van Hylckama Vlieg van Hylckama Vlieg A A van der Linden van der Linden IK IK Bertina Bertina RM RM Rosendaal Rosendaal FR FR High levels of factor IX increase the risk of venous thrombosis High levels of factor IX increase the risk of venous thrombosis Blood Blood 2000 2000 95 95 12 12 3.678 3.678 3.682 3.682. This evidence concerns the gene F9 and Venous thrombosis.