C1 INHIBITOR DEFICIENCY
C1 inhibitor is a serine-protease inhibitor that inactivates the serine esterases generated by complement activate (C1r and C1s), kallikrein of the kinin system, and activated factors X1 and XII of the clotting cascade, In the absence C1 inhibitor, C1 activation results in the depletion of the serum C4 level. (This is useful from a diagnostic point of view). C1-inhibitor deficiency also results in the inability to inactivate bradykinin in the tissues results in increased vascular permeability, manifesting as attacks of angioedema. Angioedema of the respiratory tract can lead to death from asphyxia. Angioedemea of the intestinal tissues result in recurrent episodes of severe abdominal pain due to partial intestinal obstruction, which can mimic an acute abdominal emergency.