A person present with recurrent swelling on face and lips due to emotional stress. Likely cause is

A deficiency of C1 esterase inhibitor gives rise to an autosomal dominant disorder hereditary angioedema. The C1 esterase inhibitor is a protease inhibitor whose target enzymes are C1r and C1s of the complement cascade, factor XII of the coagulation pathway, and the kallikrein system. So, any individual having the deficiency of C1 esterase inhibitor would have excessive complement activation. This causes the release of anaphylatoxins (C3a, C5a) and other inflammatory mediators. These patients therefore have episodes of edema affecting skin and mucosal surfaces such as the larynx and the gastrointestinal tract. This may result in life-threatening asphyxia or nausea, vomiting, and diarrhea after minor trauma or emotional stress.