Mutations in factor XII (FXII), plasminogen (PLG), angiopoietin-1(ANGPT1) and kininogen-1 (KNG1) have been found in this newly-defined group of primary angioedema patients with normal C1-INH (nlC1-INH) [120]; however, a significant proportion does not have a defined molecular explanation as of yet (HAE-unknown) [121, 122]. Here, SERPING1 is linked to hereditary angioedema.