Diagnosis and treatment of sideroblastic anemias: from defective heme synthesis to abnormal RNA splicing

Hematologic Manifestations in Primary Mitochondrial Diseases

Primary mitochondrial disorders (PMDs) are known for their pleiotropic manifestations in humans, affecting almost any organ or system at any time. Hematologic manifestations, such as cytopenias and sideroblastic anemia, occur in 10% to 30% of patients with confirmed PMDs. These can be the initial presenting features or complications that develop over time. Surveillance for these manifestations allows for prompt identification and treatment. This article provides an overview of the pathophysiology underpinning the hematologic effects of mitochondrial dysfunction, discussing the 3 key roles of the mitochondria in hematopoiesis: providing energy for cell differentiation and function, synthesizing heme, and generating iron-sulfur clusters. Subsequently, the diagnosis and management of mitochondrial disorders are discussed, focusing on hematologic manifestations and the specific conditions commonly associated with them. Through this, we aimed to provide a concise point of reference for those considering a mitochondrial cause for a patient's hematologic abnormality, or for those considering a hematologic manifestation in a patient with known or suspected mitochondrial disease.

Exploring Nanocarriers as Treatment Modalities for Skin Cancer

Cancer is a progressive disease of multi-factorial origin that has risen worldwide, probably due to changes in lifestyle, food intake, and environmental changes as some of the reasons. Skin cancer can be classified into melanomas from melanocytes and nonmelanoma skin cancer (NMSC) from the epidermally-derived cell. Together it constitutes about 95% of skin cancer. Basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (CSCC) are creditworthy of 99% of NMSC due to the limited accessibility of conventional formulations in skin cancer cells of having multiple obstacles in treatment reply to this therapeutic regime. Despite this, it often encounters erratic bioavailability and absorption to the target. Nanoparticles developed through nanotechnology platforms could be the better topical skin cancer therapy option. To improve the topical delivery, the nano-sized delivery system is appropriate as it fuses with the cutaneous layer and fluidized membrane; thus, the deeper penetration of therapeutics could be possible to reach the target spot. This review briefly outlooks the various nanoparticle preparations, i.e., liposomes, niosomes, ethosomes, transferosomes, transethosomes, nanoemulsions, and nanoparticles technologies tested into skin cancer and impede their progress tend to concentrate in the skin layers. Nanocarriers have proved that they can considerably boost medication bioavailability, lowering the frequency of dosage and reducing the toxicity associated with high doses of the medication.

SF3B1 mutations in myelodysplastic syndromes: A potential therapeutic target for modulating the entire disease process

Myelodysplastic syndromes (MDS) are clonal hematologic malignancies characterized by ineffective hematopoiesis and dysplasia of the myeloid cell lineage and are characterized by peripheral blood cytopenia and an increased risk of transformation to acute myeloid leukemia (AML). Approximately half of the patients with MDS have somatic mutations in the spliceosome gene. Splicing Factor 3B Subunit 1A (SF3B1), the most frequently occurring splicing factor mutation in MDS is significantly associated with the MDS-RS subtype. SF3B1 mutations are intimately involved in the MDS regulation of various pathophysiological processes, including impaired erythropoiesis, dysregulated iron metabolism homeostasis, hyperinflammatory features, and R-loop accumulation. In the fifth edition of the World Health Organization (WHO) classification criteria for MDS, MDS with SF3B1 mutations has been classified as an independent subtype, which plays a crucial role in identifying the disease phenotype, promoting tumor development, determining clinical features, and influencing tumor prognosis. Given that SF3B1 has demonstrated therapeutic vulnerability both in early MDS drivers and downstream events, therapy based on spliceosome-associated mutations is considered a novel strategy worth exploring in the future.

Iron metabolism: pathways and proteins in homeostasis

Iron is essential to human survival. The biological role and trafficking of this trace essential inorganic element which is also a potential toxin is constantly being researched and unfolded. Vital for oxygen transport, DNA synthesis, electron transport, neurotransmitter biosynthesis and present in numerous other heme and non-heme enzymes the physiological roles are immense. Understanding the molecules and pathways that regulate this essential element at systemic and cellular levels are of importance in improving therapeutic strategies for iron related disorders. This review highlights the progress in understanding the metabolism and trafficking of iron along with the pathophysiology of iron related disorders.

Congenital sideroblastic anemia model due to ALAS2 mutation is susceptible to ferroptosis

X-linked sideroblastic anemia (XLSA), the most common form of congenital sideroblastic anemia, is caused by a germline mutation in the erythroid-specific 5-aminolevulinate synthase (ALAS2) gene. In XLSA, defective heme biosynthesis leads to ring sideroblast formation because of excess mitochondrial iron accumulation. In this study, we introduced ALAS2 missense mutations on human umbilical cord blood-derived erythroblasts; hereafter, we refer to them as XLSA clones. XLSA clones that differentiated into mature erythroblasts showed an increased frequency of ring sideroblast formation with impaired hemoglobin biosynthesis. The expression profiling revealed significant enrichment of genes involved in ferroptosis, which is a form of regulated cell death induced by iron accumulation and lipid peroxidation. Notably, treatment with erastin, a ferroptosis inducer, caused a higher proportion of cell death in XLSA clones. XLSA clones exhibited significantly higher levels of intracellular lipid peroxides and enhanced expression of BACH1, a regulator of iron metabolism and potential accelerator of ferroptosis. In XLSA clones, BACH1 repressed genes involved in iron metabolism and glutathione synthesis. Collectively, defective heme biosynthesis in XLSA clones could confer enhanced BACH1 expression, leading to increased susceptibility to ferroptosis. The results of our study provide important information for the development of novel therapeutic targets for XLSA.

Coordinated missplicing of TMEM14C and ABCB7 causes ring sideroblast formation in SF3B1-mutant myelodysplastic syndrome

SF3B1 splicing factor mutations are near-universally found in myelodysplastic syndromes (MDS) with ring sideroblasts (RS), a clonal hematopoietic disorder characterized by abnormal erythroid cells with iron-loaded mitochondria. Despite this remarkably strong genotype-to-phenotype correlation, the mechanism by which mutant SF3B1 dysregulates iron metabolism to cause RS remains unclear due to an absence of physiological models of RS formation. Here, we report an induced pluripotent stem cell model of SF3B1-mutant MDS that for the first time recapitulates robust RS formation during in vitro erythroid differentiation. Mutant SF3B1 induces missplicing of ∼100 genes throughout erythroid differentiation, including proposed RS driver genes TMEM14C, PPOX, and ABCB7. All 3 missplicing events reduce protein expression, notably occurring via 5' UTR alteration, and reduced translation efficiency for TMEM14C. Functional rescue of TMEM14C and ABCB7, but not the non-rate-limiting enzyme PPOX, markedly decreased RS, and their combined rescue nearly abolished RS formation. Our study demonstrates that coordinated missplicing of mitochondrial transporters TMEM14C and ABCB7 by mutant SF3B1 sequesters iron in mitochondria, causing RS formation.

A novel ENU-induced Cpox mutation causes microcytic hypochromic anemia in mice

Mouse models of red blood cell abnormalities are important for understanding the underlying molecular mechanisms of human erythrocytic diseases. DBA.B6-Mha (Microcytic hypochromic anemia) congenic mice were generated from the cross between N-ethyl-N-nitrosourea (ENU)-mutagenized male C57BL/6J and female DBA/2J mice as part of the RIKEN large-scale ENU mutagenesis project. The mice were established by backcrossing with DBA/2J mice for more than 20 generations. These mice showed autosomal-dominant microcytic hypochromic anemia with decreased mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) levels and increased red blood cell distribution width (RDW) and plasma ferritin levels. Linkage analysis indicated that the Mha locus was located within an interval of approximately 1.95-Mb between D16Nut1 (58.35 Mb) and D16Mit185 (60.30 Mb) on mouse chromosome 16. Mutation analysis revealed that DBA.B6-Mha mice had a point mutation (c.921-2A>G) at the acceptor site of intron 4 in the coproporphyrinogen oxidase (Cpox) gene, a heme-synthesizing gene. RT-PCR revealed that the Cpox mRNA in DBA.B6-Mha mice caused splicing errors. Our results suggest that microcytic hypochromic anemia in DBA.B6-Mha mice is owing to impaired heme synthesis caused by splice mutations in Cpox. Therefore, the DBA.B6-Mha mice may be used to elucidate the molecular mechanisms underlying microcytic hypochromic anemia caused by mutations in Cpox. Although low MCV levels are known to confer malarial resistance to the host, there were no marked changes in the susceptibility of DBA.B6-Mha mice to rodent malarial (Plasmodium yoelii 17XL) infection.

Ineffective erythropoiesis and its treatment

The erythroid marrow and circulating red blood cells (RBCs) are the key components of the human erythron. Abnormalities of the erythron that are responsible for anemia can be distinguished into 3 major categories, that is, erythroid hypoproliferation, ineffective erythropoiesis, and peripheral hemolysis. Ineffective erythropoiesis is characterized by erythropoietin-driven expansion of early-stage erythroid precursors, associated with apoptosis of late-stage precursors. This mechanism is primarily responsible for anemia in inherited disorders like β-thalassemia, inherited sideroblastic anemias, and congenital dyserythropoietic anemias, as well as in acquired conditions like some subtypes of myelodysplastic syndromes (MDS). The inherited anemias due to ineffective erythropoiesis are also defined as iron loading anemias because of the associated parenchymal iron loading caused by the release of erythroid factors that suppress hepcidin production. Novel treatments specifically targeting ineffective erythropoiesis are being developed. Iron restriction through enhancement of hepcidin activity or inhibition of ferroportin function has been shown to reduce ineffective erythropoiesis in murine models of β-thalassemia. Luspatercept is a TGF-β ligand trap that inhibits SMAD2/3 signaling. Based on pre-clinical and clinical studies, this compound is now approved for the treatment of anemia in adult patients with β-thalassemia who require regular RBC transfusions. Luspatercept is also approved for the treatment of transfusion-dependent anemia in patients with MDS with ring sideroblasts, most of whom carry a somatic SF3B1mutation. While long-term efficacy and safety of luspatercept need to be evaluated both in β-thalassemia and MDS, defining the molecular mechanisms of ineffective erythropoiesis in different disorders might allow the discovery of new effective compounds.

A hemizygous p.R204Q mutation in the ALAS2 gene underlies X-linked sideroblastic anemia in an adult Chinese Han man

Background

X-linked sideroblastic anemia (XLSA) is the most common form of congenital sideroblastic anemia (CSA), and is associated with the mutations in the 5-aminolevulinate synthase 2 (ALAS2). The genetic basis of more than 40% of CSA cases remains unknown.

Methods

A two-generation Chinese family with XLSA was studied by next-generation sequencing to identify the underlying CSA-related mutations.

Results

In the study, we identified a missense ALAS2 R204Q mutation in a hemizygous Chinese Han man and in his heterozygous daughter. The male proband presented clinical manifestations at 38 years old and had a good response to pyridoxine.

Conclusions

XLSA, as a hereditary disease, can present clinical manifestations later in lives, for adult male patients with ringed sideroblasts and hypochromic anemia, it should be evaluated with gene analyses to exclude CSA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-021-00950-x.

Movement Disorders and Hematologic Diseases

Background

Movement disorders can be associated with or caused by hematological abnormalities. The objective of this review is to highlight features that will aid in the clinician's recognition and treatment of these disorders.

Methods

MESH terms relevant to movement disorders and hematologic diseases were searched to identify conditions included in this narrative, educational review.

Results

Several conditions were identified, and they were organized by hematologic categories to include red blood cell abnormalities, white blood cell abnormalities, disorders of clotting and bleeding, hematologic malignancies, and others.

Conclusions

This review will increase providers' understanding of disorders that include movement disorders and hematologic abnormalities. Basic hematologic laboratories can aid in assessment of these disorders, to include complete blood count/hemogram and peripheral blood smear. Recognition is key, especially in the setting of underlying malignancy, vitamin deficiency, or other disorder in which treatment is available.

A Novel ALAS2 Missense Mutation in Two Brothers With Iron Overload and Associated Alterations in Serum Hepcidin/Erythroferrone Levels

Iron loading anemias are characterized by ineffective erythropoiesis and iron overload. The prototype is non-transfusion dependent ß-thalassemia (NTDT), with other entities including congenital sideroblastic anemias, congenital dyserythropoietic anemias, some hemolytic anemias, and myelodysplastic syndromes. Differential diagnosis of iron loading anemias may be challenging due to heterogeneous genotype and phenotype. Notwithstanding the recent advances in linking ineffective erythropoiesis to iron overload, many pathophysiologic aspects are still unclear. Moreover, measurement of hepcidin and erythroferrone (ERFE), two key molecules in iron homeostasis and erythropoiesis, is scarcely used in clinical practice and of uncertain utility. Here, we describe a comprehensive diagnostic approach, including next-generation sequencing (NGS), in silico modeling, and measurement of hepcidin and erythroferrone (ERFE), in two brothers eventually diagnosed as X-linked sideroblastic anemia (XLSA). A novel pathogenic ALAS2 missense mutation (c.1382T>A, p.Leu461His) is described. Hyperferritinemia with high hepcidin-25 levels (but decreased hepcidin:ferritin ratio) and mild-to-moderate iron overload were detected in both patients. ERFE levels were markedly elevated in both patients, especially in the proband, who had a more expressed phenotype. Our study illustrates how new technologies, such as NGS, in silico modeling, and measurement of serum hepcidin-25 and ERFE, may help in diagnosing and studying iron loading anemias. Further studies on the hepcidin-25/ERFE axis in additional patients with XLSA and other iron loading anemias may help in establishing its usefulness in differential diagnosis, and it may also aid our understanding of the pathophysiology of these genetically and phenotypically heterogeneous entities.

Treatment of Acquired Sideroblastic Anemias

Sideroblastic anemias are a heterogeneous group of disorders unified by the presence of abnormal erythroid precursors with perinuclear mitochondrial iron deposition in the bone marrow. Based on etiology, they are classified into clonal and nonclonal. Clonal sideroblastic anemias refer to myeloid neoplasms with ring sideroblasts (RS) and frequently have somatic perturbations in the SF3B1 gene. Anemia is a major cause of morbidity in patients, and restoration of effective erythropoiesis is a major treatment goal. Morbidity includes transfusion and disease-related complications. This article focuses on treatment of acquired sideroblastic anemias and highlights areas of future investigation.

GLRX5 mutations impair heme biosynthetic enzymes ALA synthase 2 and ferrochelatase in Human congenital sideroblastic anemia

Non-syndromic microcytic congenital sideroblastic anemia (cSA) is predominantly caused by defective genes encoding for either ALAS2, the first enzyme of heme biosynthesis pathway or SLC25A38, the mitochondrial importer of glycine, an ALAS2 substrate. Herein we explored a new case of cSA with two mutations in GLRX5, a gene for which only two patients have been reported so far. The patient was a young female with biallelic compound heterozygous mutations in GLRX5 (p.Cys67Tyr and p.Met128Lys). Three-D structure analysis confirmed the involvement of Cys67 in the coordination of the [2Fe2S] cluster and suggested a potential role of Met128 in partner interactions. The protein-level of ferrochelatase, the terminal-enzyme of heme process, was increased both in patient-derived lymphoblastoid and CD34+ cells, however, its activity was drastically decreased. The activity of ALAS2 was found altered and possibly related to a defect in the biogenesis of its co-substrate, the succinyl-CoA. Thus, the patient exhibits both a very low ferrochelatase activity without any accumulation of porphyrins precursors in contrast to what is reported in erythropoietic protoporphyria with solely impaired ferrochelatase activity. A significant oxidative stress was evidenced by decreased reduced glutathione and aconitase activity, and increased MnSOD protein expression. This oxidative stress depleted and damaged mtDNA, decreased complex I and IV activities and depleted ATP content. Collectively, our study demonstrates the key role of GLRX5 in modulating ALAS2 and ferrochelatase activities and in maintaining mitochondrial function.

Reticulocyte Hemoglobin Equivalent (Ret-He) Combined with Red Blood Cell Distribution Width Has a Differentially Diagnostic Value for Thalassemias

As a type of congenital microcytic hypochromic anemia, thalassemia trait is often confused with other conditions, such as congenital sideroblastic anemia (CSA) and iron deficiency anemia, before a specific work-up is performed. However, these tests, including hemoglobin (Hb) electrophoresis, gene mutations and Prussian blue staining after bone marrow aspirate, are relatively expensive, time-consuming and invasive. To find labor-saving parameters to facilitate differential diagnosis, we retrospectively analyzed the routine blood indexes of 59 thalassemia trait cases [22 α-thalassemia (α-thal), 36 β-thalassemia (β-thal) and one α/β-thal], 21 CSA patients, and 238 iron deficiency anemia controls. Significantly higher reticulocyte Hb equivalent (Ret-He) and lower red blood cell (RBC) distribution width (RDW) were prominent in thalassemia trait. Furthermore, RDW-standard deviation (SD) was independent of the severity of anemia in thalassemia trait, similar to Ret-He in CSA. In the context of the same grades of anemia, Ret-He combined with RDW was powerful in differentiation of thalassemia from CSA and iron deficiency anemia. By receiver operation curve (ROC) analysis, Ret-He had a specificity of 67.06% and a sensitivity of 76.92% with a cutoff value of 20.9 pg for thalassemia trait in mild anemia and a specificity of 84.09% and a sensitivity of 68.42% with a cutoff value of 19.1 pg for thalassemia trait in moderate anemia. Regarding CSA, Ret-He had 92.94% specificity and 60.00% sensitivity in mild anemia, with a cutoff value of 18.1 pg. Overall, Ret-He and RDW are two convenient indexes able to differentiate thalassemia from the other two microcytic anemias, CSA and iron deficiency anemia.

Analysis of mRNA Expression Patterns in Peripheral Blood Cells of 3 Patients With Cancer After the First Fraction of 2 Gy Irradiation: An Integrated Case Report and Systematic Review

Background

Radiation therapy induces acute and chronic radiological toxicity, in particular hematological toxicity (HT). This study aimed to explore the mechanistic clue and potential predictors at the messenger RNA (mRNA) level.

Materials and Methods

Peripheral blood was collected from 3 patients with cervical cancer (CC), nasopharynx cancer (NC), and tongue cancer (TC) after the first 2 Gy fraction of radiotherapy (RT). High-throughput sequencing was used to assess mRNA profiles.

Results

Eleven genes, such as ALAS2(5-aminolevulinate synthase), SLC4A1(solute carrier family 4 member 1), HBG2(hemoglobin subunit gamma 2), TNFAIP3 (TNF α-induced protein 3), PER1 (period circadian clock 1), CCDC136 (coiled-coil domain containing 136), C9orf84 (chromosome 9 open reading frame 84), IL1B (interleukin 1β), FOSB (FosB protooncogene), NR4A2 (nuclear receptor subfamily 4), PARP15 (polymerase family member 15), had overlapping expression changes in all 3 cancers of which 3 (ALAS2, FOSB, and HBG2) are suggested as potential predictors for the early diagnosis of HT after RT.

Conclusions

ALAS2, FOSB, and HBG2 may be useful predictors of HT in patients after RT. Eleven overlapping expression mRNAs among 3 cancers might be potential predictors for early diagnosis of radiation toxicity in patients.

[Using target next-generation sequencing assay in diagnosing of 46 patients with suspected congenital anemias]

目的

评估靶向二代基因测序（NGS）在先天性贫血诊断中的价值。

方法

设计含217个先天性贫血相关致病基因的NGS基因组合——BDHAP-2014，对2014年8月至2017年7月连续就诊的临床怀疑诊断先天性贫血的患者进行NGS检测和亲代验证。

结果

共纳入46例患者，临床疑诊分别为范可尼贫血（FA）11例、先天性红细胞生成异常性贫血（CDA）8例、先天性铁粒幼红细胞性贫血（CSA）6例、先天性溶血性贫血（CHA）12例、先天性角化不良（DC）1例、铁剂难治性缺铁性贫血（IR-IDA）4例及未明原因的血细胞减少（Uc）4例。经靶向NGS检测，28例（60.9%）患者明确了诊断和（或）分型，累及12个基因共44种致病性突变。其中26例（56.5%）基因诊断结果与临床疑诊相符，包括FA（5/11，45.5%）、CSA（6/6，100.0%）、CDA（3/8, 37.5%）及CHA（12/12，100.0%）；2例（4.3%）患者的基因诊断结果与临床疑诊不一致，依据NGS纠正了诊断，包括1例DC和1例家族性噬血细胞性淋巴组织细胞增生症（FHL）；12例CHA依据基因检查结果进一步明确了溶血类型。18例（39.1%）患者未明确致病基因，最终未能明确诊断。

结论

NGS对临床疑诊先天性贫血患者具有重要的诊断价值，可为临床治疗选择提供依据。

Liver Iron Quantification with MR Imaging: A Primer for Radiologists

Iron overload is a systemic disorder and is either primary (genetic) or secondary (exogenous iron administration). Primary iron overload is most commonly associated with hereditary hemochromatosis and secondary iron overload with ineffective erythropoiesis (predominantly caused by β-thalassemia major and sickle cell disease) that requires long-term transfusion therapy, leading to transfusional hemosiderosis. Iron overload may lead to liver cirrhosis and hepatocellular carcinoma, in addition to cardiac and endocrine complications. The liver is one of the main iron storage organs and the first to show iron overload. Therefore, detection and quantification of liver iron overload are critical to initiate treatment and prevent complications. Liver biopsy was the historical reference standard for detection and quantification of liver iron content. Magnetic resonance (MR) imaging is now commonly used for liver iron quantification, including assessment of distribution, detection, grading, and monitoring of treatment response in iron overload. Several MR imaging techniques have been developed for iron quantification, each with advantages and limitations. The liver-to-muscle signal intensity ratio technique is simple and widely available; however, it assumes that the reference tissue is normal. Transverse magnetization (also known as R2) relaxometry is validated but is prone to respiratory motion artifacts due to a long acquisition time, is presently available only for 1.5-T imaging, and requires additional cost and delay for off-line analysis. The R2* technique has fast acquisition time, demonstrates a wide range of liver iron content, and is available for 1.5-T and 3.0-T imaging but requires additional postprocessing software. Quantitative susceptibility mapping has the highest sensitivity for detecting iron deposition; however, it is still investigational, and the correlation with liver iron content is not yet established. ^©RSNA, 2018.

Erythroid cell mitochondria receive endosomal iron by a "kiss-and-run" mechanism

In erythroid cells, more than 90% of transferrin-derived iron enters mitochondria where ferrochelatase inserts Fe²⁺ into protoporphyrin IX. However, the path of iron from endosomes to mitochondrial ferrochelatase remains elusive. The prevailing opinion is that, after its export from endosomes, the redox-active metal spreads into the cytosol and mysteriously finds its way into mitochondria through passive diffusion. In contrast, this study supports the hypothesis that the highly efficient transport of iron toward ferrochelatase in erythroid cells requires a direct interaction between transferrin-endosomes and mitochondria (the "kiss-and-run" hypothesis). Using a novel method (flow sub-cytometry), we analyze lysates of reticulocytes after labeling these organelles with different fluorophores. We have identified a double-labeled population definitively representing endosomes interacting with mitochondria, as demonstrated by confocal microscopy. Moreover, we conclude that this endosome-mitochondrion association is reversible, since a "chase" with unlabeled holotransferrin causes a time-dependent decrease in the size of the double-labeled population. Importantly, the dissociation of endosomes from mitochondria does not occur in the absence of holotransferrin. Additionally, mutated recombinant holotransferrin, that cannot release iron, significantly decreases the uptake of ⁵⁹Fe by reticulocytes and diminishes ⁵⁹Fe incorporation into heme. This suggests that endosomes, which are unable to provide iron to mitochondria, cause a "traffic jam" leading to decreased endocytosis of holotransferrin. Altogether, our results suggest that a molecular mechanism exists to coordinate the iron status of endosomal transferrin with its trafficking. Besides its contribution to the field of iron metabolism, this study provides evidence for a new intracellular trafficking pathway of organelles.

Recent advances in the understanding of myelodysplastic syndromes with ring sideroblasts

Myeloid neoplasms with ring sideroblasts are currently categorized within the myelodysplastic syndromes (MDS) or myelodysplastic/myeloproliferative neoplasms (MDS/MPN) in the World Health Organization classification. Recent findings have identified that the presence of ring sideroblasts in these disorders has a unique molecular basis, i.e., the somatic mutation of SF3B1, a gene encoding a splicing factor. Mutations of SF3B1 occur in up to 90% of patients with refractory anaemia with unilineage dysplasia (RARS) and 70% of those with refractory cytopenia with multilineage dysplasia and ring sideroblasts or RARS associated with marked thrombocytosis. Experimental evidence has shown that mutant SF3B1 results in the abnormal splicing of several genes, primarily due to misrecognition of 3' splice sites. The resulting aberrant mRNAs undergo nonsense-mediated mRNA decay (NMD), resulting in haploinsufficiency of canonical transcripts and protein expression. In addition, it is also possible that NMD-insensitive aberrant transcripts are translated into proteins with altered function. Patients with MDS carrying the SF3B1 mutation show a homogeneous disease phenotype characterized by isolated erythroid dysplasia and mild dysplasia in granulocytic or megakaryocytic lineages, supporting the notion that the SF3B1 mutation identifies a distinct entity within MDS. The available evidence suggests that these findings may have relevant impact on the diagnosis, classification and management of patients with these neoplasms.

Spliceosomal gene mutations in myelodysplasia: molecular links to clonal abnormalities of hematopoiesis

Genomic analyses of the myeloid malignancies and clonal disorders of hematopoiesis that may give rise to these disorders have identified that mutations in genes encoding core spliceosomal proteins and accessory regulatory splicing factors are among the most common targets of somatic mutations. These spliceosomal mutations often occur in a mutually exclusive manner with one another and, in aggregate, account for the most frequent class of mutations in patients with myelodysplastic syndromes (MDSs) in particular. Although substantial progress has been made in understanding the effects of several of these mutations on splicing and splice site recognition, functional connections linking the mechanistic changes in splicing induced by these mutations to the phenotypic consequences of clonal and aberrant hematopoiesis are not yet well defined. This review describes our current understanding of the mechanistic and biological effects of spliceosomal gene mutations in MDSs as well as the regulation of splicing throughout normal hematopoiesis.

Roles of Fe-S proteins: from cofactor synthesis to iron homeostasis to protein synthesis

Fe-S cluster assembly is an essential process for all cells. Impairment of Fe-S cluster assembly creates diseases in diverse and surprising ways. In one scenario, the loss of function of lipoic acid synthase, an enzyme with Fe-S cluster cofactor in mitochondria, impairs activity of various lipoamide-dependent enzymes with drastic consequences for metabolism. In a second scenario, the heme biosynthetic pathway in red cell precursors is specifically targeted, and iron homeostasis is perturbed, but lipoic acid synthesis is unaffected. In a third scenario, tRNA modifications arising from action of the cysteine desulfurase and/or Fe-S cluster proteins are lost, which may lead to impaired protein synthesis. These defects can then result in cancer, neurologic dysfunction or type 2 diabetes.