Using Swedish national registers, researchers identified 5,936 individuals with autism and 30,923 children without autism, the ‘control’ group, born in Sweden since 1932. For each child they had data on their maternal and paternal grandfathers’ age of reproduction and details of any psychiatric diagnosis.
They found that men who had a daughter when they were 50 or older were 1.79 times more likely to have a grandchild with autism. Men who had a son increased the risk of their grandchild having autism by 1.67 times, compared to men who had children when they were 20 to 24-years-old.
Autism is known to be caused by a combination of genetic and environmental factors. Previous studies have shown that older paternal age is a risk factor for autism in children, with fathers aged 50 or over doubling the risk of their children being diagnosed with the disorder.
The researchers say their findings suggest that mutations which occur in the male sperm cells over time are passed on to the otherwise healthy child and may influence the risk of future generations developing autism.
They go on to say that the genetic risk could accumulate over generations, or could interact with other risk factors, until it reaches a threshold, resulting in the disorder manifesting itself.
Dr Avi Reichenberg from King’s Institute of Psychiatry, and co-author of the study, said, ‘For the first time in psychiatry, we show that your father’s and grandfather’s lifestyle choices can affect you. This doesn’t mean that you shouldn’t have children if your father was old when he had you, because while the risk is increased, it is still small. However, the findings are important in understanding the complex way in which autism develops.’
The study, ‘Autism risk develops across generations: a population based study advancing grandparental and paternal age’, is published in the current issue of JAMA Psychiatry.