[Resistance to activated protein C. The most common cause of familial thrombophilia].

Resistance to activated protein C (APC) is caused by the most prevalent single gene defect associated with thromboembolic disease so far described. The majority of cases are caused by a single point mutation in the Factor V gene, which predicts replacement of Arg506 in the APC-cleavage site with a Gln. APC resistance is found in 20-60% of patients with venous thrombosis and in 3-10% of the normal population among Caucasians. In its heterozygous state, the mutation is associated with a 5-10-fold increased risk of thrombosis. Homozygosity is associated with more severe APC resistance, and a higher risk of developing thrombosis. By the age of 33 years, 8% of normals, 20% of heterozygotes, and 40% of homozygotes have had manifestations of venous thrombosis. APC resistance has been described in 60% of women with thromboembolic complications during pregnancy and in approximately 30% of women with thromboembolic complications using oral contraceptives. Development of clinical episodes of thrombosis in patients with APC resistance is likely to occur on a multifactorial basis. Hypercoagulable states may result from multigene interactions, and prothrombotic insults in patients with an inherited predisposition may precipitate thrombotic complications. In this review we present and discuss results from the recent medical literature.