Background: The nine amino acid peptide Bradykinin (BK)1–9, generated from cleavage from High-molecular-weight kininogen (HMWK) upon activation of contact system, is considered the key mediator in the pathogenesis of Hereditary Angioedema (HAE) and a significant proportion of idiopathic angioedema. This evidence concerns the gene KNG1 and hereditary angioedema.