[Familial deficiency of protein S associated with thrombophilia]

Protein S (SP) is a vitamin K-dependent plasma protein which acts as a cofactor of activated C protein in the inactivation of the factors Va and VIIIa; in addition, it enhances fibrinolysis by increasing the affinity of the enzyme for phospholipid surfaces. The congenital deficiency of SP is an autosomal dominant inherited trait, associated with a high risk of development of thrombotic phenomena at a relatively early age (young adults). We report a Spanish family which carried a congenital deficiency of SP associated with thrombotic complications; for its diagnosis we used the immunological quantification of the levels of free and total SP as well as the evaluation of the immunoelectrophoretic behavior of the inhibitor.