Meteorological factors and autism?

If I had a pound (inflation adjusted y'know) for every time the words 'correlation does not equal causation' were used with autism and related conditions in mind, my piggy bank would probably be rather full by now. Indeed such is the application of this term when referring to the wide (very wide) variety of associations made between this, that and t'other, that a backlash has seemingly emerged to counter its usage as per this Slate article.

Cool, clear water @ Wikipedia 

Of course that's not to say that correlation does not imply causation. Recently for example, a study appeared  in the very well respected New England Journal of Medicine (NEJM) by Franz Messerli* which concluded: "Chocolate consumption enhances cognitive function, which is a sine qua non for winning the Nobel Prize, and it closely correlates with the number of Nobel laureates in each country".

Whilst still wondering whether this is some kind of spoof article (apparently it's not) this study encapsulates everything about the notion of correlation ≠ causation given the multitude of other factors which might possibly influence citizens of a particular country winning the distinguished Nobel Prize. I am willing to concede however, should more 'direct' prospective evidence emerge, that eating chocolate might be part and parcel of Nobel Prize winning.

With this same logic I was intrigued to read the recent paper by Sophie St Hilaire and colleagues** (open-access) which based on an ecological study of autism concluded that precipitation and drinking water source might be associated with autism. Drinking water you say? Y'mean similar to the fish and pharmaceutics research and the Brick chlorination by-products paper? Well, similar at least.

In brief:

• Based on data derived from the study by Waldman and colleagues*** which concluded a possible link between annual precipitation and autism prevalence rates in the Western United States, the source of drinking water was analysed with respect to autism rates.
• The percentage of surface drinking water was thrown into the statistical mix as was population density, farming land, SES, risk of neurological disorder from air pollution, suicide rates and meteorological data.
• When analysing all this data, the authors concluded that precipitation was linked to autism rates but the source of drinking water was an important factor too.
• In among the other correlations, rates of autism also correlated with the suicide rate and negatively correlated with the unemployment rate.

There are some other interesting factoids to take from the authors findings and conclusions. Surface sources of drinking water potentially implying some role for environmental contamination was a primary association. More than that however, the authors seemed to rule out any significant association with contaminated run-off water derived for example from pesticide use and indeed urban pollution and autism rates. They leave the door open to air pollution as a possible factor and indeed pharmaceutical contamination of water sources; bearing in mind they did not test the drug residues in water hypothesis.

The negative correlation between autism rates and unemployment (as in high prevalence of autism being linked to low unemployment rates) goes back to other research in this area. That being said, I'm reminded about more recent investigation which seem to imply an opposite trend (high prevalence of autism linked to lower SES) so once again we have to be careful not to generalise too much.

There's no doubt that this is an interesting study despite the reliance on population facts and figures and our old friend correlation. Accepting another old adage on 'lies, damn lies and statistics' (see here****), there are some useful components from the St Hilaire study ripe for further testing. Not least the continuing theme that environment may very much be a part of the increase in reported cases of autism.

To finish, bird is the word (or did you not know?).

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* Messerli FH. Chocolate consumption, cognitive function, and Nobel Laureates. NEJM. October 2012.

** St Hilaire S. et al. An ecological study on childhood autism. Int J Health Geographics. 2012; 11: 44.

*** Waldman M. et al. Autism prevalence and precipitation rates in California, Oregon, and Washington counties. Arch Pediatr Adolesc Med. 2008; 162: 1026-1034.

**** Bartell SM. & Lewandowski TA. Administrative censoring in ecological analyses of autism and a Bayesian solution. J Environ Public Health. 2011; 2011: 202783.

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Sophie St Hilaire, Victor Ezike, Henrik Stryhn, & Michael A Thomas (2012). An ecological study on childhood autism International Journal of Health Geographics

Chlorinated byproducts and autism

Brick Township in New Jersey (USA) enjoys a few accolades. According to the 2003 FBI statistics, Brick Township was the 2nd safest place to live in America. It also features highly in terms of its educational provisions and is generally seen to be quite a nice place to live. Like every other place, Brick Township (BT) does however also enjoy a not-so-enviable part of its community. In the case of BT it is its history with landfill and in particular French's landfill.

Landfill is a world-wide issue in terms of the staggering amounts of waste we as a population produce and what we do with it. We, here in the UK, are unfortunately particularly wasteful still, having previously been dubbed the 'landfill dustbin of Europe'. We are getting better I might add, but still that label persists.

French's landfill in BT has been in the US Environmental Protection Agency's sights for quite a few years. So much so that there is a dedicated EPA entry on their website showing the various strategies and progress being made in cleaning up French's landfill.  It makes for unpleasant reading in terms of the types of contaminants identified and the history of potential contamination from the site.

The reason for my interest is this paper which has recently appeared in the journal NeuroToxicology. The paper by Guariglia and colleagues appears to question the outcomes from a previous report on BT drinking water and the occurrence of autism (which can be read here). They undertook to examine how water treated with compounds similarly detected in the BT municipal drinking water supply might affect specific breeds of mice. The compounds in question were trihalomethanes (THMs) and perchloroethylenes (PCEs) which carry some pretty significant risks following continued exposure including being carcinogens. The mice (and their mothers) were given the contaminated water both whilst pregnant and post-natally.

The findings, bearing in mind that this is a study based on a mouse model:

• Male mice seemed to be affected more by the cocktail given.
• Behaviours indicative of anxiety were increased. 
• Vocalisations in response to being separated from mother mouse were decreased. 
• Social behaviours were reduced.

I appreciate that undertaking such studies on mice is not really to anyone's taste. Even though mouse models are used widespread in science (including autism research) it doesn't necessarily make it right. Keeping the ethical aspects in mind, the results deliver some very interesting leads. Interesting because of the various associations made and how they link with quite a few aspects of autism including the gender preference. Of course, correlation does not imply causation.

This is not the first time that BT has cropped up on the autism research radar. Readers may remember this study from a decade ago which hinted that BT might be a 'hotspot' for autism diagnoses. I remember quite a lot of the media interest in this at the time, and the various links being made between environment, the superior schooling provisions in BT, etc. to account for the results. Nowadays, autism spectrum prevalence rates of 0.6% look positively low compared to the emerging data.

I would like to see a little more study undertaken based on the recent mice findings. Population sampling for similar metabolites present in humans might be a good start, particularly in BT; for which various methods for analysing various biological mediums are available (indeed some very sensitive methods available). Given the amount of data amassed by the EPA within BT, I would assume some very powerful results could be produced to contribute to any 'cause or association' discussions that could follow, if only to discount any relationship.

To end on a slightly happier note, Brick Township is dealing with French's landfill. Hopefully with the completion of these clean-up operations in future months, BT can focus on its more beautiful assets and turn the page on landfill and its potential environmental effects.