Congenital dyserythropoietic anemias (CDAs) are a heterogeneous group of inherited anemias that affect the normal differentiation–proliferation pathways of the erythroid lineage. They belong to the ...wide group of ineffective erythropoiesis conditions that mainly result in monolinear cytopenia. CDAs are classified into the 3 major types (I, II, III), plus the transcription factor-related CDAs, and the CDA variants, on the basis of the distinctive morphological, clinical, and genetic features. Next-generation sequencing has revolutionized the field of diagnosis of and research into CDAs, with reduced time to diagnosis, and ameliorated differential diagnosis in terms of identification of new causative/modifier genes and polygenic conditions. The main improvements regarding CDAs have been in the study of iron metabolism in CDAII. The erythroblast-derived hormone erythroferrone specifically inhibits hepcidin production, and its role in the mediation of hepatic iron overload has been dissected out. We discuss here the most recent advances in this field regarding the molecular genetics and pathogenic mechanisms of CDAs, through an analysis of the clinical and molecular classifications, and the complications and clinical management of patients. We summarize also the main cellular and animal models developed to date and the possible future therapies.
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Summary
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.
After the first proposed model of the red blood cell membrane skeleton 36 years ago, several additional proteins have been discovered during the intervening years, and their relationship with the ...pathogenesis of the related disorders have been somewhat defined. The knowledge of erythrocyte membrane structure is important because it represents the model for spectrin-based membrane skeletons in all cells and because defects in its structure underlie multiple hemolytic anemias. This review summarizes the main features of erythrocyte membrane disorders, dividing them into structural and altered permeability defects, focusing particularly on the most recent advances. New proteins involved in alterations of the red blood cell membrane permeability were recently described. The mechanoreceptor PIEZO1 is the largest ion channel identified to date, the fundamental regulator of erythrocyte volume homeostasis. Missense, gain-of-function mutations in the PIEZO1 gene have been identified in several families as causative of dehydrated hereditary stomatocytosis or xerocytosis. Similarly, the KCNN4 gene, codifying the so called Gardos channel, has been recently identified as a second causative gene of hereditary xerocytosis. Finally, ABCB6 missense mutations were identified in different pedigrees of familial pseudohyperkalemia. New genomic technologies have improved the quality and reduced the time of diagnosis of these diseases. Moreover, they are essential for the identification of the new causative genes. However, many questions remain to solve, and are currently objects of intensive studies.
The congenital dyserythropoietic anemias (CDAs) are hereditary disorders characterized by distinct morphologic abnormalities of marrow erythroblasts. The unveiling of the genes mutated in the major ...CDA subgroups (I-CDAN1 and II-SEC23B) has now been completed with the recent identification of the CDA III gene (KIF23). KIF23 encodes mitotic kinesin-like protein 1, which plays a critical role in cytokinesis, whereas the cellular role of the proteins encoded by CDAN1 and SEC23B is still unknown. CDA variants with mutations in erythroid transcription factor genes (KLF1 and GATA-1) have been recently identified. Molecular diagnosis of CDA is now possible in most patients.
Hereditary stomatocytoses are a wide class of hemolytic anemias characterized by alterations of ionic flux with increased cation permeability that results in inappropriate shrinkage or swelling of ...the erythrocytes, and water lost or gained osmotically. The last few years have been crucial for new acquisitions in this field in terms of identifying new causative genes and of studying their pathogenetic mechanisms. This review summarizes the main features of erythrocyte membrane transport diseases, dividing them into forms with either isolated erythroid phenotype (nonsyndromic) or extra‐hematological manifestations (syndromic), and focusing particularly on the most recent advances regarding dehydrated forms of hereditary stomatocytosis and familial pseudohyperkalemia.
High-throughput single-cell analysis is a challenging task. Label-free tomographic phase microscopy is an excellent candidate to perform this task. However, in-line tomography is very difficult to ...implement in practice because it requires a complex set-up for rotating the sample and examining the cell along several directions. We demonstrate that by exploiting the random rolling of cells while they are flowing along a microfluidic channel, it is possible to obtain in-line phase-contrast tomography, if smart strategies for wavefront analysis are adopted. In fact, surprisingly,
knowledge of the three-dimensional position and orientation of rotating cells is no longer needed because this information can be completely retrieved through digital holography wavefront numerical analysis. This approach makes continuous-flow cytotomography suitable for practical operation in real-world, single-cell analysis and with a substantial simplification of the optical system; that is, no mechanical scanning or multi-direction probing is required. A demonstration is given for two completely different classes of biosamples: red blood cells and diatom algae. An accurate characterization of both types of cells is reported, despite their very different nature and material content, thus showing that the proposed method can be extended by adopting two alternate strategies of wavefront analysis to many classes of cells.
The cargo receptor NCOA4 mediates autophagic ferritin degradation. Here we show that NCOA4 deficiency in a knockout mouse model causes iron accumulation in the liver and spleen, increased levels of ...transferrin saturation, serum ferritin, and liver hepcidin, and decreased levels of duodenal ferroportin. Despite signs of iron overload, NCOA4-null mice had mild microcytic hypochromic anemia. Under an iron-deprived diet (2–3 mg/kg), mice failed to release iron from ferritin storage and developed severe microcytic hypochromic anemia and ineffective erythropoiesis associated with increased erythropoietin levels. When fed an iron-enriched diet (2 g/kg), mice died prematurely and showed signs of liver damage. Ferritin accumulated in primary embryonic fibroblasts from NCOA4-null mice consequent to impaired autophagic targeting. Adoptive expression of the NCOA4 COOH terminus (aa 239–614) restored this function. In conclusion, NCOA4 prevents iron accumulation and ensures efficient erythropoiesis, playing a central role in balancing iron levels in vivo.
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•Genetic disruption of NCOA4 causes ferritin accumulation in tissues•NCOA4 deficiency blocks iron mobilization from ferritin storage and induces anemia•NCOA4-null mice are hypersensitive to iron overload
NCOA4 is crucial for autophagic ferritin degradation. Bellelli et al. find that genetic disruption of NCOA4 causes ferritin accumulation in tissues and defective iron mobilization from storage. NCOA4-null mice display impaired erythropoiesis associated with microcytic and hypochromic anemia, which is more pronounced in mice fed an iron-depleted diet.
Dehydrated hereditary stomatocytosis (DHS), or xerocytosis, is an autosomal dominant hemolytic anemia. Most patients with DHS carry mutations in the PIEZO1 gene encoding a mechanosensitive cation ...channel. We here demonstrate that patients with DHS have low levels of hepcidin and only a slight increase of ERFE, the erythroid negative regulator of hepcidin. We demonstrated that at the physiological level, PIEZO1 activation induced Ca2+ influx and suppression of HAMP expression in primary hepatocytes. In two hepatic cellular models expressing PIEZO1 WT and two PIEZO1 gain‐of‐function mutants (R2456H and R2488Q), we highlight altered expression of a few genes/proteins involved in iron metabolism. Mutant cells showed increased intracellular Ca2+ compared to WT, which was correlated to increased phosphorylation of ERK1/2, inhibition of the BMP‐SMADs pathway, and suppression of HAMP transcription. Moreover, the HuH7 cells, treated with PD0325901, a potent inhibitor of ERK1/2 phosphorylation, reduced the phosphorylation of ERK1/2 with the consequent increased phosphorylation of SMAD1/5/8, confirming the link between the two pathways. Another “proof of concept” for the mechanism that links PIEZO1 to HAMP regulation was obtained by mimicking PIEZO1 activation by cell Ca2+ overload, by the Ca2+ ionophore A23187. There was strong down‐regulation of HAMP gene expression after this Ca2+ overload. Finally, the inhibition of PIEZO1 by GsMTx4 leads to phenotype rescue. This is the first demonstration of a direct link between PIEZO1 and iron metabolism, which defines the channel as a new hepatic iron metabolism regulator and as a possible therapeutic target of iron overload in DHS and other iron‐loading anemias.
Summary
Guidelines on hereditary spherocytosis (HS) published in 2004 (Bolton‐Maggs et al, 2004) are here replaced to reflect changes in current opinion on the surgical management, (particularly the ...indications for concomitant splenectomy with cholecystectomy in children with mild HS, and concomitant cholecystectomy with splenectomy in those with asymptomatic gallstones). Further potential long term hazards of splenectomy are now recognised. Advances have been made in our understanding of the biochemistry of the red cell membrane which underpins the choice of tests. Biochemical assays of membranes proteins and genetic analysis may be indicated (rarely) to diagnose atypical cases. The diagnostic value of the eosin‐5‐maleimide (EMA) binding test has been validated in a number of studies with understanding of its limitations.
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