A key link between the BK-forming pathway and complement activation that is also relevant to the pathogenesis of HAE-C1-INH is the ability of factor βFXIIa (FXIIf) to activate C1r and to a lesser degree C1s (both comprises the esterase complex of C1) [69, 70] (Fig. 1). The gene discussed is SERPING1; the disease is hereditary angioedema.