Earlier this week, the prestigious scientific journal, Nature, published an article entitled "Autism Study Panned by Critics". The article discussed the controversies surrounding a recently suspended clinical trial that proposed the use of chelating agents on children with autism.
The hypothesis in this trial is that on average and relative to the control group, children with autism spectrum disorder (ASD) who undergo chelation with meso-2,3-dimercaptosuccinic acid (DMSA) will show greater improvements in communication and social behavior. The trial description says there is need for empiric evidence for effects of chelation therapy in view of prevalent use of chelation in autistic children despite lack of scientific or clinical evidence of efficacy .
I won't comment on the medical value of using chelating agents, but the article does promote some fallacies in a condescending and inappropriate manner about mercury as a possible cause, or contributing cause, of autism to those families desperately seeking answers to a now epidemic disease (1 in 150 children are diagnosed with autism- CDC, 2007). This disease is particularly irksome as there are no definitive scientific causal answers. Yet the authors act as if mercury has been eliminated as a possible mechanism, when in fact there is a gathering body of evidence linking mercury as a neurotoxin to segments of the population who show a possible genetic susceptibility based on genetic association studies. The imperious claim that the issue of mercury's role as a causal factor in autism has been settled is unsupported by the facts.
Fallacy 1) "Parents are using such therapy on children with autism because of their belief -- which has been scientifically discredited -- that mercury from vaccinations caused their children's condition."
Let's be clear. Mercury from vaccinations as a contributing factor to autism, or perhaps the threshold breaking factor, in genetically susceptible children has not been scientifically discredited.
Mercury is a known neurotoxin, found ubiquitously in the environment. Its various forms come from or are derived from , both natural sources, such as volcanic activity, and man-made sources. Background levels in the environment have increased in the post-industrial era several-fold, coming from coal power plants and other industrial sources. And, the world is only getting more toxic -- for example, China is opening two new coal power plants a week to fuel their growing economy .The effluents from these plants, including mercury, are carried in the upper atmosphere east towards North America, and are causing rises in mercury levels in the Pacific Ocean.
Mercury has long been a contaminant in food. Methyl mercury is the predominant form of mercury in the food chain and gets concentrated as it moves up the food chain: bacteria->plankton->small fish->larger predatory fish->humans and animals.
Image from Technical Report: Mercury in the Environment: Implications for Pediatricians
Goldman, Lynn R., Shannon, Michael W., the Committee on Environmental Health, Pediatrics 2001 108: 197-205
The effect of this 'bioaccumulation' is well known, and has led to dietary fish restriction recommendations from the EPA and the, FDA. Women who might become pregnant, women who are pregnant, and nursing mothers are at risk if they eat two tuna fish sandwiches a week! (The specific advice is to avoid certain species of fish, and limit fish and shellfish that are lower in mercury to 2 meals per week. Children are recommended the same guidelines but "smaller portions".
The other major route of exposure is mercury in dental amalgam, itself a topic of much controversy.
Nataf et. al. 2006 and Geier and Geier, 2006, have shown that higher body burdens of mercury, as indicated by urinary porphyrin profiles, are significantly higher in autistic children.
And the recent ruling in Vaccine Court in favor of an autistic child with mitochondrial disease highlights the importance of individual risk factors in determining associations of vaccine or other sources of mercury in causation of this disease. The court ruled in favor of link between vaccination and the onset on autism-like symptoms in a child with underlying predisposition due to mitochondrial disorder.
Bottom line is, mercury in vaccines is one source contributing to a total body burden. And, the role of inter-individual variations has not been clarified. The contention that parents' beliefs have been "scientifically discredited" is wrong.
Fallacy # 2) "Others argue that the study doesn't make scientific sense because autism has not been documented as a symptom of high-dose mercury poisoning......."
Three prominent studies (Palmer et. al., 2008, Windham et. al, 2006, Palmer et. al, 2006) document an association between environmental sources of mercury release and autism rates , , . The most recent of these studies shows a statistically relevant increase of 2.6-3.7% increase in the rate of autism based on proximity to industrial power plants.
Multiple studies have indicated the differential susceptibility of children to deleterious neurological effects of mercury, including both fish consumption and pure environmental factors (Landrigan et. al., 2002, Grandjean et. al, 1995, Ramirez et. al, 2003, Rice et. al, 2000), and the accumulation of higher concentrations of mercury in breast-fed infants than blood levels of their nursing moms.
There are undoubtedly many unknown factors with respect to retention of mercury, impairment of detoxification pathways, and elimination rates which vary in individuals, for a number of environmental and genetic factors.
Debating the merits of a particular clinical trial and the usefulness of the conclusions that could be drawn from the endpoint is fair game in approving and evaluating clinical trial design and acceptability of conduct.
To use such debate as a platform to surreptitiously proffer fallacies and assumptions as scientifically proven fact in irresponsible.
All links last accessed on July 16, 2008.
Raymond F Palmer, Stephen Blanchard, and Robert Wood, "Proximity to point sources of environmental mercury release as a predictor of autism prevalence," Health & Place (February 12, 2008), doi:S1353-8292(08)00014-2.
Raymond F Palmer et al., "Environmental mercury release, special education rates, and autism disorder: an ecological study of Texas," Health & Place 12, no. 2 (June 2006): 203-9, doi:S1353-8292(04)00117-0.
Gayle C Windham et al., "Autism spectrum disorders in relation to distribution of hazardous air pollutants in the San Francisco bay area," Environmental Health Perspectives 114, no. 9 (September 2006): 1438-44, doi:16966102.