Brazilian Admixed Population Research Articles

Challenges in selecting admixture models and marker sets to infer genetic ancestry in a Brazilian admixed population

The inference of genetic ancestry plays an increasingly prominent role in clinical, population, and forensic genetics studies. Several genotyping strategies and analytical methodologies have been developed over the last few decades to assign individuals to specific biogeographic regions. However, despite these efforts, ancestry inference in populations with a recent history of admixture, such as those in Brazil, remains a challenge. In admixed populations, proportion and components of genetic ancestry vary on different levels: (i) between populations; (ii) between individuals of the same population, and (iii) throughout the individual's genome. The present study evaluated 1171 admixed Brazilian samples to compare the genetic ancestry inferred by tri-/tetra-hybrid admixture models and evaluated different marker sets from those with small numbers of ancestry informative markers panels (AIMs), to high-density SNPs (HDSNP) and whole-genome-sequence (WGS) data. Analyses revealed greater variation in the correlation coefficient of ancestry components within and between admixed populations, especially for minority ancestral components. We also observed positive correlation between the number of markers in the AIMs panel and HDSNP/WGS. Furthermore, the greater the number of markers, the more accurate the tri-/tetra-hybrid admixture models.

Prediction of eye and hair pigmentation phenotypes using the HIrisPlex system in a Brazilian admixed population sample.

Human pigmentation is a complex trait, probably involving more than 100 genes. Predicting phenotypes using SNPs present in those genes is important for forensic purpose. For this, the HIrisPlex tool was developed for eye and hair color prediction, with both models achieving high accuracy among Europeans. Its evaluation in admixed populations is important, since they present a higher frequency of intermediate phenotypes, and HIrisPlex has demonstrated limitations in such predictions; therefore, the performance of this tool may be impaired in such populations. Here, we evaluate the set of 24 markers from the HIrisPlex system in 328 individuals from Ribeirão Preto (SP) region, predicting eye and hair color and comparing the predictions with their real phenotypes. We used the HaloPlex Target Enrichment System and MiSeq Personal Sequencer platform for massively parallel sequencing. The prediction of eye and hair color was accomplished by the HIrisPlex online tool, using the default prediction settings. Ancestry was estimated using the SNPforID 34-plex to observe if and how an individual's ancestry background would affect predictions in this admixed sample. Our sample presented major European ancestry (70.5%), followed by African (21.1%) and Native American/East Asian (8.4%). HIrisPlex presented an overall sensitivity of 0.691 for hair color prediction, with sensitivities ranging from 0.547 to 0.782. The lowest sensitivity was observed for individuals with black hair, who present a reduced European contribution (48.4%). For eye color prediction, the overall sensitivity was 0.741, with sensitivities higher than 0.85 for blue and brown eyes, although it failed in predicting intermediate eye color. Such struggle in predicting this phenotype category is in accordance with what has been seen in previous studies involving HIrisPlex. Individuals with brown eye color are more admixed, with European ancestry decreasing to 62.6%; notwithstanding that, sensitivity for brown eyes was almost 100%. Overall sensitivity increases to 0.791 when a 0.7 threshold is set, though 12.5% of the individuals become undefined. When combining eye and hair prediction, hit rates between 51.3 and 68.9% were achieved. Despite the difficulties with intermediate phenotypes, we have shown that HIrisPlex results can be very helpful when interpreted with caution.

Impact of sickle cell disease on presentation and progression of paediatric HIV: a retrospective cohort study.

HIV and sickle cell disease (SCD) are significant causes of morbidity and mortality in sub-Saharan Africa. Given their separate roles in immune dysregulation, our objective was to characterise the impact that SCD has on the presentation and progression of paediatric HIV. The study was a retrospective cohort study (study period 2004-2018). Cases of HIV+and SCD-afflicted patients (HIV+/SCD+) were obtained via electronic chart review from a paediatric HIV clinic in Kampala, Uganda and matched 1:3 with HIV+controls without SCD (HIV+/SCD-). Thirty-five HIV+/SCD+subjects and 95 HIV+/SCD- controls were analysed (39% female (51/130), age 3.6years (SD3.9)). At baseline, WHO clinical stage (64% total cohort Stage III/IV) and nutritional status (9.4% severe acute malnutrition) were similar for both groups, whereas HIV+/SCD+had higher though non-significant baseline CD4 count (1036 (SD713) vs 849 (SD638) cells/microlitre, P=0.20, two-tailed t-test). There were 19 deaths, 6 (17%) HIV+/SCD+and 13 (14%) HIV+/SCD-, with unadjusted/adjusted models showing no significant difference. Nutritional progression and clinical stage progression showed no significant differences between groups. Kaplan-Meier analysis showed a slower rate of treatment failures in the HIV+/SCD+cohort (P=0.11, log-rank survival test). Trajectory analysis showed that in the time period analysed, the HIV+/SCD+cohort showed a more rapid rise and higher total CD4 count (P=0.012, regression analysis). The study suggests that SCD does not adversely affect the progression of HIV in patients on ART. Further, HIV+/SCD+achieved higher CD4 counts and fewer HIV treatment failures, suggesting physiological effects due to SCD might mitigate HIV progression.

Genetic characterization and ancestry of the admixed population of Marajó Island, northern of Brazil, with autosomal and lineage markers

To investigate the genetic background of the Marajó population, samples from unrelated individuals were selected, with matrilineal or patrilineal local ancestry for at least three generations. A total of 72 male samples were genotyped for 27 Y-STRs, 65 for 46 AIMs and 55 were sequenced for the mtDNA control region. Low haplotype diversities were obtained for Y-STRs and mtDNA, when compared to other Brazilian admixed populations, most probably due to the small size of the population and the geographic isolation of the island. Based on HVI, significant genetic distances were found between Marajó and Brazilian populations from the North, Northeast, South and Southeast regions. For mtDNA, Native American haplogroups were the most prevalent, followed by the African and European haplogroups. For the autosomal markers, a 40.7% European ancestry was found, followed by 33.2% of Native American and 26.1% of African contributions.

Full mtDNA genome sequencing of Brazilian admixed populations: A forensic-focused evaluation of a MPS application as an alternative to Sanger sequencing methods

The use of Massive Parallel Sequencing (MPS) techniques have been proposed by the forensic community as an alternative to Sanger sequencing methods in routine forensic casework analysis regarding mitochondrial DNA (mtDNA). Interesting features of MPS include high throughput, ability to simultaneously genotype a significant number of samples by barcoding techniques, processing automation, reduced time and costs, among others. Advantages include the capability of generating full mtDNA genome sequences versus usual techniques, usually limited to hypervariable or control regions exclusively. In this work, 96 reference single-source samples from three different Brazilian cities were subjected to full mtDNA genome sequencing by MPS techniques using an early-access version of Precision ID mtDNA Whole Genome Panel on an Ion Torrent PGM platform (Thermo Fisher Scientific, Waltham, MA, USA). Complete, high-quality sequences were obtained and sequencing performance was evaluated via four different metrics. As a subset of evaluated samples have been previously submitted for Sanger sequencing of the control region, a comparative analysis of both methods’ results was conducted in order to compare technique adequacy within a forensic context. Even though this study is one of the first to report full mtDNA genome sequences for Brazilian admixed populations, the observed haplotypes exhibit a predominance of Native American and African maternal lineages in the studied sample set, reproducing results described in the literature for control regions only. Interpopulation analysis among Brazilian and 26 worldwide populations was also carried out. The results indicate that MPS-generated full mtDNA genome sequences may have great utility in forensic real casework applications, with a pronounced gain of genetic information and discrimination power provided by coding region evaluation and the enhanced capacity of heteroplasmies determination. Database construction and other relevant factors concerning implementation of such techniques in Brazilian forensic laboratories are also discussed.

Origin and age of the causative mutations in KLC2, IMPA1, MED25 and WNT7A unravelled through Brazilian admixed populations

The mutation age and local ancestry of chromosomal segments harbouring mutations associated with autosomal recessive (AR) disorders in Brazilian admixed populations remain unknown; additionally, inbreeding levels for these affected individuals continue to be estimated based on genealogical information. Here, we calculated inbreeding levels using a runs of homozygosity approach, mutation age and local ancestry to infer the origin of each chromosomal segments containing disorder-causing mutations in KLC2, IMPA1, MED25 and WNT7A. Genotyped data were generated from 18 patients affected by AR diseases and combined to the 1000 genome project (1KGP) and Simons genome diversity project (SGDP) databases to infer local ancestry. We found a major European contribution for mutated haplotypes with recent mutation age and inbreeding values found only in Native American and Middle East individuals. These results contribute to identifying the origin of and to understanding how these diseases are maintained and spread in Brazilian and world populations.

Extended HLA-G genetic diversity and ancestry composition in a Brazilian admixed population sample: Implications for HLA-G transcriptional control and for case-control association studies

Human leukocyte antigen-G (HLA-G) is a nonclassical Major Histocompatibility Complex (MHC) molecule with immunomodulatory function and restricted tissue expression. The genetic diversity of HLA-G has been extensively studied in several populations, however, the segment located upstream −1406 has not yet been evaluated. We characterized the nucleotide variation and haplotype structure of an extended distal region (−2635), all exons and the 3′UTR segment of HLA-G by next-generation sequencing (NGS) in a sample of 335 Brazilian individuals. We detected 29 variants at the HLA-G distal promoter region, arranged into 19 haplotypes, among which we identified sites that may influence transcription factor targeting. Although the variation pattern in the distal region resembled the one observed in the conventional promoter segment, molecular signature for balancing selection was observed in the promoter segment from −1406 to −1 (Tajima’s D = 2.315, P = 0.017), but not in this distal segment (D = 1.049, P = 0.118). Furthermore, the ancestry composition of this Brazilian population sample was determined by the analysis of SNPforID 34-plex ancestry informative marker (AIM) SNP panel. The distribution of HLA-G haplotypes was ancestry-dependent, corroborating previous findings and emphasizing the importance of considering the ancestry information in association studies.

Correction: Genomic ancestry and education level independently influence abdominal fat distributions in a Brazilian admixed population.

[This corrects the article DOI: 10.1371/journal.pone.0179085.].

Genomic ancestry and education level independently influence abdominal fat distributions in a Brazilian admixed population.

We aimed to identify the independent associations of genomic ancestry and education level with abdominal fat distributions in the 1982 Pelotas birth cohort study, Brazil. In 2,890 participants (1,409 men and 1,481 women), genomic ancestry was assessed using genotype data on 370,539 genome-wide variants to quantify ancestral proportions in each individual. Years of completed education was used to indicate socio-economic position. Visceral fat depth and subcutaneous abdominal fat thickness were measured by ultrasound at age 29–31y; these measures were adjusted for BMI to indicate abdominal fat distributions. Linear regression models were performed, separately by sex. Admixture was observed between European (median proportion 85.3), African (6.6), and Native American (6.3) ancestries, with a strong inverse correlation between the African and European ancestry scores (ρ = -0.93; p<0.001). Independent of education level, African ancestry was inversely associated with both visceral and subcutaneous abdominal fat distributions in men (both P = 0.001), and inversely associated with subcutaneous abdominal fat distribution in women (p = 0.009). Independent of genomic ancestry, higher education level was associated with lower visceral fat, but higher subcutaneous fat, in both men and women (all p<0.001). Our findings, from an admixed population, indicate that both genomic ancestry and education level were independently associated with abdominal fat distribution in adults. African ancestry appeared to lower abdominal fat distributions, particularly in men.

The His131Arg substitution in the FCGR2A gene (rs1801274) is not associated with the severity of influenza A(H1N1)pdm09 infection.

BackgroundThe virulence and pathogenicity of different influenza strains are responsible for a more or less severe disease. Recent studies have attempted to understand how host genetic factors may influence the clinical presentation of the disease. In the present study, the His131Arg (rs1801274) polymorphism was investigated in individuals from a Brazilian admixed population with a diagnosis of influenza A(H1N1)pdm09 infection.MethodsIn the present study, the influence of the His131Arg (rs1801274) polymorphism, a variant of the FCGR2A gene, was investigated in 436 patients with a diagnosis of influenza A(H1N1)pdm09, evaluated at health services in the northern and northeastern regions of Brazil between June 2009 and August 2010. Patients were divided into a group of non-hospitalized patients (n = 192) and a group of hospitalized patients (n = 244; 100 of them died).ResultsNo significant difference in the allele or genotype frequencies of the rs1801274 polymorphism was observed between groups (p = 0.952 and p = 0.388). Multinomial logistic regression showed no effect of the rs1801274 polymorphism on severity or death of patients from the Brazilian admixed population (p = 0.368 and p = 0.469).ConclusionsThe rs1801274 polymorphism is not associated with severe disease in patients infected with influenza A(H1N1)pdm09.

The CCR5Δ32 (rs333) polymorphism is not a predisposing factor for severe pandemic influenza in the Brazilian admixed population.

BackgroundRecent studies have tried to identify host genetic variants that could explain severe cases and deaths in infection with Influenza A(H1N1)pdm09, especially among children and young adults. CCR5 is a chemokine receptor expressed on T cells, macrophages and dendritic cells, which is an important mediator of leukocyte chemotaxis during the immune response. A deletion mutation (Δ32) in this gene interferes with the response of immune cells, impairing viral clearance. We evaluated the CCR5Δ32 polymorphism (rs333) in individuals of the Brazilian admixed population with a diagnosis of Influenza A(H1N1)pdm09 infection.MethodsA total of 330 subjects with a diagnosis of Influenza A(H1N1)pdm09, evaluated at health services in the northern and northeastern regions of Brazil between June 2009 and August 2010, were genotyped for the Δ32 deletion (rs333). The cases were classified according to the progression of infection into a group of hospitalized patients (n = 156) and a group of non-hospitalized patients (n = 174).ResultsNo significant differences in the allele or genotype frequencies of the CCR5Δ32 polymorphism were observed between non-hospitalized and hospitalized patients (p = 0.289 and p = 0.431, respectively).ConclusionThe Δ32 deletion in the CCR5 gene is not associated with an unfavorable outcome in patients infected with Influenza A(H1N1)pdm09 in the Brazilian admixed population.Electronic supplementary materialThe online version of this article (doi:10.1186/s13104-015-1299-1) contains supplementary material, which is available to authorized users.

Exploring the applicability of analysing X chromosome STRs in Brazilian admixed population

Kinship and parentage analyses always involve one sample being compared to another sample or a few samples with a specific relationship question in mind. In most cases, the analysis of autosomal STR markers is sufficient to determine the genetic kinship. However, when genetic profiles are reconstructed from supposed relatives, for whom the family configuration available for analysis is deficient, the examination may be inconclusive. This study reports practical examples of actual cases analysing the efficiency of the chromosome X STR (STR-ChrX) markers. Three cases with different degrees of efficiency and impact were selected as follows: the identification of two charred bodies in a traffic accident, in which the family setting available was not complete, and one filiation analysis resulting from rape.This is the first paper reporting the use of the multiplex STR 12 ChrX in actual cases using the software Familias 1.8 and Brazilian regional frequency data. Our study clarifies the complex analysis using this powerful tool for professionals in the forensic science community, for both civil and criminal justice. We also discuss state-of-the-art ChrX STR markers and its implications and applications for legal procedures. The data presented here should be used in other studies of complex cases to improve the progress of the current justice system.

Paleogenetic Studies in Guajajara Skeletal Remains, Maranhão State, Brazil

In the early 17th century, French and Portuguese colonizers and Jesuit priests settled in the state of Maranhão and made contact with the Guajajara, an ethnic group that lived along the margins of the Pindaré River. The Guajajara maintained contact with Brazilian national society over the centuries, including with Brazilian admixed populations, and with African slaves that flocked towards the region from the 18th century onwards. The present study investigates the origins of this admixture using mitochondrial genetic variability. The bones of 12 individuals investigated, which are currently part of the collection of theNational Museum, were tested for genetic diversity. aDNA was extracted by the phenol-chloroform method and by DNA IQ (Promega, Madison, WI, USA). Amplification of the HVS I region was performed by PCR, followed by direct sequencing using the Big Dye kit (Life Technologies, Foster City, CA, USA). This region was found to represent haplogroups of Amerindians (A, C, and D) and Africans (L, L1b, L1c, and L3). The presence of African haplogroups in Guajajara bones from as early as the 18th century is consistent with historical and anthropological data, suggesting the admixture with Africans and/or Afrodescendants. Therefore, this study demonstrates that women with African haplogroups were introduced into the Guajajara population.

A Prospective Screening of Gene Copy Number Variation in Brazilian Admixed Population Sample

Copy number variants (CNVs) represent an important source of variation in the human genome. Some CNVS embedded genes are differently distributed among the human population groups. Therefore, it is important to understand the distribution of CNV within and between populations, especially in those with admixed ancestry, such as the Brazilians. The aim of the study was to investigate the variability of a set of CNV-embedded genes in a sample of the Brazilian population. The CNV-embedded genes were chosen based on data showing that they have differential copy variation distribution between African and Europeans. Four genes (POLR2J4, PCDHB13, NPEPPS and AMY1) were investigated by qPCR in a sample of 96 Brazilians, previously classified by genetic ancestry. The gene AMY1 showed a variable copy numbers in the range of 1 to 8 copies whereas NPEPPS ranged from 1 to 5 copies. A low variability was identified for the POLR2J4 and PCDHB13 genes, showing 2 copies in frequency of 0.875 and 0.917, respectively. Genetic ancestry was not correlated to the number of copies of the AMY1and NPEPPS genes. The results provided an overview of the corresponding frequency of gene copy number variation in a sample of the Brazilian population, serving as reference for further genetic population studies, which may correlate these polymorphisms with other phenotypic features.

Interethnic diversity of NAT2 polymorphisms in Brazilian admixed populations

BackgroundN-acetyltransferase type 2 (Nat2) is a phase II drug- metabolizing enzyme that plays a key role in the bioactivation of aromatic and heterocyclic amines. Its relevance in drug metabolism and disease susceptibility remains a central theme for pharmacogenetic research, mainly because of its genetic variability among human populations. In fact, the evolutionary and ethnic-specific SNPs on the NAT2 gene remain a focus for the potential discoveries in personalized drug therapy and genetic markers of diseases. Despite the wide characterization of NAT2 SNPs frequency in established ethnic groups, little data are available for highly admixed populations. In this context, five common NAT2 SNPs (G191A, C481T, G590A, A803G and G857A) were investigated in a highly admixed population comprised of Afro-Brazilians, Whites, and Amerindians in northeastern Brazil. Thus, we sought to determine whether the distribution of NAT2 polymorphism is different among these three ethnic groups.ResultsOverall, there were no statistically significant differences in the distribution of NAT2 polymorphism when Afro-Brazilian and White groups were compared. Even the allele frequency of 191A, relatively common in African descendents, was not different between the Afro-Brazilian and White groups. However, allele and genotype frequencies of G590A were significantly higher in the Amerindian group than either in the Afro-Brazilian or White groups. Interestingly, a haplotype block between G590A and A803G was verified exclusively among Amerindians.ConclusionsOur results indicate that ethnic admixture might contribute to a particular pattern of genetic diversity in the NAT2 gene and also offer new insights for the investigation of possible new NAT2 gene-environment effects in admixed populations.