Transracial analysis provides a method of distinguishing primary associations between insulin-dependent diabetes mellitus (IDDM) and HLA class II alleles from those secondary to linkage disequilibrium. Blacks show DR-DQ relationships that are different from other races and are a useful group in which to investigate HLA-D region associations with IDDM. In this study, the frequencies of HLA-DQA1 and -DQB1 alleles in Afro-Caribbean IDDM and control subjects were compared. Alleles were identified with sequence-specific oligonucleotide probing. The DQA1 allele A3 was positively associated with IDDM (relative risk [RR] = 25.3, corrected P [Pc] < 7.0 × 10−6. The DQB1 alleles DQw2 and DQw8 were also positively associated (RR = 4.7, Pc < 6.5 × 10−3 and RR = 12.3, Pc = 3.4 × 10−3, respectively). The A1.2 and DQw6 alleles were negatively associated (RR = 0.16, Pc < 3.5 × 10−3 and RR = 0.15, Pc = 2.4 × 10−2, respectively). These findings were compared to data from other races. The positive associations with A3 and DQw2 are consistent with all racial groups investigated. The negative association with DQw6 is present in all racial groups in which it is a common allele. These findings suggest that DQ alleles, and hence DQ molecules, may directly affect predisposition to IDDM.

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