Since the first pathogenic SERPING1 mutation was described in 1987 (1), the presence of C1-INH-HAE was explained by more than 700 different mutations (2–4) in the gene encoding C1-INH (SERPING1) that can either cause decreased protein synthesis (C1-INH-HAE type I) or functional deficiency (C1-INH-HAE type II). The gene discussed is SERPING1; the disease is hereditary angioedema.