Complotypes in individuals of African origin: frequencies and possible extended MHC haplotypes.

We analyzed the frequency distribution of 106 complotypes [four allele sets of the major histocompatibility complex (MHC) genes for the complement proteins factor B, C2, C4A, and C4B] from 32 Black families residing in Boston and Washington, DC. Twenty-five different complotypes were identified, among which there were four complotypes that had not been previously observed in our large database of complotypes compiled from family studies of Boston Caucasians and that are, presumably, unique to individuals of African origin. These four African-derived complotypes are FC(1,90)0, FC63, S1C2, 17, and SC(3,2,90)0. The frequencies of two of these four unique Black complotypes, FC(1,90)0 and FC63, were increased significantly when compared to Caucasians (pcorr less than 0.00042, pcorr = 0.00294, respectively). The complotype FC(1,90)0 was in positive linkage disequilibrium with HLA-DR3 haplotypes containing the B locus antigens Bw42, Bw52, Bw53, and Bw58, while FC63 was associated with HLA-Bw70, -DR5. These findings demonstrate the extensive polymorphism of complotypes in Blacks, and also suggest that it may be possible to define unique extended haplotypes of African origin.