Of the 34 identified key gut microbiota markers that distinguished participants with different periodontal conditions, 25 taxa were correlated with duration of diabetes, dry mouth or the peripheral levels of pro-inflammatory cytokines (e.g., tumor necrosis factor-α, interferon-γ, prostaglandin E2, interleukin-17, and interleukin-6) and metabolic parameters (e.g., hemoglobin A1c), respectively. The gene discussed is IL17A; the disease is diabetes mellitus.