Although intellectual impairment is not one of the diagnostic criteria for autism spectrum disorders, half or more of all people with autism have an intellectual disability. Intellectual disability can present an equal or greater challenge to individuals with autism than do autism-specific deficits. To date, the intelligence quotient (IQ) is one of the best predictors of response to treatment among youth with autism, and it is also one of the best predictors of long-term outcomes.

Robert Schultz and his colleagues at The Children’s Hospital of Philadelphia are seeking to understand the biological mechanisms that cause intellectual disability and the high rates of it seen in autism spectrum disorders. It is not yet known whether the genetic mechanisms that affect intellectual functioning put one at increased risk for autism, whether autism affects intellectual functioning, or whether there are pleiotropic effects that affect both simultaneously.

The Simons Simplex Collection (SSC) is a repository of genetic and phenotypic data from 2,700 families that have one child with autism and unaffected parents and siblings. A new collaboration with the Interactive Autism Network (IAN) is bringing together many of these families in an online forum called SSC@IAN for new studies.

Contrary to the researchers’ hypothesis, initial analyses of data from the SSC show that the degree of intellectual disability is a poor predictor of overall genetic risk for autism. Unfortunately, IQ scores are not available for SSC parents or unaffected siblings, making it difficult to fully interpret IQ data from individuals with autism. Using a new web-based adaptive IQ test called the Adaptive Matrices Test, Schultz’s group aims to characterize IQ for all family members enrolled in SSC@IAN. This would allow the researchers to take a fresh look at SSC genetic data, modeling IQ as a deviation from predicted IQ based on sibling and parental data. By including family IQ data in their statistical analyses, Schultz’s team expects to be better able to discern the origins of intellectual impairments in autism.