JAK2V617F prevalence and allele burden in non-splanchnic venous thrombosis in the absence of overt myeloproliferative disorder

JAK2V617F Mutation in Patient with Splanchnic Vein Thrombosis

Splanchnic vein thrombosis is an uncommon life-threatening form of venous thrombosis. It is one the common complication among MPN's. In the western studies the prevalence of JAK2V617F mutation among SVT patient is high and ranges from 7 to 59%. The frequency of this mutation among Indian SVT patients is heterogenous. This was a prospective case control study. A total 52 cases of SVT and 40 controls were screened for JAK2V617F mutation along with other routine thrombophilic risk factors. Out of total 52 cases, 10 had BCS, 2 had MVT and rest 40 were of PVT/EHPVO. The JAK2V617F mutation was seen in two cases and not in controls. Among the thrombophilic markers, heterozygous FVL mutation, PC, PS and presence of APA were seen in 2, 3, 1 and 3 cases respectively. In addition, eight cases also showed deranged risk factors (5 inherited and 3 acquired), however the repeat testing was not performed due to loss of follow up. Among controls, one person showed presence of APA and one person showed multiple thrombophilic risk factor deficiency. JAK2V617F mutation was observed in 3.8% among north Indian SVT patients. The frequency of mutation is on the lower side as compared to the available Indian data. The other thrombophilia markers (both inherited and acquired) are more frequent (18%) and patients should be routinely screened for these thrombophilia markers.

[Thrombosis and platelet dysfunction in myeloproliferative neoplasms]

Myeloproliferative neoplasms are acquired hematological malignancies, mainly affecting the adult and whose morbidity and mortality stems from haemostasis disorders. The most frequently encountered complications include thrombosis, affecting preferentially the arterial territory, but also atypical locations such as splanchnic vein thrombosis. The pathophysiology of these thromboses is complex and involves different actors: blood cells, endothelium and flow conditions. Numerous studies have been conducted to identify risk factors for thrombosis. To date, only two risk factors have been validated through prospective studies (age over 60 years old, history of thrombotic events) and allow classification of patients as "low risk" and "high risk" as the basis for current treatment recommendations. Haemorrhagic manifestations, less frequent than thrombosis, are mainly related to an alteration of primary haemostasis and are therefore manifested by mucocutaneous bleeding. In these patients, platelet dysfunctions and/or acquired Willebrand syndromes can be found. The pathophysiology of thrombosis and platelet dysfunction during myeloproliferative neoplasms remains to date partially unknown. In this review, we offer to focus on physiopathological mechanisms as well as the latest advances in their understanding.

The association of the JAK2 46/1 haplotype with non-splanchnic venous thrombosis

BACKGROUND

The inherited JAK2 46/1 haplotype is strongly associated with the development of myeloproliferative neoplasms (MPNs), and its increased frequency has also been reported in splanchnic venous thrombosis (SVT). In the present study, the role of the JAK2 46/1 haplotype in non-splanchnic venous thrombosis (non-SVT) was investigated.

METHODS AND RESULTS

We genotyped 438 patients with non-SVT, 226 patients with MPNs and 459 healthy controls for three single nucleotide polymorphisms (SNPs) which tag the JAK2 46/1 haplotype (rs12342421 G>C, rs12343867 T>C and rs10974944 C>G). We found statistically significant association of the rs12342421 GC+CC genotypes (OR=1.40; p=0.023) and the rs12343867 TC+CC genotypes (OR=1.83; p=7.02 x 10(-5)) with non-SVT. We also found that the CC haplotype of these two SNPs was associated with an increased risk of the disease (OR=1.68; p=0.009). Stratification analysis indicated that the observed association of the JAK2 46/1 haplotype with non-SVT was probably largely free of confounding effect of thrombophilic risk factors. In addition, we established a strong association of SNPs rs12342421 and rs10974944 and their CG haplotype with MPNs and with JAK2 V617F-positive MPNs.

CONCLUSIONS

This study provides statistical evidence that SNPs rs12342421 and rs12343867 are associated with an increased risk of non-SVT. Consistently, haplotypes of the SNPs were also associated with non-SVT risk, suggesting that inherited genetic variation in the JAK2 gene may play a role in the pathogenesis of non-SVT. Furthermore, the reported associations of the JAK2 46/1 haplotype with MPNs as well as with the occurrence of the JAK2 V617F mutation in MPNs were confirmed.

JAK2 (V617F) mutation is not associated with thrombosis in Behcet syndrome

The Janus kinase 2(V617F) (JAK2 (V617F)) mutation is an acquired genetic defect that is considered to enhance thrombosis in Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs). Thrombosis is also a well-defined component of Behcet syndrome (BS). The aim of this study was to determine the frequency of JAK2 ( V617F ) mutation in BS-associated thrombosis. A total of 152 patients with BS (62 with thrombosis and 90 without thrombosis) were enrolled. An additional 186 patients with MPNs and 107 healthy blood donors were included to serve as diseased and healthy controls, respectively. None of the patients with BS and healthy controls carried the JAK2 (V617F) mutation, whereas 67% of patients with MPNs were positive for JAK2 ( V617F ). The frequency of thrombosis in patients with MPNs was not statistically different between carriers and non-carriers of JAK2 ( V617F ) mutation. Our data suggest that JAK2 (V617F) is not directly related to thrombosis in MPNs and in other thrombotic entities, such as BS.

Uses and abuses of JAK2 and MPL mutation tests in myeloproliferative neoplasms a paper from the 2010 William Beaumont hospital symposium on molecular pathology

JAK2V617F is sufficiently prevalent in BCR-ABL1-negative myeloproliferative neoplasms (MPNs) to be useful as a clonal marker. JAK2V617F mutation screening is indicated for the evaluation of erythrocytosis, thrombocytosis, splanchnic vein thrombosis, and otherwise unexplained BCR-ABL1-negative granulocytosis. However, the mutation does not provide additional value in the presence of unequivocal morphologic diagnosis, and its presence does not necessarily distinguish one MPN from another or provide useful prognostic information. In general, quantitative cell-based JAK2V617F mutation assays are preferred because the additional information obtained on mutant allele burden enhances diagnostic certainty and facilitates monitoring of response to treatment. JAK2 exon 12 mutation screening is indicated only in the presence of JAK2V617F-negative erythrocytosis that is associated with a subnormal serum erythropoietin level. MPL mutations are neither frequent nor specific enough to warrant their routine use for MPN diagnosis, but they may be useful in resolving specific diagnostic problems. The practice of en bloc screening for JAK2V617F, JAK2 exon 12, and MPL mutations is scientifically irrational and economically irresponsible.

Relevance of the JAK2V617F mutation in patients with deep vein thrombosis of the leg

Venous thromboembolism (VTE) can be the first presenting symptom in myeloproliferative neoplasms (MPN). Studies have demonstrated a high prevalence of the JAK2V617F mutation in patients with splanchnic vein thrombosis. Fewer studies have been done in patients with thrombosis outside the splanchnic area, showing a lower prevalence although the clinical relevance of the mutation in these patients, e.g., progression to overt MPN, remains unknown. The objective of this study was to determine the effect size of JAK2V617F in prospectively collected DNA samples of patients objectively diagnosed with deep vein thrombosis (DVT) of the leg and controls without DVT, with follow-up on JAK2V617F-positive patients to assess clinical relevance. Presence of JAK2V617F was determined in DNA samples from 187 patients with DVT and 201 controls, using quantitative RT-PCR. Hematological parameters were also analyzed. All initially JAK2V617F-positive patients were reassessed. Of 187 patients with DVT, 178 were analyzed for JAK2V617F, and in four (2.3%; 95% CI 0.1–4.4), JAK2V617F was present. Of 201 controls, 198 were analyzed; one was JAK2V617F positive (0.5%; 95% CI −0.5–1.5, OR 4.5; 95% CI 0.5–40.9). None had MPN features, nor upon reassessment after a median follow-up of 68.5 months. Four JAK2V617F-positive patients with DVT and one control without DVT did not develop overt MPN after a median follow-up of nearly 6 years. Thus, in patients with non-splanchnic venous thrombosis, JAK2V617F appears not to be clinically relevant.

JAK2 mutations across a spectrum of venous thrombosis cases

The JAK2(V617F)mutation is recurrent in polycythemia vera and essential thrombocythemia, which are myeloproliferative neoplasms frequently associated with arterial and venous thromboembolism. It has also been reported as a marker for occult myeloproliferative disorder (MPD) in patients with splanchnic venous thrombosis. Limited data are available regarding the prevalence of the JAK2(V617F) mutation in patients with thrombosis outside the splanchnic region. For the study, 321 cases of venous thrombosis in the splanchnic and nonsplanchnic regions (cerebral venous thrombosis [CVT], 70; deep venous thrombosis [DVT], 36; Budd-Chiari syndrome [BCS], 137; portal venous thrombosis [PVT], 78) were studied for the presence of JAK2 mutations. The prevalence values for the JAK2 mutation were 3% (1/36), 8.8% (12/137), 5% (4/78), and 3% (2/70) in DVT, BCS, PVT, and CVT, respectively; 19 (5.9%) of 321 cases were positive for the JAK2 mutation. Of 111 healthy subjects screened for this mutation, none were found to be carriers. Determination of the JAK2(V617F) mutation may be useful to identify patients who should be carefully observed for the development of overt MPDs. The significance of screening for this mutation in nonsplanchnic thrombosis cases needs to be analyzed in a larger series.

JAK2V617F mutation for the early diagnosis of Ph- myeloproliferative neoplasms in patients with venous thromboembolism: a meta-analysis

Recent studies suggested that JAK2V617F mutation is frequent in patients with splanchnic vein thrombosis (SVT) but not in patients with other venous thromboembolic events (VTE). However, whether screening for the JAK2V617F mutation in VTE patients is justified remains unclear. Therefore, we performed a systematic review to assess the frequency of JAK2 mutation in VTE patients and the role of JAK2V617F mutation in the diagnosis of myeloproliferative neoplasms. MEDLINE and EMBASE databases were searched. Two reviewers independently performed study selection and extracted study characteristics. Pooled odds ratios of case-control studies and weighted mean proportion of the prevalence of JAK2V617F mutation of uncontrolled series were calculated. Twenty-four studies involving 3123 patients were included. Mean prevalence of JAK2 mutation was 32.7% (95% confidence interval, 25.5%-35.9%) in SVT patients. JAK2 mutation was associated with increased risk of SVT (odds ratio, 53.98; 95% confidence interval, 13.10-222.45). Mean prevalence of JAK2 mutation in other VTE patients was low (range, 0.88%-2.57%). Presence of JAK2V617F mutation in SVT patients was associated with a subsequent diagnosis of myeloproliferative neoplasm in many patients. JAK2 mutation is strongly associated with SVT, and routine screening of JAK2 mutation appears to be indicated in these patients.

Aberrant signal transduction pathways in myeloproliferative neoplasms

The BCR-ABL-negative myeloproliferative neoplasms (MPNs), polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF), entered the spotlight in 2005 when the unique somatic acquired JAK2 V617F mutation was described in >95% of PV and in 50% of ET and PMF patients. For the very rare PV patients who do not harbor the JAK2 V617F mutation, exon 12 JAK2 mutants were discovered also to result in activated forms of JAK2. A minority of ET and PMF patients harbor mutations that constitutively activate the thrombopoietin receptor (TpoR). In bone marrow reconstitution models based on retroviral transduction, the phenotype induced by JAK2 V617F is less severe and different from the rapid fatal myelofibrosis induced by TpoR W515L. The reasons for these differences are unknown. Exactly by which mechanism(s) one acquired somatic mutation, JAK2 V617F, can promote three different diseases remains a mystery, although gene dosage and host genetic variation might have important functions. We review the recent progress made in deciphering signaling anomalies in PV, ET and PMF, with an emphasis on the relationship between JAK2 V617F and cytokine receptor signaling and on cross-talk with several other signaling pathways.

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.

The saga of JAK2 mutations and translocations in hematologic disorders: pathogenesis, diagnostic and therapeutic prospects, and revised World Health Organization diagnostic criteria for myeloproliferative neoplasms

JAK2 is a tyrosine kinase involved in cytokine signaling. The JAK2V617F point mutation, first described in 2005, results in constitutive activation of JAK2 and is now widely used as a diagnostic marker for Philadelphia chromosome negative myeloproliferative neoplasms. In recent years, more novel JAK2 mutations and fusion genes have been discovered in myeloproliferative neoplasms and other hematologic malignancies. This review aims to summarize the discovery and use of the JAK2V617F point mutation, other novel JAK2 mutations, and JAK2 translocations in diagnosing myeloproliferative neoplasms, acute myeloid leukemia, and acute lymphoid leukemia. JAK2 mutation testing is addressed, including the sensitivity and specificity of the different JAK2 mutation testing methods, clinical indications for use, and the use of quantitative JAK2 mutation testing for routine pathologic diagnosis, prognosis, and monitoring response to therapy. The relationship of JAK2 mutation to endogenous erythroid colony formation, thrombopoietin receptor mutation, polycythemia rubra vera-1 overexpression, and thrombopoietin receptor underexpression in myeloproliferative neoplasms are explored. Also discussed are the JAK2 inhibitors for clinical trials. Finally, the advantages of the newly proposed World Health Organization classification for myeloproliferative neoplasms are reviewed.

The presence of JAK2V617F in primary myelofibrosis or its allele burden in polycythemia vera predicts chemosensitivity to hydroxyurea

JAK2V617F-positive patients with essential thrombocythemia, as opposed to their mutation-negative counterparts, require lower doses of hydroxyurea (HU) for control of their platelet count. In the current study, we looked for predictors of HU response in 69 patients with primary myelofibrosis (PMF) and 56 with polycythemia vera (PV). JAK2V617F analysis was performed on bone marrow-derived DNA obtained at or near the time of diagnosis. HU response in PMF was associated with a shorter disease duration (P = 0.008), absence of previous therapy (P = 0.01), older age at diagnosis (P = 0.009), and presence of JAK2V617F (P = 0.02). On multivariable analysis, only the latter retained its significance (48% vs. 8% response in mutation positive vs. negative cases). In PV, JAK2V617F allele burden correlated directly with HU response (P = 0.05) and inversely with daily HU dose in responding patients (P = 0.02). The current study suggests that JAK2V617F presence identifies PMF patients who are likely to respond to HU therapy, and information on its allele burden helps in assigning the optimal starting dose in individual patients with PV.

JAK2V617F mutation screening as part of the hypercoagulable work-up in the absence of splanchnic venous thrombosis or overt myeloproliferative neoplasm: assessment of value in a series of 664 consecutive patients

The JAK2V617F mutation is recurrent in polycythemia vera and essential thrombocythemia, which are myeloproliferative neoplasms (MPNs) frequently associated with arterial and/or venous thromboembolism. More recently, the JAK2V617F mutation has been identified as a surrogate marker for subclinical or "occult" clonal myeloproliferation in patients with splanchnic venous thrombosis. However, information is limited regarding JAK2V617F-associated thrombosis outside the splanchnic district in patients without overt MPN. To address this issue, we retrospectively studied a consecutive series of 664 such patients who experienced thrombotic events characteristic of an MPN (500 with venous thromboembolism, 136 with stroke, and 28 with myocardial infarction at a young age). The JAK2V617F mutation was detected in only 6 (<1.0%) patients (5 with recurrent venous thromboembolism and 1 with stroke), and the mutant allele burden was low in all instances (range, 2.2%-7.5%). None of these 6 patients developed either overt MPN or recurrent thrombosis after a median follow-up of 40 months. We conclude that the prevalence of the JAK2V617F mutation in patients with nonsplanchnic venous thrombosis in the absence of MPN is too low to warrant mutation screening as part of the hypercoagulable work-up. Our study also suggests that the natural history of a JAK2V617F-positive "occult" MPN might be different from that of a typical MPN.

Host genetic variation contributes to phenotypic diversity in myeloproliferative disorders

JAK2V617F is an acquired mutation associated with polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). We tested the hypothesis that the paradox of a single disease allele associated with 3 distinctive clinical phenotypes could be explained in part by host-modifying influences. We screened for genetic variation within 4 candidate genes involved in JAK-STAT signaling, including receptors for erythropoietin (EPOR), thrombopoietin (MPL), and granulocyte colony-stimulating factor (GCSFR), and JAK2. We genotyped 32 linkage disequilibrium tag single nucleotide polymorphism (SNP) loci in 179 white patients: 84 had PV, 58 had PMF, and 37 had ET. Genotype-phenotype analysis showed 3 JAK2 SNPs (rs7046736, rs10815148, and rs12342421) to be significantly but reciprocally associated with PV (P < .001 for all; odds ratio = 0.16, 2.72, and 2.46, respectively) and ET (P < .001 for all; odds ratio = 3.05, 0.29, and 0.30, respectively) but not with PMF. Three additional JAK2 SNPs (rs10758669, rs3808850, and rs10974947) and a single EPOR SNP (rs318699) were also significantly associated with PV but not with ET or PMF. Finally, intragene haplotypes in JAK2 were significantly associated with PV only. Thus, host genetic variation may contribute to phenotypic diversity among myeloproliferative disorders, including in the presence of a shared disease allele.

Low JAK2V617F allele burden in primary myelofibrosis, compared to either a higher allele burden or unmutated status, is associated with inferior overall and leukemia-free survival

The clinical relevance of JAK2V617F allele burden in primary myelofibrosis (PMF) has not been previously studied. Bone marrow-derived DNA from 199 patients with PMF was subjected to qualitative (n=199) and quantitative (n=129) analysis for V617F. Mutational frequency was 58% and median mutant allele burden ratio in V617F-positive patients was 29% (range, 1-74%). Multivariable analysis identified older age, platelet count > or =100 x 10(9) l(-1) and peripheral blood blast percentage <3% as being associated with a positive mutational status. The mere presence of the mutation did not affect the incidence of thrombosis (P=0.78), overall survival (P=0.22) or leukemia-free survival (P=0.5). The 129 patients with allele burden information were divided into four groups: V617F-negative (n=53) and V617F-positive with mutant allele burden in the lower quartile (n=19), middle quartiles (n=38) or upper quartile (n=19) range. Kaplan-Meier plots revealed significantly shortened overall (P=0.0008) and leukemia-free (P=0.01) survival for the lower quartile, but not for upper quartile allele burden group; independent prognostic relevance was validated by multivariable analysis. We conclude that low V617F allele burden in PMF might indicate the presence of an overriding V617F-negative clone that confers a more aggressive disease phenotype.

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.