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The study of recent natural selection in human populations has important applications to human history and medicine. Positive natural selection drives the increase in beneficial alleles and plays a role in explaining diversity across human populations. By discovering traits subject to positive selection, we can better understand the population level response to environmental pressures including infectious disease. Our study examines unusual population differentiation between three large data sets to detect natural selection. The populations examined, African Americans, Nigerians, and Gambians, are genetically close to one another (F(ST) < 0.01 for all pairs), allowing us to detect selection even with moderate changes in allele frequency. We also develop a tree-based method to pinpoint the population in which selection occurred, incorporating information across populations. Our genome-wide significant results corroborate loci previously reported to be under selection in Africans including HBB and CD36. At the HLA locus on chromosome 6, results suggest the existence of multiple, independent targets of population-specific selective pressure. In addition, we report a genome-wide significant (p = 1.36 × 10(-11)) signal of selection in the prostate stem cell antigen (PSCA) gene. The most significantly differentiated marker in our analysis, rs2920283, is highly differentiated in both Africa and East Asia and has prior genome-wide significant associations to bladder and gastric cancers., (Copyright © 2011 The American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)

Genome-wide association (GWA) studies have identified common variants that are associated with a variety of traits and diseases, but most studies have been performed in European-derived populations. Here, we describe the first genome-wide analyses of imputed genotype and copy number variants (CNVs) for anthropometric measures in African-derived populations: 1188 Nigerians from Igbo-Ora and Ibadan, Nigeria, and 743 African-Americans from Maywood, IL. To improve the reach of our study, we used imputation to estimate genotypes at approximately 2.1 million single-nucleotide polymorphisms (SNPs) and also tested CNVs for association. No SNPs or common CNVs reached a genome-wide significance level for association with height or body mass index (BMI), and the best signals from a meta-analysis of the two cohorts did not replicate in approximately 3700 African-Americans and Jamaicans. However, several loci previously confirmed in European populations showed evidence of replication in our GWA panel of African-derived populations, including variants near IHH and DLEU7 for height and MC4R for BMI. Analysis of global burden of rare CNVs suggested that lean individuals possess greater total burden of CNVs, but this finding was not supported in an independent European population. Our results suggest that there are not multiple loci with strong effects on anthropometric traits in African-derived populations and that sample sizes comparable to those needed in European GWA studies will be required to identify replicable associations. Meta-analysis of this data set with additional studies in African-ancestry populations will be helpful to improve power to detect novel associations.

Objective: The objectives were to identify quantitative trait loci linked to serum adiponectin concentration and to estimate heritability in two populations of African descent., Research Methods and Procedures: We conducted a genome scan for serum adiponectin concentration in two populations of African descent. Genome-wide microsatelitte markers were typed in an African-American population consisting of 203 families from the Chicago area and in a Nigerian Yoruba population consisting of 146 families. Linkage analysis was performed to identify loci. Variance component model was used to estimate heritability., Results: Estimates of heritability adjusted for age, gender, and BMI were 0.45 and 0.70 for the African-American and Nigerian families, respectively. In both populations, adiponectin was significantly negatively correlated with BMI, height, and weight. After adjusting for age, gender, and BMI, we found evidence of genetic linkage to adiponectin on chromosomes 11 [limit of detection (LOD) score = 2.89] and 17 (LOD score = 1.35) in the Nigerian sample. Among the African-Americans, we found genetic linkage on chromosomes 2 (LOD score = 1.82), 4 (LOD score = 2.12), and 11 (LOD score = 2.33). Analysis based on combined data yielded a maximum LOD score of 3.21 on chromosome 11., Discussion: Consistency of the finding on chromosome 11 suggests that this region is likely to be involved in regulation of adiponectin, either through a primary influence on hormone levels or through pathways influencing body composition. These results suggest that adiponectin could be a potential therapeutic target for obesity.

Objective: To identify quantitative trait loci (QTL) contributing to the variation in blood pressure in a west African population., Methods: We conducted a multi-stage genome scan in a population sample from rural Nigeria. A 10 centimorgan genome-wide screen for log-transformed systolic blood pressure (SBP) and diastolic blood pressure (DBP) was first performed based on 1054 individuals from 188 families. In the second phase we performed a similar analysis in an independent sample of 621 individuals from 101 families. In a third follow-up fine mapping phase we genotyped 25 additional markers in the three regions identified in the first two phases., Results: Genome-wide significant linkage evidence was found for SBP on chromosome 7p (lod = 4.73, genome wide P < or = 0.01, point-wise P = 1.53 x 10) in the combined sample. Suggestive linkage evidence was also detected on 6q (lod = 2.9, point-wise P = 0.00013) and 7q (lod = 2.6, point-wise P = 0.00027) for SBP, and 7q (lod = 1.6, point-wise P = 0.003) for DBP., Conclusions: This study has identified several regions that may harbor genetic variants affecting the variation in blood pressure. Further association mapping under the linkage peaks will be required to refine the linkage evidence that has emerged from our analysis.

We examined the association between obesity and 13 angiotensin-converting enzyme (ACE) gene polymorphisms, including the presence (I) or absence (D) of an Alu element in intron 16 (I/D polymorphism), and performed haplotype analysis using data collected from participants of a community survey of hypertension among blacks living in Ibadan, Nigeria; Spanish Town, Jamaica; and Chicago, IL. Transmission distortion of ACE gene polymorphisms and haplotypes from heterozygous parents to affected offspring was examined in each study population. To estimate haplotypes, polymorphisms were divided into three groups based on their position on the ACE gene. No ACE gene polymorphism was consistently overtransmitted from parents to obese offspring among the three populations. However, the haplotype ACE1-ACE5 TACAT, located in the promoter region, was significantly overtransmitted from parents to obese offspring in both the U.S. and Nigerian populations. No haplotype was significantly overtransmitted from parents to obese offspring among the Jamaicans. In conclusion, we noted the overtransmission of a particular ACE gene promoter region haplotype from parents to obese offspring in two separate black populations. These data suggest that ACE gene polymorphisms may influence the development of weight gain.

Identification of genetic variants that contribute to risk of hypertension is challenging. As a complement to linkage and candidate gene association studies, we carried out admixture mapping using genome-scan microsatellite markers among the African American participants in the US National Heart, Lung, and Blood Institute's Family Blood Pressure Program. This population was assumed to have experienced recent admixture from ancestral groups originating in Africa and Europe. We used a set of unrelated individuals from Nigeria to represent the African ancestral population and used the European Americans in the Family Blood Pressure Program to provide estimates of allele frequencies for the European ancestors. We genotyped a common set of 269 microsatellite markers in the three groups at the same laboratory. The distribution of marker location-specific African ancestry, based on multipoint analysis, was shifted upward in hypertensive cases versus normotensive controls, consistent with linkage to genes conferring susceptibility. This shift was largely due to a small number of loci, including five adjacent markers on chromosome 6q and two on chromosome 21q. These results suggest that chromosome 6q24 and 21q21 may contain genes influencing risk of hypertension in African Americans.

Over the last decade, considerable effort has been invested in studying the associations between angiotensinogen (AGT) variants, AGT plasma levels and high blood pressure. Evidence accumulated to date consistently supports the relationship between the AGT locus and the protein level, while an influence on blood pressure has been difficult to establish; in both instances the predisposing molecular variants are not fully defined. An evolutionary approach, taking into account the phylogenetic relationship between all the polymorphisms at this locus, may improve our understanding of the genetic nature of these quantitative phenotypes. Accordingly we sequenced a 6.8 kb region of the AGT gene in 57 Nigerian individuals (29 with high AGT plasma levels and 28 with low AGT plasma levels). Haplotypes were grouped into seven major haplogroups and their phylogenetic relationship was established. The association between haplogroups and AGT plasma levels was investigated. A significant linear correlation was detected between haplogroup genetic distance and AGT levels, suggesting a nonrandom accumulation of risk-associated mutations during the evolutionary history of the AGT gene.

The genes in the renin-angiotensin system are important physiologic candidates in studies of the genetic susceptibility to hypertension. Limited information has been available in most studies on the extent of variation in the candidate loci or the modifying effects of different environmental settings. We consequently genotyped 13 polymorphisms at the angiotensin I-converting enzyme (ACE) locus at an average distance of 2 kb in 2776 family members from Nigeria, Jamaica and an African-American community in the US. Allele and haplotype frequencies were similar in the three populations, with modest evidence of European admixture in the US. Two markers were consistently associated with ACE level in the three samples and the proportion of variance accounted for by ACE8 was similar in the three groups. No evidence of consistent association of single markers was noted with blood pressure across the three population samples, however. Likewise, in a haplotype-based analysis, despite significant associations within each population, the findings were not replicated consistently across all three samples. We did observe, however, that the overtransmitted haplotypes among hypertensives were drawn from a single clade, suggesting that susceptibility may cluster in patterns not captured directly by our markers.

Energy requirements at rest account for 50% to 75% of total energy expenditure. Interindividual variation in resting energy expenditure (REE) has been studied for potential links to obesity and hypertension. REE is a modestly heritable trait, and yet virtually nothing is known about the genetic factors that might influence the familial patterns. The objectives of this study were to identify the genomic regions showing genetic linkage to REE variation in a Nigerian population. For linkage analysis across the genome, three hundred seventy-seven microsatellite markers were typed on DNA from 995 individuals in 153 families. A genome scan was performed using a multipoint variance component method. Heritability of REE was 0.30 after adjustment for body size. The strongest linkage signal was detected on chromosome 16 (16q22.3) with a likelihood of odds of 2.96 (p = 0.08). Linkage evidence (likelihood of odds > 1) was detected on another three chromosomal regions, namely 2q12.1, 8q21.2, and 15p11.2.

Objective: Interest in mapping genetic variants that are associated with obesity remains high because of the increasing prevalence of obesity and its complications worldwide. Data on genetic determinants of obesity in African populations are rare., Research Methods and Procedures: We have undertaken a genome-wide scan for body mass index (BMI) in 182 Nigerian families that included 769 individuals., Results: The prevalence of obesity was only 5%, yet polygenic heritability for BMI was in the expected range (0.46 +/- 0.07). Tandem repeat markers (402) were typed across the genome with an average map density of 9 cM. Pedigree-based analysis using a variance components linkage model demonstrated evidence for linkage on chromosome 7 (near marker D7S817 at 7p14) with a logarithm of odds (LOD) score of 3.8 and on chromosome 11 (marker D11S2000 at 11q22) with an LOD score of 3.3. Weaker evidence for linkage was found on chromosomes 1 (1q21, LOD = 2.2) and 8 (8p22, LOD = 2.3). Several candidate genes, including neuropeptide Y, DRD2, APOA4, lamin A/C, and lipoprotein lipase, lie in or close to the chromosomal regions where strong linkage signals were found., Discussion: The findings of this study suggest that, as in other populations with higher prevalences of obesity, positive linkage signals can be found on genome scans for obesity-related traits. Follow-up studies may be warranted to investigate these linkages, especially the one on chromosome 11, which has been reported in a population at the opposite end of the BMI distribution.

An understanding of the genetic influences on hypertension would help unravel the pathophysiology of this complex disorder and improve our understanding of causal mechanisms. Contemporary technology makes it possible to examine enough genetic markers to support a generalized search across the entire genome for candidate regions. In the present study, a family set was recruited from southwest Nigeria, and 378 microsatellite markers were typed on 792 individuals in 196 families. Multipoint variance component analysis identified linkage signals (logarithm of the odds [LOD] 1.74, P<0.0023) for systolic blood pressure on 19p (D19S714) and 19q (D19S246), whereas for diastolic blood pressure, linkage was observed on 2p (D2S1790), 3p (D3S1304), 5q (D5S1462), 7p (D7S3046), 7q (D7S821), and 10q (D10S1221). Other regions of interest (1.18