The brains of children with autism contain a built-in patchwork of defects, suggesting that the developmental disorder begins while they are growing in the womb, reported a study Wednesday.
Researchers described their findings in the New England Journal of Medicine as "direct evidence" of a prenatal origin for autism, which affects as many as one in 88 children in the United States and has no known cure.
"Building a baby's brain during pregnancy involves creating a cortex that contains six layers," said co-author Eric Courchesne, professor of neurosciences and director of the Autism Center of Excellence at University of California, San Diego.
"We discovered focal patches of disrupted development of these cortical layers in the majority of children with autism."
For the study, researchers dissected brain tissue from 11 children, aged 2 to 15, who had been diagnosed with autism spectrum disorder (ASD) and who had died, most of them by drowning.
Looking for a specific set of 25 genes that had "robust, consistent, and specific expression patterns in the cortex," they compared them to brain samples from 11 children without autism, said the study.
Researchers found that 91 percent of the autistic brains were lacking -- or showed an unusual pattern -- of the expected genetic markers in several layers of the cortex.
The signs of disorganization were found in patches across the different layers of the frontal and temporal lobes of the brain, the parts that are responsible for social function, communication, emotions and language.
"The most surprising finding was the similar early developmental pathology across nearly all of the autistic brains, especially given the diversity of symptoms in patients with autism, as well as the extremely complex genetics behind the disorder," said co-author Ed Lein of the Allen Institute for Brain Science in Seattle.
Researchers said they still don't understand why these changes come about in some children, apparently leading to autism, but not in others.
The patchwork nature of the defects does, however, provide a clue as to why autism can affect people in various degrees, from severe to mild disabilities.
It also may explain why some children respond to intensive therapy and become better communicators when identified early, since the brain may be able to rewire some connections to overcome the areas that are not working.