Molecular diversity and thrombotic risk in protein S deficiency: the PROSIT study.

PROSIT enrolled 79 protein S (PS) deficient families and found 38 genetic alterations in 53 probands. Of these, 23 mutations were selected for expression in vitro, to evaluate their role as possible causative mutations. Transient expression showed high secretion levels (>75%) for three variants (Pro35Leu, Ile521Leu, Asn542His) that were considered neutral mutations. Seven missense variants (with Gly295Asp, Leu405Pro, Arg474Pro, Gly480Asp, Met570Lys, Gly597Asp, Cys598Tyr) and 5 nonsense mutations showed low (≤10%) expression levels and were classified as severe mutations. Intermediate expression was observed for 8 variants (with Glu26Ala, Cys47Tyr, Asp88Gly, Cys134Phe, Glu163Gly, Tyr225Cys, Cys226Ser, Gly316Arg) that were evaluated by factor Va inactivation assay in order to be globally classified as severe or intermediate. Based on these results, the hazard ratio associated with causative mutations was 4.9 (95%CI 1.4-17.7) for deep vein thrombosis and/or pulmonary embolism, 5.1 (95%CI 1.1-23.9) for superficial thrombophlebitis and 4.8 (95%CI 1.8-13) for any venous thrombosis. The hazard ratio for deep vein thrombosis and/or pulmonary embolism in carriers of severe mutations only was 7.4 (95%CI 1.6-24.1). PROSIT showed that dysfunctional variants causing PS deficiency are more common than expected and confirmed that PS deficiency is associated with thrombotic risk, although risk assessment is complicated by molecular heterogeneity.