HLA-DQA1 and periodontitis: However, unlike other loci, such as HLA-DQA1* and HLA-DQB1*, which did not display significant associations with the severity or extent of periodontitis in the sample, this work identified an interesting pattern connected to two alleles of the HLA-DRB1 locus: HLA-DRB1*03 and HLA-DRB1*15.