A Quantitive Assay and Clinical Significance for JAK2^V617F Mutation in Chinese Patients with Essential Thrombocytosis

Essential thrombocytosis (ET) is a subtype of Bcr-Abl negative the chronic myeloproliferative disorders and the mutated JAK2V617F has been identified and correlated with ET. The aim of this study was to analyze the mutational status and quantitative expression of JAK2V617F mRNA transcripts in cohort of 98 Chinese patients with ET and to determine the disease features. The cohort consisted of 46 men and 52 women with median age at diagnosis was 50 years (range 17–87), granulocyte cDNA was enriched from blood samples obtained at the time of clinical assessment. A quantitative JAK2V617F measurements were made using amplification-refractory mutation sequencing polymerase chain reaction (ARMS-PCR) and capillary electrophoresis assay. Fifty-nine(60.2%) patients harboring the JAK2 V617F mutation were found, including 17 homozygous and 42 heterozygous changes. The quantitative assay by capillary electrophoresis showed that the mutated mRNA ratio was (89.9±6.7)% in the JAK2V617F homozygote and was (57.1±6.7)% in the JAK2V617F heterozygote patients, the difference was significant(P<0.005). JAK2V617F-positive ET patients were older than patients without the mutation (55 versus 38 years, p<0.001), and the patients whose age ≥ 60 years showed significantly higher JAK2 mutated RNA levels as compared to patients whose age ≤60 years(68.2% versus 80.2%, P =0.0056). Males and females had similar JAK2V617F prevalence (63.0% versus 57.7%) and frequency of homozygosity (17.4% versus 17.3%). As compared to heterozygous ET patients, higher leukocyte count was observed in homozygous ET patients (27.9×10⁹/L versus 15.2×10⁹/L, P©‚0.05), JAK2V617F-positive patients also had a higher median white cell count than wild-type patients (19.4×10⁹/L versus 9.7×10⁹/L, P©‚0.05), but there were no significant differences in hemoglobin concentration or platelet count. During follow-up, 30 patients suffered from documented thrombotic events, with 24 having JAK2V617F mutations. The rate of thrombotic complications in JAK2V617F-positive and homozygous patients was higher than in JAK2 wild-type and heterozygous patients, respectively. (52.2% versus 17.6%, 75% versus 32.8%, respectively ). Compared with patients without thrombotic events, there were higher levels of mutated JAK2 mRNA in patients with thrombotic events(76.9% versus 58.4%, P©‚0.05), thrombotic events were also significantly correlated with leukocytosis and older age. Our results suggest that there are different clinical features between JAK2V617F-positive and JAK2V617F-negative, homozygote and heterozygote, higher and lower levels of mutated JAK2 mRNA, and correlated with leukocytosis and thrombosis. Therefore, detection of the JAK2V617F mutational status and mutated JAK2 mRNA can help not only identify the disease state and progression, but also affect the management of ET patients.