- Complement protein deficiencies
- Early complement deficiencies (C1-C4)
- Increased risk of severe, recurrent pyogenic sinus and respiratory tract infections. Increased risk of SLE.
- Terminal complement deficiencies (C5–C9) Increased susceptibility to recurrent Neisseria bacteremia.
- Early complement deficiencies (C1-C4)
- Complement regulatory protein deficiencies
- C1 esterase inhibitor deficiency
- Causes hereditary angioedema (edema of skin, especially periorbital and mucosal surfaces) due to unregulated activation of kallikrein → bradykinin.
- Characterized by ¯ C1 esterase inhibitor and ¯ C4 levels.
- May be triggered by blood transfusions
- ACE inhibitors are contraindicated due to increased bradykinin levels
- C1 esterase inhibitor deficiency
- Paroxysmal nocturnal hemoglobinuria
- Defect in the PIGA gene preventing the formation of anchors for complement inhibitors, such as decay-accelerating factor (DAF/CD55) and membrane inhibitor of reactive lysis (MIRL/CD59).
- Causes complement-mediated lysis of RBCs.
- See entry in intrinsic hemolytic anemia
