Study : Lack of association between autism and four heavy metal regulatory genes
Posted Aug 01 2011 1:11pm
This study revisits the older idea that children with autism have an altered mercury (Hg) metabolism that makes them susceptible to even "safe" levels of Hg. It did this by looking for an association between autism and mutations in four genes involved in Hg metabolism.
Not surprisingly, the study found no association. I wouldn't make too much out of this result though, as interesting as it is.
For one thing, other larger genetic studies have taught us that most mutations and copy number variations that have a relation to autism only appear in a very small number of cases, typically less than one percent. If that were the case here then the current study might not have included enough participants to find the association.
Another potential problem is that there is a difference between a genetic susceptibility and what the actual biological pathway is doing. If you wanted to test the altered metabolism theory then the best way of doing so would be to devise some direct test of the metabolism. Although I suspect that might be easier said than done.
In general, I think these sorts of genetic association studies are going to be useless until we come up with a way to separate out the different forms of autism. Right now we are taking everyone with a label of "autism" and looking at them as a group and finding nothing.
That would be like taking anyone with any form of cancer and looking at them as a single group. You wouldn't get any useful relationships that way either. It is only when you separate out the different types and look at then individually that you get very useful results.
Lack of association between autism and four heavy metal regulatory genes. Neurotoxicology. 2011 Jul 20. Owens SE, Summar ML, Ryckman KK, Haines JL, Reiss S, Summar SR, Aschner M. Department of Pediatric Toxicology, Vanderbilt University School of Medicine, Nashville, TN, USA.
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.