Genetic aspects of congenital and idiopathic scoliosis

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.

In vitro and in vivo models define a molecular signature reference for human embryonic notochordal cells

Understanding the emergence of human notochordal cells (NC) is essential for the development of regenerative approaches. We present a comprehensive investigation into the specification and generation of bona fide NC using a straightforward pluripotent stem cell (PSC)-based system benchmarked with human fetal notochord. By integrating in vitro and in vivo transcriptomic data at single-cell resolution, we establish an extended molecular signature and overcome the limitations associated with studying human notochordal lineage at early developmental stages. We show that TGF-β inhibition enhances the yield and homogeneity of notochordal lineage commitment in vitro. Furthermore, this study characterizes regulators of cell-fate decision and matrisome enriched in the notochordal niche. Importantly, we identify specific cell-surface markers opening avenues for differentiation refinement, NC purification, and functional studies. Altogether, this study provides a human notochord transcriptomic reference that will serve as a resource for notochord identification in human systems, diseased-tissues modeling, and facilitating future biomedical research.

Advances in epigenetic research of adolescent idiopathic scoliosis and congenital scoliosis

Scoliosis is a three-dimensional structural deformity of the spine; more than 80% of scoliosis has no specific pathogenesis but is understood to be closely related to genetic, hormonal, and environmental factors. In recent years, the epigenetic alterations observed in scoliosis have been analyzed in numerous studies to determine the pathogenesis and progression of this condition, however, there is currently no comprehensive review of the epigenetic factors to date. We searched PubMed, Embase, and Web of Science databases for relative studies without language and date restrictions in March 2023. Twenty-five studies were included in this review and analyzed from the four main aspects of epigenetic alteration: DNA methylation, non-coding RNAs, histone modifications, and chromatin remodeling. The relationship between DNA methylation, non-coding RNAs, and scoliosis was considerably reported in the literature, and the corresponding related signaling pathways and novel biomarkers observed in scoliosis provide insights into innovative prevention and treatment strategies. However, the role of histone modifications is rarely reported in scoliosis, and few studies have investigated the relationship between scoliosis and chromatin remodeling. Therefore, these related fields need to be further explored to elucidate the overall effects of epigenetics in scoliosis.

Muscle imbalance as a cause of scoliosis: a study in a fetal lamb abdominal wall defect model

BACKGROUND

We created abdominal wall defects (AWD) in fetal lambs to investigate possible causes of scoliosis.

METHODS

We incised the upper abdominal wall (including Rectus) in 60-day gestation fetal lambs, from the midline to either the right (Group A) or left (Group B) costal margin, in 14 lambs carried by 7 ewes. They were delivered by cesarean section at term (about 145 days). Scoliosis was evaluated by anterio-posterior X-rays, determining the Cobb angle.

RESULTS

Four fetuses in Group A and 3 in Group B survived. There were 3 successful AWD lambs Group A and 2 in Group B. One lamb in each group survived with the AWD covered with a thick capsule. The convexity of spinal curve was the direction of scoliosis. Right scoliosis was only seen in the 4 Group A lambs. Left scoliosis was only seen in Group B lambs (2/3, 67%). The mean Cobb angle was 41.7 ± 11.5° in Group A and in Group B the Cobb angles were 59.6^o and 60.6°. Overall, 4/5 lambs with organ prolapse (80%) and both lambs without organ prolapse had scoliosis.

CONCLUSION

Muscle imbalance may contribute to the development of scoliosis in a fetal lamb AWD model.

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.

Cross-sectional analysis and trend of vertebral and associated anomalies in Chinese congenital scoliosis population: a retrospective study of one thousand, two hundred and eighty nine surgical cases from 2010 to 2019

PURPOSE

The objective of this article is to report associated anomaly incidences of a large CS cohort and analyze interrelationships among vertebral anomaly types and associated abnormalities.

METHODS

We retrospectively searched and extracted medical records of 1289 CS inpatients surgically treated in our institute from January 2010 to December 2019. All patients have taken spine X-ray, CT, MRI, echocardiogram, urogenital ultrasound, and systemic physical examination. We analyzed information on demographics, CS types, and associated anomalies.

RESULTS

CS type was found to be 49.1% for failure of formation (FF), 19.5% for failure of segmentation (FS), and 31.4% for mixed defects (MD). Intraspinal defects were found in 29.4% patients (16.0% for FF, 45.4% for FS, 40.5% for MD), cardiac in 13.7% (12.3% for FF, 14.3% for FS, 15.6% for MD), genitourinary in 5.8% (4.1% for FF, 6.0% for FS, 8.4% for MD), gastrointestinal in 3.6% (4.7% for FF, 1.6% for FS, 3.0% for MD), and musculoskeletal in 16.4% (10.3% for FF, 19.9% for FS, 23.7% for MD). The intraspinal and musculoskeletal defect incidences were significantly higher in patients with failure of segmentation and mixed defects. We also observed a decreasing trend for intraspinal and musculoskeletal defect incidences as well as a tendency for more failure of formation and less failure of segmentation from 2010 to 2019.

CONCLUSIONS

The intraspinal and musculoskeletal defect incidences were higher in patients with failure of segmentation and mixed defects. Strong interrelationships were found between intraspinal and musculoskeletal defects and among cardiovascular, genitourinary, and gastrointestinal defects. From 2010 to 2019, the proportion of patients with failure of formation increased significantly, causing a decrease in the intraspinal and musculoskeletal defect incidences over time. Female sex, failure of segmentation, and mixed defects could be considered risk factors for more associated anomalies in CS individuals, which would help surgeons in medical management and prenatal consultation.

Genetic variants of TBX6 and TBXT identified in patients with congenital scoliosis in Southern China

Congenital scoliosis (CS) is a spinal deformity present at birth due to underlying congenital vertebral malformation (CVM) that occurs during embryonic development. Hemivertebrae is the most common anomaly that causes CS. Recently, compound heterozygosity in TBX6 has been identified in Northern Chinese, Japanese, and European CS patient cohorts, which explains about 7%-10% of the affected population. In this report, we recruited 67 CS patients characterized with hemivertebrae in the Southern Chinese population and investigated the TBX6 variant and risk haplotype. We found that two patients with hemivertebrae in the thoracic spine and one patient with hemivertebrae in the lumbar spine carry the previously defined pathogenic TBX6 compound heterozygous variants. In addition, whole exome sequencing of patients with CS and their family members identified a de novo missense mutation (c.G47T: p.R16L) in another member of the T-box family, TBXT. This rare mutation compromised the binding of TBXT to its target sequence, leading to reduced transcriptional activity, and exhibited dominant-negative effect on wild-type TBXT. Our findings further highlight the importance of T-box family genes in the development of congenital scoliosis.

Cecr2 mutant mice as a model for human cat eye syndrome

Cat eye syndrome (CES), a human genetic disorder caused by the inverted duplication of a region on chromosome 22, has been known since the late 1890s. Despite the significant impact this disorder has on affected individuals, models for CES have not been produced due to the difficulty of effectively duplicating the corresponding chromosome region in an animal model. However, the study of phenotypes associated with individual genes in this region such as CECR2 may shed light on the etiology of CES. In this study we have shown that deleterious loss of function mutations in mouse Cecr2 effectively demonstrate many of the abnormal features present in human patients with CES, including coloboma and specific skeletal, kidney and heart defects. Beyond phenotypic analyses we have demonstrated the importance of utilizing multiple genetic backgrounds to study disease models, as we see major differences in penetrance of Cecr2-related abnormal phenotype between mouse strains, reminiscent of the variability in the human syndrome. These findings suggest that Cecr2 is involved in the abnormal features of CES and that Cecr2 mice can be used as a model system to study the wide range of phenotypes present in CES.

Emerging roles of non-coding RNAs in scoliosis

Scoliosis, a complex three‐dimensional deformity of the spine with the Cobb angle (a measure of the spinal lateral curvature) >10 degree, encompasses a spectrum of pathologies, including congenital, idiopathic, syndromic and neuromuscular aetiologies. The pathogenesis is multifactorial involving both environmental and genetic factors but the exact cellular and molecular mechanisms of disease development remain largely unknown. Emerging evidence showed that non‐coding RNAs (ncRNAs), namely microRNAs, long ncRNAs and circular RNAs, are deregulated in many orthopaedic diseases, including scoliosis. Importantly, these deregulated ncRNAs functionally participate in the initiation and progression of scoliosis. Here, we review recent progress in ncRNA research on scoliosis.

Variant morphology and arterial supply of diaphragmatic crura with probe patent foramen ovale

Crura are the posterior pillars of the tendino-muscular partition between thoracic and abdominal cavity. This study highlights bilaterally an unfamiliar morphology of diaphragmatic crura with uncommon origin of inferior phrenic artery and accompanying atrial septal defect in a 63-years-old female cadaver with scoliosis. An attempt is made to portray the clinical implications of these variations. In addition authors have discussed the embryological and genetic basis of these variations. In the recent few decades, surgical correction of scoliosis involving intervention with the crura has gained pace. Knowledge about the normal as well as variant crural morphology is imperative for the surgeons to decide the correct approach during spinal corrective surgeries and for radiologist to prevent any diagnostic pitfall. Familiarity about the variant origin of inferior phrenic artery may prevent complications during treatment of pathological conditions related to inferior phrenic artery. Preoperative awareness about the coexisting atrial septal defect is vital for anesthesiologists promoting them to administer cardioprotective anesthetic drugs. To the best of our knowledge, description of such a combination of variations in anatomical literature is rare and scarcely reported. Awareness of these anatomical variations is relevant for operating surgeons, radiologists, anesthesiologists and anatomists.

Screening of known disease genes in congenital scoliosis

Background

Congenital scoliosis (CS) is defined as a lateral curvature of the spine due to the vertebral malformations and has an incidence of 0.5–1/1,000 births. We previously examined TBX6 in Japanese CS patients and revealed that approximately 10% of CS was caused by TBX6 mutations. However, the genetic cause of remaining CS is unknown.

Methods

We recruited 78 CS patients without TBX6 mutations and major comorbidities, and investigated the genes previously reported to be associated with CS and congenital vertebral malformations by whole‐exome sequencing.

Results

We identified the compound heterozygous missense variants in LFNG in one patient. No likely disease‐causing variants were identified in other patients, however. LFNG encodes a GlcNAc‐transferase. The LFNG variants showed loss of their enzyme function.

Conclusions

A LFNG mutation is reported in a case of spondylocostal dysostosis (SCD), a skeletal dysplasia with severe malformations of vertebra and rib. The CS patient with LFNG mutations had multiple vertebral malformations including hemivertebrae, butterfly vertebrae, and block vertebrae, and rib malformations. LFNG mutations may cause a spectrum of phenotypes including CS and SCD. The current list of known disease genes could explain only a small fraction of genetic cause of CS.

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.

Summary of the first inaugural joint meeting of the International Consortium for scoliosis genetics and the International Consortium for vertebral anomalies and scoliosis, March 16-18, 2017, Dallas, Texas

Scoliosis represents the most common musculoskeletal disorder in children and affects approximately 3% of the world population. Scoliosis is separated into two major phenotypic classifications: congenital and idiopathic. Idiopathic scoliosis is defined as a curvature of the spine of 10° or greater visualized on plane radiograph and does not have associated vertebral malformations (VM). "Congenital" scoliosis (CS) due to malformations in vertebrae is frequently associated with other birth defects. Recently, significant advances have been made in understanding the genetic basis of both conditions. There is evidence that both conditions are etiologically related. A 2-day conference entitled "Genomic Approaches to Understanding and Treating Scoliosis" was held at Scottish Rite Hospital for Children in Dallas, Texas, to synergize research in this field. This first combined, multidisciplinary conference featured international scoliosis researchers in basic and clinical sciences. A major outcome of the conference advancing scoliosis research was the proposal and subsequent vote in favor of merging the International Consortium for Vertebral Anomalies and Scoliosis (ICVAS) and International Consortium for Scoliosis Genetics (ICSG) into a single entity called International Consortium for Spinal Genetics, Development, and Disease (ICSGDD). The ICSGDD is proposed to meet annually as a forum to synergize multidisciplinary spine deformity research.

Comparative analysis of serum proteome in congenital scoliosis patients with TBX6 haploinsufficiency - a first report pointing to lipid metabolism

Congenital scoliosis (CS) is a three‐dimensional deformity of the spine affecting quality of life. We have demonstrated TBX6 haploinsufficiency is the most important contributor to CS. However, the pathophysiology at the protein level remains unclear. Therefore, this study was to explore the differential proteome in serum of CS patients with TBX6 haploinsufficiency. Sera from nine CS patients with TBX6 haploinsufficiency and nine age‐ and gender‐matched healthy controls were collected and analysed by isobaric tagged relative and absolute quantification (iTRAQ) labelling coupled with mass spectrometry (MS). In total, 277 proteins were detected and 20 proteins were designated as differentially expressed proteins, which were submitted to subsequent bioinformatics analysis. Gene Ontology classification analysis showed the biological process was primarily related to ‘cellular process’, molecular function ‘structural molecule activity’ and cellular component ‘extracellular region’. IPA analysis revealed ‘LXR/RXR activation’ was the top pathway, which is a crucial pathway in lipid metabolism. Hierarchical clustering analysis generated two clusters. In summary, this study is the first proteomic research to delineate the total and differential serum proteins in TBX6 haploinsufficiency‐caused CS. The proteins discovered in this experiment may serve as potential biomarkers for CS, and lipid metabolism might play important roles in the pathogenesis of CS.

Mapping the Pairwise Choices Leading from Pluripotency to Human Bone, Heart, and Other Mesoderm Cell Types

Stem-cell differentiation to desired lineages requires navigating alternating developmental paths that often lead to unwanted cell types. Hence, comprehensive developmental roadmaps are crucial to channel stem-cell differentiation toward desired fates. To this end, here, we map bifurcating lineage choices leading from pluripotency to 12 human mesodermal lineages, including bone, muscle, and heart. We defined the extrinsic signals controlling each binary lineage decision, enabling us to logically block differentiation toward unwanted fates and rapidly steer pluripotent stem cells toward 80%-99% pure human mesodermal lineages at most branchpoints. This strategy enabled the generation of human bone and heart progenitors that could engraft in respective in vivo models. Mapping stepwise chromatin and single-cell gene expression changes in mesoderm development uncovered somite segmentation, a previously unobservable human embryonic event transiently marked by HOPX expression. Collectively, this roadmap enables navigation of mesodermal development to produce transplantable human tissue progenitors and uncover developmental processes. VIDEO ABSTRACT.

Zebrafish Developmental Models of Skeletal Diseases

The zebrafish skeleton shares many similarities with human and other vertebrate skeletons. Over the past years, work in zebrafish has provided an extensive understanding of the basic developmental mechanisms and cellular pathways directing skeletal development and homeostasis. This review will focus on the cell biology of cartilage and bone and how the basic cellular processes within chondrocytes and osteocytes function to assemble the structural frame of a vertebrate body. We will discuss fundamental functions of skeletal cells in production and secretion of extracellular matrix and cellular activities leading to differentiation of progenitors to mature cells that make up the skeleton. We highlight important examples where findings in zebrafish provided direction for the search for genes causing human skeletal defects and also how zebrafish research has proven important for validating candidate human disease genes. The work we cover here illustrates utility of zebrafish in unraveling molecular mechanisms of cellular functions necessary to form and maintain a healthy skeleton.

Five known tagging DLL3 SNPs are not associated with congenital scoliosis: A case-control association study in a Chinese Han population

Genetic etiology hypothesis is widely accepted in the development of congenital scoliosis (CS). The delta-like 3 (DLL3) gene, a member of the Notch signaling pathway, was implicated to contribute to human CS. In this study, a case-control association study was conducted to determine the association of single nucleotide polymorphism (SNP) in the DLL3 gene with CS in a Chinese Han Population. Five known tagging SNPs of the DLL3 gene were genotyped among 270 Chinese Han subjects (128 nonsyndromic CS patients and 142 matched controls). CS patients were divided into 3 types: type I-failure of formation (29 cases), type II-failure of segmentation (50 cases), and type III-mixed defects (49 cases). The 5 SNPs were analyzed by the allelic and genotypic association analysis, genotype-phenotype association analysis, and haplotype analysis. Allele frequencies of 5 tagging SNPs (SNP1: rs1110627, SNP2: rs3212276, SNP3: rs2304223, SNP4: rs2304222, and SNP5: rs2304214) in CS cases and controls were comparable and there were no available inheritance models. The SNPs were not associated with clinical phenotypes. Moreover, the 5 makers in the DLL3 gene were found to be in strong linkage disequilibrium (LD). Both global haplotype and individual haplotype analyses showed that the haplotypes of SNP1/SNP2/SNP3/SNP4/SNP5 did not correlate with the disease (P >0.05). Together, these data suggest that genetic variants of the DLL3 gene are not associated with CS in the Chinese Han population.

SNPping away at the genetic basis of adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a genetically complex disorder of spine development, defined by a lateral curvature of the spine of 10º or greater which affects children during their pubertal growth spurt. Prior linkage and candidate gene approaches to elucidating the genetic basis of AIS have been of limited use for identification of candidate genes for this condition. Genome wide association studies (GWAS) have recently identified single nucleotide polymorphisms (SNPs) in LBX1 and G protein-coupled receptor 126 (GPR126) that contribute to AIS occurrence. These discoveries support prior etiologic hypotheses regarding altered somatosensory function and skeletal growth in AIS. However, these loci account for a small percentage of the phenotypic variance associated with AIS, indicating the vast majority of the genetic causes of AIS remain to be delineated. A major translational application regarding understanding the genetic contributions to AIS relates to bracing efficacy.

Environmental aspects of congenital scoliosis

Growing evidence has proved that many aspects of our lifestyle and the environment contribute to the development of congenital disease. Congenital spinal deformities are due to anomalous development of the vertebrae including failure of formation and segmentation during embryogenesis. The causes of congenital scoliosis have not been fully identified. A variety of factors are implicated in the development of vertebral abnormalities. Previous studies have demonstrated that both genetics and environmental factors are implicated in the development of vertebral abnormalities. However, no specific cause for congenital scoliosis has been identified. In our review, we focus on the environmental factors for the development of congenital scoliosis. Various maternal exposures during pregnancy including hypoxia, alcohol use, vitamin deficiency, valproic acid, boric acid, and hyperthermia have been observed to be associated with the occurrence of congenital scoliosis. This review describes the major environmental contributors of congenital scoliosis with an emphasis on treatment aspects associated with environmental disposition in congenital scoliosis.

ptk7 mutant zebrafish models of congenital and idiopathic scoliosis implicate dysregulated Wnt signalling in disease

Scoliosis is a complex genetic disorder of the musculoskeletal system, characterized by three-dimensional rotation of the spine. Curvatures caused by malformed vertebrae (congenital scoliosis (CS)) are apparent at birth. Spinal curvatures with no underlying vertebral abnormality (idiopathic scoliosis (IS)) most commonly manifest during adolescence. The genetic and biological mechanisms responsible for IS remain poorly understood due largely to limited experimental models. Here we describe zygotic ptk7 (Zptk7) mutant zebrafish, deficient in a critical regulator of Wnt signalling, as the first genetically defined developmental model of IS. We identify a novel sequence variant within a single IS patient that disrupts PTK7 function, consistent with a role for dysregulated Wnt activity in disease pathogenesis. Furthermore, we demonstrate that embryonic loss-of-gene function in maternal-zygotic ptk7 mutants (MZptk7) leads to vertebral anomalies associated with CS. Our data suggest novel molecular origins of, and genetic links between, congenital and idiopathic forms of disease.

Scoliosis is a complex genetic disorder characterized by spinal curvature. Here, the authors present experimental zebrafish models of idiopathic and congenital scoliosis and suggest a role for dysregulated Wnt activity in scoliosis aetiology.