Older father, younger mother, bad idea for baby?

The trend for men to follow in the fertile footsteps of Michael Douglas, Mick Jagger and Rupert Murdoch by becoming fathers in later life may have unforeseen and unwanted consequences for their children.

The offspring of older fathers are more likely to do less well in intelligence tests than the children of younger men, scientists say, and it may be the result of genetic problems with the sperm of men over 45. The children of older mothers, by contrast, tend to fare better in intelligence tests than children with younger mothers. The researchers believe this may be the result of better nurturing by more mature women.

It is well established that more older men are fathering children. In 1993, for instance, about 25 per cent of births within marriage in England and Wales were to fathers aged 35 to 54, but this had risen to 40 per cent by 2003.

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Well-known older fathers include the Harry Potter actor Sir Michael Gambon, 68, whose partner Philippa Hart, 44, is reportedly pregnant with their second child. The BBC's world affairs editor, John Simpson, and his second wife, Dee Kruger, a television producer, had a son, Rafe, in January 2006, when Simpson was 61.

In women, it becomes increasingly difficult with age to conceive, but this is less so with men, who can father children for as long as they are capable of having sex – which can be well into their 70s or 80s. While there has been extensive coverage of the health problems associated with older motherhood, scant attention has been paid to any potential difficulties faced by the children of older men. However, recent studies have linked paternal age with congenital problems such as neural tube defects and a range of medical disorders of later life, such as schizophrenia, dyslexia, bipolar disorder and autism.

The latest study was based on a retrospective analysis of nearly 33,500 children born in America between 1959 and 1965, whose cognitive abilities were tested at the ages of eight months, four years and seven years. In addition to being assessed on hand-to-eye co-ordination, sensory discrimination and conceptual knowledge, the older children were also tested on their reading, spelling and arithmetic ability.

John McGrath, of the University of Queensland in Brisbane, Australia, who led the study published in the online Public Library of Science, said there was a clear decrease in performance linked to paternal age – something not seen in the children of older mothers. "We report, to our knowledge for the first time, that the offspring of older fathers show impairments on a range of neurocognitive tasks during infancy and childhood.

"The patterns of these findings were relatively consistent across ages and across neurocognitive domains," Professor McGrath said. "In light of secular trends to delayed fatherhood, the clinical implications of the mechanisms underlying these findings warrant closer scrutiny."

The study, however, could not shed light on whether those children catch up with their peers in later life.

Although women are born with all the cells that evolve into future egg cells, men produce new sperm cells throughout their lives. This was thought to protect against the sort of degradation of the sex cells seen in the female egg cells as they age.

Scientists now believe that as men age, their sperm are at an increased risk of picking up minor mutations that may be passed on to offspring and can affect their development. "While most of the neurocognitive differences were small at the individual level, these could have important implications from a public health perspective," Professor McGrath said.