Immunogenetics of mixed connective tissue disease in a Mexican Mestizo population.

OBJECTIVE The aim of this study was to determine the HLA antigens in Mexican Mestizo patients with mixed connective tissue disease (MCTD). METHODS We studied 30 patients with MCTD and 99 healthy controls. HLA-A, -B, and -DQ antigens were typed by microlymphocytotoxicity assays. DRB1, DQA1 and DQB1 alleles were oligotyped. RESULTS HLA-A2 and HLA-B35 were the most frequent MHC class I alleles in MCTD patients, although they were not statistically more frequent than in the controls. According to serological tests, the most frequent DQ allele in the patients was DQ1, which was statistically increased when compared with controls (p = 0.0051). By oligotyping, the DR1 allele and the DQB1*0501 specificities were significantly increased in the patients vs. controls (p = 0.032 and 0.027, respectively). CONCLUSION The elevated levels of DQ1 found in Mexican MCTD patients, although weak, may indicate a particular genetic susceptibility, since there are previous reports of associations of other alleles (such as DR4) with MCTD in other populations. The increase in DQB1*0501 may account for the increase in DQ1. DQB1*0501 has also been reported in black patients with anti-RNP autoantibodies, compared with black patients without anti-RNP or anti-Sm.