Linkage relationship of C2 deficiency, HLA and glyoxalase I loci.

Immunogenetic analysis of a homozygous C2-deficient individual and family members demonstrated linkage of HLA-A25, B18 and C2o. HLA-D typing showed that 5 members typed with homozygous Dw2 typing cells from an individual with C2 deficiency but not with Dw2 typing cells from 2 individuals with normal C2. The homozygous C2-deficient propositus and brother were HLA-A and B homozygous but heterozygous at the HLA-D and glyoxalase I loci. Therefore, in this family, the C2o gene is linked with two distinct haplotypes: HLA-A25, B18, Dw2, GLO1 and HLA-A25, B18, D unknown, GL02. These results could be explained by an ancestral recombinant event, which occurred between the C2o locus and HLA-D locus in which C2o segregated with HLA-B. This would suggest that the locus for the C2o gene maps between HLA-B and HLA-D on the sixth chromosome.