Pathogenic mechanism of 2 families with sporadic cleidocranial dysplasia syndrome
Objective:To investigate the pathogenic mechanism of sporadic cleidocranial dysplasia(CCD)by detecting RUNX2 gene mutation in 2 CCD families.Methods:Collection of medical history and extraction of genomic DNA from peripheral blood were per-formed in 2 sporadic CCD families.Mutation was detected using PCR and direct DNA sequencing.Swiss-Model software,SWISS-Pdb and RasMol browser were used to predict and analyze the mutant protein conformation,respectively.After construction of the eukaryot-ic vector pEGFP-N1-RUNX2,293-T cells were transfected and the fluorescent protein expression was observed.Results:The base deletion mutation c.243-260del18(p.81-86del6)was identified in the proband of family Ⅰ,which led to the deletion of 6 amino acids and changes to the secondary and tertiary conformation of the protein.Notably,parts of the spiral and folded structures were lost.The stop codon mutation c.1200C＞A(p.stop400)was detected in the proband of family Ⅱ,which caused premature termina-tion of transcription,deletion of some amino acids,truncation of the protein,and marked structural changes,including the loss of all folded structures and most corners.Analysis of subcellular localization using green fluorescent protein showed that the c.243-260del18(p.81-86del6)and c.1200C＞A(p.stop400)mutants have the same localization as the wild type,indicating that p.81-86del6 and p.stop400 have no effect on the nuclear localization of RUNX2 protein.Conclusion:RUNX2 gene mutation is the pathogenic basis of CCD,and p.stop400 is a newly detected gene mutation site for CCD.
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