With the largest study of its kind, the Autism Speaks Baby Siblings Research Consortium has further laid to rest the longstanding idea that an abnormally large infant head size is an early sign of autism spectrum disorder (ASD).
The report appears online in the Journal of the American Academy of Child and Adolescent Psychiatry.
“This large, solid study shows that parents should not regard large head circumference as a sign of autism,” comments developmental pediatrician Paul Wang, Autism Speaks senior vice president for medical research. Dr. Wang was not directly involved in the study. “Having a larger head is not a reason, in and of itself, to think about autism or to seek an evaluation for autism,” he underscores. “Parents should focus on the developmental and behavioral signs that Autism Speaks has long emphasized.”
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The new report combines findings on 695 children participating in studies at 12 sites around the world. Over the children's first three years of life, the investigators 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. In all, 84 of the children were diagnosed with ASD by age 3.
The participants included 442 younger siblings of children already diagnosed with ASD. Because autism tends to run in families, these “baby sibs” are at high risk of developing the disorder. The Autism Speaks Baby Siblings Research Consortium is dedicated to studying such high-risk infants in order to advance early detection and intervention for autism.
“It’s important to investigate possible associations that may provide important information for early diagnosis and treatment,” says lead researcher Lonnie Zwaigenbaum. “Learning more about what is not informative is equally important.” Dr. Zwaigenbaum co-directs the Autism Research Centre at Glenrose Rehabilitation Hospital, in Edmonton, Alberta. The center is a member of the Autism Speaks Autism Treatment Network.
The idea that a large head is an early sign of autism dates all the way back to Leo Kanner’s original description of autism in 1943. Since then, more than a dozen small studies have associated unusually large infant head size with high risk that a child will develop autism.
A major limitation of those studies is that they gauged what was “normal” according to standardized growth charts published by government health agencies, Dr. Zwaigenbaum notes. “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,” he says.
“While having a larger head did not predict higher risk of autism, we did not measure actual brain growth in this study,” Dr. Zwaigenbaum adds. “In fact, recent research reinforces that there is brain overgrowth early in life in children with ASD.” However, it appears that this isn’t reflected in head growth as would be measured by a physician during a checkup.
Autism Speaks funded the analysis. On an ongoing basis, it also funds the Baby Siblings Research Consortium database, which enables the group to coordinate and analyze findings from research teams around the world. Learn more about related Autism Speaks research grants here.
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