Asperger Syndrome is a genetic disorder

Fears of an autism epidemic due to a rise in reported child cases were today dismissed by psychiatrists who found evidence suggesting that adults are just as likely to be affected.

Up to 600,000 adults could have autism that has gone undiagnosed, researchers say.

A survey found that the same proportion – about one per cent – of older people had behaviour traits associated with autistic spectrum disorder, including Asperger Syndrome.

But none of those taking part in the survey had been given a formal diagnosis. Experts said the findings suggest most of the cases were ‘relatively mild’.

However, today’s children are more likely to be diagnosed, according to a study by the University of Leicester.

The findings follow studies revealing that ten times as many children are now diagnosed than 30 years ago.

Researchers, who published their finding in the influential Archives of General Psychiatry journal, used data from the 2007 UK Adult Psychiatric Morbidity Survey.

Slightly more than half of the 13,171 households contacted agreed to take part in the study, which included an autism screening questionnaire.

Those people with potential symptoms were then selected undergo a face-to-face clinical assessment called the Autism Diagnostic Observation Schedule.

Overall, they found that 0.98 per cent of adults had the disorder – roughly the same proportion that corresponding studies of children have shown.

SO WHAT IS AUTISM AND HOW IS IT CAUSED?

The diagnosis of autism is often referred to as autism spectrum disorder.

While all people with autism share three main areas of difficulty - social communication, social interaction and social imagination - their condition will affect them in different ways.

Some are able to live relatively normal everyday lives, while others will require a lifetime of specialist support.

Most scientists agree that autism is a genetic disorder. In rare cases, it has been associated with birth defects caused by agents such as heavy metals and pesticides.

But an increase in diagnoses following the 1990s led to a rise in the belief that children were developing autism after they were born.

The fact that the condition usually develops gradually – and in some cases toddlers appear to develop more normally and then regress – helped propagate this theory.

The most notable controversy in recent times was the claim that the MMR vaccine caused autism.

However this theory has been discredited by evidence showing that this is biologically implausible.

None of those diagnosed for the first time with autism were previously aware that they may have the condition, meaning thousands of adults could have gone undiagnosed.

Researcher Dr Traolach Brugha was shocked by the findings.

‘It was surprising to all of us,’ he said. ‘If this study is correct, it does put a big question mark over the autism epidemic.’

Dr Brugha said he was confident in the results, but that they should still be confirmed in other studies given the small number of people with autism found in this study.

He added that he had been disappointed to discover that none of those who got the diagnosis based on the study's clinical assessment were aware of their condition.

‘None of them had been diagnosed (previously) with autism,’ he said.

‘I think for me the issue is that people have been ignoring autism in adulthood and only focusing on children.’

The University of Leicester survey is the first to give an estimate of autism rates among adults in the general community.

Fears that the condition is becoming more and more common in children have launched both researchers and parents on a fierce search for the underlying reasons.

So far those efforts haven't paid off, however, and the much-reported claim that childhood vaccines such as the MMR could be the culprit has been widely discredited.

In fact, more and more research hints that some if not all of the increase in autism may be due to changes in how, and how often, the disorder is diagnosed.

Children who used to be classified as mentally retarded or just plain eccentric, for instance, might now get an autism-spectrum label instead.

‘That simply means more people are coming forth and being recognized,’ Dr Brugha said.

Overall, the researchers found 19 participants with autism out of a group of 2,828, corresponding to 9.8 per 1,000 adults, but there were no reliable signs that age had any influence on that rate.

Another interesting discovery was that more men than women were found to have autism, although this is likely to be a statistical anomaly based upon the relatively small sample of tests.

Eighteen per 1,000 men got the diagnosis, compared to only two per 1,000 women.

People with autism were also far more likely to live in council housing and have less education than others.