[Cleidocranial dysplasia. Description and analysis of a patient cohort]

A novel single-base deletion of the RUNX Family Transcription Factor 2 gene associated with cleidocranial dysplasia

Cleidocranial dysplasia (CCD) is a rare, autosomal dominant hereditary disorder characterized by skeletal malformations and dental abnormalities. The purpose of this study was to explore the functional role of a novel mutation in the pathogenesis of CCD. Genomic DNA was extracted from peripheral blood mononuclear cells collected from family members of a Chinese patient with CCD. An analysis of their RUNX Family Transcription Factor 2 (RUNX2) gene sequences was performed by PCR amplification and Sanger sequencing. The function of the mutant RUNX2 was studied by bioinformatics, real-time PCR, western blotting, and subcellular localization analysis. Sanger sequencing identified a novel single-base deletion (NM_001024630.4:c.132delG;NP_001019801.3: Val45Trpfs^* 99) in the RUNX2 gene present in the Chinese patient with CCD. In vitro, functional studies showed altered protein localization and increased expression of mutant RUNX2 mRNA and mutant Runt-related transcription factor 2 (RUNX2). Luciferase reporter assay demonstrated that the novel RUNX2 mutations significantly increased the transactivation activity of RUNX2 on the osteocalcin gene promoter. In conclusion, we identified a patient with sporadic CCD carrying a novel deletion/frameshift mutation of the RUNX2 gene and performed screening and functional analyses to determine the cause of the CCD phenotype. This study provides new insights into the pathogenesis of CCD.3.

The significance of RUNX2 in postnatal development of the mandibular condyle

OBJECTIVE

RUNX2, in the Runt gene family, is one of the most important transcription factors in the development of the skeletal system. Research in recent decades has shown that this factor plays a major role in the development, growth and maturation of bone and cartilage. It is also important in tooth development, mechanotransduction and angiogenesis, and plays a significant role in various pathological processes, i.e. tumor metastasization. Mutations in the RUNX2 gene correlate with the cleidocranial dysplasia (CCD) syndrome, important to dentistry, particularly orthodontics because of its dental and orofacial symptoms. Current research on experimentally-induced mouse mutants enables us to study the etiology and pathogenesis of these malformations at the cellular and molecular biological level. This study's aim is to provide an overview of the RUNX2 gene's function especially in skeletal development, and to summarize our research efforts to date, which has focused on investigating the influence of RUNX2 on mandibular growth, which is slightly or not at all altered in many CCD patients.

MATERIALS AND METHODS

Immunohistochemical analyses were conducted to reveal RUNX2 in the condylar cartilage of normal mice and of heterozygous RUNX2 knockout mice in early and late growth phases; we also performed radiographic and cephalometric analyses.

RESULTS

We observed that RUNX2 is involved in normal condylar growth in the mouse and probably plays a significant role in osteogenesis and angiogenesis. The RUNX2 also has a biomechanical correlation in relation to cartilage compartmentalization. At the protein level, we noted no differences in the occurrence and distribution of RUNX2 in the condyle, except for a short phase during the 4th and 6th postnatal weeks, so that one allele might suffice for largely normal growth; other biological factors may have compensatory effects. However, we did observe small changes in a few cephalometric parameters concerning the mandibles of heterozygous knockout animals. We discuss potential correlations to our findings by relating them to the most current knowledge about the RUNX2 biology.

The role of periodontal ligament cells in delayed tooth eruption in patients with cleidocranial dysostosis

OBJECTIVE

The clinical appearance of patients with cleidocranial dysplasia (CCD), which is caused by mutations in the RUNX2 gene, is characterized by anomalies of the clavicles, thorax, spine, pelvis and extremities and by disturbances of the skull and tooth development. Of orthodontic relevance are multiple supernumerary teeth associated with delayed tooth eruption. The present investigation is based on the hypothesis that an altered phenotypic expression of periodontal ligament (PDL) cells from CCD patients and a reduced ability of those cells to support the differentiation of bone-resorbing osteoclasts might contribute to delayed tooth eruption.

MATERIALS AND METHODS

To test this hypothesis, PDL cells from healthy donors and from two patients with clinically and molecular biologically diagnosed CCD were characterized for the basal and induced mRNA expression of osteoblast marker genes. The physiological relevance of the findings for the differentiation of osteoclasts was examined in an osteoclast assay, as well as in a co-culture model of PDL cells and osteoclast precursors.

RESULTS

Both CCD patients displayed missense mutations of the RUNX2 gene. The in vitro experiments revealed an unaltered expression of RUNX2 mRNA, however especially in CCD patient 2 there was a reduced basal expression of mRNA for the key regulatory gene for bone remodeling RANKL. Furthermore, compared to the control cells from healthy donors, these factors were less inducible by stimulation of the cultures with 1alpha,25(OH)(2)D(3). In the osteoclast assays as well as in the co-culture experiments, PDL cells from the CCD patients showed a reduced capacity to induce the differentiation of active osteoclasts.

CONCLUSIONS

These data indicate that PDL cells from CCD patients express a less distinctive osteoblastic phenotype resulting in an impaired ability to support osteoclastogenesis which might, in part, account for the delayed tooth eruption that can be observed clinically.

[Immunohistochemical study on collagen I content in the gingiva in cleidocranial dysplasia]

BACKGROUND

Patients with cleidocranial dysplasia (CCD) present a thickend and fibrotic gingiva.

PURPOSE

To the best of our knowledge it was analysed for the first time, whether this is correlated with an increased rate of collagen I in oral mucosa.

PATIENTS AND METHODS

27 soft tissue biopsies of six CCD-patients and 17 tissue samples of 12 healthy persons were labled with a monoclonal antibody against collagen I and the bound antibodies were detected with alkaline phosphatase-anti-alkaline phophatase-kit. The histological slices were analysed by a digital image recognition software under a fully automated microscope and the rate of collagen I was converted into amounts of grey tones.

RESULTS

The amount of grey tones reached from 11.909 to 15.319 in the CCD-group, and from 2752 to 12.556 in the control group. The U-Test of Mann, Whitney and Wilcoxon for two independent samples generated a rank sum of 91,50 for CCD-patients, and of 79,50 for the control group. The Z-value was 3,246, the p-value 0,005. "Fisher's exact test" identified a p-value of 0,0003.

CONCLUSIONS

The rate of collagen I in the oral mucosa seems to be increased significantly in CCD. This could explain the typical thick and fibrotic consistency of the gingiva and could be one reason for the delayed or missing dentition.