JAK2V617F mutation in platelets from essential thrombocythemia patients: correlation with clinical features and analysis of STAT5 phosphorylation status

Molecular Genetics of Thrombotic Myeloproliferative Neoplasms: Implications in Precision Oncology

Classical BCR-ABL-negative myeloproliferative neoplasms (MPN) include polycythaemia vera, essential thrombocythaemia, and primary myelofibrosis. Unlike monogenic disorders, a more complicated series of genetic mutations are believed to be responsible for MPN with various degrees of thromboembolic and bleeding complications. Thrombosis is one of the early manifestations in patients with MPN. To date, the driver genes responsible for MPN include JAK2, CALR, MPL, TET2, ASXL1, and MTHFR. Affords have been done to elucidate these mutations and the incidence of thromboembolic events. Several lines of evidence indicate that mutations in JAK2, MPL, TET2 and ASXL1 gene and polymorphisms in several clotting factors (GPIa, GPIIa, and GPIIIa) are associated with the occurrence and prevalence of thrombosis in MPN patients. Some polymorphisms within XRCC1, FBG, F2, F5, F7, F12, MMP9, HPA5, MTHFR, SDF-1, FAS, FASL, TERT, ACE, and TLR4 genes may also play a role in MPN manifestation. This review aims to provide an insightful overview on the genetic perspective of thrombotic complications in patients with MPN.

Platelets as Mediators of Thromboinflammation in Chronic Myeloproliferative Neoplasms

Chronic myeloproliferative neoplasms (MPN) are stem cell disorders driven by mutations in JAK2, CALR, or MPL genes and characterized by myeloid proliferation and increased blood cell counts. They encompass three closely related conditions, including essential thrombocythemia, polycythemia vera, and primary myelofibrosis. Elevated levels of cytokines released by clonal and non-clonal cells generate a chronic proinflammatory state that contributes to disease pathogenesis. Thrombosis represents the most common cause of morbidity and mortality in MPN, although paradoxically, patients may also present with a bleeding diathesis. The mechanisms leading to thrombosis are complex and multiple and include increased blood cells together with qualitative abnormalities of red cells, leukocytes, and platelets that favor a prothrombotic activated phenotype. The functional interplay between blood cells, the clotting cascade, and dysfunctional endothelium contributes to hypercoagulability and this process is perpetuated by the effect of inflammatory cytokines. In addition to their well-known function in hemostasis, platelets contribute to innate immunity and inflammation and play a key role in MPN thromboinflammatory state. In vivo platelet activation leads to platelet aggregate formation and exposure of adhesion molecules which favor their interaction with activated neutrophils and monocytes leading to circulating platelet-leukocyte heterotypic aggregates. Platelets are recruited to the activated endothelium further enhancing the reciprocal activation of both cell types. Crosstalk between activated cells drives cytokine production, further fuelling the self-reinforcing thromboinflammatory loop. In addition, MPN platelets provide a procoagulant scaffold which triggers the coagulation cascade and platelet-derived microparticles amplify this response. Markers of platelet, leukocyte, endothelial and coagulation activation are increased in MPN patients although prospective studies are required to determine the potential value of these parameters for identifying patients at increased thrombotic risk. Thrombosis remains the main complication of MPN patients, with a high risk of recurrence despite adequate cytoreductive and antithrombotic treatment. Deeper insight into the mechanism favoring thrombosis development in this setting may lead to novel therapeutic approaches for MPN thrombosis. Considering the critical role of inflammation in the vascular risk, concomitant targeting of inflammatory pathways could potentially impact on primary or secondary prevention strategies.

Essential thrombocythemia during treatment of acute myeloid leukemia with JAK2 V617F mutation: A case report of a CARE-compliant article

RATIONALE

The JAK2 V617F mutation is frequently found in ET, while it is rare in de novo AML. ET has a low frequency of leukemic transformation. Both secondary AML (sAML) from ET and AML with JAK2 V617F mutation have poor prognoses. Because of the low incidence of JAK2 mutation in acute myeloid leukemia (AML), the clinical features of AML with JAK2 mutation are rarely reported so far, either transformed from essential thrombocythemia (ET) or de novo AML.

PATIENT CONCERNS

In this article, we present a pediatric AML patient with the JAK2 V617F mutation.

DIAGNOSES

A diagnosis of acute megakaryoblastic leukemia was made and sAML was ruled out.

INTERVENTIONS

The patient underwent chemotherapy.

OUTCOMES

In the first two complete remission periods, we found significantly increased numbers of platelets and bone marrow megakaryocytes, which are characteristic of ET. After the third chemotherapy phase, the disease relapsed; the platelet count was reduced and continued to decrease. When disease relapsed, her family abandoned treatment.

LESSONS

These observations of our case raise two possibilities: either transient posttreatment thrombocythemia is a feature of AML with JAK2 V617F mutation, or this was a case of secondary AML. Additional information is required to reach better conclusions on the connection between AML and JAK2 mutations.

The Impact of Mean Platelet Volume (MPV) and JAK-2 Mutation on Thrombosis in Chronic Myeloproliferative Diseases

Thrombosis and bleeding are the main complications of chronic myeloproliferative diseases. Mean platelet volume (MPV) is an important indicator of the platelet activation. The aim of the present study was to assess the interrelationships between MPV, JAK-2 gene mutation and thromboembolic events in patients with ET and PV. Patients with ET (n = 60) and PV (n = 46) were compared to the secondary erythrocytosis group (n = 19); and a control group of age and sex matched healthy volunteers (n = 52). Besides demographic, clinical and laboratory data; thrombotic and hemorrhagic events were recorded for each patient. Platelet counts, MPV and JAK2 mutations were studied; and their relation with thromboembolic events were investigated using SPSS program for statistical analysis. There was no significant difference between groups regarding age (p = 0.188). Mean platelet count was significantly higher in ET group than other groups (p < 0.0001). Mean platelet count in PV group was significantly higher than control (p < 0.0001) and secondary erythrocytosis groups (p < 0.0001). In the ET group, MPV values were significantly lower than the control group and PV group. In the ET group, those with thromboembolia had lower platelet counts. There was no relation between MPV and thromboembolic event rate in PV, ET and secondary erithrocytosis groups; while no event was recorded in the control group. There was no relation between thromboembolic event rate and JAK 2 mutation. The association of JAK-2 mutation and high MPV especially in ET and PV groups does not contribute to the thromboembolic events.

Neutrophil extracellular trap formation and circulating nucleosomes in patients with chronic myeloproliferative neoplasms

The mechanisms underlying increased thrombotic risk in chronic myeloproliferative neoplasms (MPN) are incompletely understood. We assessed whether neutrophil extracellular traps (NETs), which promote thrombosis, contribute to the procoagulant state in essential thrombocythemia, polycythemia vera and myelofibrosis (MF) patients. Although MPN neutrophils showed increased basal reactive oxygen species (ROS), enhanced NETosis by unstimulated neutrophils was an infrequent finding, whereas PMA-triggered NETosis was impaired, particularly in MF, due to decreased PMA-triggered ROS production. Elevated circulating nucleosomes were a prominent finding and were higher in patients with advanced disease, which may have potential prognostic implication. Histone-MPO complexes, proposed as specific NET biomarker, were seldomly detected, suggesting NETs may not be the main source of nucleosomes in most patients, whereas their correlation with high LDH points to increased cell turn-over as a plausible origin. Lack of association of nucleosomes or NETs with thrombosis or activation markers does not support their use as predictors of thrombosis although prospective studies in a larger cohort may help define their potential contribution to MPN thrombosis. These results do not provide evidence for relevant in vivo NETosis in MPN patients under steady state conditions, although availability of standardized NET biomarkers may contribute to further research in this field.

Is JAK2V617F Mutation the Only Factor for Thrombosis in Philadelphia-Negative Chronic Myeloproliferative Neoplasms?

The most common genetic disorder in Philadelphia negative chronic myeloproliferative neoplasms is the JAK2-V617F mutation. In the present study, we aimed to determine risk factors for thrombosis in patients with essential thrombocytosis and polycythemia vera. We screened the medical records of 101 patients. Risk factors which may predict thrombosis were recorded. Venous thrombosis (VT) before diagnosis was significantly higher in JAK2 positive patients. VT after diagnosis was similar in JAK2 positive and negative groups, and was significantly higher in elderly patients. Treatment places importance on the JAK2 mutation under unmodifiable cardiovascular risk factors such as advanced age after diagnosis.

Impact of JAK2V617F Mutational Status on Phenotypic Features in Essential Thrombocythemia and Primary Myelofibrosis

Objective:

The JAK2V617F mutation is present in the majority of patients with essential thrombocythemia (ET) and primary myelofibrosis (PMF). The impact of this mutation on disease phenotype in ET and PMF is still a matter of discussion. This study aims to determine whether there are differences in clinical presentation and disease outcome between ET and PMF patients with and without the JAK2V617F mutation.

Materials and Methods:

In this single-center study, a total of 184 consecutive Philadelphia-negative chronic myeloproliferative neoplasms, 107 cases of ET and 77 cases of PMF, were genotyped for JAK2V617F mutation using the JAK2 Ipsogen MutaScreen assay, which involves allele-specific polymerase chain reaction.

Results:

ET patients positive for JAK2V617F mutation had higher hemoglobin (Hb) and hematocrit (Hct) levels, lower platelet counts, and more prevalent splenomegaly at diagnosis compared to patients negative for the JAK2V617F mutation, but rates of major thrombotic events, arterial thrombosis, and venous thrombosis were comparable between the groups. At presentation, PMF patients with JAK2V617F mutation had significantly higher Hb and Hct levels and leukocyte counts than patients without the mutation. Similar to the findings of ET patients, thromboembolic rates were similar in PMF patients with and without theJAK2V617F mutation. For ET and PMF patients, no difference was observed in rates of death with respect to JAK2V617F mutational status. Moreover, leukemic transformation rate was not different in our PMF patients with and without JAK2V617F mutation.

Conclusion:

We conclude that JAK2V617F-mutated ET patients express a polycythemia vera-like phenotype and JAK2V617F mutation in PMF patients is associated with a more pronounced myeloproliferative phenotype.

The impact of JAK2V617F mutation on different types of thrombosis risk in patients with essential thrombocythemia: a meta-analysis

To assess the effect of JAK2V617F on different thrombotic risks in essential thrombocythemia (ET) patients, we identified eligible studies from several databases including Pubmed, Embase, and Cochrane Central Register of Controlled Trials (up to November 2014). Twenty-two studies of 2922 ET patients were included in exploring the relationship between JAK2V617F and the risk of thrombosis. Compared to JAK2V617F-negative ET patients, JAK2V617F-positive ET patients had higher odd risks (ORs) of arterial thrombosis [OR = 2.59 (1.84-3.65)] and venous thrombosis [OR = 2.10 (1.53-2.88)]. The JAK2V617F-positive group was also more prone to increased risk of microcirculatory disturbances [OR = 1.50 (0.97-2.32)]. Moreover, JAK2V617F may indicate increased risk of either arterial [OR = 1.71 (1.22-2.39)] or venous thrombosis [OR = 2.90 (1.54-5.46)] before diagnosis of ET. During follow-up, JAK2V617F might not be related to arterial thrombosis [OR = 1.90 (0.90-2.08)], but rather venous thrombosis [OR = 1.95 (1.08-3.53)]. In conclusion, JAK2V617F increased the risk of arterial and venous thrombosis in ET patients, while understanding its role in microcirculatory disturbances will require further studies.

Methods for detecting mutations in the human JAK2 gene

Mutations in the JAK2 gene are prevalent in the human myeloid malignancies, being present in virtually all cases of polycythemia vera, and a significant proportion of patients with other myeloproliferative disorders. Various methods for the detection of acquired mutations in this gene are available depending on the need for sensitivity, quantification, or the ability to detect many different mutations. We summarize the various methods published and discuss their relative merits for each application. Two commonly used methods, quantitative real-time PCR (QPCR) for the detection of the JAK2 V617F mutation and high resolution melt-curve analysis (HRM) for the detection of multiple mutations within JAK2 exon 12, demonstrate the utility of each method and their limitations. The choice of methodology is dependent on the application; therefore there is no gold standard for detecting mutations in this gene.

Does thrombocyte size give us an idea about thrombocytosis etiology?

In the presence of a pathogenetic mutation in JAK2 or MPL, a differential diagnosis of essential thrombocythemia (ET) from reactive causes is relatively simple. However, in patients with suspected ET who lack JAK2 and MPL mutations, the exclusion of secondary causes is especially important. The study was aimed to explore the clinical application of particularly mean platelet volume (MPV), hemoglobin, red blood cell indices, white blood cell, serum iron profile, and C-reactive protein level in the differential diagnosis of thrombocytosis. Medical records of 49 patients, consisting of reactive thrombocytosis (RT) and ET were retrospectively reviewed. The mean MPV level in RT group was 7.49 fL, and in ET group was 8.80 fL (P < 0.01). A cutoff point of <8.33 fL was found to have significant predictive value according to ROC curve analysis. This cutoff was associated with 83% positive predictive value (PPV) and 74% negative predictive value (NPV) in the diagnosis of ET and had a sensitivity of 65% and specificity of 89% for ET. Investigation of MPV is cheap, quick, and noninvasive, and may serve as a predictor of primary thrombocytosis. High sensitivity, specificity, PPV, and NPV enable this test an important tool and a possible surrogate marker in clinical practice.

Imaging flow cytometry: coping with heterogeneity in biological systems

Imaging flow cytometry (IFC) platforms combine features of flow cytometry and fluorescent microscopy with advances in data-processing algorithms. IFC allows multiparametric fluorescent and morphological analysis of thousands of cellular events and has the unique capability of identifying collected events by their real images. IFC allows the analysis of heterogeneous cell populations, where one of the cellular components has low expression (<0.03%) and can be described by Poisson distribution. With the help of IFC, one can address a critical question of statistical analysis of subcellular distribution of proteins in a cell. Here the authors review advantages of IFC in comparison with more traditional technologies, such as Western blotting and flow cytometry (FC), as well as new high-throughput fluorescent microscopy (HTFM), and discuss further developments of this novel analytical technique.

Distinct clinical phenotypes associated with JAK2V617F reflect differential STAT1 signaling

The JAK2V617F mutation is associated with distinct myeloproliferative neoplasms, including polycythemia vera (PV) and essential thrombocythemia (ET), but it remains unclear how it generates disparate disorders. By comparing clonally-derived mutant and wild-type cells from individual patients, we demonstrate that the transcriptional consequences of JAK2V617F are subtle, and that JAK2V617F-heterozygous erythroid cells from ET and PV patients exhibit differential interferon signaling and STAT1 phosphorylation. Increased STAT1 activity in normal CD34-positive progenitors produces an ET-like phenotype, whereas downregulation of STAT1 activity in JAK2V617F-heterozygous ET progenitors produces a PV-like phenotype. Our results illustrate the power of clonal analysis, indicate that the consequences of JAK2V617F reflect a balance between STAT5 and STAT1 activation and are relevant for other neoplasms associated with signaling pathway mutations.

Novel mutations in the inhibitory adaptor protein LNK drive JAK-STAT signaling in patients with myeloproliferative neoplasms

Dysregulated Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling due to activation of tyrosine kinases is a common feature of myeloid malignancies. Here we report the first human disease-related mutations in the adaptor protein LNK, a negative regulator of JAK-STAT signaling, in 2 patients with JAK2 V617F-negative myeloproliferative neoplasms (MPNs). One patient exhibited a 5 base-pair deletion and missense mutation leading to a premature stop codon and loss of the pleckstrin homology (PH) and Src homology 2 (SH2) domains. A second patient had a missense mutation (E208Q) in the PH domain. BaF3-MPL cells transduced with these LNK mutants displayed augmented and sustained thrombopoietin-dependent growth and signaling. Primary samples from MPN patients bearing LNK mutations exhibited aberrant JAK-STAT activation, and cytokine-responsive CD34(+) early progenitors were abnormally abundant in both patients. These findings indicate that JAK-STAT activation due to loss of LNK negative feedback regulation is a novel mechanism of MPN pathogenesis.

ZFP36L1 negatively regulates erythroid differentiation of CD34+ hematopoietic stem cells by interfering with the Stat5b pathway

ZFP36L1 is a member of a family of CCCH tandem zinc finger proteins (TTP family) able to bind to AU-rich elements in the 3'-untranslated region of mRNAs, thereby triggering their degradation. The present study suggests that such mechanism is used during hematopoiesis to regulate differentiation by posttranscriptionally modulating the expression of specific target genes. In particular, it demonstrates that ZFP36L1 negatively regulates erythroid differentiation by directly binding the 3' untranslated region of Stat5b encoding mRNA. Stat5b down-regulation obtained by ZFP36L1 overexpression results, in human hematopoietic progenitors, in a drastic decrease of erythroid colonies formation. These observations have been confirmed by silencing experiments targeting Stat5b and by treating hematopoietic stem/progenitor cells with drugs able to induce ZFP36L1 expression. Moreover, this study shows that different members of ZFP36L1 family act redundantly, because cooverexpression of ZFP36L1 and family member ZFP36 determines a cumulative effect on Stat5b down-regulation. This work describes a mechanism underlying ZFP36L1 capability to regulate hematopoietic differentiation and suggests a new target for the therapy of hematopoietic diseases involving Stat5b/JAK2 pathway, such as chronic myeloproliferative disorders.

Prognostic utility of spontaneous erythroid colony formation and JAK2 mutational analysis for thrombotic events in essential thrombocythaemia

BACKGROUND

Thrombotic events in essential thrombocythaemia (ET) are difficult to predict with current risk stratification based on age and prior history of thrombosis.

AIMS

We aimed to assess the predictive value of the JAK2 V617F mutation (JAK2) and spontaneous erythroid colony (SEC) growth for the development of thrombotic events post diagnosis in patients with ET.

METHODS

Consecutive patients with ET were retrospectively identified, and clinical and laboratory correlates were evaluated. Thrombotic events were categorized according to their occurrence at or prior to diagnosis (prior thrombosis), and any time post diagnosis of ET (subsequent thrombosis). JAK2 analysis was performed by allele-specific PCR on whole blood or bone marrow.

RESULTS

A total of 62 patients was identified, median age 63 years; 67% (41/61) JAK2-positive and 47% (25/53) SEC-positive. Median follow-up was 33 months (range, 1 to 137). JAK2-positive patients showed a trend to increased prior thrombosis (27% vs 5%, P= 0.08), and a significant increase in the development of subsequent thrombosis (5-year event rate 31% vs 6%, P= 0.04), which persisted when stratified for a history of prior thrombosis (P= 0.04). Survival was not affected by JAK2 status. The SEC assay predicted an increased rate of baseline thrombosis (16% vs 0%, P= 0.04), but was not found to be predictive of any subsequent thrombotic events.

CONCLUSIONS

Patients with ET who are JAK2-positive by whole blood allele-specific PCR appear to be at increased risk of thrombotic complications, which is independent of a prior history of thrombosis.

JAK2 V617F impairs hematopoietic stem cell function in a conditional knock-in mouse model of JAK2 V617F-positive essential thrombocythemia

The JAK2 V617F mutation is found in most patients with a myeloproliferative neoplasm and is sufficient to produce a myeloproliferative phenotype in murine retroviral transplantation or transgenic models. However, several lines of evidence suggest that disease phenotype is influenced by the level of mutant JAK2 signaling, and we have therefore generated a conditional knock-in mouse in which a human JAK2 V617F is expressed under the control of the mouse Jak2 locus. Human and murine Jak2 transcripts are expressed at similar levels, and mice develop modest increases in hemoglobin and platelet levels reminiscent of human JAK2 V617F-positive essential thrombocythemia. The phenotype is transplantable and accompanied by increased terminal erythroid and megakaryocyte differentiation together with increased numbers of clonogenic progenitors, including erythropoietin-independent erythroid colonies. Unexpectedly, JAK2(V617F) mice develop reduced numbers of lineage(-)Sca-1(+)c-Kit(+) cells, which exhibit increased DNA damage, reduced apoptosis, and reduced cell cycling. Moreover, competitive bone marrow transplantation studies demonstrated impaired hematopoietic stem cell function in JAK2(V617F) mice. These results suggest that the chronicity of human myeloproliferative neoplasms may reflect a balance between impaired hematopoietic stem cell function and the accumulation of additional mutations.

Screening for MPL mutations in essential thrombocythemia and primary myelofibrosis: normal Mpl expression and absence of constitutive STAT3 and STAT5 activation in MPLW515L-positive platelets

OBJECTIVES

To evaluate the frequency of MPL W515L, W515K and S505N mutations in essential thrombocythemia (ET) and primary myelofibrosis (PMF) and to determine whether MPLW515L leads to impaired Mpl expression, constitutive STAT3 and STAT5 activation and enhanced response to thrombopoietin (TPO).

METHODS

Mutation detection was performed by allele-specific PCR and sequencing. Platelet Mpl expression was evaluated by flow cytometry, immunoblotting and real-time RT-PCR. Activation of STAT3 and STAT5 before and after stimulation with increasing concentrations of TPO was studied by immunoblotting. Plasma TPO was measured by ELISA.

RESULTS

MPLW515L was detected in 1 of 100 patients with ET and 1 of 11 with PMF. Platelets from the PMF patient showed 100% mutant allele, which was <50% in platelets from the ET patient, who also showed the mutation in granulocytes, monocytes and B cells. Mpl surface and total protein expression were normal, and TPO levels were mildly increased in the MPLW515L-positive ET patient, while MPL transcripts did not differ from controls in both MPLW515L-positive patients. Constitutive STAT3 and STAT5 phosphorylation was absent and dose response to TPO-induced phosphorylation was not enhanced.

CONCLUSIONS

The low frequency of MPL mutations in this cohort is in agreement with previous studies. The finding of normal Mpl levels in MPLW515L-positive platelets indicates this mutation does not lead to dysregulated Mpl expression, as frequently shown for myeloproliferative neoplasms. The lack of spontaneous STAT3 and STAT5 activation and the normal response to TPO is unexpected as MPLW515L leads to constitutive receptor activation and hypersensitivity to TPO in experimental models.

Src tyrosine kinase preactivation is associated with platelet hypersensitivity in essential thrombocythemia and polycythemia vera

Polycythemia vera (PV) and essential thrombocythemia (ET) are chronic myeloproliferative disorders characterized by an increased incidence of thrombo-hemorrhagic complications. The acquired somatic Janus kinase 2 (JAK2) V617F mutation is present in the majority of PV and ET patients. Because aberrant protein Tyr-phosphorylation has been associated with hematopoietic malignancies, the activity of the tyrosine kinases Src and JAK2 was analyzed in resting and thrombin-stimulated platelets from 13 PV and 42 ET patients. JAK2 was found inactive in healthy and pathological resting cells regardless of the V617F mutation. In addition, Src was inactive in all resting platelets, but in the pathological specimens it was present in a preactivated conformation as a consequence of anomalous dephosphorylation of its inhibitory phospho-Tyr527 residue, likely mediated by Src homology-2 domain-containing protein Tyr-phosphatase-2 (SHP-2), whose constitutive activity correlated with its recruitment to Src. Low thrombin concentration triggered a more rapid Src-signaling activation, higher [Ca2+]c increase, and aggregation in pathological platelets compared with controls. Thrombin-induced Src activation preceded JAK2 activation, which occurred simultaneously in normal and pathological platelets. Our results indicate that a constitutive Src kinase preactivation is implicated in platelet hypersensitivity and likely involved, at least partially, in the functional abnormalities of PV and ET platelets.

Cytogenetic abnormalities in essential thrombocythemia at presentation and transformation

Cytogenetic abnormalities in patients with essential thrombocythemia (ET) are infrequent. Their role in survival of patients and disease transformation is not extensively studied. We describe cytogenetic abnormalities in 172 patients with ET at a single institution. At presentation nine (5.2%) patients had cytogenetic abnormality and three (1.7%) additional patients acquired them during follow-up. Survival of patients with cytogenetic changes at presentation did not differ when compared to the patients with normal karyotype. The more common were abnormalities of chromosome 9 (n = 4), 20 (n = 2), 5 (n = 2), and complex abnormalities (n = 2). Forty-one patients (23.8%) had additional cytogenetic tests performed for monitoring purposes during follow-up. Five patients (2.9%) with normal karyotype transformed to myelofibrosis (MF) without developing new cytogenetic changes at transformation. Two patients (1.2%) with normal karyotypes at presentation transformed to myelodysplastic syndrome and acute myeloid leukemia, respectively. Both acquired complex cytogenetic changes at the time of transformation. There is no rationale for repeating cytogenetic tests in ET patients on follow up, unless blood cell count changes suggest possible transformation.

Association of V617F Jak2 mutation with the risk of thrombosis among patients with essential thrombocythaemia or idiopathic myelofibrosis: a systematic review

INTRODUCTION

Many studies evaluated the association of V617F Jak-2 with the risk of thrombosis in patients with essential thrombocythaemia, but the results of these studies were inconsistent. Few studies evaluated the association of V617F Jak-2 mutation with the risk of thrombosis in patients with idiopathic myelofibrosis. Therefore, we performed a systematic review of the studies that assessed the risk of thrombosis associated with V617F Jak-2 in patients with ET or IM.

MATERIALS AND METHODS

We searched MEDLINE and EMBASE databases and reference lists of retrieved articles. Odds ratios (ORs) and 95% confidence intervals (CI) were calculated for each trial and pooled.

RESULTS

We included 21 studies involving patients with essential thrombocythaemia and 6 studies patients with idiopathic myelofibrosis. In essential thrombocythaemia patients, V617F Jak-2 was associated with a significant increased risk of thrombosis (OR 1.92, 95% CI 1.45-2.53), both of venous (OR 2.49, 95% CI 1.71-3.61) and arterial (OR 1.77, 95% CI 1.29-2.43) vessels. In idiopathic myelofibrosis patients, the risk of thrombosis associated with V617F Jak-2 tended to be increased (OR 1.76, 95% CI 0.91-3.41).

CONCLUSIONS

Our systematic review suggests that V617F Jak-2 increases the risk of thrombosis in essential thrombocythaemia patients by about two fold while its role in idiopathic myelofibrosis patients is uncertain.

High prevalence of arterial thrombosis in JAK2 mutated essential thrombocythaemia: independence of the V617F allele burden

Approximately half of the patients with essential thrombocythaemia (ET) harbor the JAK2 V617F mutation. Despite a phenotypic mimicry of JAK2 V617F positive ET and polycythaemia vera (PV), the data on thromboembolic risk and correlation to JAK2 mutation status are ambiguous. On a strictly WHO defined ET cohort we evaluated possible clinical correlations to the JAK2 mutation status including a history of previous thrombosis. We used a highly sensitive quantitative real-time PCR (qPCR) assay for JAK2 V617F detection and allele burden quantification in a single institution study of 55 patients. A significantly increased prevalence of arterial thrombosis was recorded in JAK2 positive ET (p=0.001). There was no association between the mutational load and thrombosis. As compared to their JAK2 V617F negative counterparts, the JAK2 V617F positive patients had PV-like biochemical characteristics such as higher haemoglobin levels (p=0.02), lower platelet counts (p=0.002) and lower plasma EPO levels (p=0.04). The JAK2 V617F mutation per se but not the mutational load in patients with ET is associated with a PV-like phenotype and a higher prevalence of previous arterial thrombosis. This study adds further support to the contention of the JAK2 V617F mutation as a marker of increased risk of thrombosis.

Is JAK2 V617F mutation more than a diagnostic index? A meta-analysis of clinical outcomes in essential thrombocythemia

A systematic review and meta-analysis was carried out to compare the frequency of clinically significant outcomes between JAK2 V617F positive and wild type patients with essential thrombocythemia (ET). JAK2 V617F positivity in patients with ET was associated with a clear increase in the odds of thrombosis [OR=1.83 (95% CI, 1.32-2.53), p<0.0001], and much higher odds of transformation to polycythemia vera [OR=7.67 (95% CI, 2.04-28.87), p=0.0009]. The mean difference of the white blood cell count between JAK2 positive and negative patients was associated with an increased odds ratio for thrombosis (p=0.02). The JAK2 V617F mutation in patients with ET is associated with an increased risk of adverse cardiovascular outcomes via an increase in the leukocyte count.

Validity test study of JAK2 V617F and allele burden quantification in the diagnosis of myeloproliferative diseases

Several sensitive methods for the detection of JAK2 V617F mutation have been published recently, most of them based on Real Time polymerase chain reaction (PCR). However, only some of them have performed studies of diagnostic validity. This study compares three methods based on Real Time PCR to detect JAK2 V617F mutation: two based on hybridization probes (HP) and peptide nucleic acid probe (PNA) and a third employing allele specific oligonucleotide primers for JAK2 V617F quantification. One hundred forty-nine healthy subjects, 61 essential thrombocythemia (ET), 32 polycythemia vera (PV), 38 secondary thrombocytoses, and 35 secondary erythrocytoses were included. Validity test study for JAK2 617 HP PCR in PV Sensitivity (Se) was 88% and in Specificity (Sp), 100%. In ET, Se was 57% and Sp, 100%. For JAK2 617 PNA PCR in PV, Se was 94% and Sp, 97.8%. In ET, Se was 70% and Sp, 95.7%. In JAK2 V671F allelo-specific-oligonucleotide (ASO) quantitative PCR (qPCR), cutoff point of 1% was established by receiving operating characteristic (ROC) curves. In PV, Se was 93.8% and Sp, 98.5%. In ET, Se was 80% and Sp, 95.9%. Two percent of the healthy subjects were positive by JAK2 617 PNA PCR and 2% by JAK2 617 ASO qPCR. JAK2 V617F mutation was detected in healthy subjects by cloning and sequencing. JAK2 617 HP is an adequate test in differential diagnosis for both erythrocytosis and thrombocytosis. When JAK2 V617F allele burden is low, JAK2 617 ASO qPCR should be performed. Simultaneous determination of JAK2 V617F and PRV-1 overexpression does not improve the diagnostic value of JAK2 V617F tests in MPD.

Clinical correlates of JAK2V617F presence or allele burden in myeloproliferative neoplasms: a critical reappraisal

JAK2 and MPL mutations are recurrent in myeloproliferative neoplasms (MPNs). A JAK2 mutation, primarily JAK2V617F, is almost invariably associated with polycythemia vera (PV). However, JAK2V617F also occurs in the majority of patients with essential thrombocythemia (ET) or primary myelofibrosis (PMF) as well as in a much smaller percentage of those with other MPNs. The mechanism(s) behind this one allele-multiple phenotypes phenomenon has not been fully elucidated. The issue is further confounded by the presence of marked variation in JAK2V617F allele burden among mutation-positive patients. In the current communication, we discuss potential mechanisms for phenotypic diversity among JAK2V617F-positive MPNs as well as review the current literature in regard to genotype-phenotype correlations (that is clinical correlates and prognostic significance) in the context of both the presence or absence of the mutation (ET and PMF) and its allele burden (PV, ET and PMF).

Life expectancy and prognostic factors in the classic BCR/ABL-negative myeloproliferative disorders

Among the 'classic' BCR/ABL-negative chronic myeloproliferative disorders, primary myelofibrosis (PMF) is associated with a substantial life-expectancy reduction. In this disease, initial haemoglobin level is the most important prognostic factor, whereas age, constitutional symptoms, low or high leukocyte counts, blood blast cells and cytogenetic abnormalities are also of value. Several prognostic systems have been proposed to identify subgroups of patients with a different risk, which is especially important in younger individuals, who may benefit from therapies with curative potential. Essential thrombocythaemia (ET) affects the patients' quality of life more than the survival, due to the high occurrence of thrombosis, whereas polycythaemia vera (PV) has a substantial morbidity derived from thrombosis but also a certain reduction in life expectancy. Therefore, in the latter disorders, prognostic studies have focused primarily on prediction of the thrombosis, with age and a previous history of thrombosis being the main prognostic factors of such complication. The importance of higher leukocyte counts in thrombosis development has been recently pointed out in ET and PV, where a role for mutated JAK2 allele burden has also been noted. With regard to PMF, the possible association of the mutation with shorter survival and higher acute transformation rate is currently being evaluated.

JAK2-V617F mutation analysis of granulocytes and platelets from patients with chronic myeloproliferative disorders: advantage of studying platelets

There have been conflicting reports over the JAK2-V617F mutation status of platelets in chronic myeloproliferative diseases (CMPDs). The aim of this study was to analyse JAK2-V617F status, not only in granulocytes but also in platelets. The JAK2-V617F mutation was analysed in both granulocytes and platelets in 115 patients with CMPDs using direct sequencing. JAK2-V617F was detected in granulocytes from 71 of those patients, all 71 of whom also had platelet JAK2-V617F expression. The remaining 44 patients showed negative JAK2-V617F expression on granulocytes, but positive JAK2-V617F expression was detected on the platelets from nine of the 33 essential thrombocythaemia (ET) patients, one of the eight polycythaemia vera patients, and two of the three primary myelofibrosis patients. When ET patients were divided into three groups according to granulocyte and platelet JAK2-V617F status (both-positive, platelets-only positive and both-negative), the both-positive and platelets-only positive groups shared the clinical features of higher white blood cell count and frequent thrombosis. These results suggest that analysis of platelets is a more sensitive approach for detecting JAK2-V617F in CMPD patients than analysis of granulocytes. They also suggest that previous reports of the incidence of JAK2-V617F in CMPD patients, obtained using only analysis of granulocytes, could be underestimations.

The JAK2 V617F allele burden in essential thrombocythemia, polycythemia vera and primary myelofibrosis--impact on disease phenotype

BACKGROUND AND OBJECTIVES

The JAK2 V617F tyrosine kinase mutation is present in the great majority of patients with polycythemia vera (PV), and approximately half of the patients with essential thrombocythemia (ET) and primary myelofibrosis (PMF). The three distinct disease entities may be considered as three phenotypic presentations of the same JAK2 V617F positive chronic myeloproliferative disorder. Together with physiological and genetic modifiers the phenotype may be determined by the JAK2 V617F allele burden. In the present study, we aimed to asses the JAK2 mutational load and its impact on phenotype.

METHODS

A highly sensitive real-time quantitative PCR (qPCR) assay was used for quantification of the JAK2 V617F mutational load in 165 patients with Philadelphia chromosome negative chronic myeloproliferative disorders (ET = 40, PV = 95, PMF = 30).

RESULTS

We provide evidence of increasing JAK2 V617F allele burden from ET, over PV to PMF (P = 0.001 and P < 0.00001 respectively). The present data suggests the JAK2 V617F allele burden as a key determinant of the degree of myeloproliferation and myeloid metaplasia reflected by significantly higher levels of white blood cell counts (WBC) (P = 0.03), CD34 counts (P = 0.03), lactate dehydrogenase and Polycythemia Rubra Vera gene 1 levels (P = 0.03 and P < 0.00001 respectively), as well as lower platelet counts (P = 0.02) and more cases of splenomegaly (P = 0.001) in homozygous PV patients compared to their heterozygous counterparts.

CONCLUSION

The present study support the concept of the JAK2 V617F positive chronic myeloproliferative disorders as a biological continuum with phenotypic presentation in part influenced by JAK2 V617F mutational load.

Classification and diagnosis of myeloproliferative neoplasms: the 2008 World Health Organization criteria and point-of-care diagnostic algorithms

The 2001 World Health Organization (WHO) treatise on the classification of hematopoietic tumors lists chronic myeloproliferative diseases (CMPDs) as a subdivision of myeloid neoplasms that includes the four classic myeloproliferative disorders (MPDs)-chronic myelogenous leukemia, polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF)-as well as chronic neutrophilic leukemia (CNL), chronic eosinophilic leukemia/hypereosinophilic syndrome (CEL/HES) and 'CMPD, unclassifiable'. In the upcoming 4th edition of the WHO document, due out in 2008, the term 'CMPDs' is replaced by 'myeloproliferative neoplasms (MPNs)', and the MPN category now includes mast cell disease (MCD), in addition to the other subcategories mentioned above. At the same time, however, myeloid neoplasms with molecularly characterized clonal eosinophilia, previously classified under CEL/HES, are now removed from the MPN section and assembled into a new category of their own. The WHO diagnostic criteria for both the classic BCR-ABL-negative MPDs (that is PV, ET and PMF) and CEL/HES have also been revised, in the 2008 edition, by incorporating new information on their molecular pathogenesis. The current review highlights these changes and also provides diagnostic algorithms that are tailored to routine clinical practice.

Advances in molecular diagnostics of myeloproliferative disorders

Incremental advances in the molecular pathogenesis of myeloproliferative disorders (MPDs) have had a substantial impact on clinical practice in terms of both diagnosis and treatment. An array of novel molecular methods are being developed and integrated into the current battery of tests for diagnosis and monitoring of treatment response. Primarily, subjective clinico-histologic approaches to diagnosis are being replaced by more objective semimolecular diagnostic algorithms. Furthermore, identification of disease-specific molecular markers has facilitated the development of small-molecule drugs for targeted therapy. This review provides an overview of MPDs with emphasis on molecular diagnostic tests and their incorporation into contemporary diagnostic and therapeutic algorithms.

Leucocytosis in polycythaemia vera predicts both inferior survival and leukaemic transformation

Leucocytosis (leucocyte count >15 x 10(9)/l) was recently associated with thrombosis in polycythaemia vera (PV). This study sought the prognostic relevance of leucocytosis for survival and leukaemic or fibrotic transformation. Amongst 459 patients with PV seen at our institution in recent years (median age, 60 years; 56% males), 146 deaths and 88 leukaemic (n = 34) or fibrotic (n = 54) transformations were documented. Arterial or venous thrombosis occurred in 14% and 9% of patients at diagnosis and in 25% and 15% during follow-up, respectively. Multivariate analysis identified the advanced age (P < 0.0001), leucocytosis (leucocyte count >/=15 x 10(9)/l; P = 0.0006) and arterial thrombosis at diagnosis (P = 0.01) as independent predictors of inferior survival. In the absence of the first two risk factors, median survival was projected at 272 months as opposed to 108 months in the presence of both risk factors (P < 0.0001). Leucocytosis was also identified as an independent predictor of both leukaemic transformation and venous thrombosis during follow-up. Time-to-event analysis did not disclose a significant association between single or multiple cytotoxic drug exposure and either leukaemic or fibrotic transformation. The current study highlighted the prognostic relevance of leucocytosis on various aspects of the disease in PV.

Different STAT-3 and STAT-5 phosphorylation discriminates among Ph-negative chronic myeloproliferative diseases and is independent of the V617F JAK-2 mutation

The V617F JAK2 mutation reported in Ph-negative myeloproliferative diseases (MPDs) induces the constitutive activation of JAK2, which produces an increased phosphorylation of signal transducer activator of transcription (STAT). In this study, we have analyzed a series of 114 patients (54 with polycythemia vera [PV], 44 with essential thrombocythemia [ET], 12 with idiopathic myelofibrosis [IM], and 4 with myelofibrosis secondary to MPD) for the expression pattern of phosphorylated STAT-3 and STAT-5 (pSTAT-3 and pSTAT-5, respectively) by immunostaining bone marrow biopsies. We found 3 specific patterns of pSTAT-3 and pSTAT-5 expression, significantly different from the normal staining pattern: uniformly increased pSTAT-3 and pSTAT-5 expression in PV, increased pSTAT-3 and reduced pSTAT-5 expression in ET, and uniformly reduced pSTAT-3 and pSTAT-5 expression in IM. A moderate increase of pSTAT-3 and pSTAT-5 expression was observed in secondary forms of erythrocytosis and thrombocytosis. In all evaluated MPDs, the pSTAT-5 and pSTAT-3 expression pattern was not influenced by the presence of V617F JAK2 mutation. These findings underline the importance of bone marrow histology in the differential diagnosis of Ph-negative MPD and support the hypothesis that V617F mutation simply contributes with other molecular defects in allowing the PV, ET, or IM phenotype to emerge.

Cytogenetic and molecular aspects of Philadelphia negative chronic myeloproliferative disorders: clinical implications

Chronic myeloproliferative disorders (CMPD) are clonal disorders of the hematopoietic stem cell. The myeloid lineage shows increased proliferation with effective maturation, while peripheral leukocytosis, thrombocytosis or elevated red blood cell mass are found. In Philadelphia negative CMPD recurrent cytogenetic abnormalities occur, but no specific abnormality has been defined to date. The spectrum of cytogenetic aberrations is heterogeneous ranging from numerical gains and losses to structural changes including unbalanced translocations. The most common chromosomal abnormalities are 20q-, 13q-, 12p-, +8, +9, partial duplication of 1q, balanced translocations involving 8p11 and gains in 9p. Cytogenetic analysis of CMPD by conventional or molecular techniques has an important role in establishing the diagnosis of a malignant disease, adding also more information for disease outcome. Molecular studies may detect the possible role of candidate genes implicated in the neoplastic process, addressing new molecular target therapies. FIP1L1/PDGFRalpha rearrangements, as well as alterations of PDGFRbeta or FGFR1 gene have been found to be associated with specific types of CMPD. Recently, a novel somatic mutation, JAK2V617F, has been reported in most of the polycthemia vera (PV) patients, as well as in a lower percentage in essential thrombocythemia (ET) or idiopathic myelofibrosis (IMF) patients. This finding represents the most important advance in understanding of the molecular mechanisms underlined the pathogenesis of CMPD, contributing to the classification and management of patients.

Clinical correlates ofJAK2V617F allele burden in essential thrombocythemia

BACKGROUND

JAK2V617F occurs in approximately 50% of patients with essential thrombocythemia (ET). Qualitative studies of mutation analysis have previously reported an association between JAK2V617F and advanced age, higher hemoglobin level, higher leukocyte count, and lower platelet count. A possible association with thrombotic complication has also been considered.

METHODS

Allele-specific, quantitative polymerase chain reaction (PCR) analysis for JAK2V617F was performed in 176 patients with ET using genomic DNA from archived bone marrow, which was collected within 1 year (n=72 patients), between 1 and 5 years (n=64 patients), or after 5 years (n=40 patients) of diagnosis.

RESULTS

JAK2V617F was detected in 96 patients (55%), in whom mutant allele burden ranged from 1% to 100% (median, 6.3%). Neither mutational frequency (P=.37) nor mutant allele burden (P=.62) was affected by the timing of bone marrow sample collection. The presence of JAK2V617F was found to be significantly associated with higher hemoglobin level (P<.0001), lower platelet count (P=.001), higher leukocyte count (P=.008), increased incidence of venous thrombosis occurring after diagnosis (P=.02), and older age at diagnosis (P=.03). All but age retained significance in multivariable analysis. In mutation-positive patients (n=96 patients), JAK2V617F allele burden clustered between 1% and 22% in 94 cases, in whom it correlated directly and significantly with platelet and leukocyte counts, palpable splenomegaly at diagnosis, and venous thrombosis occurring after diagnosis. The latter 2 associations remained significant with the inclusion of the remaining 2 outlier cases with 100% mutant allele burden; in addition, an association with male gender became evident.

CONCLUSIONS

JAK2V617F allele burden imparts additional phenotypic effects in ET.