Six different substitution mutations were identified in four different amino acid residues of antithrombin strand 1C and the polypeptide leading into strand 4B (F402S, F402C, F402L, A404T, N405K, and P407T), and are responsible for functional antithrombin deficiency in seven independently ascertained kindreds (Rosny, Torino, Maisons-Laffitte, Paris 3, La Rochelle, Budapest 5, and Oslo) affected by venous thromboembolic disease. In all seven families, variant antithrombins with heparin-binding abnormalities were detected by crossed immunoelectrophoresis, and in six of the kindreds there was a reduced antigen concentration of plasma antithrombin. Two of the variant antithrombins, Rosny and Torino, were purified by heparin-Sepharose and immunoaffinity chromatography, and shown to have greatly reduced heparin cofactor and progressive inhibitor activities in vitro. The defective interactions of these mutants with thrombin may result from proximity of s1C to the reactive site, while reduced circulating levels may be related to siC proximity to highly conserved internal ft strands, which contain elements proposed to influence serpin turnover and intracellular degradation. In contrast, siC is spatially distant to the positively charged surface which forms the heparin binding site of antithrombin; altered heparin binding properties of siC variants may therefore reflect conformational linkage between the reactive site and heparin binding regions of the molecule. This work demonstrates that point mutations in and immediately adjacent to strand 1C have multiple, or pleiotropic, effects on this serpin, leading ultimately to failure of its regulatory function. (J.

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SummaryA family with a high incidence of spontaneous thromboembolism has been investigated and those members affected were found to have significantly depressed levels of plasma and serum heparin cofactor activity; i.e., antithrombin III and anti-Xa activity. Further studies revealed that despite a marked diminution of antithrombin III activity in these patients measurement of antithrombin III by immunological techniques showed the levels to be normal. It is concluded that this anomaly represents a defect in the synthesis of the antithrombin III molecule. The abnormality appeared to be inherited but the mode of inheritance could not be determined with the available data.

Our data indicate that women with homozygous factor V Leiden have a high probability for a favorable pregnancy outcome. The increased risk for venous thromboembolism during pregnancy and after delivery would favor heparin prophylaxis during and after pregnancy in women homozygous for factor V Leiden.

SummaryWe investigated two thrombophilia families with the "classical" type of antithrombin III deficiency, i.e., with a low antithrombin III level measured both by immunochemical and functional methods.We obtained different antithrombin III patterns in the plasma of the affected members of the two families with the modified two dimensional immunoelectrophoresis method (heparin in agarose). In one family, the electrophoretic mobility of the antithrombin III is identical with that of normal antithrombin III. In the other, the antithrombin III displayed a decreased electrophoretic mobility in the heparinized agarose gel. The relatively low affinity of this antithrombin III to heparin could be directly proved by the heparin-agarose affinity chromatography, too. These two different antithrombin III patterns were observed by other investigators at different families as well.On the basis of our simultaneous observations of these two families we propose a classification of the inherited congenital antithrombin III deficiencies.