A lack of C1-INH might result in which of the following conditions?

• A. Paroxysmal nocturnal hemoglobinuria
• B. Hereditary angioedema
• C. Hemolytic uremic syndrome
• D. Increased bacterial infections

Answer: (B)

Unregulated control of the kallikrein-kinin system because of C1-INH deficiency leads to bradykinin-driven swelling, causing hereditary angioedema. Without C1-INH, the complement and contact systems run unchecked, increasing bradykinin production and vascular permeability. This results in episodes of painless, non-itchy swelling of the skin and mucous membranes, which can involve the airway and gastrointestinal tract and may be life-threatening if the airway is affected. That’s why a lack of C1-INH most directly yields hereditary angioedema. Paroxysmal nocturnal hemoglobinuria involves loss of protective surface proteins on red cells, not bradykinin-mediated edema; hemolytic uremic syndrome is a microangiopathy with hemolysis and kidney injury; and increased bacterial infections relate to immune deficiencies rather than C1-INH–related edema. Treatments aim to replace C1-INH or block bradykinin effects.