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Across Generations: Older Fathers May Transmit Autism Risk To Their Grandkids

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In the ever-complicating discussion of how developmental disorders like autism develop, new studies continue to throw new variables into the mix. It’s pretty well thought that autism develops from a combination of genetic and environmental variables, which are still only vaguely understood. Last year, several studies came out showing that the age of the parents, and particularly the age of the father, seemed to increase a child’s risk for autism. Now, it seems that on top of the father’s age (or mother’s), it’s also the grandfather’s age at the time he conceived his child that can affect his grandchild’s risk of autism.

A new study out today in JAMA Psychiatry looked at health records from over 5,900 Swedish people with autism, and 31,000 without, born after the year 1932. The researchers knew everyone’s psychiatric histories, the ages of the grandparents when they conceived a child, and the grandchild’s risk of autism. They analyzed the data to find correlations between these variables.

For men who had a daughter when they were 50 or older, their grandchild’s risk of autism was 79% higher, compared to grandfathers who’d had their daughters between 20 and 24. For men who had sons after age 50, their risk of having a grandchild with autism was 67% higher.

"We know from previous studies that older paternal age is a risk factor for autism,” said Emma Frans, lead author of the study from Karolinska Institutet. “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."

It’s known that spontaneous (or "de novo") mutations in sperm cells can build up over time, which is believed to increase a child’s risk for autism, along with other psychiatric disorders like schizophrenia and bipolar disorder. For example, data from a study last year suggest that a 70-year old father passes on about eight times the number of mutations as a 20-year old. But the transmission of mutations seems to span more than two generations. It may be that genetic mutations can accumulate without actually leading to a disorder, until, perhaps, they are triggered by an environmental factor or pile up enough to reach a critical mass.

"We tend to think in terms of the here and now when we talk about the effect of the environment on our genome,” said study author Dr. Avi Reichenberg, from King's Institute of Psychiatry. “For the first time in psychiatry, we show that your father's and grandfather's lifestyle choices can affect you.”

The studies come at an interesting time, since the CDC has just released new estimates that suggest that 1 in 50 school-aged children in the US has autism. This is a significant jump from the previous estimate of 1 in 88. However, because the new data rely on different methods of collection, it’s unclear whether the numbers are actually climbing.

It's important to remember that the effect of the age of the grandfather was not huge, and it was only a correlation. The authors stress that the results should not make older fathers panic that they are increasing their grandchild’s autism risk. “This doesn't mean that you shouldn't have children if your father was old when he had you,” adds Reichenberg, “because whilst the risk is increased, it is still small. However, the findings are important in understanding the complex way in which autism develops.”

It’s just one more piece of the puzzle. The study offers a few new clues about how autism is transmitted across the generations and how it may develop within a child.

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