Phenotypic variations and new mutations in JAK2 V617F-negative polycythemia vera, erythrocytosis, and idiopathic myelofibrosis

Objective: The chronic myeloproliferative disorders (MPD), polycythemia vera (PV), essential thrombocytosis, and idiopathic myelofibrosis (IMF), are characterized by a spectrum of clinical features and linked by common genetic lesions in JAK2 and MPL. However, the clinical phenotypes in genetically undefined MPD patients are similar to those patients with JAK2 and MPL lesions. We, therefore, sought to determine whether there were JAK2 or MPL lesions in a well-defined, JAK2 V617F-negative MPD cohort, and to determine if clinical associations could be identified based on variations identified in these genes. Methods: We examined the JAK2 and MPL genes in JAK2 V617F-negative PV, IMF, and idiopathic erythrocytosis patients for sequence variations. Results: We identified two previously unrecognized JAK2 mutations and three previously unrecognized MPL mutations in JAK2 V617F-negative PV, erythrocytosis, and IMF patients. We identified JAK2 exon 12 lesions in 30% of JAK2 V617F-negative PV patients, and either JAK2 V617F or JAK2 exon 12 lesions in 9% of erythrocytosis patients. In IMF, in addition to the MPL gene mutation, W515K, we identified three additional mutations: 204P and two intervening sequence transitions, IVS 11/12 and 10/11. Conclusions: While the clinical phenotype of JAK2 exon 12 lesions in the MPD was predominantly erythroid, there was significant disease spectrum overlap between JAK2 V617F and JAK2 exon 12 mutations. By contrast, MPL gene mutations were not associated with erythrocytosis, but segregated primarily with the phenotypes of thrombocytosis, extramedullary disease, myelofibrosis, and osteosclerosis.