Refractory anemia with ringed sideroblasts and thrombocytosis without JAK2 V617F mutation: report of three cases

In the WHO classification, there is a provisional entity called Myelodysplastic/Myeloproliferative Neoplasm, Unclassifiable (MDS/MPN, U). Refractory anemia with ringed sideroblasts associated with marked thrombocytosis (RARS-T) was included in this category. Recently published studies report a small percentage of patients with RARS-T. Sixty percent of these have JAK2 V617F mutation, which can suggest the coexistence of two pathological conditions (MDS and MPN). In this paper, we analyzed three patients diagnosed with RARS-T in the Department of Hematology, "Fundeni" Clinical Institute, Bucharest, Romania, during the period 2005-2011. The patients were investigated with cytogenetic exam and molecular biology. In these three cases were identified morphological features of multilineage dysplasia (two-lineage dysplasia in two cases and three-lineage dysplasia in one case). In two cases, thrombocytosis was under 1000×10(3)/μL and clinical evolution was similar to the myelodysplastic syndrome (transfusion dependent anemia with response to administration of erythropoietin). In the third case, the platelets were over 1000×10(3)/μL and with response to the treatment with Hydrea, which improved anemia. JAK2 V617F mutation was not identified in any case. RARS-T remains a provisional entity and requires a complex investigation of patients for the correct diagnosis of these patients. Therapeutic options should be personalized to each case in part because there is not yet a standardized treatment of these patients.

The role of JAK2 mutations in RARS and other MDS

Acquired sideroblastic anemia with unilineage dysplasia (WHO RARS) is a clonal stem cell disorder characterized by erythroid dysplasia, mitochondrial accumulation of mitochondrial ferritin, defective erythroid maturation and anemia. A fraction of these patients also show elevated platelet counts; since 2001 this has been defined as RARS with marked thrombocytosis (RARS-T). It has recently been described that around half of RARS-T patients, along with a small subset of other MDS and mixed myelodysplastic/ myeloproliferative disorders, carry the JAK2 mutation, and that MPL mutations are found in single patients. Clinically, RARS-T patients show features of both RARS, essential thrombocythmia (ET) and to some extent also myelofibrosis. However, the degree of anemia and overall survival is more similar to RARS than myeloproliferative disorders. The occurrence of JAK2 mutations and features of ET in RARS is too frequent to be the result of chance only, and it is possible that this link may provide a key to an increased understanding of the genetic abnormalities causing ring sideroblast formation.

The JAK2V617F mutation in polycythemia vera and other myeloproliferative disorders: one mutation for three diseases?

The discovery of the JAK2V617F mutation has made the diagnosis of polycythemia vera (PV) much easier, but the pathogenesis of PV is still incompletely understood. In particular, it is not yet elucidated how a single mutation can be found in multiple myeloproliferative disorders (MPD) and myelodysplastic syndromes with ring sideroblasts and whether the sole JAK2V617F is sufficient to induce a MPD in humans. Several hypotheses are under investigation such as differences in the targeted hematopoietic stem cells (HSC), host modifier polymorphisms, intensity of JAK2V617F signaling, presence of other somatic mutations, or the presence of a pre-JAK2 event that may vary according to the MPD phenotype. Multiple studies have provided some evidence for and against each hypothesis, but it now seems possible to reconcile these hypotheses into a model that will need to be tested using newly developed tools. Recent investigations have also led to new treatment modalities that could benefit patients with PV.

Occurrence of the JAK2 V617F mutation in the WHO provisional entity: myelodysplastic/myeloproliferative disease, unclassifiable-refractory anemia with ringed sideroblasts associated with marked thrombocytosis

The JAK2/V617F mutation has been noted in essential thrombocytemia. We investigated 19 cases with refractory anemia with ringed sideroblasts (RARS), including three RARS with thrombocytosis (RARS-T). Only the RARS-T patients showed this mutation. More cases need to be analyzed to determine the prevalence of the JAK2/V617F mutation in RARS-T.

Increased megakaryocytopoiesis in Lyn-deficient mice

Previous studies in cell lines have shown Lyn kinase to be a negative regulator of thrombopoietin (TPO)-induced proliferation. To further investigate the role of Lyn during megakaryocytopoiesis, Lyn-deficient mice (lyn(-/-)) were analyzed. We observed that lyn(-/-) mice have more bone marrow-derived GPIIB (CD41) and Mpl(+) cells when compared to their wild-type littermates. In addition, colony-forming unit-megakaryocytes (CFU-MK) are increased and TPO-induced expansion of primary marrow cells yielded a greater number of mature megakaryocytes (MKs) with increased nuclear ploidy. Histopathology of bone marrow and spleens from lyn(-/-) mice showed an increase in the number of MKs. Mechanistic studies revealed that TPO stimulation of MKs from lyn(-/-) mice did not affect phosphorylation of Janus kinase 2 (JAK2), signal transducer and activator of transcription (STAT) 3, STAT5, or MAP kinase kinase (MEK). Lyn-deficient MKs supported greater TPO-mediated phosphorylation and kinase activity of both Erk1/2 (mitogen-activated protein kinase, MAPK) and Akt. In contrast, there was a reduction of tyrosine phosphorylation of the inositol phosphatase, SHIP. This is the first direct evidence using primary MKs from Lyn-deficient mice that confirms our prior data from cell lines that Lyn kinase is a negative regulator of TPO signaling.

Platelets express steroidogenic 17beta-hydroxysteroid dehydrogenases. Distinct profiles predict the essential thrombocythemic phenotype

Human blood platelets have important, regulatory functions in diverse hemostatic and pathological disorders, including vascular remodeling, inflammation, and wound repair. Microarray analysis was used to study the molecular basis of essential thrombocythemia, a myeloproliferative disorder with quantitative and qualitative platelet defects associated with cardiovascular and thrombohemorrhagic symptoms, not infrequently neurological. A platelet-expressed gene (HSD17B3) encoding type 3 17beta-hydroxysteroid dehydrogenase (previously characterized as a testis-specific enzyme catalyzing the final step in gonadal synthesis of testosterone) was selectively down-regulated in ET platelets, with reciprocal induction of the type 12 enzyme (HSD17B12). Functional 17beta-HSD3 activity corresponding to approximately 10% of that found in murine testis was demonstrated in normal platelets. The induction of HSD17B12 in ET platelets was unassociated with a concomitant increase in androgen biosynthesis, suggesting distinct functions and/or substrate specificities of the types 3 and 12 enzymes. Application of a molecular assay distinguished ET from normal platelets in 20 consecutive patients (p < 0.0001). These data provide the first evidence that distinct subtypes of steroidogenic 17beta-HSDs are functionally present in human blood platelets, and that the expression patterns of HSD17B3 and HSD17B12 are associated with an uncommon platelet disorder manifest by quantitative and qualitative platelet defects.

The JAK2V617F tyrosine kinase mutation in myelofibrosis with myeloid metaplasia: lineage specificity and clinical correlates

An association between an activating JAK2 mutation (JAK2(V617F)) and BCR/ABL-negative myeloproliferative disorders was recently reported in multiple simultaneous publications. In the current study, mutation analysis for JAK2(V617F) was performed in peripheral blood mononuclear cells (PBMC) from 157 patients with myelofibrosis with myeloid metaplasia (MMM) including 117 with agnogenic (AMM), 22 with postpolycythaemic (PPMM), and 18 with post-thrombocythaemic (PTMM) myeloid metaplasia. The detection rate for JAK2(V617F) was significantly higher in PPMM (91%; homozygous in 18%) compared with either AMM (45.3%; homozygous in 2.6%) or PTMM (38.9%; homozygous in 11.1%). Concomitant analysis in granulocytes (n=57) and CD34(+) cells (n=25) disclosed a higher incidence of homozygous JAK2(V617F) mutation but the overall mutation rate was similar to that obtained from PBMC. JAK2(V617F) was not detected in DNA derived from T cells (n=19). In AMM, the presence of JAK2(V617F) was associated with an older age at diagnosis and a history of thrombosis or pruritus. Multivariate analysis identified only age and the Dupriez prognostic score as independent prognostic factors; JAK2(V617F) had no prognostic significance. In conclusion, JAK2(V617F) is a myeloid lineage-specific event, its incidence in MMM is significantly higher with an antecedent history of polycythaemia vera (PV), and its presence in AMM does not affect prognosis but is associated with PV-characteristic clinical features.

Platelet glyoxalases in thrombocytosis

In platelets of patients suffering from thrombocytosis due to myeloproliferative disorders, glyoxalase I activity is significantly higher than in controls (P less than 0.01), while glyoxalase II levels are the same (P less than 0.3). The cellular concentration of glutathione is also increased in patients. Km values for methylglyoxal (glyoxalase I) and S-lactoylglutathione (glyoxalase II) are identical both in normal and pathological subjects, as are the thermostability of the two enzymes. The higher activity observed for glyoxalase I in patients could be related to a specific role of this enzyme in platelets.

Essential thrombocythemia: a clonal disorder of hematopoietic stem cell

We studied 5 patients with essential thrombocythemia utilizing glucose-6-phosphate dehydrogenase (G-6-PD) enzyme as a cell marker for determining clonality. One of the patients was found to be heterozygous for isoenzymes B and A in the nonhaemopoietic tissues such as fibroblasts, but manifested only isoenzyme type B in the erythrocytes, neutrophils, and platelets. Our studies support the concept that essential thrombocythemia is a clonal disorder arising in a multipotent stem cell.

Quantitation of RNA-dependent platelet DNA polymerase in patients with myeloproliferative disorders

Platelets from 28 patients with the myeloproliferative diseases (MPD) polycythaemia vera (9), essential thrombocythaemia (6), myelofibrosis with myeloid metaplasia (5) and chronic myelogenous leukaemia (8) were examined for an RNA-dependent DNA polymerase activity using standardized conditions permitting highly reproducible quantitation. Low levels of activity were detected in platelets of normal individuals, but platelets of nearly all MPD patients (25/28) possessed higher levels. The polymerase activity correlated with diagnosis (P = 0.001) and did not correlate with platelet counts (P greater than 0.2). Quantitation of this RNA-dependent DNA polymerase activity may be a useful parameter in the diagnosis of myeloproliferative disorders.

Evidence that essential thrombocythemia is a clonal disorder with origin in a multipotent stem cell

Essential thrombocythemia is characterized by proliferation of hematopoietic tissue predominantly involving megakaryocytes and resulting in marked thrombocytosis. The disorder has some clinical and laboratory features that resemble those seen in the clonal multipotent stem cell disorders chronic myelogenous leukemia, polycythemia vera, and agnogenic myeloid metaplasia. It has been argued that essential thrombocythemia should be classified together with those disorders as a myeloproliferative syndrome. However, without knowledge of the numbers and types of cells that are involved in essential thrombocythemia, this suggestion remains speculative. Three patients with thrombocytosis were studied. The diagnosis of essential thrombocythemia was considered to be firm in two patients and probable in the third one. The X-linked glucose-6-phosphate dehydrogenase locus was used as a cell marker. Whereas both A and B types of glucose-6-phosphate dehydrogenase were found in nonhematopoietic tissues, only a single-enzyme type was found in the granulocytes, red cells, and platelets from each patient. These data indicate that the disorders in these three patients are clonal and involve multipotent stem cells.

Platelet monoamine oxidase as a function of nongenetic factors

The level of platelet monoamine oxidase (MAO) has been found to be abnormally low in certain types of schizophrenia and in a number of other pathological conditions. It has been suggested that MAO in platelets may be a genetic marker for a subgroup of patients with schizophrenia; however, we have demonstrated that several nongenetic factors influence platelet MAO activity by affecting the platelet rather than the MAO enzyme protein. We have observed platelet MAO activities to be heterogeneously distributed in a given subject's platelet population, heavy platelet fractions having significantly higher specific activity than light platelet fractions. We have also found platelet MAO activity to be significantly correlated with mean platelet volume, platelet protein densities, and protein content per platelet. These changes, which might be induced by drugs and stress, could modify production, mobilization, and clearance of platelets and, hence, influence apparent MAO activity.

Plasma lactate dehydrogenase activity will be increased if detergent and platelets are present

Plasma lactate dehydrogenase activity is artifactually increased when analyzed on the SMAC (Technicon) continuous-flow analyzer. The factors responsible are incomplete centrifugation and the presence of detergent in the dilution buffer. The contribution of platelet lactate dehydrogenase in the plasma is demonstrated with a case of thrombocytosis.

Platelet-derived acid phosphatase isoenzyme in the serum in thrombocythemia

Acid phosphatase is present in platelets and is released during the clotting process. In thrombocythemic conditions, this may increase serum enzymatic activity. An illustrative case in which the determination of plasma enzymatic activity suggested a platelet origin of elevated serum levels, confirmed by isoenzyme fractionation on disk polyacrylamide gel electrophoresis is presented. It is concluded that in the presence of thrombocytosis a plasma sample is preferable to a serum sample for determination of acid phosphatase activity.

Analysis of platelets from patients with thrombocythemia for reverse transcriptase and virus-like particles

A preliminary analysis of an RNA-directed DNA polymerase was made and a C-type virus-like particle was identified in platelets from 2 patients with the myeloproliferative disorder thrombocythemia (primary, essential, hemorrhagic, or idiopathic thrombocythemia). Platelet homogenates were centrifuged through a sucrose equilibrium density gradient. Both endogenous and exogenous DNA polymerase activity was found at a density of 1.19 g/ml. No activity was seen at comparable densities in control gradients. Electron micrographs of thin sections of these platelets revealed a particle with the morphologic characteristics of a C-type virus; however, the diameter of this particle was about 80 nm, slightly lower than that commonly found for C-type particles. Critical-point dried specimens, from the fractions of the sucrose gradient at which DNA polymerase activity was found, contained particles of the same size and morphology as those in the thin sections.