words) 13Most loci identified by GWAS have been found in populations of European ancestry (EA). In 14 trans-ethnic meta-analyses for 15 hematological traits in 746,667 participants, including 184,535 15 non-EA individuals, we identified 5,552 trait-variant associations at P<5x10 -9 , including 71 16 novel loci not found in EA populations. We also identified novel ancestry-specific variants not 17 found in EA, including an IL7 missense variant in South Asians associated with lymphocyte 18 count in vivo and IL7 secretion levels in vitro. Fine-mapping prioritized variants annotated as 19 functional, and generated 95% credible sets that were 30% smaller when using the trans-ethnic 20 as opposed to the EA-only results. We explored the clinical significance and predictive value of 21 trans-ethnic variants in multiple populations, and compared genetic architecture and the impact 22 of natural selection on these blood phenotypes between populations. Altogether, our results for 23 hematological traits highlight the value of a more global representation of populations in genetic 24 studies. 25 26 4 causal variants (Li and Keating, 2014). Since blood cells play a key role in pathogen invasion, 50 defense and inflammatory responses, hematologic-associated genetic loci are particularly 51 predisposed to be differentiated across ancestral populations as a result of population history and 52 local evolutionary selective pressures (Ding et al., 2013; Lo et al., 2011; Raj et al., 2013). Given 53 the essential role of blood cells in tissue oxygen delivery, inflammatory responses, atherosclerosis, 54 and thrombosis (Byrnes and Wolberg, 2017; Chu et al., 2010; Colin et al., 2014; Tajuddin et al., 55 2016), factors that contribute to such inter-population differences in blood-cell traits may also play 56 appreciable roles in the pathogenesis of chronic diseases and health disparities between 57 populations. 58 59 5 RESULTS 60
Trans-ethnic and ancestry-specific blood-cell traits genetic associations 61We analyzed genotype-phenotype associations at up to 45 million autosomal variants in 746,667 62 participants, including 184,424 individuals of non-EA descent, for 15 traits (Figure 1, 63 Supplementary Tables 1-4, and Methods). The association results of the EA-specific meta-64 analyses are reported separately in a companion paper. In the trans-ethnic meta-analyses, we 65 identified 5,552 trait-variant associations at P<5x10 -9 , which include 71 novel associations not 66 reported in the EA-specific manuscript ( Supplementary Table 5). Of the 5,552 trans-ethnic loci, 67 128 showed strong evidence of allelic effect heterogeneity across populations (Pancestry.hetero <5x10 -68 9 ) ( Supplementary Figure 1 and Supplementary Table 5). Ancestry-specific meta-analyses 69 revealed 28 novel trait-variant associations (Figure 1 and Supplementary Tables 6-10). 70However, 19 out of these 21 novel AFR-specific associations map to chromosome 1 and are 71 associated with WBC or neutrophil counts, therefore reflecting long-range associations due...