A new case of ‘type II’ inherited protein S deficiency

SummaryProtein S inherited deficiency is associated with high risk of recurrent venous thrombotic disease (Broekmans et al, 1985a, b). Protein S exists as two forms in plasma, either free and functionally active or complexed with C4b‐binding protein (C4b BP) and inactive (Dahibäck & Stenflo, 1981). We report here the case of a 26‐year‐old woman and her brother, 28 years old, both suffering from recurrent venous thrombosis since the age of 20, diagnosed as severe protein S deficiency according to the following data: free protein S: 2.5–3% by ELISA, undetectable by electroimmunodiffusion (BID); total protein S: 13–16% by ELISA, 21–18% by EID, C4b BP: normal levels. Crossed immunoelectrophoresis using anti‐protein S antibodies revealed only traces of protein S associated with C4b BP and no free protein S. All these assays were performed in the absence of any anticoagulant therapy. Among the investigated relatives, less severe protein S deficiency was observed in three children of the propositus: total protein S levels ranging from 41% to 50% (EID), 40–53% (ELISA); free protein S levels ranging from 16% to 18% (EID), 10–12% (ELISA); normal C4b BP levels. Crossed immunoelectrophoresis revealed traces of free protein S but a significant amount of protein S associated with C4b BP. From these results, we consider, according to Comp's classification (Comp et al, 1986a), that the propositus and her brother are the second case of protein S deficiency type II to be reported in the literature while her children belong to the type I category.