RUNX2 and cleidocranial dysplasia 1: Homozygous Runx2 knockout mice (RUNX2-/-) will die of respiratory failure soon after birth and shows failure in both intramembranous and endochondral ossification, whilst heterozygous Runx2 knockout mice (RUNX2+/-) displays similar phenotype with CCD patients in hypoplastic clavicles and defective skull formation [8].