Friday, August 24, 2007

Myths and Legends of Autism: Part 1

The Myth of the Poor Excretor:

Myths have traditionally been invented to provide explanations for phenomena that were beyond the understanding of the people who made them. Thus you have fiery chariots carrying the sun across the sky, serpents swallowing the sun during an eclipse, the world being created between fire and ice or the many myths of the Cargo Cult in New Guinea and Melanesia.

Another reason for people to invent myths is to deal with unpleasant truths that they wish to ignore. This impulse has given rise, in more modern times, to “irreducible complexity” and the Myth of the Poor Excretor.

The original impetus for the Myth of the Poor Excretor was the finding, by a number of practitioners involved in “alternative” autism therapies, that autistic children often had low hair mercury levels, which conflicted with their firmly held belief that autism was due – at least in part – to mercury poisoning.

When Holmes et al completed a study of 94 autistic children and 45 age- and sex-matched controls and found that autistic children had significantly lower hair mercury levels, there were only three conclusions they could reach:

[1] Mercury protected children from autism.

[2] The hair mercury tests were screwed up.

[3] Autistic children don’t excrete mercury into their hair.

Choice [1] is strongly counterintuitive, but should not be discounted out of hand solely for that reason, since much that is true in science goes against our best intuition. Choice [3] is contrary to decades of research data on mercury metabolism in mammals and so is clearly wrong. Choice [2] appears to be the most likely explanation.

Unfortunately for the authors, the only choice that doesn’t either nullify their hard effort (as [2] would) or contradict their immutable belief that mercury causes autism (as [1] would), is the only choice that is clearly wrong. Instead of abandoning their immutable belief that mercury causes autism - as their data would suggest - they invented the Myth of the Poor Excretor.

According to this myth, autistic children are unable to excrete the mercury they receive from the environment and – more importantly – their childhood vaccines. As a result – so goes the myth – they accumulate the toxic metal and become autistic. It’s a compelling tale, except that it’s complete rubbish.

If you read the study, you will find that this “hypothesis” of "poor excretion" arrives on the scene like a deus ex machina, without any data supporting “poor excretion” in autistic children – except for their low hair mercury levels, which can be better explained in other ways - and no data supporting the implied idea that mercury accumulation in hair can be impaired by any means - apart from cutting off the blood flow to the scalp.

There are also no citations of the scientific literature to show that this “hypothesis” is supported by the researches of other scientists. There is not even any mention of how this “hypothesis” flies squarely in the face of decades of research into mercury metabolism and how that might be reconciled.

In other words, it appears to have been made up out of thin air to keep the authors from having to abandon their cherished belief that mercury causes autism.

Now, it may be true that mercury causes autism in a small number of children – the currently available data is not able to eliminate that possibility. But that is a long way from saying that mercury does cause autism. And the Holmes et al study does nothing to support either the claim that mercury causes autism or that autistic children are “poor excretors” of mercury.

As it turns out, there has been a fair bit of research into the distribution of mercury – both organic and inorganic – into hair. Stuides by Yasutake and Hachiya (2006) and Wilhelm, Muller and Idel (1996) have clearly shown that hair mercury levels are proportional to blood mercury levels at the time the hair is growing. Shi, Lane and Clarkson (1990) showed that the uptake of mercury by hair was dependent on hair growth.

And 'way back in 1986, Mottet, Body, Wilkens and Burbacher showed that the amount of mercury in the hair depended primarily on the amount of mercury in the blood. They also found that the ratio between blood and hair mercury was constant over a wide range of doses and between animals.

But, even with all of this evidence available to them, the Holmes et al authors chose instead to create the Myth of the Poor Excretor. Like most denialist myths (myths invented to ignore unpleasant truths), the survival of the myth depends largely on the existence of a large number of people who also don’t want to face reality. For whatever reason, that pool of people exists and the Myth of the Poor Excretor has persisted to the present day, some four years after its invention.

Next: The Legend of the Maverick Doctor(s)


Monday, August 20, 2007

Another Nail in the Coffin...

Although I have begun to despair that the "mercury-causes-autism" hypothesis can ever be killed, a recent study by Zhao et al has driven another nail into its coffin.

In their study - "A unified genetic theory for sporadic and inherited autism." - the authors describe exactly how spontaneous mutations could cause both sporadic autism (autism in families without a family history of autism) and familial or inherited autism.

You see, this has been the real mystery in autism (not the faux myteries of "poor excretion" and "mercury poisoning") - how families with inherited autism can show the same mutation in all affected members yet not have the same mutation as other families with inherited autism (for example, see here, here, here, here and here).

The answer, it appears, is that females with mutations associated with autism may be resistant to developing autism. Why this is so is not yet clear, but it has been shown pretty conclusively. These women may have one of the many mutations that cause autism but they do not develop the disorder themselves.

However, even those who don't develop autism are still carriers of that genetic mutation and (on average) 50% of their sons will receive that the mutation. Of the sons receiving the mutation, a high percentage of will develop autism. Additionally, about 50% of their daughters will also get the mutation, although only a few will develop autism (all who receive the mutation will be carriers).

This, of course, is not the entire story, but it is a reasonable lay summary of the article.

For those people who will immediately say, "Aha! It's those nasty chemicals/viruses/cell phones that are causing mutations in our children!", let me point out one thing:

The mutations are in the germ cells (i.e. sperm and eggs) of the parents of the autistic children. For these mutations to happen in a child and cause autism, it would have to happen at the single-cell stage (immediately after fertilization).

I encourage people to read the article for themselves - it's available free online. Don't just take my word for it. It's not an easy read, but even if you can't understand it all, you should come away with the idea that [a] this looks less and less like a simple case of "environmental toxicity" and [b] it is a much more complex issue than many of the autism "advocates" would have you believe.

Happy reading!