Different genes may be responsible for causing autism in boys than in girls, which may help explain why the condition is more common in boys. And other genes may play a role in the early onset and late onset forms of autism. What is meaningful is that the researchers found evidence for two genetic subtypes of autism, male versus female and early versus late onset. These findings could help scientists understand autism at a molecular level and seek ways to prevent it. The U.S. Centers for Disease Control and Prevention has estimated that autism was very common among U.S. children - with up to one in every 175 with the disorder. That would mean at least 300,000 U.S. schoolchildren have autism, a condition that causes trouble with learning, socialising and other behaviour. Researchers from the University of Washington Molecular Genetics, USA, did a study wherein they 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 less-severe forms of the disorder. They came up with strong support for an autism gene on chromosome 7 and less, but still compelling evidence for genes on chromosomes 3, 4 and 11. It is highly unlikely that there is only one gene responsible for autism. There may be four to six major genes and 20 to 30 others that might contribute to autism to a lesser degree. Because autism is rarer in females, it may take more risk genes for a female to have autism. There is also the possibility that there might be a biological difference in autism for females versus males. The researchers said that they were looking for genes that might put children at higher risk of autism so they could begin early treatment or perhaps even one day find a way to prevent the condition. Once these 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 have a much more dramatic effect. Also, when a gene is discovered, the underlying biology of autism at the molecular level can be discovered. And once the biology is understood, one can develop a prevention strategy including medical approaches.
American Journal of Epidemiology,
July 2006