Role of TET2 Mutations in Myeloproliferative Neoplasms

Recently, 5-hydroxymethylcytosine (5-hmC), the 6th base of DNA, was discovered as the product of the hydroxylation of 5-methylcytosine (5-mC) by the ten-eleven translocation (TET) oncogene family members. One of them, TET oncogene family member 2 (TET2), is mutated in a variety of myeloid malignancies, including in 15% of myeloproliferative neoplasms (MPNs). Recent studies tried to go further into the biological and epigenetic function of TET2 protein and 5-hmC marks in the pathogenesis of myeloid malignancies. Although its precise function remains partially unknown, TET2 appears to be an important regulator of hematopoietic stem cell biology. In both mouse and human cells, its inactivation leads to a dramatic deregulation of hematopoiesis that ultimately triggers blood malignancies. Understanding this leukemogenic process will provide tools to develop new epigenetic therapies against blood cancers.     

Characterization and Prognosis Significance of JAK2 (V617F), MPL,and CALR Mutations in Philadelphia-Negative Myeloproliferative Neoplasms

Background: The discovery of somatic acquired mutations of JAK2 (V617F) in Philadelphia-negative myeloproliferative neoplasms (Ph-negative MPNs) including polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) has not only improved rational disease classification and prognostication but also brings new understanding insight into the pathogenesis of diseases. Dosage effects of the JAK2 (V617F) allelic burden in Ph-negative MPNs may partially influence clinical presentation, disease progression, and treatment outcome. Material and Methods: Pyrosequencing was performed to detect JAK2 (V617F) and MPL (W515K/L) and capillary electrophoresis to identify CALR exon 9.0 mutations in 100.0 samples of Ph-negative MPNs (38.0 PV, 55 ET, 4 PMF, and 3 MPN-U). Results: The results showed somatic mutations of JAK2 (V617F) in 94.7% of PV, 74.5% of ET, 25.0% of PMF, and all MPN-U. A high proportion of JAK2 (V617F) mutant allele burden (mutational load > 50.0%) was predominantly observed in PV when compared with ET. Although a high level of JAK2 (V617F) allele burden was strongly associated with high WBC counts in both PV and ET, several hematological parameters (hemoglobin, hematocrit, and platelet count) were independent of JAK2 (V617F) mutational load. MPL (W515K/L) mutations could not be detected whereas CALR exon 9.0 mutations were identified in 35.7% of patients with JAK2 negative ET and 33.3% with JAK2 negative PMF. Conclusions: The JAK2 (V617F) allele burden may be involved in progression of MPNs. Furthermore, a high level of JAK2 (V617F) mutant allele appears strongly associated with leukocytosis in both PV and ET.     

Relationship of JAK2 (V617F) Allelic Burden with Clinico- Haematological Manifestations of Philadelphia-Negative Myeloproliferative Neoplasms

JAK2 (V617F) allelic burden is the main genetic driver behind and a potential differentiator between individual myeloproliferative neoplasm (MPN) subtypes. This study aimed to explore the relationship between JAK2 (V617F) allelic burden, MPN subtypes and their clinico-haematological manifestations in a Singapore-based cohort. Analysis was performed on a retrospectively collected dataset of 128 patients diagnosed with JAK2 (V617F) positive Philadelphia-negative MPNs between 2016 to 2017 in Singapore. Genomic analysis was conducted on blood samples via DNA extraction and Droplet Digital Polymerase Chain Reaction (ddPCR). The mean age was 62.4 (SD=14.1). 85 out of the 128 (66.4%) patients were male. There was a statistically significant difference in allelic burdens between the different MPN disease subtypes χ2(3) = 9.064, p=0.028, with essential thrombocytosis (ET) patients having the lowest mean JAK2 percentage allelic burden (26.5%). Patients with an allelic burden >50% had higher leukocyte counts (MWU 1016.5, p=0.001), haemoglobin levels (MWU 1287.0, p=0.045), lactate dehydrogenase levels (MWU 611.5, p=0.001), and lower platelet levels (MWU 1164.0, p=0.008). Subgroup analysis revealed none of these correlations was significant in the ET subgroup. The results are largely in concordance with previous research in Asian cohorts demonstrating the association between allelic burden and clinico-haematological manifestations of MPN. However, in the ET subgroup, the JAK2 (V617F) allelic burden do not correlate positively for haematological parameters which is only seen in Asian patients.     

Special Issues in Myeloproliferative Neoplasms

Special issues in myeloproliferative neoplasms (MPN) comprise clinical conditions with high relevance for the duration and quality of the patient’s life, but with limited evidence to support sound diagnostic and therapeutic recommendations and a low probability of being solved by the current standard of clinical research. These issues include MPN in pregnancy and in children, abdominal vein thrombosis, bleeding complications, surgery, pruritus, and leukemic transformation. Practical suggestions to guide clinical decisions in these settings remain largely empirical, but recently developed guidelines based on experts’ consensus may help to tackle these problems. This article reviews the state of the art regarding these issues, with special emphasis on experts’ consensus recommendations.     

JAK2, CALR,and MPL Mutations in Egyptian Patients With Classic Philadelphia-negative Myeloproliferative Neoplasms

BackgroundGenetic mutations have been proven to be one of the major criteria in the diagnosis and distinction of different myeloproliferative neoplasm (MPN) subtypes. Therefore, the aim of this study was to determine the molecular profile of Egyptian patients with MPN subtypes and correlate with clinicopathological status.MethodsA series of 200 patients with MPNs (92 polycythemia vera, 68 essential thrombocythemia, and 40 primary myelofibrosis) were included in this study. DNA from each sample was amplified using polymerase chain reaction to detect Janus kinase 2 (JAK2), calreticulin (CALR), and myeloproliferative leukemia virus oncogene (MPL) mutations. Sanger sequencing was used to determine the mutation types.ResultsOf the 200 samples, 44% had JAK2V617F and 10% were carrying CALR mutation with type 2 being the most frequent type in this study (55%). No MPL or JAK2 exon 12 mutations were detected. All clinical and hematological data had no differences with other populations except that our CALR-positive patients showed a decrease in the platelet count compared with JAK2V617F-positive patients.ConclusionOur study on Egyptian patients shows a specific molecular profile of JAK2 mutation, and CALR mutation type 2 was higher than type 1.     

Splanchnic Vein Thrombosis in the Myeloproliferative Neoplasms

Purpose of Review

To review the epidemiology, diagnostic challenges, pathogenesis, and treatment strategies for patients with myeloproliferative neoplasm-associated splanchnic vein thrombosis.

Recent Findings

The epidemiology of myeloproliferative neoplasm-associated splanchnic vein thrombosis (MPN-SVT) has been well characterized. While typical MPN-associated thrombosis affects older patients and involves the arterial circulation, MPN-SVT mostly impacts younger women. An association with JAK2 V617F is well-known; recent studies have demonstrated only a weak association with CALR mutations. JAK inhibition may represent a novel treatment strategy, complementing anticoagulation, and management of portal hypertension.

Summary

While the epidemiology has been well characterized, more work is needed to identify novel contributors to disease pathogenesis, beyond the JAK2 V617F mutation itself, and endothelial compromise. Testing for MPN mutations in the setting of non-cirrhotic SVT is commonplace; JAK2 V617F is the most likely to be identified. Testing for CALR or MPL mutations requires clinical judgement, though not unreasonable. The mainstay of therapy is indefinite anticoagulation; the role of direct oral anticoagulants is unclear. JAK inhibition may play a role in addressing associated splenomegaly and portal hypertension.