ANALYSIS OF HLA-DQA1 AND HLA-DQB1 GENES IN MEXICAN-AMERICANS WITH INSULIN-DEPENDENT DIABETES-MELLITUS

Mexican American patients (n = 35) with insulin-dependent diabetes mel litus (IDDM) and control subjects (n = 39) were HLA-DQA and DQB typed by the polymerase chain reaction technique combined with allele-specif ic oligonucleotide probes. Either DQB10302 or DQB1*0201 was present a mong 91% (32/35) of the patients compared to 67% (26/39) of controls. Either DQA10501 or DQA1*0301 was present in all patients (100% or 35/ 35) compared to 29/39 (74%) (OR 12.06 Pc < 0.05) of controls. All four of these genes, in cis or trans, were present in 15/35 (43%) of the p atients compared to 3/39 (8%) of controls (OR 9.0; Pc < 0.01). The pre sence of one or more non-susceptibility alleles showed a dose-related decrease in relative risk. Presence of aspartic acid (Asp) at position 57 of the DQ beta chain did not confer protection and non-Asp homozyg ozity did not confer susceptibility to IDDM in this ethnic group. In c onclusion, susceptibility to IDDM in Mexican Americans is associated w ith particular DQA and DQB combinations, illustrates dose-dependent pa rameters and contradicts the critical residue hypothesis.