 The most common types of congenital thrombophilia are those that arise as a result of overactivity of coagulation factors . They are relatively mild , and are therefore classified as " type II " defects . The most common ones are factor V Leiden ( a mutation in the F5 gene at position 1691 ) and prothrombin G20210A , a mutation in prothrombin ( at position <unk> in the 3 ' untranslated region of the gene ) . 
