Background: JAK2 V617F is the most common somatic mutation associated with the classical Philadelphia (Ph) chromosome negative myeloproliferative neoplasms (MPNs), which include essential thrombocythemia (ET), polycythemia vera (PV), and primary myelofibrosis (PMF). JAK2 V617F allele burden may be used for establishing the diagnosis, determining prognosis, and monitoring progression in these diseases. Limited data is available regarding the epidemiology of MPNs in Africa, and there is paucity of data on demographic, laboratory, and clinical features of MPNs in South Africa. This study determined the JAK2 V617F allele burden in a seven-year retrospective cohort of patients diagnosed with MPNs and described the characteristics of these diseases in a South African setting.
Methods: A laboratory database search was performed to identify patients diagnosed with ET, PV or PMF and a positive JAK2 V617F mutation, diagnosed qualitatively on Fluorescence Resonance Energy Transfer (FRET) real-time PCR and melting curve analysis. The allele burden for these patients was measured on archived residual DNA samples using a quantitative allele specific amplification (QUASA) assay. Demographic data and relevant laboratory results at presentation were analyzed.
Results: The search identified 87 patients who tested positive for JAK2 V617F mutation and fulfilled the diagnostic criteria for ET, PV or PMF from 2012 to 2018. Median age at diagnosis was 64 years with a male: female ratio of 1.2:1. ET, PV and PMF accounted for 11.5%, 44.8%, and 43.7% of the MPNs, respectively. Median allele burden for ET, PV, and PMF was 24.9%, 71.1%, and 55.8%, respectively. Allele burden was significantly lower in ET compared to PV (p = 0.0003) and PMF (p = 0.0023) and correlated with leukocytosis, neutrophilia, eosinophilia, and low erythrocyte mean cell volume (p < 0.05).
Conclusions: JAK2 V617F-positive MPNs occurred predominantly in older patients with approximately equal gender ratio. ET was the least common MPN and there was a higher proportion of PMF cases than described in studies in Europe and America. Allele burden was also relatively high for all three subtypes of MPNs when compared to other published data, which may predispose to poorer prognosis.