Correlations of JAK2–V617F mutation with clinical and laboratory findings in patients with myeloproliferative disorders

Abstract

Recently, the acquired mutation JAK2–V617F has been described in the majority of patients with myeloproliferative disorders (MPDs). In this study we evaluated its clinical and laboratory correlates in 166 patients with MPDs. The mutation was detected by allele-specific PCR in 119 patients: 81.4% (35/43) of those with polycythemia vera, 69.1% (77/111) of those with essential thrombocythemia and 58.1% (7/12) of those with idiopathic myelofibrosis. The patients carrying the mutation were older (p = 0.02) and displayed higher levels of Ht (p < 0.01) and Hb (<0.01) and lower erythropoietin levels (p < 0.01). Moreover, mutation-positive patients displayed a higher probability of having leucocytosis, splenomegaly and thrombotic events (three-fold, two-fold and two-fold, respectively) than mutation-negative patients. These correlations imply that the JAK2–V617F mutation may be useful for the classification and the management of patients with MPDs.

Introduction

The identification of the JAK2–V617F mutation is an exciting new discovery in the field of chronic myeloproliferative disorders (MPDs) [1], [2], [3], [4], [5]. This acquired mutation is characterized by a G to T transversion at nucleotide 1849 in exon 12 of the JAK2 gene, leading to a substitution of valine to phenylalanine at amino acid position 617 (V617F) of the JAK2 protein [1], [2], [3], [4], [5]. The mutation is located in the JH2 pseudokinase domain of JAK2, which is involved in the auto-inhibition of its kinase activity, and results in constitutive JAK2 activation that promotes erythropoietin hypersensitivity and growth-factor independence in transfected cell lines [2], [3], [4], and induces erythrocytosis in a murine transplant model [2]. The presence of the mutation confers a proliferative and survival advantage by rendering the cells more sensitive to incoming stimulatory signals, causing clonal expansion of hematopoietic progenitors in myeloproliferative disorders [3]. Neoplastic cells can be heterozygous for the mutation or hemizygous if they are associated with loss of heterozygosity (LOH) of 9p, where JAK2 is situated [3].

The JAK2–V617F mutation has been detected in the vast majority of patients with polycythemia vera (PV) (65–97%) [1], [2], [3], [4], [5], [6] and in a lower frequency in patients with essential thrombocythemia (ET) (23–57%) [1], [2], [3], [5], [6], [7], [8], [9] and idiopathic myelofibrosis (IMF) (35–57%) [1], [2], [3], [5], [6], [10], [11]. The mutation has also been found in a small proportion of patients with systemic mastocytosis [6], [12], chronic hypereosinophilic syndrome [6], [12], chronic neutrophilic leukemia [6], [12], chronic myelomonocytic leukemia [10], [12], juvenile myelomonocytic leukemia [13], myelodysplastic syndromes [12], [14], and acute myeloid leukemia [14]. On the other hand, the mutation is absent in patients with nonhematologic cancers [14], acute and chronic lymphocytic leukemia [14], [15], [16], Hodgkin's and non-Hodgkin's lymphomas [17], and otherwise molecularly defined MPDs, such as chronic myeloid leukemia and platelet-derived growth factor receptor-rearranged eosinophilic disorders [3], [6], [14]. The explanation for JAK2–V671F yielding different chronic myeloproliferaive disease phenotypes is still unknown.

Several techniques have been applied for the detection of the mutation, as genomic DNA-PCR-sequencing [2], [3], [7], [14], RT-PCR-sequencing [4], PCR-ARMS (amplification refractory mutation system) [6], allele-specific PCR [1], [16], PCR-restriction analysis [1], [17], and real-time PCR [16]; these techniques are characterized by a different sensitivity that could justify the variety of mutation incidence in the previous studies.

To date, several groups studied the consequences of the JAK2–V617F mutation in patients with MPDs, although its role is still under investigation. In some previous series the presence of mutation has been clearly associated with a PV phenotype, with high hematocrit (Ht) and hemoglobin (Hb) levels, high white blood cell count (WBC), low erythropoietin levels and low platelet (PLT) count [2], [7], [9]. However, there are contradictory results regarding its role in thrombosis and transformation risk, as well as its long-term prognostic relevance [1], [2], [3], [7], [9]. In this study, we performed an analysis of the JAK2–V617 mutation in different groups of patients with MPDs, aiming the demonstration of its significance and its possible correlations with clinical characteristics and laboratory findings both at diagnosis and follow-up period.