Mutations in the MESP2 gene cause spondylothoracic dysostosis/Jarcho-Levin syndrome

Evaluation and Treatment of Thoracic Insufficiency Syndrome and Early-Onset Scoliosis

Thoracic insufficiency syndrome (TIS) and early-onset scoliosis (EOS) are complex pediatric conditions involving deformities of the spine and chest wall, which can significantly impact respiratory function and overall development. Managing these conditions requires a comprehensive approach that combines precise diagnosis and innovative treatment strategies. This opinion article provides a critical discussion of the diagnosis and treatment of TIS and EOS and reflects upon the advancement of methods that are crucial for assessing these conditions and guiding treatment decisions.

Cellular and molecular control of vertebrate somitogenesis

Segmentation is a fundamental feature of the vertebrate body plan. This metameric organization is first implemented by somitogenesis in the early embryo, when paired epithelial blocks called somites are rhythmically formed to flank the neural tube. Recent advances in in vitro models have offered new opportunities to elucidate the mechanisms that underlie somitogenesis. Notably, models derived from human pluripotent stem cells introduced an efficient proxy for studying this process during human development. In this Review, we summarize the current understanding of somitogenesis gained from both in vivo studies and in vitro studies. We deconstruct the spatiotemporal dynamics of somitogenesis into four distinct modules: dynamic events in the presomitic mesoderm, segmental determination, somite anteroposterior polarity patterning, and epithelial morphogenesis. We first focus on the segmentation clock, as well as signalling and metabolic gradients along the tissue, before discussing the clock and wavefront and other models that account for segmental determination. We then detail the molecular and cellular mechanisms of anteroposterior polarity patterning and somite epithelialization.

A mutation in TBXT causes congenital vertebral malformations in humans and mice

T-box transcription factor T (TBXT; T) is required for mesodermal formation and axial skeletal development. Although it has been extensively studied in various model organisms, human congenital vertebral malformations (CVMs) involving T are not well established. Here, we report a family with 15 CVM patients distributed across 4 generations. All affected individuals carry a heterozygous mutation, T c.596A>G (p.Q199R), which is not found in unaffected family members, indicating co-segregation of the genotype and phenotype. In vitro assays show that T p.Q199R increases the nucleocytoplasmic ratio and enhances its DNA-binding affinity, but reduces its transcriptional activity compared to the wild-type. To determine the pathogenicity of this mutation in vivo, we generated a Q199R knock-in mouse model that recapitulates the human CVM phenotype. Most heterozygous Q199R mice show subtle kinked or shortened tails, while homozygous mice exhibit tail filaments and severe vertebral deformities. Overall, we show that the Q199R mutation in T causes CVM in humans and mice, providing previously unreported evidence supporting the function of T in the genetic etiology of human CVM.

Long-Term Follow-up of Untreated Adult Patients with Spondylothoracic Dysostosis (Jarcho-Levin Syndrome)

BACKGROUND

Spondylothoracic dysostosis (STD), also known as Jarcho-Levin syndrome (JLS), is a rare autosomal recessive disorder affecting the formation of the spine, characterized by a complete bilateral fusion of the ribs at the costovertebral junction, producing a "crablike" appearance of the thorax. Despite being declared a core indication for a V-osteotomy vertical expandable prosthetic titanium rib (VEPTR) expansion thoracoplasty of the posterior thorax, the natural history of STD in untreated subjects remains poorly documented. In this study, we report radiographic and pulmonary function findings and Patient-Reported Outcomes Measurement Information System (PROMIS) and 24-Item Early Onset Scoliosis Questionnaire (EOSQ-24) scores for untreated adult subjects with STD to gain insights into the natural history.

METHODS

We identified 11 skeletally mature, untreated subjects with STD. Findings on medical evaluation, demographics, radiographic parameters, pulmonary function, genetic testing results, PROMIS measures, and EOSQ-24 scores were assessed.

RESULTS

Five male and 6 female subjects (mean age, 32.3 years [range, 15 to 70 years]) with a confirmed STD diagnosis based on radiographs and genetic testing were evaluated. Mean body mass index (BMI) was 24.4 kg/m 2 (range, 18 to 38.9 kg/m 2 ), and mean thoracic height was 16 cm (range, 12 to 17 cm). Pulmonary function tests (PFTs) showed a mean forced vital capacity (FVC) of 22% of predicted, mean forced expiratory volume in 1 second (FEV1) of 24% of predicted, and FEV1/FVC ratio of 107% of predicted. The mean PROMIS dyspnea score was 40 ± 8 points (range, 27.7 to 52.1 points). The mean total EOSQ-24 score was 77.3 ± 18 points (range, 43.9 to 93.2 points).

CONCLUSIONS

Our study characterizes the natural history of STD in untreated subjects. We confirmed the expected restrictive pattern in pulmonary function, but interestingly, our subjects exhibited better EOSQ scores compared with those reported in neuromuscular populations. PFT results and thoracic height did not correspond to PROMIS and EOSQ scores, questioning the use of those parameters as a surgical indication. We therefore suggest that the STD diagnosis as an absolute indication for VEPTR expansion thoracoplasty surgery be reconsidered.

LEVEL OF EVIDENCE

Therapeutic Level IV . See Instructions for Authors for a complete description of levels of evidence.

Pudgy mouse rib deformities emanate from abnormal paravertebral longitudinal cartilage/bone accumulations

The pudgy (pu/pu) mouse, caused by a recessive mutation in the Notch family Delta like-3 gene (Dll3), has severe rib, vertebral body and intervertebral disc abnormalities. Using whole-mount preparations and serial histologic sections we demonstrate: 1) localized paravertebral longitudinal cartilage/bone accumulations (PVLC/BAs) invariably associated with branched, fused and asymmetrically spaced ribs that emanate from it laterally; 2) abnormal rib formation immediately adjacent to abnormal vertebral body and intervertebral disc formation in asymmetric right/left fashion; and 3) patterns of rib deformation that differ in each mouse. Normal BALB/c embryo and age-matched non-affected pu/+ mice assessments allow for pu/pu comparisons. The Dll3 Notch family gene is involved in normal somitogenesis via the segmentation clock mechanism. Although pathogenesis of rib deformation is initially triggered by the Dll3 gene mutation, these findings of abnormal asymmetric costo-vertebral region structure imply that differing patterns cannot be attributed to this single gene mutation alone. All findings implicate a dual mechanism of malformation: the Dll3 gene mutation leading to subtle timing differences in traveling oscillation waves of the segmentation clock and further subsequent misdirection of tissue formation by altered chemical reaction-diffusion and epigenetic landscape responses. PVLC/BAs appear as primary supramolecular structures underlying severe rib malformation associated both with time-sensitive segmentation clock mutations and subsequent reactions.

The role of Notch signaling pathway in metabolic bone diseases

Metabolic bone diseases is the third most common endocrine diseases after diabetes and thyroid diseases. More than 500 million people worldwide suffer from metabolic bone diseases. The generation and development of bone metabolic diseases is a complex process regulated by multiple signaling pathways, among which the Notch signaling pathway is one of the most important pathways. The Notch signaling pathway regulates the differentiation and function of osteoblasts and osteoclasts, and affects the process of cartilage formation, bone formation and bone resorption. Genetic mutations in upstream and downstream of Notch signaling genes can lead to a series of metabolic bone diseases, such as Alagille syndrome, Adams-Oliver syndrome and spondylocostal dysostosis. In this review, we analyzed the mechanisms of Notch ligands, Notch receptors and signaling molecules in the process of signal transduction, and summarized the progress on the pathogenesis and clinical manifestations of bone metabolic diseases caused by Notch gene mutation. We hope to draw attention to the role of the Notch signaling pathway in metabolic bone diseases and provide new ideas and approaches for the diagnosis and treatment of metabolic bone diseases.

Clinical genetics of spondylocostal dysostosis: A mini review

Spondylocostal dysostosis is a genetic defect associated with severe rib and vertebrae malformations. In recent years, extensive clinical and molecular diagnosis advancements enabled us to identify disease-causing variants in different genes for such severe conditions. The identification of novel candidate genes enabled us to understand the developmental biology and molecular and cellular mechanisms involved in the etiology of these rare diseases. Here, we discuss the clinical and molecular targets associated with spondylocostal dysostosis, including clinical evaluation, genes, and pathways involved. This review might help us understand the basics of such a severe disorder, which might help in proper clinical characterization and help in future therapeutic strategies.

Genetics of non-isolated hemivertebra: A systematic review of fetal, neonatal, and infant cases

Hemivertebra is a congenital vertebral malformation caused by unilateral failure of formation during embryogenesis that may be associated with additional abnormalities. A systematic review was conducted to investigate genetic etiologies of non-isolated hemivertebra identified in the fetal, neonatal, and infant periods using PubMed, Cochrane database, Ovid Medline, and ClinicalTrials.gov from inception through May 2022 (PROSPERO ID CRD42021229576). The Human Phenotype Ontology database was accessed May 2022. Studies were deemed eligible for inclusion if they addressed non-isolated hemivertebra or genetic causes of non-isolated hemivertebra identified in the fetal, neonatal, or infant periods. Cases diagnosed clinically without molecular confirmation were included. Systematic review identified 23 cases of non-isolated hemivertebra with karyotypic abnormalities, 2 cases due to microdeletions, 59 cases attributed to single gene disorders, 18 syndromic cases without known genetic etiology, and 14 cases without a known syndromic association. The Human Phenotype Ontology search identified 49 genes associated with hemivertebra. Non-isolated hemivertebra is associated with a diverse spectrum of cytogenetic abnormalities and single gene disorders. Genetic syndromes were notably common. Frequently affected organ systems include musculoskeletal, cardiovascular, central nervous system, genitourinary, gastrointestinal, and facial dysmorphisms. When non-isolated hemivertebra is identified on prenatal ultrasound, the fetus must be assessed for associated anomalies and genetic counseling is recommended.

Jarcho-Levin syndrome in Pakistan: a case report and review of 321 cases on the principles of diagnosis and management

Background

Jarcho-Levin syndrome (JLS) is a genetic condition that constitutes specific vertebral anomalies combined with coastal or thoracic anomalies due to specific gene mutations. Although the condition is associated typically to Puerto-Ricans, we describe the novel case of JLS in a Pakistani family that presented with respiratory distress secondary to the condition.

Case presentation

The case is a full-term girl that had a webbed neck with an undefined chest deformity. Radiology showed kyphoscoliosis and a crablike chest. Early identification of these high morbidity conditions is key to allow for optimal treatment and improved outcomes.

Conclusions

We have provided a brief breakdown of the management principles of the condition and more than 80 years after the first case of Jarcho-Levin syndrome was reported, we present the diagnostic criterion for JLS.

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.

9q34 & 16p13 chromosome duplications in autism

Epigenetic mechanisms, genetic factors, and environment influence the diversity of phenotypes developed in various diseases. Duplications in several chromosomes are well characterized in the scientific literature, but partial duplications, in some cases, present with milder forms of a disease and are yet to be understood. Fortunately, the identification of genetic diseases has now become more feasible due to several cytogenetic techniques such as microarray analysis and karyotyping. With these tools, together with other laboratory results and clinical examination, we are able to report the first case in the medical literature of double partial trisomy of chromosome 9q34 and 16p13.

MESP2 variants contribute to conotruncal heart defects by inhibiting cardiac neural crest cell proliferation

Conotruncal heart defects (CTDs) are closely related to defective outflow tract (OFT) development, in which cardiac neural crest cells (CNCCs) play an indispensable role. However, the genetic etiology of CTDs remains unclear. Mesoderm posterior 2 (MESP2) is an important transcription factor regulating early cardiogenesis. Nevertheless, MESP2 variants have not been reported in congenital heart defect (CHD) patients. We first identified four MESP2 variants in 601 sporadic nonsyndromic CTD patients that were not detected in 400 healthy controls using targeted sequencing. Reverse transcription-quantitative PCR (RT-qPCR), immunohistochemistry, and immunofluorescence assays revealed MESP2 expression in the OFT of Carnegie stage (CS) 11, CS13, and CS15 human embryos and embryonic day (E) 8.5, E10, and E11.5 mouse embryos. Functional analyses in HEK 293T cells, HL-1 cells, JoMa1 cells, and primary mouse CNCCs revealed that MESP2 directly regulates the transcriptional activities of downstream CTD-related genes and promotes CNCC proliferation by regulating cell cycle factors. Three MESP2 variants, c.346G>C (p.G116R), c.921C>G (p.Y307X), and c.59A>T (p.Q20L), altered the transcriptional activities of MYOCD, GATA4, NKX2.5, and CFC1 and inhibited CNCC proliferation by upregulating p21^cip1 or downregulating Cdk4. Based on our findings, MESP2 variants disrupted MESP2 function by interfering with CNCC proliferation during OFT development, which may contribute to CTDs. KEY MESSAGES: This study first analyzed MESP2 variants identified in sporadic nonsyndromic CTD patients. MESP2 is expressed in the OFT of different stages of human and mouse embryos. MESP2 regulates the transcriptional activities of downstream CTD-related genes and promotes CNCC proliferation by regulating cell cycle factor p21^cip1 or Cdk4.

Recapitulating the human segmentation clock with pluripotent stem cells

Pluripotent stem cells are increasingly used to model different aspects of embryogenesis and organ formation¹. Despite recent advances in in vitro induction of major mesodermal lineages and cell types^2,3, experimental model systems that can recapitulate more complex features of human mesoderm development and patterning are largely missing. Here we used induced pluripotent stem cells for the stepwise in vitro induction of presomitic mesoderm and its derivatives to model distinct aspects of human somitogenesis. We focused initially on modelling the human segmentation clock, a major biological concept believed to underlie the rhythmic and controlled emergence of somites, which give rise to the segmental pattern of the vertebrate axial skeleton. We observed oscillatory expression of core segmentation clock genes, including HES7 and DKK1, determined the period of the human segmentation clock to be around five hours, and demonstrated the presence of dynamic travelling-wave-like gene expression in in vitro-induced human presomitic mesoderm. Furthermore, we identified and compared oscillatory genes in human and mouse presomitic mesoderm derived from pluripotent stem cells, which revealed species-specific and shared molecular components and pathways associated with the putative mouse and human segmentation clocks. Using CRISPR-Cas9-based genome editing technology, we then targeted genes for which mutations in patients with segmentation defects of the vertebrae, such as spondylocostal dysostosis, have been reported (HES7, LFNG, DLL3 and MESP2). Subsequent analysis of patient-like and patient-derived induced pluripotent stem cells revealed gene-specific alterations in oscillation, synchronization or differentiation properties. Our findings provide insights into the human segmentation clock as well as diseases associated with human axial skeletogenesis.

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.

Phenotypic heterogeneity of kyphoscoliosis with vertebral and rib defects: a case series

Disorders associated with multiple vertebral segmentation defects may have additional rib anomalies in form of absence or hypoplastic ribs, fanning of ribs, etc. Spondylocostal dysostosis is genetic disorder with abnormal vertebral segmentation and rib anomalies. Diagnosis is often delayed because of non-familiarity with the characteristic features. There are six genes identified for spondylocostal dysostosis, of which SCDO5 is responsible for autosomal dominant form of the disorder. Retrospective study was conducted in Genetic and Metabolic unit of a tertiary hospital in north India over a period of 9 years. Twenty patients with a clinical diagnosis of congenital scoliosis were identified, and reviewed. Three patients were discussed in an earlier report and 11 subsequent patients, are described in this case series here. The median age at presentation was 34 months. The patients showed hemivertebrae, vertebral fusion, fusion of ribs, fanning of ribs. Hydrocephalus/ventriculomegaly was found in three cases and diastematomyelia was identified in one case. Other associated anomalies included corpus callosal agenesis, club foot and capillary malformation. One parent showed rib/spinal defects in two cases. Further studies are needed to characterise the phenotype and genetic basis of scoliosis in Indian patients.

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

Notch in skeletal physiology and disease

Notch (Notch1 through 4) are transmembrane receptors that play a fundamental role in cell differentiation and function. Notch receptors are activated following interactions with their ligands in neighboring cells. There are five classic ligands termed Jagged (Jag)1 and Jag2 and Delta-like (Dll)1, Dll3, and Dll4. Recent work has established Notch as a signaling pathway that plays a critical role in the differentiation and function of cells of the osteoblast and osteoclast lineages and in skeletal development and bone remodeling. The effects of Notch are cell-context dependent, and the four Notch receptors carry out specific functions in the skeleton. Gain- and loss-of-function mutations of components of the Notch signaling pathway result in a variety of congenital disorders with significant craniofacial and skeletal manifestations. The Notch ligand Jag1 is a determinant of bone mineral density, and Notch plays a role in the early phases of fracture healing. Alterations in Notch signaling are associated with osteosarcoma and with the metastatic potential of carcinoma of the breast and of the prostate. Controlling Notch signaling could prove useful in diseases of Notch gain-of-function and in selected skeletal disorders. However, clinical data on agents that modify Notch signaling are not available. In conclusion, Notch signaling is a novel pathway that regulates skeletal homeostasis in health and disease.

Seven additional families with spondylocarpotarsal synostosis syndrome with novel biallelic deleterious variants in FLNB

The location and/or type of variants in FLNB result in a spectrum of osteochondrodysplasias ranging from mild forms, like spondylocarpotarsal synostosis syndrome and Larsen syndrome, to severe perinatal lethal forms, such as atelosteogenesis I and III and Boomerang dysplasia. Spondylocarpotarsal synostosis syndrome is characterized by disproportionate short stature, vertebral anomalies and fusion of carpal and tarsal bones. Biallelic loss-of-function variants in FLNB are known to cause spondylocarpotarsal synostosis syndrome and 9 families and 9 pathogenic variants have been reported so far. We report clinical features of 10 additional patients from 7 families with spondylocarpotarsal synostosis syndrome due to 7 novel deleterious variants in FLNB, thus expanding the clinical and molecular repertoire of spondylocarpotarsal synostosis syndrome. Our report validates key clinical (fused thoracic vertebrae and carpal and tarsal coalition) and molecular (truncating variants in FLNB) characteristics of this condition.

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.

Diagnostic strategy in segmentation defect of the vertebrae: a retrospective study of 73 patients

Background

Segmentation defects of the vertebrae (SDV) are non-specific features found in various syndromes. The molecular bases of SDV are not fully elucidated due to the wide range of phenotypes and classification issues. The genes involved are in the Notch signalling pathway, which is a key system in somitogenesis. Here we report on mutations identified in a diagnosis cohort of SDV. We focused on spondylocostal dysostosis (SCD) and the phenotype of these patients in order to establish a diagnostic strategy when confronted with SDV.

Patients and methods

We used DNA samples from a cohort of 73 patients and performed targeted sequencing of the five known SCD-causing genes (DLL3, MESP2, LFNG, HES7 and TBX6) in the first 48 patients and whole-exome sequencing (WES) in 28 relevant patients.

Results

Ten diagnoses, including four biallelic variants in TBX6, two biallelic variants in LFNG and DLL3, and one in MESP2 and HES7, were made with the gene panel, and two diagnoses, including biallelic variants in FLNB and one variant in MEOX1, were made by WES. The diagnostic yield of the gene panel was 10/73 (13.7%) in the global cohort but 8/10 (80%) in the subgroup meeting the SCD criteria; the diagnostic yield of WES was 2/28 (8%).

Conclusion

After negative array CGH, targeted sequencing of the five known SCD genes should only be performed in patients who meet the diagnostic criteria of SCD. The low proportion of candidate genes identified by WES in our cohort suggests the need to consider more complex genetic architectures in cases of SDV.

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.

Notch Signaling in Development, Tissue Homeostasis, and Disease

Notch signaling is an evolutionarily highly conserved signaling mechanism, but in contrast to signaling pathways such as Wnt, Sonic Hedgehog, and BMP/TGF-β, Notch signaling occurs via cell-cell communication, where transmembrane ligands on one cell activate transmembrane receptors on a juxtaposed cell. Originally discovered through mutations in Drosophila more than 100 yr ago, and with the first Notch gene cloned more than 30 yr ago, we are still gaining new insights into the broad effects of Notch signaling in organisms across the metazoan spectrum and its requirement for normal development of most organs in the body. In this review, we provide an overview of the Notch signaling mechanism at the molecular level and discuss how the pathway, which is architecturally quite simple, is able to engage in the control of cell fates in a broad variety of cell types. We discuss the current understanding of how Notch signaling can become derailed, either by direct mutations or by aberrant regulation, and the expanding spectrum of diseases and cancers that is a consequence of Notch dysregulation. Finally, we explore the emerging field of Notch in the control of tissue homeostasis, with examples from skin, liver, lung, intestine, and the vasculature.

Sonographic Criteria for Diagnosing Jarcho-Levin Syndrome

This is a case study of Jarcho-Levin syndrome, which is a rare genetic disorder described as a malformation of bones in the spinal column and the ribs. This disorder can be an autosomal recessive or dominant trait. Those affected by this disorder have respiratory insufficiency and potentially other abnormalities. Recurrent respiratory infections are expected. In milder cases, surgery is a possibility, but in severe cases, prognosis is poor. OB sonography can aid in diagnosis of Jarcho-Levin syndrome in patients with no known family history of the disease, but it is particularly helpful in known at-risk cases.

Genetic identification of a common collagen disease in puerto ricans via identity-by-descent mapping in a health system

Achieving confidence in the causality of a disease locus is a complex task that often requires supporting data from both statistical genetics and clinical genomics. Here we describe a combined approach to identify and characterize a genetic disorder that leverages distantly related patients in a health system and population-scale mapping. We utilize genomic data to uncover components of distant pedigrees, in the absence of recorded pedigree information, in the multi-ethnic BioMe biobank in New York City. By linking to medical records, we discover a locus associated with both elevated genetic relatedness and extreme short stature. We link the gene, COL27A1, with a little-known genetic disease, previously thought to be rare and recessive. We demonstrate that disease manifests in both heterozygotes and homozygotes, indicating a common collagen disorder impacting up to 2% of individuals of Puerto Rican ancestry, leading to a better understanding of the continuum of complex and Mendelian disease.

Diseases often run in families. These disease are frequently linked to changes in DNA that are passed down through generations. Close family members may share these disease-causing mutations; so may distant relatives who inherited the same mutation from a common ancestor long ago. Geneticists use a method called linkage mapping to trace a disease found in multiple members of a family over generations to genetic changes in a shared ancestor. This allows scientists to pinpoint the exact place in the genome the disease-causing mutation occurred. Using computer algorithms, scientists can apply the same technique to identify mutations that distant relatives inherited from a common ancestor.

Belbin et al. used this computational technique to identify a mutation that may cause unusually short stature or bone and joint problems in up to 2% of people of Puerto Rican descent. In the experiments, the genomes of about 32,000 New Yorkers who have volunteered to participate in the BioMe Biobank and their health records were used to search for genetic changes linked to extremely short stature. The search revealed that people who inherited two copies of this mutation from their parents were likely to be extremely short or to have bone and joint problems. People who inherited one copy had an increased likelihood of joint or bone problems.

This mutation affects a gene responsible for making a form of protein called collagen that is important for bone growth. The analysis suggests the mutation first arose in a Native American ancestor living in Puerto Rico around the time that European colonization began. The mutation had previously been linked to a disorder called Steel syndrome that was thought to be rare. Belbin et al. showed this condition is actually fairly common in people whose ancestors recently came from Puerto Rico, but may often go undiagnosed by their physicians. The experiments emphasize the importance of including diverse populations in genetic studies, as studies of people of predominantly European descent would likely have missed the link between this disease and mutation.

Filamin B Loss-of-Function Mutation in Dimerization Domain Causes Autosomal-Recessive Spondylocarpotarsal Synostosis Syndrome with Rib Anomalies

Spondylocarpotarsal synostosis syndrome (SCT) is a distinct group of disorders characterized by short stature, disrupted vertebral segmentation with vertebral fusion, scoliosis, lordosis, carpal/tarsal synostosis, and lack of rib anomalies. Mutations in filamin B (FLNB) and MYH3 have been reported for autosomal-recessive and autosomal-dominant SCT, respectively. We present a family with two patients suffering from autosomal-recessive SCT with rib anomalies, including malalignment, crowding, and uneven size and shape of ribs. Whole-exome sequencing revealed a novel p.S2542Lfs^* 82 (c.7621dup) frameshift mutation in FLNB. This frameshift mutation lies in the C-terminal-most domain involved in FLNB dimerization and resulted in a 20-residue elongation, with complete familial segregation and absence in 376 normal controls. The mutant p.S2542Lfs^* 82 FLNB demonstrated a complete loss of ability to form a functional dimer in transiently transfected HEK293T cells. The p.S2542Lfs^* 82 mutation also led to significantly reduced protein levels and accumulation of the mutant protein in the Golgi apparatus. This is the first identified mutation in the dimerization domain of FLNB. This loss-of-function frameshift mutation in FLNB causes autosomal-recessive SCT with rarely reported rib anomalies. This report demonstrates the involvement of rib anomaly in SCT and its causative mutation in the dimerization domain of FLNB.

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.

Notch Signaling and the Skeleton

Notch 1 to 4 receptors are important determinants of cell fate and function, and Notch signaling plays an important role in skeletal development and bone remodeling. After direct interactions with ligands of the Jagged and Delta-like families, a series of cleavages release the Notch intracellular domain (NICD), which translocates to the nucleus where it induces transcription of Notch target genes. Classic gene targets of Notch are hairy and enhancer of split (Hes) and Hes-related with YRPW motif (Hey). In cells of the osteoblastic lineage, Notch activation inhibits cell differentiation and causes cancellous bone osteopenia because of impaired bone formation. In osteocytes, Notch1 has distinct effects that result in an inhibition of bone resorption secondary to an induction of osteoprotegerin and suppression of sclerostin with a consequent enhancement of Wnt signaling. Notch1 inhibits, whereas Notch2 enhances, osteoclastogenesis and bone resorption. Congenital disorders of loss- and gain-of-Notch function present with severe clinical manifestations, often affecting the skeleton. Enhanced Notch signaling is associated with osteosarcoma, and Notch can influence the invasive potential of carcinoma of the breast and prostate. Notch signaling can be controlled by the use of inhibitors of Notch activation, small peptides that interfere with the formation of a transcriptional complex, or antibodies to the extracellular domain of specific Notch receptors or to Notch ligands. In conclusion, Notch plays a critical role in skeletal development and homeostasis, and serious skeletal disorders can be attributed to alterations in Notch signaling.

A Single-Center Experience of CNS Anomalies or Neural Tube Defects in Patients With Jarcho-Levin Syndrome

Jarcho-Levin syndrome (JLS) is a genetic disorder characterized by distinct malformations of the ribs and vertebrae, and/or other associated abnormalities such as neural tube defect, Arnold-Chiari malformation, renal and urinary abnormalities, hydrocephalus, congenital cardiac abnormalities, and extremity malformations. The study included 12 cases at 37-42 weeks of gestation and diagnosed to have had Jarcho-Levin syndrome, Arnold-Chiari malformation, and meningmyelocele. All cases of Jarcho-Levin syndrome had Arnold-Chiari type 2 malformation; there was corpus callosum dysgenesis in 6, lumbosacral meningmyelocele in 6, lumbal meningmyelocele in 3, thoracal meningmyelocele in 3, and holoprosencephaly in 1 of the cases. With this article, the authors underline the neurologic abnormalities accompanying Jarcho-Levin syndrome and that each of these abnormalities is a component of Jarcho-Levin syndrome.

Canine disorder mirrors human disease: exonic deletion in HES7 causes autosomal recessive spondylocostal dysostosis in miniature Schnauzer dogs

Spondylocostal dysostosis is a congenital disorder of the axial skeleton documented in human families from diverse racial backgrounds. The condition is characterised by truncal shortening, extensive hemivertebrae and rib anomalies including malalignment, fusion and reduction in number. Mutations in the Notch signalling pathway genes DLL3, MESP2, LFNG, HES7 and TBX6 have been associated with this defect. In this study, spondylocostal dysostosis in an outbred family of miniature schnauzer dogs is described. Computed tomography demonstrated that the condition mirrors the skeletal defects observed in human cases, but unlike most human cases, the affected dogs were stillborn or died shortly after birth. Through gene mapping and whole genome sequencing, we identified a single-base deletion in the coding region of HES7. The frameshift mutation causes loss of functional domains essential for the oscillatory transcriptional autorepression of HES7 during somitogenesis. A restriction fragment length polymorphism test was applied within the immediate family and supported a highly penetrant autosomal recessive mode of inheritance. The mutation was not observed in wider testing of 117 randomly sampled adult miniature schnauzer and six adult standard schnauzer dogs; providing a significance of association of P_raw = 4.759e^-36 (genome-wide significant). Despite this apparently low frequency in the Australian population, the allele may be globally distributed based on its presence in two unrelated sires from geographically distant locations. While isolated hemivertebrae have been observed in a small number of other dog breeds, this is the first clinical and genetic diagnosis of spontaneously occurring spondylocostal dysostosis in a non-human mammal and offers an excellent model in which to study this devastating human disorder. The genetic test can be utilized by dog breeders to select away from the disease and avoid unnecessary neonatal losses.

Therapeutic modulation of Notch signalling--are we there yet?

The Notch signalling pathway is evolutionarily conserved and is crucial for the development and homeostasis of most tissues. Deregulated Notch signalling leads to various diseases, such as T cell leukaemia, Alagille syndrome and a stroke and dementia syndrome known as CADASIL, and so strategies to therapeutically modulate Notch signalling are of interest. Clinical trials of Notch pathway inhibitors in patients with solid tumours have been reported, and several approaches are under preclinical evaluation. In this Review, we focus on aspects of the pathway that are amenable to therapeutic intervention, diseases that could be targeted and the various Notch pathway modulation strategies that are currently being explored.

Notch signaling in skeletal health and disease

Notch receptors are single-pass transmembrane proteins that determine cell fate. Upon Notch ligand interactions, proteolytic cleavages release the Notch intracellular domain, which translocates to the nucleus to regulate the transcription of target genes, including Hairy enhancer of split (Hes) and Hes related to YRPW motif (Hey). Notch is critical for skeletal development and activity of skeletal cells, and dysregulation of Notch signaling is associated with human diseases affecting the skeleton. Inherited or sporadic mutations in components of the Notch signaling pathway are associated with spondylocostal dysostosis, spondylothoracic dysostosis and recessive brachydactyly, diseases characterized by skeletal patterning defects. Inactivating mutations of the Notch ligand JAG1 or of NOTCH2 are associated with Alagille syndrome, and activating mutations in NOTCH2 are associated with Hajdu-Cheney syndrome (HCS). Individuals affected by HCS exhibit osteolysis in distal phalanges and osteoporosis. NOTCH is activated in selected tumors, such as osteosarcoma, and in breast cancer cells that form osteolytic bone metastases. In conclusion, Notch regulates skeletal development and bone remodeling, and gain- or loss-of-function mutations of Notch signaling result in important skeletal diseases.

Clinical, genetic and environmental factors associated with congenital vertebral malformations

Congenital vertebral malformations (CVM) pose a significant health problem because they can be associated with spinal deformities, such as congenital scoliosis and kyphosis, in addition to various syndromes and other congenital malformations. Additional information remains to be learned regarding the natural history of congenital scoliosis and related health problems. Although significant progress has been made in understanding the process of somite formation, which gives rise to vertebral bodies, there is a wide gap in our understanding of how genetic factors contribute to CVM development. Maternal diabetes during pregnancy most commonly contributes to the occurrence of CVM, followed by other factors such as hypoxia and anticonvulsant medications. This review highlights several emerging clinical issues related to CVM, including pulmonary and orthopedic outcome in congenital scoliosis. Recent breakthroughs in genetics related to gene and environment interactions associated with CVM development are discussed. The Klippel-Feil syndrome which is associated with cervical segmentation abnormalities is illustrated as an example in which animal models, such as the zebrafish, can be utilized to provide functional evidence of pathogenicity of identified mutations.

Molecular diagnosis of vertebral segmentation disorders in humans

BACKGROUND

Vertebral malformations contribute substantially to the pathophysiology of kyphosis and scoliosis, common health problems associated with back and neck pain, disability, cosmetic disfigurement and functional distress.

OBJECTIVE

To provide an overview of the current understanding of vertebral malformations, at both the clinical level and the molecular level, and factors that contribute to their occurrence.

METHODS

The literature related to the following was reviewed: recent advances in the understanding of the molecular embryology underlying vertebral development and relevance to elucidation of etiologies of several known human vertebral malformation syndromes; outcomes of molecular studies elucidating genetic contributions to congenital and sporadic vertebral malformations; and complex interrelationships between genetic and environmental factors that contribute to the pathogenesis of isolated syndromic and non-syndromic congenital vertebral malformations.

RESULTS/CONCLUSION

Expert opinions extend to discussion of the importance of establishing improved classification systems for vertebral malformation, future directions in molecular and genetic research approaches to vertebral malformation and translational value of research efforts to clinical management and genetic counseling of affected individuals and their families.

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.

Genetic aspects of congenital and idiopathic scoliosis

Congenital and idiopathic scoliosis represent disabling conditions of the spine. While congenital scoliosis (CS) is caused by morphogenic abnormalities in vertebral development, the cause(s) for idiopathic scoliosis is (are) likely to be varied, representing alterations in skeletal growth, neuromuscular imbalances, disturbances involving communication between the brain and spine, and others. Both conditions are characterized by phenotypic and genetic heterogeneities, which contribute to the difficulties in understanding their genetic basis that investigators face. Despite the differences between these two conditions there is observational and experimental evidence supporting common genetic mechanisms. This paper focuses on the clinical features of both CS and IS and highlights genetic and environmental factors which contribute to their occurrence. It is anticipated that emerging genetic technologies and improvements in phenotypic stratification of both conditions will facilitate improved understanding of the genetic basis for these conditions and enable targeted prevention and treatment strategies.

Notch and disease: a growing field

Signals through the Notch receptors are used throughout development to control cellular fate choices. Our intention here is to provide an overview of the involvement of Notch signaling in human disease, which, keeping pace with the known biology of the pathway, manifests itself in a pleiotropic fashion. A pathway with such broad action in normal development, a profound involvement in the biology of adult stem cells and intricate and complex controls governing its activity, poses numerous challenges. We provide an overview of Notch related pathologies identified thus far and emphasize aspects that have been modeled in experimental systems in order to understand the underlying pathobiology and, hopefully, help the definition of rational therapeutic avenues.

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.

Scoliosis and segmentation defects of the vertebrae

The vertebral column derives from somites, which are transient paired segments of mesoderm that surround the neural tube in the early embryo. Somites are formed by a genetic mechanism that is regulated by cyclical expression of genes in the Notch, Wnt, and fibroblast growth factor (FGF) signaling pathways. These oscillators together with signaling gradients within the presomitic mesoderm help to set somitic boundaries and rostral-caudal polarity that are essential for the precise patterning of the vertebral column. Disruption of this mechanism has been identified as the cause of severe segmentation defects of the vertebrae in humans. These segmentation defects are part of a spectrum of spinal disorders affecting the skeletal elements and musculature of the spine, resulting in curvatures such as scoliosis, kyphosis, and lordosis. While the etiology of most disorders with spinal curvatures is still unknown, genetic and developmental studies of somitogenesis and patterning of the axial skeleton and musculature are yielding insights into the causes of these diseases.

Notch regulation of bone development and remodeling and related skeletal disorders

Notch signaling mediates cell-to-cell interactions that are critical for embryonic development and tissue renewal. In the canonical signaling pathway, the Notch receptor is cleaved following ligand binding, resulting in the release and nuclear translocation of the Notch intracellular domain (NICD). NICD induces gene expression by forming a ternary complex with the DNA binding protein CBF1/Rbp-Jk, Suppressor of Hairless, Lag1, and Mastermind-Like (Maml). Hairy Enhancer of Split (Hes) and Hes related with YRPW motif (Hey) are classic Notch targets. Notch canonical signaling plays a central role in skeletal development and bone remodeling by suppressing the differentiation of skeletal cells. The skeletal phenotype of mice misexpressing Hes1 phenocopies partially the effects of Notch misexpression, suggesting that Hey proteins mediate most of the skeletal effects of Notch. Dysregulation of Notch signaling is associated with diseases affecting human skeletal development, such as Alagille syndrome, brachydactyly and spondylocostal dysostosis. Somatic mutations in Notch receptors and ligands are found in tumors of the skeletal system. Overexpression of NOTCH1 is associated with osteosarcoma, and overexpression of NOTCH3 or JAGGED1 in breast cancer cells favors the formation of osteolytic bone metastasis. Activating mutations in NOTCH2 cause Hajdu-Cheney syndrome, which is characterized by skeletal defects and fractures, and JAG1 polymorphisms, are associated with variations in bone mineral density. In conclusion, Notch is a regulator of skeletal development and bone remodeling, and abnormal Notch signaling is associated with developmental and postnatal skeletal disorders.

Notch signaling in human development and disease

Mutations in Notch signaling pathway members cause developmental phenotypes that affect the liver, skeleton, heart, eye, face, kidney, and vasculature. Notch associated disorders include the autosomal dominant, multi-system, Alagille syndrome caused by mutations in both a ligand (Jagged1 (JAG1)) and receptor (NOTCH2) and autosomal recessive spondylocostal dysostosis, caused by mutations in a ligand (Delta-like-3 (DLL3)), as well as several other members of the Notch signaling pathway. Mutations in NOTCH2 have also recently been connected to Hajdu-Cheney syndrome, a dominant disorder causing focal bone destruction, osteoporosis, craniofacial morphology and renal cysts. Mutations in the NOTCH1 receptor are associated with several types of cardiac disease and mutations in NOTCH3 cause the dominant adult onset disorder CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy), a vascular disorder with onset in the 4th or 5th decades. Studies of these human disorders and their inheritance patterns and types of mutations reveal insights into the mechanisms of Notch signaling.