Large haplotype-specific differences in inter-genic distances in human MHC shown by pulsed field electrophoresis mapping of healthy and type 1 diabetic subjects.

Type 1 diabetes is associated with extended haplotypes defined by combinations of specific alleles of genes in the MHC. We have used pulsed field gel electrophoresis mapping to examine the gross structure of the Class II region of the MHC and its relationship to susceptibility to Type 1 diabetes. We have studied heterozygous members of a family in which susceptibility to Type 1 diabetes is associated with an A1/B8/DR3 haplotype and resistance with A2/B7/DR2, an unrelated diabetic DR3,4 patient and a healthy DR4,w10 subject and a DR2/Dw2 cell line. Digestion was performed with the enzymes Sst II, Mlu I, and Pvu I and hybridization with 21-hydroxylase, DRA, DQB, DOB and DPA probes. Within the DQ/DR region the DR4- and DR7-bearing haplotypes studied contain insertions of 140-150kb relative to the DR3 haplotypes whilst the DR2 haplotype in the family was smaller than the DR3 haplotypes by 130kb, whilst that in the cell line was smaller by up to 220kb. This cell line, previously thought to be homozygous by consanguinity, was also shown to be heterozygous in the DP region. Although no differences between diabetic and healthy subjects were observed within the family, these differences in long-range structure may be of importance to the etiology of Type 1 diabetes, as well as to the evolution of the MHC.