Analysis of HLA‐DQA1 and ‐DQB1 genes in Mexican Americans with insulin‐dependent diabetes mellitus

Abstract: Mexican American patients (n = 35) with insulin‐dependent diabetes mellitus (IDDM) and control subjects (n = 39) were HLA‐DQA and DQB typed by the polymerase chain reaction technique combined with allele‐specific oligonucleotide probes. Either DQBl*0302 or DQB1*0201 was present among 91% (32/35) of the patients compared to 67% (26/39) of controls. Either DQA1*0501 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 patients compared to 3/39 (8%) of controls (OR 9.0; Pc<0.01). The presence 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 β chain did not confer protection and non‐Asp homozygozity did not confer susceptibility to IDDM in this ethnic group. In conclusion, susceptibility to IDDM in Mexican Americans is associated with particular DQA and DQB combinations, illustrates dose‐dependent parameters and contradicts the critical residue hypothesis. 1993 Blackwell Munksgaard