[Novel method in diagnosis of chronic myeloproliferative disorders--detection of JAK2 mutation]

Chronic myeloproliferative disorders are clonal hematopoietic stem cell disorders characterized by proliferation of one or more myeloid cell lineages in the bone marrow. The WHO classification describes six major groups of chronic myeloproliferative disorders, as follows: chronic myeloid leukemia, chronic neutrophilic leukemia, chronic eosinophilic leukemia, polycythemia vera, essential thrombocythemia and chronic idiopathic myelofibrosis. The diagnosis of chronic myeloid leukemia and certain types of chronic eosinophilic leukemia are based on the detection of fusion genes (in chronic myeloid leukemia the BCR/ABL fusion gene, and in chronic eosinophilic leukemia the FIP1L1-PDGFRalpha gene). On the other hand molecular markers for polycythemia vera, essential thrombocythemia and chronic idiopathic myelofibrosis were lacking, making it difficult to identify these disorders clearly. The authors investigated the incidence of the newly identified somatic point mutation V617F of the Janus-2 tyrosine kinase in patients with polycythemia vera, essential thrombocythemia and myelofibrosis. Janus-2 kinase is a cytoplasmic, non-receptor protein-tyrosine kinase with a key role in signal transduction from multiple hematopoietic growth factor receptors. The mutant protein is constitutively phosphorylated and is able to activate its downstream signaling pathways in the absence of any cytokine, thereby contributing to the pathogenesis of chronic myeloproliferative disorders. The authors investigated DNA samples from 132 patients with chronic myeloproliferative disorders. The V617F mutation was detected by allele-specific polymerase chain reaction, and the patients were genotyped by a DNA tetra-primer amplification refractory mutation system assay. Approximately 73% of polycythemia vera, 60% of essential thrombocythemia and 67% of myelofibrosis showed the JAK2 V617F mutation. Using the amplification refractory mutation system assay, the frequency of homozygotes was 17.5% in polycythemia vera, 5.4% in essential thrombocythemia and 0% in myelofibrosis. The authors established an effective polymerase chain reaction based method for the identification of JAK2 mutation in the routine oncohematologic diagnostics.