However, the underlying mutation often remains unknown.12, 13 As bradykinin is believed to play an important role in the pathogenesis of clinical manifestations of HAE nC1-INH,11, 12, 14 therapies that interfere with bradykinin production or bradykinin-mediated biological activities may, in principle, also be effective in patients with these forms of HAE.11 The gene discussed is COL18A1; the disease is hereditary angioedema.