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Enlarged Brain Might Be Hallmark of Autism

Head circumference also begins to increase after age 1, study found

WEDNESDAY, Dec. 7, 2005 (HealthDay News) -- Brain enlargement may signal autism, according to a study that found evidence of abnormal brain size in children with the disorder.

Researchers at the University of North Carolina, Chapel Hill analyzed the MRIs of the brains of 51 autistic children and 25 children without autism. The children were aged 18 to 35 months. They also studied head circumference measurements from 113 children with autism and 189 children without the disorder.

"Significant enlargement was detected in cerebral cortical volumes but not cerebellar volumes in individuals with autism," the study authors wrote. "Enlargement was present in both white and gray matter, and it was generalized throughout the cerebral cortex."

The cerebral cortex, a thin layer of gray matter lying at the upper front portion of the brain, is in charge of higher-level, executive functions. The cerebellum lies behind the main mass of the brain and controls voluntary muscle movements and other activities.

The study also found that in children with autism, "head circumference appears normal at birth, with a significantly increased rate of head circumference growth appearing to begin around 12 months of age."

"The findings from this study confirm the presence of generalized cerebral cortical gray matter and white matter brain volume enlargement at age 2 in individuals with autism," the study authors concluded. "Given the strong relationship between head circumference and brain volume, the onset of this enlargement appears likely to be during the postnatal [after birth] period, and may begin as late as the latter part of the first year of life."

The study appears in the December issue of the Archives of General Psychiatry.

More information

The Nemours Foundation has more about autism.

SOURCE: American Medical Association, news release, Dec. 5, 2005
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