JAK2 Mutational Status, Hemostatic Risk Factors and Thrombophilic Factors in Essential Thrombocythemia (ET) Patients

The recently discovered JAK 2 V617F activating tyrosine-kinase mutation has been found in 50–70% of Essential Thrombocythemia (ET) patients. Increased risk of thrombosis in patients with this mutation, especially homozygous for JAK2 V617F, has been reported. Other factors that increase the risk of thrombosis arising from ET itself include hereditary thrombophilic factors like antithrombin, protein C, and protein S deficiencies, the mutation of the prothrombin gene and the Leiden mutation of factor V, the MTHFR gene mutation, but also increase or decrease level of coagulation factors. In this study we explored if indeed JAK2 V617F mutation in ET patients correlates with the presence of risk factors that would contribute to thrombotic complication and a higher risk of thrombosis. We have examined 32 patients with ET (24 females and 8 males with a mean age 56.0±14.2, observed in our department since 1993). This group included: 10 untreated patients, 10 treated with anagrelide, 9 treated with hydroxyurea and 3 with the combination of both drugs. The control group consisted of 20 healthy volunteers: 6 males and 14 females (mean age 41.4±8.3). Mean platelet count was 785±320 G/l and 250±54 G/l for ET and the control group, respectively, p<0.001. WBC count was higher in ET patients than in control group: 8.3±3.7 G/l and 5.4±1.4 G/l, p<0.001. Concentration of uPA was statistically significantly higher in patient plasma as compared to the control group (0.635±0.232 ng/ml versus 0.447±0.115 ng/ml, p<0.05). Mean uPA concentration measured in platelet lysates was similar in both groups (ET 0.317±0.135ng/109 platelets, control group 0.290±0.065ng/109 platelets). In 11 patients from ET group thrombotic complications occurred and in 7 ET patients clinically significant bleeding episodes were noticed. In two persons from control group minor thrombotic complications were observed. Patients with thrombotic complications as compared to those with bleeding episodes had higher fibrinogen and factor VIII level (420 mg/dl versus 302 mg/dl p<0.05, and 115% versus 88% p<0.05 respectively). In patients with thrombotic complications compare to patients without this complications a statistically significantly lower CD61/42b expression was detected (1.74% versus 10.00% p<0.05) suggesting platelet activation. The JAK 2 V617F point mutation was detected in 18 (60%) of ET patients and none in control group. In all cases heterozygous genotypes were determined. In 10 (37%) of ET patients the MTHFR gene mutation was detected (in 6 patients simultaneously with JAK2 mutation). In 13 (65%) persons from control group the MTHFR gene mutation was also detected. In one person homozygous genotype was determined and this person had a thrombotic complication (DVT) after delivery. The other (12) subjects had heterozygous genotype and among them here was one had minor cerebrovascular event. In two ET patients and in two control subject heterozygous genotypes for Leiden mutation was detected. In two patients and in one of the control subject simultaneously heterozygous genotypes for Leiden and for MTHFR gene mutation were discovered. No prothrombin gene G20210A mutation was found in ET or in control group. In ET patients with JAK2 point mutation the higher level of red blood cells was found (4.38±0.57 T/l and 3.86±0.55 T/l, for patients with and without mutation, respectively, p<0.05) confirming hypersensitivity of mutated hematopoietic progenitor cells to cytokines like EPO. The activity of factor XII in JAK2 positive patients was lower than in negative ones (83.2±25.5% and 109.0±20.4% respectively p<0.05). In ET patients carrying MTHFR gene mutation the higher level of plasma urokinase was observed (0.747±0.3 ng/ml and 0.547±0.2 ng/ml, for patients with and without mutation, respectively, p<0.05). This might indicate that fibrinolytic system is partly activated in ET patients, especially carrying MTHFR gene mutation, as a mechanism compensating hypercoagulable state present in these patients. In summary, in the group of patients with heterozygous JAK2 point mutation we have not observed increased frequency of thrombotic complication. To evaluate the risk of thrombosis it is necessary to assess not only JAK2 mutational status but also additional risk factors such as thrombosis and bleeding.