Brain Enlargement in Autism Due to Brain Changes Occurring Before Age 2

In 2005, researchers had found that two-year-old children with autism have brains up to 10% larger than children of the same age without autism did. Now, a follow-up study has found that the children who had enlarged brains at age two continued to have enlarged brains at ages four and five, but the amount of the enlargement was to the same degree found at age two.

This increased brain growth did not continue beyond two years of age and the changes detected at age two were due to overgrowth prior to that time point. Moreover, the study's findings revealed that the cortical enlargement was associated with increased folding on the surface of the brain (or increased surface area) and not an increase in the thickness of outer layer of the brain (or gray matter).

"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,” said Heather Cody Hazlett, PhD, assistant professor in the department of psychiatry at the University of North Carolina at Chapel Hill (UNC; USA), who is the lead author of the new study published in the May 2011 issue of journal Archives of General Psychiatry.

In both the 2005 study and the new research, Dr. Hazlett and colleagues analyzed magnetic resonance imaging (MRI) scans of the children's brains utilizing computer software developed for that purpose by Martin Styner, PhD, an assistant professor of computer science and psychiatry at UNC, and Guido Gerig, PhD, formerly at UNC and now at the University of Utah (Salt Lake City, USA).

"From earlier work by our group on head circumference or head size in children with autism, we think that brain overgrowth in many children with autism may actually be happening around the first birthday. Together these findings suggest that we should be searching for genes that may underlie the overproliferation of neurons in this early post-natal period,” said Joseph Piven, MD, senior author of the new study and director of the Carolina Institute for Developmental Disabilities (Carrboro, NC, USA).

UNC is currently leading two separate studies aimed at that goal. Dr. Hazlett leads the Brain Development in School Age Children with Autism study, which is funded by Autism Speaks. "It was important to continue to follow these children to track their brain development to see if the brain and behavioral differences we observed were maintained as the children matured,” said Dr. Hazlett.

UNC is also leading the Infant Brain Imaging Study (IBIS), a US National Institutes of Health (Bethesda, MD, USA)-funded multicenter study that includes four sites around the United States. "We are studying infant children at high genetic risk for autism, by virtue of their having an older brother or sister with autism--somewhere around 20% of those children will develop autism. We are doing brain scans and behavior assessments on those children at 6, 12, and 24 months of age to look at how the brain develops in the subgroup that develop autism before they have symptoms of autism at six months of age and over the interval that they develop autism--between 6 and 24 months of age, in most cases,” Dr. Piven said. "We are also looking at whether specific gene alterations may be responsible.”

Related Links:
University of North Carolina at Chapel Hill
Carolina Institute for Developmental Disabilities
Infant Brain Imaging Study