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HLA-DQ molecular typing detects DNA sequence variation, and distinguishes 8 DQA1 and 16 DQB1 alleles. The differences in the sequence reflects changes in structure of the cleft of the DQ molecule, which is critical for the presentation of antigens. DQA1 alleles coding for an arginine in position 52 (i.e., DQA1*R) and DQB1 alleles coding for an amino acid other than aspartic acid in position 57 (i.e., DQB1*ND) are significantly more common among type 1 diabetics than controls. These haplotypes represent the best single genetic marker for molecular epidemiology studies of type 1 diabetes.