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High altitude native populations exhibit physiological adaptations to environmental hypoxia. It has been hypothesized that two of these populations, Andeans and Tibetans, demonstrate distinct adaptive modes with the former characterized by increased blood oxygen content, and the latter characterized by increased blood flow. To investigate this hypothesis, we recruited two groups of healthy adults (ages 18-35) with highland ancestry who were born and currently reside at high altitude. The groups were: Andean Quechuas recruited in Cerro de Pasco, Peru (AND, n = 301) and Tibetan Sherpas recruited in Pheriche, Nepal (SHP, n = 64). Participants were tested in field laboratories using identical equipment and protocols, at nearly identical altitudes (4,330m and 4,371m, respectively). We assessed a wide variety of physiological variables at rest, submaximal exercise, and maximal exercise. We found that although some phenotypes aligned with the above hypothesis, the majority did not. For example, as predicted, AND displayed significantly lower (p<0.001) ventilatory equivalents for oxygen (VE/VO2) at rest. However, this trend reversed at maximal exercise, with AND displaying significantly higher (p<0.001) VE/VO2 than SHP. Further, contrary to the above hypothesis, we found no statistically significant differences in flow-mediated dilation between the groups. These results suggest that the adaptive modes of these populations are perhaps not as distinct as previously supposed. Given that this hypothesis was formulated on the basis of data taken at rest, our data highlights the importance of assessing physiology both at rest and exercise, to gain a more complete understanding of adaptation to high altitude. 

Highland native Andeans have resided at altitude for millennia. They display high aerobic capacity (VO 2 max) at altitude, which may be a reflection of genetic adaptation to hypoxia. Previous genomewide (GW) scans for natural selection have nominated Egl-9 homolog 1 gene ( EGLN1 ) as a candidate gene. The encoded protein, EGLN1/PHD2, is an O 2 sensor that controls levels of the Hypoxia Inducible Factor-α (HIF-α), which regulates the cellular response to hypoxia. From GW association and analysis of covariance performed on a total sample of 429 Peruvian Quechua and 94 US lowland referents, we identified 5 EGLN1 SNPs associated with higher VO 2 max (L⋅min −1 and mL⋅min −1 ⋅kg −1 ) in hypoxia (rs1769793, rs2064766, rs2437150, rs2491403, rs479200). For 4 of these SNPs, Quechua had the highest frequency of the advantageous (high VO 2 max) allele compared with 25 diverse lowland comparison populations from the 1000 Genomes Project. Genotype effects were substantial, with high versus low VO 2 max genotype categories differing by ∼11% (e.g., for rs1769793 SNP genotype TT = 34.2 mL⋅min −1 ⋅kg −1 vs. CC = 30.5 mL⋅min −1 ⋅kg −1 ). To guard against spurious association, we controlled for population stratification. Findings were replicated for EGLN1 SNP rs1769793 in an independent Andean sample collected in 2002. These findings contextualize previous reports of natural selection at EGLN1 in Andeans, and support the hypothesis that natural selection has increased the frequency of an EGLN1 causal variant that enhances O 2 delivery or use during exercise at altitude in Peruvian Quechua.