Genetic polymorphism of C3 and Bf in IgA nephropathy.

C3 and Bf alleles were examined in the general population, in 67 patients with biopsy-confirmed mesangial IgA nephropathy and 81 patients with other types of glomerulonephritis, from the Heidelberg and Leiden renal programmes respectively. In both populations, a significant excess of homozygous phenotype C3FF (3.4% in controls; 10.4% in IgA nephropathy) and a deficit of C3FS heterozygous phenotype (35.8% in controls; 19.4% in IgA nephropathy) were observed in patients with IgA nephropathy, but not in other types of glomerulonephritis. No difference of C3 gene frequencies was found. C3FF was associated with an adverse clinical outcome (a higher prevalence of renal failure and hypertension). A significant excess of Bf-F gene frequency was noted (0.20 in controls; 0.33 in IgA nephropathy). In addition, an excess of phenotype BfFF was found (none in controls; 10.4% in IgA nephropathy). BfFF homozygotes also carried a higher risk of an adverse outcome (renal failure and hypertension). The data suggest a role for genetically coded (presumably) immunological factors in the genesis and course of IgA nephropathy.