Cleidocranial dysplasia and novel RUNX2 variants: dental, craniofacial, and osseous manifestations

Abstract Cleidocranial dysplasia (CCD) is a skeletal disorder affecting cranial sutures, teeth, and clavicles, and is associated with the RUNX2 mutations. Although numerous patients have been described, a direct genotype-phenotype correlation for RUNX2 has been difficult to establish. Further cases must be studied to understand the clinical and genetic spectra of CCD. Objectives To characterize detailed phenotypes and identify variants causing CCD in five unrelated patients and their family members. Methodology Clinical and radiographic examinations were performed. Genetic variants were identified by exome and Sanger sequencing, data were analyzed by bioinformatics tools. Results Three cases were sporadic and two were familial. Exome sequencing successfully detected the heterozygous pathogenic RUNX2 variants in all affected individuals. Three were novel, comprising a frameshift c.739delA (p.(Ser247Valfs*)) in exon 6 (Patient-1), a nonsense c.901C>T (p.(Gln301*)) in exon 7 (Patient-2 and affected mother), and a nonsense c.1081C>T (p.(Gln361*)) in exon 8 (Patient-3). Two previously reported variants were missense: the c.673C>T (p.(Arg225Trp)) (Patient-4) and c.674G>A (p.(Arg225Gln)) (Patient-5) in exon 5 within the Runt homology domain. Patient-1, Patient-2, and Patient-4 with permanent dentition had thirty, nineteen, and twenty unerupted teeth, respectively; whereas Patient-3 and Patient-5, with deciduous dentition, had normally developed teeth. All patients exhibited typical CCD features, but the following uncommon/unreported phenotypes were observed: left fourth ray brachymetatarsia (Patient-1), normal clavicles (Patient-2 and affected mother), phalangeal malformations (Patient-3), and normal primary dentition (Patient-3, Patient-5). Conclusions The study shows that exome sequencing is effective to detect mutation across ethnics. The two p.Arg225 variants confirm that the Runt homology domain is vital for RUNX2 function. Here, we report a new CCD feature, unilateral brachymetatarsia, and three novel truncating variants, expanding the phenotypic and genotypic spectra of RUNX2 , as well as show that the CCD patients can have normal deciduous teeth, but must be monitored for permanent teeth anomalies.

A novel de novo COL1A1 mutation in a Thai boy with osteogenesis imperfecta born to consanguineous parents

Abstract Osteogenesis imperfecta (OI) is genetically heterogeneous. Mutations in COL1A1 and COL1A2 are responsible for at least 90% of the cases, which are transmitted in an autosomal dominant manner or are de novo events. We identified a Thai boy with OI whose parents were first cousins. Because the proband was the product of a consanguineous marriage, we hypothesized that he might be homozygous for a mutation in a known gene causing a recessive form of OI. Using whole exome sequencing (WES), we did not find any pathogenic mutations in any known gene responsible for an autosomal recessive form of OI. Instead, we identified a COL1A1 frameshift mutation, c.1290delG (p.Gly431Valfs*110) in heterozygosis. By Sanger sequencing, the mutation was confirmed in the proband, and not detected in his parents, indicating that it was a de novo mutation. These findings had implication for genetic counseling. In conclusion, we expanded the mutational spectrum of COL1A1 and provided another example of a de novo pathogenic mutation in heterozygosis in a patient born to consanguineous parents.