New research, led by Professor Hakon Hakonarson from the Children's Hospital of Philadelphia and published in the journal Nature, has identified for the first time common genetic variations that could explain 15 per cent of autism cases.
Several genes have been previously linked to autism, but these are rare and only account for a small number of autism cases. To search for common variants, researchers scanned the DNA of 3,100 people from 780 American families with two or more children with autism and then replicated the results by studying an additional 1,200 affected and 6,500 unaffected people.
Six variations that increase the risk of autism were discovered, all of which are located on chromosome 5 between two genes, CDH10 and CDH9. These genes code for proteins called cell adhesion molecules, which are important in making connections and communication between brain cells. One of the variations identified occurs in more than 65 per cent of cases - although the scientists estimate it only plays a major role in about 15 per cent, and that other, unknown factors are more important in the remainder.
Professor Hakonarson said: 'Because other autism researchers have made intriguing suggestions that autism arises from abnormal connections among brain cells during early development, it is very compelling to find evidence that mutations in genes involved in brain interconnections increase a child's risk of autism', adding 'there are going to be many genes involved in causing autism'.
Another study, published at the same time in the journal Molecular Psychiatry and led by Professor Tony Monaco from the Wellcome Trust Centre for Human Genetics in Oxford, UK, has also identified a link between a gene important for growth and development of brain cells and autism.
Professor Simon Baron-Cohen, from the autism research centre at the University of Cambridge, UK, said that there are now 133 genes linked to autism. He said 'The challenge for future research will be to establish which aspects of autism they can explain, how many of these genes are necessary and sufficient to cause autism and how they may interact with environmental factors'.
Autism relates to autism spectrum disorders, which involve traits such as communication and social interaction difficulties, narrow interests and repetitive behaviour. It affects about 1 in 150 children and is more commonly seen in boys.