In the latter group, the recurrent V617F mutation in the exon 14 of the JAK2 gene has been identified in 2005 [1]–[4] and is currently a key marker for MPD diagnosis [5] as this mutation is present in 90%, 60% and 50% of PV, TE and PMF respectively [6]. This evidence concerns the gene JAK2 and acquired polycythemia vera.