Familial Haemostatic Defect Associated with Reduced Prothrombin Consumption

S ummary . Ten individuals from three unrelated families suffered from an unusual inherited haemorrhagic disorder. The defect was associated with reduced prothrombin conversion as shown by a grossly abnormal prothrombin consumption index. All known plasma coagulation factors were present in adequate concentrations but in the two families tested the results were consistent with a defect of the interaction between plasma and platelets or phospholipid. Some of the affected family members exhibited a mild bleeding tendency characterized by post‐operative or post‐partum haemorrhage but none suffered spontaneous bleeding. In therapeutic trials in one of the patients both plasma and platelet transfusions were needed in order to correct the abnormality. This finding together with in vitro and other in vivo studies indicated that the abnormality is associated with an inhibitor of the interaction between plasma and phospholipid during blood coagulation. The results suggest the possibility of an abnormality of the γ‐carboxyglutamic acid residues of one or more vitamin K dependent coagulation factors but immunological and electrophoretic studies have so far failed to detect this. The findings underline the importance of a test of prothrombin conversion in screening procedures for an otherwise unexplained bleeding disorder.