There are three variants of hereditary angioedema (HAE): HAE-C1-INH Type I with low C1-INH protein and function (85% of cases; autosomal dominant); HAE-C1-INH Type II with normal protein but low function (15% of cases; autosomal dominant); and HAE Type III hereditary angioedema with normal C1 inhibitor protein and function (estrogen-dependent inherited form found mostly in females; some with defects in coagulation factor XII, HAE-FXII; others of unknown defect, HAE-Unknown) [1,2]. This evidence concerns the gene SERPING1 and hereditary angioedema.