Schizophrenia non-familial blame old dad?

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Not the sharpest? Blame old dad
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Leigh Dayton, Science writer March 10, 2009
Article from: The Australian
IF your IQ isn't up to brain surgery or a Nobel Prize, blame your ageing dad.
Intellectual whizzes, on the other hand, can thank their older mums.
The surprising conclusions come from an Australian and US team led by neuroscientist John McGrath of the University of Queensland's Brisbane-based Queensland Brain Institute.
In their study of 17,148 boys born in the US between 1959 and 1965, they found that children conceived by older fathers performed less well on a range of thinking tests given at eight months, four years and seven years than those born to younger dads.
They took into account other possible factors such as education, mental health and income, with the same result.
"While we didn't find a clean threshold above or below which there is a risk (of lower IQ), the risk increased steadily the older the dads were," Professor McGrath said yesterday.
Writing in the US journal Public Library of Science Medicine, his team said their results contrasted sharply with earlier studies showing that the older the mother at conception, the smarter the child.
According to Professor McGrath and his colleagues, the difference may lie in the male and female reproductive systems. A woman is born with a fixed number of eggs that have undergone 22 cell divisions in the womb. But sperm cells divide every 16 days after a boy reaches puberty. By age 20, the original sperm cells have divided roughly 150 times; by age 50, 840 times. The more cell divisions, the more mutations; the more mutations, the greater the chance a child will be born with physical or neurological abnormalities.
Until recently, studies of the risks of later conception focused on women. It's well known, for instance, that as women age, the likelihood increases of their having a child with the developmental and intellectual disorder Down syndrome.
In a review of the team's paper, also in PLOS Medicine, psychiatrist Mary Cannon of the Royal College of Surgeons in Ireland wrote that evidence was accumulating that advanced paternal age was a risk factor for neuropsychiatric conditions such as schizophrenia and autism, as well as physical problems such as cleft lip and palate, childhood cancers and congenital heart defects.
"The body of evidence implicating paternal age as a risk factor for a range of adverse offspring outcomes should not be ignored," she concluded.
To tease out precisely why older dads sire youngsters with IQ scores up to three points lower than younger fathers, Professor McGrath's group has begun investigating a group of 7000 babies born in Brisbane in the 1980s.
They are also studying the phenomenon in mice to identify the mechanism or mechanisms involved.
"Age is something to factor in when planning a family," Professor McGrath said.