The polymorphism of the C3b/C4b receptor in the normal population and in patients with systemic lupus erythematosus

One hundred and sixty-two unrelated, healthy normals and 118 unrelated SLE patients were subdivided by sex, race, and disease, and each group was in Hardy-Weinberg equilibrium for autosomal codominant expression of the four CR1 alleles. There were no significant phenotypic differences between males and females (P > 0.3) or between normals and SLE patients (P > 0.2). However, gene frequencies among whites (A: 0.87; B: 0.12; C: 0; D: 0.01), blacks (A; 0.74; B: 0.22; C: 0.04; D: 0) and orientals (A: 0.98; B: 0.02; C: 0; D: 0) were significantly different (P < 0.05). We had previously reported that SLE patients of phenotype AC had higher relative expression of the C allele than normals and this was confirmed: 61% (SLE, n = 5) vs 22% (normals, n = 3; P = 0.014). Total CR1/E in the AC group (193 in SLE vs 393 in normals 0.05 < P < 0.10), was suggestive of the decreased CR1 number seen in larger SLE populations regardless of phenotype. In one large three-generation family with SLE and the C allele, an association between SLE and the C allele is suggested by the presence of the C allele in all three females with SLE versus 3 of 13 healthy females. In informative families in which receptor phenotype and CR1 number/E were determined, it was possible to assign a receptor number to an allele. These data provide evidence for a cis-acting regulatory element that is inherited in association with the CR1 structural gene.