Coagulation factor IX, also known as Christmas factor, Plasma thromboplastin component and PTC, is a secreted protein which belongs to the peptidase S1 family. Coagulation factor IX / F9 contains two EGF-like domains, one Gla (gamma-carboxy-glutamate) domain and one?peptidase S1 domain. Coagulation factor IX / F9 is a vitamin K-dependent plasma protein that participates in the intrinsic pathway of blood coagulation by converting factor X to its active form in the presence of Ca2+ons, phospholipids, and factor VIIIa. Defects in Coagulation factor IX / F9 are the cause of thrombophilia due to factor IX defect which is a hemostatic disorder characterized by a tendency to thrombosis. Defects in Coagulation factor IX / F9 are also the cause of recessive X-linked hemophilia B ( HEMB ) which also known as Christmas disease.