Fifty Japanese patients with insulin-dependent diabetes mellitus (IDDM) and 94 normal subjects were genotyped for Bg/II restriction-fragment-length polymorphism (RFLP) of the T-lymphocyte-receptor β-chain (TLRβ)-region gene and analyzed in relation to HLA-DR phenotypes. The antigen frequencies of DR4 and DR9 in the IDDM population were significantly higher than those in the normal population, with relative risks of 1.87 (P < .02) and 2.42 (P < .01), respectively. Hybridization of digested DNA with the TLRβ probe revealed two alleles of 9.3 and 8.6 kilobases (kb). The allele frequency of 8.6 kb in patients with IDDM (79%) was significantly (P < .05) higher than that in normal subjects (64%). When TLRβ-region RFLP in IDDM was further analyzed with respect to the HLA-DR phenotypes, the frequency of 8.6 kb was significantly increased in patients with DR4 but not DR9 (DR4/X) and those with DR9 but not DR4 (DR9/X) compared with the frequency found in normal subjects (P < .05); the relative risks of 8.6 kb in DR4/X and DR9/X were 2.77 and 4.98, respectively. Although the frequencies of HLA-DR phenotypes and of TLRβ-region RFLP in IDDM and normal subjects were apparently different from those reported for Caucasians, this population-association study indicates that in the Japanese, genes conferring susceptibility to IDDM exist near or at the HLA-DR and the TLRβ loci, as has been demonstrated in Caucasians.

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