PROS1 and thrombophilia: Classical inherited thrombophilia includes loss-of-function variants in the genes that encode the natural anticoagulant proteins, AT, protein C (PC), and protein S (PS), and gain-of-function mutations in the genes encoding factor V (factor V Leiden (FVL)) and prothrombin (FII) (F2 c.*97G>A; previous nomenclature G20210A) [1].