The brains of children who have autism spectrum disorder are larger than those of other children, a difference that seems to arise before they are 2 years old, according to a new study.
In 2005, researchers from the University of North Carolina at Chapel Hill found that 2-year-old children with autism had brains up to 10 percent larger than other children of the same age. This new study reveals that the children with enlarged brains at age 2 continued to have enlarged brains at ages 4 and 5, but by no more than the amount at age 2.
"Brain enlargement resulting from increased folding on the surface of the brain is most likely genetic in origin and a result of an increase in the proliferation of neurons in the developing brain," study researcher Heather Cody Hazlett, an assistant professor in UNC’s Department of Psychiatry, said in a statement.
Hazlett and her colleagues conducted behavioral assessments and magnetic resonance imaging (MRI) scans on 97 children at age 2, of whom 59 had received an autism diagnosis.
About two years later, she and her colleagues repeated the tests on those same children who were still available to them: 57 in all, of whom 36 had an autism spectrum disorder diagnosis.
The researchers found that children with an autism spectrum disorder had larger brain volume (including more white and gray matter) at all ages than children without autism. However, the rate of brain growth had been similar to the rate seen in children who did not have autism.
Research has shown that the brain overgrowth occurs during the latter part of the first year of life, and the new finding reveals that there is a relationship between onset of autistic behavior and brain overgrowth, the study said.
"It is possible that brain overgrowth directly results in the development of autistic behavior, perhaps through a physical disruption of neural circuitry," the researchers wrote.
Their study appears in the May 2011 issue of Archives of General Psychiatry.
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