**5.3. Factor V deficiency**

FV is a single polypeptide encoded by chromosome 1 and primarily synthesized in the liver and some evidences show that FV is also produced by megakaryocytes [68–70]. The activated FV acts as a cofactor for FXa, to form a prothrombinase complex and it also serves as a target for APC-PS complex in inhibiting the coagulation cascade [71]. Patients with FV deficiency surprisingly do not show bleeding phenotype. Recent evidences elucidated that platelets endocytose FV from plasma, modify them intracellularly and release it at the site of injury. This platelet released FV is resistant for inhibition. If symptomatic patients usually have umbilical stump bleeding, skin and mucosal tract hemorrhage [72].
