1981; Takagi et al. 1984), the first to have its cDNA cloned (Snead et al. 1983) and characterized (Snead et al. 1985), and the first to be expressed in recombinant form (Simmer et al. 1994b). AMELX was the first gene shown to cause amelogenesis imperfecta when defective (Lagerström et al. 1991), and mouse Amelx was the first enamel gene to be knocked out (Gibson et al. 2001). This examination of enamel formed C57BL/6 Amelx+/+, Amelx+/−, and Amelx−/− mice in the light of current knowledge provides a fresh insight into dental enamel formation and amelogenin's role in it. The gene discussed is AMELX; the disease is amelogenesis imperfecta.