In addition to JAK2 V617F mutation, we screened for JAK2 exon 12 mutations in all JAK2 V617F-negative PV cases using two methods: a direct sequencing of the entire JAK2 gene exon 12 and a more senstive method (HRM) for the detection of 6 common mutations in JAK2 gene exon 12. Here, JAK2 is linked to acquired polycythemia vera.