Married cousins aid autism research

The researchers found genes and mutations associated with autism in 88 families from the Middle East, Turkey and Pakistan in which cousins married and had children with the disorder.

Evidence had hinted at such transmission in autism, and the large amount of genetic information obtainable from such families reduced the need for a much larger sample including many families with multiple affected members.

By comparing DNA from family members with and without autism, the scientists were able to close in on recessive mutations shared by people with the condition.

Recessive mutations only have an effect when two identical pieces of DNA containing the same variations are inherited. The researchers sifted through sets of chromosomes - paired bundles of DNA containing the genes - looking for places where the DNA on each chromosome was the same.

Dr Christopher Walsh, chief of genetics at the Children's Hospital Boston in Massachusetts, said: "Eventually we find a spot where all affected children have two identical chunks of DNA and where unaffected children have something different."

Just over over 6% of the cousin marriage families had large missing segments of DNA in areas previously linked to autism. Only one of these deletions completely removed a gene. The others erased sections of DNA close to genes that acted as "on/off" switches for the genes.

In total five deletions were identified affecting at least six recognised genes. The genes have different functions, but all play a role in "reinforcing" connections between neurons - a process widely thought to be the basis of learning and memory.

This network can be disrupted in a myriad of ways, and may be one mechanisms that people with a variety of autism-linked mutations share," said Dr Michael Greenberg, also from the Children's Hospital Boston.