C1S and hereditary angioedema: Hereditary angioedema due to C1-esterase inhibitor deficiency (C1-INH-HAE) is caused by reduced synthesis (C1-INH-HAE type I) or the production of an unfunctional C1-INH protein (C1-INH-HAE type II) due to mutations in the C1-INH gene (SERPING1) [3].