Novel mutation of RUNX2 gene in a patient with cleidocranial dysplasia

Background: Cleidocranial dysplasia is a rare hereditary skeletal disorder due to heterozygous loss of function mutations in the RUNX2 gene that encodes runt-related transcription factor 2 (RUNX2). Here we report a 52 year-old woman with cleidocranial dysplasia due to a novel RUNX2 mutation.

Case description: A 52 year-old Han Chinese woman presented with short stature and skeletal dysplasia that was first noted during early childhood. She was 153 cm in height and 40 kg in weight. Her skull was deformed with hypertelorism, midface hypoplasia, protrusion of chin, and dental abnormalities. Radiological examination revealed shortened clavicles and depressed skull bone and that were consistent with the clinical diagnosis of cleidocranial dysplasia. There was no family history of a similar skeletal disorder. We sequenced the RUNX2 gene and discovered a novel heterozygous mutation in exon 3 (c.476 del G, p.G159fs175X) that is predicted to cause a frameshift and premature termination that leads to the loss of the final 347 amino acid residues. This severely truncated protein is expected to be inactive.

Literature review: RUNX2 gene controls osteoblast differentiation and chondrocyte maturation. Around 90 RUNX2 mutations have been discovered in patients with cleidocranial dysplasia.

Clinical relevance: We identified a case of cleidocranial dysplasia due to a novel mutation of RUNX2 gene at exon 3 (c.476 del G).