The Importance of Evaluating the Frequency of Thrombotic Events in Patients with Polycythemia Vera JAK2 V617F Positive 111
Citation: The Importance of Evaluating the Frequency of Thrombotic Events in Patients with Polycythemia Vera JAK2 V617F Positive. American Research Journal of Hematology; 1(1): 32-37.
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Abstract:The polycythemia vera is a myeloproliferative neoplasia whose overall incidence is 0.7-2.6 cases per 100.000 inhabitants a year, what increases with the ages of the patients, independently of sex. PV patients have a higher risk of occurrence of thrombotic events, considering these are the cause of morbidity and mortality of them. The aim of this research was to evaluate the frequency of thrombotic events in patients with polycythemia vera treated in a medical center. We did a molecular analysis of the gene JAK2, evaluating the exons 12 and 14 in samples from 26 patients clinically diagnosed with the disease, in the period of March to September, 2013. As we found, 92.3% of the patients were positive to the mutation JAK2 V617F (exon 14), and 7.7% were negative also to the mutations on the exon 12. The frequency of thrombotic events in these patients was evaluated, describing the main clinical characteristics associated with this mutation. Around 29.16% of the JAK2 V617F positive patients had arterial or venous thrombosis, considering that the venous thrombosis was more frequent. The percentage of patients with the mutation JAK2 V617F, and the frequency of thrombosis in PV JAK2 positive patients demonstrated in our study, is according to the data presented in the literature. With this work, we emphasize the role of the research on this mutation into the causes of thrombotic events, especially in unusual site, pointing the myeloproliferative neoplasia as the cause of thrombophilia. Keywords: Polycythemia Vera, myeloproliferative neoplasias, JAK2 V617F, thrombotic events, venous thrombosis.
The Polycythemia Vera(PV) is a myeloproliferative neoplasia which comes from a change in the multipotent hematopoietic stem cells that causes the accumulation of erythrocytes, leukocytes, and morphologically normal platelets, independent of erythropoietin. It can bring about leukocytosis, thrombocytosis, splenomegaly, and an increased risk of thrombotic events (1,2,3). Around 95% of the patients diagnosed with PV have the mutation JAK2 V617F (19).
The PV global incidence is 0.7-2.6 cases per 100.000 inhabitants a year, what increases with the advancing age of the patients, independently of sex (4). Between the main complications of PV are the thromboembolic events that cause the morbidity and mortality of these patients (5).
Even in the absence of thrombotic events, the patients with a type of myeloproliferative neoplasia (MPN) present a hypercoagulable state, which can be identified for an increasing in the concentration of several plasmatic markers on the system of haemostatic activation (5). Besides this, studies suggest that these patients with MPN, who have the mutation JAK2 V617F, are exposed to an increasing risk of thrombotic complications, possibly because of the increased platelet and the leukocyte activation (6).
Thereby, the present work evaluated the frequency of thrombotic events in patients with polycythemia vera
(PV), positive JAK2 V617F, of one medical center, describing the main clinical characteristics associated to
this mutation, which is one of the most important criteria for the diagnosis according to the World Health
Organization - WHO (2008).
Material and Methods
They were included 31 patients with PV diagnoses according to the established criteria by WHO (2008), between March and September, 2013. Considering this total number, five patients refused to participate of the research. The project was approved by the Human Research Ethics Committee. The patients were evaluated according to the main clinical and laboratory features, emphasizing the thrombotic events preceding or posteriors to the PV diagnosis.
The blood samples were collected by peripheral puncture and routed to the Genetics Laboratory and Sector Advisory from the Federal University of Juiz de Fora/Brazil. The PCR-AE technique was performed according to standard conditions, and the product of PCR was visualized on 2% agarose gel. On the negative samples to the presence of the mutation JAK2 V617F, it was done the automatic sequencing, with the aim of identify possible changes in the exon 12 in the gene JAK2.
The sample of blood was collected in an ethylene diamine tetraacitate anticoagulated tube. The Genomic DNA was extracted with standard procedures after the total isolation of the peripheral blood samples, and stored at -20°C until the processing. The DNA was quantified using spectro photometric measurements.
All the DNA samples were genotyped for the JAK2V617F mutation situated in exon 14 by an allele-specific (AS) polymerase chain reaction (PCR), exactly as described by Baxter et al. (2005) (7). So, 1 μmol/L of a common reverse primer, 0.5 μmol/L of a forward primer specific for the mutant allele (giving a 203-bp product), and 0.5 μmol/L of another forward primer amplifying a 364-bp product from both mutant and wild type of alleles – which also serves as an internal PCR control –, were used. Samples that were positive for the mutation were subsequently analyzed via PCR-restriction fragment length polymorphism (PCR-RFLP), with the restriction endo nuclease BsaXI (New England Biolabs, Hitchin, UK), which allows an estimation between mutated and wildtype alleles. A successful amplification was confirmed by electrophoresis on an ethidium bromide, impregnated 2% agarose gel. The G-T mutation destroys a BsaXI site present in the wild-type JAK2 sequence. This approach allows both normal and mutant alleles be visualized and distinguishes homozygous and heterozygous mutations.
When the PCR was done for the preparation of the template for sequencing, the primers were not labeled with a fluorescentdye. The amplicons were treated with ExoSap (Amersham Biosciences, Piscataway, NJ) to remove the primers and dNTPs, then were sequenced by usingthe PCR as sequencing primers, and Applied Biosystems (ABI, Foster City, CA) Big Dye Terminator version3.1 on chemistry. The sequencing reactions were purifiedby using the Clean Seq System (Agencourt Bioscience, Beverly, MA), and subsequently resolved by capillary electrophoresison the ABI 3100 Prism Genetic Analyzer. The mutations were determined by comparison with the normal JAK2 sequence (accession NM-004972) and with a normal control that was included in each run.
The table 11 presents some clinico-hematological features of each patient.
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