Edinburgh's Division of Psychiatry, study leader.

Abstract
Cognitive impairment is common among individuals diagnosed with autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD). It has been suggested that some aspects of intelligence are preserved or even superior in people with ASD compared with controls, but consistent evidence is lacking. Few studies have examined the genetic overlap between cognitive ability and ASD/ADHD. The aim of this study was to examine the polygenic overlap between ASD/ADHD and cognitive ability in individuals from the general population. Polygenic risk for ADHD and ASD was calculated from genome-wide association studies of ASD and ADHD conducted by the Psychiatric Genetics Consortium. Risk scores were created in three independent cohorts: Generation Scotland Scottish Family Health Study (GS:SFHS) (n=9863), the Lothian Birth Cohorts 1936 and 1921 (n=1522), and the Brisbane Adolescent Twin Sample (BATS) (n=921). We report that polygenic risk for ASD is positively correlated with general cognitive ability (beta=0.07, P=6 × 10−7, r2=0.003), logical memory and verbal intelligence in GS:SFHS. This was replicated in BATS as a positive association with full-scale intelligent quotient (IQ) (beta=0.07, P=0.03, r2=0.005). We did not find consistent evidence that polygenic risk for ADHD was associated with cognitive function; however, a negative correlation with IQ at age 11 years (beta=−0.08, Z=−3.3, P=0.001) was observed in the Lothian Birth Cohorts. These findings are in individuals from the general population, suggesting that the relationship between genetic risk for ASD and intelligence is partly independent of clinical state. These data suggest that common genetic variation relevant for ASD influences general cognitive ability.

The research was funded by the Chief Scientist Office of the Scottish Government Health and Social Care Directorates, Scottish Funding Council, The Wellcome Trust, The Medical Research Council and Age UK.

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