A novel, complex RUNX2 gene mutation causes cleidocranial dysplasia

BACKGROUND: Haploinsufficiency of the runt-related transcription factor 2 (RUNX2) gene is known to cause cleidocranial dysplasia (CCD). Here, we investigated a complex, heterozygous RUNX2 gene mutation in a Chinese family with CCD and the pathogenesis associated with the variations. METHODS: Genomic DNA extracted from peripheral venous blood was taken from the proband, her parents and 3 siblings, and 150 normal controls. Analysis of their respective RUNX2 gene sequences was performed by PCR amplification and Sanger sequencing. Pathogenesis associated with RUNX2 mutations was investigated by performing bioinformatics, real-time PCR, western blot analysis, and subcellular localization studies. RESULTS: We identified 2 complex heterozygous mutations involving a c.398–399 insACAGCAGCAGCAGCA insertion and a c.411–412 insG frameshift mutation in exon 3 of the RUNX2 gene. The frameshift mutation changed the structure of the RUNX2 protein while did not affect its expression at the mRNA level. Transfection of HEK293T cells with a plasmid expressing the RUNX2 variant decreased the molecular weight of the variant RUNX2 protein, compared with that of the wild-type protein. Subcellular localization assays showed both nuclear and cytoplasmic localization for the mutant protein, while the wild-type protein localized to the nucleus. CONCLUSIONS: Our findings demonstrated that the novel c.398–399insACAGCAGCAGCAGCA mutation occurred alongside the c.411–412insG frameshift mutation, which resulted in RUNX2 truncation. RUNX2 haploinsufficiency was associated with CCD pathogenesis. These results extend the known mutational spectrum of the RUNX2 gene and suggest a functional role of the novel mutation in CCD pathogenesis.