Association of systemic lupus erythematosus and SLE-like syndromes with hereditary and acquired complement deficiency states.

The most prominent association of rheumatic diseases with hereditary complement deficiency is systemic lupus erythematosus (SLE) and discoid lupus erythematosus with homozygous C2 deficiency in females. The lupus disease in these patients differ from classic lupus in 1) the increased incidence of discoid lesions, 2) the low incidence of renal disease, 3) the low or absent titers of antibodies to native DNA, and 4) the infrequent finding of immunoglobulin and complement in skin lesions. The strong positive linkage disequilibrium between C2 deficiency and HLA genes raises the possibility that genes other than those determining C2 levels may have the primary role in determining predisposition to disease in these patients. However, the finding of similar diseases in certain patients with hereditary angioedema and SLE-related syndrome who have acquired deficiency of the early components of complement supports a primary role of the C2 deficiency gene in predisposing to lupus disease in these patients.