with ET diagnosed according to either previous 18 or updated 9 WHO criteria. All patients underwent laboratory screening for thrombophilia. Genomic DNA was extracted from peripheral blood granulocytes by standard procedures and was archived. All patients gave informed consent for future investigations on the archived DNA. According to these criteria, 132 out of a total of 159 patients referred to our center between 2002 and 2007 who had a stored or fresh DNA sample available for JAK2 mutational analysis were recruited. This study was approved by the institutional review board.The JAK2 V617 mutation was detected by allele-specific polymerase chain reaction according to Baxter et al. 19 The sequencing analysis was carried out according to Wolanskyj et al. 20 Heterozygous or homozygous status was defined as a mutant allele burden ≤50% or > 50%, respectively. Screening for thrombophilia included measuring antithrombin and protein C functional activities, free protein S antigen, and fasting homocysteine; searching for the FV Leiden, for the PT G20210A, and for antiphospholipid antibodies (lupus anticoagulant, anticardiolipin antibodies, and anti-β2glycoprotein I). 8,21 All the assays were performed blinded to the diagnosis and clinical history of the patients.
Study end-pointsThe events of interest were thromboses that occurred as inaugural manifestation of ET or during follow-up. Inaugural thromboses encompass the events occurring within the two years preceding the diagnosis, translating the knowledge that 75% of thromboses which indicate PV occur within this interval of time. 22 The recorded events were cerebrovascular disease [ischemic stroke or transient ischemic attack (TIA)], acute coronary syndrome (acute myocardial infarction or unstable angina pectoris), peripheral arterial thrombosis, retinal artery or vein occlusion, thrombosis of deep veins (including cerebral and splanchnic veins), and pulmonary embolism. Splanchnic venous thrombosis includes occlusion of hepatic, portal, mesenteric, and splenic veins. Moreover, superficial vein thromboses diagnosed by ultrasound objective methods were also computed. Diagnosis of first or recurrent major thrombosis was accepted only if objectively proven according to previously published criteria.
23
Clinical characteristicsThe clinical characteristics of the investigated patients are shown in Table 1. Thirty-eight (28.7%) suffered from thrombosis, arterial in two-thirds of the cases and venous in one-third. Thrombosis was inaugural in 34 cases and occurred during the follow-up in 10 (4 first thromboses and 6 recurrences). Recurrences were myocardial infarction in one case, splenic infarction in one, superficial vein thrombosis in 2, pulmonary embolism in one, and cerebral venous thrombosis in one. After diagnosis of ET, the patients with thrombosis of splanchnic or cerebral veins received long-term oral anticoagulation. All the remaining patients received antiplatelet agents, independently of the occurrence of a previous thrombosis. Forty-nine patients were presc...