New Insights Into Autism reports on a recent study:
The study in Wednesday’s issue of the Journal of the American Medical Association finds that a small head circumference at birth followed by a sudden growth spurt of the head before the end of the first year is a reliable early warning sign of autism.
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National statistics on autism spectrum disorder are hard to come by, but the incidence has been rising mysteriously. The disorder, which ranges from severe to moderate cases, affects an estimated one in 160 children in the U.S., according to UCSD researchers. It is typically diagnosed between ages 2 and 4, based on a child’s behavior — delayed speech, difficulties with social interactions, poor attention, impaired exploration of the environment and inappropriate emotional responses.
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The cause of the small brain size at birth is unknown. But the abnormally sped-up brain growth, says Dr. Courchesne, likely reflects excessive numbers of brain cells, failure of the brain to prune the hundreds of synapses that connect one neuron to another, or both. Normally, experiences sculpt the developing brain; unneeded or unused synapses are pruned away. Autistic children, in contrast, seem to suffer from the neurological equivalent of electrical overload: too many impulses, thoughts and sensations in their brain.
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[T]he scientists found that the head size at birth of the autistic children was, on average, in the 25th percentile (smaller than 75% of other newborns). But most of these children quickly began a period of such rapid brain growth that, by 6 to 14 months, they landed in the 84th percentile. By 4 or 5, their brain was the size of a typical 12-year old’s.