In another single locus study, a methylation analysis was performed on leukocyte blood cells from smokers with periodontitis, defined as “Subjects with at least three teeth exhibiting 5 mm CAL sites, in at least two different quadrants”, and significant differences in the DNA methylation levels of the IL8 promoter gene were not found compared to non-smokers with periodontitis [27] (Supplement Materials, Table S3). The gene discussed is CXCL8; the disease is periodontitis.