Children with autism have more brain cells and heavier brains compared to typically developing children, according to researchers partly funded by the National Institutes of Health. Published in the Journal of the American Medical Association on Nov. 9, 2011, the small, preliminary study provides direct evidence for possible prenatal causes of autism.
"Earlier studies of head circumference and early brain overgrowth have pointed us in this direction, but there have been few quantitative neuroanatomical studies due to the lack of post-mortem tissue from children with autism," said Thomas R. Insel, M.D., director of the National Institute of Mental Health (NIMH), part of NIH. "These new results, along with an earlier study reporting altered wiring of the prefrontal cortex, focus our attention on this critical area of the brain in autism."
The prefrontal cortex is involved in various higher order functions such as language and communication, social behavior, mood, and attention. Children who have autism tend to show deficits in such functions.
Eric Courchesne, Ph.D., of the University of San Diego School of Medicine Autism Center of Excellence, and colleagues conducted direct counts of brain cells in specific regions of the prefrontal cortex in postmortem brains of seven boys who had autism and six typically developing males, ranging in age from 2-16 years. Most participants had died in accidents, but the researchers did not base their selection on causes of death.
To assist in this task, the researchers used a computerized tissue analysis system developed by co-investigator and NIMH grantee Peter Mouton, Ph.D., of the University of South Florida, Tampa, and colleagues.
The researchers found that children with autism had 67 percent more neurons in the prefrontal cortex and heavier brains for their age compared to typically developing children. Since these neurons are produced before birth, the study's findings suggest that faulty prenatal cell birth or maintenance may be involved in the development of autism. Another possible factor that may contribute to the neuronal excess is a reduction in apoptosis, or programmed cell death, which normally occurs during the third trimester and early postnatal life.
Though small, this preliminary study examined all relevant postmortem tissue available at the time. The relative scarcity of tissue from very young children may limit future research as well, but efforts to include a larger number of samples are needed to confirm these findings and to identify patterns of age-related changes in autism.
This study was funded by Autism Speaks, Cure Autism Now, The Emch Foundation, the Simons Foundation, the Thursday Club Juniors, and the UCSD-NIH Autism Center of Excellence, which is supported by NIMH, the National Institute of Neurological Disorders and Stroke, and the Eunice Kennedy Shriver National Institute of Child Health and Human Development.
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