Detection of JAK2 exon 12 mutations in 15 patients with JAK2V617F negative polycythemia vera

To further characterize JAK2 exon 12 mutations, we performed molecular screening in 409 patients with polycythemia vera or unclear erythrocytosis with unmutated JAK2V617. The frequency of JAK2exon12 mutations was 10/63 (15.9%) in PV but only 5/346 (1.4%) in the erythrocytosis cases. Nine different mutations including four new types (D544-L545del, H538DK539LI540S, H538-K539del, V536-F547dup) were detected. In 2 cases we found evidence for the presence of cells homozygous for mutated JAK2exon12. As this was the case in only 2/15 cases with JAK2exon12 mutations (13%) homozygosity seemed to be less frequent than in V617F-mutated polycythemia vera (69%) (p