A patient with hereditary angioedema has recurrent episodes of non-pruritic, non-urticarial swelling of the face, extremities, and gastrointestinal tract. Which complement component is most likely deficient?

• A C1 inhibitor (C1-INH) ✓
• B C3
• C Factor H
• D Decay accelerating factor (CD55)

Explanation

Hereditary angioedema is caused by C1 inhibitor deficiency (autosomal dominant). Without C1-INH, uncontrolled kallikrein activation generates excess bradykinin, causing increased vascular permeability and angioedema. Unlike histamine-mediated angioedema, it is non-pruritic and does not respond to antihistamines. C3 deficiency causes recurrent infections. Factor H deficiency causes atypical HUS. CD55 deficiency causes paroxysmal nocturnal hemoglobinuria.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.