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.

Investigation of canine caudal articular process dysplasia of thoracic vertebrae using computed tomography: Prevalence and characteristics

Caudal articular process (CAP) dysplasia is a congenital vertebral malformation that results from the failure of ossification center of articular process located in vertebrae, which includes aplasia or hypoplasia. In previous studies, it was reported to be common in small and chondrodystrophic dogs however, investigated in limited breeds. So we aimed to confirm the prevalence and the characteristics of CAP dysplasia in various breeds, and also to investigate the association of CAP dysplasia and spinal cord myelopathy in neurologically abnormal dogs. In this multicenter, retrospective study, the clinical records and thoracic vertebral column computed tomographic (CT) images of 717 dogs between February 2016 and August 2021 were included and 119 dogs which also underwent magnetic resonance imaging (MRI) examination were evaluated. Overall, 337 of 717 dogs (47.0%) had at least one thoracic CAP dysplasia and the prevalence of CAP dysplasia was significantly higher in dogs with a lower body weight (P < 0.0001). A total of 66.4% of toy breeds, 39.0% of small breeds, 20.2% of medium breeds, and 6.0% of large breeds were affected by at least one CAP dysplasia. The most affected vertebra was T4 in toy (48.1%) and small breeds (20.8%), and T5 in medium (20.8%) and large breeds (5.0%). In all groups, prevalence of CAP dysplasia between T1 and T9 was higher than post-diaphragmatic vertebrae (T10-T13). Fifty nine of 119 dogs which underwent both CT and MRI examination had symptoms of spinal cord myelopathy of T3-L3 and twenty-five of 59 dogs (42.3%) had at least one thoracic CAP dysplasia. In that 25 neurologically abnormal dogs, 41 sites of intervertebral disc disease (IVDD) were detected. However, only one dog had both CAP dysplasia and herniated disc at the same level. Also, CAP dysplasia associated non-compressive spinal myelopathy at the same level was found in the other dog. Association CAP dysplasia with spinal myelopathy is speculated but is not confirmed by this study.

Disruptive NADSYN1 Variants Implicated in Congenital Vertebral Malformations

Genetic perturbations in nicotinamide adenine dinucleotide de novo (NAD) synthesis pathway predispose individuals to congenital birth defects. The NADSYN1 encodes the final enzyme in the de novo NAD synthesis pathway and, therefore, plays an important role in NAD metabolism and organ embryogenesis. Biallelic mutations in the NADSYN1 gene have been reported to be causative of congenital organ defects known as VCRL syndrome (Vertebral-Cardiac-Renal-Limb syndrome). Here, we analyzed the genetic variants in NADSYN1 in an exome-sequenced cohort consisting of patients with congenital vertebral malformations (CVMs). A total number of eight variants in NADSYN1, including two truncating variants and six missense variants, were identified in nine unrelated patients. All enrolled patients presented multiple organ defects, with the involvement of either the heart, kidney, limbs, or liver, as well as intraspinal deformities. An in vitro assay using COS-7 cells demonstrated either significantly reduced protein levels or disrupted enzymatic activity of the identified variants. Our findings demonstrated that functional variants in NADSYN1 were involved in the complex genetic etiology of CVMs and provided further evidence for the causative NADSYN1 variants in congenital NAD Deficiency Disorder.

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

Congenital scoliosis (CS) is a lateral curvature of the spine resulting from congenital vertebral malformations (CVMs) and affects 0.5–1/1000 live births. The copy number variant (CNV) at chromosome 16p11.2 has been implicated in CVMs and recent studies identified a compound heterozygosity of 16p11.2 microdeletion and TBX6 variant/haplotype causing CS in multiple cohorts, which explains about 5–10% of the affected cases. Here, we studied the genetic etiology of CS by analyzing CNVs in a cohort of 67 patients with congenital hemivertebrae and 125 family controls. We employed both candidate gene and family-based approaches to filter CNVs called from whole exome sequencing data. This identified 12 CNVs in four scoliosis-associated genes (TBX6, NOTCH2, DSCAM, and SNTG1) as well as eight recessive and 64 novel rare CNVs in 15 additional genes. Some candidates, such as DHX40, NBPF20, RASA2, and MYSM1, have been found to be associated with syndromes with scoliosis or implicated in bone/spine development. In particular, the MYSM1 mutant mouse showed spinal deformities. Our findings suggest that, in addition to the 16p11.2 microdeletion, other CNVs are potentially important in predisposing to CS.

Increased TBX6 gene dosages induce congenital cervical vertebral malformations in humans and mice

BACKGROUND

Congenital vertebral malformations (CVMs) manifest with abnormal vertebral morphology. Genetic factors have been implicated in CVM pathogenesis, but the underlying pathogenic mechanisms remain unclear in most subjects. We previously reported that the human 16p11.2 BP4-BP5 deletion and its associated TBX6 dosage reduction caused CVMs. We aim to investigate the reciprocal 16p11.2 BP4-BP5 duplication and its potential genetic contributions to CVMs.

METHODS AND RESULTS

Patients who were found to carry the 16p11.2 BP4-BP5 duplication by chromosomal microarray analysis were retrospectively analysed for their vertebral phenotypes. The spinal assessments in seven duplication carriers showed that four (57%) presented characteristics of CVMs, supporting the contention that increased TBX6 dosage could induce CVMs. For further in vivo functional investigation in a model organism, we conducted genome editing of the upstream regulatory region of mouse Tbx6 using CRISPR-Cas9 and obtained three mouse mutant alleles (Tbx6up1 to Tbx6up3 ) with elevated expression levels of Tbx6. Luciferase reporter assays showed that the Tbx6up3 allele presented with the 160% expression level of that observed in the reference (+) allele. Therefore, the homozygous Tbx6up3/up3 mice could functionally mimic the TBX6 dosage of heterozygous carriers of 16p11.2 BP4-BP5 duplication (approximately 150%, ie, 3/2 gene dosage of the normal level). Remarkably, 60% of the Tbx6up3/up3 mice manifested with CVMs. Consistent with our observations in humans, the CVMs induced by increased Tbx6 dosage in mice mainly affected the cervical vertebrae.

CONCLUSION

Our findings in humans and mice consistently support that an increased TBX6 dosage contributes to the risk of developing cervical CVMs.

Congenital block vertebrae and intervertebral disc protrusion in a young cat

Case summary

A 6-month-old domestic shorthair cat was evaluated for proprioceptive ataxia of the pelvic limbs. Over 2 months, the cat became poorly ambulatory, paraparetic with proprioceptive ataxia and developed a firm, distended bladder with intermittent overflow urinary incontinence. Block vertebrae (T1-3, T4-5 and T10-11) and lordosis were identified on radiographs of the vertebral column. MRI revealed T3/4 intervertebral disc protrusion with severe extradural compression, secondary syringohydromyelia caudal to the protrusion and generalised intervertebral disc disease throughout the cervical and thoracic vertebrae. Dorsal laminectomy at T3/4 resulted in resolution of paraparesis and marked improvement in coordination and strength. Block vertebrae are usually considered an incidental finding. In this patient, angular deformation (lordosis) and adjacent segment disease probably contributed to clinically significant intervertebral disc degeneration and protrusion.

Relevance and novel information

There are few case reports in the literature of multiple congenital vertebral malformations causing neurological deficits in cats. This is the first reported case of successful surgical management of intervertebral disc protrusion, possibly secondary to block vertebrae and lordosis in a cat.

Delta Like-1 Gene Mutation: A Novel Cause of Congenital Vertebral Malformation

Skeletal development throughout the embryonic and postnatal phases is a dynamic process, based on bone remodeling and the balance between the activities of osteoclasts and osteoblasts modulating skeletal homeostasis. The Notch signaling pathway is a regulator of several developmental processes, and plays a crucial role in the development of the human skeleton by regulating the proliferation and differentiation of skeletal cells. The Delta Like-1 (DLL1) gene plays an important role in Notch signaling. We propose that an identified alteration in DLL1 protein may affect the downstream signaling. In this article, we present for the first time two siblings with a mutation in the DLL1 gene, presenting with congenital vertebral malformation. Using variable in silico prediction tools, it was predicted that the variant was responsible for the development of disease. Quantitative reverse-transcription polymerase chain reaction (PCR) for the Notch signaling pathway, using samples obtained from patients, showed a significant alteration in the expression of various related genes. Specifically, the expression of neurogenic locus notch homolog protein 1, SNW domain-containing protein 1, disintegrin, and metalloproteinase domain-containing proteins 10 and 17, was upregulated. In contrast, the expression of HEY1, HEY2, adenosine deaminase (ADA), and mastermind-like-1 (MAML-1) was downregulated. Furthermore, in a phosphokinase array, four kinases were significantly changed in patients, namely, p27, JANK1/2/3, mitogen- and stress-activated protein kinases 1 and 2, and focal adhesion kinase. Our results suggest an implication of a DLL1 defect related to the Notch signaling pathway, at least in part, in the morphologic abnormality observed in these patients. A limitation of our study was the low number of patients and samples. Further studies in this area are warranted to decipher the link between a DLL1 defect and skeletal abnormality.

Progress and perspective of TBX6 gene in congenital vertebral malformations

Congenital vertebral malformation is a series of significant health problems affecting a large number of populations. It may present as an isolated condition or as a part of an underlying syndromes occurring with other malformations and/or clinical features. Disruption of the genesis of paraxial mesoderm, somites or axial bones can result in spinal deformity. In the course of somitogenesis, the segmentation clock and the wavefront are the leading factors during the entire process in which TBX6 gene plays an important role. TBX6 is a member of the T-box gene family, and its important pathogenicity in spinal deformity has been confirmed. Several TBX6 gene variants and novel pathogenic mechanisms have been recently revealed, and will likely have significant impact in understanding the genetic basis for CVM. In this review, we describe the role which TBX6 plays during human spine development including its interaction with other key elements during the process of somitogenesis. We then systematically review the association between TBX6 gene variants and CVM associated phenotypes, highlighting an important and emerging role for TBX6 and human malformations.