Variants near the AS3MT gene found in residents of the Argentine Andes — ScienceAlert
Residents of the high-altitude town of San Antonio de los Cobres in northern Argentina have been found to carry a group of genetic variants near the AS3MT gene that are associated with more efficient arsenic metabolism. These variants may help the body process the toxic element more safely, as it naturally enters groundwater from volcanic rocks, ScienceAlert reports.
DNA study of Andean residents
Researchers analyzed blood samples or cheek swabs from 124 women from San Antonio de los Cobres, who had varying levels of arsenic metabolites in their urine. The scientists examined millions of genetic markers and compared the results with open genomic data on populations from Peru and Colombia from the 1000 Genomes Project.
Variants near the AS3MT gene occurred significantly more often among residents of the Argentine settlement than in genetically similar groups from Peru and Colombia. According to previous studies, the AS3MT enzyme plays an important role in arsenic metabolism.
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Water with high arsenic levels
San Antonio de los Cobres is located at an altitude of about 3,775 meters on the Puna de Atacama plateau. Before a filtration system was installed in 2012, drinking water there contained about 200 micrograms of arsenic per liter — 20 times more than the World Health Organization's recommended level of 10 micrograms per liter. The region has been inhabited for at least 7,000 years, and possibly for up to 11,000 years.
In the body, arsenic is converted into several compounds. Monomethylated arsenic is a particularly toxic intermediate form, while dimethylated arsenic is more easily excreted in urine. Residents of San Antonio de los Cobres had previously been found to have less of the toxic intermediate compound and more of the form that the body can eliminate more easily.
The authors of a 2015 study published in Molecular Biology and Evolution suggested that prolonged arsenic exposure may have contributed to the natural selection of variants that reduce vulnerability to its toxic effects. A separate 2025 study involving more than 6,500 adults in Bangladesh also identified two genetic clusters — FMO and GSTO — which, together with AS3MT, affect the efficiency of arsenic metabolism.
