Genome sequencing identified a novel exonic microdeletion in the RUNX2 gene that causes cleidocranial dysplasia.

BACKGROUND AND AIMS: Cleidocranial dysplasia (CCD) represents a rare autosomal dominant skeletal dysplasia caused by mutations that induce haploinsufficiency in RUNX2, the important transcription factor of osteoblasts related to bone/cartilage development and maintenance. Clavicular hypoplasia, which involves aberrant tooth/craniofacial bone/skeletal formation, is a feature of classic CCD. RUNX2 mutations can be found in approximately 60-70% of patients with CCD, and around ∼10% of these mutations are microdeletions. The present paper describes the radiological and clinical characteristics of a 5-year-old girl who showed representative CCD features, including extra teeth, aplasia of clavicles, sloping shoulders, marked calvarial hypomineralization, and osteoporosis. MATERIALS AND METHODS: We obtained genomic DNA of her family members and performed whole-genome sequencing (WGS) for samples collected from the proband. Quantitative fluorescent PCR (QF-PCR) and specific PCR plus electrophoresis were then performed as validation assays for all participants. In vitro analysis was performed. Luciferase assay for Runx2 transcription activity and evaluation of mRNA levels of Runx2 downstream osteogenic markers were conducted. RESULTS: WGS identified a 11.38-kb microdeletion in RUNX2 comprising 8-9 exons, which was validated by QF-PCR and specific PCR plus electrophoresis. In vitro experiments confirmed the pathogenicity of this variation. CONCLUSION: The present study identified a 11.38-kb microdeletion in RUNX2 that causes CCD. The deletion in the PST domain of RUNX2 reduces its transcription activity and reduces osteogenic marker levels, eventually decreasing the differentiation of osteoblasts. These findings clarify the role of the CCD-related mechanism in the development of CCD and suggest that it is important to consider copy number variation for the suspected familial patients early.

Metabolic and biophysical study of the MFN2Ile213Thr mutant causing Hereditary Motor and Sensory Neuropathy (HMSN).

Charcot-Marie-Tooth (CMT) 2A disease, a genetic axonal nervous lesion, results from MFN2 pathogenic variation, and this gene plays a pivotal role in mitochondrial dynamics and calcium signaling. However, the underlying mechanism linking MFN2 defect to progressive dying-back of peripheral nerves is still unclear. The present work focused on analyzing one CMT2A patient from multiple perspectives. Clinical and pathologic evaluation was initially conducted on the recruited case. Subsequently, Sanger sequencing and whole-exome sequencing (WES) were performed for genetic detection. To reveal the cell metabolic alteration caused by the identified variant, this study also established and transfected plasmid vectors in HEK293 cells and analyzed cell metabolites through liquid chromatography in combination with quadrupole time-of-flight tandem mass spectrometry (UPLC Q-TOF MS). Additionally, we completed structural modeling and molecular dynamic (MD) simulation to investigate the intramolecular impact of the variant. According to our results, the clinical and neuropathologic manifestations of the proband matched with the diagnosis of CMT. The causative variant MFN2: c.638T>C: (p.Ile213Thr) was identified through genetic analysis. Moreover, metabolic pathway enrichment results demonstrated that this variant significantly affected the metabolism of sphingolipids and glycerophospholipids. MD analysis indicated that this variant crippled the binding ability of MFN2 to GTP. Taken together, our study deduced preliminary clues for the underlying mechanism by which mutant MFN2 affects cell metabolism and provided a novel perspective to understand the cellular and molecular impacts of MFN2 variants.