LINKAGE DISEQUILIBRIUM IN HLA CANNOT BE EXPLAINED BY SELECTIVE RECOMBINATION

Some combinations of HLA-A,-B and -DR antigens occur more frequently t han would be expected from their gene frequencies in the population. T his phenomenon, referred to as Linkage Disequilibrium (LD) has been th e origin of many speculations. One hypothesis to explain LD is that so me haplotypes are protected from recombination. A second hypothesis is that these HLA antigens preferentially recombine after cross-over, to create an LD haplotype. We tested these 2 hypotheses: from a pool of over 10,000 families typed in our department, we analyzed 126 families in which HLA-A:B or B:DR recombinant offspring was documented. To ove rcome a possible bias in our material, we used the nonrecombined haplo types from the same 126 families as a control group. Our results show that the number of cross-overs through LD haplotypes is not significan tly lower then would be expected if recombination occurred randomly. A lso the number of LD haplotypes created upon recombination was not sig nificantly increased.