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Lack of association between autism and four heavy metal regulatory genes

Posted Jul 30 2011 11:02am

One question that has been discussed for some time is the hypothesized role of mercury as a potential cause of autism. The basic idea is that administrative prevalences of autism went up coincident with increases in mercury exposure from vaccines. Plus, it was asserted that autism symptoms are similar to the symptoms of mercury poisoning (they aren’t).

Part of the mercury model held that there could be a genetic susceptibility to mercury in a subset of children.

Researchers at Vanderbilt University have explored the question by testing autistics for genes involved in how the body processes mercury. They did not find any link between the four genes they screened and autism.

Of course one could argue that some other gene or genes are important. One would then need to explain why mercury exposure from vaccines does not increase the risk of autism.

The paper Lack of association between autism and four heavy metal regulatory genes.

Here’s the abstract.

Neurotoxicology. 2011 Jul 20. [Epub ahead of print]
Lack of association between autism and four heavy metal regulatory genes.
Owens SE, Summar ML, Ryckman KK, Haines JL, Reiss S, Summar SR, Aschner M.
Source
Department of Pediatric Toxicology, Vanderbilt University School of Medicine, Nashville, TN, USA.
Abstract
Autism is a common neurodevelopmental disorder with genetic and environmental components. Though unproven, genetic susceptibility to high mercury (Hg) body burden has been suggested as an autism risk factor in a subset of children. We hypothesized that exposure to “safe” Hg levels could be implicated in the etiology of autism if genetic susceptibility altered Hg’s metabolism or intracellular compartmentalization. Genetic sequences of four genes implicated in the transport and response to Hg were screened for variation and association with autism. LAT1 and DMT1 function in Hg transport, and Hg exposure induces MTF1 and MT1a. We identified and characterized 74 variants in MT1a, DMT1, LAT1 and MTF1. Polymorphisms identified through screening 48 unrelated individuals from the general and autistic populations were evaluated for differences in allele frequencies using Fisher’s exact test. Three variants with suggestive p-values <0.1 and four variants with significant p-values <0.05 were followed-up with TaqMan genotyping in a larger cohort of 204 patients and 323 control samples. The pedigree disequilibrium test was used to examine linkage and association. Analysis failed to show association with autism for any variant evaluated in both the initial screening set and the expanded cohort, suggesting that variations in the ability of the four genes studied to process and transport Hg may not play a significant role in the etiology of autism.

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