Duffy blood group gene polymorphisms among malaria vivax patients in four areas of the Brazilian Amazon region

<p>Abstract</p> <p>Background</p> <p>Duffy blood group polymorphisms are important in areas where <it>Plasmodium vivax </it>predominates, because this molecule acts as a receptor for this protozoan. In the present study, Duffy blood group genotyping in <it>P. vivax </it>malaria patients from four different Brazilian endemic areas is reported, exploring significant associations between blood group variants and susceptibility or resistance to malaria.</p> <p>Methods</p> <p>The <it>P. vivax </it>identification was determined by non-genotypic and genotypic screening tests. The Duffy blood group was genotyped by PCR/RFLP in 330 blood donors and 312 malaria patients from four Brazilian Amazon areas. In order to assess the variables significance and to obtain independence among the proportions, the Fisher's exact test was used.</p> <p>Results</p> <p>The data show a high frequency of the <it>FYA/FYB </it>genotype, followed by <it>FYB/FYB, FYA/FYA</it>, <it>FYA/FYB-33 </it>and <it>FYB/FYB-33</it>. Low frequencies were detected for the <it>FYA/FY</it>^<it>X</it>, <it>FYB/FY</it>^<it>X</it>, <it>FYX/FY</it>^{<it>X </it>}and <it>FYB-33/FYB-33 </it>genotypes. Negative Duffy genotype (<it>FYB-33/FYB-33</it>) was found in both groups: individuals infected and non-infected (blood donors). No individual carried the <it>FY</it>^<it>X</it><it>/FYB-33 </it>genotype. Some of the Duffy genotypes frequencies showed significant differences between donors and malaria patients.</p> <p>Conclusion</p> <p>The obtained data suggest that individuals with the <it>FYA/FYB </it>genotype have higher susceptibility to malaria. The presence of the <it>FYB-33 </it>allele may be a selective advantage in the population, reducing the rate of infection by <it>P. vivax </it>in this region. Additional efforts may contribute to better elucidate the physiopathologic differences in this parasite/host relationship in regions endemic for <it>P. vivax </it>malaria, in particular the Brazilian Amazon region.</p

Population Genetics of GYPB and Association Study between GYPB*S/s Polymorphism and Susceptibility to P. falciparum Infection in the Brazilian Amazon

Merozoites of Plasmodium falciparum invade through several pathways using different RBC receptors. Field isolates appear to use a greater variability of these receptors than laboratory isolates. Brazilian field isolates were shown to mostly utilize glycophorin A-independent invasion pathways via glycophorin B (GPB) and/or other receptors. The Brazilian population exhibits extensive polymorphism in blood group antigens, however, no studies have been done to relate the prevalence of the antigens that function as receptors for P. falciparum and the ability of the parasite to invade. Our study aimed to establish whether variation in the GYPB*S/s alleles influences susceptibility to infection with P. falciparum in the admixed population of Brazil.Two groups of Brazilian Amazonians from Porto Velho were studied: P. falciparum infected individuals (cases); and uninfected individuals who were born and/or have lived in the same endemic region for over ten years, were exposed to infection but have not had malaria over the study period (controls). The GPB Ss phenotype and GYPB*S/s alleles were determined by standard methods. Sixty two Ancestry Informative Markers were genotyped on each individual to estimate admixture and control its potential effect on the association between frequency of GYPB*S and malaria infection.GYPB*S is associated with host susceptibility to infection with P. falciparum; GYPB*S/GYPB*S and GYPB*S/GYPB*s were significantly more prevalent in the in the P. falciparum infected individuals than in the controls (69.87% vs. 49.75%; P<0.02). Moreover, population genetics tests applied on the GYPB exon sequencing data suggest that natural selection shaped the observed pattern of nucleotide diversity.Epidemiological and evolutionary approaches suggest an important role for the GPB receptor in RBC invasion by P. falciparum in Brazilian Amazons. Moreover, an increased susceptibility to infection by this parasite is associated with the GPB S+ variant in this population

Primers designed to amplify <i>GYPB</i> exons 2, 4, 5 and 6 by PCR.

<p>Primers designed to amplify <i>GYPB</i> exons 2, 4, 5 and 6 by PCR.</p

<i>GYPB</i> haplotype frequencies determined on the re-sequencing panel on the basis of common SNPs (MAF>0.05).

a<p>SNP accounting for S (Thr) and s (Met) phenotypes.</p>b<p>Ser(G)/Thr(C).</p>c<p>The modal haplotype in each group is underlined.</p><p>Non-synonymous substitutions are underlined.</p

Estimation of admixture using Ancestry Informative Markers genotyping.

<p>Individual European, African and Native American ancestry were inferred from 60 ancestry informative markers in cases (magenta) and controls (yellow). Admixture was inferred by comparison with individuals from the putative parental populations: Europeans (red), African/African American (green) and Native Americans (blue). Admixture was estimated using the software Structure and average admixture over cases and controls is shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0016123#pone-0016123-t001" target="_blank">Table 1</a>.</p

Demographic characteristics, ancestry estimations and <i>GYPB</i>^*<i>S/s</i> genotype frequencies in cases and controls, tests for Hardy-Weinberg equilibrium and association between <i>GYPB</i>^*<i>S/s</i> genotype frequency and infection with malaria.

<p>*SD, standard deviation.</p><p>**Association persists (<i>P</i><0.02) if age, gender and European, African or Native American ancestry are included as covariates.</p

Summary of <i>GYPB</i> diversity indexes and tests of neutrality based on re-sequencing data of a subset of cases and controls and their partitions in S and s alleles (rs7683365) of the Ss blood group antigens.

<p>*The samples of cases and controls were selected so the proportion of SS, Ss and ss genotypes observed in the total set of cases and controls was matching.</p>a<p><i>P</i><0.02,</p>b<p><i>P</i><0.01,</p>c<p><i>P</i><0.001.</p