Development of mice expressing a single D-type cyclin

D-cyclins (cyclins D1, D2, and D3) are components of the core cell cycle machinery. To directly test the ability of each D-cyclin to drive development of various lineages, we generated mice expressing only cyclin D1, or only cyclin D2, or only cyclin D3. We found that these "single-cyclin" embryos develop normally until late gestation. Our analyses revealed that in single-cyclin embryos, the tissue-specific expression pattern of D-cyclins was lost. Instead, mutant embryos ubiquitously expressed the remaining D-cyclin. These findings suggest that the functions of the three D-cyclins are largely exchangeable at this stage. Later in life, single-cyclin mice displayed focused abnormalities, resulting in premature mortality. "Cyclin D1-only" mice developed severe megaloblastic anemia, "cyclin D2-only" mice presented neurological abnormalities, and "cyclin D3-only" mice lacked normal cerebella. Analyses of the affected tissues revealed that these compartments failed to sufficiently up-regulate the remaining, intact D-cyclin. In particular, we found that in cerebellar granule neuron precursors, the N-myc transcription factor communicates with the cell cycle machinery via cyclins D1 and D2, but not D3, explaining the inability of D3-only mice to up-regulate cyclin D3 in this compartment. Hence, the requirement for a particular cyclin in a given tissue is likely caused by specific transcription factors, rather than by unique properties of cyclins.

Targeted disruption of Slc19a2, the gene encoding the high-affinity thiamin transporter Thtr-1, causes diabetes mellitus, sensorineural deafness and megaloblastosis in mice

Thiamin-responsive megaloblastic anemia syndrome (TRMA) is characterized by diabetes mellitus, megaloblastic anemia and sensorineural deafness. Mutations in the thiamin transporter gene SLC19A2 cause TRMA. To generate a mouse model of TRMA, we developed an Slc19a2 targeting construct using transposon-mediated mutagenesis and disrupted the gene through homologous recombination in embryonic stem cells. Erythrocytes from Slc19a2(-/-) mice lacked the high-affinity component of thiamin transport. On a thiamin-free diet, Slc19a2(-/-) mice developed diabetes mellitus with reduced insulin secretion and an enhanced response to insulin. The diabetes mellitus resolved after 6 weeks of thiamin repletion. Auditory-evoked brainstem response thresholds were markedly elevated in Slc19a2(-/-) mice on a thiamin-free diet, but were normal in wild-type mice treated on that diet as well as thiamin-fed Slc19a2(-/-) mice. Bone marrows from thiamin-deficient Slc19a2(-/-) mice were abnormal, with a megaloblastosis affecting the erythroid, myeloid and megakaryocyte lines. Thus, Slc19a2(-/-) mice have provided new insights into the TRMA disease pathogenesis and will provide a tool for studying the role of thiamin homeostasis in diabetes mellitus more broadly.

Folate and Vitamin B(12) deficiency presenting as pancytopenia in pregnancy: a case report and review of the literature

We present a case of extreme pancytopenia in a 27-year-old pregnant woman. The initial picture was compatible with a severe hematological problem in the category of aplastic anemia, paroxysmal nocturnal hemoglobinuria or even acute leukemia. The further biochemical investigations revealed, however, a folate deficiency. Nowadays this is a very rare cause of pancytopenia. Next to this she also had a Vitamin B(12) deficiency due to intrinsic factor failure. The recent literature is discussed.

A novel mutation in the SLC19A2 gene in a Tunisian family with thiamine-responsive megaloblastic anaemia, diabetes and deafness syndrome

Thiamine-responsive megaloblastic anaemia (TRMA) syndrome with diabetes and deafness was found in two patients from a Tunisian kindred. The proband was homozygous for a novel mutation, 287delG, in the high-affinity thiamine transporter gene, SLC19A2. We demonstrated that fibroblasts from this patient exhibited defective thiamine transport. These data confirm that the SLC19A2 gene is the high-affinity thiamine carrier and that this novel mutation is responsible for TRMA syndrome.

Apoptosis in megaloblastic anemia occurs during DNA synthesis by a p53-independent, nucleoside-reversible mechanism

Deficiency of folate or vitamin B(12) (cobalamin) causes megaloblastic anemia, a disease characterized by pancytopenia due to the excessive apoptosis of hematopoietic progenitor cells. Clinical and experimental studies of megaloblastic anemia have demonstrated an impairment of DNA synthesis and repair in hematopoietic cells that is manifested by an increased percentage of cells in the DNA synthesis phase (S phase) of the cell cycle, compared with normal hematopoietic cells. Both folate and cobalamin are required for normal de novo synthesis of thymidylate and purines. However, previous studies of impaired DNA synthesis and repair in megaloblastic anemia have concerned mainly the decreased intracellular levels of thymidylate and its effects on nucleotide pools and misincorporation of uracil into DNA. An in vitro model of folate-deficient erythropoiesis was used to study the relationship between the S-phase accumulation and apoptosis in megaloblastic anemia. The results indicate that folate-deficient erythroblasts accumulate in and undergo apoptosis in the S phase when compared with control erythroblasts. Both the S-phase accumulation and the apoptosis were induced by folate deficiency in erythroblasts from p53 null mice. The complete reversal of the S-phase accumulation and apoptosis in folate-deficient erythroblasts required the exogenous provision of specific purines or purine nucleosides as well as thymidine. These results indicate that decreased de novo synthesis of purines plays as important a role as decreased de novo synthesis of thymidylate in the pathogenesis of megaloblastic anemia.

Defective high-affinity thiamine transporter leads to cell death in thiamine-responsive megaloblastic anemia syndrome fibroblasts

We have investigated the cellular pathology of the syndrome called thiamine-responsive megaloblastic anemia (TRMA) with diabetes and deafness. Cultured diploid fibroblasts were grown in thiamine-free medium and dialyzed serum. Normal fibroblasts survived indefinitely without supplemental thiamine, whereas patient cells died in 5-14 days (mean 9.5 days), and heterozygous cells survived for more than 30 days. TRMA fibroblasts were rescued from death with 10-30 nM thiamine (in the range of normal plasma thiamine concentrations). Positive terminal deoxynucleotide transferase-mediated dUTP nick end-labeling (TUNEL) staining suggested that cell death was due to apoptosis. We assessed cellular uptake of [3H]thiamine at submicromolar concentrations. Normal fibroblasts exhibited saturable, high-affinity thiamine uptake (Km 400-550 nM; Vmax 11 pmol/min/10(6) cells) in addition to a low-affinity unsaturable component. Mutant cells lacked detectable high-affinity uptake. At 30 nM thiamine, the rate of uptake of thiamine by TRMA fibroblasts was 10-fold less than that of wild-type, and cells from obligate heterozygotes had an intermediate phenotype. Transfection of TRMA fibroblasts with the yeast thiamine transporter gene THI10 prevented cell death when cells were grown in the absence of supplemental thiamine. We therefore propose that the primary abnormality in TRMA is absence of a high-affinity thiamine transporter and that low intracellular thiamine concentrations in the mutant cells cause biochemical abnormalities that lead to apoptotic cell death.

Clinicopathological features of megaloblastic anaemia in Hong Kong: a study of 84 Chinese patients

Megaloblastic anaemia is uncommon in Hong Kong. Eighty-four consecutive Chinese patients with megaloblastic anaemia were studied. There were 48 males and 36 females, with a median age at presentation of 67 years. Vitamin B12 deficiency was found in all cases, with none of the patients showing folate deficiency. The frequency of pernicious anaemia in our patients was higher than in other south-east Asian series but comparable with western ones. When compared with patients in the West, our cases showed the following main differences: virtual absence of folate deficiency, even in alcoholics; absence of associated gastric malignancies; and a high frequency of tuberculosis.

Azathioprine-induced megaloblastic anemia with pancytopenia 22 years after living-related renal transplantation

Macrocytosis and megaloblastic changes in the bone marrow are frequently seen in renal transplant recipients treated with azathioprine (Az). However, severe anemia is a rare side effect of Az. We recently observed a case of severe megaloblastic anemia with pancytopenia in a renal transplant recipient who had been receiving Az therapy for 22 years. The patient was a 46-year-old woman who had been administered Az and prednisolone at a dose of approximately 1.7 mg/kg and 0.17 mg/kg daily, respectively. A bone marrow aspiration revealed megaloblastic anemia with the depletion of myeloid cells and megakaryocytes. She did not have vitamin B12 or folate deficiency. Therefore, FK506 (tacrolimus), a macrolide produced by Streptomyces tsukubaensis, which acts directly on T cells and is known to have less myelosuppression than Az, was substituted for Az. Although the leukopenia improved, the anemia and thrombocytopenia did not improve in the short term. She developed dyspnea and severe subcutaneous bleeding of the right lower extremity due to knee contusions. Hemodialysis was started to treat her uremic state. Although it was impossible to evaluate the long-term effects of FK506 therapy for the pancytopenia in our case, the conversion from Az to a less myelosuppressive drug, such as FK506, should be considered in renal transplant recipients with severe myelosuppression caused by long-term Az treatment.

Apoptosis of late-stage erythroblasts in megaloblastic anemia: association with DNA damage and macrocyte production

An in vitro model of folate-deficient erythropoiesis has been developed using proerythroblasts isolated from the spleens of Friend virus-infected mice fed an amino acid-based, folate-free diet. Control proerythroblasts were obtained from Friend virus-infected mice fed the same diet plus 2 mg folic acid/kg diet. Our previous studies showed that, after 20 to 32 hours of culture in folate-deficient medium with 4 U/mL of erythropoietin, the folate-deficient proerythroblasts underwent apoptosis, whereas control erythroblasts survived and differentiated into reticulocytes over a period of 48 hours. The addition of folic acid or thymidine to the folate-deficient medium prevented the apoptosis of the folate-deficient erythroblasts, thereby implicating decreased thymidylate synthesis as the main cause of apoptosis in the folate-deficient erythroblasts. In the study reported here, we examined intracellular folate levels, uracil misincorporation into DNA, p53 and p21 proteins, and reticulocyte formation in erythroblasts cultured in folate-deficient or control medium. In all experiments, the folate-deficient erythroblasts cultured in folate-deficient medium gave results that varied significantly from folate-deficient erythroblasts cultured in control medium or control erythroblasts cultured in either folate-deficient or control media. Folate-deficient erythroblasts cultured in folate-deficient medium had marked decreases in all coenzyme forms of folate that persisted throughout culture, increased uracil misincorporation into DNA, persistent accumulations of p53 and p21, and decreased reticulocyte production but increased size of individual reticulocytes. A model of folate-deficient erythropoiesis based on apoptosis of late stage erythroblasts is presented. This model provides explanations for the clinical findings in megaloblastic anemia.

Evaluation of DNA analysis for evidence of apoptosis in megaloblastic anaemia

This study involved DNA analysis of bone marrow cells of 15 patients with megaloblastic anaemia. The diagnosis was based on the morphological changes seen in the bone marrow, associated with either a low red cell folate or serum vitamin B12 level and an adequate response to appropriate therapy as confirmation of the diagnosis. Flow cytometric DNA analysis showed an increase in the S and G2 phases of the cell cycle, but conventional agarose gel electrophoretic DNA analysis did not confirm the characteristic 'ladder pattern' which might have been expected in classic apoptosis. In addition, cells showing morphological changes suggestive of apoptosis, such as nuclear condensation and fragmentation, did not show evidence of DNA fragmentation using the ApopTag in situ digoxigenin nucleotide labelled, peroxidase detection system. Further studies using annexin V flow cytometric analysis and pulsed field gel electrophoresis were also unable to detect evidence of apoptosis as a significant cause of cell death in megaloblastic anaemia.

Visual evoked responses in megaloblastic anemia

Pattern shift visual evoked responses (PSVER) were studied in thirty patients suffering from severe megaloblastic anemia (mean Hb level was 4.25 +/- 1.22 g/dL) of nutritional origin. All patients lacked clinical stigmata of visual and neurologic impairment. Mean P100 latency in thirty age and sex matched controls was 96.35 +/- 6.75 ms (range 86-108 ms) and mean amplitude was 10.37 +/- 3.88 microV (range 4.8-20.8 microV). Mean P100 latency in megaloblastic anemia was 114.77 +/- 11.68 (range 91-142) ms, P < 001 vs. control) and mean amplitude was 8.85 +/- 2.8 microV (range 5.1-16.2 microV). Seventy percent cases had prolonged latency of P 100. After correction of anemia with therapeutic doses of vitamin B12 and folic acid in three months (mean Hb level was 12.08 +/- 1.86 g/dL), the mean P100 latency was 105.13 +/- 9.30 ms (range 92-121 ms P < 0.001 vs. controls) and mean amplitude was 10.72 +/- 4.13 microV (range 5.1-21.4 microV). There was significant improvement in P100 latency after correction of anemia (P < 0.01). There was a negative correlation between P100 latency and hemoglobin levels, though it was statistically not significant.

Nucleic acid composition of bone marrow mononuclear cells in cobalamin deficiency

Recent studies using anion exclusion chromatography have suggested that uracil is misincorporated into the DNA of patients with megaloblastic anemia to levels detectable by nonradioactive methods. We have investigated the nucleotide composition of DNA from the bone marrow mononuclear cells of eight patients with cobalamin deficiency and compared this with that found in normal subjects. The median level of uracil in the megaloblastic group was 0.082 mol% of cytosine (approx. 0.02 mol% of all bases in DNA), which was similar to that found in the control group (median 0.085 mol% of cytosine) and may be attributable, at least in part, to artefactual deamination of deoxycytidine monophosphate during the DNA hydrolysis. Our findings give no support for the view that, by overwhelming the uracil N-glycosidase mechanism, the degree of uracil misincorporation in megaloblastic anemia is sufficient to increase the steady state level of uracil in the DNA by amounts detectable by nonradioactive methods. Using high performance liquid chromatography, we have also demonstrated normal levels of methylcytosine in the DNA of megaloblastic subjects.

[Megaloblastic anemia: 30 cases in a district hospital]

The high incidence of megaloblastic anemia observed at our institution (2.1% of hospital admissions) prompted us to analyze the causes of cobalamin and/or folate deficiency in 30 patients admitted during the period 1983-1991 to the Medical Department of Locarno District Hospital. The study population includes 19 women and 11 men with a mean age of 69 years (range 28-91 years). All patients had severe macrocytic anemia (mean hemoglobin 74 +/- 23 g/l, MCV 121 +/- 12 fl), striking megaloblastic changes in aspirated marrow, and an elevated serum level of LDH (2170 +/- 2150 U/l). 19 patients had associated thrombocytopenia, 12 leukopenia and 11 both thrombocytopenia and leukopenia. Treatment led to prompt reticulocytosis and correction of megaloblastic changes in all patients, as well as to nearly complete resolution of the neurologic disorder in a patient with severe spastic ataxia. In 15 patients, megaloblastic anemia was caused by folate deficiency related to alcoholism (n = 6, mean age 55 years) and old age or poverty (n = 9, mean age 73 years). Cobalamin deficiency was present in 9 patients (mean age 69 years); it was due to pernicious anemia in 6 patients and to malabsorption in 2, while the cause remained unexplained in 1. The last patients (mean age 76 years) had deficiency of both cobalamin and folate, related to alcoholism (n = 3) or poverty (n = 3).

[Megaloblastic anemia associated with chronic diarrhea. A prospective and multicenter study in Lima]

Since 1986 we have been observing an increased number of patients with megaloblastic anaemia (MA) associated to chronic diarrhea. In 60% of the cases we could not identify any etiologic factor. In the last three years a prospective study in Lima (Peru) has been carried on aimed to investigate this aspect; patients with diseases recognized to be associated to MA were excluded. 45 patients were included age average 37.5 years, all of them have a confirmed diagnosis by bone marrow; 64% with low serum B12 and folic acid, 20% with low serum B12, and 16% with low serum folic acid. Gastric biopsies did not show atrophy in 67%; intragastric pH was lower than 4 in 50% duodenal content culture was positive in 35% (6/17) to aerobic gram negative agents; 62% (5/8) of duodenal biopsies, 83% (5/6) of jejunal biopsies, 4/4 (100%) of ileal biopsies, showed diverse structural changes; 100% did not show Diphyllobothrium pacificum. All these findings make us suggest that a significative number of patients with MA and chronic diarrhea in Lima are related to small bowel bacterial overgrowth. These bacteria can "sequestrate" or consume folates and cobalamines besides the direct damage they can cause to intestinal morphology. Future studies are needed to confirm our proposal and define if these cases belong to a variety of tropical sprue.

Imerslund-Gräsbeck syndrome in two brothers: renal biopsy and ultrastructural findings

In two Chinese siblings with Imerslund-Gräsbeck syndrome, light microscopy of renal biopsies showed no remarkable change. Ultrastructurally, there were small possible focal defects in the glomerular basement membrane. Neither podocytes nor tubular cells showed evident change. No electron dense deposit was found. Our observations on renal ultrastructure differ from the previous five reports. The literature on renal pathology of this syndrome is reviewed.

Cytoplasmic vacuolization of enterocytes: an unusual histopathologic finding in juvenile nutritional megaloblastic anemia

We report a case of juvenile nutritional megaloblastic anemia with emphasis on the histologic findings in the upper gastrointestinal system, including the previously unreported feature of periodic acid-Schiff (PAS)-negative, Alcian blue-negative cytoplasmic vacuoles (CV) in duodenal enterocytes. These CV were reminiscent of those described in abetalipoproteinemia; however, the patient's lipid profile was normal. All histopathologic changes in the upper gastrointestinal tract (with the exception of mild reflux esophagitis) reverted to normal following parenteral administration of vitamin B12. This case supports the notion that CV in enterocytes are a component (albeit a rare one) of the histopathology in cobalamin deficiency.

[Ultrastructural study of the megakaryocytes in megaloblastic anemia]

The ultrastructure of the megakaryocytes in the bone marrow from 14 cases of megaloblastic anemia was studied. The commonest change observed was that the development of the nucleus lagged behind that of the cytoplasm. There were some evidences supporting the theory of ineffective thrombocytopoiesis. The mechanism of the relationship between the changes of morphology and function based on the impaired DNA synthesis and methylation due to folate and vitamin B12 deficiency were also discussed.

Bone marrow iron in nutritional anaemias

Bone marrow smears of 168 patients with nutritional anaemias attending the Dr. J.C. Patel, Department of Hematology, K.E.M. Hospital were stained by Prussian blue method for iron (haemosiderin). Iron in the bone marrow was classified as absent, decreased, normal or increased. Amongst 93 cases with transferrin saturation (TS) of less than 16% and normoblastic erythropoiesis, bone marrow iron was absent in 48 (51.6%) and decreased in 45 (48.4%). In 50 cases with TS of less than 16% and marrow showing megaloblasts and/or giant myelocytes and metamyelocytes, bone marrow iron was absent in 15 (30%), decreased in 22 (44%), normal in 7 (14%) and increased in 6 (12%). In 25 cases with TS over 16% and megaloblastic erythropoiesis, bone marrow iron was absent in 4 (16%), decreased in 1 (4%), normal in 7 (28%) and increased in 13 (52%). In 150 (89.3%) patients out of 168, bone marrow iron and TS gave concordant results whereas in 18 (10.7%), the results were discordant; former was encountered in cases of uncomplicated iron deficiency while latter was found with megaloblastic morphology of the marrow. It is concluded that there is a good correlation between TS and bone marrow iron and hence, either of the criteria can be used for the diagnosis of iron deficiency especially when it is not complicated by megaloblastosis.

Thymidylate synthesis and utilization via the de novo pathway in normal and megaloblastic human bone marrow cells

We have measured the thymidylate synthetase activity of intact bone marrow cells using a 3H2O release assay. The mean thymidylate synthetase activity of vitamin B12- or folate-deficient megaloblastic marrow cells was reduced only in severely anaemic patients. There was a correlation between thymidylate synthetase activity and RBC in patients with megaloblastic haemopoiesis. The mean rate of incorporation into DNA of 6-3H deoxyuridine was similar in megaloblastic and normoblastic marrows. The rate of thymidylate synthesis exceeded its incorporation into DNA in all marrows, and the mean ratio between synthesis and incorporation was similar in normoblastic and megaloblastic patients, being independent of both thymidylate synthetase activity and RBC. Thus de novo thymine nucleotides were not utilized more efficiently in megaloblastic marrow cells. These data suggest that impaired thymidylate synthesis may not be the central defect in megaloblastic haemopoiesis, and that there is only a single pool of thymidine triphosphate in human bone marrow cells.

The bone marrow in nutritional deficiencies

The overwhelming majority of nutritional deficiencies that affect the bone marrow and blood are due to the lack of vitamin B12, folic acid, or iron or combinations thereof. The two vitamins are closely related in DNA synthesis, whereas iron is the most abundant heavy metal in the body and is chiefly utilized for hemoglobin synthesis. Concomitant conditions of vitamin B12 and/or folate deficiency along with iron deficiency are not infrequent, and one type of anemia may mask the other. It is important to establish the correct diagnoses, as therapy directed at the wrong deficiency may hide the real deficiency with disastrous results. Specific diagnostic tests are now available to determine definitive diagnoses, and specific therapy is readily available to restore and maintain a normal nutrient status.

Erythromyeloid lineage fidelity is conserved in erythroleukaemia

Blast cells from eight patients with erythroleukaemia and one with erythroid blast crisis of chronic myeloid leukaemia were studied for the co-expression of cell surface myeloid and erythroid markers, and the phenotype compared with that of erythroblasts from two patients with megaloblastic anaemia. The technique of dual indirect immunofluorescence was used with a panel of seven mouse monoclonal antibodies against well-defined myeloid antigens (CD11b, 13, 14, 15, 33 and HLA-DR) and a rat antibody, YTH89.1, specific for glycophorin A. No dual fluorescence, emanating from myeloid or erythroid lineage markers, was found to occur in either the neoplastic or non-neoplastic erythroid cells studied. These data support the hypothesis that lineage fidelity is conserved in leukaemia.