Men over 40 are six times more likely to father a child with autism than their younger peers, a study has found.

Research involving more than 130,000 children has revealed that the risk of autism rises steadily with advancing paternal age. However, there was no link with increasing maternal age, the researchers, who included a team from the Institute of Psychiatry at King's College London, say.

The finding suggests that men may have their own biological clock which affects their capacity to produce healthy offspring as they age in a similar way to women.

The risk of birth abnormalities such as spina bifida increases sharply with advancing age in mothers but is popularly thought to be unaffected by the age of the father.

However, experts say that this may be because fathers have not been studied as closely as mothers. ''A lot of research has focused on mothers, and fathers have not had the same attention. It may be problem is the same [in both sexes] but the research has not been done,'' said a spokesperson for the Progress Educational Trust, a charity supporting research into fertility.

The new study, published in Archives of General Psychiatry, suggests ageing in men and women may increase the risk of different kinds of birth abnormality.

The research was carried out among 132,271 Jewish children born in Israel in the 1980s by Dr Abraham Reichenberg, from the Mount Sinai School of Medicine in New York, and colleagues from the Institute of Psychiatry in London.

The results showed that among fathers aged 15 to 29 when their child was born, the risk of autism was six in every 10,000 children.

Among fathers aged 30 to 39, nine in 10,000 children suffered autism (50 per cent higher), going up to 32 in 10,000 (almost six times higher) for fathers aged 40 to 49.

The risk was even higher among fathers aged 50 and over, although the sample size was small.

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