Although the exact cause of autism is still a mystery, there is general agreement that early, aberrant neural development underlies the disorder. Possible explanations for this abnormality include accelerated neural development and/or macrocephaly, resulting in a larger brain and head size.
Going a step beyond anatomy, researchers from North Carolina who specialize in neurodevelopmental disorders investigated brain volume and head circumference (HC) in children with autism. Their results suggest that generalized enlargement of certain areas of the brain may begin as early as the first year of life.
Heather Cody Hazlett, Ph.D., from the University of North Carolina in Chapel Hill, and colleagues studied 51 children with autism and compared them to a control group of 25 children. The latter group included 11 children with nonautistic developmental delay (DD) and 14 with typical development (TP).
In addition, a retrospective analysis was done on longitudinal HC data in 113 autistic children and 189 controls. All of the autistic subjects met the Diagnostic and Statistical Manual of Mental Disorders (DSV-IV) criteria for the disorder.
All the children were imaged on a 1.5-tesla MRI scanner (Signa, GE Healthcare, Chalfont St. Giles, U.K.). Those with autism and DD were scanned under moderate sedation. TP children were scanned without sedation but while they were sleeping.
"Image acquisition was designed to maximize gray- and white-tissue contrast for the 18- to 35-month-old children," the authors explained. The imaging protocol included a coronal T1-weighted sequence and a coronal proton density/T2-weighted, 2D dual fast spin-echo sequence. The images, which were coregistered with a custom-created pediatric brain template atlas, were read by co-author Dr. James Provenzale from Duke University Medical Center in Durham, NC (Archives of General Psychiatry, December 2005, Vol. 62:12, pp. 1366-1376).
According to the results, autistic subjects showed significant enlargement in total brain volume, total tissue volume, total gray-matter volume, and total white-matter volume in comparison to the controls. In addition, there was evidence to suggest increased cerebrospinal fluid volume. The percentage of increases in brain volume in autistic subjects ranged from 4% to 6.1%. Also, children with autism had significant enlargement in total cerebral cortical volume.
"This approximately 5% overall enlargement appears primarily to be the result of increases in both (gray-matter) and (white-matter) volumes of the cerebral cortex," the authors explained. "Cerebral cortical enlargement in our sample appeared to be the result of a generalized enlargement in the (frontal, temporal, and parietal-occipital lobes)."
In terms of head circumference, the autism group exhibited an increased rate of HC growth starting at around 12 months of age. This group continued through the age interval.
"Given the strong relationship between HC and brain volume, the onset of this enlargement appears likely to be during the postnatal period, and may begin as late as the latter part of the first year of life," they explained.
Based on the results, Hazlett's group hypothesized that a presymptomatic period in autism may occur in which intervention may be most effective. The next phase of the team's research will be to study older autistic children and those with a higher IQ.
By Shalmali Pal
AuntMinnie.com staff writer
January 3, 2006
Related Reading
MR 'eye' studies offer glimpse into ocular movement, function, September 2, 2005
Autistic brain seen to recall letters differently, December 13, 2004
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