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May 25, 2011 -- A common brain defect occurs in about 75% of people with autism, molecular analysis of autistic brains reveals.
It's becoming clear that there are many different causes of autism and that autism takes many different forms. Some researchers have proposed that the various "autisms" may even be different diseases.
But now a research team led by Daniel H. Geschwind, MD, PhD, director of the UCLA Center for Autism Research and Treatment, finds that the vast majority of people with autism may share the same underlying defect in brain development.
"Is there some convergence, some commonality among the various forms of autism? That is the question we asked, and we showed that there is," Geschwind tells WebMD.
"It's definitely a very striking finding," Robert Ring, PhD, tells WebMD. Ring, vice president of translational research for the advocacy group Autism Speaks, was not involved in the study. However, most of the brains analyzed in the study came from the Autism Speaks tissue-banking program.
Geschwind's team analyzed postmortem samples from the brains of 19 people with autism and from 17 normal brains (and from three additional brains as part of a validation study). The researchers extracted RNA from the brains, allowing them to analyze how genes express themselves in brain cells.
"If DNA is the overall blueprint for the body, RNA is what is read out of the blueprint," Geschwind says. "And what is read out of the blueprint in each tissue in the body is different."
Normal brains, they found, are alike in that for about 500 genes, gene expression in the temporal lobes -- which regulate hearing, language, and the processing and interpreting of sounds -- is very different from gene expression in the frontal lobe, which plays a role in judgment, creativity, emotions, and speech.
But in as many as 75% of the autistic brains there was very little difference in gene expression between the temporal and frontal lobes.
In the autistic brains, genes related to synaptic function -- information sharing between neuronal brain cells -- were turned down to low levels of expression.
"This points to a developmental patterning defect," Geschwind says. "That means the usual patterning of the brain -- the way different parts of the brain hook up -- might be altered in autism."
"This supports a longstanding view that the development of normal brain physiology is disturbed in autism," Ring says. "Up to this point, we have been limited to trying to deduce from the genetic findings. Here we have specific evidence that something has gone wrong during development."
Geschwind notes that this research is in the earliest stages and that much more work is needed to identify exactly what goes awry during brain development in people with autism.
It's impossible to analyze brain tissue in living people, so the current technique can't be used to diagnose autism. But Geschwind says that if future research identifies specific byproducts of abnormal gene expression in the brain, it might be possible to develop a test.
Geschwind and Ring offer their thanks to the many families whose donation of tissue samples made the study possible. Ring notes that the Autism Tissue Program seeks many more donors, with and without autism. More information is available at the autismtissueprogram.org web site.
Geschwind and colleagues report their findings in the May 25 advance online issue of the journal Nature.