DNA fragments complementary to cloned sequences encoding HLA-D region class II antigen α- and β-chains were determined by genomic blotting with DNA from HLA-typed members of 22 complete families, 12 of which had a proband with insulin-dependent diabetes mellitus (IDDM). Analysis of genotypes showed that the DNA sequences were linked to HLA-DR and permitted confirmation of recombinations in two families. Digestion with the restriction enzymes BamHI, EcoRI, and Pstl and hybridization with an HLA-D region β-chain cDNA probe confirmed a BamHI 3.7 kilobase (kb) fragment present at low frequency among diabetic individuals and a BamHI 3.2 kb fragment that was also decreased among the diabetic subjects compared with siblings (P < 0.05) as well as nonrelated control siblings (P < 0.02) and their parents (P < 0.01). BamHI 12.0 kb (P < 0.05) and 5.8 kb (P < 0.02, P < 0.02), EcoRI 20 kb (P < 0.05, P < 0.02), and Pstl 6.0 kb (P < 0.05) fragments were more frequent in diabetic individuals compared with nonrelated control siblings or their parents, respectively. Analysis of individual haplotypes revealed that HLA-DR4-containing chromosomes were heterogeneous among controls but that the diabetic individuals showed a similar pattern of restriction fragment length polymorphism. Genomic blotting of blood lymphocyte DNA with a cDNA clone encoding the chain of HLA-D region class II antigens permits detection of fragments that are strongly associated With IDDM.

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