Angioedema can be further classified as: histaminergic (through IgE independent or dependent mechanisms), idiopathic, hereditary (HAE type I [HAE-1], HAE type II [HAE-2] and HAE with normal C1 inhibitor [HAE-nC1-INH]), acquired (C1-inhibitor [C1-INH] deficiency from a secondary cause) and ACE inhibitor-induced. The gene discussed is SERPING1; the disease is angioedema.