ALX1 and frontonasal dysplasia: For example, ALX1, a regulator of cartilage and craniofacial development in vertebrates (Zhao et al., 1993; Zhao et al., 1996; Dee et al., 2013), was one of the most highly upregulated genes in both pleurodont SDL and mesenchymal tissues, and it is likely that the severe and relatively early craniofacial phenotypes of ALX1 mutations (frontonasal dysplasia) before initiation of odontogenesis have hampered identification of this gene as a regulator of tooth development and/or replacement in mammals.