A consideration of the evidence that genetic defects in planar cell polarity contribute to the etiology of human neural tube defects

PCP-dependent polarized mechanics in the cortex of individual cells during convergent extension

Convergent extension (CE) is a key process for tissue elongation during vertebrate development and is driven by polarized cell behaviors. Here, we used a novel image-based technique to investigate the mechanical properties of individual cells undergoing CE. Our results suggest a PCP- and Septin-dependent mechanical gradient, where cortical tension is higher at the anterior face of the cells compared with their posterior face. Disruption of PCP protein Vangl2 or its downstream effector Septin7 eliminates this mechanical polarity. These findings demonstrate a link between actin organization, PCP signaling, and mechanical polarization, providing new avenues into the mechanochemical regulation of cellular behaviors during CE.

Planar Cell Polarity Signaling: Coordinated Crosstalk for Cell Orientation

The planar cell polarity (PCP) system is essential for positioning cells in 3D networks to establish the proper morphogenesis, structure, and function of organs during embryonic development. The PCP system uses inter- and intracellular feedback interactions between components of the core PCP, characterized by coordinated planar polarization and asymmetric distribution of cell populations inside the cells. PCP signaling connects the anterior-posterior to left-right embryonic plane polarity through the polarization of cilia in the Kupffer's vesicle/node in vertebrates. Experimental investigations on various genetic ablation-based models demonstrated the functions of PCP in planar polarization and associated genetic disorders. This review paper aims to provide a comprehensive overview of PCP signaling history, core components of the PCP signaling pathway, molecular mechanisms underlying PCP signaling, interactions with other signaling pathways, and the role of PCP in organ and embryonic development. Moreover, we will delve into the negative feedback regulation of PCP to maintain polarity, human genetic disorders associated with PCP defects, as well as challenges associated with PCP.

Identification and functional analysis of rare HECTD1 missense variants in human neural tube defects

Neural tube defects (NTDs) are severe malformations of the central nervous system that arise from failure of neural tube closure. HECTD1 is an E3 ubiquitin ligase required for cranial neural tube closure in mouse models. NTDs in the Hectd1 mutant mouse model are due to the failure of cranial mesenchyme morphogenesis during neural fold elevation. Our earlier research has linked increased extracellular heat shock protein 90 (eHSP90) secretion to aberrant cranial mesenchyme morphogenesis in the Hectd1 model. Furthermore, overexpression of HECTD1 suppresses stress-induced eHSP90 secretion in cell lines. In this study, we report the identification of five rare HECTD1 missense sequence variants in NTD cases. The variants were found through targeted next-generation sequencing in a Chinese cohort of 352 NTD cases and 224 ethnically matched controls. We present data showing that HECTD1 is a highly conserved gene, extremely intolerant to loss-of-function mutations and missense changes. To evaluate the functional consequences of NTD-associated missense variants, functional assays in HEK293T cells were performed to examine protein expression and the ability of HECTD1 sequence variants to suppress eHSP90 secretion. One NTD-associated variant (A1084T) had significantly reduced expression in HEK293T cells. All five NTD-associated variants (p.M392V, p.T801I, p.I906V, p.A1084T, and p.P1835L) reduced regulation of eHSP90 secretion by HECTD1, while a putative benign variant (p.P2474L) did not. These findings are the first association of HECTD1 sequence variation with NTDs in humans.

Functional analysis of germline VANGL2 variants using rescue assays of vangl2 knockout zebrafish

Developmental studies have shown that the evolutionarily conserved Wnt Planar Cell Polarity (PCP) pathway is essential for the development of a diverse range of tissues and organs including the brain, spinal cord, heart and sensory organs, as well as establishment of the left-right body axis. Germline mutations in the highly conserved PCP gene VANGL2 in humans have only been associated with central nervous system malformations, and functional testing to understand variant impact has not been performed. Here we report three new families with missense variants in VANGL2 associated with heterotaxy and congenital heart disease p.(Arg169His), non-syndromic hearing loss p.(Glu465Ala) and congenital heart disease with brain defects p.(Arg135Trp). To test the in vivo impact of these and previously described variants, we have established clinically-relevant assays using mRNA rescue of the vangl2 mutant zebrafish. We show that all variants disrupt Vangl2 function, although to different extents and depending on the developmental process. We also begin to identify that different VANGL2 missense variants may be haploinsufficient and discuss evidence in support of pathogenicity. Together, this study demonstrates that zebrafish present a suitable pipeline to investigate variants of unknown significance and suggests new avenues for investigation of the different developmental contexts of VANGL2 function that are clinically meaningful.

Identification and Functional Analysis of Rare HECTD1 Missense Variants in Human Neural Tube Defects

Neural tube defects (NTDs) are severe malformations of the central nervous system that arise from failure of neural tube closure. HECTD1 is an E3 ubiquitin ligase required for cranial neural tube closure in mouse models. NTDs in the Hectd1 mutant mouse model are due to the failure of cranial mesenchyme morphogenesis during neural fold elevation. Our earlier research has linked increased secretion of extracellular heat shock protein 90 (eHSP90) to aberrant cranial mesenchyme morphogenesis in the Hectd1 model. Furthermore, overexpression of HECTD1 suppresses stress-induced eHSP90 secretion in cell lines. In this study, we report the identification of five rare HECTD1 missense sequence variants in NTD cases. The variants were found through targeted next-generation sequencing in a Chinese cohort of 352 NTD cases and 224 ethnically matched controls. We present data showing that HECTD1 is a highly conserved gene, extremely intolerant to loss-of-function mutations and missense changes. To evaluate the functional consequences of NTD-associated missense variants, functional assays in HEK293T cells were performed to examine protein expression and the ability of HECTD1 sequence variants to suppress eHSP90 secretion. One NTD-associated variant (A1084T) had significantly reduced expression in HEK293T cells. All five NTD-associated variants (p.M392V, p.T801I, p.I906V, p.A1084T, and p.P1835L) reduced regulation of eHSP90 secretion by HECTD1, while a putative benign variant (p.P2474L) did not. These findings are the first association of HECTD1 sequence variation with human disease and suggest that sequence variation in HECTD1 may play a role in the etiology of human NTDs.

A quest for genetic causes underlying signaling pathways associated with neural tube defects

Neural tube defects (NTDs) are serious congenital deformities of the nervous system that occur owing to the failure of normal neural tube closures. Genetic and non-genetic factors contribute to the etiology of neural tube defects in humans, indicating the role of gene-gene and gene-environment interaction in the occurrence and recurrence risk of neural tube defects. Several lines of genetic studies on humans and animals demonstrated the role of aberrant genes in the developmental risk of neural tube defects and also provided an understanding of the cellular and morphological programs that occur during embryonic development. Other studies observed the effects of folate and supplementation of folic acid on neural tube defects. Hence, here we review what is known to date regarding altered genes associated with specific signaling pathways resulting in NTDs, as well as highlight the role of various genetic, and non-genetic factors and their interactions that contribute to NTDs. Additionally, we also shine a light on the role of folate and cell adhesion molecules (CAMs) in neural tube defects.

Loss-of-Function of p21-Activated Kinase 2 Links BMP Signaling to Neural Tube Patterning Defects

Closure of the neural tube represents a highly complex and coordinated process, the failure of which constitutes common birth defects. The serine/threonine kinase p21-activated kinase 2 (PAK2) is a critical regulator of cytoskeleton dynamics; however, its role in the neurulation and pathogenesis of neural tube defects (NTDs) remains unclear. Here, the results show that Pak2^-/- mouse embryos fail to develop dorsolateral hinge points (DLHPs) and exhibit craniorachischisis, a severe phenotype of NTDs. Pak2 knockout activates BMP signaling that involves in vertebrate bone formation. Single-cell transcriptomes reveal abnormal differentiation trajectories and transcriptional events in Pak2^-/- mouse embryos during neural tube development. Two nonsynonymous and one recurrent splice-site mutations in the PAK2 gene are identified in five human NTD fetuses, which exhibit attenuated PAK2 expression and upregulated BMP signaling in the brain. Mechanistically, PAK2 regulates Smad9 phosphorylation to inhibit BMP signaling and ultimately induce DLHP formation. Depletion of pak2a in zebrafish induces defects in the neural tube, which are partially rescued by the overexpression of wild-type, but not mutant PAK2. The findings demonstrate the conserved role of PAK2 in neurulation in multiple vertebrate species, highlighting the molecular pathogenesis of PAK2 mutations in NTDs.

CIC missense variants contribute to susceptibility for spina bifida

Neural tube defects (NTDs) are congenital malformations resulting from abnormal embryonic development of the brain, spine, or spinal column. The genetic etiology of human NTDs remains poorly understood despite intensive investigation. CIC, homolog of the Capicua transcription repressor, has been reported to interact with ataxin-1 (ATXN1) and participate in the pathogenesis of spinocerebellar ataxia type 1. Our previous study demonstrated that CIC loss of function (LoF) variants contributed to the cerebral folate deficiency syndrome by downregulating folate receptor 1 (FOLR1) expression. Given the importance of folate transport in neural tube formation, we hypothesized that CIC variants could contribute to increased risk for NTDs by depressing embryonic folate concentrations. In this study, we examined CIC variants from whole-genome sequencing (WGS) data of 140 isolated spina bifida cases and identified eight missense variants of CIC gene. We tested the pathogenicity of the observed variants through multiple in vitro experiments. We determined that CIC variants decreased the FOLR1 protein level and planar cell polarity (PCP) pathway signaling in a human cell line (HeLa). In a murine cell line (NIH3T3), CIC loss of function variants downregulated PCP signaling. Taken together, this study provides evidence supporting CIC as a risk gene for human NTD.

Wnt/planar cell polarity signaling controls morphogenetic movements of gastrulation and neural tube closure

Gastrulation and neurulation are successive morphogenetic processes that play key roles in shaping the basic embryonic body plan. Importantly, they operate through common cellular and molecular mechanisms to set up the three spatially organized germ layers and to close the neural tube. During gastrulation and neurulation, convergent extension movements driven by cell intercalation and oriented cell division generate major forces to narrow the germ layers along the mediolateral axis and elongate the embryo in the anteroposterior direction. Apical constriction also makes an important contribution to promote the formation of the blastopore and the bending of the neural plate. Planar cell polarity proteins are major regulators of asymmetric cell behaviors and critically involved in a wide variety of developmental processes, from gastrulation and neurulation to organogenesis. Mutations of planar cell polarity genes can lead to general defects in the morphogenesis of different organs and the co-existence of distinct congenital diseases, such as spina bifida, hearing deficits, kidney diseases, and limb elongation defects. This review outlines our current understanding of non-canonical Wnt signaling, commonly known as Wnt/planar cell polarity signaling, in regulating morphogenetic movements of gastrulation and neural tube closure during development and disease. It also attempts to identify unanswered questions that deserve further investigations.

Pathogenesis of neural tube defects: The regulation and disruption of cellular processes underlying neural tube closure

Neural tube closure (NTC) is crucial for proper development of the brain and spinal cord and requires precise morphogenesis from a sheet of cells to an intact three-dimensional structure. NTC is dependent on successful regulation of hundreds of genes, a myriad of signaling pathways, concentration gradients, and is influenced by epigenetic and environmental cues. Failure of NTC is termed a neural tube defect (NTD) and is a leading class of congenital defects in the United States and worldwide. Though NTDs are all defined as incomplete closure of the neural tube, the pathogenesis of an NTD determines the type, severity, positioning, and accompanying phenotypes. In this review, we survey pathogenesis of NTDs relating to disruption of cellular processes arising from genetic mutations, altered epigenetic regulation, and environmental influences by micronutrients and maternal condition. This article is categorized under: Congenital Diseases > Genetics/Genomics/Epigenetics Neurological Diseases > Genetics/Genomics/Epigenetics Neurological Diseases > Stem Cells and Development.

Biomechanical regulation of planar cell polarity in endothelial cells

Cell polarity refers to the uneven distribution of certain cytoplasmic components in a cell with a spatial order. The planar cell polarity (PCP), the cell aligns perpendicular to the polar plane, in endothelial cells (ECs) has become a research hot spot. The planar polarity of ECs has a positive significance on the regulation of cardiovascular dysfunction, pathological angiogenesis, and ischemic stroke. The endothelial polarity is stimulated and regulated by biomechanical force. Mechanical stimuli promote endothelial polarization and make ECs produce PCP to maintain the normal physiological and biochemical functions. Here, we overview recent advances in understanding the interplay and mechanism between PCP and ECs function involved in mechanical forces, with a focus on PCP signaling pathways and organelles in regulating the polarity of ECs. And then showed the related diseases caused by ECs polarity dysfunction. This study provides new ideas and therapeutic targets for the treatment of endothelial PCP-related diseases.

Exploring epigenomic mechanisms of neural tube defects using multi-omics methods and data

Neural tube defects (NTDs) are a heterogeneous set of malformations attributed to disruption in normal neural tube closure during early embryogenesis. An in-depth understanding of NTD etiology and mechanisms remains elusive, however. Among the proposed mechanisms, epigenetic changes are thought to play an important role in the formation of NTDs. Epigenomics covers a wide spectrum of genomic DNA sequence modifications that can be investigated via high-throughput techniques. Recent advances in epigenomic technologies have enabled epigenetic studies of congenital malformations and facilitated the integration of big data into the understanding of NTDs. Herein, we review clinical epigenomic data that focuses on DNA methylation, histone modification, and miRNA alterations in human neural tissues, placental tissues, and leukocytes to explore potential mechanisms by which candidate genes affect human NTD pathogenesis. We discuss the links between epigenomics and gene regulatory mechanisms, and the effects of epigenetic alterations in human tissues on neural tube closure.

Spina Bifida: A Review of the Genetics, Pathophysiology and Emerging Cellular Therapies

Spina bifida is the most common congenital defect of the central nervous system which can portend lifelong disability to those afflicted. While the complete underpinnings of this disease are yet to be fully understood, there have been great advances in the genetic and molecular underpinnings of this disease. Moreover, the treatment for spina bifida has made great advancements, from surgical closure of the defect after birth to the now state-of-the-art intrauterine repair. This review will touch upon the genetics, embryology, and pathophysiology and conclude with a discussion on current therapy, as well as the first FDA-approved clinical trial utilizing stem cells as treatment for spina bifida.

The role of Lrp6-mediated Wnt/β-catenin signaling in the development and intervention of spinal neural tube defects in mice

Neural tube defects (NTDs) are among the common and severe birth defects with poorly understood etiology. Mutations in the Wnt co-receptor LRP6 are associated with NTDs in humans. Either gain-of-function (GOF) or loss-of-function (LOF) mutations of Lrp6 can cause NTDs in mice. NTDs in Lrp6-GOF mutants may be attributed to altered β-catenin-independent noncanonical Wnt signaling. However, the mechanisms underlying NTDs in Lrp6-LOF mutants and the role of Lrp6-mediated canonical Wnt/β-catenin signaling in neural tube closure remain unresolved. We previously demonstrated that β-catenin signaling is required for posterior neuropore (PNP) closure. In the current study, conditional ablation of Lrp6 in dorsal PNP caused spinal NTDs with diminished activities of Wnt/β-catenin signaling and its downstream target gene Pax3, which is required for PNP closure. β-catenin-GOF rescued NTDs in Lrp6-LOF mutants. Moreover, maternal supplementation of a Wnt/β-catenin signaling agonist reduced the frequency and severity of spinal NTDs in Lrp6-LOF mutants by restoring Pax3 expression. Together, these results demonstrate the essential role of Lrp6-mediated Wnt/β-catenin signaling in PNP closure, which could also provide a therapeutic target for NTD intervention through manipulation of canonical Wnt/β-catenin signaling activities.

Summary: Conditional ablation of Lrp6 in dorsal neural folds causes spinal neural tube defects that can be rescued by genetic activation of β-catenin or maternal supplementation of Wnt signaling agonists.

The cell polarity protein Vangl2 in the muscle shapes the neuromuscular synapse by binding to and regulating the tyrosine kinase MuSK

The development of the neuromuscular junction (NMJ) requires dynamic trans-synaptic coordination orchestrated by secreted factors, including Wnt family morphogens. To investigate how these synaptic cues in NMJ development are transduced, particularly in the regulation of acetylcholine receptor (AChR) accumulation in the postsynaptic membrane, we explored the function of Van Gogh-like protein 2 (Vangl2), a core component of Wnt planar cell polarity signaling. We found that conditional, muscle-specific ablation of Vangl2 in mice reproduced the NMJ differentiation defects seen in mice with global Vangl2 deletion. These alterations persisted into adulthood and led to NMJ disassembly, impaired neurotransmission, and deficits in motor function. Vangl2 and the muscle-specific receptor tyrosine kinase MuSK were functionally associated in Wnt signaling in the muscle. Vangl2 bound to and promoted the signaling activity of MuSK in response to Wnt11. The loss of Vangl2 impaired RhoA activation in cultured mouse myotubes and caused dispersed, rather than clustered, organization of AChRs at the postsynaptic or muscle cell side of NMJs in vivo. Our results identify Vangl2 as a key player of the core complex of molecules shaping neuromuscular synapses and thus shed light on the molecular mechanisms underlying NMJ assembly.

Whole exome sequencing identifies potential candidate genes for spina bifida derived from mouse models

Spina bifida (SB) is the second most common nonlethal congenital malformation. The existence of monogenic SB mouse models and human monogenic syndromes with SB features indicate that human SB may be caused by monogenic genes. We hypothesized that whole exome sequencing (WES) allows identification of potential candidate genes by (i) generating a list of 136 candidate genes for SB, and (ii) by unbiased exome-wide analysis. We generated a list of 136 potential candidate genes from three categories and evaluated WES data of 50 unrelated SB cases for likely deleterious variants in 136 potential candidate genes, and for potential SB candidate genes exome-wide. We identified 6 likely deleterious variants in 6 of the 136 potential SB candidate genes in 6 of the 50 SB cases, whereof 4 genes were derived from mouse models, 1 gene was derived from human nonsyndromic SB, and 1 gene was derived from candidate genes known to cause human syndromic SB. In addition, by unbiased exome-wide analysis, we identified 12 genes as potential candidates for SB. Identification of these 18 potential candidate genes in larger SB cohorts will help decide which ones can be considered as novel monogenic causes of human SB.

Imaging Planar Cell Polarity Proteins in Xenopus Neuroectoderm

Planar cell polarity (PCP) refers to coordinated cell polarization in the plane of the tissue. Genetic studies in Drosophila identified several core PCP genes, whose products function together in a signaling pathway that regulates cell shape, epithelial tissue organization and remodeling during morphogenesis. PCP is detected by the asymmetric distribution of core PCP proteins at different borders of epithelial cells. Believed to be critical for signaling, this segregation is studied by a variety of techniques, such as direct immunostaining and imaging of fluorescent PCP protein fusions or fluorescence recovery after photobleaching (FRAP). All of the above techniques can be applied to the analysis of the Xenopus neural plate to study the dynamics of tissue polarization, making this system one of the best vertebrate PCP models. This chapter describes how to image PCP proteins in Xenopus neuroectoderm for both fixed and live samples. These robust cellular techniques will contribute to mechanistic studies of PCP in vertebrate embryos.

Hypermethylation of PI3K-AKT signalling pathway genes is associated with human neural tube defects

Neural tube defects (NTDs) are a group of common and severe congenital malformations. The PI3K-AKT signalling pathway plays a crucial role in the neural tube development. There is limited evidence concerning any possible association between aberrant methylation in PI3K-AKT signalling pathway genes and NTDs. Therefore, we aimed to investigate potential associations between aberrant methylation of PI3K-AKT pathway genes and NTDs. Methylation studies of PI3K-AKT pathway genes utilizing microarray genome-methylation data derived from neural tissues of ten NTD cases and eight non-malformed controls were performed. Targeted DNA methylation analysis was subsequently performed in an independent cohort of 73 NTD cases and 32 controls to validate the methylation levels of identified genes. siRNAs were used to pull-down the target genes in human embryonic stem cells (hESCs) to examine the effects of the aberrant expression of target genes on neural cells. As a result, 321 differentially hypermethylated CpG sites in the promoter regions of 30 PI3K-AKT pathway genes were identified in the microarray data. In target methylation analysis, CHRM1, FGF19, and ITGA7 were confirmed to be significantly hypermethylated in NTD cases and were associated with increased risk for NTDs. The down-regulation of FGF19, CHRM1, and ITGA7 impaired the formation of rosette-like cell aggregates. The down-regulation of those three genes affected the expression of PAX6, SOX2 and MAP2, implying their influence on the differentiation of neural cells. This study for the first time reported that hypermethylation of PI3K-AKT pathway genes such as CHRM1, FGF19, and ITGA7 is associated with human NTDs.

BAC Recombineering and Transgenesis to Study Cell Polarity and Polarized Tissue Morphogenesis in Mice

Planar cell polarity (PCP) signaling plays a critical role in coordinating cell polarity during various organogenesis processes in mammals, and its disruption is causal to numerous congenital disorders in humans. To elucidate its actions in mammals, mouse genetics is an indispensable approach. Given that both gain- and loss-of-function of many PCP genes often cause similar defects, the standard mouse transgenic approach may not always be ideal for studying PCP genes in their wild-type and mutant forms. Here we describe using BAC (bacterial artificial chromosomes) transgenes as a versatile and effective alternative. Transgenes made from BACs, which are genomic clones 100-200 kb in size, can more faithful recapitulate endogenous gene expression levels and patterns. Bacterial based recombination system can be used to efficiently introduce mutations, fluorescent protein tags, and LoxP sites for conditional expressions. Cre can also be inserted into BACs to map the contribution of cells expressing any PCP gene of interest, and study PCP mediated tissue morphogenesis.

Vangl2-environment interaction causes severe neural tube defects, without abnormal neuroepithelial convergent extension

Planar cell polarity (PCP) signalling is vital for initiation of mouse neurulation, with diminished convergent extension (CE) cell movements leading to craniorachischisis, a severe neural tube defect (NTD). Some humans with NTDs also have PCP gene mutations but these are heterozygous, not homozygous as in mice. Other genetic or environmental factors may interact with partial loss of PCP function in human NTDs. We found that reduced sulfation of glycosaminoglycans interacts with heterozygosity for the Lp allele of Vangl2 (a core PCP gene), to cause craniorachischisis in cultured mouse embryos, with rescue by exogenous sulphate. We hypothesised this glycosaminoglycan-PCP interaction may regulate CE but, surprisingly, DiO labeling of the embryonic node demonstrates no abnormality of midline axial extension in sulfation-depleted Lp/+ embryos. Positive-control Lp/Lp embryos show severe CE defects. Abnormalities were detected in the size and shape of somites that flank the closing neural tube in sulfation-depleted Lp/+ embryos. We conclude that failure of closure initiation can arise by a mechanism other than faulty neuroepithelial CE, with possible involvement of matrix-mediated somite expansion, adjacent to the closing neural tube.

Unraveling the complex genetics of neural tube defects: From biological models to human genomics and back

Neural tube defects (NTDs) are a classic example of preventable birth defects for which there is a proven-effective intervention, folic acid (FA); however, further methods of prevention remain unrealized. In the decades following implementation of FA nutritional fortification programs throughout at least 87 nations, it has become apparent that not all NTDs can be prevented by FA. In the United States, FA fortification only reduced NTD rates by 28-35% (Williams et al., 2015). As such, it is imperative that further work is performed to understand the risk factors associated with NTDs and their underlying mechanisms so that alternative prevention strategies can be developed. However, this is complicated by the sheer number of genes associated with neural tube development, the heterogeneity of observable phenotypes in human cases, the rareness of the disease, and the myriad of environmental factors associated with NTD risk. Given the complex genetic architecture underlying NTD pathology and the way in which that architecture interacts dynamically with environmental factors, further prevention initiatives will undoubtedly require precision medicine strategies that utilize the power of human genomics and modern tools for assessing genetic risk factors. Herein, we review recent advances in genomic strategies for discovering genetic variants associated with these defects, and new ways in which biological models, such as mice and cell culture-derived organoids, are leveraged to assess mechanistic functionality, the way these variants interact with other genetic or environmental factors, and their ultimate contribution to human NTD risk.

A silent epidemic of major congenital malformations in Tigray, northern Ethiopia: hospital-based study

Congenital malformations are defects of the morphogenesis of organs or body during the pregnancy period and are identifiable at pre- or postnatal. They are identified as the major cause of child mortality worldwide. There is a need to understand the prevalence of congenital malformations in Tigray and Ethiopia in general as surveillance data are lacking. Hence, this study was designed to investigate the burden of major congenital malformations in the Tigray Region, Northern Ethiopia. Hospital-based cross-sectional study was conducted to identify neonates with major congenital anomalies in the labor ward admitted at six major public hospitals of Tigray region, Ethiopia between January 2018 and 2019. All newborns/neonates delivered in all study hospitals during the study period were considered as the study population. The prevalence of major congenital anomalies and the distribution of each type of major congenital anomalies within total birth were calculated. Data on maternal, and newborn demographic characteristics was collected. Statistical analysis was done using SPSS and p value < 0.05 was considered significant. A total of 12,225 births and terminations were recorded in the six hospitals during the study period. Of total 12,225 births and terminations examined, 383 births had major congenital malformations and the overall prevalence of congenital malformations was 3.13% of the total births examined. Congenital anomalies (CAs) of the central nervous system specifically neural tube defects (NTDs) were the commonest anomalies in this study, found in 68.7% (263NTDs/383 CAs) of the neonates with CAs. The overall prevalence of NTDs was 2.15% (263/12,225 births) of the total births examined. Maternal factors such as women 20 years of age or younger (p < 0.0001) and women older than 35 years of age (p < 0.0001), abortion history (p < 0.0001), gravidity above 4 (p = 0.005), were more likely associated with an increased risk of babies with congenital anomalies. Fetal factors including gestational ages below 28 weeks (p < 0.0001) and above 40 weeks (p < 0.0001) were strongly associated with an increased risk of babies with congenital anomalies. However, these associated factors were not resulted from multivariable logistic regression analysis. Thus, the result might be affected by possible confounding factors. This study has shown a high prevalence of major congenital anomalies in the study community. Of the total congenital anomalies observed, most of neonates are affected with neural tube defects, a birth defect with well–established evidence having folic acid deficiency or insufficiency is the predominant cause of spina bifida and anencephaly. This just screams urgency to implement effective/mandatory/ programs to get all women of reproductive age an adequate folic acid to prevent spina bifida and anencephaly.

New mouse models for high resolution and live imaging of planar cell polarity proteins in vivo

The collective polarization of cellular structures and behaviors across a tissue plane is a near universal feature of epithelia known as planar cell polarity (PCP). This property is controlled by the core PCP pathway, which consists of highly conserved membrane-associated protein complexes that localize asymmetrically at cell junctions. Here, we introduce three new mouse models for investigating the localization and dynamics of transmembrane PCP proteins: Celsr1, Fz6 and Vangl2. Using the skin epidermis as a model, we characterize and verify the expression, localization and function of endogenously tagged Celsr1-3xGFP, Fz6-3xGFP and tdTomato-Vangl2 fusion proteins. Live imaging of Fz6-3xGFP in basal epidermal progenitors reveals that the polarity of the tissue is not fixed through time. Rather, asymmetry dynamically shifts during cell rearrangements and divisions, while global, average polarity of the tissue is preserved. We show using super-resolution STED imaging that Fz6-3xGFP and tdTomato-Vangl2 can be resolved, enabling us to observe their complex localization along junctions. We further explore PCP fusion protein localization in the trachea and neural tube, and discover new patterns of PCP expression and localization throughout the mouse embryo.

Identification of the Key Regulators of Spina Bifida Through Graph-Theoretical Approach

Spina Bifida (SB) is a congenital spinal cord malformation. Efforts to discern the key regulators (KRs) of the SB protein-protein interaction (PPI) network are requisite for developing its successful interventions. The architecture of the SB network, constructed from 117 manually curated genes was found to self-organize into a scale-free fractal state having a weak hierarchical organization. We identified three modules/motifs consisting of ten KRs, namely, TNIP1, TNF, TRAF1, TNRC6B, KMT2C, KMT2D, NCOA3, TRDMT1, DICER1, and HDAC1. These KRs serve as the backbone of the network, they propagate signals through the different hierarchical levels of the network to conserve the network’s stability while maintaining low popularity in the network. We also observed that the SB network exhibits a rich-club organization, the formation of which is attributed to our key regulators also except for TNIP1 and TRDMT1. The KRs that were found to ally with each other and emerge in the same motif, open up a new dimension of research of studying these KRs together. Owing to the multiple etiology and mechanisms of SB, a combination of several biomarkers is expected to have higher diagnostic accuracy for SB as compared to using a single biomarker. So, if all the KRs present in a single module/motif are targetted together, they can serve as biomarkers for the diagnosis of SB. Our study puts forward some novel SB-related genes that need further experimental validation to be considered as reliable future biomarkers and therapeutic targets.

The Biological Significance and Implications of Planar Cell Polarity for Nephrology

The orientation of cells in two-dimensional and three-dimensional space underpins how the kidney develops and responds to disease. The process by which cells orientate themselves within the plane of a tissue is termed planar cell polarity. In this Review, we discuss how planar cell polarity and the proteins that underpin it govern kidney organogenesis and pathology. The importance of planar cell polarity and its constituent proteins in multiple facets of kidney development is emphasised, including ureteric bud branching, tubular morphogenesis and nephron maturation. An overview is given of the relevance of planar cell polarity and its proteins for inherited human renal diseases, including congenital malformations with unknown aetiology and polycystic kidney disease. Finally, recent work is described outlining the influence of planar cell polarity proteins on glomerular diseases and highlight how this fundamental pathway could yield a new treatment paradigm for nephrology.

Cell non-autonomy amplifies disruption of neurulation by mosaic Vangl2 deletion in mice

Post-zygotic mutations that generate tissue mosaicism are increasingly associated with severe congenital defects, including those arising from failed neural tube closure. Here we report that neural fold elevation during mouse spinal neurulation is vulnerable to deletion of the VANGL planar cell polarity protein 2 (Vangl2) gene in as few as 16% of neuroepithelial cells. Vangl2-deleted cells are typically dispersed throughout the neuroepithelium, and each non-autonomously prevents apical constriction by an average of five Vangl2-replete neighbours. This inhibition of apical constriction involves diminished myosin-II localisation on neighbour cell borders and shortening of basally-extending microtubule tails, which are known to facilitate apical constriction. Vangl2-deleted neuroepithelial cells themselves continue to apically constrict and preferentially recruit myosin-II to their apical cell cortex rather than to apical cap localisations. Such non-autonomous effects can explain how post-zygotic mutations affecting a minority of cells can cause catastrophic failure of morphogenesis leading to clinically important birth defects.

Perspectives on urological care in spina bifida patients

Spina bifida (SB) is a neurogenetic disorder with a complex etiology that involves genetic and environmental factors. SB can occur in two major forms of open SB or SB aperta and closed SB or SB occulta. Myelomeningocele (MMC), the most common neural tube defects (NTDs), occurs in approximately 1 in 1,000 births. Considering non-genetic factors, diminished folate status is the best-known factor influencing NTD risk. The methylenetetrahydrofolate reductase (MTHFR) gene has been implicated as a risk factor for NTDs. The primary disorder in the pathogenesis of MMC is failed neural tube closure in the embryonic spinal region. The clinical manifestation of SB depends on clinical type and severity. SB can be detected in the second trimester using ultrasound which will reveal specific cranial signs. The management of MMC traditionally involves surgery within 48 h of birth. Prenatal repair of MMC is recommended for fetuses who meet maternal and fetal Management of Myelomeningocele Study (MOMS) specified criteria. Urological manifestations of SB include urinary incontinence, urolithiasis, sexual dysfunction, renal dysfunction, and urinary tract infection. Renal failure is among the most severe complications of SB. The most important role of the urologist is the management of neurogenic bladder. Medical management with clean intermittent catheterization and anticholinergic treatment is generally considered the gold standard of therapy. However, when this therapy fails surgical reconstruction become the only remaining option. This review will summarize the pathogenesis, risk factors, genetic contribution, diagnostic test, and management of SB. Lastly, the urologic outcomes and therapies are reviewed.

Myelomeningocele genotype-phenotype correlation findings in cilia, HH, PCP, and WNT signaling pathways

BACKGROUND

Myelomeningocele (MMC) is the most severe and frequent type of spina bifida. Its etiology remains poorly understood. The Hedgehog (Hh), Wnt, and planar cell polarity (PCP) signaling pathways are essential for normal tube closure, needing a structural-functional cilium for its adequate function. The present study aimed to investigate the impact of different gene variants (GV) from those pathways on MMC genotype-subphenotype correlations.

METHODS

The study comprised 500 MMC trios and 500 controls, from 16 Telethon centers of 16 Mexican states. Thirty-four GVs of 29 genes from cilia, Hh, PCP, and Wnt pathways, were analyzed, by an Illumina on design microarray. The total sample (T-MMC) was stratified in High-MMC (H-MMC) when thoracic and Low-MMC (L-MMC) when lumbar-sacral vertebrae affected. STATA/SE-12.1 and PLINK software were used for allelic association, TDT, and gene-gene interaction (GGI) analyses, considering p value <.01 as statistically significant differences (SSD).

RESULTS

Association analysis showed SSD for COBL-rs10230120, DVL2-rs2074216, PLCB4-rs6077510 GVs in T-MMC and L-MMC, and VANGL2-rs120886448 in T-MMC and H-MMC, and INVS-rs7024375 exclusively in L-MMC. TDT assay showed SSD preferential transmissions of C2CD3-rs826058 in H-MMC, and LRP5-rs3736228, and BBS2-rs1373 in L-MMC. Statistically significant GGI was observed in four in T-MMC, four completely different in L-MMC, and one in H-MMC. Interestingly, no one repeated in subphenotypes.

CONCLUSIONS

Our results support an association of GVs in Hh, Wnt, PCP, and cilia pathways, with MMC occurrence location, although further validation is needed. Furthermore, present results show a distinctive panel of gene-variants in H-MMC and LMMC subphenotypes, suggesting a feasible genotype-phenotype correlation.

Chiari 1 malformation and exome sequencing in 51 trios: the emerging role of rare missense variants in chromatin-remodeling genes

Type 1 Chiari malformation (C1M) is characterized by cerebellar tonsillar herniation of 3–5 mm or more, the frequency of which is presumably much higher than one in 1000 births, as previously believed. Its etiology remains undefined, although a genetic basis is strongly supported by C1M presence in numerous genetic syndromes associated with different genes. Whole-exome sequencing (WES) in 51 between isolated and syndromic pediatric cases and their relatives was performed after confirmation of the defect by brain magnetic resonance image (MRI). Moreover, in all the cases showing an inherited candidate variant, brain MRI was performed in both parents and not only in the carrier one to investigate whether the defect segregated with the variant. More than half of the variants were Missense and belonged to the same chromatin-remodeling genes whose protein truncation variants are associated with severe neurodevelopmental syndromes. In the remaining cases, variants have been detected in genes with a role in cranial bone sutures, microcephaly, neural tube defects, and RASopathy. This study shows that the frequency of C1M is widely underestimated, in fact many of the variants, in particular those in the chromatin-remodeling genes, were inherited from a parent with C1M, either asymptomatic or with mild symptoms. In addition, C1M is a Mendelian trait, in most cases inherited as dominant. Finally, we demonstrate that modifications of the genes that regulate chromatin architecture can cause localized anatomical alterations, with symptoms of varying degrees.

Snx3 is important for mammalian neural tube closure via its role in canonical and non-canonical WNT signaling

Disruptions in neural tube (NT) closure result in neural tube defects (NTDs). To understand the molecular processes required for mammalian NT closure, we investigated the role of Snx3, a sorting nexin gene. Snx3^-/- mutant mouse embryos display a fully-penetrant cranial NTD. In vivo, we observed decreased canonical WNT target gene expression in the cranial neural epithelium of the Snx3^-/- embryos and a defect in convergent extension of the neural epithelium. Snx3^-/- cells show decreased WNT secretion, and live cell imaging reveals aberrant recycling of the WNT ligand-binding protein WLS and mis-trafficking to the lysosome for degradation. The importance of SNX3 in WNT signaling regulation is demonstrated by rescue of NT closure in Snx3^-/- embryos with a WNT agonist. The potential for SNX3 to function in human neurulation is revealed by a point mutation identified in an NTD-affected individual that results in functionally impaired SNX3 that does not colocalize with WLS and the degradation of WLS in the lysosome. These data indicate that Snx3 is crucial for NT closure via its role in recycling WLS in order to control levels of WNT signaling.

Neural Tube Defects and Associated Anomalies before and after Folic Acid Fortification

OBJECTIVE

To examine the prevalence and types of neural tube defects and the types of anomalies co-occurring with neural tube defects in 6 years before fortification of cereal grain flour with folic acid (1992-1998) and 20 years after fortification (1999-2018) in South Carolina, a state with a historically high prevalence of these birth defects.

STUDY DESIGN

The prevalence of neural tube defects was determined by active and passive surveillance methods in South Carolina since 1992. The types of neural tube defects and co-occurring malformations were determined by prenatal ultrasound and post-delivery examination.

RESULTS

In the 6 prefortification years, 363 neural tube defects were identified among 279 163 live births and fetal deaths (1/769), 305 (84%) of which were isolated defects of the calvaria or spine. In the 20 fortification years, there were significant reductions in the prevalence and percentage of isolated defects: 938 neural tube defects were identified among 1 165 134 live births and fetal deaths (1/1242), 696 (74.2%) of which were isolated. The current prevalence of neural tube defects in South Carolina (0.56/1000 live births and fetal deaths) is comparable with that nationwide.

CONCLUSIONS

The continued occurrence of neural tube defects, the majority of which are isolated, after folic acid fortification of cereal grain flours suggests that additional prevention measures are necessary to reduce further the prevalence of these serious defects of the brain and spine.

Burden of rare deleterious variants in WNT signaling genes among 511 myelomeningocele patients

Genes in the noncanonical WNT signaling pathway controlling planar cell polarity have been linked to the neural tube defect myelomeningocele. We hypothesized that some genes in the WNT signaling network have a higher mutational burden in myelomeningocele subjects than in reference subjects in gnomAD. Exome sequencing data from 511 myelomeningocele subjects was obtained in-house and data from 29,940 ethnically matched subjects was provided by version 2 of the publicly available Genome Aggregation Database. To compare mutational burden, we collapsed rare deleterious variants across each of 523 human WNT signaling genes in case and reference populations. Ten WNT signaling genes were disrupted with a higher mutational burden among Mexican American myelomeningocele subjects compared to reference subjects (Fishers exact test, P ≤ 0.05) and seven different genes were disrupted among individuals of European ancestry compared to reference subjects. Gene ontology enrichment analyses indicate that genes disrupted only in the Mexican American population play a role in planar cell polarity whereas genes identified in both populations are important for the regulation of canonical WNT signaling. In summary, evidence for WNT signaling genes that may contribute to myelomeningocele in humans is presented and discussed.

Association between rare variants in specific functional pathways and human neural tube defects multiple subphenotypes

BACKGROUND

Neural tube defects (NTDs) are failure of neural tube closure, which includes multiple central nervous system phenotypes. More than 300 mouse mutant strains exhibits NTDs phenotypes and give us some clues to establish association between biological functions and subphenotypes. However, the knowledge about association in human remains still very poor.

METHODS

High throughput targeted genome DNA sequencing were performed on 280 neural tube closure-related genes in 355 NTDs cases and 225 ethnicity matched controls, RESULTS: We explored that potential damaging rare variants in genes functioning in chromatin modification, apoptosis, retinoid metabolism and lipid metabolism are associated with human NTDs. Importantly, our data indicate that except for planar cell polarity pathway, craniorachischisis is also genetically related with chromatin modification and retinoid metabolism. Furthermore, single phenotype in cranial or spinal regions displays significant association with specific biological function, such as anencephaly is associated with potentially damaging rare variants in genes functioning in chromatin modification, encephalocele is associated with apoptosis, retinoid metabolism and one carbon metabolism, spina bifida aperta and spina bifida cystica are associated with apoptosis; lumbar sacral spina bifida aperta and spina bifida occulta are associated with lipid metabolism. By contrast, complex phenotypes in both cranial and spinal regions display association with various biological functions given the different phenotypes.

CONCLUSIONS

Our study links genetic variant to subphenotypes of human NTDs and provides a preliminary but direct clue to investigate pathogenic mechanism for human NTDs.

Closing in on Mechanisms of Open Neural Tube Defects

Neural tube defects (NTDs) represent a failure of the neural plate to complete the developmental transition to a neural tube. NTDs are the most common birth anomaly of the CNS. Following mandatory folic acid fortification of dietary grains, a dramatic reduction in the incidence of NTDs was observed in areas where the policy was implemented, yet the genetic drivers of NTDs in humans, and the mechanisms by which folic acid prevents disease, remain disputed. Here, we discuss current understanding of human NTD genetics, recent advances regarding potential mechanisms by which folic acid might modify risk through effects on the epigenome and transcriptome, and new approaches to study refined phenotypes for a greater appreciation of the developmental and genetic causes of NTDs.

WDR34 mutation from anencephaly patients impaired both SHH and PCP signaling pathways

Neural tube defects (NTDs) are debilitating human congenital abnormalities due to failure of neural tube closure. Sonic Hedgehog (SHH) signaling is required for dorsal-ventral patterning of the neural tube. The loss of activation in SHH signaling normally causes holoprosencephaly while the loss of inhibition causes exencephaly due to failure in neural tube closure. WDR34 is a dynein intermedia chain component which is required for SHH activation. However, Wdr34 knockout mouse exhibit exencephaly. Here we screened mutations in WDR34 gene in 100 anencephaly patients of Chinese Han population. Compared to 1000 Genome Project data, two potentially disease causing missense mutations of WDR34 gene (c.1177G>A; p.G393S and c.1310A>G; p.Y437C) were identified in anencephaly patients. These two mutations did not affect the protein expression level of WDR34. Luciferase reporter and endogenous target gene expression level showed that both mutations are lose-of-function mutations in SHH signaling. Surprisingly, WDR34 could promote planar cell polarity (PCP) signaling and the G393S lost this promoting effect on PCP signaling. Morpholino knockdown of wdr34 in zebrafish caused severe convergent extension defects and pericardial abnormalities. The G393S mutant has less rescuing effects than both WT and Y437C WDR34 in zebrafish. Our results suggested that mutation in WDR34 could contribute to human NTDs by affecting both SHH and PCP signaling.

Rare copy number variations of planar cell polarity genes are associated with human neural tube defects

Select single-nucleotide variants in planar cell polarity (PCP) genes are associated with increased risk for neural tube defects (NTDs). However, whether copy number variants (CNVs) in PCP genes contribute to NTDs is unknown. Considering that CNVs are implicated in several human developmental disorders, we hypothesized that CNVs in PCP genes may be causative factors to human NTDs. DNA from umbilical cord tissues of NTD-affected fetuses and parental venous blood samples were collected. We performed a quantitative analysis of copy numbers of all exon regions in the VANGL1, VANGL2, CELSR1, SCRIB, DVL2, DVL3, and PTK7 genes using a CNVplex assay. Quantitative real-time PCR (qPCR) was carried out to confirm the results of CNV analysis. As a result, 16 CNVs were identified among the NTDs. Of these CNVs, 5 loci were identified in 11 NTD probands with CNVs involving DVL2 (exons 1-15), VANGL1 (exons 1-7, exon 8), and VANGL2 (exons 5-8, exons 7 and 8). One CNV (DVL2 exons 1-15) was a duplication and the remaining 15 CNVs were deletions. Eleven CNVs were confirmed by qPCR. One de novo CNV in VANGL1 and one DVL2 were detected from two cases. Compared with unaffected control populations in 1000 Genome, ExAC, MARRVEL, DGV, and dbVar databases, the frequencies of de novo deletion in VANGL1 (1.14%) and de novo duplication in DVL2 (0.57%) were significantly higher in our NTD subjects (p < 0.05). This study demonstrates that de novo CNVs in PCP genes, notably deletions in VANGL1 and gains in DVL2, could contribute to the risk of NTDs.

Somatic mutations in planar cell polarity genes in neural tissue from human fetuses with neural tube defects

Extensive studies that have sought causative mutation(s) for neural tube defects (NTDs) have yielded limited positive findings to date. One possible reason for this is that many studies have been confined to analyses of germline mutations and so may have missed other, non-germline mutations in NTD cases. We hypothesize that somatic mutations of planar polarity pathway (PCP) genes may play a role in the development of NTDs. Torrent™ Personal Genome Machine™ (PGM) sequencing was designed for selected PCP genes in paired DNA samples extracted from the tissues of lesion sites and umbilical cord from 48 cases. Sanger sequencing was used to validate the detected mutations. The source and distribution of the validated mutations in tissues from different germ layers were investigated. Subcellular location, western blotting, and luciferase assays were performed to better understand the effects of the mutations on protein localization, protein level, and pathway signaling. ix somatic mutations were identified and validated, which showed diverse distributions in different tissues. Three somatic mutations were novel/rare: CELSR1 p.Gln2125His, FZD6 p.Gln88Glu, and VANGL1 p.Arg374His. FZD6 p.Gln88Glu caused mislocalization of its protein from the cytoplasm to the nucleus, and disrupted the colocalization of CELSR1 and FZD6. This mutation affected non-canonical WNT signaling in luciferase assays. VANGL1 p.Arg374His impaired the co-localization of CELSR1 and VANGL1, increased the protein levels of VANGL1, and influenced cell migration. In all, 7/48 (14.5%) of the studied NTD cases contained somatic PCP mutations. Somatic mutations in PCP genes (e.g., FZD6 and VANGL1) are associated with human NTDs, and they may occur in different stages and regions during embryonic development, resulting in a varied distribution in fetal tissues/organs.

Mouse Models of Neural Tube Defects

During embryonic development, the central nervous system forms as the neural plate and then rolls into a tube in a complex morphogenetic process known as neurulation. Neural tube defects (NTDs) occur when neurulation fails and are among the most common structural birth defects in humans. The frequency of NTDs varies greatly anywhere from 0.5 to 10 in 1000 live births, depending on the genetic background of the population, as well as a variety of environmental factors. The prognosis varies depending on the size and placement of the lesion and ranges from death to severe or moderate disability, and some NTDs are asymptomatic. This chapter reviews how mouse models have contributed to the elucidation of the genetic, molecular, and cellular basis of neural tube closure, as well as to our understanding of the causes and prevention of this devastating birth defect.

Embryology of Spinal Dysraphism and its Relationship to Surgical Treatment

Spinal dysraphism is an umbrella term that encompasses a number of congenital malformations that affect the central nervous system. The etiology of these conditions can be traced back to a specific defect in embryological development, with the more disabling malformations occurring at an earlier gestational age. A thorough understanding of the relevant neuroembryology is imperative for clinicians to select the correct treatment and prevent complications associated with spinal dysraphism. This paper will review the neuroembryology associated with the various forms of spinal dysraphism and provide a clinical-pathological correlation for these congenital malformations.

Mutations associated with human neural tube defects display disrupted planar cell polarity in Drosophila

Planar cell polarity (PCP) and neural tube defects (NTDs) are linked, with a subset of NTD patients found to harbor mutations in PCP genes, but there is limited data on whether these mutations disrupt PCP signaling in vivo. The core PCP gene Van Gogh (Vang), Vangl1/2 in mammals, is the most specific for PCP. We thus addressed potential causality of NTD-associated Vangl1/2 mutations, from either mouse or human patients, in Drosophila allowing intricate analysis of the PCP pathway. Introducing the respective mammalian mutations into Drosophila Vang revealed defective phenotypic and functional behaviors, with changes to Vang localization, post-translational modification, and mechanistic function, such as its ability to interact with PCP effectors. Our findings provide mechanistic insight into how different mammalian mutations contribute to developmental disorders and strengthen the link between PCP and NTD. Importantly, analyses of the human mutations revealed that each is a causative factor for the associated NTD.

MicroRNA targeting of the non-canonical planar cell polarity pathway in the developing neural tube

MicroRNAs (miRNAs) provide context-dependent transcriptional regulation of genes comprising signalling networks throughout the developing organism including morphogenesis of the embryonic neural tube (NT). Using a high-sensitivity, high-coverage microarray analysis platform, miRNA expression in the murine embryonic NT during the critical stages of its formation was examined. Analysis of a number of differentially expressed (DE) miRNAs enabled identification of several gene targets associated with cellular processes essential for normal NT development. Using computational pathway analysis, interactive biologic networks and functional relationships connecting DE miRNAs with their targeted messenger RNAs (mRNAs) were identified. Potential mRNA targets and a key signal transduction pathway governing critical cellular processes indispensable for normal mammalian neurulation were also identified. RNA preparations were also used to hybridize both miRNA arrays and mRNA arrays allowing miRNA-mRNA target analysis using data of DE miRNAs and DE mRNAs - co-expressed in the same developing NT tissue samples. Identification of these miRNA targets provides key insight into the epigenetic regulation of NT development as well as into potential mechanistic underpinning of NT defects. SIGNIFICANCE OF THE STUDY: This study underscores the premise that microRNAs are potential coordinators of normal neural tube (NT) formation, via regulation of the crucial, planar cell polarity pathway. Any alteration in their expression during neurulation would result in abnormal NT development.

The etiopathogenic and morphological spectrum of anencephaly: a comprehensive review of literature

Anencephaly is a severe malformation of the central nervous system (CNS), being one of the most common types of neural tube defects. It is defined as total or partial absence of the calvarium, with absence of the brain. Anencephaly has an incidence of 1 to 5 in every 1000 births, and the mortality rate is 100% during intrauterine life or within hours or days after birth. The etiology of anencephaly remains unclear, but various maternal-related environmental and genetic risk factors have been reported, which include diabetes, obesity, exposure to different drugs or toxins, genetic polymorphisms and mutations, as well as positive family history for neural tube defects. One of the most important nutritional factors in the development of anencephaly is folate deficiency. Methylenetetrahydrofolate reductase (MTHFR) gene codes the enzyme involved in the intracellular metabolism of folic acid; the 677C-T polymorphism of this gene causes the thermolability of the enzyme and decreased enzymatic activity, which is also dependent of folate plasmatic level. Etiopathogenesis of anencephaly includes several mutations in various other genes, such as: platelet-derived growth factor receptor alpha (PDGFRA), cadherin epidermal growth factor (EGF) laminin G (LAG) seven-pass G-type receptor 1 (CELSR1), Vang-like 1 (VANGL1) and Vang-like 2 (VANGL2), the last two being involved in the process of neurulation. Screening tests include maternal serum alpha-fetoprotein level and ultrasound (US) examination. During the first trimester US screening, anencephaly is now detected in all cases, but in order to decrease the complication rate of pregnancy termination, the diagnosis should be established as soon as possible, during the pregnancy confirmation US. We conclude that given that anencephaly is a severe malformation of the CNS, morphological characterization could improve the screening by US that is mandatory in the first trimester in order to plan the best, safe and early management.

The search for genetic determinants of human neural tube defects

PURPOSE OF REVIEW

An update is presented regarding neural tube defects (NTDs) including spina bifida and anencephaly, which are among the most common serious birth defects world-wide. Decades of research suggest that no single factor is responsible for neurulation failure, but rather NTDs arise from a complex interplay of disrupted gene regulatory networks, environmental influences and epigenetic regulation. A comprehensive understanding of these dynamics is critical to advance NTD research and prevention.

RECENT FINDINGS

Next-generation sequencing has ushered in a new era of genomic insight toward NTD pathophysiology, implicating novel gene associations with human NTD risk. Ongoing research is moving from a candidate gene approach toward genome-wide, systems-based investigations that are starting to uncover genetic and epigenetic complexities that underlie NTD manifestation.

SUMMARY

Neural tube closure is critical for the formation of the human brain and spinal cord. Broader, more all-inclusive perspectives are emerging to identify the genetic determinants of human NTDs.

Whole-Exome Sequencing Identifies Damaging de novo Variants in Anencephalic Cases

BACKGROUND

Anencephaly is a lethal neural tube defect (NTD). Although variants in several genes have been implicated in the development of anencephaly, a more complete picture of variants in the genome, especially de novo variants (DNVs), remains unresolved. We aim to identify DNVs that play an important role in the development of anencephaly by performing whole-exome DNA sequencing (WES) of proband-parent trios.

RESULTS

A total of 13 DNVs were identified in 8 anencephaly trios by WES, including two loss of function (LoF) variants detected in pLI > 0.9 genes (SPHKAP, c.2629_2633del, and NCOR1, p.Y1907X). Damaging DNVs were identified in 61.5% (8/13) of the anencephalic cases. Independent validation was conducted in an additional 502 NTD cases. Gene inactivation using targeted morpholino antisense oligomers and rescue assays were conducted in zebrafish, and transfection expression in HEK293T cells. Four DNVs in four cases were identified and predicted to alter protein function, including p.R328Q in WD repeat domain phosphoinositide-interacting 1 (WIPI1). Three variants, p.G313R, p.T418M, and p.L406P, in the WIPI1 gene were identified from the independent replication cohort consisting of 502 cases. Functional analysis suggested that the wipi1 p.L406P and p.R328Q variants most likely displayed loss-of-function effects during embryonic development.

CONCLUSION

De novo damaging variants are the main culprit for majority of anencephalic cases. Missense variants in WIPI1 may play a role in the genetic etiology of anencephaly, and LoF variants in SPHKAP and NCOR1 may also contribute to anencephaly. These findings add to our existing understanding of the genetic mechanisms of NTD formation.

Update on the Role of the Non-Canonical Wnt/Planar Cell Polarity Pathway in Neural Tube Defects

Neural tube defects (NTDs), including spina bifida and anencephaly, represent the most severe and common malformations of the central nervous system affecting 0.7–3 per 1000 live births. They result from the failure of neural tube closure during the first few weeks of pregnancy. They have a complex etiology that implicate a large number of genetic and environmental factors that remain largely undetermined. Extensive studies in vertebrate models have strongly implicated the non-canonical Wnt/planar cell polarity (PCP) signaling pathway in the pathogenesis of NTDs. The defects in this pathway lead to a defective convergent extension that is a major morphogenetic process essential for neural tube elongation and subsequent closure. A large number of genetic studies in human NTDs have demonstrated an important role of PCP signaling in their etiology. However, the relative contribution of this pathway to this complex etiology awaits a better picture of the complete genetic architecture of these defects. The emergence of new genome technologies and bioinformatics pipelines, complemented with the powerful tool of animal models for variant interpretation as well as significant collaborative efforts, will help to dissect the complex genetics of NTDs. The ultimate goal is to develop better preventive and counseling strategies for families affected by these devastating conditions.

A review of genetic factors underlying craniorachischisis and omphalocele: Inspired by a unique trisomy 18 case

Very few cases of craniorachischisis (CRN) with concomitant omphalocele (OMP) in the setting of trisomy 18 are reported in literature. Solitary midline closure defects are estimated to be more prevalent in trisomy 18 compared to the general population. Neurulation defect comparisons include anencephaly 0-2% versus 0.0206%, spina bifida 1-3% versus 0.0350%, and encephalocele 0-2% versus 0.0082% [Parker et al. (2010); Birth Defects Research. Part A: Clinical and Molecular Teratology, 88:1008-1016; Springett et al. (2015); American Journal of Medical Genetics. Part A, 167A:3062-3069]. The solitary anterior malformation OMP has been reported as high as 6% with trisomy 18 [Springett et al. (2015); American Journal of Medical Genetics. Part A, 167A:3062-3069]. We report the third published case of CRN with concomitant OMP observed in a likely trisomy 18 fetus that screened positive by noninvasive prenatal screening. Furthermore, we review and analyze the current literature to augment understanding of the genetic basis for anterior and posterior closure defects such as CRN and OMP. Although the current genetic lexicon lacks any definitive association with the simultaneous defects presented, previous research elucidated various genes related to anterior or posterior closure interruption individually. By consolidating current research, the authors advance knowledge of interconnected genetic pathology and direct future genetic mapping efforts.

Overexpression of Grainyhead-like 3 causes spina bifida and interacts genetically with mutant alleles of Grhl2 and Vangl2 in mice

The genetic basis of human neural tube defects (NTDs), such as anencephaly and spina bifida (SB), is complex and heterogeneous. Grainyhead-like genes represent candidates for involvement in NTDs based on the presence of SB and exencephaly in mice carrying loss-of-function alleles of Grhl2 or Grhl3. We found that reinstatement of Grhl3 expression, by bacterial artificial chromosome (BAC)-mediated transgenesis, prevents SB in Grhl3-null embryos, as in the Grhl3 hypomorphic curly tail strain. Notably, however, further increase in expression of Grhl3 causes highly penetrant SB. Grhl3 overexpression recapitulates the spinal NTD phenotype of loss-of-function embryos, although the underlying mechanism differs. However, it does not phenocopy other defects of Grhl3-null embryos such as abnormal axial curvature, cranial NTDs (exencephaly) or skin barrier defects, the latter being rescued by the Grhl3-transgene. Grhl2 and Grhl3 can form homodimers and heterodimers, suggesting a possible model in which defects arising from overexpression of Grhl3 result from sequestration of Grhl2 in heterodimers, mimicking Grhl2 loss of function. This hypothesis predicts that increased abundance of Grhl2 would have an ameliorating effect in Grhl3 overexpressing embryo. Instead, we observed a striking additive genetic interaction between Grhl2 and Grhl3 gain-of-function alleles. Severe SB arose in embryos in which both genes were expressed at moderately elevated levels that individually do not cause NTDs. Furthermore, moderate Grhl3 overexpression also interacted with the Vangl2Lp allele to cause SB, demonstrating genetic interaction with the planar cell polarity signalling pathway that is implicated in mouse and human NTDs.

High burden of neural tube defects in Tigray, Northern Ethiopia: Hospital-based study

Introduction

Neural tube defects are the major causes of fetal loss and considerable disabilities in infants. Currently, there is no significant research on the incidence of Neural tube defects in the Tigray region of Ethiopia.

Objective

To determine the incidence and clinical pattern of the Neural Tube Defects.

Methods

A hospital-based cross-sectional study was conducted from October 2016 to June 2017. All pregnancy outcomes were examined for any externally visible birth defects and neurological integrity by trained midwives under the supervision of senior obstetrics and gynecology and a neurosurgeon. Data were collected using a survey tool to collect maternal and newborn demographic data and a checklist developed to capture newborns with Neural Tube Defects. Data were analyzed using SPSS version 20. The prevalence of NTDs was calculated per 10,000 births.

Result

Out of the 14,903 births during the study period, a total of 195 infants were born afflicted with Neural Tube Defects. The burden of infants with anencephaly and spina bifida was 66.4 and 64.4 per 10, 000 births, respectively. The overall incidence rate of NTDs in this study was 131 per 10, 000 births of which 23% were liveborn and 77% were stillborn. The highest burden of Neural Tube Defects was observed in Adigrat Hospital from Eastern Zone of Tigray (174 per 10,000 births) and Lemlem Karl Hospital from Southern Zone of Tigray (304 per 10,000 births) compared to Kahsay Abera Hospital from Western Zone (72.8 per 10,000 births) and Sihul Hospital from North Western Zone of Tigray (69.8 per 10,000 births).

Conclusion and recommendation

Assuming that the non folic acid preventable rate should be 5 per 10,000 births, our prevalence rate is 131 per 10,000 births, and then we have a rate or an epidemic that is 26 times what it should be. This just emphasizes the urgency to implement effective programs to get all women of reproductive age to have adequate folic acid to prevent all of folic acid-preventable spina bifida and anencephaly, which would prevent 96% (125/130) of spina bifida and anencephaly in the Tigray Provence.

Whole exome sequencing identifies novel predisposing genes in neural tube defects

BACKGROUND

Neural tube defects (NTD) are among the most common defects affecting 1:1000 births. They are caused by a failure of neural tube closure during development. Their clinical presentation is diverse and dependent on the site and severity of the original defect on the embryonic axis. The etiology of NTD is multifactorial involving environmental factors and genetic variants that remain largely unknown.

METHODS

We have conducted a whole exome sequencing (WES) study in five new NTD families and pooled the results with WES data from three NTD families and 43 trios that were previously investigated by our group. We analyzed the data using biased candidate gene and unbiased gene burden approaches.

RESULTS

We identified four novel loss-of-function variants in three genes, MTHFR, DLC1, and ITGB1, previously associated with NTD. Notably, DLC1 carried two protein truncating variants in two independent cases. We also demonstrated an enrichment of variants in MYO1E involved in cytoskeletal remodeling. This enrichment reached borderline significance in a replication cohort supporting the association of this new candidate gene to NTD.

CONCLUSION

These data provide some key insights into the pathogenic mechanisms of human NTD and demonstrate the power of next-generation sequencing in deciphering the genetics of this complex trait.

Insights into the Etiology of Mammalian Neural Tube Closure Defects from Developmental, Genetic and Evolutionary Studies

The human neural tube defects (NTD), anencephaly, spina bifida and craniorachischisis, originate from a failure of the embryonic neural tube to close. Human NTD are relatively common and both complex and heterogeneous in genetic origin, but the genetic variants and developmental mechanisms are largely unknown. Here we review the numerous studies, mainly in mice, of normal neural tube closure, the mechanisms of failure caused by specific gene mutations, and the evolution of the vertebrate cranial neural tube and its genetic processes, seeking insights into the etiology of human NTD. We find evidence of many regions along the anterior–posterior axis each differing in some aspect of neural tube closure—morphology, cell behavior, specific genes required—and conclude that the etiology of NTD is likely to be partly specific to the anterior–posterior location of the defect and also genetically heterogeneous. We revisit the hypotheses explaining the excess of females among cranial NTD cases in mice and humans and new developments in understanding the role of the folate pathway in NTD. Finally, we demonstrate that evidence from mouse mutants strongly supports the search for digenic or oligogenic etiology in human NTD of all types.