• Prior to the description of the JAK2 V617F mutation, a set of positive markers including 1) "spontaneous" growth of erythrocyte precursors (EEC) in absence of added erythropoietin (EPO) [29]; 2) endogenous megakaryocytic colony formation [30]; 3) decreased expression of c-MPL at platelet or megakaryocyte cell surface; 4) polycythemia rubra vera protein 1 (PRV-1) and 5) nuclear factor erythroid 2 (NF-E2) mRNA over expression in polymorphonuclear cells were initially described in PV patients. This evidence concerns the gene JAK2 and acquired polycythemia vera.