22 August, 2006

Autism linked to delayed brain development - health - 21 August 2006 - New Scientist

Autism linked to delayed brain development - health - 21 August 2006 - New Scientist
Autism may be the result of a delay in neuronal development in the first year of life, despite the fact that autistic children have larger brains, a new study suggests.

The findings challenge a previously held theory that brain abnormalities characteristic of autism were due to faster development.

Brain scans, using magnetic resonance imaging (MRI), have shown that children with autism have brains that are enlarged by around 10%. However, although the children’s brains are larger in size, they appear to lack the neuronal development of healthy children, the researchers say.

Stephen Dager at the University of Washington School of Medicine, US, and colleagues examined the brains of children aged three and four. They compared the brain development of children with autism to children with normal development using a technique known as T2 relaxation, which measures the water properties of brain tissue. As the brain develops, water gets incorporated into neurons and changes from being mobile to tightly bound.

During normal development, this process occurs at a dramatic pace for the first six months, and then continues at a slower pace until 18 months.

Critical stages
Surprisingly, they found that water was more mobile in autistic brain tissue, suggesting that there is actually a delay in neuronal development. This delay was found to be more specific to grey matter distributed at the surface of the brain.

The delay could be cause by inflammation in the first year of life, Dager suggests. “If you’ve got inflammation, it can affect connectivity at a critical stage of brain development.” This may lead to learning difficulties as the child develops, he suggests. “For example, a child has certain key developmental stages for learning language and if you miss those it can be harder to learn that language.”

Some children may have a gene that makes them more likely to produce an inflammatory response early in life, Dager speculates.

Gene hunt
“I think these results are an interesting development, but most research still has no direct link to treatment,” says Matthew Belmonte, senior research associate at the Autism Research Centre at the University of Cambridge in the UK.

“Until we know exactly what it is that causes the abnormal development of grey matter we cannot develop drug treatments,” he adds.

Current research has focused on finding candidate genes that might cause rapid early development, but Dager’s study suggests that other avenues of research could be more appropriate. “One might look at genes that cause a susceptibility to inflammation instead,” he says.

Journal reference: Neurology (vol 67, p 632)
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