Children of older fathers perform less well in intelligence tests during infancy

Mar 09, 2009

Children of older fathers perform less well in a range of cognitive tests during infancy and early childhood, according to a study published this week in the open-access journal PLoS Medicine. In contrast, the study finds that children with older mothers gain higher scores in the same tests - designed to measure the ability to think and reason, including concentration, learning, memory, speaking and reading skills.

The age at which men and women are having is increasing in the developed world, but whilst the "" - the effect of increasing maternal age on reduced fertility - is widely-discussed, the consequences of increased are not as well known. Recent evidence demonstrates a link between and specific health problems in their children, including birth deformities and cancer, as well as such as autism and schizophrenia.

This new study by John McGrath, of the Queensland Brain Institute, in Australia, and colleagues, investigates the link between a father's age and their child's general cognitive ability, by reanalyzing an existing dataset of 33,437 children born between 1959 and 1965 in the United States. This data formed part of the US Collaborative Perinatal Project (CPP), which tested each child in the dataset at 8 months, 4 years and 7 years of age with a number of widely-used intelligence scales - including assessments of sensory discrimination and hand-eye coordination, conceptual and physical coordination, and at 7 years reading, spelling and arithmetic ability.

Crucially in their reanalysis of this dataset, McGrath and colleagues adjusted their study to take into account socio-economic factors. They used two models: one that focused on physical factors including the parents' age, and a second that indexed social factors such as maternal and paternal education and family income. They found that the older the father, the more likely the child was to have lower scores on the various tests used by the CPP - with the exception of one measure of physical coordination. The researchers also grouped the children by their mother's age and found that in contrast, the older the mother the higher the scores of the child in the cognitive tests.

Previous researchers have suggested that the children of older mothers may perform better because they experience a more nurturing home environment; if this is the case, this study suggests that children of older fathers do not necessarily experience the same benefit. The researchers advance several hypotheses as possibilities to explain the association between advanced paternal age and children's cognitive ability, including genetic and social arguments. Unlike a woman's eggs - which are formed when she herself is in the womb - a man's sperm accumulates over his lifetime, which previous studies have suggested can mean increased incidence of mutations in the sperm at an older age. However, as emphasized in an expert commentary on the findings by Mary Cannon (Royal College of Surgeons in Ireland) - who was uninvolved with the study - genetic and social factors can operate in conjunction. "New explanatory models are needed that can encompass socio-cultural and interpersonal factors as well as biological variables", she argues. Given the trend towards older maternal and paternal ages in the developing world, policy-makers may want to consider promoting an awareness of the risks to children that this study associates with delayed fatherhood.

More information: Saha S, Barnett AG, Foldi C, Burne TH, Eyles DW, et al. (2009) Advanced paternal age is associated with impaired neurocognitive outcomes during infancy and childhood. PLoS Med 6(3): e1000040. doi:10.1371/journal.pmed.1000040

Source: Public Library of Science

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not rated yet Mar 09, 2009
This sort of result has been hypothesized as likely in light of recent breakthroughs in the understanding of 'epigenetic' factors (ie. heritable factors aside from the base DNA sequence). Certain epigenetic factors which change over the course of a lifetime (such as the distribution of histone proteins that control which portions of DNA are deactivated) are in turn passed on to the offspring. The repercussions of it haven't been worked out yet.. but I've found the whole thing somewhat startling, since I'd been living on the assumption that my heritable traits were not subject to my decisions.

(if you're unfamiliar with epigenetics and it sounds like I'm a quack or troll, try a quick Google search)

As far as making conclusions about epigenetics, the study above is of course not sufficient to draw conclusions in itself. Perhaps some day a connection will be found.
not rated yet Mar 09, 2009
From a related article on physorg, the following paragraph seems applicable:
"As men age, successive germ cell replications occur, and de novo [new, not passed from parent to offspring] mutations accumulate monotonously as a result of DNA copy errors," the authors continue. "Women are born with their full supply of eggs that have gone through only 23 replications, a number that does not change as they age. Therefore, DNA copy errors should not increase in number with maternal age. Consistent with this notion, we found smaller effects of increased maternal age on the risk of bipolar disorder in the offspring."

This offers a contrary explanation to the epigenetic hypothesis I brought up in my comment above.. and seems to make more sense in light of the findings. (though it's possible that both genetic and epigenetic mutations could be at work.. in part because mutations in histone distribution may occur in replication as well)

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