The majority of individuals with autism spectrum disorder (ASD) show cognitive impairment. This study, published in Molecular Psychiatry, therefore provides some of the first evidence that ASD-related genes might actually be associated with higher intelligence.
Study co-author Professor Nick Martin of the Queensland Institute for Medical Research, said: 'Links between autism and better cognitive function [...] 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, on average, a small intellectual advantage in those who carry them, provided they are not affected by autism.'
All the same, the advantage gained from carrying ASD-related genes was small indeed. The NHS Choices website observes that 'less than 0.5 percent of the difference seen in people's cognitive scores was explained by how many of the ASD-linked genetic variants they carried'.
The research used data from 9,863 Scottish people, who were taking part in the Generation Scotland: Scottish Family Health Study. All participants had their genomes checked for genetic variants that had been previously associated with ASD.
As ASD can result in speech and language difficulties, measures of cognitive ability were calculated using four separate assessments of non-verbal intelligence.
ASD encompasses a number of conditions sharing some features, such as poor social interaction and communication. Around 70 percent of affected individuals show below average intelligence but among the remainder many show above average intelligence, especially among those diagnosed with Asperger's syndrome (an increasingly controversial diagnosis).
The researchers conclude that these results could help towards unravelling the complex relationship between ASD and intelligence.
Dr Toni-Kim Clarke of the University of Edinburgh, who led the study, said: 'As we begin to understand how genetic variants associated with autism impact brain function, we may begin to further understand the nature of autistic intelligence.'
The researchers tried to confirm their correlation using data from two earlier Scottish samples – the Lothian birth cohorts of 1921 and 1936 - and the Brisbane Adolescent Twin Study (BATS) from Australia. The result could only be replicated for the BATS group.
The study also looked at the possible influence on intelligence of genes associated with attention deficit hyperactivity disorder but failed to find a correlation.