That the K14-Cre;Fam20Aflox/flox mice, in which Fam20A is inactivated in the epithelium but is intact in the connective tissue, showed severe gingival epithelium overgrowth, which suggested that the gingival overgrowth in human patients suffering from AIGFS might occur primarily due to proliferation of the epithelium. The gene discussed is FAM20A; the disease is amelogenesis imperfecta type 1G.