Thus, the knockout mice with Runx2−/− lack osteoblasts and bones,[8] whereas the heterozygous mice (Runx2+/−) show abnormalities similar to those of CCD.[9] Quantitative real-time PCR results showed that the RUNX2 level was downregulated to 60% in patient II:1 family 1. This evidence concerns the gene RUNX2 and cleidocranial dysplasia 1.