The world's largest search for genes linked to autism has uncovered new mutations believed to raise a child's risk of developing the brain disorder.
Scans of DNA from nearly 1,200 families with two or more children affected by autism have broadened the list of genes involved with the condition and will allow doctors to screen more young people for autism at an early age, when therapies are most effective.
Autism typically disrupts a person's ability to communicate and form social relationships, leading to serious behavioural problems. The five-year gene search is the first part of the Autism Genome Project, a collaboration of more than 120 scientists at 50 institutions around the world. Part of the study, published in Nature Genetics yesterday, involved checking for so-called copy number variations, in which there is either an extra or missing copy of a gene.
The search found two new mutations - one in an unknown gene on chromosome 11, and the second a defect in a protein called neurexin 1, which works with a brain messenger chemical called glutamate to enable neighbouring neurons to communicate with one another.
Anthony Monaco, an autism genetics expert at Oxford University and leader of the UK part of the study, said 10% to 20% of cases could be down to additional or missing copies of crucial genes. Inheriting more mutated forms of key genes may lead to a more severe form of the condition.
Geraldine Dawson, a co-author at the University of Washington's Autism Centre, said: "As we identify these genes we will be able to screen young children for autism at an early age and begin interventions earlier, which can have a dramatic effect for some children."
Last year doctors at St Thomas' hospital in London revealed that autism and similar disorders were more common than suspected. They screened children aged nine and 10 and diagnosed autism or related disorders in more than 1%. Previously there were thought to be four to five cases per 10,000.
The researchers did not find that autism was becoming more common but believe it is now diagnosed more often. It affects nearly four times as many boys as girls.
The second phase of the project is due to begin this year when researchers focus on the genes identified and conduct a more intense search for other genetic factors.
The search has only been possible because of recent advances in biomedical technology, in particular gene chips, which allow fast testing of entire genomes, "There are going to be a lot more diseases that give up their culprits because of this technology," said Prof Monaco.
