The clinical significance of the lack of arterial or venous thrombosis in patients with congenital prothrombin or FX deficiency.

Several reports have dealt with the occurrence of both arterial and venous thrombosis in patients with haemophilia A, haemophilia B, and von Willebrand disease. Similar thrombotic events have been occasionally reported also in rare congenital coagulation disorders, particularly in fibrinogen or FVII deficiencies. On the contrary no sure venous or arterial thrombotic event has ever been reported in congenital prothrombin or Factor X deficiency. The significance of this observation is discussed. This discrepancy cannot be explained on the basis of the rarity of the two conditions, since in similarly rare congenital bleeding disorders such as FV or FXIII deficiency a few patients with thrombosis have been described. It appears that only these two defects are able to allow a sure protection from thrombosis. These observations may indirectly support the rationale for the use of direct thrombin or Factor X inhibitors in the prophylaxis and/or therapy of thrombotic manifestations.