Animal studies showed that tooth development was arrested in RUNX2 null mice at the late bud stage and normal in heterozygous RUNX2 mutant mice (D’Souza et al., 1999; Adhami et al., 2015), in contrast to the findings that there are supernumerary teeth seen in CCD patients with RUNX2 mutations or copy variations. Here, RUNX2 is linked to cleidocranial dysplasia 1.