Worse Health Status and Higher Incidence of Health Disorders in Rhesus Negative Subjects

Rhesus-positive and Rhesus-negative persons differ in the presence-absence of highly immunogenic RhD protein on the erythrocyte membrane. The biological function of the RhD molecule is unknown. Its structure suggests that the molecular complex with RhD protein transports NH₃ or CO₂ molecules across the erythrocyte cell membrane. Some data indicate that RhD positive and RhD negative subjects differ in their tolerance to certain biological factors, including, Toxoplasma infection, aging and fatique. Present cross sectional study performed on 3,130 subjects) showed that Rhesus negative subjects differed in many indices of their health status, including incidences of many disorders. Rhesus negative subjects reported to have more frequent allergic, digestive, heart, hematological, immunity, mental health, and neurological problems. On the population level, a Rhesus-negativity-associated burden could be compensated for, for example, by the heterozygote advantage, but for Rhesus negative subjects this burden represents a serious problem.     

MHC allele frequency distributions under parasite-driven selection: A simulation model

Background  

The extreme polymorphism that is observed in major histocompatibility complex (MHC) genes, which code for proteins involved in recognition of non-self oligopeptides, is thought to result from a pressure exerted by parasites because parasite antigens are more likely to be recognized by MHC heterozygotes (heterozygote advantage) and/or by rare MHC alleles (negative frequency-dependent selection). The Ewens-Watterson test (EW) is often used to detect selection acting on MHC genes over the recent history of a population. EW is based on the expectation that allele frequencies under balancing selection should be more even than under neutrality. We used computer simulations to investigate whether this expectation holds for selection exerted by parasites on host MHC genes under conditions of heterozygote advantage and negative frequency-dependent selection acting either simultaneously or separately.     

Association between HLA-Cw*0602 polymorphism and psoriasis risk: a meta-analysis

Numerous studies have evaluated the association between human leukocyte antigen (HLA) Cw*0602 polymorphism and psoriasis risk. However, the results have been inconsistent. We made a meta-analysis of the association between HLA-Cw*0602 polymorphism and psoriasis risk. Eighteen studies were retrieved, reporting a total of 3419 psoriasis patients and 3297 healthy controls. The associations between HLA-Cw*0602 polymorphism and psoriasis risk were estimated by pooled odds ratio (OR) and 95% confidence interval (95%CI). We found significant associations between HLA-Cw*0602 polymorphism and psoriasis risk in the comparisons of positive versus negative alleles (OR = 4.55, 95%CI = 3.65-5.67, P < 0.00001); positive homozygote versus negative homozygote combined with heterozygote (OR = 14.00, 95%CI = 8.47-23.15, P < 0.00001); positive homozygote combined with heterozygote versus negative homozygote (OR = 5.11, 95%CI = 3.86-6.76, P < 0.00001); positive homozygote versus negative homozygote (OR = 23.03, 95%CI = 13.95-38.00, P < 0.00001), and positive homozygote versus heterozygote (OR = 4.21, 95%CI = 2.35- 7.00, P < 0.00001). In conclusion, the positive allele of HLA-Cw*0602 polymorphism appears to be a risk factor for psoriasis.     

Heterozygote advantage and the maintenance of polymorphism for multilocus traits

Explaining how polymorphism is maintained in the face of selection remains a puzzle since selection tends to erode genetic variation. Provided an infinitely large unsubdivided population and no frequency-dependance of selective values, heterozygote advantage is the text book explanation for the maintenance of polymorphism when selection acts at a diallelic locus. Here, we investigate whether this remains true when selection acts at multiple diallelic loci. We use five different definitions of heterozygote advantage that largely cover this concept for multiple loci. Using extensive numerical simulations, we found no clear associations between the presence of any of the five definitions of heterozygote advantage and the maintenance of polymorphism at all loci. The strength of the association decreases as the number of loci increases or as recombination decreases. We conclude that heterozygote advantage cannot be a general mechanism for the maintenance of genetic polymorphism at multiple loci. These findings suggest that a correlation between the number of heterozygote loci and fitness is not warranted on theoretical ground.     

An asymmetric model of heterozygote advantage at major histocompatibility complex genes: degenerate pathogen recognition and intersection advantage

We characterize the function of MHC molecules by the sets of pathogens that they recognize, which we call their "recognition sets." Two features of the MHC-pathogen interaction may be important to the theory of polymorphism construction at MHC loci: First, there may be a large degree of overlap, or degeneracy, among the recognition sets of MHC molecules. Second, when infected with a pathogen, an MHC genotype may have a higher fitness if that pathogen belongs to the overlapping portion, or intersection, of the two recognition sets of the host, when compared with a genotype that contains that pathogen in only one of its recognition sets. We call this benefit "intersection advantage," gamma, and incorporate it, as well as the degree of recognition degeneracy, m, into a model of heterozygote advantage that utilizes a set-theoretic definition of fitness. Counterintuitively, we show that levels of polymorphism are positively related to m and that a high level of recognition degeneracy is necessary for polymorphism at MHC loci under heterozygote advantage. Increasing gamma reduces levels of polymorphism considerably. Hence, if intersection advantage is significant for MHC genotypes, then heterozygote advantage may not explain the very high levels of polymorphism observed at MHC genes.     

Preliminary observations of MHC class I A region polymorphism in three populations of Chinese-origin rhesus macaques

Rhesus macaques are an animal model for the study of a variety of human diseases. The Chinese rhesus macaques have been widely used in biomedical research in recent years. However, the polymorphism of major histocompatibility complex (MHC) class I A region among different local populations of Chinese rhesus macaques has never been investigated. In this study, we identified 46 Mamu-A alleles by cDNA cloning and sequencing on a cohort of 53 Chinese rhesus monkeys including Zhiming, Chuanxi, and Fujian populations, of which 5 were first reported in rhesus monkeys. The frequencies of alleles were identified for each population. The result suggests that the repertoire of allelic variants of MHC class I A region found in different populations of Chinese macaques is largely non-overlapping. The frequencies of alleles and the popular allele are also different for different populations. PCR-SSP experiment further confirms the different frequencies of two alleles, Mamu-A*026:01 and Mamu-A*022:01, in additional 99 Zhiming monkeys and 191 Chuanxi monkeys. Our findings have important practical implications in that the origin of the individuals and the genetic polymorphism of the monkeys need to be considered at the level of local populations for Chinese rhesus monkeys in biomedical research. Further immunogenetic work is needed to investigate the MHC polymorphism among different populations of Chinese rhesus macaques and to reveal the functional implication of such polymorphism and disease outcome correlations.     

Adaptation at Specific Loci. II. Demographic and Biochemical Elements in the Maintenance of the Colias Pgi Polymorphism

Demographically oriented sampling in the wild and biochemical study of allozymes in the laboratory have been used to probe maintenance of the phosphoglucose isomerase polymorphism of Colias butterflies.—The several alleles at this locus show negative or no covariation among their frequencies in the wild. This rules out Wahlund effects as a cause of observations of heterozygote excess at this locus in broods that fly as single cohorts. Unusually heavy mortality among adults, due to drought stress or other causes, can preclude manifestation of differential survivorship among phosphoglucose isomerase genotypes. In broods composed of overlapping cohorts, heterozygote deficiency, apparently due to Wahlund effects in time as cohorts of different survivorship experience mix, can be found. Heterozygotes at this locus fly under a broader range of weather conditions than other genotypes.—Previously detected kinetic differentiation among the genotypes extends in greater magnitude to the glycolytic reaction direction, as well as to a broader range of test conditions than examined before. The heterozygote 3/4 is strikingly heterotic for several measures of kinetic functional effectiveness. Other heterozygotes are sometimes heterotic, more often intermediate (but not exactly so, nor additive in any sense) in properties between homozygotes.—Predictions are made from the biochemical analysis and from the insects' thermal ecology concerning distributions of the genotypes in the wild. Some agree with facts already established. Others are tested and confirmed from data already on hand. Still others are to be tested as reported in an accompanying paper.—All available evidence points to a combination of heterozygote advantage and fluctuating-environment selection as responsible for maintaining this polymorphism. There is considerable evidence for the operation of protein-structural constraint on the range of adaptations possible at this locus.     

Red Queen Processes Drive Positive Selection on Major Histocompatibility Complex (MHC) Genes

Major Histocompatibility Complex (MHC) genes code for proteins involved in the incitation of the adaptive immune response in vertebrates, which is achieved through binding oligopeptides (antigens) of pathogenic origin. Across vertebrate species, substitutions of amino acids at sites responsible for the specificity of antigen binding (ABS) are positively selected. This is attributed to pathogen-driven balancing selection, which is also thought to maintain the high polymorphism of MHC genes, and to cause the sharing of allelic lineages between species. However, the nature of this selection remains controversial. We used individual-based computer simulations to investigate the roles of two phenomena capable of maintaining MHC polymorphism: heterozygote advantage and host-pathogen arms race (Red Queen process). Our simulations revealed that levels of MHC polymorphism were high and driven mostly by the Red Queen process at a high pathogen mutation rate, but were low and driven mostly by heterozygote advantage when the pathogen mutation rate was low. We found that novel mutations at ABSs are strongly favored by the Red Queen process, but not by heterozygote advantage, regardless of the pathogen mutation rate. However, while the strong advantage of novel alleles increased the allele turnover rate, under a high pathogen mutation rate, allelic lineages persisted for a comparable length of time under Red Queen and under heterozygote advantage. Thus, when pathogens evolve quickly, the Red Queen is capable of explaining both positive selection and long coalescence times, but the tension between the novel allele advantage and persistence of alleles deserves further investigation.     

Heterozygote Advantage and the Evolution of a Dominant Diploid Phase

The life cycle of eukaryotic, sexual species is divided into haploid and diploid phases. In multicellular animals and seed plants, the diploid phase is dominant, and the haploid phase is reduced to one, or a very few cells, which are dependent on the diploid form. In other eukaryotic species, however, the haploid phase may dominate or the phases may be equally developed. Even though an alternation between haploid and diploid forms is fundamental to sexual reproduction in eukaryotes, relatively little is known about the evolutionary forces that influence the dominance of haploidy or diploidy. An obvious genetic factor that might result in selection for a dominant diploid phase is heterozygote advantage, since only the diploid phase can be heterozygous. In this paper, I analyze a model designed to determine whether heterozygote advantage could lead to the evolution of a dominant diploid phase. The main result is that heterozygote advantage can lead to an increase in the dominance of the diploid phase, but only if the diploid phase is already sufficiently dominant. Because the diploid phase is unlikely to be increased in organisms that are primarily haploid, I conclude that heterozygote advantage is not a sufficient explanation of the dominance of the diploid phase in higher plants and animals.     

Major histocompatibility complex (MHC) heterozygote superiority to natural multi-parasite infections in the water vole (Arvicola terrestris)

The fundamental role of the major histocompatibility complex (MHC) in immune recognition has led to a general consensus that the characteristically high levels of functional polymorphism at MHC genes is maintained by balancing selection operating through host–parasite coevolution. However, the actual mechanism by which selection operates is unclear. Two hypotheses have been proposed: overdominance (or heterozygote superiority) and negative frequency-dependent selection. Evidence for these hypotheses was evaluated by examining MHC–parasite relationships in an island population of water voles (Arvicola terrestris). Generalized linear mixed models were used to examine whether individual variation at an MHC class II DRB locus explained variation in the individual burdens of five different parasites. MHC genotype explained a significant amount of variation in the burden of gamasid mites, fleas (Megabothris walkeri) and nymphs of sheep ticks (Ixodes ricinus). Additionally, MHC heterozygotes were simultaneously co-infected by fewer parasite types than homozygotes. In each case where an MHC-dependent effect on parasite burden was resolved, the heterozygote genotype was associated with fewer parasites, and the heterozygote outperformed each homozygote in two of three cases, suggesting an overall superiority against parasitism for MHC heterozygote genotypes. This is the first demonstration of MHC heterozygote superiority against multiple parasites in a natural population, a mechanism that could help maintain high levels of functional MHC genetic diversity in natural populations.     

Selection in natural and experimental populations of Drosophila pseudoobscura

The inverted gene arrangements of Drosophila pseudoobscura were used by Th. Dobzhansky in pioneering analyses of natural selection. Recent experiments have shed light on the mechanisms of selection contributing to the balanced polymorphism for the gene arrangements. In experimental populations, both major components of fitness, viability and fertility, are frequency dependent, and rare genotypes often have a selective advantage. Viabilities are also density dependent. The frequency dependence and density dependence of the fitness components are not universal. Some karyotypes are strongly influenced by frequency or density, some are slightly influenced, and some do not appear to be influenced at all. The role of heterozygote advantage in the selection on the gene arrangements is not clear. It is probably one important element in the overall selection, but viability and fertility do not always show a heterozygote advantage. Viability and fertility components of selection seem to be about equally important in changing inversion frequencies. Male mating success is an important component of selection in natural populations, and in one population rare male karyotypes have been found to have a pronounced mating advantage.     

Selection for the α-Thalassemia Genes

Extremely high incidences of single and double deletions of α-globin genes are known among Asian populations. To study possible mechanisms for the maintenance of such deletions, mathematical analyses have been conducted. It has been shown that a stable polymorphism can be achieved easily through heterozygote advantage using deterministic models. The results strongly suggest that high incidences of single and double deletion of α-globin genes among Asian populations are maintained by some type of heterozygote advantage.     

Virus-immune dynamics determined by prey-predator interaction network and epistasis in viral fitness landscape

The emergence and persistence of polymorphism within populations generally requires specific regimes of natural or sexual selection. Here, we develop a unified theoretical framework to explore how polymorphism at targeted loci can be generated and maintained by either disassortative mating choice or balancing selection due to, for example, heterozygote advantage. To this aim, we model the dynamics of alleles at a single locus A in a population of haploid individuals, where reproductive success depends on the combination of alleles carried by the parents at locus A. Our theoretical study of the model confirms that the conditions for the persistence of a given level of allelic polymorphism depend on the relative reproductive advantages among pairs of individuals. Interestingly, equilibria with unbalanced allelic frequencies were shown to emerge from successive introduction of mutants. We then investigate the role of the function linking allelic divergence to reproductive advantage on the evolutionary fate of alleles within the population. Our results highlight the significance of the shape of this function for both the number of alleles maintained and their level of genetic divergence. Large number of alleles are maintained with substantial replacement of alleles, when disassortative advantage slowly increases with allelic differentiation . In contrast, few highly differentiated alleles are predicted to be maintained when genetic differentiation has a strong effect on disassortative advantage. These opposite effects predicted by our model explain how disassortative mate choice may lead to various levels of allelic differentiation and polymorphism, and shed light on the effect of mate preferences on the persistence of balanced and unbalanced polymorphism in natural population.

     

ACE and LRPAP1 insertion-deletion polymorphisms in a northern Ivory Coast population

The ACE and the LRPAP1 gene insertion-deletion polymorphisms were determined in 133 healthy individuals sampled from Ouangolodougou, a village located in northern Ivory Coast. No sex differences were found in ACE and LRPAP1 gene frequencies. The ACE insertion and deletion alleles had frequencies of 0.346 and 0.654, respectively. The ACE gene was not in Hardy-Weinberg equilibrium because of an excess of heterozygote genotypes and a deficiency of I/I genotypes compared to the expected values. Statistical analysis showed a significantly lower frequency of I/I genotypes in the Ivory Coast population compared to Sudan, Kenya, African Americans, and African Brazilians (p < 0.05), whereas no differences were found with respect to Somalia. Conversely, the frequencies of the insertion and deletion alleles in the Ivorian population did not differ from those of other African populations. The LRPAP1 insertion and deletion allele frequencies found in our study (0.192 and 0.808, respectively) did not differ significantly from the Czech and Spanish populations, the only two populations previously characterized for this polymorphism. However, the frequency of the I/I genotype was significantly lower than the frequencies observed in the European samples. Because of the limited information on the LRPAP1 gene polymorphism distribution in worldwide populations, it was not possible to draw any conclusion.     

Pathogen resistance and genetic variation at MHC loci

Abstract.— Balancing selection in the form of heterozygote advantage, frequency-dependent selection, or selection that varies in time and/or space, has been proposed to explain the high variation at major histocompatibility complex (MHC) genes. Here the effect of variation of the presence and absence of pathogens over time on genetic variation at multiallelic loci is examined. In the basic model, resistance to each pathogen is conferred by a given allele, and this allele is assumed to be dominant. Given that s is the selective disadvantage for homozygotes (and heterozygotes) without the resistance allele and the proportion of generations, which a pathogen is present, is e , fitnesses for homozygotes become (1 — s )^(n-1)e and the fitnesses for heterozygotes become (1 — s )^(n-2)e, where n is the number of alleles. In this situation, the conditions for a stable, multiallelic polymorphism are met even though there is no intrinsic heterozygote advantage. The distribution of allele frequencies and consequently heterozygosity are a function of the autocorrelation of the presence of the pathogen in subsequent generations. When there is a positive autocorrelation over generations, the observed heterozygosity is reduced. In addition, the effects of lower levels of selection and dominance and the influence of genetic drift were examined. These effects were compared to the observed heterozygosity for two MHC genes in several South American Indian samples. Overall, resistance conferred by specific alleles to temporally variable pathogens may contribute to the observed polymorphism at MHC genes and other similar host defense loci.     

Distribution of ABO and rhesus blood groups in Abraka, Delta State, Nigeria.

Blood group systems are determined early in intrauterine life, specific to the individual and therefore significant in management and identification. Seven hundred and ninety five volunteer students of the Abraka campus of Delta State University were analyzed in this 4-year retrospective study. Amongst ABO system, blood group O was most common followed by A, B and AB respectively. Rhesus positive was more common than Rhesus negative in the rhesus system. Gender had no significant effect on both blood group systems studied. In the combined ABO and Rhesus blood groups, O positive was most common followed by A positive, B positive, AB positive O negative and A negative respectively. This study documents ABO and Rhesus blood group distribution patterns amongst south southern Nigerians. Findings will be useful in maintaining a register of possible donors, for effective management of medical emergencies.     

Natural selection on a leaf-shape polymorphism in the ivyleaf morning glory (Ipomoea hederacea)

Leaf shape is one of the most variable plant traits. Previous work has provided much indirect evidence that leaf-shape variation is adaptive and that leaf shape influences thermoregulation, water balance, and resistance to natural enemies. Nevertheless, there is little direct evidence that leaf shape actually affects plant fitness. In this study, we first demonstrate that populations of the ivyleaf morning glory, Ipomoea hederacea, in North and South Carolina are frequently polymorphic at a locus that influences leaf shape. We then employ several field experiments to show that this polymorphism is subject to selection. In two of the experiments, at different sites, heterozygotes enjoyed a fitness advantage over both homozygotes. At a third site, in one year directional selection favored lobed leaves, whereas in a second year the pattern of fitnesses was consistent with similar directional selection or heterozygote superiority. Computer simulations of heterozygote advantage under the high selfing rates of I. hederacea indicate that balancing selection of the magnitude observed can by itself stabilize the polymorphism, although spatially and temporally variable selection may also contribute to its long-term maintenance.     

A model of assortative mating with partial dominance.

A model of assortative mating incorporating partial dominance is proposed for a single locus with two alleles. It is derived by starting from an arbitrary genotypic distribution and finding symmetric and non-selective mating frequencies which duplicate this distribution. Numerical values are imputed to genotypes, the homozygotes having numerically equal values, opposite in sign, and the heterozygote having a value determined by the gene and heterozygote frequencies. The model is specified in a canonical form which reveals the correlation between mates based on genotypic values, and relates the correlation to the fixation index. It permits negative as well as positive values of the fixation index. It is shown that this general model includes several particular cases, in equilibrium phase, occurring in the literature.     

Parasite-mediated selection drives an immunogenetic trade-off in plains zebras (Equus quagga)

Pathogen evasion of the host immune system is a key force driving extreme polymorphism in genes of the major histocompatibility complex (MHC). Although this gene family is well characterized in structure and function, there is still much debate surrounding the mechanisms by which MHC diversity is selectively maintained. Many studies have investigated relationships between MHC variation and specific pathogens, and have found mixed support for and against the hypotheses of heterozygote advantage, frequency-dependent or fluctuating selection. Few, however, have focused on the selective effects of multiple parasite types on host immunogenetic patterns. Here, we examined relationships between variation in the equine MHC gene, ELA-DRA, and both gastrointestinal (GI) and ectoparasitism in plains zebras (Equus quagga). Specific alleles present at opposing population frequencies had antagonistic effects, with rare alleles associated with increased GI parasitism and common alleles with increased tick burdens. These results support a frequency-dependent mechanism, but are also consistent with fluctuating selection. Maladaptive GI parasite ‘susceptibility alleles’ were reduced in frequency, suggesting that these parasites may play a greater selective role at this locus. Heterozygote advantage, in terms of allele mutational divergence, also predicted decreased GI parasite burden in genotypes with a common allele. We conclude that an immunogenetic trade-off affects resistance/susceptibility to parasites in this system. Because GI and ectoparasites do not directly interact within hosts, our results uniquely show that antagonistic parasite interactions can be indirectly modulated through the host immune system. This study highlights the importance of investigating the role of multiple parasites in shaping patterns of host immunogenetic variation.     

The importance of association between angiotensin-converting enzyme (ACE) Gene I/D polymorphism and diabetic peripheral neuropathy

Background

Diabetic peripheral neuropathy (DPN) is a microvascular complication of diabetes mellitus (DM) due to decreasing quality of life. In the present study, it is aimed to evaluate angiotensin-converting enzyme (ACE) Gene I/D polymorphism in Turkish population.

Materials and methods

Two hundred and thirty-five DPN patients and two hundred and eighty-one controls were enrolled in this study. Genomic DNA was isolated and genotyped using polymerase chain reaction (PCR) analyses for the ACE gene I/D polymorphism.

Results

Baseline characteristics of the DPN patients according to ACE genotypes were similar, except for history of hypertension. The frequency of II genotype was significantly higher in patients with positive history of hypertension than the patients with negative history of hypertension (p = 0.013). DD genotype of I/D polymorphism was found to be a susceptibility factor for DPN in homozygous form (p = 0.032). According to allele frequencies, D allele of I/D polymorphism was found to be a susceptibility factor for DPN (p = 0.031).

Conclusion

ACE gene I/D polymorphism may research in DM patients to determine genetic predisposition for DPN. It can be useful for taking early measures and avoiding DPN in a Turkish population.