The gradual allele frequency change over time observed for of both the NOS3 rs1799983 and the EGLN1 rs1769792 SNP allows us to address whether the Andes were initially peopled by individuals genetically predisposed with a reduced susceptibility to hypoxic stress–assuming that individuals suffering from symptoms of AMS, HAPE, CMS would have returned to lower altitudes–or whether the descendants of these early pioneers adapted to the environmental stressor over time1, 4. This evidence concerns the gene NOS3 and ablepharon macrostomia syndrome.