W515L Mutation Research Articles

MPL W515L mutation in Chinese patients with myeloproliferative diseases

As JAK2 V617F, MPL W515L is a novel acquired mutation that induces constitutive cytokine-independent activation of the JAK-STAT pathway in myeloproliferative disorders (MPD). The discovery of this mutation provides a novel mechanism for activation of signal transduction in hematopoietic malignancies. To investigate its prevalence in Chinese patients with MPD, we introduced allele-specific PCR (AS-PCR) combined with sequence analysis to simultaneously screen MPL W515L and JAK2 V617F mutations in 190 MPD patients. MPL W515L mutation was found to be harbored in only one of 102 patients, who had essential thrombocythemia (ET, 1.0%) and was not detected in patients with polycythemia vera (PV), idiopathic myelofibrosis (IMF), and chronic myelogenous leukemia (CML). Sixty-eight BCR/ABL-negative MPD patients (46.3%) were found harboring JAK2 V617F mutation (PV, 62.5%; ET, 42.1%; IMF 38.1%). Furthermore, MPL W515L and JAK2 V617F mutations were not detected in patients of acute myeloid leukemia, acute lymphoblastic leukemia, myelodysplastic syndromes, and CML. It has been shown that MPL W515L mutations may contribute to the primary molecular pathogenesis of Chinese patients with ET.

Relation between JAK2 V617F Mutation and Chronic Myeloproliferative Disorders.

The chronic myeloproliferative disorders (cMPDs) are a group of clonal malignant tumors of the hematological system, and derived from the pluripotential hemopoietic stem cells, manifested as the proliferation of one or more series of cells in the bone marrow as well as the occurrence of excessive mature or naive cells in the peripheral blood. It was reported by several research groups that there was the acquired JAK2 V617F mutation in the majority of the PV patients and in a part of the ET or PMF patients, which provided the new ideas for the investigation of the pathogenesis of BCR/ABL- cMPDs. In the present study, the JAK2 V617F mutation was detected in a larger collection of Chinese cMPD patients, to give a picture of the incidence of JAK2 V617F mutation in the Asian pollutions. A total of 523 patients with the cMPDs, including 278 males and 245 females, were analyzed. Their median age was 50 years old (7 to 83 years old). According to the WHO diagnostic criteria, among the 523 patients were 88 cases of CML at the chronic phase (including 59 males and 29 females with a median age of 40 years old), 25 of CML complicated with myelofibrosis, 116 of PV (64 males and 52 females; a median age of 53; among them were six cases of PV with the secondary myelofibrosis), 153 of ET (63 males and 91 females; a median age of 50; 15 cases of ET with the secondary myelofibrosis), 142 of PMF (71 males and 71 females; a median age of 53.5), four of unclassified CMPD (CMPD-U) (2 males and 2 females; a median age of 60), seven of high eosinophil syndrome (HES) (6 males and 1 female; a median age of 32), and 13 of chronic eosinophilic leukemia (13 males; a median age of 34). In addition, 140 of healthy adults were included in the control group. Allele-specific PCR (ASP) was applied to identify JAK2 V617F mutation, the mutation status was analyzed by PCR-RFLP, and the results were confirmed by sequence analysis. The mutation load was calculated by the ratio of T/G. Then explore the correlation between the allele load and the clinical, hematologic features. To those without JAK2 V617F, MPL W515L mutation was analyzed. JAK2 V617F was detected in 66%(346/523) of all patients (94%(109/116) in PV, 79%(122/153) in ET, 78%(111/142) in PMF, 75%(3/4) in CMPD-U and 14%(1/7) in HES).Majority of patients carried JAK2 V617F mutation were heterozygous, homozygote was found in only 5 cases (4 in PV and 1 in ET). The mutation load in majority patients (71.5%) was low, PV>ET>MF when compared with mutation load (p=0.003). Hemoglobin level was significantly related to high mutation load in PV (p=0.033, r=0.203). Bone marrow megakaryocyte counts were found to be marked increased in ET with high JAK2 V617F loads (P=0.024, r=0.205), and hepatomegaly in PMF was also significiently associated with high JAK2 V617F mution load (p=0.003, 0.001)(p=0.001, r=0.315). Oue data showed that1.Majority of cMPD patients, especialy with PV, carried JAK2 V617F mutation, but JAK2 V617F was absent in CML;2.98% of JAK2 V617F mutation occurs in a heterozygous status, only 4 patients with PV and 1 with ET were homozygouse.;3.PV> ET> MF when compared with mutation load. High JAK2 V617F loads were found to be significantly associated with higher hemoglobin level in PV and higher bone marrow megakaryocyte counts in ET;4.The correlation between hepatomegaly and JAK2 V617F mutation load were also found in PMF.