Washington, May 3 : A study has found that brain enlargement in children with autism is due to brain changes that occur before the age of 2.

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 children of the same age without autism.

Now a follow-up study by UNC researchers has found that the children who had enlarged brains at age 2 continued to have enlarged brains at ages 4 and 5, but the amount of the enlargement was to the same degree found at age 2.

This increased brain growth did not continue beyond 2 years of age and the changes detected at age 2 were due to overgrowth prior to that time point.

In addition, the study found 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," Heather Cody Hazlett, PhD, assistant professor in the Department of Psychiatry, who is the lead author of the new study, said.

In both the 2005 study and the new study, Hazlett and colleagues analysed magnetic resonance imaging (MRI) scans of the children''s brains using 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.

"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," Joseph Piven, MD, senior author of the new study and director of the Carolina Institute for Developmental Disabilities, said.

"Together these findings suggest that we should be searching for genes that may underlie the over-proliferation of neurons in this early post-natal period," he said.

UNC is currently leading two separate studies aimed at that goal. 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 behavioural differences we observed were maintained as the children matured," Hazlett said.

UNC is also leading the Infant Brain Imaging Study (IBIS), a National Institutes of Health-funded multi-centre study which includes four sites around the U. S.

"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 percent of those children will develop autism," Piven said.

"We are doing brain scans and behaviour 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
6 months of age and over the interval that they develop autism - between 6 and 24 months of age, in most cases.

"We are also looking at whether specific gene alterations may be responsible," he added.

The study is published in the May 2011 issue of Archives of General Psychiatry. (ANI)