In 2007, additional JAK2 mutations in exon 12 were described in JAK2V617F-negative patients with PV [8]; JAK2 mutational frequencies, in PV, are estimated at 97% for JAK2V617F and 3% for other JAK2 mutations, including JAK2 exon 12. This evidence concerns the gene JAK2 and acquired polycythemia vera.