Older fathers are more likely to have children with autism spectrum disorders (ASD), a new study has found.
The report, published in the September issue of Archives of General Psychiatry, reveals that men over the age of 40 are six times more likely to have children with ASD than those under the age of 30.
Autism affects people's social and language skills and results in repetitive patterns of behaviour.
Researchers from the institute of psychiatry at Kings College London and the Mount Sinai school of medicine in New York analysed children born during the 1980s in Israel at the age of 17 to assess whether they had any psychiatric disorders.
Even after socioeconomic status and the mother's age had been taken into account, the researchers found a significant increase in ASD in children of older fathers.
They propose that the trend may be due to genetic mechanisms such as spontaneous mutations in sperm-producing cells or alterations in genetic "imprinting," which affects gene expression.
"It is important to keep in mind, however, that age at paternity is influenced by the sociocultural environment and varies across societies and over time," the researchers wrote.
"In a given population, a change in the sociocultural environment could produce a change in paternal age at birth. In theory, it could thereby lead to a change in the incidence of genetic causes of autism."
According to the researchers, the study "provides the first convincing evidence that advanced paternal age is a risk factor for autism spectrum disorder".