Researchers are intending a wider scale study following the results of a study looking at the effects of parental age on instances of autism. The initial study of Danish families found that children born to a parent over age 35 are at greater risk of developing an autism spectrum disorder — but the researchers are confused as why this is and why the risk is the same whether just one or both parents are older.
“Parental age doesn’t appear to be synergistic. That is having an older mom and an older dad doesn’t increase risk more than having one or the other,” said Marissa King, a professor at the Yale School of Management, who was not involved in the study. “The data clearly demonstrate that older parents are more likely to have kids with autism, but it doesn’t establish why that is the case,” King said.
The findings go against previous theories that perhaps older sperm or eggs have more mutations that could increase the likelihood of having a child with autism. For example, one 2010 study found that having an older mother increases a child’s risk of autism, but having an older father only increases the risk if the mom is under the age of 30.
Erik Thorlund Parner at the University of Aarhus School of Public Health in Denmark said that if the results could be explained by genetic problems due to older sperm or eggs, then having both an older sperm and an older egg together should equal an even higher risk of autism for the child. Yet this was not the case.
“We do not really have a qualified guess on the explanation to the non-additive effect,” Parner, who led the study, said. “I don’t believe that one can yet say anything conclusive about whether (having an) older parent is biologically related to autism.”
The researchers collected information on more than 9,500 children in Denmark who had been diagnosed with an autism spectrum disorder (ASD).
In the study, children born to fathers in their late thirties had up to a 28 percent higher risk of being diagnosed with an ASD than children born to fathers under age 35.
For children born to fathers over age 40, the risk for developing an ASD was 37 to 55 percent greater than for children of fathers under age 35.
Similar to the findings on fathers, children whose mothers had them in their late 30s were 21 to 37 percent more likely to develop autism than children with mothers under age 35.
Children born to mothers over age 40 were 28 to 65 percent more likely to have autism than children with mothers under age 35.
All figures were not affected by the age of the other parent.
Parner said he and his colleagues are planning on an even larger analysis of autism and parental age using data from Denmark, Finland, Israel, Norway, Sweden and Western Australia.