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Brain Size of Children Yields Clues to Autism

Children with autism tend to have larger brains than children without autism, a study suggests.

May 2, 2011 -- Children with autism tend to have larger brains than children without autism, a study suggests.

The study shows larger brains are the result of accelerated brain growth around the children’s first birthday.

Researchers from the University of North Carolina also report that the brain overgrowth in kids who develop autism occurs in the temporal lobe white matter of the brain.

This finding could lead to a better understanding of the genes that drive autism, which, in turn, could lead to earlier identification and treatment of the disorder, study researcher Joseph Piven, MD, tells WebMD.

There is no medical test to identify autism. The disorder is typically diagnosed at age 3 based on behavioral and developmental clues. But subtle signs of autism are often present long before this age.

Piven, who directs the University of North Carolina’s Carolina Institute for Developmental Disabilities, has been conducting brain-imaging studies to assess the role of brain size in autism for close to two decades.

His research team is now following high-risk children from infancy in an effort to identify patterns of brain development and behavior that predict autism.

Comparing Brain Sizes

The study, led by University of North Carolina assistant professor of psychiatry Heather Cody Hazlett, PhD, included children who had been diagnosed with autism by the age of 2.

Research involving these children, published in 2005 by the University of North Carolina research team, linked larger brain size at age 2 and slightly larger head circumferences started around the age of 1 to autism.

The brains of the 2-year-olds with autism were up to 10% larger than the 2-year-olds without the disorder.

In the new study, the researchers again performed magnetic resonance imaging (MRI) on the brains of 38 children with autism spectrum disorder (ASD) and 21 children without autism. The children were between the ages of 4 and 5 at the time of the follow-up imaging.

The older children with ASD still showed enlargements in the region of the brain identified in the earlier imaging study, compared to children without autism. But their rate of brain growth for the two groups was similar, suggesting that the accelerated growth occurred before age 2.

“Head size seemed to be no different at birth and up to about 12 months of age,” Piven says. “But starting around the first birthday, this was no longer true.”

The finding that the increase appeared to be limited to the surface area of the brain and not the gray matter also has significance.

“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,” Hazlett says in a news release.

The Role of Genes

Hazlett and colleagues are continuing to follow the children in an effort to learn more about the differences in brain development patterns between kids with and without autism.

Piven is leading the effort to follow children at risk for autism from the age of 6 months.

He hopes to have 500 infant siblings of children with autism in this study before enrollment ends.

Genes play a big role in autism, and roughly 20% of these siblings can be expected to develop ASD, Piven tells WebMD.

The children in the study will be followed closely, with brain imaging and behavioral testing conducted at 6, 12, and 24 months.

“The idea is that by following the trajectory of brain development and behavior in individual children over time we will begin to understand autism better,” Piven says.

Funded by the National Institutes of Health and the National Alliance for Medical Image Computing, the study appears in the May issue of the Archives of General Psychiatry.

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