In the on-going search to find the cause of Autistic Spectrum Disorders, the latest research says different genes may be responsible for causing autism in boys than in girls, and the discovery may help explain why the condition is more common in boys.
Researchers at the University of Washington also say that other genes may play a role in the early onset and late onset forms of autism.
The researchers say they have found evidence for two genetic subtypes of autism, male versus female and early versus late onset and this may help scientists understand autism at a molecular level and find ways to prevent it.
According to the U.S. Centers for Disease Control and Prevention, autism is very common among U.S. children and as many as 1 in every 175 have the disorder.
This equates to at least 300,000 U.S. schoolchildren with some form of autism, a condition characterised by problems with learning, socializing and behaviour issues.
For the study the researchers examined the DNA of 169 families with at least two siblings who met the strict criteria for autism.
They also scanned the DNA of 54 other families that had members with autism and other forms of the disorder, such as Asperger syndrome.
They found strong evidence for an autism gene on chromosome 7 and "less, but still compelling evidence" for genes on chromosomes 3, 4 and 11.
Gerard Schellenberg, a professor of medicine at the University of Washington who led the study says it is highly unlikely that there is only one gene responsible for autism and there may be 4 to 6 major genes and 20 to 30 others that might contribute to autism to a lesser degree.
Schellenberg says because autism is rarer in females, it may take more risk genes for a female to have autism and there also is the possibility that there might be a biological difference in autism for females versus males.
The researchers were looking for genes that might put children at higher risk of autism so they could begin early treatment or possibly in future find a way to prevent the condition.
Geraldine Dawson, the director of the UW's Autism Center and co-author of the study, says once susceptibility genes are discovered infants can be screened to identify those at risk early in life.
Early identification can lead to early intervention, which could be more effective, says Dawson.
The study is published in the journal Molecular Genetics.