Molecular Defects in Human Antithrombin III Deficiency

The presence, and unopposed action, of activated coagulation factors in the circulation would result in clot or thrombus formation within intact blood vessels, with potentially life-threatening consequences. Such events are prevented, in the non-pathological state, by the presence in plasma of circulating inhibitors of coagulation. The most abundant of these is a plasma glycoprotein known for historical reasons as antithrombin III (AT-III).1, 2 Genetic disorders that reduce functional activity of AT-III leave individuals at risk for thromboembolism. The majority of those affected suffer at least one such episode by their fifth decade, with the proportion of AT-III-deficient patients clinically affected rising by roughly 1% per year of life.3–6 In this article we summarize recent progress in defining the molecular defects involved in hereditary antithrombin III deficiency, in the context of the normal structure and function of this important serine protease inhibitor.