There are several arguments for the assumption that the kallikrein-kinin system (KKS) also known as the "contact system" or "contact activation system" might be involved in the pathogenesis: (a) the causative mutations are in the FXII gene, and FXII is part of KKS; (b) KKS activation with the release of bradykinin at the end of the cascade is known to cause the acute attacks of HAE due to C1-INH deficiency; and (c) corticosteroids and antihistamines are therapeutically ineffective for the treatment of swelling in HAE-FXII, therefore, histamine does not seem to play a major role in HAE-FXII. Here, SERPING1 is linked to hereditary angioedema.