C7 and periodontitis: These 22 genes represent the top candidates as biomarkers to diagnose periodontitis, with 11 of these potential biomarkers found either extracellularly or on the surface of host cells (MZB1, MERTK, SCAMP5, C7, CR2, SMPDL3B, SLC17A9, BMP6, ST6GAL1, C1orf68, and LAX1).