JAK2 and acquired polycythemia vera: JAK2 (V617F) mutation (Janus kinase 2), occurring within exon 14 of JAK2 and located on 9p24 is the most frequent mutation in MPN, ranging from roughly 96% in PV to 65% in ET and PMF.[11, 13] This mutation affects the auto-inhibitory domain (JH2, pseudokinase) of JAK2 leading to constitutive activation of JAK2 and JAK/STAT signaling.