Progress in the understanding of the genetic etiology of vertebral segmentation disorders in humans

Spinal scoliosis: insights into developmental mechanisms and animal models

Spinal scoliosis, a prevalent spinal deformity impacting both physical and mental well-being, has a significant genetic component, though the exact pathogenic mechanisms remain elusive. This review offers a comprehensive exploration of current research on embryonic spinal development, focusing on the genetic and biological intricacies governing axial elongation and straightening. Zebrafish, a vital model in developmental biology, takes a prominent role in understanding spinal scoliosis. Insights from zebrafish studies illustrate genetic and physiological aspects, including notochord development and cerebrospinal fluid dynamics, revealing the anomalies contributing to scoliosis. In this review, we acknowledge existing challenges, such as deciphering the unique dynamics of human spinal development, variations in physiological curvature, and disparities in cerebrospinal fluid circulation. Further, we emphasize the need for caution when extrapolating findings to humans and for future research to bridge current knowledge gaps. We hope that this review will be a beneficial frame of reference for the guidance of future studies on animal models and genetic research for spinal scoliosis.

Analyzing Risk Factors for Delayed Extubation Following Posterior Approach Surgery for Congenital Scoliosis: A Retrospective Cohort Study

STUDY DESIGN

Retrospective cohort study.

OBJECTIVES

Investigate the risk factors for delayed extubation after posterior approach orthopedic surgery in patients with congenital scoliosis.

METHODS

The clinical data of patients who received surgery for congenital scoliosis at the First Affiliated Hospital of Xinjiang Medical University between January 2021 and July 2023 have been gathered. Patients are categorized into the usual and the delayed extubation groups, depending on the duration of tracheal intubation after surgery. The study employs univariate and multivariate logistic regression models to examine the clinical characteristics of the two cohorts and discover potential risk factors linked to delayed extubation. In addition, a prediction model is created to visually depict the significance of each risk factor in terms of weight according to the nomogram.

RESULTS

A total of 119 patients (74.8% females), with a median age of 15 years, are included. A total of 32 patients, accounting for 26.9% of the sample, encountered delayed extubation. Additionally, 13 patients (10.9%) suffered perioperative complications, with pneumonia being the most prevalent. The multivariate regression analysis revealed that the number of osteotomy segments, postoperative hematocrit, postoperative Interleukin-6 levels, and weight are predictive risk factors for delayed extubation.

CONCLUSIONS

Postoperative hematocrit and Interleukin-6 level, weight, and number of osteotomy segments can serve as independent risk factors for predicting delayed extubation, with combined value to assist clinicians in evaluating the risk of delayed extubation of postoperative congenital scoliosis patients, improving the success rate of extubation, and reducing postoperative treatment time in the intensive care unit.

Concurrent of compound heterozygous variant of a novel in-frame deletion and the common hypomorphic haplotype in TBX6 and inherited 17q12 microdeletion in a fetus

BACKGROUND

TBX6, a member of the T-box gene family, encodes the transcription factor box 6 that is critical for somite segmentation in vertebrates. It is known that the compound heterozygosity of disruptive variants in trans with a common hypomorphic risk haplotype (T-C-A) in the TBX6 gene contribute to 10% of congenital scoliosis (CS) cases. The deletion of chromosome 17q12 is a rare cytogenetic abnormality, which often leads to renal cysts and diabetes mellitus. However, the affected individuals often exhibit clinical heterogeneity and incomplete penetrance.

METHODS

We here present a Chinese fetus who was shown to have CS by ultrasound examination at 17 weeks of gestation. Trio whole-exome sequencing (WES) was performed to investigate the underlying genetic defects of the fetus. In vitro functional experiments, including western-blotting and luciferase transactivation assay, were performed to determine the pathogenicity of the novel variant of TBX6.

RESULTS

WES revealed the fetus harbored a compound heterozygous variant of c.338_340del (p.Ile113del) and the common hypomorphic risk haplotype of the TBX6 gene. In vitro functional study showed the p.Ile113del variant had no impact on TBX6 expression, but almost led to complete loss of its transcriptional activity. In addition, we identified a 1.85 Mb deletion on 17q12 region in the fetus and the mother. Though there is currently no clinical phenotype associated with this copy number variation in the fetus, it can explain multiple renal cysts in the pregnant woman.

CONCLUSIONS

This study is the first to report a Chinese fetus with a single amino acid deletion variant and a T-C-A haplotype of TBX6. The clinical heterogeneity of 17q12 microdeletion poses significant challenges for prenatal genetic counseling. Our results once again suggest the complexity of prenatal genetic diagnosis.

Posterior Corrective Surgery for Type II Congenital Kyphosis: SRS-Schwab Grade 4 Osteotomy or Vertebral Column Resection?

OBJECTIVE

Surgical decision-making for congenital kyphosis (CK) with failure of anterior segmentation (type II) has been contradictory regarding the trade-off between the pursuit of correction rate and the inherent risk of the osteotomy procedure. This study was designed to compare the clinical and radiographic measurement in type II CK underwent SRS-Schwab Grade 4 osteotomy and vertebral column resection (VCR), the most-adapted osteotomy techniques for CK, and to propose the strategy to select between the two procedures.

METHODS

This retrospective observational comparative study evaluated surgical outcomes in type II CK patients underwent VCR or SRS-Schwab Grade 4 osteotomy at our institution between January 2015 and January 2020. Patients operated with VCR and SRS-Schwab Grade 4 osteotomy were allocated to Group 1 and Group 2 respectively. Radiographic parameters and SRS-22 quality of life metrics were assessed at pre-operation, post-operation, and during follow-up visits for both groups, allowing for a comprehensive comparison of surgical outcomes.

RESULTS

Thirty-one patients (19 patients in Group 1 and 12 patients in Group 2) aged 16.3 ± 10.4 years were recruited. Correction of segmental kyphosis was similar between groups (51.1 ± 17.6° in Group 1 and 48.4 ± 19.8° in Group 2, p = 0.694). Group 1 had significantly longer operation time (365.9 ± 81.2 vs 221.4 ± 78.9, p < 0.001) and more estimated blood loss (975.2 ± 275.8 ml vs 725.9 ± 204.3 mL, p = 0.011). Alert event of intraoperative sensory and motor evoked potential (SEP and MEP) monitoring was observed in 1 patient of Group 2. Both groups had 1 transient post operative neurological deficit respectively.

CONCLUSION

SRS-Schwab Grade 4 osteotomy was suitable for kyphotic mass when its apex is the upper unsegmented vertebrae or the neighboring disc, or when the apical vertebrae with an anterior/posterior (A/P) height ratio of vertebral body higher than 1/3. VCR is suitable when the apex is located within the unsegmented mass with its A/P height ratio lower than 1/3. Proper selection of VCR and SRS-Schwab Grade 4 osteotomy according to our strategy, could provide satisfying radiographic and clinical outcomes in type II CK patients during a minimum of 2 years follow-up. Patients undergoing VCR procedure might have longer operation time, more blood loss and higher incidence of peri- and post-operative complications.

Maternal risk factors for congenital vertebral formation and mixed defects: A population-based case-control study

Background

The etiology and risk factors of congenital vertebral anomalies are mainly unclear in isolated cases. Also, there are no reports on the risk factors for different subgroups of vertebral anomalies. Therefore, we assessed and identified potential maternal risk factors for these anomalies and hypothesized that diabetes, other chronic diseases, smoking, obesity, and medication in early pregnancy would increase the risk of congenital vertebral anomalies.

Methods

All cases with congenital vertebral anomalies were identified in the Finnish Register of Congenital Malformations from 1997 to 2016 for this nationwide register-based case-control study. Five matched controls without vertebral malformations were randomly selected. Analyzed maternal risk factors included maternal age, body mass index, parity, smoking, history of miscarriages, chronic diseases, and prescription drug purchases in early pregnancy.

Results

The register search identified 256 cases with congenital vertebral malformations. After excluding 66 syndromic cases, 190 non-syndromic malformations (74 formation defects, 4 segmentation defects, and 112 mixed anomalies) were included in the study. Maternal smoking was a significant risk factor for formation defects (adjusted odds ratio 2.33, 95% confidence interval 1.21-4.47). Also, pregestational diabetes (adjusted odds ratio 8.53, 95% confidence interval 2.33-31.20) and rheumatoid arthritis (adjusted odds ratio 13.19, 95% confidence interval 1.31-132.95) were associated with mixed vertebral anomalies.

Conclusion

Maternal pregestational diabetes and rheumatoid arthritis were associated with an increased risk of mixed vertebral anomalies. Maternal smoking increases the risk of formation defects and represents an avoidable risk factor for congenital scoliosis.

Level of evidence

III.

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.

Deep phenotyping of the neuroimaging and skeletal features in KBG syndrome: a study of 53 patients and review of the literature

BACKGROUND

KBG syndrome is caused by haploinsufficiency of ANKRD11 and is characterised by macrodontia of upper central incisors, distinctive facial features, short stature, skeletal anomalies, developmental delay, brain malformations and seizures. The central nervous system (CNS) and skeletal features remain poorly defined.

METHODS

CNS and/or skeletal imaging were collected from molecularly confirmed individuals with KBG syndrome through an international network. We evaluated the original imaging and compared our results with data in the literature.

RESULTS

We identified 53 individuals, 44 with CNS and 40 with skeletal imaging. Common CNS findings included incomplete hippocampal inversion and posterior fossa malformations; these were significantly more common than previously reported (63.4% and 65.9% vs 1.1% and 24.7%, respectively). Additional features included patulous internal auditory canal, never described before in KBG syndrome, and the recurrence of ventriculomegaly, encephalic cysts, empty sella and low-lying conus medullaris. We found no correlation between these structural anomalies and epilepsy or intellectual disability. Prevalent skeletal findings comprised abnormalities of the spine including scoliosis, coccygeal anomalies and cervical ribs. Hand X-rays revealed frequent abnormalities of carpal bone morphology and maturation, including a greater delay in ossification compared with metacarpal/phalanx bones.

CONCLUSION

This cohort enabled us to describe the prevalence of very heterogeneous neuroradiological and skeletal anomalies in KBG syndrome. Knowledge of the spectrum of such anomalies will aid diagnostic accuracy, improve patient care and provide a reference for future research on the effects of ANKRD11 variants in skeletal and brain development.

Exploring the association between congenital vertebral malformations and neural tube defects

Congenital vertebral malformations (CVMs) and neural tube defects (NTDs) are common birth defects affecting the spine and nervous system, respectively, due to defects in somitogenesis and neurulation. Somitogenesis and neurulation rely on factors secreted from neighbouring tissues and the integrity of the axial structure. Crucial signalling pathways like Wnt, Notch and planar cell polarity regulate somitogenesis and neurulation with significant crosstalk. While previous studies suggest an association between CVMs and NTDs, the exact mechanism underlying this relationship remains unclear. In this review, we explore embryonic development, signalling pathways and clinical phenotypes involved in the association between CVMs and NTDs. Moreover, we provide a summary of syndromes that exhibit occurrences of both CVMs and NTDs. We aim to provide insights into the potential mechanisms underlying the association between CVMs and NTDs, thereby facilitating clinical diagnosis and management of these anomalies.

COL11A2 as a candidate gene for vertebral malformations and congenital scoliosis

Human vertebral malformations (VMs) have an estimated incidence of 1/2000 and are associated with significant health problems including congenital scoliosis (CS) and recurrent organ system malformation syndromes such as VACTERL (vertebral anomalies; anal abnormalities; cardiac abnormalities; tracheo-esophageal fistula; renal anomalies; limb anomalies). The genetic cause for the vast majority of VMs are unknown. In a CS/VM patient cohort, three COL11A2 variants (R130W, R1407L and R1413H) were identified in two patients with cervical VM. A third patient with a T9 hemivertebra and the R130W variant was identified from a separate study. These substitutions are predicted to be damaging to protein function, and R130 and R1407 residues are conserved in zebrafish Col11a2. To determine the role for COL11A2 in vertebral development, CRISPR/Cas9 was used to create a nonsense mutation (col11a2L642*) as well as a full gene locus deletion (col11a2del) in zebrafish. Both col11a2L642*/L642* and col11a2del/del mutant zebrafish exhibit vertebral fusions in the caudal spine, which form due to mineralization across intervertebral segments. To determine the functional consequence of VM-associated variants, we assayed their ability to suppress col11a2del VM phenotypes following transgenic expression within the developing spine. While wildtype col11a2 expression suppresses fusions in col11a2del/+ and col11a2del/del backgrounds, patient missense variant-bearing col11a2 failed to rescue the loss-of-function phenotype in these animals. These results highlight an essential role for COL11A2 in vertebral development and support a pathogenic role for two missense variants in CS.

Maternal Risk Factors for Congenital Vertebral Anomalies: A Population-Based Study

BACKGROUND

The spectrum of congenital vertebral defects varies from benign lesions to severe, life-threatening conditions. The etiology and maternal risk factors remain mainly unclear in isolated cases. Hence, we aimed to assess and identify potential maternal risk factors for these anomalies. Based on previous studies, we hypothesized that maternal diabetes, smoking, advanced maternal age, obesity, chronic diseases, and medication used during the first trimester of pregnancy might increase the risk of congenital vertebral malformations.

METHODS

We performed a nationwide register-based case-control study. All cases with vertebral anomalies (including live births, stillbirths, and terminations for fetal anomaly) were identified in the Finnish Register of Congenital Malformations from 1997 to 2016. Five matched controls from the same geographic region were randomly selected for each case. Analyzed maternal risk factors included age, body mass index (BMI), parity, smoking, history of miscarriages, chronic diseases, and prescription drugs dispensed during the first trimester of pregnancy.

RESULTS

In total, 256 cases with diagnosed congenital vertebral anomalies were identified. After excluding 66 malformations associated with known syndromes, 190 nonsyndromic malformation cases were included. These were compared with 950 matched controls. Maternal pregestational diabetes was a significant risk factor for congenital vertebral anomalies (adjusted odds ratio [OR], 7.30 [95% confidence interval (CI), 2.53 to 21.09). Also, rheumatoid arthritis (adjusted OR, 22.91 [95% CI, 2.67 to 196.40]), estrogens (adjusted OR, 5.30 [95% CI, 1.57 to 17.8]), and heparins (adjusted OR, 8.94 [95% CI, 1.38 to 57.9]) were associated with elevated risk. In a sensitivity analysis using imputation, maternal smoking was also significantly associated with an elevated risk (adjusted OR, 1.57 [95% CI, 1.05 to 2.34]).

CONCLUSIONS

Maternal pregestational diabetes and rheumatoid arthritis increased the risk of congenital vertebral anomalies. Also, estrogens and heparins, both of which are frequently used in assisted reproductive technologies, were associated with an increased risk. Sensitivity analysis suggested an increased risk of vertebral anomalies with maternal smoking, warranting further studies.

LEVEL OF EVIDENCE

Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.

Molecular diagnosis and novel genes and phenotypes in a pediatric thoracic insufficiency cohort

Thoracic insufficiency syndromes are a genetically and phenotypically heterogeneous group of disorders characterized by congenital abnormalities or progressive deformation of the chest wall and/or vertebrae that result in restrictive lung disease and compromised respiratory capacity. We performed whole exome sequencing on a cohort of 42 children with thoracic insufficiency to elucidate the underlying molecular etiologies of syndromic and non-syndromic thoracic insufficiency and predict extra-skeletal manifestations and disease progression. Molecular diagnosis was established in 24/42 probands (57%), with 18/24 (75%) probands having definitive diagnoses as defined by laboratory and clinical criteria and 6/24 (25%) probands having strong candidate genes. Gene identified in cohort patients most commonly encoded components of the primary cilium, connective tissue, and extracellular matrix. A novel association between KIF7 and USP9X variants and thoracic insufficiency was identified. We report and expand the genetic and phenotypic spectrum of a cohort of children with thoracic insufficiency, reinforce the prevalence of extra-skeletal manifestations in thoracic insufficiency syndromes, and expand the phenotype of KIF7 and USP9X-related disease to include thoracic insufficiency.

Zebrafish: an important model for understanding scoliosis

Scoliosis is a common spinal deformity that considerably affects the physical and psychological health of patients. Studies have shown that genetic factors play an important role in scoliosis. However, its etiopathogenesis remain unclear, partially because of the genetic heterogeneity of scoliosis and the lack of appropriate model systems. Recently, the development of efficient gene editing methods and high-throughput sequencing technology has made it possible to explore the underlying pathological mechanisms of scoliosis. Owing to their susceptibility for developing scoliosis and high genetic homology with human, zebrafish are increasingly being used as a model for scoliosis in developmental biology, genetics, and clinical medicine. Here, we summarize the recent advances in scoliosis research on zebrafish and discuss the prospects of using zebrafish as a scoliosis model.

Abnormal TNS3 gene methylation in patients with congenital scoliosis

Background

Congenital scoliosis (CS) is a congenital deformity of the spine resulting from abnormal and asymmetrical development of vertebral bodies during pregnancy. However, the etiology and mechanism of CS remain unclear. Epigenetics is the study of heritable variations in gene expression outside of changes in nucleotide sequence. Among these, DNA methylation was described first and is the most characteristic and most stable epigenetic mechanism. Therefore, in this study, we aim to explore the association between genome methylation and CS which are not been studied before.

Methods

Two pairs of monozygotic twins were included, with each pair involving one individual with and one without CS. Agilent SureSelect XT Human Methyl-Sequencing was used for genome methylation sequencing. MethylTarget was used to detect methylation levels in target regions. Immunohistochemistry was performed to visualize expression of associated genes in candidate regions.

Results

A total of 75 differentially methylated regions were identified, including 24 with an increased methylation level and 51 with a decreased methylation level in the CS group. Nine of the differentially methylated regions were selected (TNS3, SEMAC3, GPR124, MEST, DLK1, SNTG1, PPIB, DEF8, and GRHL2). The results showed that the methylation level of the promoter region of TNS3 was 0.72 ± 0.08 in the CS group and 0.43 ± 0.06 in the control group (p = 0.00070 < 0.01). There was no significant difference in the degree of methylation of SEMAC3, GPR124, MEST, DLK1, SNTG1, PPIB, DEF8, or GRHL2 between the two groups. Immunohistochemistry showed significantly decreased TNS3 expression in the cartilage of the articular process in CS (CS: 0.011 ± 0.002; control: 0.018 ± 0.006, P = 0.003 < 0.01).

Conclusion

Compared with the control group, high-level methylation of the TNS3 promoter region and low TNS3 expression in the cartilage layer of the articular process characterize CS. Thus, DNA methylation and TNS3 may play important roles in the pathogenesis of CS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05730-x.

Towards clinical applications of in vitro-derived axial progenitors

The production of the tissues that make up the mammalian embryonic trunk takes place in a head-tail direction, via the differentiation of posteriorly-located axial progenitor populations. These include bipotent neuromesodermal progenitors (NMPs), which generate both spinal cord neurectoderm and presomitic mesoderm, the precursor of the musculoskeleton. Over the past few years, a number of studies have described the derivation of NMP-like cells from mouse and human pluripotent stem cells (PSCs). In turn, these have greatly facilitated the establishment of PSC differentiation protocols aiming to give rise efficiently to posterior mesodermal and neural cell types, which have been particularly challenging to produce using previous approaches. Moreover, the advent of 3-dimensional-based culture systems incorporating distinct axial progenitor-derived cell lineages has opened new avenues toward the functional dissection of early patterning events and cell vs non-cell autonomous effects. Here, we provide a brief overview of the applications of these cell types in disease modelling and cell therapy and speculate on their potential uses in the future.

Factors Associated with Postoperative Respiratory Complications following Posterior Spinal Instrumentation in Children with Early-onset Scoliosis

Objective

To investigate the incidence and risk factors of postoperative respiratory complications (PRCs) in children with early‐onset scoliosis (EOS) following posterior spine deformity surgery (PSDS) based on growth‐friendly techniques, so as to help improve the safety of surgery.

Methods

A retrospective study of children with EOS admitted for PSDS based on growth‐friendly techniques from October 2013 to October 2018 was reviewed at a single center. There were 73 children (30 boys, 43 girls) who fulfilled the criteria in this research. The mean age of the patients was 7 ± 6.2 years. Patients were divided into the groups with and without PRCs. Variables that might affect the PRCs during the perioperative period, including general factors, radiographic factors, laboratory factors and surgical factors, were analyzed using univariate analysis to evaluate the potential risk factors. The variables that were significantly different were further analyzed by binary logistic regression analysis to identify the independent factors of PRCs.

Results

All the 73 children included 42 idiopathic scoliosis (57.5%), 12 congenital scoliosis (16.4%), 10 syndromic scoliosis (13.7%) and nine neuromuscular scoliosis (12.3%). PRCs were detected in 16 children (21.9%) with nine different PRCs. The total frequency of detected PRCs was 54, including pleural effusion (25.9%), postoperative pneumonia (20.4%), hypoxemia (18.5%), atelectasis (14.8%), prolonged intubation with mechanical positive pressure ventilatory support (PIMPPVS) (7.4%), bronchospasm (3.7%), reintubation (3.7%), delayed extubation (3.7%) and pneumothorax (1.9%). Results of univariate testing demonstrated that the following six variables were statistically different (P < 0.05): nonidiopathic scoliosis, combined with pulmonary comorbidities, pretransferrin < 200 mg/dL, prealbumin < 3.5 g/dL, anesthesia time ≥ 300 min and blood loss to total blood volume ratio (BL/TBV) ≥ 15%. Binary logistic regression analysis confirmed that BL/TBV≥15% (odd ratio OR = 29.188, P = 0.010), combined with pulmonary comorbidities (OR = 19.216, P = 0.012), pretransferrin < 200 mg/dL (OR = 11.503, p = 0.024), and nonidiopathic scoliosis (OR = 7.632, P = 0.046) were positively linear correlated with PRCs in children with EOS following PSDS.

Conclusion

PRCs has a higher incidence in children with EOS following PSDS. BL/TBV ≥15%, combined with pulmonary comorbidities, pre‐transferrin < 200 mg/dL, and nonidiopathic scoliosis play an important role for the development of PRCs in this population.

Increasing Prevalence and High Risk of Associated Anomalies in Congenital Vertebral Defects: A Population-based Study

BACKGROUND

Congenital vertebral anomalies are a heterogeneous group of diagnoses, and studies on their epidemiology are sparse. Our aim was to investigate the national prevalence and mortality of these anomalies, and to identify associated anomalies.

METHODS

We conducted a population-based nationwide register study and identified all cases with congenital vertebral anomalies in the Finnish Register of Congenital Malformations from 1997 to 2016 including live births, stillbirths, and elective terminations of pregnancy because of major fetal anomalies. Cases were categorized based on the recorded diagnoses, associated major anomalies were analyzed, and prevalence and infant mortality were calculated.

RESULTS

We identified 255 cases of congenital vertebral anomalies. Of these, 92 (36%) were diagnosed with formation defects, 18 (7.1%) with segmentation defects, and 145 (57%) had mixed vertebral anomalies. Live birth prevalence was 1.89 per 10,000, and total prevalence was 2.20/10,000, with a significantly increasing trend over time (P<0.001). Overall infant mortality was 8.2% (18/219); 3.5% (3/86) in patients with formation defects, 5.6% (1/18) in segmentation defects, and 12.2% (14/115) in mixed vertebral anomalies (P=0.06). Co-occurring anomalies and syndromes were associated with increased mortality, P=0.006. Majority of the cases (82%) were associated with other major anomalies affecting most often the heart, limbs, and digestive system.

CONCLUSIONS

In conclusion, the prevalence of congenital vertebral anomalies is increasing significantly in Finnish registers. Detailed and systematic examination is warranted in this patient population to identify underlying comorbidities as the majority of cases are associated with congenital major anomalies.

LEVEL OF EVIDENCE

Level III.

Developments in Congenital Scoliosis and Related Research from 1992 to 2021: A Thirty-Year Bibliometric Analysis

BACKGROUND

Many studies, mainly original articles and reviews, have been reported on congenital scoliosis (CS), but there is a lack of bibliometric analyses. This study aimed to systematically analyze the developments and focuses in CS and related research fields.

METHODS

Data were retrieved from the Web of Science Core Collection database, and the top 100 most-cited studies were analyzed emphatically. The Web of Science Results Analysis and Citation Report was used to analyze different aspects of the literature. CiteSpace was used to analyze the cooperation network, reference co-citation, burst keywords, and burst citations.

RESULTS

The final analysis included 749 studies. CS and related research has been rapidly expanding. Several journals have published relevant studies and most-cited studies on this topic. Cooperation was noted among authors, institutions, and countries/regions in multiple instances. Surgical techniques (hemivertebra resection/posterior vertebral column resection/vertical expandable prosthetic titanium rib/double approach/grade 4 osteotomy) was one of the most common research focuses. In addition, research on genetics and molecular biology related to CS has become an emerging trend as a result of advances in basic science.

CONCLUSIONS

Over time, research on CS and in related fields has gained greater attention and has been expanding continuously, showing a trend toward globalization. We recommend that researchers focus on the progress of surgical techniques, advances in molecular biology and genetics, and characteristics of CS. The top clusters, most-cited articles, and references with the strongest burst citations should be studied further.

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.

3D-printed drill guide template, a promising tool to improve pedicle screw placement accuracy in spinal deformity surgery: A systematic review and meta-analysis

PURPOSE

This study aimed to compare the pedicle screw placement accuracy and surgical outcomes between 3D-printed (3DP) drill guide template technique and freehand technique in spinal deformity surgery.

METHODS

A comprehensive systematic literature search of databases (PubMed, Embase, Cochrane Library, and Web of Science) was conducted. The meta-analysis compared the pedicle screw placement accuracy and other important surgical outcomes between the two techniques.

RESULTS

A total of seven studies were included in the meta-analysis, comprising 87 patients with 1384 pedicle screws placed by 3DP drill guide templates and 88 patients with 1392 pedicle screws placed by freehand technique. The meta-analysis results revealed that the 3DP template technique was significantly more accurate than the freehand technique to place pedicle screws and had a higher rate of excellently placed screws (OR 2.22, P < 0.001) and qualifiedly placed screws (OR 3.66, P < 0.001), and a lower rate of poorly placed screws (OR 0.23, P < 0.001). The mean placement time per screw (WMD-1.99, P < 0.05), total screw placement time (WMD-27.86, P < 0.001), and blood loss (WMD-104.58, P < 0.05) were significantly reduced in the 3DP template group compared with the freehand group. Moreover, there was no significant statistical difference between the two techniques in terms of the operation time and correction rate of main bend curve.

CONCLUSIONS

This study demonstrated that the 3DP drill guide template was a promising tool for assisting the pedicle screw placement in spinal deformity surgery and deserved further promotion.

A review of the hemivertebrae and hemivertebra resection

Hemivertebra (HV) is a congenital spinal abnormality. Most hemivertebrae have normal growth plates so create a progressive deformity with growth leading to asymmetric loads on adjacent vertebrae which also show an asymmetric growth. We review the condition and its treatment.

Fgf4 maintains Hes7 levels critical for normal somite segmentation clock function

During vertebrate development, the presomitic mesoderm (PSM) periodically segments into somites, which will form the segmented vertebral column and associated muscle, connective tissue, and dermis. The periodicity of somitogenesis is regulated by a segmentation clock of oscillating Notch activity. Here, we examined mouse mutants lacking only Fgf4 or Fgf8, which we previously demonstrated act redundantly to prevent PSM differentiation. Fgf8 is not required for somitogenesis, but Fgf4 mutants display a range of vertebral defects. We analyzed Fgf4 mutants by quantifying mRNAs fluorescently labeled by hybridization chain reaction within Imaris-based volumetric tissue subsets. These data indicate that FGF4 maintains Hes7 levels and normal oscillatory patterns. To support our hypothesis that FGF4 regulates somitogenesis through Hes7, we demonstrate genetic synergy between Hes7 and Fgf4, but not with Fgf8. Our data indicate that Fgf4 is potentially important in a spectrum of human Segmentation Defects of the Vertebrae caused by defective Notch oscillations.

A comprehensive diagnostic approach combining phylogenetic disease bracketing and CT imaging reveals osteomyelitis in a Tyrannosaurus rex

Traditional palaeontological techniques of disease characterisation are limited to the analysis of osseous fossils, requiring several lines of evidence to support diagnoses. This study presents a novel stepwise concept for comprehensive diagnosis of pathologies in fossils by computed tomography imaging for morphological assessment combined with likelihood estimation based on systematic phylogenetic disease bracketing. This approach was applied to characterise pathologies of the left fibula and fused caudal vertebrae of the non-avian dinosaur Tyrannosaurus rex. Initial morphological assessment narrowed the differential diagnosis to neoplasia or infection. Subsequent data review from phylogenetically closely related species at the clade level revealed neoplasia rates as low as 3.1% and 1.8%, while infectious-disease rates were 32.0% and 53.9% in extant dinosaurs (birds) and non-avian reptiles, respectively. Furthermore, the survey of literature revealed that within the phylogenetic disease bracket the oldest case of bone infection (osteomyelitis) was identified in the mandible of a 275-million-year-old captorhinid eureptile Labidosaurus. These findings demonstrate low probability of a neoplastic aetiology of the examined pathologies in the Tyrannosaurus rex and in turn, suggest that they correspond to multiple foci of osteomyelitis.

Development of a straight vertebrate body axis

The vertebrate body plan is characterized by the presence of a segmented spine along its main axis. Here, we examine the current understanding of how the axial tissues that are formed during embryonic development give rise to the adult spine and summarize recent advances in the field, largely focused on recent studies in zebrafish, with comparisons to amniotes where appropriate. We discuss recent work illuminating the genetics and biological mechanisms mediating extension and straightening of the body axis during development, and highlight open questions. We specifically focus on the processes of notochord development and cerebrospinal fluid physiology, and how defects in those processes may lead to scoliosis.

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.

KIAA1217: A novel candidate gene associated with isolated and syndromic vertebral malformations

Vertebral malformations (VMs) are caused by alterations in somitogenesis and may occur in association with other congenital anomalies. The genetic etiology of most VMs remains unknown and their identification may facilitate the development of novel therapeutic and prevention strategies. Exome sequencing was performed on both the discovery cohort of nine unrelated probands from the USA with VMs and the replication cohort from China (Deciphering Disorders Involving Scoliosis & COmorbidities study). The discovery cohort was analyzed using the PhenoDB analysis tool. Heterozygous and homozygous, rare and functional variants were selected and evaluated for their ClinVar, HGMD, OMIM, GWAS, mouse model phenotypes, and other annotations to identify the best candidates. Genes with candidate variants in three or more probands were selected. The replication cohort was analyzed by another in-house developed pipeline. We identified rare heterozygous variants in KIAA1217 in four out of nine probands in the discovery cohort and in five out of 35 probands in the replication cohort. Collectively, we identified 11 KIAA1217 rare variants in 10 probands, three of which have not been described in gnomAD and one of which is a nonsense variant. We propose that genetic variations of KIAA1217 may contribute to the etiology of VMs.

Notochord vacuoles absorb compressive bone growth during zebrafish spine formation

The vertebral column or spine assembles around the notochord rod which contains a core made of large vacuolated cells. Each vacuolated cell possesses a single fluid-filled vacuole, and loss or fragmentation of these vacuoles in zebrafish leads to spine kinking. Here, we identified a mutation in the kinase gene dstyk that causes fragmentation of notochord vacuoles and a severe congenital scoliosis-like phenotype in zebrafish. Live imaging revealed that Dstyk regulates fusion of membranes with the vacuole. We find that localized disruption of notochord vacuoles causes vertebral malformation and curving of the spine axis at those sites. Accordingly, in dstyk mutants the spine curves increasingly over time as vertebral bone formation compresses the notochord asymmetrically, causing vertebral malformations and kinking of the axis. Together, our data show that notochord vacuoles function as a hydrostatic scaffold that guides symmetrical growth of vertebrae and spine formation.

Dstyk mutation leads to congenital scoliosis-like vertebral malformations in zebrafish via dysregulated mTORC1/TFEB pathway

Congenital scoliosis (CS) is a complex genetic disorder characterized by vertebral malformations. The precise etiology of CS is not fully defined. Here, we identify that mutation in dual serine/threonine and tyrosine protein kinase (dstyk) lead to CS-like vertebral malformations in zebrafish. We demonstrate that the scoliosis in dstyk mutants is related to the wavy and malformed notochord sheath formation and abnormal axial skeleton segmentation due to dysregulated biogenesis of notochord vacuoles and notochord function. Further studies show that DSTYK is located in late endosomal/lysosomal compartments and is involved in the lysosome biogenesis in mammalian cells. Dstyk knockdown inhibits notochord vacuole and lysosome biogenesis through mTORC1-dependent repression of TFEB nuclear translocation. Inhibition of mTORC1 activity can rescue the defect in notochord vacuole biogenesis and scoliosis in dstyk mutants. Together, our findings reveal a key role of DSTYK in notochord vacuole biogenesis, notochord morphogenesis and spine development through mTORC1/TFEB pathway.

Congenital scoliosis is a complex genetic disorder characterized by vertebral malformation. Here, the authors demonstrate that loss of dstyk leads to scoliosis in zebrafish due to dysregulated biogenesis of notochord vacuoles and that DSTYK is required for lysosome biogenesis through mTORC1 regulation.

TBX6 missense variants expand the mutational spectrum in a non-Mendelian inheritance disease

Congenital scoliosis (CS) is a birth defect with variable clinical and anatomical manifestations due to spinal malformation. The genetic etiology underlying about 10% of CS cases in the Chinese population is compound inheritance by which the gene dosage is reduced below that of haploinsufficiency. In this genetic model, the trait manifests as a result of the combined effect of a rare variant and common pathogenic variant allele at a locus. From exome sequencing (ES) data of 523 patients in Asia and two patients in Texas, we identified six TBX6 gene-disruptive variants from 11 unrelated CS patients via ES and in vitro functional testing. The in trans mild hypomorphic allele was identified in 10 of the 11 subjects; as anticipated these 10 shared a similar spinal deformity of hemivertebrae. The remaining case has a homozygous variant in TBX6 (c.418C>T) and presents a more severe spinal deformity phenotype. We found decreased transcriptional activity and abnormal cellular localization as the molecular mechanisms for TBX6 missense loss-of-function alleles. Expanding the mutational spectrum of TBX6 pathogenic alleles enabled an increased molecular diagnostic detection rate, provided further evidence for the gene dosage-dependent genetic model underlying CS, and refined clinical classification.

TBX6 compound inheritance leads to congenital vertebral malformations in humans and mice

Congenital vertebral malformations (CVMs) are associated with human TBX6 compound inheritance that combines a rare null allele and a common hypomorphic allele at the TBX6 locus. Our previous in vitro evidence suggested that this compound inheritance resulted in a TBX6 gene dosage of less than haploinsufficiency (i.e. <50%) as a potential mechanism of TBX6-associated CVMs. To further investigate this pathogenetic model, we ascertained and collected 108 Chinese CVM cases and found that 10 (9.3%) of them carried TBX6 null mutations in combination with common hypomorphic variants at the second TBX6 allele. For in vivo functional verification and genetic analysis of TBX6 compound inheritance, we generated both null and hypomorphic mutations in mouse Tbx6 using the CRISPR-Cas9 method. These Tbx6 mutants are not identical to the patient variants at the DNA sequence level, but instead functionally mimic disease-associated TBX6 variants. Intriguingly, as anticipated by the compound inheritance model, a high penetrance of CVM phenotype was only observed in the mice with combined null and hypomorphic alleles of Tbx6. These findings are consistent with our experimental observations in humans and supported the dosage effect of TBX6 in CVM etiology. In conclusion, our findings in the newly collected human CVM subjects and Tbx6 mouse models consistently support the contention that TBX6 compound inheritance causes CVMs, potentially via a gene dosage-dependent mechanism. Furthermore, mouse Tbx6 mutants mimicking human CVM-associated variants will be useful models for further mechanistic investigations of CVM pathogenesis in the cases associated with TBX6.

Regulatory Network of the Scoliosis-Associated Genes Establishes Rostrocaudal Patterning of Somites in Zebrafish

Gene regulatory networks govern pattern formation and differentiation during embryonic development. Segmentation of somites, precursors of the vertebral column among other tissues, is jointly controlled by temporal signals from the segmentation clock and spatial signals from morphogen gradients. To explore how these temporal and spatial signals are integrated, we combined time-controlled genetic perturbation experiments with computational modeling to reconstruct the core segmentation network in zebrafish. We found that Mesp family transcription factors link the temporal information of the segmentation clock with the spatial action of the fibroblast growth factor signaling gradient to establish rostrocaudal (head to tail) polarity of segmented somites. We further showed that cells gradually commit to patterning by the action of different genes at different spatiotemporal positions. Our study provides a blueprint of the zebrafish segmentation network, which includes evolutionarily conserved genes that are associated with the birth defect congenital scoliosis in humans.

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A core network establishes rostrocaudal polarity of segmented somites in zebrafish

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mesp genes link the segmentation clock with the FGF signaling gradient

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Gradual patterning is done by the action of different genes at different positions

A comprehensive review of the diagnosis and management of congenital scoliosis

PURPOSE

To provide the reader with a comprehensive but concise understanding of congenital scoliosis METHODS: We have undertaken to summarize available literature on the pathophysiology, epidemiology, and management of congenital scoliosis.

RESULTS

Congenital scoliosis represents 10% of pediatric spine deformity and is a developmental error in segmentation, formation, or a combination of both leading to curvature of the spine. Treatment options are complicated by balancing growth potential with curve severity. Often associated abnormalities of cardiac, genitourinary, or intraspinal systems are concurrent and should be evaluated as part of the diagnostic work-up. Management balances the risk of progression, growth potential, lung development/function, and associated risks. Surgical treatment options involve growth-permitting systems or fusions.

CONCLUSION

Congenital scoliosis is a complex spinal problem associated with many other anomalous findings. Treatment options are diverse but enable optimization of management and care of these children.

An N-Ethyl-N-Nitrosourea (ENU) Mutagenized Mouse Model for Autosomal Dominant Nonsyndromic Kyphoscoliosis Due to Vertebral Fusion

Kyphosis and scoliosis are common spinal disorders that occur as part of complex syndromes or as nonsyndromic, idiopathic diseases. Familial and twin studies implicate genetic involvement, although the causative genes for idiopathic kyphoscoliosis remain to be identified. To facilitate these studies, we investigated progeny of mice treated with the chemical mutagen N-ethyl-N-nitrosourea (ENU) and assessed them for morphological and radiographic abnormalities. This identified a mouse with kyphoscoliosis due to fused lumbar vertebrae, which was inherited as an autosomal dominant trait; the phenotype was designated as hereditary vertebral fusion (HVF) and the locus as Hvf. Micro-computed tomography (μCT) analysis confirmed the occurrence of nonsyndromic kyphoscoliosis due to fusion of lumbar vertebrae in HVF mice, consistent with a pattern of blocked vertebrae due to failure of segmentation. μCT scans also showed the lumbar vertebral column of HVF mice to have generalized disc narrowing, displacement with compression of the neural spine, and distorted transverse processes. Histology of lumbar vertebrae revealed HVF mice to have irregularly shaped vertebral bodies and displacement of intervertebral discs and ossification centers. Genetic mapping using a panel of single nucleotide polymorphic (SNP) loci arranged in chromosome sets and DNA samples from 23 HVF (eight males and 15 females) mice, localized Hvf to chromosome 4A3 and within a 5-megabase (Mb) region containing nine protein coding genes, two processed transcripts, three microRNAs, five small nuclear RNAs, three large intergenic noncoding RNAs, and 24 pseudogenes. However, genome sequence analysis in this interval did not identify any abnormalities in the coding exons, or exon-intron boundaries of any of these genes. Thus, our studies have established a mouse model for a monogenic form of nonsyndromic kyphoscoliosis due to fusion of lumbar vertebrae, and further identification of the underlying genetic defect will help elucidate the molecular mechanisms involved in kyphoscoliosis. © 2018 The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Olfactomedin-like protein OLFML1 inhibits Hippo signaling and mineralization in osteoblasts

Congenital scoliosis is a lateral curvature of the spine that is due to the presence of vertebral anomalies. Although genetic and environmental factors are involved in the pathogenesis of congenital scoliosis, the specific cause of only a small number of individuals has been identified to date. We identified a de novo missense mutation in the olfactomedin-like 1 (OLFML1) gene by whole-exome sequencing of a patient with congenital scoliosis. Then, we carried out further functional investigation in mice. An assessment of the tissue distribution of Olfml1 revealed it to be prominently expressed in developing skeletal tissues, specifically osteoblasts. Short hairpin RNA-mediated knockdown of Olfml1 in osteoblasts induced the translocation of Yes-associated protein (YAP) transcriptional coactivator from the cytoplasm to the nucleus, which accelerated the Hippo signaling pathway to promote osteoblast mineralization. In contrast, experimentally induced gain of function of Olfml1 retained YAP in the cytoplasm. There appears to exist a novel cell-autonomous mechanism by which osteoblasts avoid excess mineralization through Olfml1. Our results also indicate that mutation of OLFML1 leads to impaired osteoblast differentiation and abnormal development of bone tissue.

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.

Current Concepts - Congenital Scoliosis

Background:

Congenital scoliosis is one of the ‘difficult to treat’ scenarios which a spine surgeon has to face. Multiple factors including the age of child at presentation, no definite pattern of deformity and associated anomalies hinder the execution of the ideal treatment plan. All patients of congenital scoliosis need to be investigated in detail. X rays and MRI of spine is usually ordered first. Screening investigations to rule out VACTERL (Visceral, Anorectal, Cardiac, Tracheo-esophageal fistula, Renal and Lung) abnormalities are required. They are cardiac echocardiography and ultrasonography of abdomen and pelvis. CT scan is required to understand the complex deformity and is helpful in surgical planning.

Methods:

A comprehensive medical literature review was done to understand the current surgical and non surgical treatment options available. An attempt was made to specifically study limitations and advantages of each procedure.

Results:

The treatment of congenital scoliosis differs with respect to the age of presentation. In adults with curves more than 50 degrees or spinal imbalance the preferred treatment is osteotomy and correction. In children the goals are different and treatment strategy has to be varied according to the age of patient. A single or two level hemivertebra can easily be treated with hemivertebra excision and short segment fusion. However, more than 3 levels or multiple fused ribs and chest wall abnormalities require a guided growth procedure to prevent thoracic insufficiency syndrome. The goal of management in childhood is to allow guided spine growth till the child reaches 10 - 12 years of age, when a definitive fusion can be done. The current research needs to be directed more at the prevention and understanding the etiology of the disease. Till that time, diagnosing the disease early and treating it before the sequels set in, is of paramount importance.

Conclusion:

The primary aim of treatment of congenital scoliosis is to allow the expansion of chest and abdominal cavity, while keeping the deformity under control. Various methods can be categorized into definitive (hemivertebrectomy) or preventive (guided growth). Casting, Growth rods, Convex Epiphysiodesis are all guided growth measures. The guided growth procedure either ‘corrects the deformity’ or will have to be converted to a final fusion surgery once the child completes the spinal growth which is preferably done around 10 - 12 years of age. Future directions should aim at genetic counselling and early detection.

Osmotic and Heat Stress Effects on Segmentation

During vertebrate embryonic development, early skin, muscle, and bone progenitor populations organize into segments known as somites. Defects in this conserved process of segmentation lead to skeletal and muscular deformities, such as congenital scoliosis, a curvature of the spine caused by vertebral defects. Environmental stresses such as hypoxia or heat shock produce segmentation defects, and significantly increase the penetrance and severity of vertebral defects in genetically susceptible individuals. Here we show that a brief exposure to a high osmolarity solution causes reproducible segmentation defects in developing zebrafish (Danio rerio) embryos. Both osmotic shock and heat shock produce border defects in a dose-dependent manner, with an increase in both frequency and severity of defects. We also show that osmotic treatment has a delayed effect on somite development, similar to that observed in heat shocked embryos. Our results establish osmotic shock as an alternate experimental model for stress, affecting segmentation in a manner comparable to other known environmental stressors. The similar effects of these two distinct environmental stressors support a model in which a variety of cellular stresses act through a related response pathway that leads to disturbances in the segmentation process.

Mice with an N-Ethyl-N-Nitrosourea (ENU) Induced Tyr209Asn Mutation in Natriuretic Peptide Receptor 3 (NPR3) Provide a Model for Kyphosis Associated with Activation of the MAPK Signaling Pathway

Non-syndromic kyphosis is a common disorder that is associated with significant morbidity and has a strong genetic involvement; however, the causative genes remain to be identified, as such studies are hampered by genetic heterogeneity, small families and various modes of inheritance. To overcome these limitations, we investigated 12 week old progeny of mice treated with the chemical mutagen N-ethyl-N-nitrosourea (ENU) using phenotypic assessments including dysmorphology, radiography, and dual-energy X-ray absorptiometry. This identified a mouse with autosomal recessive kyphosis (KYLB). KYLB mice, when compared to unaffected littermates, had: thoraco-lumbar kyphosis, larger vertebrae, and increased body length and increased bone area. In addition, female KYLB mice had increases in bone mineral content and plasma alkaline phosphatase activity. Recombination mapping localized the Kylb locus to a 5.5Mb region on chromosome 15A1, which contained 51 genes, including the natriuretic peptide receptor 3 (Npr3) gene. DNA sequence analysis of Npr3 identified a missense mutation, Tyr209Asn, which introduced an N-linked glycosylation consensus sequence. Expression of wild-type NPR3 and the KYLB-associated Tyr209Asn NPR3 mutant in COS-7 cells demonstrated the mutant to be associated with abnormal N-linked glycosylation and retention in the endoplasmic reticulum that resulted in its absence from the plasma membrane. NPR3 is a decoy receptor for C-type natriuretic peptide (CNP), which also binds to NPR2 and stimulates mitogen-activated protein kinase (MAPK) signaling, thereby increasing the number and size of hypertrophic chondrocytes. Histomorphometric analysis of KYLB vertebrae and tibiae showed delayed endochondral ossification and expansion of the hypertrophic zones of the growth plates, and immunohistochemistry revealed increased p38 MAPK phosphorylation throughout the growth plates of KYLB vertebrae. Thus, we established a model of kyphosis due to a novel NPR3 mutation, in which loss of plasma membrane NPR3 expression results in increased MAPK pathway activation, causing elongation of the vertebrae and resulting in kyphosis.

TBX6 null variants and a common hypomorphic allele in congenital scoliosis

BACKGROUND

Congenital scoliosis is a common type of vertebral malformation. Genetic susceptibility has been implicated in congenital scoliosis.

METHODS

We evaluated 161 Han Chinese persons with sporadic congenital scoliosis, 166 Han Chinese controls, and 2 pedigrees, family members of which had a 16p11.2 deletion, using comparative genomic hybridization, quantitative polymerase-chain-reaction analysis, and DNA sequencing. We carried out tests of replication using an additional series of 76 Han Chinese persons with congenital scoliosis and a multicenter series of 42 persons with 16p11.2 deletions.

RESULTS

We identified a total of 17 heterozygous TBX6 null mutations in the 161 persons with sporadic congenital scoliosis (11%); we did not observe any null mutations in TBX6 in 166 controls (P<3.8×10(-6)). These null alleles include copy-number variants (12 instances of a 16p11.2 deletion affecting TBX6) and single-nucleotide variants (1 nonsense and 4 frame-shift mutations). However, the discordant intrafamilial phenotypes of 16p11.2 deletion carriers suggest that heterozygous TBX6 null mutation is insufficient to cause congenital scoliosis. We went on to identify a common TBX6 haplotype as the second risk allele in all 17 carriers of TBX6 null mutations (P<1.1×10(-6)). Replication studies involving additional persons with congenital scoliosis who carried a deletion affecting TBX6 confirmed this compound inheritance model. In vitro functional assays suggested that the risk haplotype is a hypomorphic allele. Hemivertebrae are characteristic of TBX6-associated congenital scoliosis.

CONCLUSIONS

Compound inheritance of a rare null mutation and a hypomorphic allele of TBX6 accounted for up to 11% of congenital scoliosis cases in the series that we analyzed. (Funded by the National Basic Research Program of China and others.).

Timing embryo segmentation: dynamics and regulatory mechanisms of the vertebrate segmentation clock

All vertebrate species present a segmented body, easily observed in the vertebrate column and its associated components, which provides a high degree of motility to the adult body and efficient protection of the internal organs. The sequential formation of the segmented precursors of the vertebral column during embryonic development, the somites, is governed by an oscillating genetic network, the somitogenesis molecular clock. Herein, we provide an overview of the molecular clock operating during somite formation and its underlying molecular regulatory mechanisms. Human congenital vertebral malformations have been associated with perturbations in these oscillatory mechanisms. Thus, a better comprehension of the molecular mechanisms regulating somite formation is required in order to fully understand the origin of human skeletal malformations.

Loss of col8a1a function during zebrafish embryogenesis results in congenital vertebral malformations

Congenital vertebral malformations (CVM) occur in 1 in 1000 live births and in many cases can cause spinal deformities, such as scoliosis, and result in disability and distress of affected individuals. Many severe forms of the disease, such as spondylocostal dystostosis, are recessive monogenic traits affecting somitogenesis, however the etiologies of the majority of CVM cases remain undetermined. Here we demonstrate that morphological defects of the notochord in zebrafish can generate congenital-type spine defects. We characterize three recessive zebrafish leviathan/col8a1a mutant alleles ((m531, vu41, vu105)) that disrupt collagen type VIII alpha1a (col8a1a), and cause folding of the embryonic notochord and consequently adult vertebral column malformations. Furthermore, we provide evidence that a transient loss of col8a1a function or inhibition of Lysyl oxidases with drugs during embryogenesis was sufficient to generate vertebral fusions and scoliosis in the adult spine. Using periodic imaging of individual zebrafish, we correlate focal notochord defects of the embryo with vertebral malformations (VM) in the adult. Finally, we show that bends and kinks in the notochord can lead to aberrant apposition of osteoblasts normally confined to well-segmented areas of the developing vertebral bodies. Our results afford a novel mechanism for the formation of VM, independent of defects of somitogenesis, resulting from aberrant bone deposition at regions of misshapen notochord tissue.

Retinoic acid-dependent regulation of miR-19 expression elicits vertebrate axis defects

Retinoic acid (RA) is involved in multifarious and complex functions necessary for vertebrate development. RA signaling is reliant on strict enzymatic regulation of RA synthesis and metabolism. Improper spatiotemporal expression of RA during development can result in vertebrate axis defects. microRNAs (miRNAs) are also pivotal in orchestrating developmental processes. While mechanistic links between miRNAs and axial development are established, the role of miRNAs in regulating metabolic enzymes responsible for RA abundance during axis formation has yet to be elucidated. Our results uncovered a role of miR-19 family members in controlling RA metabolism through the regulation of CYP26A1 during vertebrate axis formation. Global miRNA expression profiling showed that developmental RA exposure suppressed the expression of miR-19 family members during zebrafish somitogenesis. A reporter assay confirmed that cyp26a1 is a bona fide target of miR-19 in vivo. Transient knockdown of miR-19 phenocopied axis defects caused by RA exposure. Exogenous miR-19 rescued the axis defects induced by RA exposure. Taken together, these results indicate that the teratogenic effects of RA exposure result, in part, from repression of miR-19 expression and subsequent misregulation of cyp26a1. This highlights a previously unidentified role of miR-19 in facilitating vertebrate axis development via regulation of RA signaling.

Spatiotemporal disorder in the axial skeleton development of the Mesp2-null mouse: a model of spondylocostal dysostosis and spondylothoracic dysostosis

Spondylocostal dysostosis (SCDO) is a genetic disorder characterized by severe malformation of the axial skeleton. Mesp2 encodes a basic helix-loop-helix type transcription factor that is required for somite formation. Its human homologue, Mesp2, is a gene affected in patients with SCDO and a related vertebral disorder, spondylothoracic dysostosis (STDO). This work investigated how the loss of Mesp2 affects axial skeleton development and causes the clinical features of SCDO and STDO. We first confirmed, by three-dimensional computed tomography scanning, that Mesp2-null mice exhibited mineralized tissue patterning resembling the radiological features of SCDO and STDO. Histological observations and in situ hybridization probing for extracellular matrix molecules demonstrated that the developing vertebral bodies in Mesp2-null mice were extensively fused with rare insertions of intervertebral tissue. Unexpectedly, the intervertebral tissues were mostly fused longitudinally in the vertebral column, instead of exhibiting extended formation, as was expected based on the caudalized properties of Mesp2-null somite derivatives. Furthermore, the differentiation of vertebral body chondrocytes in Mesp2-null mice was spatially disordered and largely delayed, with an increased cell proliferation rate. The quantitative three-dimensional immunofluorescence image analyses of phospho-Smad2 and -Smad1/5/8 revealed that these chondrogenic phenotypes were associated with spatially disordered inputs of TGF-β and BMP signaling in the Mesp2-null chondrocytes, and also demonstrated an amorphous arrangement of cells with distinct properties. Furthermore, a significant delay in ossification in Mesp2-null vertebrae was observed by peripheral quantitative computed tomography. The current observations of the spatiotemporal disorder of vertebral organogenesis in the Mesp2-null mice provide further insight into the pathogenesis of SCDO and STDO, and the physiological development of the axial skeleton.

A fluorescence spotlight on the clockwork development and metabolism of bone

Biological phenomena that exhibit periodic activity are often referred as biorhythms or biological clocks. Among these, circadian rhythms, cyclic patterns reflecting a 24-h cycle, are the most obvious in many physiological activities including bone growth and metabolism. In the late 1990s, several clock genes were isolated and their primary structures and functions were identified. The feedback loop model of transcriptional factors was proposed to work as a circadian core oscillator not only in the suprachiasmatic nuclei of the anterior hypothalamus, which is recognized as the mammalian central clock, but also in various peripheral tissues including cartilage and bone. Looking back to embryonic development, the fundamental architecture of skeletal patterning is regulated by ultradian clocks that are defined as biorhythms that cycle more than once every 24 h. As post-genomic approaches, transcriptome analysis by micro-array and bioimaging assays to detect luminescent and fluorescent signals have been exploited to uncover a more comprehensive set of genes and spatio-temporal regulation of the clockwork machinery in animal models. In this review paper, we provide an overview of topics related to these molecular clocks in skeletal biology and medicine, and discuss how fluorescence imaging approaches can contribute to widening our views of this realm of biomedical science.

A mechanism for gene-environment interaction in the etiology of congenital scoliosis

Congenital scoliosis, a lateral curvature of the spine caused by vertebral defects, occurs in approximately 1 in 1,000 live births. Here we demonstrate that haploinsufficiency of Notch signaling pathway genes in humans can cause this congenital abnormality. We also show that in a mouse model, the combination of this genetic risk factor with an environmental condition (short-term gestational hypoxia) significantly increases the penetrance and severity of vertebral defects. We demonstrate that hypoxia disrupts FGF signaling, leading to a temporary failure of embryonic somitogenesis. Our results potentially provide a mechanism for the genesis of a host of common sporadic congenital abnormalities through gene-environment interaction.

Fusionless procedures for the management of early-onset spine deformities in 2011: what do we know?

While attempts to understand them better and treat them more effectively, early-onset deformities have gained great pace in the past few years. Large patient series with long follow-ups that would provide high levels of evidence are still almost non-existent. That there is no safe treatment algorithm defined and agreed upon for this patient population continues to pose a challenge for pediatric spine surgeons. In this review, authors who are well known for their research and experience in the treatment of early-onset scoliosis (EOS) have come together in order to answer those questions which are most frequently asked by other surgeons. The most basic eight questions in this field have been answered succinctly by these authors and a current overview is provided.