Our understanding of the genetic basis of myeloproliferative neoplasms began in 2005, when the JAK2 (V617F) mutation was identified in polycythemia vera, essential thrombocythemia, and primary myelofibrosis.
In 2005, a somatic activating mutation in the JAK2 nonreceptor tyrosine kinase (JAK2V617F) was identified in most patients with PV and in a significant proportion of patients with ET and PMF.
Furthermore, erlotinib, a JAK2 inhibitor, was able to inhibit JAK2V617F-positive PV MC progenitor cells, indicating that malignant MC progenitor cells are a potential cellular target for such JAK2 inhibitor-directed therapy.
These findings suggest that, despite the phenotypical difference, the outcome of JAK2 exon 12 mutations-positive PV is similar to that of JAK2 (V617F)-positive PV.
The JAK2 617V>F mutation triggers erythropoietin hypersensitivity and terminal erythroid amplification in primary cells from patients with polycythemia vera.
Clinically suspected PV with low serum erythropoietin and absent JAK2(V617F), together with the bone marrow findings of erythroid hyperplasia and subtle megakaryocytic atypia, should prompt an evaluation for an exon 12 mutation.
JAK2 mutations define polycythemia vera (PV), CALR and MPL mutations are specific to JAK2 unmutated essential thrombocythemia (ET) and primary myelofibrosis (PMF).
Here, we describe a clonal and recurrent mutation in the JH2 pseudo-kinase domain of the Janus kinase 2 (JAK2) gene in most (> 80%) polycythaemia vera patients.
Previously, groundbreaking investigations in Ph(-) CMPD detected an acquired mutation in the Janus kinase 2 (JAK2) in the majority of patients with polycythaemia vera (PV) and in up to 50% of patients with essential thrombocythaemia (ET) and chronic idiopathic myelofibrosis (CIMF).
Janus kinase-2 (JAK2) is mutated in a high proportion of patients with polycythemia vera and in a smaller number with essential thrombocythemia and primary myelofibrosis.
Polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) constitute the BCR-ABL1-negative myeloproliferative neoplasms and are characterized by mutually exclusive Janus kinase 2 (JAK2), calreticulin (CALR), and myeloproliferative leukemia virus oncogene (MPL) mutations; respective frequencies of these mutations are approximately 95%, 0%, and 0% in PV, 60%, 20%, and 3% in ET, and 60%, 25%, and 7% in PMF.
Given that the identical somatic activating mutation in the JAK2 tyrosine kinase gene (JAK2(V617F)) is observed in most individuals with polycythemia vera, essential thrombocythemia and primary myelofibrosis, there likely are additional genetic events that contribute to the pathogenesis of these phenotypically distinct disorders.
These data indicate that loss of wild-type clones at the progenitor level is a feature of MF (primary MF, post-ET MF, and post-PV MF), presumably due to expansion of the JAK2V617F clone and that this characteristic is surprisingly independent of JAK2V617F homozygosity, suggesting that additional genomic lesions may contribute to this unique molecular process that distinguishes MF from ET and PV.