By Jasminee Sahoye

A study has discovered that men who have children at older ages are more likely to have grandchildren with autism compared to younger grandfathers.

The study was led by King’s College London’s Institute of Psychiatry, Karolinska Institute in Sweden and the Queensland Brain Institute in Australia.

Researchers identified 5,936 individuals from Swedish national registers with autism and 30,923 healthy controls born in Sweden since 1932.

The study found the risk of autism in the grandchild increased the older the age of the grandfather at the time his son or daughter was born. 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 when they were 50 or older were 1.67 times more likely to have a grandchild with autism, compared to men who had children when they were 20-24.

“We tend to think in terms of the here and now when we talk about the effect of the environment on our genome. For the first time in psychiatry, we show that your father’s and grandfather’s lifestyle choices can affect you. This doesn’t mean you shouldn’t have children if your father was old when he had you, because whilst the risk is increased, it is still small. However, the findings are important in understanding the complex way in which autism develops,” said Dr. Avi Reichenberg, from King’s Institute of Psychiatry and co-author of the report.

Emma Frans, lead author of the study from Karolinska Institute said: “We know from previous studies that older paternal age is a risk factor for autism. This study goes beyond that and suggests that older grandpaternal age is also a risk factor for autism, suggesting that risk factors for autism can build up through generations.”

Autism is known to be caused by a combination of genetic and environmental factors. Previous studies have shown older paternal age is a risk factor for autism in children: fathers aged 50 or older have a more than doubled risk to have a child diagnosed with autism compared to younger fathers.

And in a related study, another set of researchers at the Karolinska Institute, Sweden and King’s College London wanted to find out the possible associations between maternal age and autism.  During their analysis of past studies they also found that non-heritable and environmental factors may play a role in children’s risk for autism.

The researchers compared the risk of autism in different groups of material age (under 20, 24-29, 30-34, and 35+). They found that children of mothers older than 35 years had a 30% increased risk for autism. Children of mothers under 20 had the lowest risk of developing autism.

The association between advancing maternal age and risk for autism was stronger for male offspring and children diagnosed in more recent years.

The analysis included 25,687 cases of autism spectrum disorder and over 8.6 million control subjects, drawn from the 16 epidemiological papers that fit inclusion criteria for the study as defined by the investigators. The researchers identified and discussed several potential underlying causes of the association between maternal age and risk for autism such as increased occurrence of gene alteration during the aging process and the effects of exposure to environmental toxins over time.

“The study makes us confident there is an increased risk for autism associated with older maternal age, even though we do not know what the mechanism is. It has been observed in high quality studies from different countries, including the U.S. All studies controlled for paternal age which is an independent risk factor for autism,” said Sven Sandin, the lead author.