Prevalence and clinicopathologic correlates of JAK2 exon 12 mutations in JAK2V617F-negative polycythemia vera.

After accounting for misdiagnosis and treatment effect, allele-specific (AS)-PCR detects the JAK2V617F mutation in >95% of polycythemia vera (PV) patients. Using database inquiry, we identified 6 of a total 220 cases with PV that were JAK2V617F-negative (prevalence=3%). Of these, five cases ( approximately 80%) were found to harbor one of the two JAK2 exon 12 mutations (F537-K539delinsL or N542-E543del) in bone marrow (BM) and/or peripheral blood cells. Similar screening of six additional cases - three each with idiopathic erythrocytosis (IE) or otherwise unexplained erythrocytosis (UE) - did not reveal either JAK2V617F or JAK2 exon 12 mutations. We found JAK2 exon 12 mutations in PV cases to be readily detected by both DNA sequencing and AS-PCR, regardless of whether BM or peripheral blood cells were used as the source for DNA. Although erythroid hyperplasia was the predominant histologic feature on BM examination, megakaryocyte abnormalities and reticulin fibrosis were noted in most PV patients harboring exon 12 mutations. However, similar BM morphologic changes can also be seen in some JAK2V617F-positive PV cases; therefore, distinct genotype-phenotype association cannot be established.     

Usefulness of JAK2V617F mutation in distinguishing idiopathic erythrocytosis from polycythemia vera

Idiopathic erythrocytosis (IE) is a primary erythrocytosis not fulfilling the criteria for polycythemia vera (PV) diagnosis. In order to verify the relationship between IE and PV, we screened JAK2V617F mutation in a consecutive series of 11 IE and, for comparison, in 15 PV. JAK2V617F mutation was screened by both cDNA sequencing and mutation specific PCR in both peripheral blood and bone marrow samples. All 11 IE tested negative for JAK2V617F mutation, which, conversely, occurred in 11/15 (73.3%) PV. Our results demonstrate that JAK2V617F is absent in IE and may represent a useful molecular marker for distinguishing IE from PV.     

A refined diagnostic algorithm for polycythemia vera that incorporates mutation screening for JAK2V617F

Historically, red cell mass (RCM) measurement has been promoted as an accurate indicator of the body’s red cell content. Both the Polycythemia Vera Study Group and a committee sponsored by the World Health Organization have endorsed its inclusion in their diagnostic criteria without supporting evidence of diagnostic accuracy from a systematic study. Over the years, it has become evident that RCM measurement is a cumbersome and costly test and, as a result, it has been abandoned by many hematologists in practice. The recent discovery that a somatic JAK2-activating mutation, JAK2^V617F, is almost invariably associated with polycythemia vera further supports the use of diagnostic algorithms that are based on biologic parameters in place of traditional diagnostic criteria that are based on RCM measurement. Therefore, a contemporary approach to the diagnosis of polycythemia vera starts with peripheral blood mutation screening for JAK2^V617F as well as measurement of serum erythropoietin. The results of these tests, along with the clinical scenario, determine the need for further investigation, including bone marrow examination.     

Genetic Basis of MPN: Beyond JAK2-V617F

The clonal blood disorders polycythemia vera, essential thrombocythemia and primary myelofibrosis belong to the BCR-ABL1-negative myeloproliferative neoplasms and are specified by increased production of terminally differentiated myeloid cells. Clonal evolution, disease initiation and progression are influenced by genetic alterations, often affecting cytokine signaling and gene expression. This review outlines somatic changes discovered in myeloproliferative neoplasms and how these genetic aberrations influence the pathogenesis of myeloproliferative neoplasms. Furthermore, genetic responses to drug treatments in myeloproliferative neoplasms are discussed.     

Prospective identification of high-risk polycythemia vera patients based on JAK2(V617F) allele burden.

The aim of this study was to determine whether the burden of JAK2(V617F) allele correlated with major clinical outcomes in patients with polycythemia vera (PV). To this end, we determined JAK2 mutant allele levels in granulocytes of 173 PV patients at diagnosis. The mean (+/-s.d.) mutant allele burden was 52% (+/-29); 32 patients (18%) had greater than 75% mutant allele. The burden of JAK2(V617F) allele correlated with measurements of stimulated erythropoiesis (higher hematocrit, lower mean cell volume, serum ferritin and erythropoietin levels) and myelopoiesis (higher white cell count, neutrophil count and serum lactate dehydrogenase) and with markers of neutrophil activation (elevated leukocyte alkaline phosphatase and PRV-1 expression). As compared to those with less than 25% mutant allele, patients harboring greater than 75% JAK2(V617F) allele were at higher relative risk (RR) of presenting larger spleen (RR 4.7; P<0.001) or suffering from pruritus (RR 3.1; P<0.001). In these patients, the risk of requiring chemotherapy (RR 1.8; P=0.001) or developing major cardiovascular events (RR 7.1; P=0.003) during follow up were significantly increased. We conclude that a burden of JAK2(V617F) allele greater than 75% at diagnosis points to PV patients with high-risk disease.     

JAK2 V617F, MPL W515L and JAK2 exon 12 mutations in Chinese patients with primary myelofibrosis

Objective: JAK2 V617F, MPL W515L and JAK2 exon 12 mutations are novel acquired mutations that induce constitutive cytokine-independent activation of the JAK-STAT pathway in myeloproliferative disorders (MPD). The discovery of these mutations provides novel mechanism for activation of signal transduction in hematopoietic malignancies. This research was to investigate their prevalence in Chinese patients with primary myelofibrosis (PMF). Methods: We introduced allele-specific PCR (AS-PCR) combined with sequence analysis to simultaneously screen JAK2 V617F, MPL W515L and JAK2 exon 12 mutations in 30 patients with PMF. Results: Fifteen PMF patients (50.0%) carried JAK2 V617F mutation, and only two JAK2 V617F-negative patients (6.7%) harbored MPL W515L mutation. None had JAK2 exon 12 mutations. Furthermore, these three mutations were not detected in 50 healthy controls.Conclusion: MPL W515L and JAK2 V617F mutations existed in PMF patients but JAK2 exon 12 mutations not. JAK2 V617F and MPL W515L and mutations might contribute to the primary molecular pathogenesis in patients with PMF.     

原发性血小板增多症骨髓病理及JAK2-V617F突变分析

目的:分析原发性血小板增多症（essential thrombocythemia,ET）患者的骨髓病理及JAK2-V617F突变特点。方法:回顾109例ET患者的临床资料,并与继发性血小板增多症(secondary thrombocythemia,ST)进行比较。结果:ET骨髓病理巨核细胞体积明显增大,核多分叶、多核易见,成簇、成片状分布,ST巨核细胞体积未见明显增大及异常分布。ET患者JAK2-V617F突变阳性率为 57.83%,ST患者JAK2-V617F突变均为阴性。JAK2-V617F突变阳性组WBC、Hb、骨髓纤维化、初诊血栓事件高于阴性组,差异有统计学意义（P<0.05)。JAK2-V617F突变阳性组年龄、Plt、骨髓粒系、红系百分比及巨核细胞计数与阴性组比较,无显著性差异（P>0.05）;JAK2-V617F突变阳性组无血栓生存率较阴性组低,差异有统计学意义（P<0.05）。结论:ET的骨髓病理特征明显,骨髓活检与JAK2-V617F基因检查相结合对ET诊断及治疗具有重要意义。