MHC associations with IDDM in a Chinese population were studied to investigate genetic susceptibility to the disorder. The frequency of HLA-DR3 was significantly higher in the diabetic patients (19/49 [38.7%] vs. control subjects, 11/105 [10.5%], Pc < 1.3 × 10−3, RR = 5.3 [CI 2.3–12.1]), whereas DR4 was not (11/49 [22.4%] vs. 28/105 [26.7%], NS). The frequency of DR3/4 heterozygosity was higher in the diabetic patients (6/49 [12.2%] vs. control subjects, 0/105 [0%], P = 1.7 × 10−3, RR = 31.5 [CI 3.8–263.6]). The frequency of DR3/9 heterozygosity also was higher in the diabetic patients (6/49 [12.2%] vs. control subjects, 2/105 [1.9%], P = 0.03, RR = 6.2 [CI 3.0–12.7]). No significant associations were noted between DQB1 alleles and IDDM. Among DR4-positive subjects, the frequency of DQB1 allele DQB1*0302 was higher in the diabetic patients (10*11 [90.0%] vs. control subjects, 12/24 [50%], Pc < 0.05, RR = 7.0 [CI 1.3–38.0]), and the frequency of DQB1*0401 was significantly lower in the diabetic patients (2/11 [18.2%] vs. control subjects, 16/24 [66.7%], Pc = 0.04, RR = 0.1 [CI 0.02–0.46]). No DR4 subtype was associated significantly with IDDM. The frequency of DQA1*0501, a DQA1 allele, was higher in diabetic patients (22/41 [53.7%] vs. control subjects, 20/95 [21.1%], Pc < 3 × 10−3, RR = 4.3 [CI 2.0–9.3]). The frequency of DQA1*0301, which has been associated consistently with IDDM in other ethnic groups, was not significantly higher in the diabetic patients in this study (27/41 [65.9%] vs. control subjects, 53/95 [55.8%], NS). The frequency of the DR4 haplotype DRB1*0405-DQA1*0301-DQB1*0401 was lower among DR4- positive diabetic patients (2/10 [20%] vs. DR4-positive control subjects, 12/21 [57.1%], NS), in direct contrast with Japanese populations. These results suggest that if DQB1 and DQA1 alleles determine IDDM susceptibility, other MHC factors must modify their effect.

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