Hereditary Angioedema — Therapies Old and New

Hereditary angioedema is a rare syndrome characterized by episodic, nonpruritic, localized subcutaneous and submucosal swelling. Laryngeal edema can precipitate fatal respiratory obstruction. Nearly 50 years ago, Donaldson and Evans linked hereditary angioedema with a deficiency of the plasma inhibitor of the first component of complement, C1 inhibitor — a serine protease inhibitor that inactivates target proteases by means of irreversible binding.1 Its primary targets are the complement proteases C1r and C1s (for which it is the sole plasma inhibitor), the coagulation-system proteases factors XIa and XIIa, and the contact-system protease kallikrein (Figure 1). C1 inhibitor deficiency causes dysregulation in these . . .