Various substances involved in the progression or activity of periodontal disease, including cytokines (ILs, TNF-α, receptor activator of nuclear factor-κB ligand, and osteoprotegerin) and lipids (prostaglandin E2 and leukotriene), have been detected in GCF [29, 30], and some have been verified as markers of periodontal disease [31, 32]. The gene discussed is TNFRSF11B; the disease is periodontal disorder.