DQA1 and DQB1 promoter diversity and linkage disequilibrium with class II haplotypes in Mexican Mestizo population.

The upstream sequences in the 5' flanking region of HLA class II genes, regulate their expression and contribute to the development of immunological diseases. We analyzed 105 healthy unrelated Mexican Mestizos for QAP and QBP polymorphism. DNA typing for DRB1, DQA1, DQB1, QAP1 and QBP1 was done using a standardized PCR-SSOP. Although all QAP alleles previously described were found in Mexicans, the distribution differed as compared to other populations. QAP-3.1, 4.1 and 4.2 were the most frequent alleles and were associated with DQA1*03, *0501 and *0402 respectively. The prevalent QBP alleles were 3.21, 3.1 and 4.1 found mainly associated with DQB1*0302, *0301 and *0501. Linkage disequilibria between the promoter and the corresponding DQA1 and DQB1 allele, are in general the same as described by others. A total of 61 different haplotypes were defined, only six of them with a frequency above 4%. The haplotypes DRB1*0407-QAP-3.1-DQA1*03-QBP-3.21-DQB1*0302 (HF = 14.37%) and DRB1*0802-QAP-4.2-DQA1*0401-QBP-4.1-DQB1*0402 (HF = 14.22%), which have an Amerindian ancestry, are the most frequent in Mexicans. Some rare combinations were detected such as DRB1*0405-QAP-1.3-DQA1*0101/4-QBP-5.11/5.12-DQB1*0501 and DRB1*0403-QAP-3.2-DQA1*03-QBP-3.21-DQB1*0302, probably due to ancient recombination events. This knowledge is relevant as a basis to evaluate functional implications and to explore the role of promoter diversity in disease expression.