Human adaptation, demography and cattle domestication: an overview of the complexity of lactase persistence in Africa

Abstract Lactase persistence (LP) is a genetically-determined trait that is prevalent in African, European and Arab populations with a tradition of animal herding and milk consumption. To date, genetic analyses have identified several common variants that are associated with LP. Furthermore, data have indicated that these functional alleles likely have been maintained in pastoralist populations due to the action of recent selection, exemplifying the ongoing evolution of anatomically modern humans. Additionally, demographic history has also played a role in the geographic distribution of LP and associated alleles in Africa. In particular, the migration of ancestral herders and their subsequent admixture with local populations were integral to the spread of LP alleles and the culture of pastoralism across the continent. The timing of these demographic events was often correlated with known major environmental changes and/or the ability of domesticated cattle to resist/avoid infectious diseases. This review summarizes recent advances in our understanding of the genetic basis and evolutionary history of LP, as well as the factors that influenced the origin and spread of pastoralism in Africa.</jats:p

1284-P: Genetic and Lifestyle Associations with Cardiometabolic Traits and Diabetes Risk Factors in Ethnically Diverse Africans

African ancestry populations are underrepresented in human genetic studies, which leaves a knowledge gap about genetic and environmental risk factors for metabolic disease which can bias healthcare treatment. To alleviate these shortcomings, we conducted a series of genome-wide association studies of cardiometabolic traits in a diverse sampling of ∼2,500 (max sample size) ethnically and geographically diverse Africans from populations practicing agriculturalist, hunter-gatherer, and pastoralist subsistence strategies. This study includes the Fulani pastoralists who have a relatively high incidence of adult-onset diabetes, despite having a low average body mass index (BMI) . All individuals in the present study are sampled from rural populations that have relatively homogeneous lifestyles and diet within a community. This unique aspect to the study cohort allows for within- and between- group comparisons to identify trait variation attributable to genetics vs. lifestyle variation. Subjects were genotyped on a new African-focused SNP array from the Human Heredity and Health in Africa (H3 Africa) consortium. Genome-wide data was imputed based on a panel of African whole-genome sequences and data from the 1000 genomes project, resulting in a total of million variants for trait association analysis. Genetic associations were tested for BMI, blood pressure, and blood biomarkers of cardiometabolic health. We checked for replication of genotype/phenotype associations by comparison to large non-African cohorts studied for the same traits. We find that most associations identified in non-African populations do not replicate in the Africans. However, we identified a number of novel loci associated with cardiometabolic traits in the African populations. This study has important implications for identifying genetic risk factors that may play a role in metabolic disease in individuals of African ancestry. Funded by ADA Pathway award 1-19-VSN-02. Disclosure D.Hui: None. T.B.Nyambo: None. S.Chanock: None. S.A.Tishkoff: None. D.Harris: None. M.Mcquillan: None. M.Hansen: None. A.Ranciaro: None. W.Beggs: None. S.W.Mpoloka: None. D.Woldemeskel: None. A.K.K.Njamnshi: None. Funding American Diabetes Association (1-19-VSN-02) ; National Institutes of Health (R35 GM134957-01, R01AR076241, 5T32DK007314-39, 1OT3HL142479-01, 1OT3HL142478-01, 1OT3HL142481-01, 1OT3HL142480-01, 1OT3HL147154-01) </jats:sec

Genetic Origins of Lactase Persistence and the Spread of Pastoralism in Africa

In humans, the ability to digest lactose, the sugar in milk, declines after weaning because of decreasing levels of the enzyme lactase-phlorizin hydrolase, encoded by LCT. However, some individuals maintain high enzyme amounts and are able to digest lactose into adulthood (i.e., they have the lactase-persistence [LP] trait). It is thought that selection has played a major role in maintaining this genetically determined phenotypic trait in different human populations that practice pastoralism. To identify variants associated with the LP trait and to study its evolutionary history in Africa, we sequenced MCM6 introns 9 and 13 and ∼2 kb of the LCT promoter region in 819 individuals from 63 African populations and in 154 non-Africans from nine populations. We also genotyped four microsatellites in an ∼198 kb region in a subset of 252 individuals to reconstruct the origin and spread of LP-associated variants in Africa. Additionally, we examined the association between LP and genetic variability at candidate regulatory regions in 513 individuals from eastern Africa. Our analyses confirmed the association between the LP trait and three common variants in intron 13 (C-14010, G-13907, and G-13915). Furthermore, we identified two additional LP-associated SNPs in intron 13 and the promoter region (G-12962 and T-956, respectively). Using neutrality tests based on the allele frequency spectrum and long-range linkage disequilibrium, we detected strong signatures of recent positive selection in eastern African populations and the Fulani from central Africa. In addition, haplotype analysis supported an eastern African origin of the C-14010 LP-associated mutation in southern Africa

191-LB: Impact of Subsistence and Genetics on Lipid Profiles in Ethnically Diverse Africans

African Americans are at higher risk for cardiometabolic disease relative to individuals with European ancestry. Yet, populations with African ancestry are greatly under-represented in human genomics studies. To alleviate this bias and better distinguish the roles of genetics and environment on cardiometabolic traits, we conducted targeted metabolomics to measure levels of &amp;gt;700 lipids in 718 Africans and integrated with genomic data from &amp;gt;7M single nucleotide polymorphisms genotyped in the same individuals. These individuals are from 14 ethnic groups from diverse regions of Africa (Botswana, Cameroon, Ethiopia, Tanzania) and with diverse subsistence patterns (agriculturalists, pastoralists, hunter-gatherers). In contrast to US populations, most individuals were sampled from rural areas with relatively homogenous diets and, thus, we could better quantify lipids typically found at low levels in US individuals. Furthermore, several groups have similar genetic ancestry but distinct diets, and vice versa, enabling us to distinguish the role of genetic ancestry and environment on lipid variation. We identified 305 independent genetic variants associated with 103 lipid species, &amp;gt;50 of which have not previously been reported in similar studies of European/US populations (e.g. at ROCK2, ARHGEF28, DHODH, ALDH1A2). We observe correlations between subsistence and lipid profiles but show that genetic ancestry also plays an important role in variation within and between populations. For example, Eastern African pastoralists with a diet rich in milk and blood have relatively high levels of di-and tri-glycerides, but within each lipid class, levels are influenced by genotype. The Fulani pastoralists from Cameroon, with a high incidence of hypertension and diabetes but low BMI, also have relatively high levels of triglycerides, suggesting diet is predominantly influencing lipid levels and that genetic factors unrelated to lipid metabolism are influencing risk for disease in that population. Disclosure R. Ma: None. H. Li: Consultant; Self; Eli Lilly and Company. C. Burant: None. S. A. Tishkoff: None. M. Hansen: None. A. Ranciaro: None. S. R. Thompson: None. W. Beggs: None. S. W. Mpoloka: None. G. G. Mokone: None. T. B. Nyambo: None. G. Michailidis: None. Funding American Diabetes Association (1-19-VSN-02 to S.A.T.); National Institutes of Health (GM134957-01) </jats:sec

Effects of Natural Selection and Gene Conversion on the Evolution of Human Glycophorins Coding for MNS Blood Polymorphisms in Malaria-Endemic African Populations

Malaria has been a very strong selection pressure in recent human evolution, particularly in Africa. Of the one million deaths per year due to malaria, more than 90% are in sub-Saharan Africa, a region with high levels of genetic variation and population substructure. However, there have been few studies of nucleotide variation at genetic loci that are relevant to malaria susceptibility across geographically and genetically diverse ethnic groups in Africa. Invasion of erythrocytes by Plasmodium falciparum parasites is central to the pathology of malaria. Glycophorin A (GYPA) and B (GYPB), which determine MN and Ss blood types, are two major receptors that are expressed on erythrocyte surfaces and interact with parasite ligands. We analyzed nucleotide diversity of the glycophorin gene family in 15 African populations with different levels of malaria exposure. High levels of nucleotide diversity and gene conversion were found at these genes. We observed divergent patterns of genetic variation between these duplicated genes and between different extracellular domains of GYPA. Specifically, we identified fixed adaptive changes at exons 3-4 of GYPA. By contrast, we observed an allele frequency spectrum skewed toward a significant excess of intermediate-frequency alleles at GYPA exon 2 in many populations; the degree of spectrum distortion is correlated with malaria exposure, possibly because of the joint effects of gene conversion and balancing selection. We also identified a haplotype causing three amino acid changes in the extracellular domain of glycophorin B. This haplotype might have evolved adaptively in five populations with high exposure to malaria

Effects of Natural Selection and Gene Conversion on the Evolution of Human Glycophorins Coding for MNS Blood Polymorphisms in Malaria-Endemic African Populations

Malaria has been a very strong selection pressure in recent human evolution, particularly in Africa. Of the one million deaths per year due to malaria, more than 90% are in sub-Saharan Africa, a region with high levels of genetic variation and population substructure. However, there have been few studies of nucleotide variation at genetic loci that are relevant to malaria susceptibility across geographically and genetically diverse ethnic groups in Africa. Invasion of erythrocytes by Plasmodium falciparum parasites is central to the pathology of malaria. Glycophorin A (GYPA) and B (GYPB), which determine MN and Ss blood types, are two major receptors that are expressed on erythrocyte surfaces and interact with parasite ligands. We analyzed nucleotide diversity of the glycophorin gene family in 15 African populations with different levels of malaria exposure. High levels of nucleotide diversity and gene conversion were found at these genes. We observed divergent patterns of genetic variation between these duplicated genes and between different extracellular domains of GYPA. Specifically, we identified fixed adaptive changes at exons 3–4 of GYPA. By contrast, we observed an allele frequency spectrum skewed toward a significant excess of intermediate-frequency alleles at GYPA exon 2 in many populations; the degree of spectrum distortion is correlated with malaria exposure, possibly because of the joint effects of gene conversion and balancing selection. We also identified a haplotype causing three amino acid changes in the extracellular domain of glycophorin B. This haplotype might have evolved adaptively in five populations with high exposure to malaria