HLA-DRB1 and periodontitis: These alleles were also associated with severe periodontitis (Stages III–IV): DRB1*03 (OR = 7.71; 95% CI [1.68, 35.5], p = 0.003) and DRB1*15 (OR = 21.2; 95% CI [0.97, 461], p = 0.005).