Most patients with HAE have genetic mutations resulting in either deficient levels of normally functioning C1-INH (HAE-1; 85% of HAE cases with functional C1-INH deficiency) or C1-INH proteins that are dysfunctional, even though levels may be normal (HAE-2; ~15% of cases with functional C1-INH deficiency).4 A third type of HAE has recently been identified in which C1-INH levels and function are normal (HAE-nC1-INH)1; these cases seem to be related to a variety of different genetic mutations.4,5 The following information pertains primarily to HAE-1 and HAE-2. The gene discussed is SERPING1; the disease is hereditary angioedema.