The differential diagnoses of HAE-1/2 include HAE-3 (ie, HAE with normal C1-INH), acquired C1-INH deficiency (AAE), ACE-induced angioedema, mast cell mediator-induced angioedema (eg, chronic spontaneous urticaria, allergic angioedema), and idiopathic angioedema (Figure 2). Here, SERPING1 is linked to chronic idiopathic urticaria.