Children playing with blocksBoys with autism spectrum disorders (ASD) are more likely to have asynchronous IQ development than girls on the spectrum or than typically developing children. Researchers compared scores of tests measuring verbal and spatial intelligence, respectively, and found that boys with ASD had the most significant difference between the two scores, but that those differences had largely reached equilibrium by age ten. The findings may aid in understanding some of the behaviors of boys on the spectrum.

Data came from the Simons Simplex Commons database, a collection of information on families who have one child with ASD, but whose siblings do not have autism. The researchers analyzed data from a pair of intelligence quotient (IQ) tests about 2,000 children aged four to 17. The verbal IQ test evaluated children’s skills in understanding and speaking to others. The non-verbal test quantified children’s abilities in spatial concepts like building or drawing.

In groups of typically developing children, about 70% score more-or-less equally on the two tests while 15% have better verbal skills and another 15% have better spatial skills. However, in children with autism, only 59% have equivalent scores and 27% of children with ASD score significantly higher on the non-verbal test. The researchers found that 804 children with autism from the study cohort had unequal scores. Of those, 523 children were between ages four and nine, indicating that younger children account for most of the asynchronous development. Boys with higher non-verbal scores were over-represented among those with unequal development, accounting for 490 of the 804 children. Girls were equally likely to score higher in verbal or spatial skills.

These findings may explain why boys seem to have more difficulties in social settings than girls, since a later development of verbal intelligence might result in missing out on communicative information from peers. The results may also be indicative of a pattern of asynchronous development among children with autism.

This research is published in the American Journal on Intellectual and Developmental Disabilities.

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