In people who do not have autism, genetic variations that increase the risk of autism spectrum disorders appear to confer a small boost in cognitive abilities. In a study published March 10th in the journal Molecular Psychiatry, researchers found that individuals whose genomes harbored the greatest number of autism-associated genetic variations performed better on tests of verbal fluency, logical memory, and vocabulary, as well as in general assessments of cognitive ability.

The relationship between autism and intelligence is complex. Many people with autism have intellectual impairments, but some studies have also found that for certain cognitive functions––particularly non-verbal skills—people with autism have above-average abilities.

No single gene determines whether a person will develop autism. Indeed, the total number of genes contributing to risk discovered so far, numbers in the hundreds. Thus, many genetic factors are thought to play a role, simultaneously, in affected individuals. A wide array of genetic factors likely influence cognitive ability in people without the disorder, as well. Scientists suspect that hundreds or even thousands of genetic factors may influence intelligence, although any single gene's impact on cognitive ability is probably subtle.

In the new study, a team of scientists at the University of Edinburgh was led by Andrew McIntosh, M.D., recipient of an Independent Investigator grant in 2010. The team included David Porteous, Ph.D., a 2008 NARSAD Distinguished Investigator. The researchers searched for an influence of autism-related genes on cognitive ability in the general population. They also considered whether genetic variations associated with attention-deficit hyperactivity disorder (ADHD) influenced cognitive ability. Children with ADHD often have below-average intelligence; specific cognitive difficulties, including short-term memory and reading comprehension, have been associated with the disorder.  

The researchers analyzed data from three previous studies, which together included more than 12,000 people. They analyzed each person’s genome sequence to determine how many known autism- or ADHD-associated variants were present, then compared this with data on each person's cognitive abilities. They found that individuals with the most autism-related variants in their genomes performed better on tests of cognitive ability, particularly verbal fluency, logical memory and vocabulary. The team found no consistent link between ADHD genes and cognitive abilities within the group.

The effect of autism genes on intelligence in the study population was small: The authors found that less than half a percent of the variations in cognitive scores could be attributed to the autism-related genes included in their analysis. Still, the researchers say their findings demonstrate a relationship between intelligence and autism-related genetic factors, even in people who do not have autism spectrum disorders.

Read the abstract.