Hereditary angioedema (HAE) is a rare disease associated with C1 inhibitor (C1-INH) deficiency or dysfunction caused by SERPING 1 mutations (HAE type 1 or 2 [HAE-1/2]), resulting in recurrent swelling episodes affecting subcutaneous or submucosal tissues [1–3]. The gene discussed is SERPING1; the disease is hyperinsulinemic hypoglycemia, familial, 4.