RUNX2 and cleidocranial dysplasia 1: Cleidocranial dysplasia (CCD) is a rare genetic syndrome with an estimated prevalence of 1:1.000.000 and characterised by autosomal dominant inheritance.1 It is caused by mutations affecting the core-binding factor subunit alpha-1 (Cbfa1)2 on the chromosome 6p21.3 Involved in the differentiation of osteoblasts,4 Cbfa1 is part of the fibroblast growth factor and bone morphogenetic protein pathways in the development of teeth and bones.5 Cbfa1 is also a major regulator of chondrocyte differentiation,6 related to endochondral formation of long bones and vertebrae.