Frequency of the JAK2 Mutation and Its Usefulness as a Marker for Treatment Response and Disease Progression in Korean Patients with Chronic Myeloproliferative Disorders.

Background: The recent discovery of a single point mutation in the JAK2 gene (V617F) is a major advance in our understanding of the pathogenesis of BCR/ABL-negative chronic myeloproliferative disorders (CMPD). The frequency of the JAK2 V617F mutation in CMPD differs according to methods and research groups. We investigated the frequency of JAK2 mutations in Korean CMPD patients and demonstrated their usefulness as a new molecular marker for treatment response and disease progression in BCR/ABL-negative CMPD using quantitative real time PCR and pyrosequencing.

Methods: Seventy-eight patients with BCR/ABL-negative CMPD comprising 42 cases of essential thrombocythemia (ET), 26 of polycythemia vera (PV), 7 with idiopathic myelofibrosis (MF), and 3 unclassifiable (UC) CMPD were enrolled in this study. A 364-bp PCR product containing the JAK2 V617F mutation was sequenced in both directions from total bone marrow cells. Restriction enzyme-based assessment with BsaXI was also used to search for JAK2 mutations. A quantitative real-time PCR-based allelic discrimination assay and pyrosequencing (Pyrosequencer PSQ96) were used to quantify the JAK2 V617F mutation status.

Results: A single JAK2 V617F point mutation was identified in 20 (77%) of 26 patients with PV, 12 (26%) of 42 with ET, 7 (100%) of 7 with MF, and 2 (67%) of 3 with UC. The V617F mutation was present in over half of Korean patients with BCR/ABL-negative CMPD, giving an overall frequency of 53%. The proportion of mutant alleles ranged from 36 to 100% in the real-time PCR and pyrosequencing analysis. Patients with MF had a higher percentage of JAK2 mutant alleles than patients with ET (MF>PV>ET). PV patients (n=8) with a good response (phlebotomy only) had a relatively low proportion (58.9±20.1%) of the JAK2 mutant, while patients (n=9) showing a poor response (additional chemotherapy) initially had a higher proportion (76.6±19.0%; p=0.04185).

Conclusion: The frequency of the JAK2 V617F mutation in Korean patients with PV was lower than that in reports from Western countries, although the overall frequency in Korean patients with BCR/ABL-negative CMPD was similar to previous reports. The results also suggest that the JAK2 mutation (quantification of JAK2 mutant alleles) can be used as a new marker for treatment response and disease progression in BCR/ABL-negative CMPD using quantitative real-time PCR or pyrosequencing.