A range of relatively rare disorders of the complement system, in some cases because of inadequate secretion, in others because there is mutation in the gene encoding one of the components. Deficiencies of the classic pathway cause a predisposition to immune complex diseases because of the role of complement in clearance of immune complexes. A general consequence is also impaired opsonization with a greater chance of infection. C1s deficiency is associated with early-onset multiple autoimmune diseases; homozygous deficiency of C4a is associated with systemic lupus erythematosus and with type I diabetes; homozygous deficiency of C4b is associated with susceptibility to bacterial meningitis; complement C9 deficiency is associated with increased susceptibility to meningococcal infections; complement factor H deficiency can cause various phenotypes, including asymptomatic, recurrent bacterial infections and renal failure. See also C3 nephritic factor.
Subjects: Medicine and Health.