MSX1 and tooth agenesis: Mutations of MSX1 have been associated with non-syndromic cleft palate and tooth agenesis in humans, and Msx1-deficient mice exhibit severe craniofacial abnormalities, cleft palate, and absence of teeth (Satokata and Maas, 1994; Zhang et al., 2002; Nieminen et al., 2003).