A small study that examined brains from children who died found abnormal patterns of cell growth in autistic children. The research bolsters evidence that something before birth might cause autism, at least in some cases.
Clusters of disorganised brain cells were discovered in tissue samples from brain regions important for regulating social functioning, emotions and communication - which can all be troublesome for children with autism.
The abnormalities were found in 10 of 11 children with autism, but in only one of 11 children without the disease. The brains were donated to science after death; causes of death included drowning, accidents, asthma and heart problems.
The authors said the clusters, detected with sophisticated lab tests, were likely defects that occurred during the second or third trimesters of pregnancy.
"Because this points to the biological onset in prenatal life, it calls sharply into question other popular notions about autism," including the scientifically debunked falsehood that childhood vaccines might be involved, said lead author Eric Courchesne, an autism researcher at the University of California, San Diego.
Experts not involved in the latest study called the results preliminary and said larger studies were needed to determine if the unusual brain development found in the study caused problems, and if it was truly common in autism or even in people without the disorder. What caused the unusual structure wasn't known, Courchesne said, adding, "It could be gene mutations and environmental factors together."
Scientists have been working for decades to find the cause of autism, and they increasingly believe its origins begin before birth. In addition to genetics, previous research suggests other factors might include infections during pregnancy, preterm birth and fathers' older age at conception.
Other scientists have suggested that autism may be linked with abnormalities in the brain's frontal region, and that for at least some children, problems begin before birth. "But this research provides probably some of the most elegant evidence for those two very important biological themes," said Janet Lainhart, an autism researcher at the University of Wisconsin.
The study follows Courchesne-led research suggesting that abnormal gene activity leads to an excessive number of brain cells in the brain's prefrontal cortex, located behind the forehead. The same region and adjacent areas of the brain were implicated in the new study.
His studies suggest that in children later diagnosed with autism, genetic networks that regulate prenatal brain cell growth are faulty.
Larger studies are needed to determine how common the abnormalities are and what might be the cause.