RUNX2 and cleidocranial dysplasia 1: It is well known that RUNX2 is indispensable in the process of osteogenesis, homozygous deletion of RUNX2 in mice resulted in complete loss of osteoblasts [71,72,73] and haploinsufficiency of RUNX2 in humans leads to a disease known as cleidocranial dysplasia, which is characterized by defects in bone formation [42,71,74,75].