An abnormal antithrombin III (AT III) with low heparin affinity: AT III Clichy

Summary We have identified an inherited qualitative deficiency of antithrombin III (AT III) in a family with apparently no increased incidence of venous thrombosis. Plasma antithrombin and anti-Xa activities were normal, but the interaction with heparin, heparan sulphate and low molecular weight heparin was uniformly decreased. An immunoblotting technique performed in plasma showed normal complex formation with thrombin. By using heparin-Sepharose affinity chromatography and crossed immunoelectrophoresis, the variant could be separated: at least two fractions of low affinity AT III were obtained. A minor one had no antiprotease activity; the other one was further purified to homogeneity and found to have normal specific activity in absence of heparin and a 50% decreased activity in presence of heparin. We propose to call this new variant AT III Clichy.