Functional EPAS1/HIF2A missense variant is associated with hematocrit in Andean highlanders.

Hypoxia-inducible factor pathway genes are linked to adaptation in both human and nonhuman highland species. EPAS1, a notable target of hypoxia adaptation, is associated with relatively lower hemoglobin concentration in Tibetans. We provide evidence for an association between an adaptive EPAS1 variant (rs570553380) and the same phenotype of relatively low hematocrit in Andean highlanders. This Andean-specific missense variant is present at a modest frequency in Andeans and absent in other human populations and vertebrate species except the coelacanth. CRISPR-base-edited human cells with this variant exhibit shifts in hypoxia-regulated gene expression, while metabolomic analyses reveal both genotype and phenotype associations and validation in a lowland population. Although this genocopy of relatively lower hematocrit in Andean highlanders parallels well-replicated findings in Tibetans, it likely involves distinct pathway responses based on a protein-coding versus noncoding variants, respectively. These findings illuminate how unique variants at EPAS1 contribute to the same phenotype in Tibetans and a subset of Andean highlanders despite distinct evolutionary trajectories.

Genetic variants at the EGLN1 locus associated with high-altitude adaptation in Tibetans are absent or found at low frequency in highland Andeans.

EGLN1 encodes the hypoxia-inducible factor (HIF) pathway prolyl hydroxylase 2 (PHD2) that serves as an oxygen-sensitive regulator of HIF activity. The EGLN1 locus exhibits a signature of positive selection in Tibetan and Andean populations and is associated with hemoglobin concentration in Tibetans. Recent reports provide evidence for functional roles of protein-coding variants within the first exon of EGLN1 (rs186996510, rs12097901) that are linked to an adaptive signal in Tibetans, yet whether these same variants are present and contribute to adaptation in Andean highlanders is unknown. We determined the frequencies of these adaptive Tibetan alleles in Quechua Andeans resident at high altitude (4,350 m) in addition to individuals of Nepali ancestry resident at sea level. The rs186996510 C (minor) allele previously found at high frequency in Tibetans is absent in Andean (G: 100%) and rare among Nepali (C: 11.8%, G: 88.2%) cohorts. The minor G allele of rs12097901 is found at similarly low frequencies in Andeans (G: 12.7%, C: 87.3%) and Nepalis (G: 23.5%, C: 76.5%) compared to Tibetans. These results suggest that adaptation involving EGLN1 in Andeans involves different mechanisms than those described in Tibetans. The precise Andean adaptive variants remain to be determined.

Evolutionary history of Tibetans inferred from whole-genome sequencing.

The indigenous people of the Tibetan Plateau have been the subject of much recent interest because of their unique genetic adaptations to high altitude. Recent studies have demonstrated that the Tibetan EPAS1 haplotype is involved in high altitude-adaptation and originated in an archaic Denisovan-related population. We sequenced the whole-genomes of 27 Tibetans and conducted analyses to infer a detailed history of demography and natural selection of this population. We detected evidence of population structure between the ancestral Han and Tibetan subpopulations as early as 44 to 58 thousand years ago, but with high rates of gene flow until approximately 9 thousand years ago. The CMS test ranked EPAS1 and EGLN1 as the top two positive selection candidates, and in addition identified PTGIS, VDR, and KCTD12 as new candidate genes. The advantageous Tibetan EPAS1 haplotype shared many variants with the Denisovan genome, with an ancient gene tree divergence between the Tibetan and Denisovan haplotypes of about 1 million years ago. With the exception of EPAS1, we observed no evidence of positive selection on Denisovan-like haplotypes.

Genetic structure in the Sherpa and neighboring Nepalese populations.

BACKGROUND: We set out to describe the fine-scale population structure across the Eastern region of Nepal. To date there is relatively little known about the genetic structure of the Sherpa residing in Nepal and their genetic relationship with the Nepalese. We assembled dense genotype data from a total of 1245 individuals representing Nepal and a variety of different populations resident across the greater Himalayan region including Tibet, China, India, Pakistan, Kazakhstan, Uzbekistan, Tajikistan and Kirghizstan. We performed analysis of principal components, admixture and homozygosity. RESULTS: We identified clear substructure across populations resident in the Himalayan arc, with genetic structure broadly mirroring geographical features of the region. Ethnic subgroups within Nepal show distinct genetic structure, on both admixture and principal component analysis. We detected differential proportions of ancestry from northern Himalayan populations across Nepalese subgroups, with the Nepalese Rai, Magar and Tamang carrying the greatest proportions of Tibetan ancestry. CONCLUSIONS: We show that populations dwelling on the Himalayan plateau have had a clear impact on the Northern Indian gene pool. We illustrate how the Sherpa are a remarkably isolated population, with little gene flow from surrounding Nepalese populations.

Genetic variation in SENP1 and ANP32D as predictors of chronic mountain sickness.

Chronic mountain sickness (CMS) is a serious illness that affects life-long high-altitude residents. A recent study analyzed whole genome sequence data from residents of Cerro de Pasco (Peru) in an effort to identify the genetic basis of CMS and reported SENP1 (rs7963934) and ANP32D (rs72644851) to show signatures consistent with natural selection and protective against CMS (Zhou et al. 2013 ). We set out to replicate these observations in two Andean cohorts from Cerro de Pasco, consisting of 84 CMS cases and 91 healthy controls in total. We report evidence of association for rs7963934 (SENP1) in the combined cohorts (meta-analysis p=8.8x10(-4) OR 2.91, CI 1.56-5.5, I=0). The direction of effect was the same as in the original publication. We did not observe any significant correlation between rs72644851 (ANP32D) and the CMS phenotype, within or across cohorts (meta-analysis p=0.204, OR 1.37, CI 0.84-2.241, I=0). Our results provide independent evidence in support of a role for SENP1 in CMS in individuals of Quechua ancestry and suggest the SENP1 and ANP32D signatures of selection are in tight linkage disequilibrium (LD).