The V617F activating mutations in the Janus kinase 2 (JAK2) gene occur in a significant proportion of patients with Philadelphia-negative myeloproliferative neoplasias (MPNs). Additional mutations in exon 12 of JAK2 have been reported in rare cases of MPNs. Mutations other than these, however, have not been fully studied. It is believed that these mutations allow the activation loop of the kinase domain to move away from the pseudokinase domain, thus leading to constitutive activation of the JAK2-STAT pathway. We report that based on testing approximately 20,000 patients with clinical suspicion of MPNs, we detected new mutations in exons 13 and 14, in addition to those reported in exon 12, that in aggregate should be routinely tested for in patients with MPNs. Using a sensitive reverse transcription-polymerase chain reaction (RT-PCR) and direct sequencing approaches of plasma RNA, we detected mutations in approximately 20% of these patients. The exon 14 mutations include complete deletion of exon 14 (D596-N622 del), L624P, I641V, H606Q, and C618R. In exon 13, we detected R564L, R564Q, V567A, V567L, G571R, G571S, L579F, H587N and S591L. All these mutations are in the pseudokinase domain and are expected to inactivate the auto-inhibitory function of this domain on the kinase domain. This data suggests that testing for JAK2 mutations should not be restricted to the V617F and exon 12 mutations, but perhaps should include most of the pseudokinase domain. Furthermore, testing for mutations using plasma RNA is highly sensitive and should replace DNA-based testing because of the relative abundance of the RNA and the ease in detecting deletion of the entire exon.
Third AACR International Conference on Molecular Diagnostics in Cancer Therapeutic Development-- Sep 22-25, 2008; Philadelphia, PA