Genetic studies found heterozygous mutations of the runt-related transcription factor 2 (RUNX2) gene, which is located at 6p21, to be responsible for the development of cleidocranial dysplasia.51A mutation in the APC gene located on chromosome 5q22.2 is found to be a causative factor for Gardner's syndrome. Here, RUNX2 is linked to cleidocranial dysplasia 1.