HLA-DRB1 and periodontitis: Frequencies of HLA-A9 and -B15, HLA-DQA1*03:01, HLA-DQB1*03:02 and HLADQB1*03:05 alleles, as well as that of the HLA-DRB1*04:01 allele, were significantly higher in patients with aggressive periodontitis compared with control subjects among Caucasians and Iranian patients.12,18