Sideroblasts, siderocytes, and sideroblastic anemia

Light microscopic morphology of blood cells of non-descript indigenous Zoar chicken of Mizoram, India

Identifying and analysing distinct blood cells is crucial for the diagnosis and treatment of diseases in the field of biomedicine. The present study was undertaken to study the cytomorphological and cytochemical characteristics of the blood cells of Zoar, a non-descript indigenous breed of chicken extensively reared under backyard poultry farming in Mizoram, India. For this study, 2 mL of blood samples were aseptically collected from the wings veins of 12 chickens and were processed for light microscopic study under standard protocols. The matured erythrocytes were elliptical, while the immature erythrocytes appeared oval. The heterophils were positive for SBB (SBB), Periodic Acid Schiff (PAS), acid phosphatase, alkaline phosphatase and Arylsulphatase while the eosinophils were positive for SBB, PAS, alkaline phosphatase, cytochrome oxidase and peroxidase. The basophils of were positive for toluidine blue while the thrombocytes were positive for PAS. These cytochemical and cytoenzymatic staining properties plays a very important role in diagnosis, differentiation, and classification of leukaemias.

Transient Sideroblastic Anemia Post-COVID-19 Infection

A 57-year-old gentleman presented to the hospital with progressive fatigue and dyspnea on exertion three months after recovering from COVID-19. He was noted to have severe anemia with reticulocytopenia. After excluding vitamin deficiencies and heavy metal toxicities, a bone marrow aspirate and biopsy were performed, which showed erythroid predominant trilineage maturing hematopoiesis with 79% ring sideroblasts and no dysplasia. SF3B1 mutation was negative. He was diagnosed with sideroblastic anemia and became transfusion-dependent. He was treated with an erythropoiesis-stimulating agent and luspatercept with transient improvement in anemia. After 12 months of treatment, anemia spontaneously improved. Repeat bone marrow biopsy showed hypercellular marrow with 39% ringed sideroblasts. We suspect that this possibly was a delayed manifestation of COVID-19 infection.

SLC25A38 congenital sideroblastic anemia: Phenotypes and genotypes of 31 individuals from 24 families, including 11 novel mutations, and a review of the literature

The congenital sideroblastic anemias (CSAs) are a heterogeneous group of inherited disorders of erythropoiesis characterized by pathologic deposits of iron in the mitochondria of developing erythroblasts. Mutations in the mitochondrial glycine carrier SLC25A38 cause the most common recessive form of CSA. Nonetheless, the disease is still rare, there being fewer than 70 reported families. Here we describe the clinical phenotype and genotypes of 31 individuals from 24 families, including 11 novel mutations. We also review the spectrum of reported mutations and genotypes associated with the disease, describe the unique localization of missense mutations in transmembrane domains and account for the presence of several alleles in different populations.

Optical Imaging and High-Accuracy Quantification of Intracellular Iron Contents

Precise quantification of intracellular iron contents is important to biomedical applications of magnetic nanoparticles. Current approaches for iron quantification rely on specialized instruments while most only yield iron quantities averaged over plenty of cells. Here, a simple and robust approach, combining digital optical microscopy with the Beer-Lambert's law, that allows for imaging stainable iron distribution in individual cells and the quantification of stainable iron contents with an unprecedented accuracy of femtogram per pixel, is presented. It is further shown that this approach enables studying of the internalization and reduction dynamics of super-paramagnetic iron oxide nanoparticles (SPIONs) by stem cells in single cell level.

Understanding Sideroblastic Anemia: An Overview of Genetics, Epidemiology, Pathophysiology and Current Therapeutic Options

Sideroblastic anemia (SA) consists of a group of inherited and acquired anemias of ineffective erythropoiesis characterized by the accumulation of ring sideroblasts in the bone marrow due to disrupted heme biosynthesis. Congenital sideroblastic anemia (CSA) is rare and has three modes of inheritance: X-linked (XLSA), autosomal recessive (ARCSA), and maternal. Acquired SA is more common and can be a result of myelodysplastic syndromes (MDS) or other, generally reversible causes. The diagnostic approach to SA includes a work-up for reversible causes and genetic testing for CSA based on clinical suspicion, family history and genetic pedigree. The treatment of SA depends on the underlying etiology but remains primarily supportive with vitamin B6 supplementation for select cases of XLSA, thiamine for thiamine-responsive megaloblastic anemia subtype, red blood cell transfusions for symptomatic patients and iron chelation therapy for iron overload. The management of anemia in MDS subtypes with ring sideroblasts remains unique and includes the recently approved erythroid maturation agent, Luspatercept. Although there is currently no curative therapy for CSA, anecdotal reports of hematopoietic stem cell transplant demonstrate remissions in selective, non-syndromic cases. This review summarizes the genetics, pathophysiology, diagnosis and treatment of SA for general practitioners and clinical hematologists.

The molecular genetics of sideroblastic anemia

The sideroblastic anemias (SAs) are a group of inherited and acquired bone marrow disorders defined by pathological iron accumulation in the mitochondria of erythroid precursors. Like most hematological diseases, the molecular genetic basis of the SAs has ridden the wave of technology advancement. Within the last 30 years, with the advent of positional cloning, the human genome project, solid-state genotyping technologies, and next-generation sequencing have evolved to the point where more than two-thirds of congenital SA cases, and an even greater proportion of cases of acquired clonal disease, can be attributed to mutations in a specific gene or genes. This review focuses on an analysis of the genetics of these diseases and how understanding these defects may contribute to the design and implementation of rational therapies.

The phenotypic spectrum of germline YARS2 variants: from isolated sideroblastic anemia to mitochondrial myopathy, lactic acidosis and sideroblastic anemia 2

YARS2 variants have previously been described in patients with myopathy, lactic acidosis and sideroblastic anemia 2 (MLASA2). YARS2 encodes the mitochondrial tyrosyl-tRNA synthetase, which is responsible for conjugating tyrosine to its cognate mt-tRNA for mitochondrial protein synthesis. Here we describe 14 individuals from 11 families presenting with sideroblastic anemia and YARS2 variants that we identified using a sideroblastic anemia gene panel or exome sequencing. The phenotype of these patients ranged from MLASA to isolated congenital sideroblastic anemia. As in previous cases, inter- and intra-familial phenotypic variability was observed, however, this report includes the first cases with isolated sideroblastic anemia and patients with biallelic YARS2 variants that have no clinically ascertainable phenotype. We identified ten novel YARS2 variants and three previously reported variants. In vitro amino-acylation assays of five novel missense variants showed that three had less effect on the catalytic activity of YARS2 than the most commonly reported variant, p.(Phe52Leu), associated with MLASA2, which may explain the milder phenotypes in patients with these variants. However, the other two missense variants had a more severe effect on YARS2 catalytic efficiency. Several patients carried the common YARS2 c.572 G>T, p.(Gly191Val) variant (minor allele frequency =0.1259) in trans with a rare deleterious YARS2 variant. We have previously shown that the p.(Gly191Val) variant reduces YARS2 catalytic activity. Consequently, we suggest that biallelic YARS2 variants, including severe loss-of-function alleles in trans of the common p.(Gly191Val) variant, should be considered as a cause of isolated congenital sideroblastic anemia, as well as the MLASA syndromic phenotype.

Physiologic Expression of Sf3b1(K700E) Causes Impaired Erythropoiesis, Aberrant Splicing, and Sensitivity to Therapeutic Spliceosome Modulation

More than 80% of patients with the refractory anemia with ring sideroblasts subtype of myelodysplastic syndrome (MDS) have mutations in Splicing Factor 3B, Subunit 1 (SF3B1). We generated a conditional knockin mouse model of the most common SF3B1 mutation, Sf3b1(K700E). Sf3b1(K700E) mice develop macrocytic anemia due to a terminal erythroid maturation defect, erythroid dysplasia, and long-term hematopoietic stem cell (LT-HSC) expansion. Sf3b1(K700E) myeloid progenitors and SF3B1-mutant MDS patient samples demonstrate aberrant 3' splice-site selection associated with increased nonsense-mediated decay. Tet2 loss cooperates with Sf3b1(K700E) to cause a more severe erythroid and LT-HSC phenotype. Furthermore, the spliceosome modulator, E7017, selectively kills SF3B1(K700E)-expressing cells. Thus, SF3B1(K700E) expression reflects the phenotype of the mutation in MDS and may be a therapeutic target in MDS.

A recurring mutation in the respiratory complex 1 protein NDUFB11 is responsible for a novel form of X-linked sideroblastic anemia

The congenital sideroblastic anemias (CSAs) are a heterogeneous group of inherited blood disorders characterized by pathological mitochondrial iron deposition in erythroid precursors. Each known cause has been attributed to a mutation in a protein associated with heme biosynthesis, iron-sulfur cluster biogenesis, mitochondrial translation, or a component of the mitochondrial respiratory chain. Here, we describe a recurring mutation, c.276_278del, p.F93del, in NDUFB11, a mitochondrial respiratory complex I-associated protein encoded on the X chromosome, in 5 males with a variably syndromic, normocytic CSA. The p.F93del mutation results in respiratory insufficiency and loss of complex I stability and activity in patient-derived fibroblasts. Targeted introduction of this allele into K562 erythroleukemia cells results in a proliferation defect with minimal effect on erythroid differentiation potential, suggesting the mechanism of anemia in this disorder.

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.

Refractory anemia with ring sideroblasts

Refractory anemia with ring sideroblasts (RARS) is a subtype of myelodysplastic syndrome (MDS) characterized by 15% or more ring sideroblasts in the bone marrow according to the WHO classification. After Perls staining, ring sideroblasts are defined as erythroblasts in which there are 5 or more siderotic granules covering at least a third of the nuclear circumference. The iron deposited in perinuclear mitochondria of ring sideroblasts is present in the form of mitochondrial ferritin. The molecular basis of MDS with ring sideroblasts has remained unknown until recently. In 2011, whole exome sequencing studies revealed somatic mutations of SF3B1, a gene encoding a core component of RNA splicing machinery, in myelodysplasia with ring sideroblasts. The close relationship between SF3B1 mutation and ring sideroblasts is consistent with a causal relationship, and makes SF3B1 the first gene to be associated with a specific morphological feature in MDS. RARS is mainly characterized by isolated anemia due to ineffective erythropoiesis, and its clinical course is generally benign, although there is a tendency to worsening of anemia in most patients over time. By contrast, refractory cytopenia with multilineage dysplasia and ring sideroblasts (RCMD-RS) is characterized by pancytopenia and dysplasia in two or more myeloid cell lineages. More importantly, patients with RCMD-RS have a higher risk of developing bone marrow failure or progressing to acute myeloid leukemia (AML). Refractory anemia with ring sideroblasts (RARS-T) associated with marked thrombocytosis is a myelodysplastic/myeloproliferative neoplasm associated with both SF3B1 and JAK2 or MPL mutations. RARS-T may develop from an SF3B1 mutated RARS through the acquisition of a JAK2 or MPL mutations in a subclone of hematopoietic cells.

hem6: an ENU-induced recessive hypochromic microcytic anemia mutation in the mouse

Mouse models have proven invaluable for understanding erythropoiesis. Here, we describe an autosomal recessive, inherited anemia in the mouse mutant hem6. Hematologic and transplantation analyses reveal a mild, congenital, hypochromic, microcytic anemia intrinsic to the hematopoietic system that is associated with a decreased red blood cell zinc protoporphyrin to heme ratio, indicative of porphyrin insufficiency. Intercross matings show that hem6 can suppress the porphyric phenotype of mice with erythropoietic protoporphyria (EPP). Furthermore, iron uptake studies in hem6 reticulocytes demonstrate defective incorporation of iron into heme that can be partially corrected by the addition of porphyrin precursors. Gene expression and enzymatic assays indicate that erythroid 5-aminolevulinic acid synthase (Alas2) is decreased in hem6 animals, suggesting a mechanism that could account for the anemia. Overall, these data lead to the hypothesis that hem6 encodes a protein that directly or indirectly regulates the expression of Alas2.

Ultrastructural features of bone marrow cells from patients with acquired sideroblastic anemia

The ultrastructural findings of the bone marrow cells from 15 patients with acquired sideroblastic anemia are presented. The red cell precursors from all patients showed the presence of electron-dense material in the mitochondria, representing most probably iron deposits. A great number of these mitochondria were completely destroyed. The erythropoietic precursors from one of the patients showed markedly elongated mitochondria that measured up to 3 microm. In addition numerous cytoplasmic vacuoles were observed. The red cell precursors from 60% of the patients showed signs of dyserythropoiesis, such as incomplete nuclear division and nuclear distortion. The polymorphonuclears from 47% of the patients presented nuclear abnormalities expressed as nuclear bridges, appendices, and blebs. In addition, phagocytosis of red blood cells was observed. The results of the study underline the advantages of the transmission electron microscope examination in visualization of intricate alterations in hematopoietic cells that cannot be detected with a light microscope.

The myelodysplastic syndrome(s): a perspective and review highlighting current controversies

The myelodysplastic syndrome (MDS) includes a diverse group of clonal and potentially malignant bone marrow disorders characterized by ineffective and inadequate hematopoiesis. The presumed source of MDS is a genetically injured early marrow progenitor cell or pluripotential hematopoietic stem cell. The blood dyscrasias that fall under the broad diagnostic rubric of MDS appear to be quite heterogeneous, which has made it very difficult to construct a coherent, universally applicable MDS classification scheme. A recent re-classification proposal sponsored by the World Health Organization (WHO) has engendered considerable controversy. Although the precise incidence of MDS is uncertain, it has become clear that MDS is at least as common as acute myelogenous leukemia (AML). There is considerable overlap between these two conditions, and the former often segues into the latter; indeed, the distinction between AML and MDS can be murky, and some have argued that the current definitions are arbitrary. Despite the discovery of several tantalizing pathophysiological clues, the basic biology of MDS is incompletely understood. Treatment at present is generally frustrating and ineffective, and except for the small subset of patients who exhibit mild marrow dysfunction and low-risk cytogenetic lesions, the overall prognosis remains rather grim. In this narrative review, we highlight recent developments and controversies within the context of current knowledge about this mysterious and fascinating cluster of bone marrow failure states.

X-linked sideroblastic anaemia with ataxia: another mitochondrial disease?

OBJECTIVES

The syndrome of X-linked sideroblastic anaemia with ataxia is rare, described only twice in the literature. The aim was to obtain clinical neurological and haematological data about this rare syndrome throughout adult life.

METHODS

A family is described with two affected brothers and two affected maternal uncles. The family was evaluated clinically. Haematological investigations included full blood count, blood film, iron studies, free erythrocyte protoporphyrin (FEP) concentrations and a bone marrow examination where possible.

RESULTS

Core neurological features included motor delay, ataxia evident from early childhood, and dysarthria. Neurological features were non-progressive until the fifth decade when slow progression became evident. Some family members showed mild spasticity. Patients usually have a mild asymptomatic anaemia or a borderline decreased mean corpuscular volume. Blood film examination showed Pappenheimer bodies. Bone marrow examination showed ring sideroblasts, indicating raised erythrocyte iron. Free erythrocyte protoporphyrin (FEP) concentrations were raised.

CONCLUSIONS

Haematological features are subtle and can be easily overlooked, and individual patients may not display all the abnormal features. X-linked ataxias are rare and incorrect genetic advice may be given if the diagnostic haematological features of X-linked sideroblastic anaemia are overlooked. Males with early onset ataxia should have a haematological evaluation including a blood film, with a bone marrow examination if abnormal blood count indices and measurement of FEP concentrations raise suspicion. The condition has parallels with Pearson's syndrome and Friedreich's ataxia. All three conditions are associated with mitochondrial iron handling defects and ataxia. The human ATP binding cassette gene (hABC7) is a candidate gene and requires further investigation.

Accumulation of iron in erythroblasts of patients with erythropoietic protoporphyria

We have studied the iron metabolism in nine patients with erythropoietic protoporphyria (EPP) and three patients with sideroblastic anaemia (SA). All, except one EPP patient were iron deficient. The SA patients had a secondary haemochromatosis. The bone marrow aspirates of patients with SA and also three patients with EPP had a high incidence of ring sideroblasts. Ultrastructural examination of the bone marrow consistently showed finely dispersed electron-dense deposits localized in mitochondria of erythroblasts in all patients with EPP and SA. Mitochondrial electron energy-loss spectroscopy (EELS) indicated identical iron compounds in erythroblasts of all EPP and SA patients. These findings indicate that the mitochondrial iron utilization is disturbed in EPP and SA. The observation of mitochondrial iron deposition in erythroblasts in EPP and SA suggests that this failure is not of pathognomonic value for diagnosis of SA, but is apparently the result of an inefficient haem synthesis, in EPP due to a defective ferrochelatase. The mitochondrial iron deposition does not depend on the iron status (iron overload or iron deficiency) of the EPP patient.

Microcytic anemia. Differential diagnosis and management of iron deficiency anemia

Microcytic anemia is defined as the presence of small, often hypochromic, red blood cells in a peripheral blood smear and is usually characterized by a low MCV (less than 83 micron 3). Iron deficiency is the most common cause of microcytic anemia. The absence of iron stores in the bone marrow remains the most definitive test for differentiating iron deficiency from the other microcytic states, ie, anemia of chronic disease, thalassemia, and sideroblastic anemia. However, measurement of serum ferritin, iron concentration, transferrin saturation and iron-binding capacity, and, more recently, serum transferrin receptors may obviate proceeding to bone marrow evaluation. The human body maintains iron homeostasis by recycling the majority of its stores. Disruptions in this balance are commonly seen during menstruation, pregnancy, and gastrointestinal bleeding. Although the iron-absorptive capacity is able to increase upon feedback regarding total body iron stores or erythropoietic activity, this physiologic response is minimal. Significant iron loss requires replacement with iron supplements. The vast majority of patients respond effectively to inexpensive and usually well-tolerated oral iron preparations. In the rare circumstances of malabsorption, losses exceeding maximal oral replacement, or true intolerance, parenteral iron dextran is effective. In either form of treatment, it is necessary to replete iron stores in addition to correcting the anemia.

The effects of inhibition of heme synthesis on the intracellular localization of iron in rat reticulocytes

These studies assessed the fate and localization of incoming iron in 6-8-day rat reticulocytes during inhibition of heme synthesis by succinylacetone. Succinylacetone inhibition of heme synthesis increased iron uptake by increasing the rate of receptor recycling without affecting receptor KD for transferrin, transferrin uptake, or total receptor number. Its net effect was to amplify the number of surface transferrin receptors by recruitment of receptors from an intracellular pool. Despite increased iron influx in inhibited cells, only 2-4% of total incoming iron was diverted into ferritin. The majority of incoming iron (65-80%) in succinylacetone-inhibited cells was recovered in the stroma, where ultrastructural and enzymic analyses revealed it to be accumulated mainly in mitochondria. Intramitochondrial iron (70-75%) was localized mainly in the inner membrane fraction. Removal of succinylacetone restored heme synthesis, utilizing iron accumulated within mitochondria for its support. Thus, inhibition of heme synthesis in rat reticulocytes results in accumulation of incoming iron in a functional mobile intramitochondrial precursor iron pool used directly for heme synthesis. Under normal conditions, there is no significant intracellular or intramitochondrial iron pool in reticulocytes, which are therefore dependent upon continuous delivery of transferrin-bound iron to maintain heme synthesis. Ferritin plays an insignificant role in iron metabolism of reticulocytes.

Drug-induced red cell dyscrasias

Major advances have been made in recent years in our understanding of the pathogenetic mechanisms of drug-induced blood dyscrasias, particularly those involving the red cell. Among the latter, hemolytic anemia is the most common. Drug-induced red cell destruction may occur on an immune basis or through disruption by the drug of red cell metabolism. The immunological basis of drug-induced hemolysis is reviewed with emphasis on the clinical and laboratory manifestations, differential diagnosis and the major mechanisms involved. Drug-induced oxidative hemolysis both in normal individuals and in those with certain enzymopathies, notably glucose-6-phosphate dehydrogenase deficiency, is summarized. Drugs may also produce red cell dyscrasias by acting on the immature erythroid compartment. Some of these inhibit erythroid growth by as yet poorly understood mechanisms. Others exert more specific metabolic effects in erythroid precursors. These include drugs which interfere with DNA synthesis causing megaloblastic erythropoiesis and those which disrupt mitochondrial function and the synthesis of heme manifested by sideroblastic erythropoiesis. A brief consideration of heme biosynthesis and the action of drugs which are associated with sideroblastic anemia, including the antituberculous agents, lead, alcohol and chloramphenicol is presented. Finally, where pertinent, an updated listing of drugs involved in red cell dyscrasias is included.

Haem arginate treatment for hereditary sideroblastic anaemia

It has been shown that haem arginate treatment increases blood cell counts, improves the sideroblast status of the bone marrow and normalises decreased activities of haem synthesising enzymes in some patients with acquired sideroblastic anaemia, or with other types of myelodysplastic syndromes. 4 patients with hereditary sideroblastic anaemia (HSA), belonging to two families, were therefore treated with haem arginate infusions, 3 mg/kg, on 4 consecutive days, and thereafter weekly for 10 wk. No effect was observed on the mildly anaemic haemoglobin levels or on the red cell counts. However, the initially low or low-normal myeloid to erythroid ratio in the marrow increased in all patients. A consistent decrease in the percentage of ring sideroblasts and other abnormal sideroblasts was seen in 1 patient (Family A), and a temporary decrease of abnormal sideroblasts took place during the most intensive treatment period in 2 other patients (Family B). Two of three initially abnormal haem synthesising enzyme activities became normal in Family A, whereas no clearly consistent effects on the haem synthesising enzymes were observed in Family B. The present study shows that haem arginate infusions can normalise the activities of haem synthesising enzymes in some patients with HSA. Further studies are needed to evaluate the impact of haem infusions on the iron balance of these patients.

Hereditary sideroblastic anaemia and autosomal inheritance of erythrocyte dimorphism in a Dutch family

Size distribution curves of red blood cells were used to detect the presence of microcytes in peripheral blood of members of a Dutch family with hereditary sideroblastic anaemia. 22 of 49 members of this family have a bimodal erythrocyte volume distribution curve and a dimorphic blood picture. The pattern of inheritance of this morphological abnormality is clearly autosomal. It is suggested that the study of red blood cell size distribution curves may add valuable information on the pattern of inheritance in other families with hereditary sideroblastic anaemia.

Chronic myelomonocytic leukemia following refractory anemia with sideroblasts: report of two cases

We report 2 patients with idiopathic refractory sideroblastic anemia who developed chronic myelomonocytic leukemia 1 to 5 yr later. This observation supports the decision of the FAB cooperative group to include both conditions in the category of myelodysplastic syndrome.

Sideroachrestic anemia with iron loading: treatment with desferrioxamine

A case of nontransfusion-dependent sideroachrestic anemia (SA) with hemosiderosis is described that showed significant improvement of hemosiderosis and fibrosis of the liver following treatment with desferrioxamine. The anemia, although not transfusion dependent, did not allow continued therapy with phlebotomies. Following the removal of about 16 g iron over 4.5 years, normalization of serum ferritin and reversal of fibrosis of the liver were observed. Management problems and the prognostic implications of desferrioxamine therapy are discussed.

Myelodysplastic syndromes: pathogenesis, functional abnormalities, and clinical implications

The myelodysplastic syndromes represent a preleukaemic state in which a clonal abnormality of haemopoietic stem cell is characterised by a variety of phenotypic manifestations with varying degrees of ineffective haemopoiesis. This state probably develops as a sequence of events in which the earliest stages may be difficult to detect by conventional pathological techniques. The process is characterised by genetic changes leading to abnormal control of cell proliferation and differentiation. Expansion of an abnormal clone may be related to independence from normal growth factors, insensitivity to normal inhibitory factors, suppression of normal clonal growth, or changes in the immunological or nutritional condition of the host. The haematological picture is of peripheral blood cytopenias: a cellular bone marrow, and functional abnormalities of erythroid, myeloid, and megakaryocytic cells. In most cases marrow cells have an abnormal DNA content, often with disturbances of the cell cycle: an abnormal karyotype is common in premalignant clones. Growth abnormalities of erythroid or granulocyte-macrophage progenitors are common in marrow cultures, and lineage specific surface membrane markers indicate aberrations of differentiation. Progression of the disorder may occur through clonal expansion or through clonal evolution with a greater degree of malignancy. Current attempts to influence abnormal growth and differentiation have had only limited success. Clinical recognition of the syndrome depends on an acute awareness of the signs combined with the identification of clonal and functional abnormalities.

Hereditary sideroblastic anaemia and ataxia: an X linked recessive disorder

We report two families in which a non-progressive spinocerebellar syndrome and a sideroblastic anaemia are segregating together in an X linked recessive fashion. Four males in two generations of one family and a fifth male from an unrelated family had both conditions. Both the sideroblastic anaemia and the spinocerebellar syndrome differ from those which have previously been reported to be inherited in an X linked recessive manner. The association of these two clinically distinct disorders in two unrelated families suggests that they are either two closely linked loci which have undergone simultaneous mutation or pleiotropic effects of an altered allele at a single locus. All the heterozygous women had normal neurological examinations and normal haematocrits and red cell indices. Some had ring sideroblasts on bone marrow examination, a dimorphic peripheral blood smear, and raised serum free erythrocyte protoporphyrin, suggesting that a proportion of heterozygotes can be detected by appropriate haematological studies.

Pathologic Sideroblasts and Siderocytes Associated with Chloramphenicol Therapy in a Dog

Siderotic granules were recognized in blood erythrocytes from a male Boxer dog with suppurative prostatitis, cystitis and pyelonephritis that was being given high dosage chloramphenicol therapy. Siderotic inclusions were recognized in the cytoplasm of 96% of the rubricytes and metarubricytes in a bone marrow aspirate. Siderotic inclusions were numerous and in some cases formed a ring around the nucleus. This perinuclear location suggested that pathologic mitochondrial iron accumulation had occurred, resulting in the formation of "ringed" sideroblasts. The occurrence of pathologic sideroblasts was confirmed by electron microscopy. Blood siderocytes and bone marrow sideroblasts disappeared after cessation of chloramphenicol therapy.

Prevalence and distribution of ringed sideroblasts in primary myelodysplastic syndromes

In order to determine the prevalence and percentage distribution of ringed sideroblasts in primary myelodysplastic syndromes, the results of Prussian blue staining were analysed in 133 cases. Ringed sideroblasts ranging from 1 to 86% of cells were found in 76 (57%) cases. The cases of primary myelodysplastic syndrome corresponding to the group entitled "acquired idiopathic sideroblastic anaemia" had between 21 and 86% ringed sideroblasts; these were also found in 40% (26/65) cases corresponding to refractory anaemia with excess of blasts. Seven of the 22 cases having morphological features of refractory anaemia with excess of blasts in transformation had ringed sideroblasts. It would appear that cases of acquired idiopathic sideroblastic anaemia have at least 20% ringed sideroblasts; they also seem to occur frequently in refractory anaemia with excess of blasts.

Erythroid and granulocyte/macrophage progenitor cells in primary acquired sideroblastic anemia

In order to study the pathogenesis of primary acquired sideroblastic anemia (PASA), bone marrow and/or peripheral blood specimens obtained from four patients with PASA were cultured for erythroid colony-forming units (CFU-E), erythroid burst-forming units (BFU-E), and granulocyte/macrophage colony-forming units (GM-CFU). The number of CFU-E was markedly decreased in all four patients. CFU-E colonies consisted exclusively of normal-appearing erythroblasts, while ringed sideroblasts were observed only in scattered single erythroblasts or in small erythroblast aggregates. In one case, very few BFU-E colonies containing both normal-appearing erythroblasts and ringed sideroblasts were detected. In addition, the number of GM-CFU was significantly decreased in three out of the four cases. These findings may suggest that there are abnormalities in the pluripotent hemopoietic stem cells at least in some cases of PASA.

Idiopathic refractory sideroachrestic anemia (IRSA) progressing to acute mixed lymphoblastic-myelomonoblastic leukemia. Case report and review of the literature

A longitudinal observation of a patient with idiopathic refractory sideroachrestic anemia (IRSA) progressing to acute mixed lymphoblastic-myelomonoblastic leukemia is reported. The leukemia was characterized by morphology, immunological cell markers, and dissociated clinical responsiveness to vincristine/prednisone and arabinosylcytosine/6-thioguanine. Attention is paid to the hematological changes prior to leukemia development. Acute leukemia was best heralded in this patient by a severe deterioration of dyserythropoiesis and by an increase of blasts in the marrow to more than 5%. The observed preleukemic features are compared to those described in the literature.

Erythroblast iron metabolism in sideroblastic marrows

The uptake of iron by bone marrow erythroblasts and its intracellular distribution have been studied in 23 patients with primary sideroblastic anaemia (SA), five patients with secondary SA and one patient with only non-ringed sideroblasts. EM of erythroblasts from 18 cases showed both mitochondrial iron deposits and cytoplasmic ferritin aggregates in all cases except the patient with only non-ringed sideroblasts. Iron uptake by erythroblasts in whole bone marrow was normal but there was a decreased incorporation into haem and an increased incorporation into cell stroma. Age matching of erythroblasts using Percoll density gradient centrifugation indicated that stromal iron incorporation was high at all stages of erythroblast development even before haem synthesis had become a major metabolic activity and in intermediate and late erythroblasts a real decrease in haem synthesis appeared less certain. These observations, together with the inability to correct the abnormality in vitro with either pyridoxal phosphate or delta amino-laevulinic acid suggest that the primary defect in SA may be an abnormality of mitochondrial iron metabolism rather than an abnormality of haem synthesis.

Sideroblastic anaemia. A review of seven paediatric cases

Sideroblastic Anaemias are characterised by a) chronic hypochromic anemia, b) ringed sideroblasts in the bone marrow, c) an increase in total body iron, d) ineffective erythropoiesis and e) often abnormal concentrations of F.E.P. A classification of Sideroblastic Anaemia is given and the pathophysiology of Sideroblastic Anaemia is discussed. A series of seven paediatric cases with Sideroblastic Anaemia is presented and the results of studies of the iron, vitamin B6 and porphyrin metabolism are discussed. In two cases arguments for an ALA-synthetase deficiency are given. All five males were diagnosed as hereditary X-linked Sideroblastic Anaemia, one female as I.R.S.A. and the other female, who showed the features of the X-linked type, as congenital Sideroblastic Anaemia.

The laboratory evaluation of microcytic red blood cells

Microcytic red blood cell states are common clinical problems in both adult and pediatric age groups. The recent widespread availability of electronic blood cell counters for performing routine blood counts has increased the detection of microcytic red blood cells. Physicians must workup both symptomatic and asymptomatic patients with microcytic red blood cells before they can initiate proper therapy and/or counseling. The purpose of this review is threefold: (1) to discuss the causes of microcytic red blood cells in terms of disorders of decreased heme production vs. disorders of decreased globin production, (2) to review the clinical laboratory tests useful in differentiating microcytic red blood cell states, and (3) to present a practical approach for the laboratory workup of microcytic red blood cells.

The anemia of inflammatory disease in the dog. I. The nature of the problem

The anemia of inflammatory disease(AID) in the dog is an almost invariable complication of infection, inflammation and disseminated or necrotizing neoplastic disease. Clinically innocuous, it is important only in the greater understanding of the mechanisms controlling circulating erythrocyte quantity and quality. The etiology and pathogenesis include a shortened red cell life-span, disordered iron metabolism, depressed bone marrow response to the anemia and a disordered iron storage. The laboratory features of a moderate anemia, normal bone marrow cellular pattern, depression iron metabolism and reticuloendothelial iron sequestration make a final diagnosis of AID dependent on ruling out other etiologic mechanisms which may obscure or aggravate the anemia of the inflammatory disease in the dog.

The activities of delta-aminolaevulinic acid synthase and haem synthase in experimental sideroblastic anaemia. Effect of mitochondrial iron excess on the enzyme activity in peripheral red blood cells

Experimental sideroblastic anaemia was produced in normal and in iron loaded guinea pigs by intraperitoneal (i.p.) administration of isoniazid and cycloserine. Subsequently, the activities of delta-aminolaevulinic acid synthase (ALA-S) and of haem synthase in peripheral red blood cells were measured and in particular the relationships of enzyme activities to the iron status were examined. The ALA-S activity showed a similar decrease in all animals with sideroblastic anaemia. The haem synthase activity was increased probably due to secondary induction, but it was significantly less increased in animals with the highest values for iron status. This finding indicates that mitochondrial iron accumulation may have limited the compensatory increase of haem synthase activity. It is likely that also in human sideroblastic anaemia mitochondrial iron overload may have a secondary limiting effect on the haem synthase activity in erythroid cells.

Sideroblasts and haemosiderin in thyrotoxicosis

Bone marrow sideroblasts and haemosiderin were studied in 19 thyrotoxic patients before therapy and in the euthyroid state. The proportion of sideroblasts and the amount of haemosiderin were significantly higher in the hyperthyroid than in the euthyroid phase. Pathological sideroblasts with coarse perinuclear iron granules were found before therapy but not in the euthyroid phase. It is concluded that during thyrotoxicosis the supply of iron into erythroblasts is greater than the amount used for haemoglobin synthesis.

Energy-dispersive X-ray analysis of the mitochondria of sideroblastic anaemia

Energy-dispersive X-ray analysis has been performed on marrow sideroblasts obtained from 10 patients with sideroblastic anaemias or erythroleukaemia (six primary refractory sideroblastic anaemia, two pyridoxine-responsive, one secondary sideroblastic anaemia, two erythroleukaemia). Irrespective of the nature of the disorder associated with the presence of sideroblasts, X-ray analysis of siderotic mitochondria consistently revealed the presence of iron and phosphorus with the average Fe/P intensity ratio measuring 1.4-1.5. Other elements variably detected within siderotic mitochondria included calcium, lead, potassium and zinc. Variation in the presence of these latter elements was detected not only between different patients, but also within different samples taken at different times from a single patient and even among different cells of the same sample. Despite the detection of lead in siderotic mitochondria of a significant number of patients (five out of seven), there was no clinical evidence of lead toxicity. The elemental composition of the intramitochondrial deposits in sideroblasts was distinct from that of ferritin or haemosiderin and probably consists of ferric phosphate, possibly, ferric orthophosphate (FePO4).

Multiple enzymatic defects in mitochondria in hematological cells of patients with primary sideroblastic anemia

Activities of mitochondrial enzymes in blood cells from 69 patients with primary sideroblastic anemia were determined to elucidate the pathogenesis of the disease. In erythroblasts of patients with primary acquired type the activities of both delta-aminolevulinic acid synthetase and mitochondrial serine protease were inevitably decreased. The susceptibility to the protease of apo-delta-aminolevulinic acid synthetase prepared from erythroblasts of patients with this type was within the normal range, in contrast to that of pyridoxine-responsive anemia. The activities of mitochondrial enzymes such as cytochrome oxidase, serine protease, and oligomycin-sensitive ATPase, except citrate synthetase, were usually decreased in mature granulocytes of the patients. Patients with hereditary sideroblastic anemia also had decreased delta-aminolevulinic acid synthetase activity in erythroblasts, and decreased serine protease activity in both erythroblasts and mature granulocytes. Mature granulocytes obtained from patients with pyridoxine-responsive anemia before therapy had decreased cytochrome oxidase activity, however, the activity increased to a normal level when the patients were in remission. The activities of other mitochondrial enzymes in mature granulocytes were within normal range in these patients before pyridoxine therapy. The activities of these mitochondrial enzymes in lymphocytes were within normal range in all groups of patients with primary sideroblastic anemia. We suggest that patients with primary acquired, and possibly also those with hereditary sideroblastic anemia have impaired mitochondrial function in both erythroblasts and granulocytes. That only anemia is observed in these patients is because a functional abnormality of mitochondria in erythroblasts is most important because of the role of mitochondria in the formation of heme in erythrocyte development. In contrast to these two types of sideroblastic anemia, only delta-aminolevulinic acid synthetase in both erythroblasts and granulocytes seems to be impaired in patients with pyridoxine-responsive anemia.