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The germline JAK2 46/1 haplotype has been associated with the development of JAK2V617F-positive as well as JAK2V617F-negative myeloproliferative neoplasms (MPNs). In this study we examined the role of the 46/1 haplotype in the etiology and clinical presentation of patients with splanchnic vein thrombosis (SVT), in which MPNs are the most prominent underlying etiological factor. The single-nucleotide polymorphism rs12343867, which tags 46/1, was genotyped in 199 SVT patients. The 46/1 haplotype was overrepresented in JAK2V617F-positive SVT patients compared with controls (P < .01). Prevalence of the 46/1 haplotype in JAK2V617F-negative SVT patients did not differ from prevalence in the controls. However, JAK2V617F-negative SVT patients with a proven MPN also exhibited an increased frequency of the 46/1 haplotype (P = .06). Interestingly, 46/1 was associated with increased erythropoiesis in JAK2V617F-negative SVT patients. We conclude that the 46/1 haplotype is associated with the development of JAK2V617F-positive SVT. In addition, our findings in JAK2V617F-negative SVT patients indicate an important role for the 46/1 haplotype in the etiology and diagnosis of SVT-related MPNs, independent of JAK2V617F, that requires further exploration.

The germline JAK246/1 haplotype has been associated with the development of JAK2V617F-positive as well as JAK2V617F-negative myeloproliferative neoplasms (MPNs). In this study we examined the role of the 46/1 haplotype in the etiology and clinical presentation of patients with splanchnic vein thrombosis (SVT), in which MPNs are the most prominent underlying etiological factor. The single-nucleotide polymorphism rs12343867, which tags 46/1, was genotyped in 199 SVT patients. The 46/1 haplotype was overrepresented in JAK2V617F-positive SVT patients compared with controls (P< .01). Prevalence of the 46/1 haplotype in JAK2V617F-negative SVT patients did not differ from prevalence in the controls. However, JAK2V617F-negative SVT patients with a proven MPN also exhibited an increased frequency of the 46/1 haplotype (P= .06). Interestingly, 46/1 was associated with increased erythropoiesis in JAK2V617F-negative SVT patients. We conclude that the 46/1 haplotype is associated with the development of JAK2V617F-positive SVT. In addition, our findings in JAK2V617F-negative SVT patients indicate an important role for the 46/1 haplotype in the etiology and diagnosis of SVT-related MPNs, independent of JAK2V617F, that requires further exploration.

In Budd-Chiari syndrome (BCS), thrombosis develops in the hepatic veins or inferior vena cava. To study the relationship between hypofibrinolysis and BCS, we measured plasma levels of fibrinolysis proteins in 101 BCS patients and 101 healthy controls and performed a plasma-based clot lysis assay. In BCS patients, plasminogen activator inhibitor 1 (PAI-1) levels were significantly higher than in controls (median, 6.3 vs 1.4 IU/mL, P < .001). Thrombin-activatable fibrinolysis inhibitor and plasmin inhibitor levels were lower than in controls (13.8 vs 16.9 μg/mL and 0.91 vs 1.02 U/L, both P < .001). Median plasma clot lysis time (CLT) was 73.9 minutes in cases and 73.0 minutes in controls (P = .329). A subgroup of cases displayed clearly elevated CLTs. A CLT above the 90th or 95th percentile of controls was associated with an increased risk of BCS, with odds ratios of 2.4 (95% confidence interval, 1.1-5.5) and 3.4 (95% confidence interval, 1.2-9.7), respectively. In controls, only PAI-1 activity was significantly associated with CLT. Analysis of single nucleotide polymorphisms of fibrinolysis proteins revealed no significant differences between cases and controls. This case-control study provides the first evidence that an impaired fibrinolytic potential, at least partially caused by elevated PAI-1 levels, is related to the presence of BCS.

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No relevant conflicts of interest to declare.

No relevant conflicts of interest to declare.

No relevant conflicts of interest to declare.

Abstract 4213

High mobilization into peripheral blood of putative endothelial progenitor cells (EPCs) has been proposed as a characteristic of primary myelofibrosis (PMF) among the myeloproliferative neoplasms (MPNs). Endothelial colony forming cells (ECFCs) are a distinct colony type with robust proliferative potential and vessel forming capacity in vivo, and candidates to represent true EPCs. Low number of circulating ECFCs, however, imposes analytical work out in order to use this measurement as a feasible biological indicator of EPC mobilization. Here we report the assessment of ECFCs in patients with MPNs, based on a high number of patients in order to characterize the MPN categories and patients' clinical phenotype that better correlate with such measurement.One hundred thirty nine patients with PMF, 32 patients with essential thrombocythemia (ET) or polycythemia vera (PV) and 22 normal subjects were studied. ECFCs were grown in vitro by plating mononuclear cells, obtained from 40 ml of peripheral blood, onto collagen treated culture plates in the presence of EGM-2MV medium, according to Ingram et al (Blood, 2004). Medium was changed every 3 days. Plates were scored for the presence of ECFC every 2 days, starting from 10 days of culture and up to 28 days. JAK-2V617F mutation was assessed on patients granulocytes by semi-nested PCR.Patients with PMF had a significant higher (p<0.5) median frequency of ECFCs in peripheral blood (0.48 ECFC/10 ml, range 0–6) with respect to normal subjects (0.14, range 0–0.5) and patients with ET (0.25, range 0–1) or PV (0.13, range 0–0.57). Frequency was higher (p<0.05) in patients with prefibrotic PMF (0.86 ECFC/10 ml; n=36) than in patients with fibrotic PMF (0.41/10 ml; n=103). A history of previous splanchnic vein thrombosis (SVT) was associated to statistically higher (p<0.01) ECFC frequency (1.45 ECFC/10 ml; n=21) compared to patients without thrombosis (0.46/10 ml; n=118), as well as to healthy subjects, either with or without history of thrombosis (0.29 and 0.14, respectively, p<0.05 for both). At univariate analysis, increased expression of circulating ECFCs in PMF was associated with younger age (r = − 0.22, p<0.02), diagnosis of prefibrotic myelofibrosis (r = 0.72, p<0.01) and history of splanchnic vein thrombosis (r = 0.68, p<0.001). No correlation was found with the JAK-2 mutational status. At multivariate analysis all the three characteristics maintained an independent association. Since there was no association between the frequency of circulating ECFCs and the time from the onset of SVT, and since patients with an idiopathic SVT had marginal increase in ECFCs frequency compared to healthy subjects, we favored the hypothesis that an increased frequency of circulating ECFC is associated with the myeloproliferative phenotype more than with thrombosis per se. Finally, in the whole population of patients, a direct relationship (r= 0.71, p< 0.02) between the frequency of circulating ECFCs and the index of vascular splenomegaly (spleen index / number of circulating hematopoietic CD34+ cells) was evidenced.Increased mobilization into peripheral blood of ECFCs is a distinctive and new biomarker of prefibrotic myelofibrosis. In addition, this study addresses to the hypothesis that mobilization of ECFCs in MPNs is associated with high risk of SVT and with increased vasculature in the spleen, suggesting a potential role for EPCs in neoangiogenetic processes in this organ.No relevant conflicts of interest to declare.