Brain Enlargement Prior to Age Two an Indication of Autism
In 2005, researchers with the University of North Carolina at Chapel Hill discovered that two-year-old children with autism spectrum disorders (ASD) had brains that were up to 10 percent larger than other children of the same age. However, the cause and the timing of the enlargement have been unknown. The UNC researchers continued their study of the autistic brain in children, and found that although their brains continue to show enlargement, the rate of overgrowth does not appear to increase after toddlerhood.
Increased Brain Volume May Affect Neural Circuitry
"Brain enlargement [occurring in the latter part of the first year of life] 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 study researcher Heather Cody Hazlett, an assistant professor in UNC’s Department of Psychiatry at the Carolina Institute for Developmental Disabilities.
Hazlett and colleagues performed MRI scans and behavioral assessments on 97 two-year-old children of whom 59 had received a diagnosis of autism. Two years later, the tests were repeated on the same children that were available to them – 57 in all, 36 with autism.
At all ages, children with ASD had, on average, 6% larger brain volume and 9% more volume in the cerebral cortex, a region of the brain that is responsible for receiving input from the environment and processing memory and attention, than children without the disorder. The autistic children also had more surface area in the cortex, suggesting that new nerve cells are being produced and pushed to the surface.
However, after age 2, although the total brain size remains larger, the rate of growth is relatively normal as compared with non-autistic children of similar ages.
“This study strongly suggests that much of the enlargement in the brains of children with autism takes place before the age of two,” says Dr. Joseph Piven, senior study author and director of the Institute. “And the results suggest a mechanism not thought of before in autism, that there is increased production of neurons in the [cerebral cortex] of the brain.”
The researchers further suggest that the brain overgrowth directly leads to the behavioral abnormalities seen in ASD, “perhaps through a physical disruption of neural circuitry” or faulty synaptic development.
The results of the study may help scientists better understand the critical early phases of autism and could help direct research into possible new interventions. The researchers will now focus more intently on brain changes in children between the ages of six months to 24 months in hopes of narrowing down the interval where they are able to see the abnormalities occurring.
“Direct evidence of the timing of early brain volume overgrowth in autism will focus future studies on this narrow window of brain development, providing important insights into potential underlying neural mechanisms and highlighting a potentially important period for early intervention and possible prevention," the authors write.
UNC-Chapel Hill is currently leading two studies into brain development in children with autism. The Brain Development in School Age Children with Autism study is funded by Autism Speaks and continues to follow the children as they mature. The Infant Brain Imaging Study (IBIS) is funded by the National Institutes of Health and is studying infants at high genetic risk for autism due to having a sibling with the condition.
Hazlett H, et al "Early brain overgrowth in autism associated with an increase in cortical surface area before age 2 years" Arch Gen Psychiatry 2011; 68: 467-476.