Phenotype and genotype in the myeloproliferative disorders.

The WHO classification of myeloproliferative disorders (MPDs) encompasses a variety of clinical entities including three, essential thrombocythaemia (ET), polycythemia vera (PV), and primary myelofibrosis (PMF), that deserve separate classification because they share in common many features not found in the other disease entities (1). Despite their unique characteristics, distinguishing between ET, PV, and PMF can be clinically challenging because of the overlapping features of these disorders and the absence of disease-specific markers. Although the discovery of the janus kinase 2 (JAK2) V617F mutation was a major breakthrough in this regard as well as with respect to pathogenesis (2–5), our knowledge regarding the molecular basis of the MPDs remains incomplete. The purpose of this article is to discuss the relationship between phenotype and genotype in MPDs, and in particular, the potential importance of the JAK2 V617F mutation and other molecular abnormalities with respect to the diagnosis of these disorders.