Researchers looked at 3,871 people with autistic spectrum disorder (ASD) and compared their genes to those of almost 10,000 people without the condition.
Because of the sheer amount of data generated from this research, the researchers used new statistical methods to work out how many genes were likely to be involved in the development of ASD. By setting their statistical cut-off points so that their 'false discovery rate' was very low (five percent), they found that 22 genes were implicated in ASD. But by setting the false discovery rate to ten percent, 33 genes were associated with the disorder.
'These findings tell us that there are a relatively large number of genes that, when damaged, substantially increase an individual's chance of developing autism,' co-author Dr David Cutler from the Emory University School of Medicine in Atlanta told HealthDay. 'Autism does not have one cause, but a very, very large number of potential causes.'
'Before these studies, only 11 autism genes had been identified with high confidence, and we have now more than quadrupled that number,' said Dr Stephan Sanders, assistant professor of psychiatry at the University of California, San Francisco, who conducted the research.
The genes were classed into three broad groups. Some were involved in the formation of synapses, affecting how neurons send signals in the brain; some affected transcription, thereby altering the protein that the genes code for. The third group affected the way DNA is 'packed up' and stored within cells, which also affects how genes are expressed.
The research has raised questions about whether genetic screening for autism is possible.
Carol Povey, director of the National Autistic Society's Centre for Autism, commented on the study, saying: 'Autism is a highly complex story of genes not only interacting with other genes, but with non-genetic factors too.'
'Research like this helps us to understand the genetics involved in certain forms of autism and opens up the possibility of whole families gaining a better understanding of a condition they may share. However, we are still a long way from knowing what causes autism.'