What is the mortality and morbidity associated with complement deficiencies?

Updated: Apr 28, 2021
  • Author: Robert A Schwartz, MD, MPH; Chief Editor: Michael A Kaliner, MD  more...
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Individuals with complement deficiencies that hinder opsonization present with frequent recurrent infections and a high rate of morbidity and mortality. Deficiency of C3, the major opsonin, results in recurrent pyogenic infections, particularly with encapsulated bacteria.

Deficiencies of early classical pathway components (C1, C4, C2) do not usually predispose individuals to severe infections but are associated with autoimmune disorders, especially SLE.

Patients with a defect in formation of the MAC have a lesser degree of morbidity and mortality than, for example, patients with a defect in C3; the deficiency in the lytic component of the complement cascade is thought to have some protective effect against the generation of full-blown sepsis. These patients are at high risk for recurrent infection with Neisseria gonorrhoeae or Neisseria meningitidis. Severe pyogenic infections and sepsis occur in children and neonates who have a deficiency of a MAC component.

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