SAN DIEGO — There appear to be no differences in the mean head circumference between children with and without autism, results from a population-based case-control study show.
The finding differs from other smaller studies that have reported increased rates of macrocephaly in autistic children, Carrie Jones, M.D., said at the annual meeting of the Society for Developmental and Behavioral Pediatrics.
Those studies have proposed that accelerated brain growth in the first years of life is an early biologic marker for a subgroup of children with autism, “but the results are based on very small groups of children, and they may or may not be representative of the general population of kids with autism,” said Dr. Jones, of the M.I.N.D. Institute at the University of California, Davis. “Also, they have rarely been correlated with other growth parameters such as weight and height, [and] they rarely have been paired with children from the same population.”
For the study, known as Childhood Autism Risks from Genetics and the Environment (CHARGE), Dr. Jones and her associates recruited 175 children with autism aged 2–5 years through six centers that provide developmental disability services to children and adults in Northern and Southern California. Diagnoses were confirmed with the Autism Diagnostic Interview-Revised and the Autism Diagnostic Observational Schedule.
The investigators used birth records to identify 43 control children from the general population who were matched to the case population for age, gender, and geographic location.
All study participants received a medical exam that included measurement of head circumference, weight, and height. All parameters were plotted by age and gender on National Health and Nutrition Examination Survey III growth charts.
Dr. Jones and her associates found that the mean head circumference of both cases and controls was at the 59th percentile. About 12% of both cases and controls were at or above the 95th percentile, which was higher than expected.
“In linear regression models, the strongest predictor of head circumference was weight,” she said. “The heavier kids tended to have bigger heads, but autism vs. general population group membership did not predict head circumference.”
The next steps in the study are to examine earlier growth parameters from medical records for trajectories over time in both groups.
“We are also going to measure parent head circumference so we can see correlation with child head circumference,” she said.