A limb-girdle myopathy phenotype of RUNX2 mutation in a patient with cleidocranial dysplasia: a case study and literature review

Detection and diagnosis of cleidocranial dysplasia by panoramic radiography: a retrospective study

BACKGROUND

Cleidocranial dysplasia (CCD) is a rare and underdiagnosed congenital disorder in dentistry. The purpose of this study was to illustrate and quantify the maxillofacial bone abnormalities detected on panoramic radiographs from a relatively large retrospective case series and to provide a series of diagnostic references for dentists to indicate the presence of disease and help in making an early and accurate diagnosis.

METHODS

The dental panoramic radiographs of thirty CCD patients aged 11 to 45 years (18 males and 12 females) were examined retrospectively. The dentition states, including supernumerary teeth and impacted teeth, were recorded. Twelve quantified measurements were adopted to determine the abnormalities of maxillofacial bones, including the degree of the zygomatic arch downward bend, bicondylar breadth, ramal height, mandibular height, mandibular aspect ratio, mandibular body height, condylar height, coronoid height, distance between the coronoid process and the condyle, bigonial width, gonial angle and best-fit gonial circle diameter. The Wilcoxon rank-sum test was used to compare the findings of the CCD patients with those of their matched controls (n = 300).

RESULTS

Supernumerary teeth were detected in 27 patients (90.0%), and all 30 patients presented impacted teeth. Compared to the matched controls, the CCD patients had a significantly larger degree of zygomatic arch downward bend (ZAD), a larger diameter of the best-fit gonial circle (BGC), and a shorter distance between the coronoid process and the condyle (DCC) in panoramic radiographs (P < 0.001). According to the reference cutoff values established from the 5th or 95th percentile of the measurements in the control group, ZAD higher than 6.90 mm, DDC less than 22.37 mm and BGC higher than 52.41 mm were significantly associated with the CCD features identified. Other panoramic measurements were not significantly different between the two groups.

CONCLUSIONS

Panoramic radiographs had great value in the diagnosis of CCD. In this study, we identified some dental and maxillofacial features on panoramic radiographs from a relatively large retrospective case series of CCD. A series of reliable quantitative indicators were provided for dentists that can indicate the presence of disease and improve the diagnostic specificity.

A Novel 90-kbp Deletion of RUNX2 Associated with Cleidocranial Dysplasia

Cleidocranial dysplasia (CCD) is a rare autosomal dominant skeletal dysplasia caused by runt-related transcription factor 2 (RUNX2) mutations. In addition to the regular missense, small or large fragment deletions are the common mutation types of RUNX2. This study aimed to find the rules of deletions in RUNX2. The clinical information of one Chinese CCD family was collected. Genomic DNA was extracted for whole-exome sequencing (WES). Bioinformatics analyzed the pathogenicity of the variants. Polymerase chain reaction (PCR) and Sanger sequencing were carried out using specific primers. RT-PCR and Q-PCR were also used to detect the mRNA level of RUNX2. The CCD studies related with deletions in RUNX2 from 1999 to 2021 from HGMD and PubMed were collected and analyzed for the relationship between the phenotypes and the length of deleted fragments. The proband presented typical CCD features, including delayed closure of cranial sutures, clavicle dysplasia, abnormal teeth. WES, PCR with specific primers and Sanger sequencing revealed a novel heterozygous 90-kbp deletion in RUNX2 (NG_008020.2 g.103671~193943), which caused a substitution (p.Asn183Ile) and premature termination (p.Asp184*). In addition, the mRNA expression of RUNX2 was decreased by 75.5% in the proband. Herein, 31 types of deletions varying from 2 bp to 800 kbp or covering the whole gene of RUNX2 were compared and the significant phenotypic difference was not found among these deletions. The CCD phenotypes were related with the final effects of RUNX2 mutation instead of the length of deletion. WES has the defects in identifying large indels, and direct PCR with specific primers and Sanger sequencing could make up for the shortcoming.

Molecular Genetics of Cleidocranial Dysplasia

Cleidocranial dysplasia (CCD) is a genetic disorder with an autosomal dominant inheritance pattern. CCD characterized by abnormal clavicles, patent sutures and fontenelles, supernumerary teeth and short stature. Approximately 60-70% of CCD patients have mutations in the RUNX2 gene. The RUNX2 gene is an essential transcription factor for chondrocyte maturation, osteoblast differentiation and bone formation. Runx2 regulates mesenchymal cell proliferation in sutures and suture closure by inducing the signaling pathways of the genes of Fgf, Pthlh, hedgehog and Wnt. Material and Methods: We summarized molecular genetics aspects of CCD. Result: Approximately 94% of CCD patients have dental anomalies, the most common of which are supernumerary tooth. Dental anomalies are not determined solely by gene mutations of RUNX2, but are also affected by modifier genes, environmental factors, epigenetic factors and copy number variations. Conclusion: a definite diagnosis of CCD should include the patient's clinical history, symptoms and signs, as well as genetic analyses.

A novel gene mutation of Runx2 in cleidocranial dysplasia

Haploinsufficiency of the runt-related transcription factor 2 (Runx2) gene is widely known to be responsible for cleidocranial dysplasia (CCD). To date, more than 190 mutations in Runx2 gene have been reported to be related to CCD. In this study, a novel mutation of Runx2 gene was observed in a female with CCD. Genomic DNA was extracted from peripheral venous blood of the proband and eleven members of her family. Genetic testing on these twelve people identified a novel missense mutation (c.895 T>C, Y299H) in exon 5 of the RUNX2 gene in the proband. This mutation results in an amino acid change at codon 895 (P.Tyr 299 His.) from a tryptophan codon (TAT) to a histidine codon (CAT). Our finding may further extend the known mutation spectrum of the RUNX2 gene, and facilitate prenatal genetic diagnosis of CCD in the future.