Of the 80 men we have studied, we have previously described DVT, PE, and mesenteric artery thrombosis in 6 with Klinefelter syndrome [17], 4 of whom had high Factor VIII, 3 of whom had high Factor XI, and 1 who was heterozygous for the G20210A Prothrombin gene mutation. Here, F2 is linked to Klinefelter syndrome.