RUNX2 and cleidocranial dysplasia 1: To investigate the crosstalk between RUNX2 and 1α,25-dihydroxyvitamin D3 (1α,25-(OH)2D3) in human dental follicle cells (hDFCs) during osteoclast formation, we established a co-culture system of hDFCs from CCD patient and healthy donors with peripheral blood mononuclear cells (PBMCs).