Men who fathered children after turning 50 increased their grandchildren's risk of developing autism, a study found. (Credit: Getty Images)

Men who have children after they turn 50 not only increase their children's risk for developing autism, but may increase their grandchildren's risk for developing it, too, researchers at Sweden's Karolinska Institutet found.

Compared with men who father children in their 20s, older men who had daughters were 1.79 times more likely to have autistic grandchildren, and older men who had sons were 1.67 times more likely to have them, according to the study published today in the Journal of the American Medical Association, or JAMA.

"This could accumulate if both grandparents and you yourself [have] children at an older age," said lead researcher, Emma Frans, who is getting her PhD in medical epidemiology at the Karolinska Institutet. "But clearly the issue about when you should have your child is quite complex."

In the United States, about 1 in 50 school age children has autism, according to a Centers for Disease Control and Prevention survey. This indicates that at least one million children are autistic.

Frans and her colleagues examined data from Sweden's patient registries, which date back to 1932 and include grandparent information for nearly 37,000 children, about 6,000 of whom were diagnosed with autism. Frans said previous studies found that older fathers and older mothers were also more likely to have autistic children, but this study indicates that it can skip a generation.

Men may play a significant role in autism development because their reproductive cells are more prone to mutation, Frans said. Although female reproductive cells divide and replicate 24 times, male reproductive cells continue reproducing throughout a man's life. By the time he is 20, his reproductive cells have undergone 200 divisions. By the time he is 40, his reproductive cells have undergone 600 divisions.

"Every time the cell divides, there's a risk something goes wrong, which can result in manifestation of mutation," Frans said.

The study is an important piece of the medical literature, but it doesn't mean that older parents should be discouraged from having children, said Lori Warner, director of the HOPE Center for Autism at Beaumont Hospitals in Michigan. Researchers have also examined whether pollution and prenatal folic acid contribute to autism development, so there are many factors at play to consider, she said.

The study is also based on data rather than experiments done in a lab, so while Frans and her colleagues can identify correlation, they can't identify causation, Warner said.

"The age of your parents, you can't control," Warner said. "It's helpful for you to know that your dad was 60 when he had you, and you might be more at risk. But whether that should stop you from having a child at a certain age, that shouldn't be a deciding factor."