C3 polymorphism, HLA and chronic renal failure in Spaniards.

C3 allele frequencies were studied in 196 unrelated normal Spaniards. The results fit the Hardy-Weinberg equilibrium. No rare variants were detected. The C3 frequency was close but slightly higher than that found in other Caucasoid populations, and higher than that found in Negroids and Orientals. Spanish Basques also showed a high C3F frequency. A North-South decreasing C3F gradient was recorded and compared to other gradients (HLA-D/DR, height, etc.) thought to be due to natural selection. Lod scores in 28 Spanish families excluded C3 gene assignment at less than 45 cM of HLA/GLO linkage group; no significant linkage disequilibrium was found between C3 and HLA. C3F was also significantly increased in 20 chronic renal failure (CRF) patients as compared to 196 controls; this would support the existence of functional differences between C3F and C3S alleles.