NCIt definition : A rare genetic disorder with an autosomal recessive pattern of inheritance. It is
caused by the ineffective or decreased biosynthesis of the third complement component,
C3. C3 deficiency may also be acquired acutely post-infection or chronically from
co-morbid autoimmune disorders. If C3 is adequately synthesized, its rapid depletion
may result in a functional deficiency. Clinical signs of the inherited deficiency
present within the first decade of life and are consistent with the signs of recurrent
systemic infection or immune complex disease. Deficiency of serum C3 and its major
cleavage product, C3b, will decrease the effective humoral immune response to encapsulated
bacteria. Deficiency of C3 also impairs clearance of circulating immune complexes
and therefore predisposes to rheumatic and renal disease.;
Alternative definition : NICHD: Lack of production of functional C3 protein, due to a genetic defect. Patients
present at an early age with overwhelming infections with encapsulated bacteria. Patients
may also present with systemic lupus erythematosus, autoimmune glomerulonephritis,
or juvenile idiopathic arthritis-like syndromes.;