Increased head growth not a risk marker for autism

August 25, 2014

Investigators from the Baby-Sibs Research Consortium have found no connection between head size and autism in a recent study published in Journal of the American Academy of Child and Adolescent Psychiatry.

The study, the largest of its kind, drew on data gathered from 695 children participating in studies at 12 sites around the world, including 442 younger siblings of children diagnosed with autism spectrum disorder (ASD). Over the children's first three years of life, investigators led by NeuroDevNet's Dr. Lonnie Zwaigenbaum found no overall difference in head size or growth between those who developed typically, those who developed autism and those who showed other developmental delays. Eighty-four of the participating children were diagnosed with ASD by age three.

Findings from the study lay to rest accepted notions established in the earliest days of ASD diagnosis. According to Autism Speaks, the idea that a large head is an early sign of autism dates back to Leo Kanner’s original 1943 description of the disorder. Since then, more then a dozen small studies have found an association between unusually large infant head size with high risk that a child will develop autism.

“It’s important to investigate possible associations that may provide important information for early diagnosis and treatment," said ASD research project co-lead Dr. Lonnie Zwaigenbaum. As lead investigator on the latest head circumference study, and co-director of the Autism Research Centre at Glenrose Rehabilitation Hospital, in Edmonton, Alberta, Zwaigenbaum said, learning more about what is not informative is equally important.”

A limitation that affected earlier studys, he said, “normal” head growth was derived from standardized charts published by government health agencies. “It’s important that children with ASD be compared to other children from the same community, rather than to historical comparisons based on plotting on a growth chart,” Zwaigenbaum reflected.

"While having a larger head did not predict higher risk of autism, we did not measure actual brain growth in this study,” he added. “In fact, recent research reinforces that there is brain overgrowth early in life in children with ASD.”

it appears that this isn’t reflected in head growth as would be measured by a physician during a checkup. "It's not so much that the head fails to accommodate a larger brain, it's probably more about cortical thickness than brain volume per se," said Zwaigenbaum. Findings published in late August indicate a lack of pruning of neuronal growth in the brains of children with autism.

"Truthfully," he added, "there is no simple relationship between brain growth and symptoms."