Heterozygous HbAC but not HbAS is associated with higher newborn birthweight among women with pregnancy-associated malaria

G6PD and HBB polymorphisms in the Senegalese population: prevalence, correlation with clinical malaria

Background

Host genetic factors contribute to the variability of malaria phenotypes and can allow a better understanding of mechanisms involved in susceptibility and/or resistance to Plasmodium falciparum infection outcomes. Several genetic polymorphisms were reported to be prevalent among populations living in tropical malaria-endemic regions and induce protection against malaria. The present study aims to investigate the prevalence of HBB (chr11) and G6PD (chrX) deficiencies polymorphisms among Senegalese populations and their associations with the risk for severe Plasmodium falciparum malaria occurrence.

Methods

We performed a retrospective study with 437 samples, 323 patients recruited in hospitals located in three different endemic areas where malaria episodes were confirmed and 114 free malaria controls. The patients enrolled were classified into two groups: severe malaria (SM) (153 patients) and uncomplicated malaria (UM) (170 patients). PCR and DNA sequencing assessed host genetic polymorphisms in HBB and G6PD. Using a multivariate regression and additive model, estimates of the impact of human HBB and G6PD polymorphisms on malaria incidence were performed.

Results

Six frequent SNPs with minor allele frequencies (MAF) > 3% were detected in the HBB gene (rs7946748, rs7480526, rs10768683, rs35209591, HbS (rs334) and rs713040) and two in the G6PD gene (rs762515 and rs1050828 (G6PD-202 G > A). Analysis of selected HbS polymorphism showed significant association with protective effect against severe malaria with a significant p-value = 0.033 (OR 0.38, 95% CI [0.16-0.91]) for SM vs. UM comparison. Surprisingly, our study did not identify the protective effect of variant HbC polymorphism against severe malaria. Finally, we found some of the polymorphisms, like HbS (rs334), are associated with age and biological parameters like eosinophils, basophils, lymphocytes etc.

Conclusion

Our data report HBB and G6PD polymorphisms in the Senegalese population and their correlation with severe/mild malaria and outcome. The G6PD and HBB deficiencies are widespread in West Africa endemic malaria regions such as The Gambia, Mali, and Burkina Faso. The study shows the critical role of genetic factors in malaria outcomes. Indeed, genetic markers could be good tools for malaria endemicity prognosis.

Natural Acquired Immunity to Malaria Antigens among Pregnant Women with Hemoglobin C Trait

Hemoglobin C is the second most common structural hemoglobinopathy in Africa, and carriers have a reduced risk of severe malaria. However, the effect of HbAC on the antibody response to malaria antigens in pregnancy has not been studied. Here, we measured PfEMP1-specific antibodies in plasma samples from 74 Beninese pregnant women with either HbAA or HbAC. IgG-mediated inhibition of VAR2CSA+ infected erythrocytes adhesion to chondroitin sulfate A (CSA) was also tested. PfEMP1-specific IgG levels to VAR2CSA were significantly lower in HbAC women, suggesting less exposure to VAR2CSA. In contrast, the percentage of VAR2CSA+-infected erythrocytes adhesion to CSA was not different between HbAA and HbAC women. Moreover, IgG levels to PfEMP1 variants associated with severe malaria were not significantly different between groups. The findings indicate similar exposure to Plasmodium falciparum parasites expressing PfEMP1 variants causing severe malaria, and justify more comprehensive studies of hemoglobinopathy-related qualitative and quantitative differences in PfEMP1-specific antibody responses.

Revisiting the malaria hypothesis: accounting for polygenicity and pleiotropy

The malaria hypothesis predicts local, balancing selection of deleterious alleles that confer strong protection from malaria. Three protective variants, recently discovered in red cell genes, are indeed more common in African than European populations. Still, up to 89% of the heritability of severe malaria is attributed to many genome-wide loci with individually small effects. Recent analyses of hundreds of genome-wide association studies (GWAS) in humans suggest that most functional, polygenic variation is pleiotropic for multiple traits. Interestingly, GWAS alleles and red cell traits associated with small reductions in malaria risk are not enriched in African populations. We propose that other selective and neutral forces, in addition to malaria prevalence, explain the global distribution of most genetic variation impacting malaria risk.

PfEMP1-Specific Immunoglobulin G Reactivity Among Beninese Pregnant Women With Sickle Cell Trait

BACKGROUND

Sickle cell trait (HbAS) protects against severe Plasmodium falciparum malaria but not against placental malaria (PM). In this study, P falciparum erythrocyte membrane protein (PfEMP1)-specific antibodies were measured in HbAA and HbAS Beninese pregnant women as a proxy of exposure to specific PfEMP1 variants.

METHODS

Plasma samples collected at delivery from 338 HbAA and 63 HbAS women were used to measure immunoglobulin (Ig)G levels to 6 recombinant PfEMP1 proteins and 3 corresponding native proteins expressed on the infected erythrocyte (IE) surface. Immunoglobulin G-mediated inhibition of VAR2CSA+ IEs adhesion to chondroitin sulfate A (CSA) was also tested.

RESULTS

Levels of PfEMP1-specific IgG were similar in the 2 groups, except for native IT4VAR09 on IEs, where IgG levels were significantly higher in HbAS women. Adjusted odds ratios for women with positive IgG to HB3VAR06 and PFD1235w suggest a lower risk of infection with these virulent variants among HbAS individuals. The percentage of IEs binding to CSA did not differ between HbAA and HbAS women, but it correlated positively with levels of anti-VAR2CSA and parity. Women with PM had lower levels of anti-VAR2CSA-specific IgG and lower IgG-mediated inhibition of IE adhesion to CSA.

CONCLUSIONS

The findings support similar malaria exposure in HbAA and HbAS women and a lack of HbAS-dependent protection against placental infection among pregnant women.

ABO blood group should be considered and reported when red blood cell exchange transfusion is used to treat Plasmodiumfalciparum Malaria patients

Laboratory and epidemiologic studies have clarified how persons born with malaria-resistant red blood cells (RBCs)-like group-O, sickle-trait, and C-trait RBCs-are protected against death or severe disease due to Plasmodiumfalciparum (Pf) infection. Compared to malaria-promoting RBCs-like non-O or hemoglobin-AA RBCs-inborn RBC protection against severe Pf malaria can be profound: up to 10-fold greater. Given that "the Berlin patient" success showed patients do not have to be born with disease-resistant cells to benefit from them, why have the biologically plausible benefits of exchange transfusion (ET) of malaria-resistant RBCs not yet been evaluated? Unfortunately, a 2013 ET-for-malaria meta-analysis could not quantify the impact on mortality of ET of malaria-resistant RBCs because RBC malaria resistance variables (ABO group, hemoglobin type, enzyme levels, etc.) had not been reported in any of the ET studies used in that meta-analysis. To promote evaluation of the therapeutic impact of specific malaria-resistant RBCs, we urge clinicians to always report ABO blood group (and all other RBC malaria-resistance variables they are aware of) when they use ET to rescue Pf-infected patients. Prudent selection of donor RBCs has successfully optimized ET for sickle cell disease patients, and this precedent suggests selection of special malaria-resistant donor RBCs may optimize ET for Pf-malaria patients. Given that ET is used worldwide as a rescue adjunct, we feel it is most prudent to now assume-until proven otherwise-that considering and reporting the Pf-malaria-resistance variables of the RBCs to be transfused-at least ABO status-will help optimize ET-for-malaria.

"Dual-gene" malaria-resistance: Therapeutically-rational exchange (T-REX) of group-O sickle trait and group-O C-traittrait red blood cells can be evaluated in Benin and Nigeria

BACKGROUND

Using indicators of disease severity, clinicians can predict which Plasmodium falciparum (Pf) malaria patients being treated with artesunate or quinine are likely to die despite these drugs. Effective "rescue adjuncts" are needed when drugs alone are inadequate. "Therapeutically-rational exchange" (T-REX) of special malaria-resistant red blood cells (RBCs) has been proposed to optimize adjunctive exchange transfusion.

METHODS

Studies were reviewed that (1) quantified how group-O status and "sickle-trait" (HbAS) and "C-trait" (HbAC) hemoglobins affect Pf mortality, risk of thrombosis, or birth outcomes for women with pregnancy associated malaria (PAM), (2) reported prevalences of "dual-gene" malaria-resistant RBCs, or (3) reflected the level of exchange-transfusion and malaria-related expertise in Benin and Nigeria.

RESULTS

Data show that the malaria- and thrombosis-resistance of RBCs depend on specific genes and the patient's clinical status and medical history. In malaria-endemic Benin and Nigeria, prevalences of "dual-gene" malaria-resistant group-O HbAS and group-O HbAC RBCs are substantial, and both malaria- and exchange-related expertise are outstanding.

CONCLUSIONS

T-REX of "dual-gene" malaria-resistant RBCs is feasible in Benin and Nigeria and warrants evaluation as a rescue adjunct for 3 subsets of Pf-malaria patients. For therapeutic use, group-O HbAS RBCs are likely to be more effective than non-O HbAS RBCs for Pf-infected patients who (1) have a history of thrombosis or (2) are taking birth-control hormones while group-O HbAC RBCs may substantially improve birth outcomes for women with PAM. Studies suggest it is prudent to assume - until proven otherwise - that T-REX of "dual-gene" malaria-resistant RBCs can improve ("personalize") rescue of these patient subsets.

Impact of Hemoglobin S Trait on Cell Surface Antibody Recognition of Plasmodium falciparum-Infected Erythrocytes in Pregnancy-Associated Malaria

Background

Sickle cell trait (HbAS) confers partial protection against malaria by reducing the adhesion of Plasmodium falciparum-infected erythrocytes to host receptors, but little is known about its potential protection against placental malaria.

Methods

Using flow cytometry, we assessed the recognition of HbAA and HbAS VAR2CSA-expressing infected erythrocytes, by plasma from 159 Beninese pregnant women with either HbAA (normal) or HbAS. Using multivariate linear models adjusted for gravidity, parasite infection at delivery, glucose-6-phosphate dehydrogenase deficiency, and α-thalassemia carriage, we observed significantly reduced cell surface antibody binding of HbAS-infected erythrocytes by plasma from HbAS compared with HbAA women (P < 10^–3).

Results

The difference in cell surface antibody binding was only observed when infected erythrocytes and plasma were associated according to the same hemoglobin genotype. Similar levels of VAR2CSA-specific antibody were measured by enzyme-linked immunosorbent assay in the 2 groups, suggesting that the altered interaction between VAR2CSA and HbAS women’s antibodies could reflect abnormal display of VAR2CSA on HbAS erythrocytes.

Conclusions

Our data stress the need for assessments of erythrocyte disorders such as the sickle cell trait in a population group when studying immunological responses to P falciparum.