Evidence for linkage between the loci coding for the binding protein for the fourth component of human complement (C4BP) and for the C3b/C4b receptor.

Three pedigrees informative for the segregation of genetic variants of the binding protein for the fourth component of complement (C4BP) and C3b/C4b receptor (C3bR) have been identified. There were 10 informative meioses with no recombinants, indicating a close linkage between the loci encoding C4BP and C3bR, C4BP and C3bR [maximum lod (logarithm of odds of linkage) score: 2.4 at recombinant fraction = 0.0]. In addition, in the four unrelated individuals who were doubly heterozygous (C4BP*1, C4BP*2, C3bR*A, C3bR*B), the infrequent allele C4BP*2 segregated together with the uncommon allele C3bR*B, supporting the hypothesis of linkage between C4BP and C3bR and suggesting that linkage disequilibrium exists between these particular alleles. We conclude that the loci encoding C3bR and C4BP, two functionally related molecules, are linked.