NCIt definition : A broad classification for rare genetic disorders with mostly autosomal recessive
patterns of inheritance. They are caused by the ineffective or decreased biosynthesis
of complement components. Complement deficiencies may also be acquired acutely post-infection
or chronically from co-morbid autoimmune disorders. If complement components are adequately
synthesized, their rapid depletion may result in functional deficiencies. Clinical
signs of inherited deficiencies present within the first decade of life and are consistent
with the signs of recurrent systemic infection or immune complex disease. Complement
deficiencies decrease the effectiveness of the humoral immune response. Of all the
complement deficiencies, C3 deficiency is associated with the poorest prognosis since
it presents at an early age, when susceptibility to recurrent infection is great.
Deficiencies of C3 and of the classical activating pathway components: C1, C4, C2
also predispose to immune complex disease.;
Alternative definition : NICHD: A genetic deficiency of any component of the complement system, which may be
associated with various pathologic conditions depending on the protein and activation
pathway involved.;