HLA-DQA1 Introns 2 and 3 Sequencing: DQA1 Sequencing-Based Typing and Characterization of a Highly Polymorphic Microsatellite at Intron 3 of DQA1*0505

DQA1 class II gene encodes the α-chain of the human leukocyte antigen (HLA)-DQ heterodimer. Sequencing-based typing (SBT) for HLA genes is the most powerful methodology described. However, most of the SBT procedures reported for HLA class II genes are not able to define complete exon 2 region. For that purpose, we have characterized introns 2 and 3 from most DQA1 alleles to design amplification procedures that were able to obtain complete exon 2 and 3 sequences from DQA1 genes. This coding information allowed us to reduce the number of ambiguities for DQA1 typing. DQA1 intron 2 and 3 characterization demonstrated the presence of two polymorphisms for alleles with the same exons 2 and 3 sequence from DQA1*05 group. Different samples including the DQA1*050101 alleles showed a single nucleotide polymorphism at position 53 of intron 2 (G53T). Additional haplotypic analysis showed the possible association of T53 allele with the Ax-Cw5-B18-DR17-DQ2 extended haplotype. On the other hand, DQA1*0505 sequencing from different control samples noticed the existence of a microsatellite (TTTC/AAAG)n located at position 126 of intron 3. Fragment length analysis demonstrated a high polymorphism for this short tandem repeat system (0505STR), defining alleles that ranged from 8 to 20 repetitions in our population.