Older parents more likely to have an autistic child… but scientists are stumped as to whyChildren born to fathers over 40 had up to 55%
greater risk of developing autism compared to children with fathers under 35
Children born to a parent over 35 are at greater risk for developing an autism spectrum disorder – but the risk is the same whether just one or both parents are older, researchers said.
The findings, from University of Aarhus School of Public Health in Denmark, cast doubt on the theory that older sperm or eggs have more mutations that could increase the odds of having a child develop autism.
Older parents: The data demonstrates older parents are more likely to have children with autism, but doesn't establish why that's the case
Study leader Erik Thorlund Parner said if genetic problems from older sperm or eggs were to blame you would expect to see an even higher risk of autism in children with two older parents.
Yet Professor Parner and his colleagues did not find a higher risk of autism among children with two older parents compared with just one.
'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,' said Professor Marissa King from Yale School of Management, who wasn't involved in the study.
The researchers collected information on more than 9,500 children in Denmark who had been diagnosed with an autism spectrum disorder.
These disorders range from mild Asperger's Syndrome to severe mental retardation and social disability.
In the new study, children born to fathers in their late thirties had up to a 28 per cent higher risk of being diagnosed with an autism spectrum disorder than kids born to fathers under age 35. The increase in risk was not tied to the mother's age.
Children born to fathers over 40 had a 37 to 55 per cent greater risk of developing an autism spectrum disorder compared to children of fathers under 35, and the mother's age didn't seem to matter.
According to the Centers for Disease Control and Prevention, about 10 in 1,100 children have an autism spectrum disorder.
Children whose mothers had them in their late 30s were 21 to 37 per cent more likely to develop autism than children with mothers under 35. The father's age did not change the numbers.
Just like with fathers over age 40, children born to mothers over 40 were 28 to 65 per cent more likely to have autism than children with mothers under age 35, regardless of the age of their dad.
'The result was surprising in that there was no additive effect of maternal and paternal age,' Parner said.
Some earlier studies have also found that older parents are more likely to have a child with autism, but they have not had consistent results.
For example, one 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 mother is under the age of 30.
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.