OBJECTIVETo investigate the molecular etiology of three patients with sporadic cleidocranial dysplasia (CCD) and to provide genetic counseling and prenatal diagnosis for the family members based on the identified mutations.

METHODSGenomic DNA was extracted from peripheral blood samples using a standard method. All 7 coding exons of the RUNX2 gene and their flanking intronic sequences were amplified by PCR and sequenced directly. The PCR products of the exons with mutations from the three patients were cloned into a T-vector. Positive clones were sequenced.

RESULTSThe three patients who have the typical CCD phenotypes involving clavicles, calvarium, stature, and teeth have carried various frameshift mutations in the RUNX2 gene. Patient 1 has a gross deletion of 80 nucleotides in exon 1 (c.227_306del), which caused a frameshift beginning at the Q/A repeat of the polypeptide and a premature termination (p.Ala76GlyfsX58). Patient 2 has a 2-bp duplication in exon 2 (c.471_472dupGG), which also caused a frameshift and a premature termination (p.Ala158GlyfsX19). Patient 3 has a T duplication in exon 7 (c.1321dupT), which caused a frameshift and a premature termination (p.Ser370PhefsX13) as well.

CONCLUSIONThe three novel mutations in RUNX2 are the underlying molecular mechanism for the CCD phenotypes of three sporadic Chinese patients, respectively. These have broadened the mutation spectrum of RUNX2 gene and provided a molecular basis for the genetic counseling and prenatal diagnosis for the affected families.