An abnormality of blood clotting that increases the risk of THROMBOSIS. This can be congenital (present from birth) or acquired. The former include several genetic alterations leading to deficiencies of naturally occurring anticoagulants, for example antithrombin deficiency, deficiencies of Protein C and Protein S and genetic anomalies which increase the levels of certain blood components which assist clotting, such as Factor V Leiden and the prothrombin gene mutation syndrome. Acquired thrombophilias include ANTIPHOSPHOLIPID SYNDROME as found in SYSTEMIC LUPUS ERYTHEMATOSUS (SLE) and similar autoimmune conditions, disseminated cancer (that is cancer which has metastasised), pregnancy and oestrogen ingestion as with oral contraceptives. Persons with thrombophilia have an increased risk of VENOUS THROMBOEMBOLISM (VTE).