Polymorphic Alu insertions in six Brazilian African-derived populations

A review of ancestrality and admixture in Latin America and the caribbean focusing on native American and African descendant populations

Genomics can reveal essential features about the demographic evolution of a population that may not be apparent from historical elements. In recent years, there has been a significant increase in the number of studies applying genomic epidemiological approaches to understand the genetic structure and diversity of human populations in the context of demographic history and for implementing precision medicine. These efforts have traditionally been applied predominantly to populations of European origin. More recently, initiatives in the United States and Africa are including more diverse populations, establishing new horizons for research in human populations with African and/or Native ancestries. Still, even in the most recent projects, the under-representation of genomic data from Latin America and the Caribbean (LAC) is remarkable. In addition, because the region presents the most recent global miscegenation, genomics data from LAC may add relevant information to understand population admixture better. Admixture in LAC started during the colonial period, in the 15th century, with intense miscegenation between European settlers, mainly from Portugal and Spain, with local indigenous and sub-Saharan Africans brought through the slave trade. Since, there are descendants of formerly enslaved and Native American populations in the LAC territory; they are considered vulnerable populations because of their history and current living conditions. In this context, studying LAC Native American and African descendant populations is important for several reasons. First, studying human populations from different origins makes it possible to understand the diversity of the human genome better. Second, it also has an immediate application to these populations, such as empowering communities with the knowledge of their ancestral origins. Furthermore, because knowledge of the population genomic structure is an essential requirement for implementing genomic medicine and precision health practices, population genomics studies may ensure that these communities have access to genomic information for risk assessment, prevention, and the delivery of optimized treatment; thus, helping to reduce inequalities in the Western Hemisphere. Hoping to set the stage for future studies, we review different aspects related to genetic and genomic research in vulnerable populations from LAC countries.

Inferring paternal history of rural African-derived Brazilian populations from Y chromosomes

OBJECTIVES

Quilombo remnants are relics of communities founded by runaway or abandoned African slaves, but often with subsequent extensive and complex admixture patterns with European and Native Americans. We combine a genetic study of Y-chromosome markers with anthropological surveys in order to obtain a portrait of quilombo structure and history in the region that has the largest number of quilombo remnants in the state of São Paulo.

METHODS

Samples from 289 individuals from quilombo remnants were genotyped using a set of 17 microsatellites on the Y chromosome (AmpFlSTR-Yfiler). A subset of 82 samples was also genotyped using SNPs array (Axiom Human Origins-Affymetrix). We estimated haplotype and haplogroup frequencies, haplotype diversity and sharing, and pairwise genetic distances through F_ST and R_ST indexes.

RESULTS

We identified 95 Y chromosome haplotypes, classified into 15 haplogroups. About 63% are European, 32% are African, and 6% Native American. The most common were: R1b (European, 34.2%), E1b1a (African, 32.3%), J1 (European, 6.9%), and Q (Native American, 6.2%). Genetic differentiation among communities was low (F_ST  = 0.0171; R_ST  = 0.0161), and haplotype sharing was extensive. Genetic, genealogical and oral surveys allowed us to detect five main founder haplotypes, which explained a total of 27.7% of the Y chromosome lineages.

CONCLUSIONS

Our results showed a high European patrilineal genetic contribution among the founders of quilombos, high amounts of gene flow, and a recent common origin of these populations. Common haplotypes and genealogical data indicate the origin of quilombos from a few male individuals. Our study reinforces the importance of a dual approach, involving the analysis of both anthropological and genetic data.

Estimation of inbreeding and substructure levels in African-derived Brazilian quilombo populations

This article deals with the estimation of inbreeding and substructure levels in a set of 10 (later regrouped as eight) African-derived quilombo communities from the Ribeira River Valley in the southern portion of the state of São Paulo, Brazil. Inbreeding levels were assessed through F-values estimated from the direct analysis of genealogical data and from the statistical analysis of a large set of 30 molecular markers. The levels of population substructure found were modest, as was the degree of inbreeding: in the set of all communities considered together, F-values were 0.00136 and 0.00248 when using raw and corrected data from their complete genealogical structures, respectively, and 0.022 and 0.036 when using the information taken from the statistical analysis of all 30 loci and of 14 single-nucleotide polymorphic loci, respectively. The overall frequency of consanguineous marriages in the set of all communities considered together was ∼ 2%. Although modest, the values of the estimated parameters are much larger than those obtained for the overall Brazilian population and in general much smaller than the ones recorded for other Brazilian isolates. To circumvent problems related to heterogeneous sampling and virtual absence of reliable records of biological relationships, we had to develop or adapt several methods for making valid estimates of the prescribed parameters.

Interethnic admixture and the evolution of Latin American populations

A general introduction to the origins and history of Latin American populations is followed by a systematic review of the data from molecular autosomal assessments of the ethnic/continental (European, African, Amerindian) ancestries for 24 Latin American countries or territories. The data surveyed are of varying quality but provide a general picture of the present constitution of these populations. A brief discussion about the applications of these results (admixture mapping) is also provided. Latin American populations can be viewed as natural experiments for the investigation of unique anthropological and epidemiological issues.

Genomic ancestry of rural African-derived populations from Southeastern Brazil

OBJECTIVES

xMany Africans were brought to Brazil as slaves. The runaway or abandoned slaves founded isolated communities named quilombos. There are many quilombo remnants in Vale do Ribeira region in the southern part of São Paulo State. The aim of our study was to contribute to understanding the origins of these populations, through admixture studies.

METHODS

We genotyped 307 unrelated DNA samples obtained from ten quilombo populations from Vale do Ribeira region, using a panel of 48 INDEL polymorphisms. We estimated genetic differentiation between populations (F(ST) ) and genomic ancestry from these populations. Our data were compared to a similar study performed in quilombo remnants from the Brazilian Amazon region.

RESULTS

Population admixture estimates showed high degree of miscegenation in the quilombo remnants from Vale do Ribeira (average admixture estimates at 39.7% of African, 39.0% of European and 21.3% of Amerindian contribution). The proportions of ancestral genes varied greatly among individuals, ranging from 7.3 to 69.5%, 12.9 to 68.3%, and 7.3 to 58.5% (African, European, and Amerindian, respectively). Genetic differentiation between these populations was low (all F(ST) values <5%), indicating gene flow between them. Both groups of quilombos, from Vale do Ribeira and Amazon, presented similar patterns of admixture.

CONCLUSIONS

INDEL markers were useful to evidence the triple interbreeding among African, European, and Amerindian in the formation of quilombo populations. The low F(ST) values suggested gene flow among quilombos from Vale do Ribeira. Our data highlight the important role of Amerindians in the formation of quilombo populations.

Multilocus family-based association analysis of seven candidate polymorphisms with essential hypertension in an african-derived semi-isolated brazilian population

Background. It has been widely suggested that analyses considering multilocus effects would be crucial to characterize the relationship between gene variability and essential hypertension (EH). Objective. To test for the presence of multilocus effects between/among seven polymorphisms (six genes) on blood pressure-related traits in African-derived semi-isolated Brazilian populations (quilombos). Methods. Analyses were carried out using a family-based design in a sample of 652 participants (97 families). Seven variants were investigated: ACE (rs1799752), AGT (rs669), ADD2 (rs3755351), NOS3 (rs1799983), GNB3 (rs5441 and rs5443), and GRK4 (rs1801058). Sensitivity analyses were further performed under a case-control design with unrelated participants only. Results. None of the investigated variants were associated individually with both systolic and diastolic BP levels (SBP and DBP, respectively) or EH (as a binary outcome). Multifactor dimensionality reduction-based techniques revealed a marginal association of the combined effect of both GNB3 variants on DBP levels in a family-based design (P = 0.040), whereas a putative NOS3-GRK4 interaction also in relation to DBP levels was observed in the case-control design only (P = 0.004). Conclusion. Our results provide limited support for the hypothesis of multilocus effects between/among the studied variants on blood pressure in quilombos. Further larger studies are needed to validate our findings.

Multilocus analyses of seven candidate genes suggest interacting pathways for obesity-related traits in Brazilian populations

We investigated whether variants in major candidate genes for food intake and body weight regulation contribute to obesity-related traits under a multilocus perspective. We studied 375 Brazilian subjects from partially isolated African-derived populations (quilombos). Seven variants displaying conflicting results in previous reports and supposedly implicated in the susceptibility of obesity-related phenotypes were investigated: β2-adrenergic receptor (ADRB2) (Arg16Gly), insulin induced gene 2 (INSIG2) (rs7566605), leptin (LEP) (A19G), LEP receptor (LEPR) (Gln223Arg), perilipin (PLIN) (6209T > C), peroxisome proliferator-activated receptor-γ (PPARG) (Pro12Ala), and resistin (RETN) (-420 C > G). Regression models as well as generalized multifactor dimensionality reduction (GMDR) were employed to test the contribution of individual effects and higher-order interactions to BMI and waist-hip ratio (WHR) variation and risk of overweight/obesity. The best multilocus association signal identified in the quilombos was further examined in an independent sample of 334 Brazilian subjects of European ancestry. In quilombos, only the PPARG polymorphism displayed significant individual effects (WHR variation, P = 0.028). No association was observed either with the risk of overweight/obesity (BMI ≥ 25 kg/m2), risk of obesity alone (BMI ≥ 30 kg/m2) or BMI variation. However, GMDR analyses revealed an interaction between the LEPR and ADRB2 polymorphisms (P = 0.009) as well as a third-order effect involving the latter two variants plus INSIG2 (P = 0.034) with overweight/obesity. Assessment of the LEPR-ADRB2 interaction in the second sample indicated a marginally significant association (P = 0.0724), which was further verified to be limited to men (P = 0.0118). Together, our findings suggest evidence for a two-locus interaction between the LEPR Gln223Arg and ADRB2 Arg16Gly variants in the risk of overweight/obesity, and highlight further the importance of multilocus effects in the genetic component of obesity.

Association of polymorphisms at the ADIPOR1 regulatory region with type 2 diabetes and body mass index in a Brazilian population with European or African ancestry

Association studies between ADIPOR1 genetic variants and predisposition to type 2 diabetes (DM2) have provided contradictory results. We determined if two single nucleotide polymorphisms (SNP c.-8503G>A and SNP c.10225C>G) in regulatory regions of ADIPOR1 in 567 Brazilian individuals of European (EA; N = 443) or African (AfA; N = 124) ancestry from rural (quilombo remnants; N = 439) and urban (N = 567) areas. We detected a significant effect of ethnicity on the distribution of the allelic frequencies of both SNPs in these populations (EA: -8503A = 0.27; AfA: -8503A = 0.16; P = 0.001 and EA: 10225G = 0.35; AfA: 10225G = 0.51; P < 0.001). Neither of the polymorphisms were associated with DM2 in the case-control study in EA (SNP c.-8503G>A: DM2 group -8503A = 0.26; control group -8503A = 0.30; P = 0.14/SNP 10225C>G: DM2 group 10225G = 0.37; control group 10225G = 0.32; P = 0.40) and AfA populations (SNP c.-8503G>A: DM2 group -8503A = 0.16; control group -8503A = 0.15; P = 0.34/SNP 10225C>G: DM2 group 10225G = 0.51; control group 10225G = 0.52; P = 0.50). Similarly, none of the polymorphisms were associated with metabolic/anthropometric risk factors for DM2 in any of the three populations, except for HDL cholesterol, which was significantly higher in AfA heterozygotes (GC = 53.75 +/- 17.26 mg/dL) than in homozygotes. We conclude that ADIPOR1 polymorphisms are unlikely to be major risk factors for DM2 or for metabolic/anthropometric measurements that represent risk factors for DM2 in populations of European and African ancestries.

Mobile DNA elements in primate and human evolution

Roughly 50% of the primate genome consists of mobile, repetitive DNA sequences such as Alu and LINE1 elements. The causes and evolutionary consequences of mobile element insertion, which have received considerable attention during the past decade, are reviewed in this article. Because of their unique mutational mechanisms, these elements are highly useful for answering phylogenetic questions. We demonstrate how they have been used to help resolve a number of questions in primate phylogeny, including the human-chimpanzee-gorilla trichotomy and New World primate phylogeny. Alu and LINE1 element insertion polymorphisms have also been analyzed in human populations to test hypotheses about human evolution and population affinities and to address forensic issues. Finally, these elements have had impacts on the genome itself. We review how they have influenced fundamental ongoing processes like nonhomologous recombination, genomic deletion, and X chromosome inactivation.

Tracking Alu evolution in New World primates

Background

Alu elements are Short INterspersed Elements (SINEs) in primate genomes that have proven useful as markers for studying genome evolution, population biology and phylogenetics. Most of these applications, however, have been limited to humans and their nearest relatives, chimpanzees. In an effort to expand our understanding of Alu sequence evolution and to increase the applicability of these markers to non-human primate biology, we have analyzed available Alu sequences for loci specific to platyrrhine (New World) primates.

Results

Branching patterns along an Alu sequence phylogeny indicate three major classes of platyrrhine-specific Alu sequences. Sequence comparisons further reveal at least three New World monkey-specific subfamilies; AluTa7, AluTa10, and AluTa15. Two of these subfamilies appear to be derived from a gene conversion event that has produced a recently active fusion of AluSc- and AluSp-type elements. This is a novel mode of origin for new Alu subfamilies.

Conclusion

The use of Alu elements as genetic markers in studies of genome evolution, phylogenetics, and population biology has been very productive when applied to humans. The characterization of these three new Alu subfamilies not only increases our understanding of Alu sequence evolution in primates, but also opens the door to the application of these genetic markers outside the hominid lineage.