OLDER men are far more likely to father autistic children, according to new research.

A study involving more than 100,000 children found that those born to fathers aged 40 and over were nearly six times more likely to suffer from autism and related disorders than those with a father under 30.

Scientists from the Institute of Psychiatry at King’s College, London and Mount Sinai School of Medicine in New York, said that their research supported the theory that men also have a “biolog-ical clock” when it comes to producing healthy babies.

They described the findings as “the first convincing evidence that advanced paternal age is a risk factor for autism spectrum disorder”. However the authors could not find a link between a mother’s advancing age and autism.

The exact causes of autism remain unknown, but cases of it and related conditions such as Asperger’s syndrome — known collectively as autism spectrum disorders (ASDs) — have increased tenfold in the past two decades. They now affect the lives of more than half a million families in Britain. A recent study suggested that the rate could be as high as 116 ASD cases per 10,000 children.

According to the Office of National Statistics, the number of new fathers aged over 40 rose by about a third in the five years to 2004, when 75,810 older men became parents. Only 32,000 men aged over 40 became fathers in 1983.

Abraham Reichenberg, lead researcher in the latest study, said that genetic mutations in the sperm of older men may be responsible for the increased risk of their children developing ASDs.

Autism is a lifelong disability affecting the way that a person communicates and relates to others. People with autism have impaired social interactions, communication and imagination, including repetitive patterns of behaviour.

Better diagnosis has contributed to the rising rates of autism, but experts also believe that there may be more cases. Scientists have dismissed suggestions that the increase might be linked to the use of MMR, the combined childhood vaccine given to protect against measles, mumps and rubella.

The latest study, published in the Archives of General Psychiatry, analysed 132,271 Jewish children born during the 1980s in Israel. The researchers found that, if the father was aged 15 to 29 when the child was born, the risk of autism was 6 in every 10,000 children. If the father was 30 to 39, then 9 in 10,000 children suffered autism (1.6 times higher), going up to 32 in 10,000 (5.75 times higher) for fathers aged 40 to 49. The risk was even higher for older fathers.

“This research adds to our knowledge that men also have a biological clock when it comes to reproducing,” Dr Reichenberg said. “The sample size for the over-50s was small, so we added it to the results for fathers aged over 40, but our research suggests that very old fathers have around nine times the risk. “The research shows a linear effect — with every ten years, the risk doubles.”

The researchers emphasised that the results related to autism and could not necessarily be generalised to apply to related disorders such as Asperger’s syndrome. But they added: “This data suggests a significant association between advancing paternal age and risk of ASD.”

They said that there were several genetic factors which could be at play, including spontaneous mutations in sperm-producing cells, or discrepancies in how genes are expressed.

Although the fact that all the children were Jewish was a limitation of the study, Dr Reichenberg did not believe it affected the results. More research was needed to see if the findings were replicated across other racial and ethnic backgrounds.

ASDs have been linked with abnormalities in children’s brain development which occur before, during, or soon after birth. The advancing age of parents has also been linked to brain development.

Dr Reichenberg and his team discuss several possible genetic mechanisms to explain the paternal age effect but add: “It is important to keep in mind, however, that age at paternity is influenced by the sociocultural environment and varies across societies and over time.”

The National Autistic Society (NAS), Britain’s leading charity for the condition, said yesterday that the causes of autism were complex and required further investigation.

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