Polymorphic restriction endonuclease sites linked to the HLA-DR alpha gene: localization and use as genetic markers of insulin-dependent diabetes.

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Abstract
Polymorphic restriction endonuclease sites within the HLA-DR.alpha. gene have been defined, localized, and used as genetic markers in the analysis of susceptibility to insulin-dependent diabetes mellitus (IDDM). Hybridization of Bgl II-digested human genomic DNA with a cDNA clone for the HLA-DR .alpha. chain (pDR.alpha.-1) has revealed three allelic restriction fragment lengths: 3.8 kilobase pairs(kb), 4.2 kb, and 4.5 kb. Hybridization of EcoRV-digested human genomic DNA with the same probe has revealed two allelic polymorphic restriction fragment lengths: 9.2 and 13.0 kb. By analysis of double digests of genomic DNA from individuals homozygous for each of the allelic variants, the polymorphic restriction sites were found to be clustered near the 3'' end of the HLA-DR.alpha. gene. The observed correlations of DR.alpha. Bgl II restriction site variants with serologically determined DR specificities suggest linkage disequilibrium between the DR.alpha. and DR.beta. loci. The 3.8-kb fragment is correlated with the DR1 type (Pc = 4.4 .times. 10-4); and the 4.2-kb fragment, with a subset (B8,DR3) of the DR3 type (Pc = 5.1 .times. 10-4) and with the DR6 type. The segregation pattern of HLA-DR.alpha. polymorphic Bgl II restriction fragments was analyzed in six IDDM families. The observed association of IDDM with the Bgl II 4.2-kb DR.alpha. restriction variant is higher than with existing serological markers and supports the utility of this approach in elucidating IDDM inheritance.