SERPING1 and hyperinsulinemic hypoglycemia, familial, 4: Hereditary angioedema (HAE) due to C1 esterase inhibitor (C1‐INH) deficiency (C1‐INH‐HAE) is a rare disorder caused by mutations in the SERPING1 gene.1 Functional deficiency of the C1‐INH protein leads to disinhibition of the complement2 and contact3 enzyme cascades, causing overproduction of bradykinin and resulting in increased vascular permeability and fluid leakage to surrounding tissues.4, 5 HAE is characterized by unpredictable, acute, recurring episodes of angioedema in subcutaneous and/or submucosal tissues.