Susceptibility to type I diabetes has been shown to be highly correlated with the presence of an amino acid other than Asp at position 57 of the DQ β-chain (non-Asp57) and also with the presence of an Arg at position 52 of the DQ α-chain (Arg52). In this study we analyzed the DQA1 and DQB1 gene polymorphisms in 65 patients from central Italy and 93 randomly selected control subjects. Polymerase chain reaction amplification of DNA encoding the first polymorphic domain of the DQB1 and DQA1 chains was performed, and DQB1 gene polymorphism was evaluated by dot blot analysis using 11 sequence-specific oligonucleotide probes. For DQA1 typing, a new simple procedure based on allele-specific amplification and analysis of heteroduplex DNA molecules formed by the annealing of mismatched allelic strands was used. This technique allows the discrimination of Arg52 and non-Arg52 DQA1 alleles. We then calculated by logistic regression the contribution of these genetic markers to the development of diabetes. Frequencies and odds ratios relative to the amino acid in position 57 of the DQ β-chain and the amino acid in position 52 of the DQ α-chain showed that the highest odds ratio (odds ratio = 161; 95% confidence interval 19–1386) was that of the homozygous combination of the two susceptibility markers (non-Asp57 and Arg52). Based on the incidence estimates of type I diabetes in the continental Italian population, the annual incidence rate of the disease was estimated for the different genotypes grouped according to the number of potentially formed susceptible heterodimers as 212.53, 12.60, 3.24, and 1.33/100,000 individuals per yr for the 4, 2 , 1 , and 0 susceptible heterodimers groups, respectively.

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