Scientists from Taiwan have identified a genetic variation that could make certain populations more susceptible to arsenic poisoning. 

Organic arsenic intake from seafood is one of the major arsenic exposure routes in humans, but its metabolism in the body is not fully understood. Although not as toxic as inorganic arsenic, it's build up in the body can cause concern for health. People living on Asian islands or coastal areas, such as Japan and Taiwan, are well known to have a relatively high background of arsenic in their urine, which is usually attributed to the high levels of seafood consumed in these areas. But Asian immigrants in the US show elevated urinary arsenic metabolites even after living in New York for years, explains Yaw-Huei Hwang at the National Taiwan University in Tapei. This has prompted a genetic link to be explored. 

Some genes can exist in different forms (or polymorphs), which could effect how different dietary species, such as organic arsenic, are metabolised in the body. Hwang's team sampled the urine of 50 people after eating oysters and identified the form of three genes, known as As3MT, PNP and GSTO1, that are known to affect the metabolism of inorganic arsenic in each person. In people with the higher urinary arsenic levels, the As3MT gene existed in one particular polymorph, which is also the most common form in people from Korea and Japan, explains Hwang. 

This As3MT polymorph may not be efficient at may not be as efficient at metabolising organic arsenic, says Hwang, which could explain the ethnic variations in background urinary arsenic metabolites. 'The metabolism of dietary arsenic species in people with different genetic polymorphisms is of great concern,' he adds.  

Walt Klimecki, who researches how genetic differences affect arsenic metabolism at the University of Arizona says 'this exploratory study's finding of a genetic association between variants in As3MT  and the biotransformation of seafood arsenic, generally considered to be a harmless arsenic exposure, is provocative given the known substrate spectrum of As3MT. Larger studies of this kind with defined diets will be needed to advance our ability to distinguish harmful from harmless arsenic exposure.'

Hwang now plans to further characterise the association of organic and inorganic arsenic metabolism by exposure monitoring and investigating the potential health effects. 

Jennifer Newton

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