RUNX2 and cleidocranial dysplasia 1: Paradoxically, CCD has been considered a disorder characterized by deficient osteogenesis [14] because Runt-related transcription factor-2 (RUNX2) is the master gene involved in regulating osteoblast differentiation and osteogenesis [15], and various RUNX2 mutations have been identified in about 70% of CCD patients [16].