Hereditary angioedema (HAE) is a rare, autosomal dominant disease characterized by unpredictable, recurrent swelling affecting the skin and submucosal tissue, including the gastrointestinal (GI) tract.1–3 Most cases of HAE are caused by mutations in the gene SERPING1, which encodes C1 inhibitor (C1-INH).1 This type of HAE is known as HAE with C1-INH deficiency or HAE-C1-INH. The gene discussed is SERPING1; the disease is hyperinsulinemic hypoglycemia, familial, 4.