They found autistic kids had larger brain volume and greater brain surface area, though they did not show a difference in cortical thickness. The rate of brain growth was about the same in children with and without autism.
The findings suggest that the brain overgrowth is occurring prior to age 2, and perhaps prior to age 1, she said.
Data on head circumference of children with ASD compared with control children suggests that increased head size in autism starts at around age 1, according to background information in the article. Behavioral changes of children who were developing normally at 6 months are often noticed by 12 months in kids later diagnosed with autism.
Prior research has linked greater brain surface area to genes that promote the proliferation of neurons.
"What we know is that the mechanism for the folding of the brain is genetic in origin, resulting from an increase in the proliferation of neurons," she said.
Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at Steven and Alexandra Cohen Children's Medical Center of New York, said the findings are interesting, although they don't have immediate clinical applications.
However, understanding that the "brain overgrowth" at age 2 remains stable through age 4 -- meaning that it doesn't become more pronounced, nor does other kids' brain size catch up -- does suggest that researchers should start looking even earlier in life to see when the brain overgrowth begins.
"It does encourage researchers to more closely evaluate brain development in the months just before and after a child's first birthday, since this is when early signs of autism often manifest initially and when changes in head size also become evident," Adesman said.
What's also unknown is whether the brain overgrowth seen in young children with autism coincides with or precedes the onset of symptoms, he added.
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