Researchers have found a link between a grandfather’s age and an increased risk for autism in his grandchildren. In fact, men who fathered children at age 50 or older were almost twice as likely as younger fathers to have a grandchild with autism.
For the study, lead author Emma Frans and colleagues reviewed data on births in Sweden beginning in 1932. Among the tens of thousands of births, the database they used had information about grandparental age for nearly 6000 autism cases and for almost 31,000 controls (families with no autistic children).
Specifically, grandfathers who had a daughter when they were 50 or older were 1.79 times more likely to have an autistic grandchild.
If they had a son at age 50 or older, they were 1.67 times more likely to have an autistic grandchild.
Whether grandpa was on the mother’s side or the father’s side of the family didn’t seem to make much difference.
Interestingly, this study found that the age-related increase in autism risk was independent of the age of the autistic child’s own parents. Other studies, however, have identified a link between older parental age (particularly for fathers) and autism risk.
As an explanation for the findings, the researchers point to other studies suggesting that new genetic mutations occurring over the father’s lifetime might pass to offspring and be linked to autism.
If this is possible for dad, then it’s also possible for grandpa to have made a contribution to any autism-related gene changes. Research does suggest a strong contribution of new mutations to the occurrence of autism in families.
If environmental factors are interacting with these genes in the risk for autism, then the findings seem to suggest that we need to not only look at current environmental factors, but also go back at least two generations.
“Considering our finding linking grandpaternal age and risk of schizophrenia, we propose that a proportion of age-related de novo mutations are phenotypically silent in the offspring, but can still influence risk of autism in subsequent generations, perhaps via the interaction with other susceptibility factors,” said the researchers.
“This indirect mechanism is consistent with the evidence that some mutations associated with neurodevelopmental disorders can occur in apparently healthy individuals.”
In other words, the accumulation of mutations required for autism to actually manifest might take a few generations to reach threshold. It’s a possibility that non-autistic individuals are walking around with these genetic differences, just not in sufficient numbers to be considered “autism.”
Other recent work has shown that this accumulation of parentally “silent” genetic changes could add up to autism in the child of two people carrying them. Now it appears that being the grandchild of someone with these changes is risky too.
Source: JAMA Psychiatry