Jan 31 2008
Autism spectrum disorder (ASD) is a neurological disorder that includes a wide range of symptoms including reduced social interactiveness and cognitive impairment. At the mild end of the spectrum it is not clear if it is even appropriate to consider the symptoms a disorder and there are those who prefer to characterize such individuals as part of normal human diversity. But more severe manifestations can be significantly impairing.
In the last decade there has been a public controversy over whether or not vaccines in general, or specifically the mercury-based preservative thimerosal in some vaccines, is a major cause of autism. The scientific evidence is very clear – there is no link between vaccines and autism. In addition, the scientific evidence increasingly points to a host of genetic factors as the primary cause of autism. The vaccine-autism hypothesis is subject to falsification from multiple lines of evidence, but there are two that are dramatic and definitive. The first was the removal of thimerosal from most childhood vaccines by 2002. If thimerosal causes autism and was responsible for an increase in ASD diagnosis, then removing thimerosal from vaccines should reduce ASD diagnosis – it didn’t.
The second line of evidence has to do with the timing of the onset of ASD. If A causes B then A must precede B. If it can be shown that B actually occurs prior to A then that would eliminate A as a cause. This is basic logic, something physicians rely upon routinely to help them evaluate possible causes of symptoms and diseases. One of the pieces of evidence proponents of the vaccine-autism hypothesis point to is the fact that parents often notice the onset of autism symptoms shortly after their children receive their first series of vaccines. The scientific community has regarded this as nothing but a coincidence – a post hoc ergo propter hoc (after this therefore because of this) logical fallacy.
The requirement for autism to follow vaccination gives us another opportunity to definitively falsify the vaccine-autism hypothesis. And now we have some good evidence that autism in many cases does in fact precede vaccination. Sara Webb from the University of Washington’s Autism Center has just published a study looking at head circumference in normal and autistic children. She found that in 60% of the 28 autistic boys studied they had accelerated head growth prior to the onset of symptoms of autism. There was no comparison group, but historical controls were used – meaning that it is already well established from routine measurements that children tend to stay on their percentile curves throughout early development. About this study she is quoted as saying:
“This abnormal or accelerated rate of head circumference growth is a biological marker for autism. It occurs before the onset of behavioral symptoms at 12 months of age such as a child’s failure to respond to their name, a preoccupation with certain objects, not pointing to things, a lack of interest in other people and the absence of babbling.
The study needs to be replicated with larger numbers of subjects and a control group, but these early results are compelling. If true it will allow pediatricians to screen for ASD prior to the onset of noticeable symptoms, pushing the diagnosis for many ASD children back prior to being given vaccines.
Head circumference is also not the only line of evidence that is pushing the diagnosis of autism earlier. Several studies looking at home video of autistic children, children with other disabilities, and developmentally normal children show that children with autism display certain features that can reliably predict they will have autism as early as 12 months old. More subtle features are present as early as 8 months old, but these children as not as reliably distinguished from normal controls.
Even more impressively, a study by Philip Teitelbaum showed that careful analysis of the movements of infants from home video could reliably detect autism as early as 4-6 months, and perhaps even from birth.
Taken together there is copious evidence that autism is a primarily genetic disorder that is present at birth, with subtle but increasing signs that separate ASD children from non-ASD children as they age. These fact are incompatible with the vaccine-autism hypothesis. Defenders of the vaccine-autism claim have no answer to this evidence, except to ignore it when possible and dismiss it without justification when forced to confront it. But denying the early onset of autism is becoming increasingly difficult as we learn more about this condition.
To summarize, the vaccine-autism hypothesis has the virtue of being a scientific hypothesis in that it is amenable to falsification. It has now been falsified by multiple independent lines of evidence:epidemiological, genetic, and now clinical. Clinging to a failed hypothesis far beyond the point of falsification is a hallmark of pseudoscience and ideology, and clearly that is what we are dealing with here.
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