Thimersal Does Not Cause Autism

Autism is one of the most severe and disruptive of all childhood disorders - with a high level of disruption that of course lasts well into adulthood. With both genetic and environmental elements at work in it, autism (which affects boys at least three times more often than girls and is found in all races and throughout the world) is a communicative disorder that interferes with an individual's ability to form social relationships as well as to communicate with others.

As might well be expected to be the case with any severe condition the etiology of which is understood a number of "folk" explanations for the condition have developed, including the idea that childhood vaccinations (and especially the mercury-based preservative Thimerosal that is used in the formulation of many vaccines) is responsible for triggering the condition.

This paper argues against any connection between Thimerosal and autism (or rather argues that no such condition has yet been established; it would not be good science to argue that such a connection will never be established). However, and this is an important initial caveat to make, simply because no connection has been found does not mean that all such "folk" explanations of medical or scientific phenomena should be dismissed.

Scientists, and especially medical researchers, are sometimes too quick to assume that those who lack formal training in the sciences are entirely unqualified to make the kinds of observations that lead to scientific breakthroughs, but this is simply not true. Anyone who is intelligent and careful can make important, scientific observations about the world around us.

This is what parents, baffled by the affects of autism on their children, have attempted to do: The fact that they have (in so far as current scientific investigation has so far consistently demonstrated) been wrong does not mean that any future claims about the world by non-scientists can be dismissed out of hand rather than through careful scientific evidence. It seems unlikely that advocacy groups would have looked to Thimerosal as a possible cause of autism if the disease were itself better understood.

However, it remains one of the most mysterious of (relatively) common cognitive disorders. Autism is distinguished by a number of often dramatic and sometimes even violent symptoms that often prevent autistic children from being educated and prevent autistic adults from forming non-familial relationships or holding down jobs. Autism is primarily marked by significant withdrawal from the world and an extreme aversion to entering the social spaces of other people as well as by a range of behaviors that may appear bizarre to others (Smith etal, 1994; Paluszny, 1979).

A number of studies have investigated whether there is any link between childhood vaccines and autism. Such a link was originally proposed by the children of parents with autism, in part because the symptoms of autism often appear soon after vaccinations (this is not surprising since the onset of autistic symptoms tends to occur at the same time in all children; this age is also - for unrelated reasons - the time at which most children are receiving one of their sets of childhood vaccines.

The other reason that Thimerosal has been selected by advocacy groups as a possible cause (or if not cause at least "trigger" of autism) is that it is a mercury-based product. Most people are aware of the fact that mercury in some forms is highly toxic; it is not therefore surprising that parents whose children have been diagnosed as autistic after being vaccinated with a serum that contains mercury should question its safety.

However, as the Federal Drug Administration notes, it is important to understand the properties of the specific mercury compound in question: Thimerosal, which is approximately 50% mercury by weight, has been one of the most widely used preservatives in vaccines. It is metabolized or degraded to ethylmercury and thiosalicylate. Ethylmercury is an organomercurial that should be distinguished from methylmercury, a related substance that has been the focus of considerable study (http://www.fda.gov/cber/vaccine/thimerosal.htm#thi).

Methylmercury is a neurotoxin of considerable potency; the toxicity of ethylmercury is certainly lower, although it may prompt allergic reactions and (as is true of all substances) is certainly toxic at some level. One of the most comprehensive studies of the link between vaccinations and the preservatives in them and autism was published last year in the New England Journal of Medicine.

Titled "A Population-Based Study of Measles, Mumps and Rubella Vaccination and Autism," authors Kreesten Meldgaard etal found there to be no link between the Thimerosal in vaccination preparations and autism. This piece of research is certainly a compelling argument against any connection; it is perhaps not, however, the final word on the subject that its authors argue it to be. While its findings are sound, they are limited to the MMR vaccine; this is not the only vaccine that can contain Thimerosal.

This paper is based upon epidemiological research rather than biological research; in other words, it is a correlation study between vaccination type, timing and the onset of autism vis-a-vis "standard" rates of autism. This alone makes one part of the case against a connection between autism and vaccination. Other research based not on post-facto epidemiological studies but rather on the biology of autism (and in general of auto-immune syndromes) must be considered as well.

Other researchers have investigated this aspect of a possible connection between vaccinations and autism and have again found that there is no link between the biology of autism and mercury as a trigger (although heavy metals are triggers for some types of auto-immune responses. For example, Trottier et al. (1999) found that rather than environmental triggers (which would include vaccinations), the primary cause for autism appears to be genetic.

(Their work did not exclude the possibility that environment factors might not trigger autism in a genetically susceptible individual, but found no evidence that Thimerosal was one of these triggers.) They concluded that there is certainly a biological element to autism and one that is linked to inheritance, but that environment may also play a role. (This is hardly surprising; nearly every disease is affected by both genetic and environmental factors).

In summary, the prevailing view is that autism is caused by a pathophysiologic process arising from the interaction of an early environmental insult and a genetic predisposition (p. 115). Comi etal (1999) found the same concatenation of environmental and genetic factors to be at play in the onset of autism. An increased number of autoimmune disorders [in patients' families] suggests that in some families with autism, immune dysfunction could interact with various environmental factors to.