PROS1 and acquired polycythemia vera: Prothrombotic disorder n = 36 (54%)Hyperhomocysteinemia (n = 13), antiphospholipid syndrome (n = 9), hormone replacement therapy (n = 2), Factor V Leiden mutation (n = 3), Protein C deficiency (n = 2), Polycythaemia vera (n = 2), myeloproliferative syndrome (n = 1), Protein S deficiency (n = 1), antitrombin III deficiency (n = 1), disseminated coagulation (n = 1), essential thrombocytosis (n = 1)