The Analysis And Significance Of JAK2 And TET2 Gene Mutation In Myeloproliferative Neoplasm

JAK2 V617F mutation is an acquired, clonal mutation occurred in hematopoietic stem/progenitor cells from myeloproliferative neoplasm (MPN) patients, which is first simultaneously reported by several groups in 2005. Extensive investigations about JAK2 V617F mutation were performed subsequently around the world. JAK2 V617F mutation is found in 65%～97%,23%～60%,35%～64% and 20% of patients with polycythemia vera (PV),essential thrombocythemia (ET) primary myelofibrosis (PMF) and chronic neutrophil leukemia (CNL), respectively. As the role of JAK2 V617F mutation in the pathogenesis of MPN is gradually known, the World Health Organization (WHO) brought new classification and diagnostic standards to MPN, which emphasizedq the importance of JAK2 V617F mutation and other molecular or cytogenetic incidents in MPN. However, JAK2 V617F not only occures in MPNs, but in 5% of myelodysplastic syndrome (MDS) patients. Additionally, it is still remained to figure out why a single mutation causes different phenotypes in clinic, and how JAK2 V617F-negative MPN arises. Whether there are any other unknown oncogenic or anti-oncogenic incidents promoting the pathogenesis or influencing the phenotypes in MPN is not known and to be resolved. In 2008, Delhommeau reported the recurrent mutations in ten-eleven translocation 2 (TET2) gene, a new potential tumor suppressor gene, in MPN patients. Presently, TET2 mutation is frequently found in JAK2 V617F -positive or -negetive MPNs, MDSs, de nove or secondary acute myeloid leukemia (AML). The main mutations include frame-shift, nonsense and missense mutations in multiple sites, especially in the 3th and 11th exons of TET2 gene. It is true that there are some researches about JAK2 V617F mutation, but little is known about the incidence and clinical features of TET2 gene mutation in Chinese MPN patients. Therefore, in our this work, the incidence and clinical characteristics of JAK2 V617F and TET2 gene mutation, the effct of TET2 and JAK2 V617F gene mutation on MPN patients were investagated.Firstly, samples of peripheral blood or bone marrow from 40 Chinese MPN patients were collected, and the whole genomic DNAs were extracted. Subsequently, allele-specific fluorescent real-time quantitative PCR was carried out to test the JAK2 V617F mutation. Meanwhile, TET2 gene was amplified by PCR and sequenced directly. Sequencing results were compared with the human genome database provided by National Center for Biotechnology Information (NCBI) to analyse TET2 gene mutation. Finally, clinical features of TET2 gene mutation and the effct of TET2 and JAK2 V617F gene mutation on MPN patients were studied.The results showed that JAK2 V617F mutation took place in 28 MPN patients, accounting for 70% of the total 40 patients. Among them, 16 cases were PV patients, accounting for 76.2% of PV patients tested,7 cases were ET patients, accounting for 53.8% of ET patients tested, and 5 cases were MPN patients who cann't be classified exactly. JAK2 V617F-positive PV patients had a higher occurrence age than JAK2 V617F-negative patiens(P=0.020); JAK2 V617F-positive ET patiens had a higher count of leukocytes(P=0.026) and lower platelets(P=0.048) than JAK2 V617F-negative patients. Meanwhile,4 cases (10%) of the MPN patients were found to have TET2 gene mutation, of whom two cases were PV patients, and the other two were ET patients. All the four mutations were located in the 11th exon of TET2 gene. The first mutation was located in the 5548th nucleotide where the base T was substituted by base G, which caused 1721th amino acid of leucine replaced by tryptophan; The second one was the 5670th base A changing into base G, leading to 1762th amino acid of isoleucine replaced by valine; The third one was the 6269th base G changing into base A, which was a synonymous mutation; The last one was the 6364th base G changing into base A, resulting in the 1993th amino acid of arginine replaced by glutamine. JAK2 V617F mutation occured in all the four patients with TET2 gene mutation. Statistics analysis showed that the age,sex,the count of leukocytes,erythrocytes and platelets,the concentration of hemoglobin between TET2-mutant and -wild type patiens were not significantly different.From all above, it could be concluded that JAK2 V617F mutation occures in the most of MPN patients and there are some significant clinical differences between JAK2 V617F-positive and -negative patiens. But TET2 gene mutation only exists in a small fraction of MPN patients, which is mostly located in the 11th exon of TET2 gene. TET2 gene mutation can coexist with JAK2 V617F mutation in the same MPN patients. TET2 gene mutation seems to have nothing to do with the patient's age and sex, it also has no effects on the count of leukocytes,erythrocytes,platelets and the concentration of hemoglobin of MPN patients.