The Irish Times - Thursday, August 23, 2012

BENEDICT CAREY

OLDER MEN are more likely than young men to father a child who develops autism or schizophrenia, because of random mutations that become more numerous with advancing paternal age, scientists reported yesterday, in the first study to quantify the effect as it builds each year. The age of mothers had no bearing on the risk for these disorders, the study found.

Experts said the finding was hardly reason to forgo fatherhood later in life, though it may have some influence on reproductive decisions. The overall risk to a man in his 40s or older is in the range of 2 per cent at most, and there are other contributing biological factors that are unknown.

But the study, published online in the journal Nature, provides support for the argument that the surging rate of autism diagnoses over recent decades is attributable in part to the increasing average age of fathers, which could account for as many as 30 per cent of cases.

The findings also counter the long-standing assumption that the age of the mother is the most important factor in determining the odds of a child having developmental difficulties. The risk of chromosomal abnormalities such as Down syndrome increases for older mothers but when it comes to some complex developmental and psychiatric problems the lions share of the genetic risk originates in the sperm, not the egg, the study found.

Previous studies had strongly suggested as much but the new report quantifies that risk for the first time, calculating how much it accumulates each year.

The research team found the average child born to a 20-year-old father had 25 random mutations that could be traced to paternal genetic material. The number increased steadily by two mutations a year, reaching 65 mutations for offspring of 40-year-old men. The average number of mutations coming from the mothers side was 15, no matter her age, the study found.

This study provides some of the first solid scientific evidence for a true increase in the condition of autism, said Dr Fred Volkmar, director of the Child Study Centre at the Yale School of Medicine, who was not involved in the research. It is extremely well done and the sample meticulously characterised.

The new investigation, led by the Icelandic firm Decode Genetics, analysed genetic material taken from blood samples of 78 parent-child trios, focusing on families in which parents with no signs of a mental disorder gave birth to a child who developed autism or schizophrenia.

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Older fathers linked to autism and schizophrenia in children