It is well established that autism tends to run in families but this is one of the first studies to indicate that epigenetic changes may be involved in increasing the risk of having a child who develops autism.

London - Many cases of autism are caused by faulty sperm and eggs, with older men more likely to father a child with the condition, researchers believe.

Three large-scale studies have highlighted the importance of mistakes in the DNA of eggs and sperm to the development of autism.

One in seven cases of autism in families where just one child has the condition are caused this way, the respected journal Nature reports.

The studies also showed sperm to contain more of these mistakes than eggs - and the older the man, the more errors linked to autism were found in his sperm.

It is thought that up to 90 percent of a child’s risk of developing autism is written in their genes but little is known about the many genes involved.

In order to find out more, three teams of researchers - including some from Yale and Harvard universities - scrutinised the DNA of hundreds of parents of children with autism and of the youngsters themselves. Unaffected siblings were also studied.

The projects revealed the importance of genetic flaws called “de novo mutations”.

We usually think of disease- causing genetic mistakes appearing in a parent’s DNA and being passed to their child.

But the de novo mutations first appear in the child’s DNA and are caused by problems with sperm or egg production.

The research team headed by the University of Washington showed sperm to be a much bigger culprit than eggs.

For every four mutations traced back to sperm, there was just one that began life in an egg.

The finding fits with previous studies that show that older fathers are slightly more likely to have an autistic child than their younger counterparts. One study found that a man aged 40 and over is almost six times more likely to have an autistic child as a man in his 20s or teens.

Pooling the results of the three studies revealed three genes to be peppered by these de novo mutations.

The scientists said that it is likely that hundreds of genes are involved in autism and their study shows the picture to be even more complex than thought.

It is hoped that unravelling the genetics will speed up both the search for new treatments for the condition and the development of diagnostic tests.

Autism, and related conditions such as Asperger’s syndrome, affect more than one in 100 British children - ten times as many as just 30 years ago. But, with the causes unclear, current treatment consists of managing individual symptoms, such as hyperactivity.

Stephen Sanders, who led the project headed by Yale University, said: “With every new gene we discover, we learn more about potential treatments for patients with autism.”

The lead scientist on the third project, Mark Daly of Massachusetts General Hospital, said: “These results clearly demonstrate the potential of DNA sequencing technology to articulate specific risk factors for autism.

“We have only scratched the surface but, with continued collaborative efforts, these gene discoveries will point us towards the underlying biological roots of autism.”

Kevin Mitchell, a Trinity College Dublin geneticist, said work such as this would allow the underlying cause of autism to be treated, rather than just the symptoms. - Daily Mail