Background:Cleidocranial dysplasia (CCD) is an autosomal dominant disease that affects the skeletal system.Common symptoms of CCD include hypoplasia or aplasia of the clavicles,delayed or even absent closure of the fontanels,midface hypoplasia,short stature,and delayed eruption of permanent and supumerary teeth.Previous studies reported a connection between CCD and the haploinsufficiency of runt-related transcription factor 2 (RUNX2).Here,we report a sporadic Chinese case presenting typical symptoms of CCD.Methods:We made genetic testing on this sporadic Chinese case and identified a novel RUNX2 frameshift mutation:c.1111dupT.In situ immunofluorescence microscopy and osteocalcin promoter luciferase assay were performed to compare the functions of the RUNX2 mutation with those of wild-type RUNX2.Results:RUNX2 mutation was observed in the perinuclear region,cytoplasm,and nuclei.In contrast,wild-type RUNX2 was confined in the nuclei,which indicated that the subcellular compartmentalization of RUNX2 mutation was partially perturbed.The transactivation function on osteocalcin promoter of the RUNX2 mutation was obviously abrogated.Conclusions:We identified a sporadic CCD patient carrying a novel insertion/frameshift mutation of RUNX2.This finding expanded our understanding of CCD-related phenotypes.