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).
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.'
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.