Autistic children may have tiny anomalies in their genes that potentially trigger the condition, researchers say.

In the largest investigation into the genetic causes of autism, scientists have identified key parts of the human genome that may explain why the condition often runs in families.

The exact causes of autism are not known, but the preliminary findings of the Autism Genome Project add to evidence that minuscule, rare variations in genes may heighten risk of the condition.

More than 120 scientists from 19 countries have studied nearly 1,200 families that have at least two members with autism spectrum disorders (ASD).

A child whose sibling has ASD has an estimated one in twenty chance of developing the condition. The findings suggest that genetic variations in the chemical messenger system, which “wires up” the brain during early development, may be partly responsible.

The study, published online today by the journal Nature Genetics, has also focused attention on a previously overlooked part of chromosome 11, a large macromolecule of DNA among the 23 pairs of chromosomes found in human cells.

Sub-microscopic anomalies, such as tiny deletions or the multiplication of genetic material, are relatively common in humans and are not necessarily harmful. But evidence suggests that these anomalies may increase the odds of having — or even cause — autism if they affect certain sites associated with the disorder.

Anthony Bailey, Professor of Psychology at Oxford University, who led one of four scientific teams involved in the study, said: “For the first time we could examine the genome of a huge sample of families compared to previous studies, and examine their genome in much finer detail.

“We could pick up things that we had not seen before in smaller studies and found a surprisingly high number of variations in particular areas.”

Some of the common variations found by the scientists affected components of the brain’s glutamate neurotransmitter system, which increases brain activity and plays an important role in helping brain cells to communicate.

Genetic abnormalities in this pivotal system have been regarded as prime suspects for the development of autism.

Fred Kavalier, of the British Society for Human Genetics, said: “This research has identified new genes that make up part of the complicated autism jigsaw. Further research will be needed to understand these genes better, in the hope that they will be useful in designing new treatments.

“A cure for autism is a long way off, but this is one small step in the right direction.”

Arrested development

One in 100 British children is said to suffer from autistic spectrum disorders, which affect more than 500,000 families

Boys are four times more likely than girls to develop the condition Autistic children have problems with language and social interaction and many exhibit significant mental impairment

Those with Asperger’s syndrome have similar social difficulties but can achieve normal language milestones Scientists estimate that about 10 per cent of autism cases can be ascribed to single-gene disorders or to chromosomal abnormalities that affect the brain’s development

Source: National Austistic Society, Autism Genome Project

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