Hemoglobin E Among Minority Groups Of Yunnan,Southwest China:Natural Selection And Origin

Hemoglobin E(HbE)is produced by the substitution of the amino acid in position 26 by lysine.HbE heterozygote(HbEA)usually has no sever clinical manifestations,and HbE homozygote(HbEE)may have a hypochromic microcytic anemia.When the coinheritance of HbE with other types of β-thalassemia,the clinical manifestations usually have great heterogeneity.HbE is widely distributed in Southeast Asia.In many areas of Thailand,Laos and Cambodia,the incidence of HbE is as high as 60%,which also known as the "HbE triangle".In China,Yunnan is the region with the highest prevalence of HbE and the results of previous studies show that the prevalence of HbE in Achang ethnic group is the highest,up to 39%.Historically,the high prevalence of malaria in tropical and subtropical regions was consistent with the geographic distribution of hemoglobinopathies,so it is generally thought that the high incidence of hemoglobinopathies has been associated with the selection pressure of malaria.At present,a lot of evidences have supported the malaria resistance of sickle cell anemia(HbS)and α-thalassemia,in contrast,the evolutionary interaction between HbE and malaria still remain more controversial.Evidences of HbE-based resistance to malaria in molecular biology mechanism,epidemiology,correlation analysis and population genetic evolution contradict with each other.However,as an ethnic group with the highest prevalence of HbE in China,there is still a lack of research on the relationship between HbE and malaria selection in this population.Therefore,to explore the relationship between HbE and selection pressure in this region is of great significance to further understand the malaria-adaptive evolution of the human genome.[Objective]To provide supplementary content and evidence for the controversial theory of HbE malaria hypothesis by the population genetic evolution analysis and phenotype analysis.[Method](1)Globin gene mutation detection,blood routine tests and hemoglobin analysis were performed on 1265 individuals to analyze genotype and phenotype.(2)Whole exome sequencing(WES)was used to genotyping on 130 samples of Achang and Deang populations.27 tagSNPs,including HbE,with genome spanning 744kb,were screened for genetic evolution analysis as follows:Haplotype was phasing from the WES data by SHAPEIT software.Hardy-Weinberg equilibrium(HWE)and linkage disequilibrium(LD)were performed by Plink1.9 and Haploview 4.2 software.Extended haplotype homozygosity(EHH)and integrated haplotype score(iHS)were calculated using rehh package in R 3.6.1 software.The HbE age was estimated according to EHH value and recombination rate.The phylogenetic network was constructed using HbE and four nearby SNP loci through the NeighborNet method of SplitsTree4 V4.15.1 software.[Result](1)A total of 26 genotypes were identified in 1265 cases with HbE mutation,of which the most common was HbEA(61.82%),followed by βE/βcombining with-α3.7/α α(18.58%)and HbEE(3.16%).Compared with HbEA,hemoglobin(Hb)and mean corpuscular volume(MCV)levels were significantly reduced in group of HbEE,βE/β+and HbEA combining with standard α-thalassemia,and the level of Hb F was significantly increased in the βE/β+group.All genotypes were characterized by hypochromic microcytic anemia or without anemia.(2)Genetic evolution analysis showed that the pattern of LD of HbE extended beyond 100kb,EHH of the ancestral allele decays more rapidly than that of the HbE allele and iHS value of the HbE site was extremely negative,which supported the effect of natural selection on HbE in Achang and Deang populations.(3)Based on the EHH value,the HbE age was roughly estimated to have occurred about 2550～3060 years ago.(4)The haplotype diversity of HbE and surrounding 4 tagSNPs and the phylogenetic network suggested a single origin of the HbE in Achang and Deang populations.[Conclusion](1)HbE has a diversity and complicated mutation spectrum in Dehong,Yunnan.There is heterogeneity in hematological phenotype:HbEA usually has no sever clinical manifestation;HbE homozygotes show a feature of hypochromic microcytic anemia or without anemia and HbE/β-thalassemia has a more severe anemia than that of HbEA.(2)There is a nature selection on HbE in Achang and Deang populations,which was probably caused by malaria in combination with malaria epidemic history.(3)HbE have occurred between 2550 and 3060 years ago in Achang and Deang populations,which is a recent event.(4)HbE may have a single origin in Achang and Deang populations in Yunnan.