Strong linkage disequilibria among HLA-Bw50, BfS1, and HLA-DR3/DR7, and mapping of the Bf locus.

Based on genotypic and phenotypic studies we have found strong linkage disequilibria in Caucasians among the genes HLA-Bw50, BfS1, and HLA-DR3 and/or -DR7. The relative disequilibria, which are among the highest described in man, are delta r (BfS1, DR7) = 0.51, delta r (Bw50, BfS1, DR7) = 0.36, delta r (Bw50, DR3 or 7) = 0.72, delta r (BfS1, DR3 or 7) = 0.91, delta r (Bw50, BfS1, DR3 or 7) = 0.73. The previously described high delta r (Bw50, BfS1) and delta r (Bw50, DR7) have also been confirmed. A B parallel DR crossover family is also presented that, together with previously reported recombinant families, confirms that the Bf locus resides between HLA-B and HLA-DR. These data suggest the existence of a supergene complex of Bw50, BfS1, DR3/7 (or MB2), and hypotheses to account for the observed disequilibria are discussed.