A 19-year-old woman develops recurrent episodes of painless facial and laryngeal swelling without urticaria, triggered by dental extraction and minor trauma. During an episode, C3 and C1q are normal while C4 is markedly reduced. The mediator responsible for the angioedema and its inheritance pattern are:

• A Histamine from mast cell degranulation, autosomal dominant
• B Bradykinin generated by unopposed factor XII activation, autosomal dominant ✓
• C Leukotriene C4 from arachidonic acid pathway, autosomal recessive
• D C3a generated by classical pathway activation, autosomal dominant

Explanation

Hereditary angioedema is an autosomal dominant C1 inhibitor deficiency. Unchecked C1r/C1s and factor XII activity generate bradykinin, which increases vascular permeability and causes the swelling; there is characteristically no urticaria because histamine is not involved. The low C4 during attacks reflects ongoing classical pathway consumption, whereas C3 remains normal, a pattern that distinguishes it from acquired complement-consuming states.

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.