ACE and angioedema: In patients with HAE type 1 and 2, the influence of estrogen on attack frequency and severity has been described extensively.44Previously suggested mechanisms for this observation are the increase of FXII levels, decrease of C1-inhibitor levels, induction of the release of nitric oxide and impairment of the functionality of angiotensin converting enzyme.44, 45The specific characteristics of HAE-FXII suggest the influence of estrogen on FXII might be an important factor in the development of angioedema.