• linkage disequilibrium;
  • HLA-DQA1 and DQB1;
  • PCR-SBT;

Althought it is a valuable tool for the identification of HLA alleles, sequence-based typing (SBT) presents difficulties when used to determine HLA-DQA1 and -DQB1 alleles. Specifically, some HLA-DQA1 alleles have a three-base deletion at codon 56 of exon 2 that interferes with the sequencing read. Moreover, the frequently used primers for HLA-DQB1 may co-amplify the HLA-DQB2 pseudogene. To overcome these problems, we amplified DQA1 exon 2 using five group-specific polymerase chain reactions (PCRs) which allowed separation of deleted from non-deleted DQA1 alleles. DQB1 exon 2 was amplified using two group-specific amplifications. To increase typing resolution, we also analyzed DQA1 exons 1, 3 and 4 and DQB1 exon 3 by PCR using sequence-specific primers (PCR-SSP) or SBT analysis. Using this method we found some important associations between DQA1 and DQB1 alleles: DQA1*05011 and DQB1*0201, DQA1*0505 and DQB1*03011, DQA1*01021 and DQB1*06, DQA1*01022 and DQB1*0502.