Studies conducted at the Karolinska Institutet and Uppsala University in Sweden show that some indigenous groups in the Andes of northern Argentina have increased resistance to arsenic. The researchers also identified the gene that underlies the altered metabolism and protects against exposure to arsenic. This study is the first to show that some humans have genetically adapted to a polluted environment.
Arsenic occurs naturally in the bedrock in many places in the world and is one of the most potent carcinogens in our environment. People are exposed mainly through drinking water and food, especially rice and various rice products. People living in the Argentinian Andes have likely been exposed to high levels of arsenic in drinking water for thousands of years. The present study shows that residents who live in this region today have a clearly higher frequency of gene variants that enable the body to efficiently handle arsenic by methylating and excreting a less-toxic arsenic metabolite. By contrast, people who lack the protective gene variant produce a more-toxic arsenic metabolite if they are exposed to arsenic. Other communities in neighbouring areas without the same historical arsenic exposure have significantly lower frequencies of the protective gene variant. The results have been first published online on 3 March in the journal Molecular Biology and Evolution.
The researchers have identified changes in the main gene for arsenic metabolism, as the cause of the altered metabolism. Their results suggest that people have adapted to arsenic via an increase in the frequency of protective variants of this specific gene. This study is a striking example of how humans have been able to adapt to local, sometimes harmful, environmental conditions. Those who survived the exposure to arsenic lived longer and had more children. Thus, the protective gene variants are very common in some regions of the Andes today. Only a few such examples have previously been described in man.
Karin Broberg, researcher at the Institute of Environmental Medicine (IMM) at Karolinska Institutet says:
“Our study shows that there are not only extra-susceptible individuals, but also individuals who are particularly tolerant to environmental toxic substances. This phenomenon is probably not unique to arsenic, but also applies to other toxic substances in food and the environment, to which humans have been exposed for a long time. The results also highlight the necessity to be observant and not base health risk assessments for chemicals on data from people who may have strong genetic tolerance to the particular chemical.”
And Carina Schlebusch says:
“Only few other studies have found evidence of local adaptation in humans; for instance adaptation to high altitude conditions and the malaria parasite. This study adds another example of how humans have adapted, in a relatively short time, to tolerate an environmental stressor that they encountered when they settled in a new area.”
The researchers will now study whether other populations with historical arsenic exposure show an equivalent adaptation, and examine if other toxic substances in the environment can result in increased frequency of genetic variants that provide resistance in humans.
(Source: Karolinska Institutet press release, 04.03.2015)
