Is Autism on the Rise?
Excerpt from article by Graham Lawton published in 'The Scientist' - August 2005
Everyone knows this disturbing disorder is reaching epidemic proportions. But all may not be what it seems says Graham Lawton in August 2005 edition of 'The Scientist'.
There seems to be a steady rise in the number of children diagnosed with autism in many different countries like UK, US, Denmark, Australia and China. The question Lawton asks is - "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", says Lawton. "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."
He suggests that perhaps there's actually 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.
Lawton goes on to explain that 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. Autism is characterized by communication problems, difficulty in socializing and a lack of imagination. It is not a single disorder, but comes in many forms, which merge into other disorders. There is no biochemical or genetic test, so diagnosis has to be made by observing behavior. Autistic children also often have other medical conditions, such as hyperactivity, Tourette's syndrome, anxiety and depression.
Lawton says that because of this ambiguity, autism is considered part of a continuum within a broader class of so-called "pervasive developmental disorders" referred to as PDDs - which are basically any serious abnormality in a child's development.
Autism itself is divided into three categories: autistic disorder, Asperger's syndrome which is 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. 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 1990s, 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.
Eric Fombonne of McGill University in Montreal, Canada, a long-standing sceptic of the epidemic hypothesis says, "This massive broadening of the definition of autism, particularly at the middle or end of the spectrum, is one of the main factors responsible for the rise in cases."
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" which is the huge increase in the public awareness of autism following the 1988 film starring Dustin Hoffman. Awareness has also increased massively among healthcare workers. 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 mother'. Now it is a no-blame disease and parents are more willing to accept the label.
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 as they know that this is often the best way to get the child some help.
Attention has shifted to what epidemiologists 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 Developmental Services (DDS) announced a chilling figure that captured the world's autism. In the 16 years to 2002, cases rose from 2778 to 20,377. 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. Firstly, the figures are raw numbers from public services, not a proper epidemiological study. Critics point out that they are not corrected for changes in diagnostic criteria or for the growing awareness of autism. 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 percent, and the age group 0 to 14 rose even more steeply, by 26 percent.
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," says the report.
Lawton tells us that some researchers like the notable 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 criticized, 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. This view is difficult to substantiate, but in 2001 a team led by Helen Heussler of Nottingham University, UK, 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 Heusslere team found a hidden hoard of 56. That's over a tenfold rise in numbers, which puts the Californian 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 1970's 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 percent of autistic children were correctly diagnosed. She also thinks that prisons and institutions are full of autistic adults laboring under wrong diagnoses such as treatment-resistant schizophrenia or ADHD.
Lawton proposes that ultimately it maybe 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 Charlton. Even the arch-sceptic, Fombonne accepts this, "We must entertain the possibility," he says. "But we don't have the evidence."
Now researchers are looking to answer another question: Is the incidence of autism continuing to rise? There is a tried and tested method of tackling this sort of question by carrying out a large prevalence study among a particular age group, and then repeating 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 a states.
Back in July 1998, Fombonne and Suniti Chakrabarti of the Child Development Center in Stafford, UK, 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.
Lawton concludes that it doesn't mean we should stop searching for the causes of autism.
He says that the disorder itself is real, and if researchers knew what was behind it, much suffering could be averted.