Different genes may be responsible for causing autism in boys than in girls, researchers said last week, a finding that may help explain why the condition is more common in boys.
And, writing in the journal Molecular Genetics, they said other genes might play a role in the early onset and late onset forms of autism.
"What is meaningful is that we have found evidence for two genetic subtypes of autism, male versus female and early versus late onset," said Geraldine Dawson, a professor of psychology and director of the University of Washington's Autism Center.
The findings could help scientists understand autism at a molecular level and seek ways to prevent it, she said.
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 less-severe forms of the disorder, such as Asperger syndrome.
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, said Gerard Schellenberg, a professor of medicine at the University of Washington who led the study.
"It is highly unlikely that there is only one gene responsible for autism," Schellenberg said in a statement.