Leader genes acting in cell cycle regulation, such as CTNNB1, FOS, JUN, GRB2, PIK3CA, and PIK3R1, may affect homeostasis in both colonic cells and periodontal tissues, causing, if dysregulated, colonic cell proliferation and malignant transformation, on the one hand, and periodontitis development and progression, on the other, as described in Table 2 [22,23,24,25,26,27,28,29,30,31,32]. The gene discussed is GRB2; the disease is periodontitis.