Ovalocytosis Research Articles

Pseudohyperkalaemia Associated with Southeast Asian Ovalocytosis—a Case Report

Pseudohyperkalaemia Associated with Southeast Asian Ovalocytosis—a Case Report

RESPIRATORY FAILURE ASSOCIATED WITH DISTAL RENAL TUBULAR ACIDOSIS IN AN OLDER ADULT WITH SOUTHEAST ASIAN OVALOCYTOSIS AND CONCOMITANT THYROTOXIC ATRIAL FIBRILLATION

Distal renal tubular acidosis (dRTA) is characterized by hyperchloremic hypokalemic metabolic acidosis, nephrocalcinosis and metabolic bone disease. It has been associated with Southeast Asian Ovalocytosis (SAO), particularly in malaria endemic region. We present a case of an older adult with dRTA who presented with respiratory failure as a result of hyperchloremic normal anion gap metabolic acidosis, in association with nephrocalcinosis and SAO, however, without hypokalaemia due to concurrent acute kidney injury. Oxygen therapy was able to be weaned off after treatment with alkali supplementation. Distal RTA may be associated with SAO, and early recognition and treatment of dRTA is paramount in preventing complications such as chronic kidney disease, metabolic bone disease and life-threatening respiratory arrest.

An induced pluripotent stem cell line (MUSIi019-A) generated from a patient with distal renal tubular acidosis carrying a compound heterozygous mutation in solute carrier family 4 member 1 (SLC4A1) gene

Distal renal tubular acidosis (dRTA), a disease characterized by the failure of the distal nephron to secrete acid into the urine, can be caused by mutations in SLC4A1 gene encoding erythroid and kidney anion exchanger 1 (AE1). Here, an induced pluripotent stem cell (iPSC) line was generated from a patient with dRTA and hemolytic anemia carrying compound heterozygous SLC4A1 mutations containing c.1199_1225del (p.Ala400_Ala408del), resulting in Southeast Asian ovalocytosis (SAO), and c.1331C>A (p.Thr444Asn). Peripheral blood mononuclear cells (PBMCs) were reprogrammed using Sendai viral reprogramming. The established iPSC line, MUSIi019-A, exhibited pluripotent property and retained the same mutations observed in the patients.

The in vitro red blood cell microvesiculation exerts procoagulant activity of blood cell storage in Southeast Asian ovalocytosis

Southeast Asian ovalocytosis (SAO) is characterized by the misfolding of band 3 protein in red blood cells (RBC). The abnormal structure of the band 3 protein results in dysmorphic RBC and related functions. Previous data showed that in vitro storage under hypothermic conditions alters band 3 protein structure and function. Microvesiculation includes shedding of RBC membranes, called RBC-derived microparticles/extracellular vesicles (RMP/EVs), and storage lesions. Unfortunately, there is no evidence of RBC microvesiculation under in vitro storage conditions in heterozygous SAO individuals. This study determined the generation of REVs and procoagulant activity during the storage of SAO blood samples in southern Thailand. Venous blood was collected from eight SAO and seven healthy individuals, preserved in citrate phosphate dextrose-adenine 1 (CPDA-1) at 4 °C for 35 days. The absolute numbers of REVs and PS-expressing RBCs were analyzed using flow cytometry. The procoagulant activity of the produced extracellular vesicles was determined by a clotting time assay. The results showed a significant increase in the number of REVs and PS-expressing RBCs in the SAO blood samples. Significantly correlated PS externalization and procoagulant activity were observed in the SAO blood samples. These lines of evidence indicate that the abnormality of the Band 3 protein is possibly involved in aberrant microvesiculation, exerting procoagulant activity in vitro. Increased pools of REV production and abnormal storage lesions in SAO blood samples should be a concern. Notably, the mechanisms underlying membrane vesiculation depend on the extent of blood cell storage under hypothermic conditions.

Impaired trafficking and instability of mutant kidney anion exchanger 1 proteins associated with autosomal recessive distal renal tubular acidosis

BackgroundMutations in solute carrier family 4 member 1 (SLC4A1) encoding anion exchanger 1 (AE1) are the most common cause of autosomal recessive distal renal tubular acidosis (AR dRTA) in Southeast Asians. To explain the molecular mechanism of this disease with hematological abnormalities in an affected family, we conducted a genetic analysis of SLC4A1 and studied wild-type and mutant AE1 proteins expressed in human embryonic kidney 293T (HEK293T) cells.MethodsSLC4A1 mutations in the patient and family members were analyzed by molecular genetic techniques. Protein structure modeling was initially conducted to evaluate the effects of mutations on the three-dimensional structure of the AE1 protein. The mutant kidney anion exchanger 1 (kAE1) plasmid construct was created to study protein expression, localization, and stability in HEK293T cells.ResultsWe discovered that the patient who had AR dRTA coexisting with mild hemolytic anemia carried a novel compound heterozygous SLC4A1 mutations containing c.1199_1225del (p.Ala400_Ala408del), resulting in Southeast Asian ovalocytosis (SAO), and c.1331C > A (p.Thr444Asn). Homologous modeling and in silico mutagenesis indicated that these two mutations affected the protein structure in the transmembrane regions of kAE1. We found the wild-type and mutant kAE1 T444N to be localized at the cell surface, whereas the mutants kAE1 SAO and SAO/T444N were intracellularly retained. The half-life of the kAE1 SAO, T444N, and SAO/T444N mutants was shorter than that of the wild-type protein.ConclusionThese results suggest impaired trafficking and instability of kAE1 SAO/T444N as the likely underlying molecular mechanism explaining the pathogenesis of the novel SLC4A1 compound heterozygous mutation identified in this patient.

Band 3-mediated Plasmodium vivax invasion is associated with transcriptional variation in PvTRAg genes.

The Plasmodium vivax reticulocyte invasion process is still poorly understood, with only a few receptor-ligand interactions identified to date. Individuals with the Southeast Asian ovalocytosis (SAO) phenotype have a deletion in the band 3 protein on the surface of erythrocytes, and are reported to have a lower incidence of clinical P. vivax malaria. Based on this observation, band 3 has been put forward as a receptor for P. vivax invasion, although direct proof is still lacking. In this study, we combined functional ex vivo invasion assays and transcriptome sequencing to uncover a band 3–mediated invasion pathway in P. vivax and potential band 3 ligands. Invasion by P. vivax field isolates was 67%-71% lower in SAO reticulocytes compared with non-SAO reticulocytes. Reticulocyte invasion was decreased by 40% and 27%-31% when blocking with an anti-band 3 polyclonal antibody and a PvTRAg38 peptide, respectively. To identify new band 3 receptor candidates, we mRNA-sequenced schizont-stage isolates used in the invasion assays, and observed high transcriptional variability in multigene and invasion-related families. Transcriptomes of isolates with low or high dependency on band 3 for invasion were compared by differential expression analysis, which produced a list of band 3 ligand candidates with high representation of PvTRAg genes. Our ex vivo invasion assays have demonstrated that band 3 is a P. vivax invasion receptor and confirm previous in vitro studies showing binding between PvTRAg38 and band 3, although the lower and variable inhibition levels observed suggest the involvement of other ligands. By coupling transcriptomes and invasion phenotypes from the same isolates, we identified a list of band 3 ligand candidates, of which the overrepresented PvTRAg genes are the most promising for future research.

Respiratory muscle paralysis in a patient with hypokalemia associated with Southeast Asian ovalocytosis: A case report

The AMJ is a peer-reviewed, triannual health journal published by Anuradhapura Clinical Society (ACS).The Journal strives to be a forum for all health professionals to publish original research and review articles in their area of expertise. The AMJ publishes articles in clinical medicine, public health and health promotion. Our priority is given to manuscripts on health related issues which affects the communities living in rural tropical communities. Established as a journal in 2006 as a publication parallel to ACS annual scientific sessions, the journal was relaunched as a proper journal in 2013. Anuradhapura Medical Journal is a member of COPE and is included on DOAJ.

Detection of Red Blood Cell Membrane Proteins in Myelodysplastic Syndromes Using Eosin-5-Maleimide (EMA) Staining by Flow Cytometry.

Background: Eosin-5-Maleimide (EMA)-based flow cytometry binds to red blood cell (RBC) membrane-associated proteins which can be used to detect red blood cell (RBC) membrane disorders. Myelodysplastic syndromes (MDS) are stem cell disorders resulting in ineffective hematopoiesis which is commonly present with anemia and erythroid dysplasia. Objectives: We aimed to study RBC membrane defects in MDS using flow cytometry for EMA staining. Methods: We enrolled anemic patients who were diagnosed with low-risk MDS (R-IPSS score ≤ 3.5), RBC membrane disorders [hereditary spherocytosis (HS) and Southeast Asian ovalocytosis (SAO)], and normal controls. Complete blood count (CBC) and flow cytometry for EMA staining were performed. Results: There were 16 cases of low-risk MDS, 6 cases of RBC membrane disorders, and 15 control cases. Mean fluorescence intensity (MFI) of EMA binding test in the RBC membrane disorders was significantly lower than controls (17.6 vs. 24.3, p < 0.001), but the EMA binding test in the low-risk MDS was not significantly different than the controls (26.5 vs. 24.3, p = 0.08). Conclusion: the RBC membrane defect in low-risk MDS was not demonstrated as having detection ability using EMA binding test with flow cytometry.

Prevalence and aetiologies of anaemia among first trimester pregnant women in Sri Lanka; the need for revisiting the current control strategies

BackgroundThe Sustainable development goals, which focus strongly on equity, aim to end all forms of malnutrition by 2030. However, a significant cause of intergenerational transfer of malnutrition, anaemia in pregnancy, is still a challenge. It is especially so in the low- and middle-income settings where possible context-specific aetiologies leading to anaemia have been poorly explored. This study explores the prevalence of etiological factors significantly contributing to anaemia in pregnancy in Sri Lanka, a lower-middle-income country with a high prevalence of malnutrition albeit robust public health infrastructure.MethodsAll first-trimester pregnant women registered in the public maternal care programme in the Anuradhapura district from July to September 2019 were invited to participate in Rajarata Pregnancy Cohort (RaPCo). After a full blood count analysis, high-performance liquid chromatography, peripheral blood film examination, serum B12 and folate levels were performed in anaemic participants, guided by an algorithm based on the red cell indices in the full blood count. In addition, serum ferritin was tested in a random subsample of 213 participants. Anaemic women in this subsample underwent B12 and folate testing.ResultsAmong 3127 participants, 14.4% (95%CI 13.2–15.7, n = 451) were anaemic. Haemoglobin ranged between 7.4 to 19.6 g/dl. 331(10.6%) had mild anaemia. Haemoglobin ≥13 g/dl was observed in 39(12.7%). Microcytic, normochromic-normocytic, hypochromic-normocytic and macrocytic anaemia was observed in 243(54%), 114(25.3%), 80(17.8%) and two (0.4%) of full blood counts in anaemic women, respectively. Microcytic anaemia with a red cell count ≥5 * 106 /μl demonstrated a 100% positive predictive value for minor haemoglobinopathies. Minor hemoglobinopathies were present in at least 23.3%(n = 105) of anaemic pregnant women. Prevalence of iron deficiency, B12 deficiency and Southeast Asian ovalocytosis among the anaemic was 41.9% (95%CI 26.4–59.2), 23.8% (95%CI 10.6–45.1) and 0.9% (95%CI 0.3–2.3%), respectively. Folate deficiency was not observed.ConclusionEven though iron deficiency remains the primary cause, minor hemoglobinopathies, B 12 deficiency and other aetiologies substantially contribute to anaemia in pregnancy in this study population. Public health interventions, including screening for minor hemoglobinopathies and multiple micronutrient supplementation in pregnancy, should be considered in the national programme for areas where these problems have been identified.

Etiology and outcome of non-immune hydrops fetalis in relation to gestational age at diagnosis and intrauterine treatment.

To determine the etiology and outcome of non-immune hydrops fetalis (NIHF) according to gestational age at diagnosis and intrauterine treatment. A total of 122 NIHF cases were included. Medical records and ultrasonographic images were reviewed. The etiology, outcome, and intrauterine treatment were assessed. The etiology was determined in 100 cases, and Hb Bart's disease was the most common. Two cases each of homozygous Southeast Asian ovalocytosis (SAO) and hemoglobin Constant Spring (Hb CS) were found. NIHF diagnosed in early gestation (<24 weeks) had a higher rate of chromosomal abnormalities and fetal demise. Intrauterine treatment was given in 18 cases, and 50% had successful live births. Hb Bart's disease was the most common cause of NIHF. SAO and Hb CS were associated with hydrops. NIHF in gestational age <24 weeks was associated with chromosomal abnormalities and fetal demise. Intrauterine treatment should be offered in selected cases.

An incidental finding of a Southeast Asian ovalocytosis patient in Sri Lanka: a case report and review of the literature

Sri Lanka Journal of Medicine is the official journal of the Kandy Society of Medicine. It is a peer-reviewed journal currently published biannually. Original articles, reviews, brief reports, case reports, points of view, and letters to the editor, in all fields of medical science and practice are accepted for publication.The Sri Lanka Journal of Medicine is now indexed in DOAJ

Clinical and Laboratory Features of Hemoglobin La Desirade Variant in Association with Sickle Cell and Alpha Thalassemia Genes.

Abstract &#x0D; Hemoglobin La Desirade (Hb La Desirade) is an unstable hemoglobin variant characterized by amino acid Alanine (Ala) replacing Valine (Val) at position 129 (H7) in the beta chain. Hb La Desirade exhibits a decreased oxygen affinity and normal heme-heme interaction. Interestingly, on analysis by standard electrophoresis, it migrates in the same region as normal HbA, and HbA actually represents a combination of HbA and Hb La Desirade together. This variant was reported as compound heterozygous with other Hemoglobin variants such as HbS, HbC or beta thalassemia, and more recently with Southeast Asian ovalocytosis and Hb Louisville with varying clinical manifestations. Herein, we describe the clinical and laboratory findings in a number of Omani Arab families who presented to our service for various reasons, presenting with Hemoglobin La Desirade with sickle gene and alpha thalassemia. Our patients with Hb La Desirade trait, were clinically asymptomatic with no evidence of anemia. However when it is associated with other abnormal hemoglobin variants such as HbS, leading to sickle/La Desirade compound heterozygosity, there was mild anemia with significant degree of hypochromia and microcytosis. The most striking feature was that the levels of HbS and HbA were almost equal on HPLC, and these cases could be misdiagnosed as sickle cell trait (SCT). However, the levels of Hb S in these compound heterozygotes (40.4-45.9) were higher than normally seen for the diagnosis of SCT in this population.&#x0D;

Perforated Acute Appendicitis with Accidental Mesodiverticular Band in a Southeast Asian Ovalocytosis: An Unfortunate Occurrences

Perforated Acute Appendicitis with Accidental Mesodiverticular Band in a Southeast Asian Ovalocytosis: An Unfortunate Occurrences

Southeast Asian Ovalocytosis and Hemoglobinopathies in Newborns: Prevalence, Molecular, and Hematologic Analyses.

Southeast Asian ovalocytosis (SAO) is an inherited red blood cell (RBC) membrane disorder, whereas hemoglobinopathies are inherited globin gene disorders. In an area where both diseases are prevalent, the interaction between them resulting in variable hematologic parameters can be encountered. However, little is known about the genetic interaction of SAO and thalassemia. We investigated the prevalence of SAO and hemoglobinopathy genotypes among newborns in southern Thailand. This study was carried out on 297 newborns recruited consecutively at Naradhiwas Rajanagarindra Hospital in the south of Thailand. The SAO was identified on blood smear examination and polymerase chain reaction analysis. Thalassemia genotypes were defined. Hematologic parameters and hemoglobin (Hb) profiles were recorded and analyzed. Among 297 newborns, 15 (5.1%) carried SAO, whereas 70 (23.6%) had thalassemia with 15 different thalassemia genotypes. Abnormal Hb including Hb C, Hb Q-Thailand, and Hb D-Punjab were observed in 5 newborns. It was found in the nonthalassemic newborns that RBC count, Hb, and hematocrit of the nonthalassemic newborns with SAO were significantly lower than those without SAO. The same finding was also observed in the thalassemic newborns; RBC count, Hb, and hematocrit of the thalassemic newborns with SAO were significantly lower than those without SAO. However, the mean corpuscular volume, mean corpuscular Hb, and RBC distribution width of the SAO-newborns were significantly higher. Both SAO and hemoglobinopathy genotypes are common in southern Thailand. One should take this into consideration when evaluating neonatal anemia and other hematologic abnormalities. Identification of both genetic defects and long-term monitoring on the clinical outcome of this genetic interaction should be essential to understand the pathogenesis of these common genetic disorders in the region.

A case series of distal renal tubular acidosis, Southeast Asian ovalocytosis and metabolic bone disease

BackgroundFamilial distal renal tubular acidosis (dRTA) associated with mutations of solute carrier family 4 membrane − 1 (SLC4A1) gene could co-exist with red cell membrane abnormality, Southeast Asian ovalocytosis (SAO). Although this association is well described in Southeast Asian countries, it is less frequently found in Sri Lanka.Case presentationWe describe six patients who had dRTA co-existing with SAO. All of them initially presented with severe hypokalemia and paralysis. They presented within a period of six months to the Teaching Hospital Anuradhapura, Sri Lanka.All had metabolic acidosis indicated by low serum bicarbonate. Three of them were having underlying chronic kidney disease as well. Those three patients had mixed high and normal anion gap metabolic acidosis indicated by low delta ratio. In all dRTA was confirmed by presence of normal anion gap, hyperchloraemia, high urine pH and positive urine anion gap.Examination of blood films of all of them revealed presence of stomatocytes and macro-ovalocytosis compatible with SAO.In relation to complications of dRTA, two patients had medullary nephrocalcinosis. Three patients had biochemical evidence of osteomalacia, with two of them having radiological evidence of diffuse osteosclerosis. One patient had secondary hyperparathyroidism and a pathological fracture.ConclusionsErythrocyte in SAO is exceptionally rigid and this abnormality is said to be evolved as it protects against Plasmodium vivax malaria and cerebral malaria cause by Plasmodium falciparum. Although two families of SAO was described earlier, SAO and dRTA combination was reported only once in a patient from Anuradhapura district.Distal renal tubular acidosis, SAO combination and its related complications including nephrocalcinosis, chronic kidney disease and metabolic bone disease was not described in Sri-Lankan literature. This case series emphasize the importance of investigating recurrent/ chronic hypokalemia to diagnose dRTA and its associations, as early correction of acidosis could prevent development of chronic kidney disease and metabolic bone disease.

Clinical Diagnosis of Red Cell Membrane Disorders: Comparison of Osmotic Gradient Ektacytometry and Eosin Maleimide (EMA) Fluorescence Test for Red Cell Band 3 (AE1, SLC4A1) Content for Clinical Diagnosis.

The measurement of band 3 (AE1, SLC4A1, CD233) content of red cells by eosin-5- maleimide (EMA) staining is swiftly replacing conventional osmotic fragility (OF) test as a tool for laboratory confirmation of hereditary spherocytosis across the globe. Our group has systematically evaluated the EMA test as a method to screen for a variety of anemias in the last 10 years, and compared these results to those obtained with the osmotic gradient ektacytometry (osmoscans) which we have used over three decades. Our overall experience allowed us to characterize the distinctive patterns with the two tests in several congenital erythrocyte membrane disorders, such as hereditary spherocytosis (HS), hereditary elliptocytosis (HE), Southeast Asian Ovalocytosis (SAO), hereditary pyropoikilocytosis (HPP) variants, erythrocyte volume disorders, various red cell enzymopathies, and hemoglobinopathies. A crucial difference between the two methodologies is that osmoscans measure red blood cell deformability of the entire sample of RBCs, while the EMA test examines the band 3 content of individual RBCs. EMA content is influenced by cell size as smaller red cells have lower amount of total membrane than larger cells. The SAO mutation alters the EMA binding site resulting in a lower EMA MCF even as the band 3 content itself is unchanged. Thus, EMA scan results should be interpreted with caution and both the histograms and dot plots should be analyzed in the context of the clinical picture and morphology.

Expression of South East Asian Ovalocytic Band 3 Disrupts Erythroblast Cytokinesis and Reticulocyte Maturation.

Southeast Asian Ovalocytosis results from a heterozygous deletion of 9 amino acids in the erythrocyte anion exchange protein AE1 (band 3). The report of the first successful birth of an individual homozygous for this mutation showed an association with severe dyserythropoietic anemia. Imaging of the proband’s erythrocytes revealed the presence of band 3 at their surface, a reduction in Wr(b) antigen expression, and increases in glycophorin C, CD44, and CD147 immunoreactivity. Immunoblotting of membranes from heterozygous Southeast Asian Ovalocytosis red cells showed a quantitative increase in CD44, CD147, and calreticulin suggesting a defect in reticulocyte maturation, as well as an increase in phosphorylation at residue Tyr359 of band 3, and peroxiredoxin-2 at the membrane, suggesting altered band 3 trafficking and oxidative stress, respectively. In vitro culture of homozygous and heterozygous Southeast Asian Ovalocytosis erythroid progenitor cells produced bi- and multi-nucleated cells. Enucleation was severely impaired in the homozygous cells and reduced in the heterozygous cells. Large internal vesicular accumulations of band 3 formed, which co-localized with other plasma membrane proteins and with the autophagosome marker, LC3, but not with ER, Golgi or recycling endosome markers. Immunoprecipitation of band 3 from erythroblast cell lysates at the orthochromatic stage showed increased interaction of the mutant band 3 with heat shock proteins, ubiquitin and cytoskeleton proteins, ankyrin, spectrin and actin. We also found that the mutant band 3 forms a strong interaction with non-muscle myosins IIA and IIB, while this interaction could not be detected in wild type erythroblasts. Consistent with this, the localization of non-muscle myosin IIA and actin was perturbed in some Southeast Asian Ovalocytosis erythroblasts. These findings provide new insights toward understanding in vivo dyserythropoiesis caused by the expression of mutant membrane proteins.

Case report on Southeast Asian ovalocytosis: A patient with type 1 renal tubular acidosis and an asymptomatic patient incidentally found

Two male patients were found to have Southeast Asian ovalocytosis - one incidentally and the other one during the investigations of the aetiology for hypokalemic paralysis. Southeast Asian ovalocytosis is found almost exclusively in Southeast Asia (1, 2). Familial renal tubular acidosis can co-exist with south East Asian ovalocytosis in the same patient (2). Anionexchanger 1 gene AE1 mutation is the underlying pathology and both can originate from the same mutation (2). This can be asymptomatic as in case 1 and can be symptomatic as in case 2. Symptomatic patients need oral potassium and bicarbonate replacement and follow up. After initial clinical assessment and investigations of case 2, he was given intravenous potassium replacement. The correction of metabolic acidosis was made by giving oral sodium bicarbonate 600mg twice daily. Eventually he made full recovery and did not develop further similar episodes.

Blood Cells: Morphology and Clinical Relevance, 2nd edn, G.Gulati and J.Caro, ASCP Press, Chicago, 2019. ISBN 978‐089189‐6234

This book is an annotated atlas, which will have a useful role in diagnostic haematology laboratories. The images are of high quality and are generally taken at a consistent magnification so that they are readily comparable with each other. The book is very up-to-date incorporating, for example, the 2016 World Health Organization Classification of Tumours of Haematopoietic and Lymphoid Tissues. A self-assessment chapter is a useful inclusion, which could be first used either before or after reading the book, depending on the degree of experience of the reader. The annotations of the images are based on the authors’ considerable experience and no references are cited. Occasionally a reference would have been appreciated; for example, what is the evidence that the in vitro phenomenon of platelet satellitism is associated with an increased incidence of thromboembolism? The level of accuracy is high, although I did find two figures with their legends reversed and it is Perls stain not Perl stain. What might be added to a further edition? Circulating tumour cells are mentioned but not illustrated and I could not find a description of South-East Asian ovalocytosis or of the distinctive features of paroxysmal cold haemoglobinuria (the combination of spherocytes, small agglutinates and erythrophagocytosis). But these are mere quibbles. Haematologists and biomedical scientists will appreciate having this book on their laboratory shelves.

Advances in understanding the pathogenesis of red cell membrane disorders

Hereditary erythrocyte membrane disorders are caused by mutations in genes encoding various transmembrane or cytoskeletal proteins of red blood cells. The main consequences of these genetic alterations are decreased cell deformability and shortened erythrocyte survival. Red blood cell membrane defects encompass a heterogeneous group of haemolytic anaemias caused by either (i) altered membrane structural organisation (hereditary spherocytosis, hereditary elliptocytosis, hereditary pyropoikilocytosis and Southeast Asian ovalocytosis) or (ii) altered membrane transport function (overhydrated hereditary stomatocytosis, dehydrated hereditary stomatocytosis or xerocytosis, familial pseudohyperkalaemia and cryohydrocytosis). Herein we provide a comprehensive review of the recent literature on the molecular genetics of erythrocyte membrane defects and their reported clinical consequences. We also describe the effect of low-expression genetic variants on the high inter- and intra-familial phenotype variability of erythrocyte structural defects.