C3 alleles in diseases associated with C3 activation.

C3 genetic polymorphism was examined by immunofixation electrophoresis in 100 healthy controls and in patients with three diseases in which this complement protein appears to be involved pathogenically (IgA nephropathy 31; membranoproliferative glomerulonephritis 33; systemic lupus erythematosus 30). C3S (0.80) and C3F (0.20) frequencies in controls were similar to those published in the literature, as were the frequencies of the C3 phenotypes C3S (0.65), C3SF (0.29), and C3F (0.06). No patient group had frequencies which differed significantly from controls. Thus, the previously reported association between C3*F and IgA nephropathy was not confirmed, and no relationships between C3 polymorphism and systemic lupus erythematosus or membranoproliferative glomerulonephritis were recognized.