The Arsenic-Proof People of the Andes

​They call arsenic the Poison of Kings and the King of Poison, but like any king, some people evade your reign. For arsenic, those people live beyond its poisonous grasp up in the Andes mountains. They're the first human population that has been found with a tolerance related to arsenic metabolism, and in a new paper released in Molecular Biology and Evolution, scientists have highlighted to the exact genetic shifts that make this possible.

A team of Swedish researchers travelled to San Antonio de los Cobres, a town in northwestern Argentina. There is evidence of people living in this region since at least 1,500 BCE, and judging from mummies found nearby, arsenic has been in the water the whole time. The volcanic bedrock in the region gives the groundwater high levels of arsenic, which was in turn, showing up in the town's drinking water until a filtration system was put in place in 2012.

The researchers performed a genome-wide survey of 124 women. Based on interviews, the women were mainly of indigenous, Atacameño origin with little Hispanic ancestry, and their families had lived in the area for at least two to three generations.

Then the researchers took a look at the women's urine.

Not only were the women from San Antonio de los Cobres able to metabolize arsenic more efficiently, as the researchers predicted, but they were able to localize where their genomes had adapted in order to do so—a set of nucleotide variants in the gene AS3MT.

Researchers have long suspected that AS3MT had som​ething to do with how our bodies metabolize arsenic, and it's pretty exciting to know exactly where and what variations make a sort of protective haplotype.

Genetically similar haplotypes appear in other Native American populations as well as Peruvians and the Kinh population in Ho Chi Minh City, Vietnam. Karin Broberg, lead author of the study wanted to stress that the researchers "have not analyzed if this tolerance related to arsenic metabolism protects them for all health problems from arsenic." She wrote in an email, "Arsenic is a very potent poison with many toxic effects," which means that it's still important to reduce the arsenic in the drinking water in the town."

In fact, it varies from person to person, but living in certain places, like San Antonio de los Cobres make it practically a necessity. Up in the mountains they're free from the tyrannical reign of the king of the poisons.

Correction: An earlier version of this story suggested that the residents of San Antonio de los Cobres have a full immunity to arsenic; that is incorrect.