Children fathered by men at age 40 and older have a higher risk of developing autism, possibly because of mutations or other genetic changes, researchers reported on Monday.
The study "provides the first convincing evidence that advanced paternal age is a risk factor for autism spectrum disorder," said the authors from Mount Sinai School of Medicine, New York, and the Institute of Psychiatry, King's College London.
The findings were based on a look at thousands of children born in Israel during the 1980s. All males and three-fourths of the females born in the time period involved were checked by Israeli draft officials at age 17 and any psychiatric disorders were recorded.
"Offspring of men 40 years or older were 5.75 times more likely to have (autism disorders) compared with offspring of men younger than 30 years," said the study published in the Archives of General Psychiatry.
"Advancing maternal age showed no association," it added.
Autism can cause symptoms ranging from social isolation to repetitive and damaging behaviour and sometimes mental retardation.
The problem has become increasingly common, affecting 50 in every 10,000 children in the United States, in part due to greater awareness and changes in diagnoses, the study said.
The report said several genetic mechanisms might be behind the paternal age association found, including spontaneous mutations in sperm-producing cells.