Recurrent facial/oropharyngeal/laryngeal edema in a patient has low C4, normal C3 and normal factor B. The phathogenesis is most likely due to:

Ans. is 'b' i.e., esterase deficiency Angioedema without urticaria and characteristic laboratory features suggest the diagnosis of hereditary angio neuro edemaImmunology of Hereditary Angioneurotic edemaHereditary angioneurotic edema occurs due to the loss of Cl inhibitor (regulatory protein)Cl inhibitor irreversibly inhibits the activity of several serine proteinase enzymes which includeTwo enzymes i.e. Clr and Cls together, they initiate classical pathway of complement system Two enzymes that participate in the contact activation system of blood clotting - factor Xlla and kallikrein.Deficiency of C1 inhibitor leads to a failure to regulate these two pathways. This unregulated activity results in excessive production of vasoactive mediators which includes.C2kinin (a proteolytic product of C2 formed by action of Cls)Bradykinin (produced by cleavage of high molecular weight kininogen by kallikrein)The excessive production of these vasoactive amines causes fluid accumulation in the tissues and epiglottic swelling.The excessive production of these vasoactive amines is caused by the increased breakdown of their respective precursor molecules i.e. C2, C4and kininogenC/f of Hereditary angio neuro edema.Episodes of Laryngeal edema.Prominence of recurrent gastrointestinal attacks.Lack of pruritus and of urticarial lesions.Laboratory diagnosis of hereditary angio neuro edemaLaboratory diagnosis depends on demonstrating a deficiency of Ci inhibitor (Ci INH)Levels of C{ are normal but its substrate C4and C2are chronically depleted and fall further during attacksDuring clinical attacks there is elevated level of bradykinin and reduced levels of prekallikrein and high molecular weight kininogen