Different classifications have been considered, identifying the release of bradykinin as the final common pathway of angioedema, secondary to the alteration of the kallikrein–kinin system, such as a congenital or acquired (such as autoimmune and lymphoproliferative disorders) defect of the levels (type I) or function (type II) of gene encoding human C1 esterase inhibitor (SERPING), and mutations in genes encoding factor XII [6], plasmin (HAE-PLG), and kininogen-1 (HAE-KNG). The gene discussed is KNG1; the disease is angioedema.