Hemoglobin Variants Influence Plasmodium Falciparum Sexual Differentiation

It has long been recognized that individuals who express variations of the hemoglobin-A (HbA) protein experience less severe malaria disease. As malaria remains to be one of the most significant infectious diseases in history, this human adaptation has led to the persistence of HbA variants (HbVARs) in the population. The intricate lifecycle of the parasite which causes the most cases of clinical malaria, Plasmodium falciparum, relies on both asexual and sexual reproductive cycles, with host to vector transmission reliant on sexual stage gametocyte formation. Multiple epidemiological studies have shown that HbVARs may influence gametocyte production during P. falciparum infection, with greater gametocyte numbers reported in individuals with hemoglobin variant containing erythrocytes (Hb VAR-Ery) when compared to hemoglobin A containing erythrocytes (Hb A-Ery). Here we provide experimental support for these studies by showing significantly higher sexual differentiation rates among parasites grown in Hb S containing erythrocytes (Hb S-Ery) obtained from sickle cell patients than those differentiated in Hb A-Ery (p=0.038). Because the digestion of hemoglobin is such an integral part of the intraerythrocytic cycle, we then sought to determine whether there was a difference between the hydrolysis efficiencies of HbA and other hemoglobin variants (HbVAR). By using a prominent recombinant P. falciparum hemoglobinase we found the hydrolysis efficiency of HbA to be significantly (p=0.0058) more efficient after 24 hours compared to a HbVAR sample containing mixed amounts of HbA, HbF, and HbS. To further determine whether there is a link between hemoglobin digestion efficiency and sexual differentiation, we therapeutically inhibited the hemoglobin digestion and hemozoin formation process in a culture of P. falciparum using sub-optimal doses of chloroquine diphosphate. We found a significant difference (p<0.001) among gametocyte conversion rates between treated and non-treated cultures, as well as a moderate negative correlation between hemozoin formation and gametocyte conversion rate (Pearson r=0.72, p=0.008). Gene expression analysis also revealed patterns of expression that were consistent with increased gametocytogenesis. We conclude that hemoglobin type plays a significant role in the process of sexual conversion in P. falciparum. Though further studies should be completed in order to confirm these results, these findings may suggest hemoglobin digestion efficiency as a causative factor for sexual differentiation. As individuals with hemoglobinopathies make up approximately 7% of the global population, and malaria infection rates have been shown to differ depending on these genetic dynamics, these findings may support the creation of targeted initiatives to reduce transmission specifically in areas where there is a high percentage of hemoglobinopathy carriage. Disclosures No relevant conflicts of interest to declare.

mRNA Analysis of Frameshift Mutations with Stop Codon in the Last Exon: The Case of Hemoglobins Campania [α1 cod95 (−C)] and Sciacca [α1 cod109 (−C)]

An insertion or deletion of a nucleotide (nt) in the penultimate or the last exon can result in a frameshift and premature termination codon (PTC), giving rise to an unstable protein variant, showing a dominant phenotype. We described two α-globin mutants created by the deletion of a nucleotide in the penultimate or the last exon of the α1-globin gene: the Hb Campania or α1 cod95 (−C), causing a frameshift resulting in a PTC at codon 102, and the Hb Sciacca or α1 cod109 (−C), causing a frameshift and formation of a PTC at codon 133. The carriers showed α-thalassemia alterations (mild microcytosis with normal Hb A2) and lacked hemoglobin variants. The 3D model indicated the α-chain variants’ instability, due to the severe structural alterations with impairment of the chaperone alpha-hemoglobin stabilizing protein (AHSP) interaction. The qualitative and semiquantitative analyses of the α1mRNA from the reticulocytes of carriers highlighted a reduction in the variant cDNAs that constituted 34% (Hb Campania) and 15% (Hb Sciacca) of the total α1-globin cDNA, respectively. We developed a workflow for the in silico analysis of mechanisms triggering no-go decay, and its results suggested that the reduction in the variant mRNA was likely due to no-go decay caused by the presence of a rare triplet, and, in the case of Hb Sciacca, also by the mRNA’s secondary structure variation. It would be interesting to correlate the phenotype with the quantity of other frameshift mRNA variants, but very few data concerning α- and β-globin variants are available.

Screening for hemoglobinopathy with capillary electrophoresis in adult patients

Hemoglobinopathy screening is frequently needed in adult patients, including prenatal carrier screen, workup of unexplained anemia, and bone marrow donor and recipient screening. However, the preferred test method for screening of hemoglobinopathy is not well established due to limited guidance from professional societies. American College of Obstetricians and Gynecologists’ Committee on Genetics recommended hemoglobin electrophoresis as the screening method of hemoglobinopathy in pregnancy; nevertheless, electrophoresis employs various methodologies, including acid gel electrophoresis, alkaline gel electrophoresis, and capillary electrophoresis (CE) with alkaline buffer. For other adult patient populations who need hemoglobinopathy screening, no clear guidelines dictate the method of choice. A previous study has shown that CE captures major hemoglobinopathies with comparable performance to high-performance liquid chromatography (HPLC) in pediatric patients but no study has investigated using CE alone in adult patient screening. In this retrospective study, we evaluated the utility of CE as a screening method to rule out clinically significant hemoglobin variants. During eight months, 312 adult patients without previously identified hemoglobin variants had hemoglobinopathy screening performed using a comprehensive testing algorithm. This cascade algorithm screens for hemoglobinopathy using both CE (Capillarys, Sebia, Paris, France) and HPLC (laboratory-developed test) with reflex to more advanced variant identification such as mass spectrometry and genetic analyses. Categories of abnormal findings were reviewed to determine if hemoglobinopathy can be identified by using CE only. The patient population mainly consists of pregnant women and anemic patients with hematologic malignancies with an average age of 42. Out of the 312 screened patients, 47 had abnormal results. The most frequent condition was elevated hemoglobin F (N=25) ranging 2-5% seen in leukemia patients on chemotherapy attributed to bone marrow stress. Eight cases of beta plus thalassemia (featuring hemoglobin A2 >4%) and 3 cases of hemoglobin C trait were identified in patients with little to mild clinical manifestations (red blood cell indices suggesting anemia). Decreased hemoglobin A2 fraction was observed in 7 patients, and potential causes were alpha thalassemia or iron deficiency. Other less common hemoglobinopathies included heterozygote A2 prime (N=3, a benign delta chain variant that migrates separately from hemoglobin A2 on CE) and hemoglobin G-Philadelphia (N=1). All of the abnormal results are identifiable by CE alone, although HPLC and more advanced methods help confirm the diagnosis. Our study shows that CE as the first line of screening method would rule out major hemoglobinopathies in adults. There have been reports that rare but clinically significant hemoglobin variants like hemoglobin Malmo may not be detected by CE, and therefore, certain pre-test probability factors need to be considered when testing for hemoglobinopathies, such as race/ethnicity background, family history, red blood cell indices, and iron deficiency status.

Difference in hemoglobin %A2 between homozygous hemoglobin A and hemoglobin S-trait patients as measured by capillary electrophoresis

Introduction/Objective Quantitation by high-performance liquid chromatography (HPLC) of hemoglobin %A2 is often not used in evaluation for thalassemia of hemoglobin S-trait patients, due to analytical interference from glycated hemoglobin S1d to increase %A2. In contrast, an increase in %A2 for S-trait when measured by capillary electrophoresis (CE) has been reported, without known analytical interference. This observation has not been re- evaluated in modern versions of CE, however. For validation exercises associated with startup of CE at our institution, we compared distributions of %A2 among A patients and S-trait patients using Sebia “Capillarys® 2” CE. Methods/Case Report %A2 is provided in two Sebia “Capillarys® 2” methods: analysis of A1c (method 1, M1) and analysis of hemoglobin variants (method 2, M2). To minimize effect of potential preselection for thalassemia among M2 samples, we first evaluated distributions of %A2 for A and S-trait among M1 samples. We then evaluated correlation of A2 measurements between M1 and M2. Statistical analyses were conducted using R programming. Results (if a Case Study enter NA) Using M1, %A2 for S-trait patients (2.61±0.31%, n=116) was higher than for A patients (2.11±0.27%, n=108) (p<0.001), with difference=0.42-0.57 %A2 (95% confidence interval, CI). %A2 by M1 was consistently less than %A2 by M2, for both A and S-trait (p>0.25): for A, M1/M2=0.89±0.05 (n=35); for S-trait, M1/M2=0.88±0.05 (n=32). Decreased %A2 by M1 compared to M2 may in part be due to separation in M1 of a glycated form of A2. Using M2, %A2 for S-trait patients (3.05±0.29%, n=32) was higher than for A patients (2.41±0.29%, n=35) (p<0.001), with difference=0.50-0.76 %A2 (CI). M2 results were consistent with M1 data when combined with the observed M1/M2 ratios. Conclusion Results suggest a physiological increase in %A2 in S-trait patients compared to A patients, not likely to be attributable to thalassemia. The average increase is ~0.6 %A2 for hemoglobin variant analysis by CE.

Challenges in Hemoglobin A1C Measurement in 183 Patients with Diabetes having Hemoglobin Variants and Chemically Modified Derivatives

Diabetes is considered as one of the most common metabolic disorder. It has challenged in terms of diagnosis,monitoring and management in the patients with type-2 diabetes. Glycosylated Hemoglobin (HbA1c) hasrecently been validated for the diagnosis diabetes in non-fasting condition, long term blood glycose monitoringand also predicting its complications in the patients. National Glycohemoglobin Standardization Program andInternational Federation of Clinical chemistry have been collaborating for the harmonization of HbA1cmethods and directing the laboratories to maintain strict quality goals. However, standardization of variousHbA1c methods being used worldwide still needs consideration especially in diabetic patients havinghemoglobin variants. The main objectives are to review HbA1c methods and address challenges in itsmeasurement methodology for the patients with diabetes mellitus having hemoglobin variants or chemicallymodified derivatives. Thus, to provide guidance to the clinical pathologist for selection of appropriate methodfor their laboratories.

Erythroid spectrin binding modulates peroxidase and catalase activity of heme proteins

Hemoglobin oxidation due to oxidative stress and disease conditions leads to generation of ROS (reactive oxygen species) and membrane attachment of hemoglobin in-vivo, where its redox activity leads to peroxidative damage of membrane lipids and proteins. Spectrin, the major component of the RBC membrane skeleton, is known to interact with hemoglobin and, here this interaction is shown to increase hemoglobin peroxidase activity in the presence of reducing substrate ABTS (2, 2-Azino-Bis-3-Ethylbenzothiazoline-6-Sulfonic Acid). It is also shown that in the absence of reducing substrate, spectrin forms covalently cross-linked aggregates with hemoglobin which display no peroxidase activity. This may have implications in the clearance of ROS and limiting peroxidative damage. Spectrin is found to modulate the peroxidase activity of different hemoglobin variants like A, E, and S, and of isolated globin chains from each of these variants. This may be of importance in disease states like sickle cell disease and HbE-β-thalassemia, where increased oxidative damage and free globin subunits are present due to the defects inherent in the hemoglobin variants associated with these diseases. This hypothesis is corroborated by lipid peroxidation experiments. The modulatory role of spectrin is shown to extend to other heme proteins, namely catalase and cytochrome-c. Experiments with free heme and Raman spectroscopy of heme proteins in the presence of spectrin show that structural alterations occur in the heme moiety of the heme proteins on spectrin binding, which may be the structural basis of increased enzyme activity.

Compound heterozygosity for hemoglobin S and hemoglobin E in a family of Proto-Australoid origin: a case report

Background Hemoglobin S and E are commonly occurring hemoglobin variants among distinctly separate tribal populations of Central and Northeast India, respectively. Combined heterozygosity for hemoglobin S and E or hemoglobin SE disease is a benign clinical condition with rare incidence. Reports of approximately 46 hemoglobin SE cases are available worldwide. We conducted a screening program to study the prevalence of hemoglobin variants among the tribal population working in the tea estates of Northeast India. A total of 551 subjects were screened, and complete blood count was performed. Based on their hematological profiles, hemoglobin typing was done for 218 subjects. Case presentation We describe a case of an adolescent male of Munda tribe diagnosed as double heterozygous for hemoglobin S and E. On screening of the nuclear family of the subject, the mother was found to have hemoglobin E disease and father as hemoglobin S trait. Both siblings of the subject were diagnosed as hemoglobin E trait. Conclusion This is the first case of compound heterozygous for hemoglobin S and E to be reported from the tea tribes of Assam, India.

Genetic Background of Congenital Erythrocytosis

True erythrocytosis is present when the red cell mass is greater than 125% of predicted sex and body mass, which is reflected by elevated hemoglobin and hematocrit. Erythrocytosis can be primary or secondary and congenital or acquired. Congenital defects are often found in those diagnosed at a young age and with a family history of erythrocytosis. Primary congenital defects mainly include mutations in the Erythropoietin receptor gene but SH2B3 has also been implicated. Secondary congenital erythrocytosis can arise through a variety of genetic mechanisms, including mutations in the genes in the oxygen sensing pathway, with high oxygen affinity hemoglobin variants and mutations in other genes such as BPMG, where ultimately the production of erythropoietin is increased, resulting in erythrocytosis. Recently, mutations in PIEZ01 have been associated with erythrocytosis. In many cases, a genetic variant cannot be identified, leaving a group of patients with the label idiopathic erythrocytosis who should be the subject of future investigations. The clinical course in congenital erythrocytosis is hard to evaluate as these are rare cases. However, some of these patients may well present at a young age and with sometimes catastrophic thromboembolic events. There is little evidence to guide the management of congenital erythrocytosis but the use of venesection and low dose aspirin should be considered.

Unexpected Detection of Abnormal Hemoglobin Variants During Routine HbA1c Analysis by HPLC Technique: Challenges and Opportunities in HbA1c Testing

Background: Glycated Hemoglobin A1c (HbA1c) assay is most widely used in diabetic patients for assessing long-term control of glycemia. The presence of hemoglobin variants may be an incidental finding and can interfere with HbA1c measurements. The aim of the present study is to investigate the prevalence and impact of interference of different abnormal hemoglobin variants on HbA1c measurements during routine HbA1c testing. Methods: A total of 12,092 HbA1c samples were collected from January to August 2018. HbA1c quantification was carried out on a Variant II Bio-Rad’s HPLC analyzer. Abnormal chromatograms were further analyzed using the extended-run high-pressure liquid chromatography (HPLC) analysis in the A2/F mode. Results: The samples were examined for presence of abnormal variants. Samples producing abnormal chromatograms were further analyzed in A2/F mode to characterize hemoglobin variants. Abnormal variants were identified in 126 (1%) samples, and 74 (0.59%) sickle cell traits (SCT) were the most common variant in our findings. Moreover, 30 (0.24%) cases were eluted in the variant window in A1c mode, which on further analysis were found to be Hb E & Hb D traits. Furthermore, 3 (0.02%) cases were eluted at a RT <1 min as (unknown) and identified as Hb H. Also,19 (0.15%) samples were eluted in the P3 window at different retention times. Conclusion: Observing each chromatograph after the analysis can help us in identifying silent hemoglobin variants in routine HbA1c testing. Knowledge and awareness of common hemoglobin variants affecting measurement of HbA1c is imperative to avoid reporting of falsely low HbA1c values in diabetic population.