HLA-DQA1 AND DQB1 GENE POLYMORPHISMS IN TYPE-I DIABETIC-PATIENTS FROMCENTRAL ITALY AND THEIR USE FOR RISK PREDICTION

Susceptibility to type I diabetes has been shown to be highly correlat ed with the presence of an amino acid other than Asp at position 57 of the DO beta-chain (non-Asp 57 ) and also with the presence of an Arg at position 52 of the DO alpha-chain (Arg52). In this study we analyze d the DQA1 and DQB1 gene polymorphisms in 65 patients from central Ita ly and 93 randomly selected control subjects. Polymerase chain reactio n amplification of DNA encoding the first polymorphic domain of the DQ B1 and DQA1 chains was performed, and DQB1 gene polymorphism was evalu ated by dot blot analysis using 11 sequence-specific oligonucleotide p robes. For DQA1 typing, a new simple procedure based on allele-specifi c amplification and analysis of heteroduplex DNA molecules formed by t he annealing of mismatched allelic strands was used. This technique al lows the discrimination of Arg 52 and non-Arg52 DQA1 alleles. We then calculated by logistic regression the contribution of these genetic ma rkers to the development of diabetes. Frequencies and odds ratios rela tive to the amino acid in position 57 of the DO beta-chain and the ami no acid in position 52 of the DQ alpha-chain showed that the highest o dds 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 th e 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, an d 0 susceptible heterodimers groups, respectively.