Identification of Copy Number Variants in a Southern Chinese Cohort of Patients with Congenital Scoliosis

Mitochondrial genes modulate the phenotypic expression of congenital scoliosis syndrome caused by mutations in the TBXT gene

BACKGROUND

Congenital scoliosis (CS) is a spinal disorder caused by genetic-congenital vertebral malformations and may be associated with other congenital defects or may occur alone. It is genetically heterogeneous and numerous genes contributing to this disease have been identified. In addition, CS has a wide range of phenotypic and genotypic variability, which has been explained by the intervention of genetic factors like modifiers and environment genes. The aim of the present study was to determine the possible cause of CS in a Tunisian patient and to examine the association between mtDNA mutations and mtDNA content and CS.

METHODS

Here we performed Whole-Exome Sequencing (WES) in a patient presenting clinical features suggestive of severe congenital scoliosis syndrome. Direct sequencing of the whole mitochondrial DNA (mtDNA) was also performed in addition to copy number quantification in the blood of the indexed case. In silico prediction tools, 3D modeling and molecular docking approaches were used.

RESULTS

The WES revealed the homozygous missense mutation c.512A > G (p.H171R) in the TBXT gene. Bioinformatic analysis demonstrated that the p.H171R variant was highly deleterious and caused the TBXT structure instability. Molecular docking revealed that the p.H171R mutation disrupted the monomer stability which seemed to be crucial for maintaining the stability of the homodimer and consequently to the destabilization of the homodimer-DNA complex. On the other hand, we hypothesized that mtDNA can be a modifier factor, so, the screening of the whole mtDNA showed a novel heteroplasmic m.10150T > A (p.M31K) variation in the MT-ND3 gene. Further, qPCR analyses of the patient's blood excluded mtDNA depletion. Bioinformatic investigation revealed that the p.M31K mutation in the ND3 protein was highly deleterious and may cause the ND3 protein structure destabilization and could disturb the interaction between complex I subunits.

CONCLUSION

We described the possible role of mtDNA genetics on the pathogenesis of congenital scoliosis by hypothesizing that the presence of the homozygous variant in TBXT accounts for the CS phenotype in our patient and the MT-ND3 gene may act as a modifier gene.

Core planar cell polarity genes VANGL1 and VANGL2 in predisposition to congenital vertebral malformations

Congenital scoliosis (CS), affecting approximately 0.5 to 1 in 1,000 live births, is commonly caused by congenital vertebral malformations (CVMs) arising from aberrant somitogenesis or somite differentiation. While Wnt/ß-catenin signaling has been implicated in somite development, the function of Wnt/planar cell polarity (Wnt/PCP) signaling in this process remains unclear. Here, we investigated the role of Vangl1 and Vangl2 in vertebral development and found that their deletion causes vertebral anomalies resembling human CVMs. Analysis of exome sequencing data from multiethnic CS patients revealed a number of rare and deleterious variants in VANGL1 and VANGL2, many of which exhibited loss-of-function and dominant-negative effects. Zebrafish models confirmed the pathogenicity of these variants. Furthermore, we found that Vangl1 knock-in (p.R258H) mice exhibited vertebral malformations in a Vangl gene dose- and environment-dependent manner. Our findings highlight critical roles for PCP signaling in vertebral development and predisposition to CVMs in CS patients, providing insights into the molecular mechanisms underlying this disorder.

Genetic interrogation for sequence and copy number variants in systemic lupus erythematosus

Early-onset systemic lupus erythematosus presents with a more severe disease and is associated with a greater genetic burden, especially in patients from Black, Asian or Hispanic ancestries. Next-generation sequencing techniques, notably whole exome sequencing, have been extensively used in genomic interrogation studies to identify causal disease variants that are increasingly implicated in the development of autoimmunity. This Review discusses the known casual variants of polygenic and monogenic systemic lupus erythematosus and its implications under certain genetic disparities while suggesting an age-based sequencing strategy to aid in clinical diagnostics and patient management for improved patient care.

Molecular landscape of congenital vertebral malformations: recent discoveries and future directions

Vertebral malformations (VMs) pose a significant global health problem, causing chronic pain and disability. Vertebral defects occur as isolated conditions or within the spectrum of various congenital disorders, such as Klippel-Feil syndrome, congenital scoliosis, spondylocostal dysostosis, sacral agenesis, and neural tube defects. Although both genetic abnormalities and environmental factors can contribute to abnormal vertebral development, our knowledge on molecular mechanisms of numerous VMs is still limited. Furthermore, there is a lack of resource that consolidates the current knowledge in this field. In this pioneering review, we provide a comprehensive analysis of the latest research on the molecular basis of VMs and the association of the VMs-related causative genes with bone developmental signaling pathways. Our study identifies 118 genes linked to VMs, with 98 genes involved in biological pathways crucial for the formation of the vertebral column. Overall, the review summarizes the current knowledge on VM genetics, and provides new insights into potential involvement of biological pathways in VM pathogenesis. We also present an overview of available data regarding the role of epigenetic and environmental factors in VMs. We identify areas where knowledge is lacking, such as precise molecular mechanisms in which specific genes contribute to the development of VMs. Finally, we propose future research avenues that could address knowledge gaps.

Prenatal Diagnosis and Outcomes in Fetuses with Hemivertebra

Background: There are few studies on the burden of chromosomal abnormalities and single gene disorders in fetal hemivertebra (HV). We aim to investigate the cytogenetic and monogenic risk and evaluate prenatal outcomes of fetal HV. Method: This study included fetuses diagnosed with HV divided into two groups: isolated HV and non-isolated HV. Data on other sonographic structural anomalies, chromosomal and sub-chromosomal abnormalities, monogenic variations detected by WES, and prenatal outcomes are recorded and reviewed. Results: Among 109 fetal HV cases, forty-seven (43.1%) non-isolated HV cases were associated with structural anomalies. Chromosomal test results were available in 58 cases, identifying six (10.3%) chromosomal aberrations involved in four isolated and two non-isolated HV. WES identified four (likely) pathogenic variants in three cases among 16 fetuses with HV, involving three novel variants, 1250G > T and c.1277G> inherited from parents, respectively, in DLL3 and c.7213C > A ** in the FLNB. The live birth rate (LB) was higher in the isolated fetal HV group than in the non-isolated group (67.7% (42/62) vs. 12.5% (12/47), p < 0.001). Conclusion: This study emphasizes the risk of cytogenetic abnormalities in isolated HV. WES yields a diagnostic rate of 18.3% in HV with normal CMA, probably aiding the prenatal counseling and management of fetal HV.