If MMR doesn't cause autism, then what on earth does?

Autism disturbs something core to our being human. Cases appear to be increasing, yet numerous studies have failed to find a link with vaccines, diet or genes

Why should a mental disorder with severe social and psychological consequences be on the rise? The increase in autism, the condition characterised by social withdrawal, has puzzled psychiatrists and alarmed parents. Some parents have blamed the MMR (measles, mumps and rubella) vaccine and the current scare about MMR is largely fuelled by fears about autism. Today, the Government is to launch a £3m publicity campaign to rebut claims that MMR is linked with autism and bowel disease and try to restore confidence in the vaccine. This leaves unanswered, however, the question of what is happening with autism.

Why should a mental disorder with severe social and psychological consequences be on the rise? The increase in autism, the condition characterised by social withdrawal, has puzzled psychiatrists and alarmed parents. Some parents have blamed the MMR (measles, mumps and rubella) vaccine and the current scare about MMR is largely fuelled by fears about autism. Today, the Government is to launch a £3m publicity campaign to rebut claims that MMR is linked with autism and bowel disease and try to restore confidence in the vaccine. This leaves unanswered, however, the question of what is happening with autism.

Few mental disorders attract as much attention as autism. In the social world in which we live, the capacity to read situations and respond appropriately is crucial to success and can mean the difference between popularity and loneliness. "Autism disturbs something that is core to our being human. That is why it fascinates," says Francesca Happé, an autism expert at the Institute of Psychiatry, London.

In some sufferers, autism is disguised by high intelligence and may go unrecognised throughout their lives. The eccentric academic with a collection of rocks in the attic, an encyclopaedic knowledge of train timetables and a non-existent social life may be suffering from autism. For this reason, estimates of the numbers affected vary hugely - from 5,000 to 500,000. No national register is kept of autism cases; the diagnosis is difficult and the criteria for the condition keep changing.

Classic autism, first described by Leo Kanner in 1943, is marked by repetitive behaviour and abnormal communication and interaction. This is thought to affect 30,000 people in the UK, about five in every 10,000, a figure that has remained largely unchanged in 50 years.

However, in the last 20 years, it has become clear that many more people are affected by autistic spectrum disorders, including Asperger's syndrome, a milder version of classic autism reflected in what some experts have called "mind blindness" - an inability to read social situations. They lack the gene for charm.

Given the range of the diagnosis, it is not surprising there is confusion about the numbers. In the mid-1960s classic autism was estimated to affect 5 people in 10,000 based on a survey in Middlesex. More than a decade later, in 1979, a survey in Camberwell, south London, confirmed this figure among children with a low IQ of under 70. However, among those with a higher IQ there was a much larger group of children - 15 in every 10,000 - with some features suggestive of autism.

Studies in Sweden and in Edinburgh in the 1990s concluded that the true figure was more than four times as high when people with Asperger's syndrome and similar social impairments were included, at 91 people in 10,000. On the basis of these figures, the National Autistic Society estimates there are 115,000 people with low IQ and autism who need support and a further 403,500 with average or high ability who are more mildly affected.

Most experts believe that because autism is a spectrum of disorders with no clear boundaries, the apparent rise in cases is due to growing awareness and shifts in the diagnosis. "Many people do believe there is an increase in cases, but the most obvious and least worrying reason is because of changes in the diagnostic criteria and improved recognition," said Ms Happé. The jury, however, is still out. Recent research by Christopher Gillberg of the University of Gothenburg, Sweden, published at the end of last year suggested the rise may be real.

Dr Fiona Scott, research co-ordinator at the autism research centre at the University of Cambridge said: "We face the problem of working out whether the rise is real, because of a shift in diagnosis or because of growing awareness."

Autism is known to run in families and is thought to be the result of brain damage. However, it is unclear whether the damage happens before, during or after birth. It is also selective, affecting only that part of the brain involved in understanding other people. Some children who appear to be developing normally and then suffer a setback have regressive autism, a condition similar to Heller's syndrome, also called childhood disintegrative disorder. This has been linked with a trauma or medical accident that caused the child to lose skills it had developed, and cases of regressive autism cause particular anxiety among parents who search for a cause.

If there is a genetic susceptibility to autism there may be some environmental factor that triggers it in vulnerable people. But the condition is not entirely genetically determined because there are identical twins (with identical genes) where one has it, while the other does not.

One theory is that diet may be a cause and some parents have put their autistic children on diets free of wheat or milk and claimed to see an improvement. Much excitement was also generated around the hormone secretin, but subsequent trials failed to demonstrate a link between autism and secretin.

The latest candidate as a potential trigger for autism in vulnerable children is the MMR vaccine. But most experts agree this is not supported by the facts. At a health department press conference on MMR last Monday, Stephen Evans of the Medicines Control Agency said that when MMR vaccination was introduced in 1988, coverage of the child population went from zero to 90 per cent in little more than a year.

"There was a step change in MMR coverage but there was no step change in autism. Had there been a genetic susceptibility to autism in the population we would have seen a step change in cases and no increase thereafter."

The National Autistic Society is calling for more research. Dr Fiona Scott says: "Most experts feel the evidence does not show MMR is linked with autism but if the rise is occurring, we ought to look at the possible causes and if that includes looking at MMR then so be it."