Bradykinin is the main mediator of increased vascular permeability in patients with HAE [6] [7] During acute attacks of HAE, kallikrein is insufficiently inhibited because of the deficiency in C1-INH, the kallikrein-kinin system becomes activated, and at the end of the cascade, an increased amount of bradykinin is produced that results in the edema seen in patients with HAE. Here, SERPING1 is linked to hereditary angioedema.