Current perspectives on the genetic causes of neural tube defects

Molecular Insight into the Effect of a Single-Nucleotide Polymorphic Variation on the Structure and Dynamics of Methionine Synthase Reductase and Its Association with Neural Tube Defects

Neural tube defects (NTDs) are among the common and severe congenital malformations in neonates. According to a WHO report, nearly three lakh babies are affected per year worldwide by NTDs. Most studies revealed that folate deficiency is the key element to promote NTD with other oligogenic and multifactorial elements. This folate is metabolized by the FOCM (folate one-carbon metabolism) pathway. The most important step in the FOCM pathway is the conversion of methionine to homocysteine, which is guided by the enzyme MTRR. Several single-nucleotide polymorphisms (SNPs) in the MTRR gene are strongly associated with the progression of NTD. A nonsynonymous allelic variant (rs1532268) of the protein leads to a missense mutation at the 202nd position from serine to leucine (S202L) and is associated with a higher disease prevalence in different populations. In our study, this SNP indicates a 2-fold increase in the risk of disease progression (p-value of 0.03; OR 2.76; 95% CI 1.08-7.11). Here, extensive molecular dynamics simulations and interaction network analysis reveal that the change of 202nd serine to leucine alters the structures of the FAD and NAD binding domains, which restricts the ligand binding. The S202L variation alters the functional dynamics that might impede the electron transport chain along the NADP(H)→ FAD→ FMN pathway and hamper phosphorylation by kinases like GSK-3 and CaM-II during the posttranscriptional modification of the protein. The present study provides functional insights into the effect of the genetic variations of the MTRR gene on the NTD disease pathogenesis.

Congenital Spinal Lipomatous Malformations. Part 1. Spinal Lipomas, Lipomyeloceles, and Lipomyelomeningoceles

Background: Lumbosacral spinal lipomas and lipomyeloceles are usually identified in early childhood. Terminology, histopathology, and diagnosis for these malformations can be confusing. Materials and Methods: This is a PubMed review with comparison of embryology, gross, and histopathology, and reporting requisites for these and related closed spinal malformations. Results: The spinal lipoma group (congenital spinal lipomatous malformations) includes subcutaneous, transdural, intradural, and noncontiguous malformations stretching through the entire lower spinal region. This lipomyelocele trajectory overlaps the embryonic tail's caudal eminence. Histopathologically, the lipomyelocele spectrum is a heterogeneous, stereotypical set of findings encountered from dermis to spinal cord. Diagnosis requires detailed correlation of images, intraoperative inspection, and histopathology. Conclusions: Appropriate terminology and clinicopathologic correlation to arrive at a diagnosis is a critical activity shared by pathologist and clinician. Prognostic and management differences depend on specific diagnoses. Familial and genetic influences play little if any role in patient management in closed spinal malformations.

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.

Myelomeningocele (open spina bifida) - surgical management

Myelomeningocele has been recognized since ancient times although written descriptions began not before the 17th century. Among all serious congenital malformations, myelomeningocele is unique that is has a steady and considerable prevalence while being compatible with life. It has a dismal prognosis when left untreated where virtually all die within the first year while aggressive treatment have a profound effect on survival and quality of life. Effective surgical treatment became possible parallel to the treatment of hydrocephalus in the late 1950s. Advent of the shunt systems undoubtedly changed the morbidity and mortality rates due to associated hydrocephalus. Aggressive and effective treatment improved survival rates but also those suffering physical and mental disabilities have increased as well. Ethical and socioeconomic concerns have led to proposal for selective treatment criteria which have raised arguments on medical and ethico-legal rounds. After the swing of the pendulum between early treatment in all affected children and selective treatment of those who fulfilled the criteria for good prognosis, early myelomeningocele repair is practiced widely unless the infant is critically ill.Incidence of myelomeningocele has been decreasing especially in the Western world, partly due to prenatal diagnosis and elective terminations, dietary folate supplementation. Still, it is the most common central nervous system malformation and one of the leading causes of paraplegia, worldwide. Unfortunately, gains in the management of myelomeningocele have been mainly on antenatal diagnosis and prevention while efforts on understanding its cause, mechanisms involved are still tentative. Concerning the surgical management, no revolutionary modification improving outcome has been introduced unlike other fields of neurosurgery.Medical management of a child with myelomeningocele requires a lifelong effort of several disciplines including urology, orthopedics physical and social therapy besides neurosurgery. The initial and probably the most crucial step begin with proper repair of the lesion. The aim of surgery, with its simplest definition should be towards maintaining the medical condition of the newborn. In other words, consequences of an open spinal cord segment with associated malformations have to be avoided with appropriate measures. Comparable to the surgical treatment of any congenital malformation, myelomeningocele repair consist of reversing the failed steps of normal neural tube closure. This requires a thorough understanding of the normal and abnormal embryological sequence of events in formation of the spinal cord. Although the purpose of this chapter is to describe the basic concepts and technique of myelomeningocele repair, contemporary information and progress on epidemiology, and etiology and embryology is presented with discussion of controversial issues regarding the selection process, optimal time for surgery and technical modifications.

Junctional neurulation: a unique developmental program shaping a discrete region of the spinal cord highly susceptible to neural tube defects

In higher vertebrates, the primordium of the nervous system, the neural tube, is shaped along the rostrocaudal axis through two consecutive, radically different processes referred to as primary and secondary neurulation. Failures in neurulation lead to severe anomalies of the nervous system, called neural tube defects (NTDs), which are among the most common congenital malformations in humans. Mechanisms causing NTDs in humans remain ill-defined. Of particular interest, the thoracolumbar region, which encompasses many NTD cases in the spine, corresponds to the junction between primary and secondary neurulations. Elucidating which developmental processes operate during neurulation in this region is therefore pivotal to unraveling the etiology of NTDs. Here, using the chick embryo as a model, we show that, at the junction, the neural tube is elaborated by a unique developmental program involving concerted movements of elevation and folding combined with local cell ingression and accretion. This process ensures the topological continuity between the primary and secondary neural tubes while supplying all neural progenitors of both the junctional and secondary neural tubes. Because it is distinct from the other neurulation events, we term this phenomenon junctional neurulation. Moreover, the planar-cell-polarity member, Prickle-1, is recruited specifically during junctional neurulation and its misexpression within a limited time period suffices to cause anomalies that phenocopy lower spine NTDs in human. Our study thus provides a molecular and cellular basis for understanding the causality of NTD prevalence in humans and ascribes to Prickle-1 a critical role in lower spinal cord formation.

Expanding the mutational spectrum associated to neural tube defects: literature revision and description of novel VANGL1 mutations

BACKGROUND

Neural Tube Defects (NTD) are a common class of birth defects that occur in approximately 1 in 1000 live births. Both genetic and nongenetic factors are involved in the etiology of NTD. Planar cell polarity (PCP) genes plays a critical role in neural tube closure in model organisms. Studies in humans have identified nonsynonymous mutations in PCP pathway genes, including the VANGL genes, that may play a role as risk factors for NTD.

METHODS

Here, we present the results of VANGL1 and VANGL2 mutational screening in a series of 53 NTD patients and 27 couples with a previous NTD affected pregnancy.

RESULTS

We identified three heterozygous missense variants in VANGL1, p.Ala187Val, p.Asp389His, and p.Arg517His, that are absent in controls and predicted to be detrimental on the protein function and, thus, we expanded the mutational spectrum of VANGL1 in NTD cases. We did not identify any new variants having an evident pathogenic effect on protein function in VANGL2. Moreover, we reviewed all the rare nonsynonymous or synonymous variants of VANGL1 and VANGL2 found in patients and controls so far published and re-evaluated them for their pathogenic role by in silico prediction tools. Association tests were performed to demonstrate the enrichment of deleterious variants in reviewed cases versus controls from Exome Variant Server (EVS).

CONCLUSION

We showed a significant (p = 7.0E-5) association between VANGL1 rare genetic variants, especially missense mutations, and NTDs risk.

Organization of the neuroepithelial actin cytoskeleton is regulated by heparan sulfation during neurulation

Heparan sulfate and cytoskeletal actin microfilaments have both been shown to be important regulators of neural tube closure during embryonic development. To determine the functional relationship of these two molecules in formation of the spinal neural tube, we cultured ARC mouse embryos at embryonic day E8.5 in the presence of chlorate, a competitive inhibitor of glycosaminoglycan sulfation, and examined the effects on organization of actin microfilaments in the neuroepithelium. Compared against embryos cultured under control conditions, chlorate-treated embryos had shortened posterior neuropore, a loss of median hinge point formation and increased bending at the paired dorsolateral hinge points. Furthermore, apical organization of actin microfilaments in the neuroepithelial cells was absent, and this was associated with convex bending of the neuroepithelium. The results suggest that heparan sulfate is an important determinant of cytoskeletal actin organization during spinal neurulation, and that its biological action is dependent on sulfation of the heparan molecule.

Roles of planar cell polarity pathways in the development of neural [correction of neutral] tube defects

Neural tube defects (NTDs) are the second most common birth defect in humans. Despite many advances in the understanding of NTDs and the identification of many genes related to NTDs, the fundamental etiology for the majority of cases of NTDs remains unclear. Planar cell polarity (PCP) signaling pathway, which is important for polarized cell movement (such as cell migration) and organ morphogenesis through the activation of cytoskeletal pathways, has been shown to play multiple roles during neural tube closure. The disrupted function of PCP pathway is connected with some NTDs. Here, we summarize our current understanding of how PCP factors affect the pathogenesis of NTDs.

Role of chromatin remodeling gene Cecr2 in neurulation and inner ear development

The loss of Cecr2, which encodes a chromatin remodeling protein, has been associated with the neural tube defect (NTD) exencephaly and open eyelids in mice. Here, we show that two independent mutations of Cecr2 are also associated with specific inner ear defects. Homozygous mutant 18.5 days post coitus (dpc) fetuses exhibited smaller cochleae as well as rotational defects of sensory cells and extra cell rows in the inner ear reminiscent of planar cell polarity (PCP) mutants. Cecr2 was expressed in the neuroepithelium, head mesenchyme, and the cochlear floor. Although limited genetic interaction for NTDs was seen with Vangl2, a microarray analysis of PCP genes did not reveal a direct connection to this pathway. The mechanism of Cecr2 action in neurogenesis and inner ear development is likely complex.

Nonsynonymous substitution rate (Ka) is a relatively consistent parameter for defining fast-evolving and slow-evolving protein-coding genes

Background

Mammalian genome sequence data are being acquired in large quantities and at enormous speeds. We now have a tremendous opportunity to better understand which genes are the most variable or conserved, and what their particular functions and evolutionary dynamics are, through comparative genomics.

Results

We chose human and eleven other high-coverage mammalian genome data–as well as an avian genome as an outgroup–to analyze orthologous protein-coding genes using nonsynonymous (Ka) and synonymous (Ks) substitution rates. After evaluating eight commonly-used methods of Ka and Ks calculation, we observed that these methods yielded a nearly uniform result when estimating Ka, but not Ks (or Ka/Ks). When sorting genes based on Ka, we noticed that fast-evolving and slow-evolving genes often belonged to different functional classes, with respect to species-specificity and lineage-specificity. In particular, we identified two functional classes of genes in the acquired immune system. Fast-evolving genes coded for signal-transducing proteins, such as receptors, ligands, cytokines, and CDs (cluster of differentiation, mostly surface proteins), whereas the slow-evolving genes were for function-modulating proteins, such as kinases and adaptor proteins. In addition, among slow-evolving genes that had functions related to the central nervous system, neurodegenerative disease-related pathways were enriched significantly in most mammalian species. We also confirmed that gene expression was negatively correlated with evolution rate, i.e. slow-evolving genes were expressed at higher levels than fast-evolving genes. Our results indicated that the functional specializations of the three major mammalian clades were: sensory perception and oncogenesis in primates, reproduction and hormone regulation in large mammals, and immunity and angiotensin in rodents.

Conclusion

Our study suggests that Ka calculation, which is less biased compared to Ks and Ka/Ks, can be used as a parameter to sort genes by evolution rate and can also provide a way to categorize common protein functions and define their interaction networks, either pair-wise or in defined lineages or subgroups. Evaluating gene evolution based on Ka and Ks calculations can be done with large datasets, such as mammalian genomes.

Reviewers

This article has been reviewed by Drs. Anamaria Necsulea (nominated by Nicolas Galtier), Subhajyoti De (nominated by Sarah Teichmann) and Claus O. Wilke.

Spina bifida with associated malformations of the central nervous system in Dorper-cross sheep

CASE HISTORY

In 2008, six lambs within a flock of Dorper-cross sheep were born with musculoskeletal and neurological disease. Clinical signs included hindlimb weakness, and urinary incontinence.

CLINICAL FINDINGS

All lambs had focal, inverted areas of alopecic skin over the caudal sacrum, and short, often kinked tails. Four affected lambs were subject to euthanasia, and necropsied. On gross examination, the arches of sacral vertebrae were absent, and spinal nerves and meninges were adherent to the overlying subcutis. Other gross lesions included narrow, elongated skulls, herniation of the occipital lobes into the caudal fossas, hydrocephalus, and syringomyelia. One lamb had coning of the cerebellar vermis, but cerebellar herniation through the foramen magnum was not identified.

DIAGNOSIS

Spina bifida, with associated malformations of the central nervous system.

CLINICAL RELEVANCE

Examination of breeding records suggested either an autosomal recessive or partially penetrant autosomal dominant pattern of inheritance. Because of the associated tail lesions it is proposed that the pathogenesis of this syndrome involves a defect in development of the tail bud (secondary neurulation), that tethering of the spinal cord resulted in the clinical signs, and abnormal pressure of the cerebral spinal fluid resulted in the defects in the skull and brain.

Degree of genetic homozygosity and distribution of AB0 blood types among patients with spina bifida occulta and spina bifida aperta

INTRODUCTION

Assuming that spina bifida (SB) is a genetically controlled disease, the aim of our study was to evaluate the degree of genetic homozygosity and the distribution of AB0 blood types among patients with SB occulta and SB aperta by the homozygously recessive characteristics (HRC) test.

MATERIAL AND METHODS

Our study included an analysis of the presence, distribution and individual combination of 15 selected genetically controlled morpho-physiological traits in a sample of 100 patients with SB (SB occulta N = 50 and SB aperta N = 50) and a control group of individuals (N = 100).

RESULTS

We found a statistically significant difference between the mean values for genetic homozygosity (SB 4.5 ±0.3; control 3.0 ±0.2, p < 0.001) and also differences in the presence of certain individual combinations of such traits. In 12 (80.0%) of the 15 observed characteristics, recessive homozygosity was expressed to a greater degree among the group of SB patients, while for 9 (60.0%) of the traits this level of difference was statistically significant (Σ(χ) (2) = 266.3, p < 0.001). There was no difference in average homozygosity of such genetic markers between groups of SB occulta and SB aperta patients, but the type of individual variation in the two studied groups significantly differed. In the group of patients with SB the frequency of 0 blood group was significantly increased while B blood group was significantly decreased.

CONCLUSIONS

Our results clearly show that there is a populational genetic difference in the degree of genetic homozygosity and variability between the group of patients with SB and individuals without clinical manifestations, indicating a possible genetic component in the aetiopathogenesis of spina bifida.

Global DNA hypomethylation is associated with NTD-affected pregnancy: A case-control study

BACKGROUND

Neural tube defects are severe, common birth defects that result from failure of neural tube closure. They are considered to be a multifactorial disorder, and our knowledge of causal mechanisms remains limited. We hypothesized that abnormal DNA methylation occurs in NTD-affected fetuses. The correlations of global DNA methylation levels with complexity of NTDs and known risk factors of NTDs, MTHFR genotype and fever, were analyzed.

METHODS

A hospital-based case-control study was performed. Epidemiologic data, pathologic diagnosis, and methylenetetrahydrofolate reductase (MTHFR) genotype analysis were completed. Array comparative genomic hybridization was used to exclude cytogenetic abnormalities. Global DNA methylation statuses were determined for both brain and skin tissue.

RESULTS

Sixty-five NTD-affected fetuses and 65 normal controls matched for gestational and maternal ages were collected. In brain tissue, global DNA methylation levels were significantly decreased in cases compared with controls (4.12 vs. 4.99%; p < 0.001). DNA hypomethylation (<4.35%) resulted in a significant 5.736-fold increased risk for NTDs (95% confidence interval, 1.731-19.009; p = 0.004). Nonisolated NTDs had lower levels of global DNA methylation than did isolated NTDs (3.77 vs. 4.70%; p = 0.022). After stratifying subjects by MTHFR genotype, we observed a skewed distribution of global DNA methylation levels. For genotype C/C, global DNA methylation status was the same in the two groups (4.51 vs. 4.72%; p = 0.687). For T/T, cases had significantly lower global methylation levels than did controls (5.23 vs. 3.79%; p < 0.001).

CONCLUSIONS

Global DNA hypomethylation in fetal brain tissue was associated with NTD-affected pregnancy. DNA methylation levels were correlated with NTD complexity. The MTHFR genotype contributed to global DNA hypomethylation. Birth Defects Research (Part A), 2010. (c) 2010 Wiley-Liss, Inc.

Nontumor lesions of spinal cord and spine

Nontumor lesions of the spinal cord and spine include developmental disorders, cystic tumor-like lesions, vascular disorders, infective diseases, demyelinating diseases, degenerative diseases, metabolic and toxic disorders, and spinal cord injury. In addition, diseases of the spine and extradural spaces secondarily cause spinal cord injury. Aside from tumors, these include developmental abnormalities, inflammatory diseases, nontumor space-occupying lesions, and tumor-like lesions such as lipomas, vascular malformations, and cysts. Awareness is required of hemostatic agents used during surgery and subsequently presenting as space-occupying lesions, which have to be differentiated from recurrent lesions. On the therapeutic front, stem cell transplantation into spinal cord for treatment of neurodegenerative disorders, spinal cord injury, and multiple sclerosis is a challenging prospect.

Contribution of VANGL2 mutations to isolated neural tube defects

Vangl2 was identified as the gene defective in the Looptail (Lp) mouse model for neural tube defects (NTDs). This gene forms part of the planar cell polarity (PCP) pathway, also called the non-canonical Frizzled/Dishevelled pathway, which mediates the morphogenetic process of convergent extension essential for proper gastrulation and neural tube formation in vertebrates. Genetic defects in PCP signaling have strongly been associated with NTDs in mouse models. To assess the role of VANGL2 in the complex etiology of NTDs in humans, we resequenced this gene in a large multi-ethnic cohort of 673 familial and sporadic NTD patients, including 453 open spina bifida and 202 closed spinal NTD cases. Six novel rare missense mutations were identified in seven patients, five of which were affected with closed spinal NTDs. This suggests that VANGL2 mutations may predispose to NTDs in approximately 2.5% of closed spinal NTDs (5 in 202), at a frequency that is significantly different from that of 0.4% (2 in 453) detected in open spina bifida patients (p = 0.027). Our findings strongly implicate VANGL2 in the genetic causation of spinal NTDs in a subset of patients and provide additional evidence for a pathogenic role of PCP signaling in these malformations.

Alx3-deficient mice exhibit folic acid-resistant craniofacial midline and neural tube closure defects

Neural tube closure defects are among the most frequent congenital malformations in humans. Supplemental maternal intake of folic acid before and during pregnancy reduces their incidence significantly, but the mechanism underlying this preventive effect is unknown. As a number of genes that cause neural tube closure defects encode transcriptional regulators in mice, one possibility is that folic acid could induce the expression of transcription factors to compensate for the primary genetic defect. We report that folic acid is required in mouse embryos for the specific expression of the homeodomain gene Alx3 in the head mesenchyme, an important tissue for cranial neural tube closure. Alx3-deficient mice exhibit increased failure of cranial neural tube closure and increased cell death in the craniofacial region, two effects that are also observed in wild type embryos developing in the absence of folic acid. Folic acid cannot prevent these defects in Alx3-deficient embryos, indicating that one mechanism of folic acid action is through induced expression of Alx3. Thus, Alx3 emerges as a candidate gene for human neural tube defects and reveals the existence of induced transcription factor gene expression as a previously unknown mechanism by which folic acid prevents neural tube closure defects.

A patient with DiGeorge syndrome with spina bifida and sacral myelomeningocele, who developed both hypocalcemia-induced seizure and epilepsy

DiGeorge syndrome - a component of the 22q11 deletion syndrome - causes a disturbance in cervical neural crest migration that results in parathyroid hypoplasia. Patients can develop hypocalcemia-induced seizures. Spina bifida is caused by failure of neurulation, including a disturbance in the adhesion processes at the neurula stage. Spina bifida has been reported as a risk factor for epilepsy. We report, for the first time, the case of a patient with DiGeorge syndrome with spina bifida and sacral myelomeningocele, who developed both hypocalcemia-induced seizures and epilepsy. The patient had spina bifida and sacral myelomeningocele at birth. At the age of 13 years, he experienced a seizure for the first time. At this time, the calcium concentration was normal. An electroencephalogram (EEG) proved that the seizure was due to epilepsy. Antiepileptic medications controlled the seizure. At the age of 29, the patient's calcium concentration began to reduce. At the age of 40, hypocalcemia-induced seizure occurred. At this time, the calcium concentration was 5.5mg/dL (reference range, 8.7-10.1mg/dL). The level of intact parathyroid hormone (PTH) was 6 pg/mL (reference range, 10-65 pg/mL). Chromosomal and genetic examinations revealed a deletion of TUP-like enhancer of split gene 1 (tuple1)-the diagnostic marker of DiGeorge syndrome. Many patients with DiGeorge syndrome have cardiac anomalies; however, our patient had none. We propose that the association among DiGeorge syndrome, spina bifida, epilepsy, cardiac anomaly, 22q11, tuple1, and microdeletion inheritance should be clarified for appropriate diagnosis and treatment.

ATX expression and LPA signalling are vital for the development of the nervous system

Autotaxin (ATX) is a secreted glycoprotein widely present in biological fluids, originally isolated from the supernatant of melanoma cells as an autocrine motility stimulation factor. Its enzymatic product, lysophosphatidic acid (LPA), is a phospholipid mediator that evokes growth-factor-like responses in almost all cell types through G-protein coupled receptors. To assess the role of ATX and LPA signalling in pathophysiology, a conditional knockout mouse was created. Ubiquitous, obligatory deletion resulted to embryonic lethality most likely due to aberrant vascular branching morphogenesis and chorio-allantoic fusion. Moreover, the observed phenotype was shown to be entirely depended on embryonic, but not extraembryonic or maternal ATX expression. In addition, E9.5 ATX null mutants exhibited a failure of neural tube closure, most likely independent of the circulatory failure, which correlated with decreased cell proliferation and increased cell death. More importantly, neurite outgrowth in embryo explants was severely compromised in mutant embryos but could be rescued upon the addition of LPA, thus confirming a role for ATX and LPA signalling in the development of the nervous system. Finally, expression profiling of mutant embryos revealed attenuated embryonic expression of HIF-1a in the absence of ATX, suggesting a novel effector pathway of ATX/LPA.

Sec24b selectively sorts Vangl2 to regulate planar cell polarity during neural tube closure

Craniorachischisis is a rare but severe birth defect that results in a completely open neural tube. Mouse mutants in planar cell polarity (PCP) signalling components have deficits in the morphological movements of convergent extension that result in craniorachischisis. Using a forward genetic screen in mice, we identified Sec24b, a cargo-sorting member of the core complex of the endoplasmic reticulum (ER)-to-Golgi transport vesicle COPII, as critical for neural tube closure. Sec24bY613 mutant mice exhibit craniorachischisis, deficiencies in convergent extension and other PCP-related phenotypes. Vangl2, a key component of the PCP-signalling pathway critical for convergent extension, is selectively sorted into COPII vesicles by Sec24b. Moreover, Sec24bY613 genetically interacts with a loss-of-function Vangl2 allele (Vangl2LP), causing a marked increase in the prevalence of spina bifida. Interestingly, the Vangl2 looptail point mutants Vangl2D255E and Vangl2S464N, known to cause defects in convergent extension, fail to sort into COPII vesicles and are trapped in the ER. Thus, during COPII vesicle formation, Sec24b shows cargo specificity for a core PCP component, Vangl2, of which proper ER-to-Golgi transport is essential for the establishment of PCP, convergent extension and closure of the neural tube.

[Recent perspectives on the development of the central nervous system and the genetic background of neural tube defects]

Neural tube defects are rare and mostly lethal malformations. The pattern of inheritance of these malformations is multifactorial, rendering the identification of the underlying causes. Numerous studies have been conducted to elucidate the genetic basis of the development of the central nervous system. Essential signaling pathways of the development of the central nervous system include the planar cell polarity pathway, which is important for the initiation of neural tube closure as well as sonic hedgehog pathway, which regulates the neural plate bending. Genes and their mutations influencing the different stages of neurulation have been investigated for their eventual role in the development of these malformations. Among the environmental factors, folic acid seems to be the most important modifier of the risk of human neural tube defects. Genes of the folate metabolism pathways have also been investigated to identify mutations resulting in increased risk of NTDs. In this review the author has attempted to summarize the knowledge on neural tube defects, with special regard to genetic factors of the etiology.

Recent perspectives on the genetic background of neural tube defects with special regard to iniencephaly

Iniencephaly is a rare and mostly lethal type of neural tube defect. The pattern of inheritance of this group of malformations is multifactorial, rendering the identification of the underlying causes. Numerous studies have been conducted to elucidate the genetic basis of human neurulation. Essential signaling pathways of the development of the CNS include the planar cell polarity pathway, which is important for the initiation of neural tube closure, as well as the sonic hedgehog pathway, which regulates the neural plate bending. Genes influencing the different stages of neurulation have been investigated for their eventual role in the development of these malformations. Among the environmental factors, folic acid seems to be the most important modifier of the risk of human neural tube defects. Genes of the folate metabolism pathways have also been investigated to identify mutations resulting in increased risk of neural tube defects. In this review we have attempted to summarize the knowledge on iniencephaly and neural tube defects, with special regard to genetic factors of the etiology.

Modeling neural tube defects in the mouse

Neural tube defects (NTDs) are among the most common structural birth defects observed in humans. Mouse models provide an excellent experimental system to study the underlying causes of NTDs. These models not only allow for identification of the genes required for neurulation, they provide tractable systems for uncovering the developmental, pathological and molecular mechanisms underlying NTDs. In addition, mouse models are essential for elucidating the mechanisms of gene-environment and gene-gene interactions that contribute to the multifactorial inheritance of NTDs. In some cases these studies have led to development of approaches to prevent NTDs and provide an understanding of the underlying molecular mechanism of these therapies prevent NTDs.

Planar cell polarity signaling: from fly development to human disease

Most, if not all, cell types and tissues display several aspects of polarization. In addition to the ubiquitous epithelial cell polarity along the apical-basolateral axis, many epithelial tissues and organs are also polarized within the plane of the epithelium. This is generally referred to as planar cell polarity (PCP; or historically, tissue polarity). Genetic screens in Drosophila pioneered the discovery of core PCP factors, and subsequent work in vertebrates has established that the respective pathways are evolutionarily conserved. PCP is not restricted only to epithelial tissues but is also found in mesenchymal cells, where it can regulate cell migration and cell intercalation. Moreover, particularly in vertebrates, the conserved core PCP signaling factors have recently been found to be associated with the orientation or formation of cilia. This review discusses new developments in the molecular understanding of PCP establishment in Drosophila and vertebrates; these developments are integrated with new evidence that links PCP signaling to human disease.

Prevalence and outcome of congenital heart disease in patients with neural tube defect

A prospective clinical study was designed to establish the risk factors, the prevalence, and the progress of congenital heart defects in children with neural tube defects. Study included 90 children with a mean age of 13.5 +/- 30.4 months. There were 53 (59%) patients with spina bifida occulta and 37 (41%) patients with spina bifida aperta. The overall prevalence of congenital heart disease was 27.8% (40.5% in spina bifida aperta and 18.9% in spina bifida occulta; P = .024). There was no statistically significant difference for maternal age, usage of periconceptional folate, and maternal diabetes between the patient and control groups. The authors conclude that congenital heart defects are more common than reported in neural tube defects, and screening echocardiograms are warranted. This should be kept in mind especially in patients requiring minor or major surgical procedures. Furthermore, routine obstetric examination and therefore the use of periconceptional folic acid during pregnancy is still lacking in our country.

Central nervous system birth defects in surgically treated infants in Sarajevo region of Bosnia and Herzegovina

Congenital anomalies of the central nervous system (CNS) are common. The prevalence of these anomalies shows considerable geographical variation and female predominance. The aim of this work was to obtain the frequency of different CNS congenital anomalies types and their sex distribution among cases hospitalized in a Department of Neurosurgery, University of Sarajevo Clinics Center, Bosnia and Herzegovina, during the period January 2001 to December 2004. Retrospective study was carried out on the basis of the clinical records. Standard methods of descriptive statistics were performed for the data analysis. A total of 103 cases were surgically treated in the period from 2001 through 2004. Out of that number 56 (54.4%) were female patients, while 47 (46.6%) were male patients. Seven different CNS birth defect types were found in this investigation. These were: spina bifida (42 cases or 40.78%), congenital hydrocephalus (35 cases or 33.98%), arachnoid cyst (15 cases or 14.56%), Dandy-Walker syndrome (5 cases or 4.85%), dermoid cyst (4 cases or 3.88%), one of Arnold-Chiari syndrome (0.98%) and one of encephalocele (0.98%). According to this investigation, CNS congenital birth defects were slightly higher in females (54.4%). The most frequent types were spina bifida (40.78%) both in females (22.33%) and in males (18.45%), hydrocephalus (33.98%) and arachnoid cyst (14.56%). The anomalies of the other organ systems, associated with CNS anomalies obtained in this investigation, were pes equinovarus, cheiloschisis, cardiomegaly and palatoschisis. They were found in six cases (5.82%), equal in both sexes.

Split notochord syndrome with congenital unilateral Horner's sign

A 2-year-old boy exhibited congenital right Horner's sign and right finger, wrist, and elbow flexion arthrogryposis. He had dyspnea and feeding difficulty 12 hours after birth. Radiologic examination revealed a thoracoabdominal intestinal tube and mediastinal cystic lesion at the right side, with vertebral anomaly at the cervical level. Histopathologically, the intestinal tube was diagnosed as bowel duplication. Because the mediastinal lesion could not be resected surgically, no histopathological diagnosis was made. Embryologically, the combination of transdiaphragmatic duplication, mediastinal cystic lesion, anterior spina bifida, and hemivertebra suggested notochord malformation. The diagnosis was split notochord syndrome, an extremely rare embryological malformation syndrome. Congenital unilateral Horner syndrome often has unknown etiology. In this case, cervical vertebral anomalies and mediastinal cystic lesion implied a compressed nerve root, resulting in Horner syndrome and right finger, wrist, and elbow flexion joint contracture. Split notochord syndrome should be included in differential diagnosis of congenital unilateral Horner syndrome.

Modeling homeoprotein intercellular transfer unveils a parsimonious mechanism for gradient and boundary formation in early brain development

Morphogens are molecules inducing morphogenetic responses from cells and cell ensembles. The concept of morphogen is related to that of positional value, as the generation of morphological and physiological characteristics is function of position. Based on the observation that homeoproteins, a category of transcription factors with morphogenetic functions, traffic between abutting cells and, very often, regulate their own expression, we develop here a biophysical model of homeoprotein propagation and study the associated mathematical equations. This mode of cell signaling can generate domains of homeoprotein expression. We study both the transient and steady-state regimes and, in this latter regime, we obtain various morphogenetic gradients, depending on the value of some parameters, such as morphogen synthesis, degradation rates and efficiency of intercellular passage. The same equations, applied to pairs of homeoproteins with auto-activation and reciprocal inhibition properties, account for border formation. They also allow us to compute how specific perturbations can either be buffered or lead to modifications in the position of borders between adjacent areas. The model developed here, based on experimental data, and avoids theoretical obstacles associated with pluricellularity. It extends the idea that Bicoid homeoprotein is a morphogen in the fly embryo syncitium to most homeoproteins and to pluricellular systems. Because the position of borders between brain areas is of primary physiological importance, our model might lead to original views regarding epigenetic inter-individual variations and the origin of neurological and psychiatric diseases. In addition, it provides new hypotheses regarding the molecular basis of brain evolution.

Toward understanding the genetic basis of neural tube defects

Neural tube defects (NTDs) represent a common group of severe congenital malformations that result from failure of neural tube closure during early development. Their etiology is quite complex involving environmental and genetic factors and their underlying molecular and cellular pathogenic mechanisms remain poorly understood. Animal studies have recently demonstrated an essential role for the planar cell polarity pathway (PCP) in mediating a morphogenetic process called convergent extension during neural tube formation. Alterations in members of this pathway lead to NTDs in vertebrate models, representing novel and exciting candidates for human NTDs. Genetic studies in NTDs have focused mainly on folate-related genes based on the finding that perinatal folic acid supplementation reduces the risk of NTDs by 60-70%. A few variants in these genes have been found to be significantly associated with an increased risk for NTDs. The candidate gene approach investigating genes involved in neurulation has failed to identify major causative genes in the etiology of NTDs. Despite this history of generally negative findings, we are achieving a rapid and impressive progress in understanding the genetic basis of NTDs, based mainly on the powerful tool of animal models.