Type I (Insulin-dependent) diabetes (IDD) is significantly associated with genes of the HLA region, especially the alleles HLA-DR3 and -DR4. However, only a small proportion of individuals with these alleles develop IDD, so the serologically defined markers are not very specific. The identification of subtypes more strongly associated with IDD than are the conventional DR serotypes would provide markers with increased specificity and improve our understanding of the genetics of susceptibility to IDD. The overall goal of this proposal is to define HLA-DR subtypes by means of DNA polymorphisms and provide better markers for susceptibility to IDD. In summary, the specific aims are: to use DNA probes for the HLA-DR and DC genes to identify restriction fragment (RF) polymorphisms in the HLA-D region; to determine the frequencies of the RF's and RF haplotypes in IDD's and controls; to test the hypothesis that certain subtypes of DR3 and DR4 have greater specificity for IDD than do the serological types themselves. Family studies will be carried out in part using our large resource of frozen material. Lymphocytes have been stored from HLA-typed family members of more than 100 IDD's. These cells will be expanded with Interleukin-2, to yield sufficient DNA for analysis. DNA will also be obtained from control families, and from random samples of IDD's and controls, who will be HLA-typed. DNA will be studied by hybridization with HLA-DR and DC probes, after digestion with restriction endonucleases and Southern blotting. RF differences between individuals will be studied in families to confirm Mendelian segregation and linkage with HLA. Subtypes of DR types will be detected as differences among RF patterns associated with a single DR type. Identification of such subtypes will increase both the specificity and the resolution of HLA-linked markers for IDD. Better markers will allow a more precise definition of susceptible individuals and will ultimately help identify, at the DNA level, the genes for susceptibility to IDD.
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