Familial hypofibrinolysis and venous thrombosis.

Nine patients with, and 11 without, venous thromboses (DVT) from two families were studied. In family 1, four members with, and one without, DVT had t-PA activity below the lower limit of the controls (21.3 IU/ml, n = 19) after 20 min venous occlusion (VO). After VO t-PA antigen (t-PA:Ag) was below the lowest value of the controls (22.8 ng/ml) in all five cases with low t-PA activity. All the family members, both with and without thrombosis, had normal t-PA inhibitor activities (PAI). In family 2 t-PA activity after VO was low in three symptomatic and four asymptomatic family members. t-PA:Ag was also low in four of these. PAI level was normal in all but one family member. Mild type I von Willebrand's disease was discovered in four members of family 2. Deficient t-PA:Ag response was found in two of these. Antithrombin III, protein C and protein S were normal in both families. It is concluded that low fibrinolytic capacity, independent of PAI, is associated with familial DVT. Our data suggests autosomal dominant inheritance.