Autism – The Epidemic That Never Was

Autism Diva, reproduced from New Scientist

RICHARD Miles will never forget the winter of 1989. The 34-year-old company director and his family spent that Christmas on the island of Jersey in the English Channel, where he had grown up. It was also then that he first noticed something was badly wrong with his 14-month-old son Robert. The bright, sociable child, who had already started talking, became drowsy and unsteady on his feet. Then he started bumping into furniture. Within weeks his language had dried up and he would no longer make eye contact. “It was as if the lights went out,” says Miles. His son was eventually diagnosed with autism.

Miles, who now campaigns for more research into autism, is convinced that his son is part of an autism epidemic. Ten years ago, he points out, Jersey had just three autistic children in special-needs education. It now has 69. Robert was one of a cluster of nine children on the island diagnosed around the same time.

Similar rises have been reported across the world, from Australia to the US, and from Denmark to China. Back in the 1970s, specialists would typically see four or five cases of autism in a population of 10,000. Today they routinely find 40, 50 or even 60 cases. Perhaps the starkest illustration of autism’s relentless rise comes from California. In 2003, the state authorities stunned the world when they announced that over the previous 16 years, the number of people receiving health or education services for autism had risen more than sixfold. The world’s media went into overdrive.

What could be causing so many children to lose their footing on a normal developmental trajectory and crash-land into the nightmare world of autism? The change has occurred too suddenly to be genetic in origin, which points to some environmental factor. But what? There is no shortage of suspects. In the UK, blame is often laid at the door of the combined measles, mumps and rubella (MMR) vaccine. In the US, mercury added to a range of childhood shots has been accused. Food allergies, viral infections, antibiotics and other prescription drugs have all been fingered, often by campaign groups run by mystified and angry parents. The problem is that none of these suggested causes has any solid scientific evidence to support it (see “The usual suspects”).

Perhaps there’s a simple explanation for this: there is no autism epidemic. On the face of it that sounds ridiculous – just look at the figures. But talk to almost any autism researcher and they will point to other explanations for the rise in numbers. Some say it’s still an open question, but others are adamant that the autism epidemic is a complete myth. And if the most recent research is anything to go by, they could be right. Studies designed to track the supposedly increasing prevalence of autism are coming to the conclusion that, in actual fact, there is no increase at all. “There is no epidemic,” says Brent Taylor, professor of community child health at University College London.

Autism is a developmental disorder sometimes noticeable from a few months of age but not usually diagnosed until a child is 3 or 4 years old. It is characterised by communication problems, difficulty in socialising and a lack of imagination (see “What is autism”). It is not a single disorder, but comes in many forms, which merge into other disorders and eventually into “normality”. There is no biochemical or genetic test, so diagnosis has to be made by observing behaviour. Autistic children also often have other medical conditions, such as hyperactivity, Tourette’s syndrome, anxiety and depression. The upshot is that “one person’s autism is not another person’s autism,” says epidemiologist Jim Gurney of the University of Minnesota in Minneapolis.

In recognition of this ambiguity, autism is considered part of a continuum within a broader class of so-called “pervasive developmental disorders” (PDDs) – basically any serious abnormality in a child’s development. Autism itself is divided into three categories: autistic disorder, Asperger’s syndrome (sometimes called “high-functioning autism”), and pervasive developmental disorder-not otherwise specified (PDD-NOS), sometimes called mild or atypical autism. Together these three make up the autistic spectrum disorders.

“Californian authorities stunned the world when they announced a sixfold rise in autism over the past 16 years”
Confused? You’re not the only one. The difficulty of placing children with developmental problems on this spectrum has led to several major shifts in the way autism is diagnosed in the past 30 years. In the late 1970s, the autism label was kept for those with severe problems such as “gross language deficits” and “pervasive lack of responsiveness”. But since 1980 the diagnostic criteria have been revised five times, including the addition of PDD-NOS in 1987 and Asperger’s in 1994.

This massive broadening of the definition of autism, particularly at the milder end of the spectrum, is one of the main factors responsible for the rise in cases, says Eric Fombonne of McGill University in Montreal, Canada, a long-standing sceptic of the epidemic hypothesis. Tellingly, around three-quarters of all diagnoses of autism today are for Asperger’s and PDD-NOS, both of which are much less severe than the autism of old. “There is no litmus test for who is autistic and who is not,” says Tony Charman of the Institute of Child Health at University College London.

Changes in diagnostic criteria apart, there are other reasons to believe that autism is simply being diagnosed more often now than in the past. One is the “Rain Man effect” – the huge increase in the public awareness of autism following the 1988 film starring Dustin Hoffman. Awareness has also increased massively among healthcare workers. “Twenty years ago there were maybe 10 autism specialists in the country. Now there are over 2000,” says Taylor.

Another factor is that one of the stigmas of autism has largely disappeared. Until about 10 years ago a prominent idea was that autism was caused by an unloving “refrigerator mother”. Now it is a no-blame disease. “Parents are more willing to accept the label,” says Taylor. One expert New Scientist spoke to went as far as to describe autism as “trendy”.

Finally, while some parents still have to fight for help for their autistic children, far more services are now available. This has encouraged doctors to label borderline or ambiguous cases as autism – they know this is often the best way to get the child some help. It also makes autism an attractive diagnosis for parents. “I hear stories of parents who are anxious to get a particular diagnosis if that is what is required to obtain the services their child needs,” says Sydney Pettygrove, a paediatrician at the Arizona Health Sciences Center in Tucson. In the UK, says Simon Baron-Cohen of the Autism Research Centre at the University of Cambridge, “in every town there are trained clinicians who can make a diagnosis.”

It is hard to quantify these trends, but many epidemiologists now believe that they can account for the apparent rise in autism the general public and media take for granted. Proving it, however, is difficult – if not impossible. The main problem is that an epidemiological study carried out in the 1980s simply cannot be compared with one done last week. There will be so many differences in diagnostic procedures and in the willingness of doctors and parents to label a child autistic that comparisons are meaningless. “You can’t control for everything,” says Charman.

And so attention has shifted to what epidemiologists sniffily refer to as “service provider data”, such as the California figures. Ever since 1973, the authorities there have been keeping records of the number of people receiving some kind of state help in connection with autism. In 2003, California’s Department of Developmental Services (DDS) announced a chilling figure that captured the world’s attention. In the 16 years to 2002, cases rose from 2778 to 20,377 (see Graph). Among autism campaigners these figures are often cited as incontrovertible and final proof of the existence of the autism epidemic.

But there are serious problems with this interpretation. First, the figures are raw numbers from public services, not a proper epidemiological study. Critics point out they are not corrected for changes in diagnostic criteria or for the growing awareness of autism.

“Prisons and institutions could be full of autistic adults labouring under wrong diagnoses such as schizophrenia”
There is evidence, for example, that as the California autism numbers have risen, diagnoses of mental retardation have fallen. Researchers at Boston University School of Medicine in Massachusetts have found a similar pattern in the UK. This effect, dubbed “diagnostic substitution”, cannot explain all the increase but is one example of how diagnostic fashions can skew the data.

Another potential flaw is that the California figures don’t take into account the fact that the state’s population is growing rapidly. Between 1987 and 1999, the total population rose by nearly 20 per cent, and the age group 0 to 14 rose even more steeply, by 26 per cent.

As a result of these doubts and unknowns in the California figures, most epidemiologists refuse to draw firm conclusions from them. “The report doesn’t change anything,” says Charman. “It’s not a systematic study.” In fact, the preface of the most recent California report contains a health warning not to read too much into the numbers. “The information should not be used to draw scientifically valid conclusions,” it says.

Some researchers, notably Robert Byrd of the MIND Institute at the University of California, Davis, have attempted to correct for all the unknowns. In an analysis published on the state DDS website nearly three years ago, Byrd concluded that the rise is real. “Autism rates are increasing,” he told New Scientist. Some scientists accept that Byrd’s analysis lays to rest the idea that population growth could have significantly swelled the figures. But his methods for investigating the other potential sources of bias have been heavily criticised, and tellingly, Byrd has not yet succeeded in getting his study published in a peer-reviewed journal. Until he does, it is hard to know how much weight to give his conclusions.

Perhaps the strongest case against the “better diagnosis” theory is that, if true, there should be a “hidden hoard” of autistic adults who were never properly diagnosed in childhood. To parent Richard Miles, this is compelling. “My doctor cannot believe that he could have missed so many cases in the past,” he says. But Taylor disagrees. As a former general practitioner, he says there are many children today diagnosed with autism who would not have been labelled as such in the past.

This view is difficult to substantiate, but in 2001 a team led by Helen Heussler of Nottingham University, UK, had a crack. They re-examined the data from a 1970 survey of 13,135 British children. The original survey found just five autistic children, but using modern diagnostic criteria Heussler’s team found a hidden hoard of 56. That’s over a tenfold rise in numbers, which puts the California figures in perspective. Heussler and her colleagues concluded that “estimates from the early 1970s may have seriously underestimated the prevalence”.

Lorna Wing, a veteran autism researcher at the Institute of Psychiatry in London, agrees. In the 1970s she spent a lot of time working with special-needs children in the London district of Camberwell. Wing reckons that at the time, fewer than 10 per cent of autistic children were correctly diagnosed. She also thinks that prisons and institutions are full of autistic adults labouring under wrong diagnoses such as treatment-resistant schizophrenia or ADHD.

Ultimately, however, it may be impossible to tell whether there has been a genuine rise in the incidence of autism over the past 30 years. “There is no clear evidence that there has been an increase, but there’s no proof that there hasn’t,” says Charman. Even the arch-sceptic Fombonne accepts this. “We must entertain the possibility,” he says. “But we don’t have the evidence.”

But researchers can answer another question: is the incidence of autism continuing to rise? There is a tried and tested method of tackling this sort of question. You carry out a large prevalence study among a particular age group, and then repeat it a few years later with a new set of individuals, in the same place and using exactly the same methods. Several such studies into autism are ongoing, notably one funded by the US Centers for Disease Control and Prevention in Atlanta, which will look at changes in incidence across 11 states.

One team, however, is ahead of the game. Back in July 1998, Fombonne and Suniti Chakrabarti of the Child Development Centre in Stafford, UK [This is the Doc and the center that diagnosed Megan, trivia fans], started screening every child born in a four-year window (1992 to 1995) who lived in a defined area of Staffordshire, 15,500 children in total. As a result, they established baseline figures for autistic spectrum disorders – about 62 per 10,000. Then they did it again, in exactly the same place and exactly the same way, this time with all the children born between 1996 and 1998. In June this year, they reported that the prevalence of autism was unchanged (American Journal of Psychiatry, vol 162, page 1133). “This study suggests that epidemic concerns are unfounded,” concludes Fombonne.

Similar surveys need to be done in other parts of the world to rule out the possibility that there is something unusual about Staffordshire. And the Staffordshire result has failed to convince campaigners and parents, including Miles. But what is clear is that after the first direct test of whether autism is rising, it’s 1-0 to the sceptics.

That doesn’t mean we should stop searching for the causes of autism. The disorder itself is real, and if researchers knew what was behind it much suffering could be averted. But the Staffordshire surveys do suggest that there is no environmental problem that is triggering autism in ever-greater numbers and which must be identified as a matter of urgency. That will not be much comfort to families with autistic children. But it should make everyone else feel a bit more secure.

What is autism?

The developmental disorder that is now called autism was first described by doctors in 1943. Psychiatrists say there are three key features: lack of imagination, communication difficulties, and problems interacting with others. In practice, those affected have a bewildering range of strange behaviours. These can include fear of physical contact, hearing and visual problems, bizarre obsessions and a touching inability to lie.

Apart from the fact that about three-quarters of those affected are male, it is hard to make generalisations because the condition varies widely between patients. Contrary to popular belief, freakish talents for maths or music, say, are uncommon. In fact, about three-quarters of people with autism have learning difficulties, but those who do not may manage to hold down a job.

Parents usually realise something is wrong because children fail to develop normally. But up to one third of cases are “regressive” – children seem to go backwards when they are about two, losing their language and social skills.

In psychological terms, people with autism seem to lack “theory of mind” – the recognition that other individuals may hold a different perspective on things than themselves. This leaves them in a bewildering world where people seem to act according to incomprehensible rules and behave in meaningless ways. They also have impaired “executive function”, the ability to plan future actions. And patients have weak “central coherence”, the ability to extract meaning from experiences without getting bogged down in details. In other words, they can’t see the wood for the trees.

Clare Wilson

The usual suspects

Both genes and environmental factors play a role in the development of autism. But if there has indeed been a sudden rise in cases, the only possible cause is an environmental change because our genes can’t be altering that fast. Numerous candidates have been proposed.

“LEAKY GUT”

Thanks partly to anecdotal reports linking autism with bowel problems, some researchers believe that the condition could be caused by various dietary components leaking through the gut wall into the bloodstream, allowing them to reach the brain. One possible cause could be increased use of antibiotics disturbing the natural balance of gut bacteria.

There have been some reports of people with autism doing better on diets that exclude dairy foods and gluten, a protein found in wheat and barley. And a few small studies have found that some patients seem to improve after injections of the gut hormone secretin, which could possibly be related. But neither of these approaches have been borne out by larger placebo-controlled trials.

MMR JAB

The combined measles, mumps and rubella (MMR) vaccine was fingered by gastroenterologist Andrew Wakefield, formerly of the Royal Free Hospital in London. He suggested that giving children three vaccines simultaneously could damage their gut. Along with vociferous campaigning by parents, this led to a fall in uptake in the UK of this important childhood vaccine.

However, numerous large-scale studies showed no link between receiving the vaccine and developing autism. A recent study from Japan may prove the final nail in the coffin for the MMR theory. It found that diagnosed cases in that country continued to rise even after the triple jab was withdrawn (Journal of Child Psychology and Psychiatry, vol 46, p 572).

MERCURY IN VACCINES

In the US, mercury is public enemy number one. The mercury-containing preservative thimerosal – which has been used in a range of childhood vaccines although it is now being phased out – is claimed to cause autism by damaging the developing brain directly. But a review last year by the US Institutes of Medicine rejected a causal link between autism and either mercury or the MMR jab.