Intra-HLA recombinations in juvenile diabetes mellitus.

Complete HLA and Bf typing of 18 families with juvenile diabetes mellitus (J.D.M.) showed that of 68 children, 9 bore recombinant haplotypes (13%). This frequency is significantly higher than the currently accepted 1.6% for intra-HLA recombinations with a p of 1.3 X 10(6) (binomial expansion) and may be related to the J.D.M. gene itself. Five of the nine crossovers were between HLA-A and B, and four between HLA-B and D. In one informative A/B recombination, Bf segregated with the HLA-B-D segment while in another two, it segregated in cis with HLA-A. This suggests the existence of two genetic sequences within the HLA region, one with Bf on the A site and a second one with Bf on the D site.