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Glucose-6-phosphate isomerase (GPI) deficiency, a genetic disorder responsible for chronic nonspherocytic hemolytic anemia, is the second most common red blood cell glycolytic enzymopathy. We report three patients from two unrelated families of Czech and Slovak origin with macrocytic hemolytic anemia due to GPI deficiency. The first patient had 15% of residual GPI activity resulting from two new heterozygous missense mutations c.478T > C and c.1414C > T leading to substitutions p.(Ser160Pro) and p.(Arg472Cys). Two other patients (siblings) inherited the same c.1414C > T p.(Arg472Cys) mutation in a homozygous constitution and lost approximately 89% of their GPI activity. Erythroid hyperplasia with dysplastic features was observed in the bone marrow of all three patients. Low hepcidin/ferritin ratio and elevated soluble transferrin receptor detected in our GPI-deficient patients suggest disturbed balance between erythropoiesis and iron metabolism contributing to iron overload.

Bone marrow histological features of sickle cell anaemia (SCA) patients during early stages and in the asymptomatic phase of the disease appear an interesting area of study, representing early-stage consequences of SCA with a close relation to its pathophysiology. Unfortunately, this field of research has never been specifically addressed before. Bone marrow biopsies from 26 consecutive Black African SCA patients (M:F=1.6:1; age 2-17 years), free of clinical signs of chronic bone marrow damage, with no recent history of symptomatic vaso-occlusive episodes, and waiting for haematopoietic stem cell transplantation (HSCT), underwent morphological, immunohistochemical and electron microscopy evaluation. Additional comparison with three bone marrow specimens from post-HSCT SCA patients and 10 bone marrow specimens from AS healthy carriers was performed. Bone marrow of SCA patients was normocellular or slighly hypercellular in all cases. Erythroid hyperplasia was a common feature. Myeloid lineage was slightly decreased with normal to slightly diminished neutrophilic granulocytes; CD68 positive monocytic-macrophagic cells appeared slightly increased, with a predominant CD163 positive M2/M(Hb) phenotype. A positive correlation was found between haemoglobin values and number of bone marrow erythroid cells (R2=0.15, p=0.05). Intravascular and interstitial clusters of erythroid sickle cells were found in bone marrow of pre-HSCT homozygous SS SCA patients, as well as heterozygous AS healthy carriers, and the single post-HSCT patient matched to an AS health carrier donor.

Growth differentiation factor-15 (GDF-15) is a member of TGF-β superfamily. Among hematopoietic cells, this factor is mainly produced by erythroid series and is recently considered a biomarker of ineffective erythropoiesis (IE). Whether IE induces enhanced GDF-15 expression or is prompted by it, has remained elusive. In this study we investigated how high levels of GDF-15 contribute to IE-associated erythroid dysplasia. We assessed mRNA levels of GDF-15 during erythroid maturation as well as in patients with IE using qRT-PCR. Later, the erythroid colony-forming capacity of GDF-15-treated hematopoietic stem cells (HSCs) was evaluated by CFC assay. Any effect of elevated levels of GDF-15 on erythroid maturation was ultimately examined by expression analysis of erythroid-associated transcription factors and flow cytometry analysis of CD235a expression. GDF-15 mRNA expression increased during erythroid differentiation and also in β-thalassemia and MDS patients which was directly correlated with erythropoiesis severity. Treating the cells with high GDF-15 concentration (50 ng/ml) resulted in an approximate 30% decline in the capacity of erythroid colony formation of HSCs and CD235a positive cells. Additionally, erythroid-specific transcription factors showed significant down-regulation in the early stages of erythroid differentiation. According to the expression level of GDF-15 and the role it plays in the erythroid system, high-levels of this factor could be an auto-modulatory mechanism to control the excessive production of erythroid cells.

The generation of a functional erythrocyte from a committed progenitor requires significant changes in gene expression during a time of hemoglobin accumulation, rapid cell division, and nuclear condensation. Congenital Dyserythropoietic Anemia type I (CDA-I), is an autosomal recessive disease that presents with erythroid hyperplasia in the bone marrow. Erythroblasts in patients with CDA-I are frequently binucleate, have chromatin bridging, and defective chromatin condensation. CDA-1 is most commonly caused by mutations in Codanin-1 (CDAN1). The function of CDAN1 is poorly understood but it is thought to regulate histone incorporation into nascent DNA during cellular replication. The study of CDA-1 has been limited by lack of in vitro models that recapitulate key features of the disease and most studies on CDAN1 function have been done in non-erythroid cells. To model CDA-I we generated HUDEP2 mutant lines with deletion or mutation of R1042 of CDAN1, mirroring mutations found in CDA-1 patients. CDAN1 mutant cell lines had decreased viability, increased intercellular bridges, and binucleate cells. Further, they had alterations in histone acetylation associated with prematurely elevated erythroid gene expression, including gamma-globin. Together, these data imply a specific functional role for CDAN1, specifically R1042 on exon 24, in the regulation of DNA replication and organization during erythroid maturation. Most importantly, generation of models with specific patient mutations, such as R1042, will provide further mechanistic insight into CDA-I pathology.

Erythropoiesis in the bone marrow and spleen depends upon intricate interactions between the resident macrophages and erythroblasts. Our study focuses on identifying the role of the Nuclear Factor Erythroid 2-related factor 2 (Nrf2) during recovery from stress erythropoiesis. To that end, we induced stress erythropoiesis in Nrf2(+/+) and Nrf2 null mice and evaluated macrophage subsets known to support erythropoiesis and erythroid cell populations. Our results confirm macrophage and erythroid hypercellularity after acute blood loss. Importantly, Nrf2 depletion results in a marked numerical reduction of F4/80(+)/CD169(+)/CD11b(+) macrophages, which is more prominent under the induction of stress erythropoiesis. The observed macrophage deficiency is concomitant to a significantly impaired erythroid response to acute stress erythropoiesis in both the murine bone marrow and spleen. Additionally, peripheral blood reticulocyte counts as a response to acute blood loss is delayed in Nrf2 deficient mice compared to age-matched controls (11.0 ± 0.6% vs. 14.8 ± 0.6%, p≤0.001). Interestingly, we observe macrophage hypercellularity in conjunction with erythroid hyperplasia in the bone marrow during stress erythropoiesis in Nrf2(+/+) controls, with both impaired in Nrf2(−/−) mice. We further confirm the finding of macrophage hypercellularity in another model of erythroid hyperplasia, the transgenic sickle cell mouse, characterized by hemolytic anemia and chronic stress erythropoiesis. Our results demonstrate the role of Nrf2 in stress erythropoiesis in the bone marrow and that macrophage hypercellularity occurs concurrently with erythroid expansion during stress erythropoiesis. Macrophage hypercellularity is a previously underappreciated feature of stress erythropoiesis in sickle cell disease and recovery from blood loss.

Senna occidentalis (S. occidentalis) is a toxic leguminous plant that contaminates crops and has been shown to be toxic to several animal species. All parts of the plant are toxic, but most of the plant's toxicity is due to its seeds. Despite its toxicity, S. occidentalis is widely used for therapeutic purposes in humans. The aim of the present work was to investigate, for the first time, the effects of the chronic administration of S. occidentalis seeds on hematopoietic organs, including the bone marrow and spleen. Fifty male Wistar rats were divided into five groups of 10 animals. Rats were treated with diets containing 0% (control), 0.5% (So0.5), 1% (So1), or 2% (So2) S. occidentalis seeds for a period of 90 days. Food and water were provided ad libitum, except to pair-fed (PF) group which received the same amount of ration to those of So2 group, however free of S. occidentalis seeds. It was verified that rats treated with 2% S. occidentalis seeds presented changes in hematological parameters. The blood evaluation also showed a significant decrease of the Myeloid/Erythroid (M/E) ratio. Chronic treatment with S. occidentalis promoted a reduction in the cellularity of both the bone marrow and spleen. Additionally, we observed changes in bone marrow smears, iron stores and spleen hemosiderin accumulation. Histological analyses of bone marrow revealed erythroid hyperplasia which was consistent with the increased reticulocyte count. These findings suggest that the long-term administration of S. occidentalis seeds can promote blood toxicity.

The clinical and biological manifestations of visceral leishmaniasis are often confusing, most particularly because it can mimic and lead to a variety of hematological disorders. The aim of this study was to investigate the hematologic abnormalities observed in infantile visceral leishmaniasis from January 2000 and December 2013. The study included 35 children with a mean age of 3.5 years. Clinical manifestations were dominated by splenomegaly, fever, and paleness, defining the classic triad in 16% of our patients. Anemia was present in all patients. Leukopenia was found in 51% of the cases. Thrombocytopenia was observed in 48% of our patients and 36% had pancytopenia. All cases were confirmed by the presence of Leishman bodies (amastigotes) in the bone marrow smears. Quantitative and qualitative megakaryocyte abnormalities were found. Similarly, dysgranulopoiesis was observed in 31% of the cases, eosinophilia was present in 6%, erythroid hypoplasia in 3%, and erythroid hyperplasia in 34%. Different features of dyserythropoiesis were revealed in 71% of the patients with images of hemophagocytosis in 6% and multiple dysplasias in 9%. The knowledge of these hematological abnormalities associated with infantile visceral leishmaniasis can assist us in searching for Leishman bodies in the bone marrow smears to provide a diagnosis more quickly without necessarily resorting to more sophisticated tests.

Objectives 1) To study the mechanisms of anemia, erythroid hyperplasia, and red blood cell (RBC) clearance in murine models of sickle cell disease (Sickle) and β-thalassemia (Th1/Th1); 2) To determine the contribution of the phospholipid scramblase enzyme to phosphatidylserine (PS) exposure and RBC death in Sickle and Th1/Th1 mice. Methods We used a combination of flow-cytometric analysis and assays for phospholipid remodeling to determine the extent and sites of erythroid hyperplasia, PS exposure, and cell death. Results 1) Sickle RBCs have a much shorter half-life than Th1/Th1 RBCs (0.8 days vs 11 days). A significant proportion of Th1/Th1 peripheral reticulocytes mature into erythrocytes, however, ∼fivefold fewer Sickle reticulocytes mature. While erythroid hyperplasia exists in both Sickle and Th1/Th1 mice, Th1/Th1 produce fourfold more RBCs than necessary to maintain steady state, while Sickle produce no excess RBCs. 2) 61% of Sickle and 34% of Th1/Th1 RBCs are scramblase + as measured by internalization assays of the fluorescent phospholipid NBD-PC. The majority of NBD-PC + RBCs are also annexin-V + , supporting a mechanistic link between scramblase activity and PS exposure. A proportion of both reticulocytes and older RBCs in Sickle and Th1/Th1 mice have active scramblase, and the degree of scramblase activation in these strains correlates with the propensity for RBC death. Conclusions Sickle and Th1/Th1 mice are both anemic, with significant erythroid hyperplasia. Th1/Th1 mice display ineffective erythropoiesis while Sickle mice show rapid peripheral destruction of RBCs. PS exposure and phospholipid scramblase activity serve as markers of RBCs with altered phospholipid asymmetry and greater propensity for cell death.

The proliferation and differentiation of erythroid cells is a highly regulated process that is controlled primarily at the level of interaction of erythropoietin (Epo) with its specific cell surface receptor (EpoR). However, this process is deregulated in mice infected with the Friend spleen focus-forming virus (SFFV). Unlike normal erythroid cells, erythroid cells from SFFV-infected mice are able to proliferate and differentiate in the absence of Epo, resulting in erythroid hyperplasia and leukemia. Over the past 20 years, studies have been carried out to identify the viral genes responsible for the pathogenicity of SFFV and to understand how expression of these genes leads to the deregulation of erythropoiesis in infected animals. The studies have revealed that SFFV encodes a unique envelope glycoprotein which interacts specifically with the EpoR at the cell surface, resulting in activation of the receptor and subsequent activation of erythroid signal transduction pathways. This leads to the proliferation and differentiation of erythroid precursor cells in the absence of Epo. Although the precise mechanism by which the viral protein activates the EpoR is not yet known, it has been proposed that it causes dimerization of the receptor, resulting in constitutive activation of Epo signal transduction pathways. While interaction of the SFFV envelope glycoprotein with the EpoR leads to Epo-independent erythroid hyperplasia, this is not sufficient to transform these cells. Transformation requires the viral activation of the cellular gene Sfpi-1, whose product is thought to block erythroid cell differentiation. By understanding how SFFV can deregulate erythropoiesis, we may gain insights into the causes and treatment of related diseases in man.

Maintenance of iron homeostasis must balance the demand for iron due to heme synthesis, which is driven by hematopoiesis, and the restricted intestinal uptake of iron, which otherwise limits absorption of this toxic element. The consequences of perturbed iron homeostasis are witnessed in inherited forms of beta-thalassemia in which erythroid hyperplasia results in enhanced intestinal iron absorption despite tissue iron overload. To gain a better understanding of intestinal factors that are induced when iron homeostasis is disrupted, a panel of monoclonal antibodies that recognize intestinal microvillous membrane proteins of the beta-thalassemic Hbbd(th3)/Hbbd(th3) mouse was established. The monoclonal antibodies were screened by differential Western blotting against normal and beta-thalassemic mouse intestine to identify antigens modulated in the disease state. Here we report the initial characterization of one immunoreactive species that is up-regulated in beta-thalassemic mouse intestine and the tentative identification of this antigen as sucrase-isomaltase. Studies in Caco-2 cells revealed the rather unexpected finding that expression of this intestinal hydrolase is increased in response to iron toxicity.

Gene therapy for beta-thalassemia is based on the transplantation of genetically-modified autologous hematopoietic stem cells (HSC) into patients affected by the severe form of disease. The genetic treatment of the hemoglobinopathies poses the general challenge of efficient level of gene transfer into HSC and high and persistent transgene expression, in the differentiated progeny of a genetically modified stem cell. The validation of a gene therapy approach to thalassemia requires to obtain results of gene correction in a broad number of patients’ cells, since different molecular defects in the beta-globin gene lead to the clinical phenotype. The heterogeneity in the molecular defects and in the proportion of alpha and non-alpha (beta, gamma and delta) chains will represent a key element to set a threshold in the amount of vector-derived beta-chain required to correct a thalassemic phenotype. Additionally, the impact of some biological parameters, such as the degree of BM erythroid hyperplasia, the BM subpopulations proportion and the apoptotic index, on the successful correction of thalassemic phenotype needs to be studied in the perspective of clinical translation. In order to address these issues, we collected samples from BM aspirates and isolated CD34+ cells from 25 beta+ and beta0 thalassemic patients, characterized by different genotypes and biochemical profiles of globin chains synthesis. A novel, erythroid specific LV expressing human beta-globin from a minimal promoter enhanced by only 2 LCR elements (HS2 and HS3) was used to transduce BM derived CD34+ cells at high efficiency (>80%). The efficacy of the beta-globin LV in correcting the human thalassemic phenotype was tested in an in vitro model of erythropoiesis and in the human-mouse hematological chimera. Upon transduction, normal level of HbA expression was achieved in erythroblastic cultures and BFU-E, associated with a progression towards erythroid maturation, which was impaired in mock-transduced thalassemic cells. Molecular analysis showed proviral integrity, with no detectable rearrangements and an average proviral copy number of 2.4. Analysis of specific globin chains proportion and contribution to phenotype correction in the context of different genotypes is under evaluation.

Bone atrophy is generally thought to be the etiology of the decreased skeletal mass and fractures found in patients with ineffective hematopoiesis and associated erythroid hyperplasia. A bone biopsy from a patient with chronic erythroid hyperplasia and diffuse cortical osteopenia revealed a normal trabecular bone volume, excess osteoid, numerous osteoblasts, and increased osteoclastic resorptive surface. The increased fractional labeled surfaces and widely spaced double tetracycline labels indicated accelerated bone turnover, despite demonstrable iron deposits at the calcification front and cement lines and a low serum level of 25-hydroxyvitamin D. The relationship between the expanded marrow space and trabecular bone suggests that local marrow factors may be responsible for the rapid bone remodeling.

Summary A non-transfused, 43 year old Caucasian female presented with acute haemolytic anaemia and splenomegaly. Sections of bone marrow showed erythroid hyperplasia. The patient's red blood cells gave a negative reaction with polyspecific antiglobulin serum, but a positive reaction with specific anti-IgM. A heat eluate prepared from her red cells showed anti-Vel specificity. Her serum agglutinated only Vel-positive cells including her own. All papain pre-treated red cells including her own and Velnegative cells were completely haemolysed at 37°C. The percentage of haemolysis of Vel-positive cells was greater than that of Velnegative cells.

Cyclohexanone oxime (CHO) was given po to male and female Fischer 344 rats at dose levels of 10, 25, 75, 150, and 300 mg/kg, five times a week for a period of 2 weeks. Control animals received distilled water. All animals given intermediate dose levels (10, 25, 75, and 150 mg/kg) and one half of the animals which were dosed at the high dose (300 mg/kg) as well as one half of the controls were terminated 14 days after administration of the first dose. The remaining rats received no treatment for an additional 14 days and were sacrificed on Day 28 of the study (recovery phase). Dose-related decreases in erythrocyte number, hemoglobin, and hematocrit, with an accompanying increase in reticulocytes and circulating nucleated erythrocytes, were observed in both sexes at Day 14. Methemoglobin levels, determined only at the high dose, were elevated in both sexes at this time. Splenomegaly and hepatomegaly were observed in both sexes at 14 and 28 days. Histopathological examination of the spleen and bone marrow revealed dose-related erythroid hyperplasia at 14 days which subsided by Day 28. The above effects were more pronounced in males. Erythrocyte numbers were only slightly depressed and reticulocytes mildly elevated in males at Day 28. Hematological values were not statistically different from controls in females at this time. These results suggest that CHO induces oxidative damage to the erythrocyte, resulting in a hemolytic anemia accompanied by increased erythropoiesis. The toxic effects appear reversible upon cessation of exposure.

A new reciprocal, apparently balanced translocation between chromosomes 12 and 19, t(12;19)(q13;q13.3), was detected in 5% (3/59) of patients with FAB M1 or M2 acute nonlymphocytic leukemia. In either case, this translocation was part of complex but different cytogenetic abnormalities. None of the patients had a significant response to therapy. In one instance, however, the translocation was found at first relapse after 2 years of complete remission, and no information regarding the karyotype at disease onset was available. Hematologically common to these patients were marked marrow erythroid hyperplasia and severely abnormal erythropoiesis despite normal serum B12 and folate levels. A direct association between t(12;19) and these hematologic findings will have to be established as more cases with this chromosomal abnormality are identified.

GROWTH of a population of cells is determined by the size of the growth fraction, the rate of proliferation of that fraction as reflected in cell cycle parameters, and by the rate of cell loss. Cell loss of a compartment is due to cell death and to differentiation. Eventually, differentiation results in an end cell which is incapable of further division and which will eventually die or disappear by other ways. Regulation of growth can take place at all three levels. In normal tissues, cell production matches cell loss under normal physiological conditions. When regeneration occurs following damage, a temporary imbalance in favour of an increase of the population occurs, but the balance is restored shortly after the original size of the population has been attained. Some degree of 'overshoot ' is usually observed, but thereafter equilibrium is rapidly restored. In transplantable solid tumours the proliferating fraction of cells progressively decreases and the percent cell loss increases w~th increasing volume, while the cell cycle parameters remain rather constant [1]. This results in a flattening of the growth curve as the turnout cell population increases its size. A similar pattern of growth may apply to human acute myeloid leukaemia (AML) [2] and is reported for the BNML leukaemic growth in the spleen compartment by Hagenbeek et ak in this Proceedings [3]; following irradiation of a turnout a repopulation occurs during which the fraction of proliferating cells is decreased, but so are the cell cycle time and the cell loss from the tumour [l]. The factors which determine such changes in the 'kinetics' of growing cell populations are largely unknown, but the recognition of certain stimulators of cell proliferation and of chalones has provided some hope of developing means of manipulating turnout cell populations in vivo. Cellular proliferation of certain tumours both in animals and in man, e.g. mammary carcinoma and prostatic carcinoma can be influenced by hormones. Rauscher and Friend type erythroblastosis in mice is promoted by exogenous erythropoietin or by hypoxia and inhibited by hypertransfusion induced polycythemia [445]. The erythroid hyperplasia in Di Guglielmo's syndrome decreases following hypertransfusion [7]. In some cases of chronic myeloid leukaemia (CML), oscillations in the number of peripheral leukaemic cells were observed which suggest the operation of a feedback mechanism [8]. These various observations have suggested that certain cancers and certain leukaemic cells are responsive to physiological regulation mechanisms to a limited extent. Provided this is correct, the logical approach is to identify these mechanisms and subsequently investigate their applicability in bringing the malignant growth under control.

A deleted F group chromosome was observed in five patients with myeloproliferative and lymphoproliferative diseases. Three patients had a small F chromosome with both arms deleted, 19p-q-. Each of these patients had a different disease, acute myelomonocytic leukemia (AMML), lymphosarcoma (LSA), and erythroleukemia, respectively. One patient had a hyperplastic marrow and erythroid hyperplasia for a year prior to the development of acute myelogenous leukemia (AML), and had a small F chromosome with del(20)(q12) which is similar to the small F chromosome reported in patients with polycythemia vera. No banding studies were available on one patient with sideroblastic anemia and possible erythroleukemia. These cytogenetic findings lead us to believe that: (1) there is a high incidence of F chromosome abnormalities in cases with abnormal erythropoiesis; (2) erythroid diseases may be predisposed to the small F chromosome abnormality, which is enhanced by treatment, such as irradiation; and (3) the cells with a small F chromosome are rather stable and can gradually replace cytogenetically normal cells without affecting the clinical course of the diseases, and it is the emergence of additional chromosomal abnormalities in these cells which signal a poor prognosis.

Trypanosoma vivax infection of sheep and goats, although manifesting varying severity in individual animals, was characterized by an initial phase of “crisis” lasting several weeks which was associated with high fluctuating parasitaemia, a marked drop in red cell values, leucopaenia and a transient macrocytosis which was later replaced by microcytosis. Many animals died during this phase. Animals which survived the crisis passed into a recovery phase characterized by low infrequent parasitaemia, a recovery of the red cell values, sometimes attaining pre-infection values, and leucocytosis. Mortality was generally higher in goats than in sheep and with “wild strains” isolated from cattle and inoculated directly into experimental animals than with the laboratory-adapted strain 36 15 . The anaemia associated with crisis was haemolytic, with a variable decrease in 51 Cr-red cell survival, the degree of shortening being related to the degree of anaemia at the time of measurement. The spleen was the major site of red cell destruction in animals with mild anaemia while the liver was the major site in severely anaemic animals. The bone marrow showed erythroid hyperplasia early in crisis but terminally the percentage of erythrogenic elements drifted towards normal. There was a gross increase in the red marrow mass of the long bones, but regenerative forms of red cells were consistently absent from the blood of severely anaemic animals, suggesting some interference with marrow function. Splenectomy reduced the incubation period of T. vivax in sheep but did not affect the duration and mortality of the disease, nor did it ameliorate the anaemia or affect the intensity and frequency of parasitaemia.

The evolution of erythromonocytic leukemia has been studied in two patients. One (Case 1) presented with DiGuglielmo's syndrome manifested by erythroid hyperplasia, dyserythropoiesis, periodic acid-Schiff-positive erythroblasts, normal heme biosynthesis and ineffective erythropoiesis. In vitro stimulation of the patient's bone marrow with exogenous erythropoietin demonstrated decreased responsiveness. Progressive infiltration of the bone marrow and peripheral blood with primitive monocytic cells was accompanied by an increased number of hypodiploid cells. The second patient (Case 2) presented with a picture of polycythemia vera, progressing to myelofibrosis and terminating as erythromonocytic leukemia in which a paroxysmal nocturnal hemoglobinuria-like defect was demonstrated in the erythroid cells. The leukemic cells were hyperdiploid. It is concluded that erythromonocytic leukemia may result from clonal evolution occurring in any of the myeloproliferative syndromes.

The course of trypanosomiasis was observed over a period of 68 days in eight red sokoto goats experimentally infected with Trypanosoma vivax strain Y58. The goats developed parasitaemia five days after infection; the intensity of parasitaemia varied within and between individual goats. The course of the disease was acute, subacute or chronic. Anaemia was the principal clinicopathological feature of the disease. The rate of development of anaemia was not related to the degree of parasitaemia. Other clinical signs included emaciation, weakness, rough hair coat, profuse lacrimation and development of corneal opacity. Bone marrow of infected goats showed marked erythroid hyperplasia. Erythrophagocytosis and haemosiderosis in the bone marrow, liver and spleen were the principal histopathogical features in infected goats.

deficiency to develop when the patient began to improve from the aplastic crisis since this is the time of marked erythroid hyperplasia. Serial studies would make it possible to determine whether evidence of folio acid deficiency is more definite at one stage of the crisis than at another. DR. SHOJANIA. I should like to emphasize that folic acid deficiency is almost certainly not the cause of most aplastic crises. However, mild deficiency of folic acid is quite common and may be a contributing factor at least in some instances.