[Molecular biological analysis of hereditary thrombophilia--genetic characterization of protein S deficiency].

Protein S is a plasma glycoprotein, which functions as a cofactor for activated protein C in the protein C pathway and also directly inhibits factors Va and Xa, independently of protein C. In plasma, protein S circulates as a free molecule (40%) or in a complex with C4b-binding protein (60%). Only a free protein S acts as an anticoagulant and its activity is lost by binding to C4b-binding protein. The physiological importance of protein S has been established by observations in patients with hereditary protein S deficiency who have an increased risk of developing thrombosis. Several previous studies reported that hereditary protein S deficiency was as common as protein C deficiency and that approximately 5% of hereditary thrombophilia was caused by protein S deficiency. But molecular biological analysis of protein S deficiency is not as advanced as protein C deficiency because the genetic characterization of protein S deficiency is limited by the presence of the inactive pseudogene that is highly homologous to the active true gene. Only a few previous studies have examined the genetic features of hereditary protein S deficiency. Further investigation is needed to characterize the pathophysiology and molecular basis of hereditary protein S deficiency.