Ninety patients ≥12 years of age with HAE type I or II who experienced at least 4 HAE attacks over 2 months prior to screening were randomized to one of four treatment sequences: self‐administered C1‐INH(SC) 40 IU/kg (N = 45) or 60 IU/kg (N = 45) twice weekly for 16 weeks, preceded or followed by twice weekly placebo for 16 weeks. The gene discussed is SERPING1; the disease is hereditary angioedema.