Gelfand et al. [16] conducted a double-blind placebo-controlled trial with danazol and concluded that it effectively prevents attacks in HAE and acts to correct the underlying biochemical abnormality (i.e., C1 esterase inhibitor levels increased three to four times, and levels of the fourth component of complement (C4) increased 15 times). The gene discussed is C1S; the disease is hereditary angioedema.