MSX2 and dental enamel hypoplasia: Both, Msx2 and Sp6 mouse mutants, exhibit enamel hypoplasia, while humans with AI carry mutations in the human homologues of MSX2 or SP6 genes (Satokata et al., 2000; Bei et al., 2004; Suda et al., 2006; Nakamura et al., 2008; Utami et al., 2011; Babajko et al., 2014; Smith et al., 2020).