COL18A1 and hereditary angioedema: Angioedema can be further classified as: mast cell-mediated (i.e., through immunoglobulin E [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 drug-induced (e.g., ACE inhibitors) (see Fig. 3 for classification of angioedema) [1].