Characterization of hereditary red blood cell membranopathies using combined targeted next-generation sequencing and osmotic gradient ektacytometry

Understanding Rare Anemias: Emerging Frontiers for Diagnosis and Treatment

Background-This review provides a comprehensive overview of rare anemias, emphasizing their hereditary and acquired causes, diagnostic advancements, and evolving treatment strategies. It outlines the significance of rare anemias within public health, historical challenges in recognition and treatment, and the role of European initiatives like ENERCA and EuroBloodNet in advancing care. Content-This document discusses diagnostic technologies like next-generation sequencing and the impact of artificial intelligence, alongside the promising avenues of gene therapy, targeted drug treatments, and stem cell transplantation. It underscores the importance of a patient-tailored approach, advances in diagnostic tools, and the necessity for continued research, patient advocacy, and international collaboration to improve outcomes for individuals with rare anemias.

Hereditary Spherocytosis: Can Next-Generation Sequencing of the Five Most Frequently Affected Genes Replace Time-Consuming Functional Investigations?

Congenital defects of the erythrocyte membrane are common in northern Europe and all over the world. The resulting diseases, for example, hereditary spherocytosis (HS), are often underdiagnosed, partly due to their sometimes mild and asymptomatic courses. In addition to a broad clinical spectrum, this is also due to the occasionally complex diagnostics that are not available to every patient. To test whether next-generation sequencing (NGS) could replace time-consuming spherocytosis-specific functional tests, 22 consecutive patients with suspected red cell membranopathy underwent functional blood tests. We were able to identify the causative genetic defect in all patients with suspected HS who underwent genetic testing (n = 17). The sensitivity of the NGS approach, which tests five genes (ANK1 (gene product: ankyrin1), EPB42 (erythrocyte membrane protein band4.2), SLC4A1 (band3), SPTA1 (α-spectrin), and SPTB (β-spectrin)), was 100% (95% confidence interval: 81.5-100.0%). The major advantage of genetic testing in the paediatric setting is the small amount of blood required (<200 µL), and compared to functional assays, sample stability is not an issue. The combination of medical history, basic laboratory parameters, and an NGS panel with five genes is sufficient for diagnosis in most cases. Only in rare cases, a more comprehensive functional screening is required.

Genetic mutation analysis of hereditary spherocytosis in Guangxi Zhuang Autonomous Region

Hereditary spherocytosis (HS) is a common, hereditary hemolytic anemia (HHA) that is attributed to the disturbance of five erythrocyte membrane proteins. HS is also common in Guangxi, China. Target region capture high-throughput sequencing technology was used to analyze genetic mutations found in HS patients. Pedigree analysis was also performed, in some cases, to provide an optimized approach for the etiological diagnosis of complex, hereditary hemolytic anemia. Blood samples from the probands and their families were assessed by laboratory tests, target region capture high-throughput sequencing technology, and Sanger sequencing. We detected 79 HS patients from 37 unrelated families. The mutations observed in these patients were found mainly in four HS-related genes. These included SLC4A1, which was mutated in 31.65% of patients (25/79), SPTA1 (30.78% (24/79)), EPB42 (6.33% (5/79)), and SPTB (5.06% (4/79)). Composite genotype was observed in 26.58% (21/79) of patients and included mutations in two or more HS-related genes or mutations in HS-related genes combined with thalassemia or G6PD deficiency. No significant differences in clinical symptoms were found among patients of various genotypes except total bilirubin. Mean reticulocyte volume (MRV) and mean sphered cell volume (MSCV) of the composite genotype were significantly different from other groups. A total of 28 mutation types were found in HS-related genes. Using high-throughput sequencing technology, we also found some cases that had been misdiagnosed. MRV and MSCV are more significant in compound mutations as sensitive determinants of HS. High-throughput sequencing technology can be used to provide a more effective etiological diagnostic method for HS, with high efficiency and specificity.

Variant spectrum of PIEZO1 and KCNN4 in Japanese patients with dehydrated hereditary stomatocytosis

Hereditary stomatocytosis (HSt) is a type of congenital hemolytic anemia caused by abnormally increased cation permeability of erythrocyte membranes. Dehydrated HSt (DHSt) is the most common subtype of HSt and is diagnosed based on clinical and laboratory findings related to erythrocytes. PIEZO1 and KCNN4 have been recognized as causative genes, and many related variants have been reported. We analyzed the genomic background of 23 patients from 20 Japanese families suspected of having DHSt using a target capture sequence and identified pathogenic/likely pathogenic variants of PIEZO1 or KCNN4 in 12 families.

Clinical utility of targeted next-generation sequencing panel in routine diagnosis of hereditary hemolytic anemia: A national reference laboratory experience

INTRODUCTION

Hereditary hemolytic anemias (HHA) comprise a heterogeneous group of disorders resulting from defective red blood cell (RBC) cytoskeleton, RBC enzyme deficiencies, and hemoglobin (Hb) synthesis disorders such as thalassemia or sideroblastic anemia.

MATERIALS AND METHODS

Our hemolytic anemia diagnostic next-generation sequencing (NGS) panel includes 28 genes encoding RBC cytoskeletal proteins, membrane transporter, RBC enzymes, and certain bilirubin metabolism genes. The panel covers the complete coding region of these genes, splice junctions, and, wherever appropriate, deep intronic or regulatory regions are also included. Four hundred fifty-six patients with unexplained hemolytic anemia were evaluated using our NGS panel between 2015 and 2019.

RESULTS

We identified pathogenic/likely pathogenic variants in 111/456 (24%) patients that were responsible for the disease phenotype (e.g., moderate to severe hemolytic anemia and hyperbilirubinemia). Approximately 40% of the mutations were novel. As expected, 45/456 (10%) patients were homozygous for the promoter polymorphism in the UGT1A1 gene, A(TA)₇ TAA (UGT1A1*28). 8/45 homozygous UGT1A1*28 cases were associated with additional pathogenic mutations causing hemolytic anemia, likely exacerbating hyperbilirubinemia. The most common mutated genes were membrane cytoskeleton genes SPTA1, and SPTB, followed by PKLR. Complex interactions between SPTA1 low expression alleles, alpha-LELY and alpha-LEPRA alleles, and intragenic SPTA1 variants were associated with hereditary pyropoikilocytosis and autosomal recessive hereditary spherocytosis in 23/111 patients.

CONCLUSIONS

Our results demonstrate that hemolytic anemia is underscored by complex molecular interactions of previously known and novel mutations in RBC cytoskeleton/enzyme genes, and therefore, NGS should be considered in all patients with clinically unexplained hemolytic anemia and in neonates with hyperbilirubinemia. Moreover, low expression alleles alpha-LELY and alpha-LEPRA should be included in all targeted HHA panels.

Five Years' Experience with Gene Panel Sequencing in Hereditary Hemolytic Anemia Screened by Routine Peripheral Blood Smear Examination

BACKGROUND

Hereditary hemolytic anemia (HHA) is defined as a group of heterogeneous and rare diseases caused by defects of red blood cell (RBC) metabolism and RBC membrane, which leads to lysis or premature clearance. The aim of this study was to investigate individuals with HHA for potential disease-causing variants in 33 genes reported to be associated with HHA.

METHODS

A total of 14 independent individuals or families diagnosed with suspected HHA, and in particular, RBC membranopathy, RBC enzymopathy, and hemoglobinopathy, were collected after routine peripheral blood smear testing. A custom designed panel, including the 33 genes, was performed using gene panel sequencing on the Ion Torrent PGM™ Dx System. The best candidate disease-causing variants were confirmed by Sanger sequencing.

RESULTS

Several variants of the HHA-associated genes were detected in 10 out of 14 suspected HHA individuals. After excluding those variants predicted to be benign, 10 pathogenic variants and 1 variant of uncertain significance (VUS) were confirmed in 10 individuals with suspected HHA. Of these variants, the p.Trp704Ter nonsense variant of EPB41 and missense p.Gly151Asp variant of SPTA1 were identified in two out of four hereditary elliptocytoses. The frameshift p.Leu884GlyfsTer27 variant of ANK1, nonsense p.Trp652Ter variant of the SPTB, and missense p.Arg490Trp variant of PKLR were detected in all four hereditary spherocytosis cases. Missense p.Glu27Lys, nonsense p.Lys18Ter variants, and splicing errors such as c.92 + 1G > T and c.315 + 1G > A within HBB were identified in four beta thalassemia cases.

CONCLUSIONS

This study provides a snapshot of the genetic alterations in a cohort of Korean HHA individuals and demonstrates the clinical utility of using gene panels in HHA. Genetic results can provide precise clinical diagnosis and guidance regarding medical treatment and management for some individuals.

Case report: Variants in the ERCC4 gene as a rare cause of cerebellar ataxia with chorea

Variants in the ERCC4 gene have been described to be associated with the following autosomal recessive diseases: xeroderma pigmentosum group F (XPF), xeroderma pigmentosum type F/Cockayne syndrome (XPF/CS), Fanconi anemia complementation group Q (FANCQ), and XFE progeroid syndrome (XFEPS). In this paper, we present a case of a 53-year-old Caucasian female patient with rare variants in the ERCC4 gene. When she was 42 years old, falls and loss of balance occurred. At the age of 48, involuntary, uncoordinated movements of the upper limbs and head, tongue stereotypes (licking and extending movements), speech problems (dysarthria), memory deterioration, and hearing loss occurred. Since childhood, she has shown hypersensitivity to UV radiation. The neurological examination revealed chorea syndrome, cerebellar ataxia, dysarthria, and bilateral hearing loss. She has numerous pigmented lesions on the skin. Brain MRI demonstrated massive cortico-subcortical atrophy. The neuropsychological examination revealed dysfunctions in the executive domain in terms of attention, working memory, organizing, and planning activities. The genetic diagnostics was performed which excluded spinocerebellar ataxia types 1, 2, 3, 6, and 17, Huntington's disease, and FMR1 premutation. In the genetic analysis of next-generation sequencing (NGS), two variants: c.2395C > T and c.1349G > A in the ERCC4 gene were identified in a heterozygote configuration. So far, a few cases of ERCC4 gene variants, which are associated with nucleotide excision repair pathways, have been described in connection with symptoms of cerebellar ataxia. In patients with ERCC4 biallelic variants, the adult neurological phenotype can sometimes be the first symptom and reason for access to genetic testing. The aforementioned case highlights the occurrence of rare genetic causes of progressive neurodegenerative diseases in adults, especially with the spectrum of autosomal recessive nucleotide excision repair pathway disorders (NERDs).

Effect of primary lesions in cytoskeleton proteins on red cell membrane stability in patients with hereditary spherocytosis

We investigated by targeted next generation sequencing the genetic bases of hereditary spherocytosis in 25 patients and compared the molecular results with the biochemical lesion of RBC membrane obtained by SDS-PAGE analysis. The HS diagnosis was based on available guidelines for diagnosis of congenital hemolytic anemia, and patients were selected because of atypical clinical presentation or intra-family variability, or because presented discrepancies between laboratory investigation and biochemical findings. In all patients but 5 we identified pathogenic variants in SPTA1, SPTB, ANK1, SLC4A1, EPB42 genes able to justify the clinical phenotype. Interestingly, a correspondence between the biochemical lesion and the molecular defect was identified in only 11/25 cases, mostly with band 3 deficiency due to SLC4A1 mutations. Most of the mutations in SPTB and ANK1 gene didn’t hesitate in abnormalities of RBC membrane protein; conversely, in two cases the molecular lesion didn’t correspond to the biochemical defect, suggesting that a mutation in a specific cytoskeleton protein may result in a more complex RBC membrane damage or suffering. Finally, in two cases the HS diagnosis was maintained despite absence of both protein defect and molecular lesion, basing on clinical and family history, and on presence of clear laboratory markers of HS. The study revealed complex relationships between the primary molecular lesion and the final effect in the RBC membrane cytoskeleton, and further underlines the concept that there is not a unique approach to the diagnosis of HS.

Haemoglobin Bristol-Alesha in a child with non-spherocytic severe haemolytic anaemia and marked anisochromic poikilocytosis with basophilic stippling and amorphous intracellular content

Here we describe a retrospective study of a 10-year-old girl, adopted from India, and referred to the Rare Anemias Unit for the diagnosis of a severe haemolytic anaemia of unknown etiology. Blood film examination revealed markedly abnormal red cell morphology characterised by a mixture of very pale (hypochromic) cells with basophilic stippling and macrocytic cells containing coarse basophilic dots and an amorphous material of unknown origin. With a presumptive diagnosis of pyruvate kinase deficiency (PK), the patient had been splenectomised at 7 years of age with a partial recovery of the anaemia and a decrease of the blood transfusion rate. Three years after splenectomy, the patient was revisited and a haemoglobin stability test was performed with a positive result. Accordingly, the correct diagnosis was an unstable haemoglobinopathy. Targeted next generation sequencing (t-NGS) revealed haemoglobin Bristol-Alesha, a hyper unstable haemoglobinopathy associated with severe haemolytic anaemia. Since unstable haemoglobins do not necessarily have specific red cell morphological abnormalities, our findings reinforce the need to include, the haemoglobin stability test, in the first diagnostic approach of hemolytic anaemias of unknown etiology.

Concomitant Hereditary Spherocytosis and Pyruvate Kinase Deficiency in a Spanish Family with Chronic Hemolytic Anemia: Contribution of Laser Ektacytometry to Clinical Diagnosis

Background: Hereditary spherocytosis (HS) and pyruvate kinase deficiency (PKD) are the most common causes of hereditary chronic hemolytic anemia. Here, we describe clinical and genetic characteristics of a Spanish family with concomitant β-spectrin (SPTB) c.647G>A variant and pyruvate kinase (PKLR) c.1706G>A variant. Methods: A family of 11 members was studied. Hematological investigation, hemolysis tests, and specific red cell studies were performed in all family members, according to conventional procedures. An ektacytometric study was performed using the osmoscan module of the Lorca ektacytometer (MaxSis. RR Mechatronics). The presence of the SPTB and PKLR variants was confirmed by t-NGS. Results: The t-NGS genetic characterization of the 11 family members showed the presence of a heterozygous mutation for the β-spectrin (SPTB; c.647G>A) in seven members with HS, three of them co-inherited the PKLR variant c.1706G>A. In the remaining four members, no gene mutation was found. Ektacytometry allowed a clear diagnostic orientation of HS, independently from the PKLR variant. Conclusions: This family study allows concluding that the SPTB mutation, (c.647G>A) previously described as likely pathogenic (LP), should be classified as pathogenic (P), according to the recommendations for pathogenicity of the American College of Medical Genetics and the Association for Molecular Pathology. In addition, after 6 years of clinical follow-up of the patients with HS, it can be inferred that the chronic hemolytic anemia may be attributable to the SPTB mutation only, without influence of the concomitant PKLR. Moreover, only the family members with the SPTB mutation exhibited an ektacytometric profile characteristic of HS.

Microfluidics Approach to the Mechanical Properties of Red Blood Cell Membrane and Their Effect on Blood Rheology

In this article, we describe the general features of red blood cell membranes and their effect on blood flow and blood rheology. We first present a basic description of membranes and move forward to red blood cell membranes’ characteristics and modeling. We later review the specific properties of red blood cells, presenting recent numerical and experimental microfluidics studies that elucidate the effect of the elastic properties of the red blood cell membrane on blood flow and hemorheology. Finally, we describe specific hemorheological pathologies directly related to the mechanical properties of red blood cells and their effect on microcirculation, reviewing microfluidic applications for the diagnosis and treatment of these diseases.

A novel SPTB mutation causes hereditary spherocytosis via loss-of-function of β-spectrin

Hereditary spherocytosis (HS) is the most frequently observed chronic non-immune hemolytic disorder caused by altered red cell membrane function. SPTB gene mutation is one of the most common causes of HS, but pathogenicity analyses and pathogenesis research on these mutations have not been widely conducted. In this study, a novel heterozygous mutation of the SPTB gene (c.1509_1518del; p.K503Nfs*67) was identified in a Chinese family with HS by whole-exome sequencing (WES) and was then confirmed by Sanger sequencing. Next, the pathogenicity and pathogenesis of this mutation were studied using peripheral blood. We found that this mutation disrupted the synthesis and localization of β-spectrin and weakened the interaction between β-spectrin and ankyrin, which may be caused by the nonsense-mediated mRNA degradation pathway. These changes lead to the transformation of discoid erythrocytes into spherocytes, resulting in hemolytic anemia. Therefore, we classified this novel mutation as a pathogenic mutation leading to loss-of-function of β-spectrin. It would be insightful to perform the same mutation test and to provide genetic counseling to other relatives of the proband. Our study increases the current understanding of the molecular mechanisms related to mutations in SPTB.

Red cell ektacytometry in two patients with chronic hemolytic anemia and three new α-spectrin variants

Red blood cell (RBC) morphology is, in general, the key diagnostic feature for hereditary spherocytosis (HS) and hereditary elliptocytosis (HE). However, in hereditary pyropoikilocytosis (HPP), the severe clinical form of HE, the morphological diagnosis is difficult due to the presence of a RBC morphological picture characterized by a mixture of elliptocytes, spherocytes, tear-drop cells, and fragmented cells. This difficulty increases in new-borns and/or patients requiring frequent transfusions, making impossible the prediction of the disease course or its severity. Recently, it has been demonstrated that the measurement of osmotic gradient ektacytometry (OGE), using a laser-assisted optical rotational ektacytometer LoRRca (MaxSis, RR Mechatronics), allows a clear differentiation between HS and HE, where the truncated osmoscan curve reflects the inability of the already elliptical cells to deform further under shear stress in the face of hypotonicity. In HPP, however, the RBCs appear to have a significantly decreased ability to maintain deformability in these conditions, and the classical trapezoidal profile of HE is less evident or indistinguishable from HS. Here, two unrelated patients with hereditary hemolytic anemia (HHA) due to HPP and HS, respectively, are described with the joint inheritance of a complex set of five genetic defects. Two of these defects are novel alpha-spectrin gene (SPTA1) variants, one is a microdeletion that removes the entire SPTA1 gene, and two are well-known low-expression polymorphic alleles: α-LELY and α-LEPRA. In the HPP patient (ID1), with many circulating spherocytes, the interactions between the two SPTA1 gene variants may lead, in addition to an elongation defect (elliptocytes), to a loss of membrane stability and vesiculation (spherocytes), and RBCs appear to have a significantly decreased ability to maintain deformability in hypotonic conditions. Due to this, the classical trapezoidal profile of HE may become less evident or indistinguishable from HS. The second patient (ID2) was a classical severe form of HS with the presence of more than 20% of spherocytes and few pincered cells. The severity of clinical manifestation is due to the coinheritance of a microdeletion of chromosome 1 that removes the entire SPTA1 gene with a LEPRA SPTA1 variant in trans. The diagnostic interest of both observations is discussed.

Facilitating EMA binding test performance using fluorescent beads combined with next‐generation sequencing

The eosin‐5′‐maleimide (EMA) binding test is widely used as diagnostic test for hereditary spherocytosis (HS), one of the most common haemolytic disorders in Caucasian populations. We recently described the advantages of replacing the use of healthy control blood samples with fluorescent beads in a modified EMA binding assay. In this study we further explore this novel approach. We performed targeted next‐generation sequencing, modified EMA binding test and osmotic gradient ektacytometry on consecutive individuals referred to our laboratory on the suspicion of HS. In total, 33 of 95 carried a (likely) pathogenic variant, and 24 had variants of uncertain significance (VUS). We identified a total 79 different (likely) pathogenic variants and VUS, including 43 novel mutations. Discarding VUS and recessive mutations in STPA1, we used the occurrence of (likely) pathogenic variants to generate a diagnostic threshold for our modified EMA binding test. Twenty‐one of 23 individuals with non‐SPTA1 (likely) pathogenic variants had EMA ≥ 43.6 AU, which was the optimal threshold in receiver operating characteristic (ROC) analysis. Accuracy was excellent at 93.4% and close to that of osmotic gradient ektacytometry (98.7%). In conclusion, we were able to simplify the EMA‐binding test by using rainbow beads as reference and (likely) pathogenic variants to define an accurate cut‐off value.

Targeted Next Generation Sequencing and Diagnosis of Congenital Hemolytic Anemias: A Three Years Experience Monocentric Study

Congenital hemolytic anemias (CHAs) are heterogeneous and rare disorders caused by alterations in structure, membrane transport, metabolism, or red blood cell production. The pathophysiology of these diseases, in particular the rarest, is often poorly understood, and easy-to-apply tools for diagnosis, clinical management, and patient stratification are still lacking. We report the 3-years monocentric experience with a 43 genes targeted Next Generation Sequencing (t-NGS) panel in diagnosis of CHAs; 122 patients from 105 unrelated families were investigated and the results compared with conventional laboratory pathway. Patients were divided in two groups: 1) cases diagnosed with hematologic investigations to be confirmed at molecular level, and 2) patients with unexplained anemia after extensive hematologic investigation. The overall sensitivity of t-NGS was 74 and 35% for families of groups 1 and 2, respectively. Inside this cohort of patients we identified 26 new pathogenic variants confirmed by functional evidence. The implementation of laboratory work-up with t-NGS increased the number of diagnoses in cases with unexplained anemia; cytoskeleton defects are well detected by conventional tools, deserving t-NGS to atypical cases; the diagnosis of Gardos channelopathy, some enzyme deficiencies, familial siterosterolemia, X-linked defects in females and other rare and ultra-rare diseases definitely benefits of t-NGS approaches.

Rare anemias in adolescents

Anemia can be the consequence of a single disease or an expression of external factors mainly nutritional deficiencies. Genetic issues are important in the primary care of adolescents because a genetic diagnosis may not be made until adolescence when the teenager presents with the first signs or symptoms of the condition. This situation is relatively frequent for rare anemias (RA) an important, and relatively heterogeneous group of rare diseases (RD) where anemia is the first and most relevant clinical manifestation of the disease. RA are characterized by their low prevalence (< 1 per 10,000 individuals), and, in some cases, by their complex mechanism. For these reasons, RA are little known, even among health professionals, and patients tend to remain undiagnosed or misdiagnosed for long periods of time, making it impossible to know the prognosis of the disease or to carry out genetic counseling for future pregnancies. Since this situation is an important cause of anxiety for both adolescent patients and their families, the physician's knowledge of the natural history of a genetic disease will be the key factor for the anticipatory guidance for diagnosis and clinical follow-up. RA can be due to three primary causes: 1.Bone marrow erythropoietic defects, 2. Excessive destruction of mature red blood cells (hemolysis), and 3. Blood loss (bleeding). More than 80% of RAs are hereditary, and about 20% remain undiagnosed but when their first clinical manifestations appear during childhood or adolescence, they are frequently misdiagnosed with iron deficiency. For this reason, RA are today an important clinical and social health problem worldwide.