PAX genes and human neural tube defects: an amino acid substitution in PAX1 in a patient with spina bifida

A novel case of homozygous PAX1 mutation associated with hypoparathyroidism

The PAX1 gene plays an important role in the development of the parathyroid glands and the thymus. Mouse knockout models of PAX1, PAX3, and PAX9 have been found to have hypoplastic or absent parathyroid glands. To our knowledge, there are no reported cases of PAX1-associated hypoparathyroidism in humans. We present a case of hypoparathyroidism in a 23-month-old boy with a homozygous pathogenic variant in the PAX1 gene (PAX1 NM_006192.5 c.463_465del variant), predicted to cause an in-frame deletion of asparagine at position 155 (p.Asn155del) of the PAX1 protein. The hypoparathyroidism was unmasked after the patient developed significant hypocalcemia while receiving GoLYTELY (polyethylene glycol 3350, sodium sulfate anhydrous, sodium bicarbonate, sodium chloride, potassium chloride) for bowel cleanout. The patient had mild and asymptomatic hypocalcemia prior to hospitalization. The patient was noted to have inappropriately normal parathyroid hormone (PTH) level at the time of documented hypocalcemia thereby suggesting a diagnosis of hypoparathyroidism.

Plain language summary

The first human case of hypoparathyroidism associated with a rare genetic disorder: a case report of PAX1 gene mutation The paired box (PAX) gene family is important for embryo development. One subfamily, PAX1, is necessary for development of the spinal column, thymus (important for the immune system development), and parathyroid (helps regulate the amount of calcium in the body). We present the case of a 23-month-old boy with known PAX1 gene mutation who came in with episodes of vomiting and poor growth. His presentation was thought to be most likely related to constipation. He was started on bowel cleanout medication and intravenous fluids. However, his calcium that had been mildly low subsequently dropped to very low levels. The level of parathyroid hormone (which helps regulate calcium levels) was inappropriately normal, meaning that his body was unable to make more, and was consistent with hypoparathyroidism. He was treated with calcium supplements and vitamin D and calcium levels normalized. He continues to be on calcium and vitamin D and calcium levels have remained stable. Doctors should keep this complication in mind when treating patients with PAX1 gene mutation.

Prenatal diagnosis of acrania/exencephaly/anencephaly sequence (AEAS): additional structural and genetic anomalies

OBJECTIVES

To analyse additional structural and genetic anomalies in fetuses with acrania/exencephaly/anencephaly sequence (AEAS).

METHODS

A retrospective analysis of 139 fetuses with AEAS diagnosed between 2006 and 2020 in a single tertiary referral ultrasound department.

RESULTS

The median gestational age at diagnosis decreased from 15 weeks in 2006 to 13 weeks in 2020 (- 0.21 per each year; p = 0.009). In 103 fetuses, the defects were limited to the neural tube (NTD) (74.1%), in 36 fetuses (25.9%), there were additional structural non-NTD anomalies. The most common were ventral body wall defects present in 17.8% (23/139), followed by anomalies of the limbs (7.2%; 10/139), face (6.5%; 9/139) and heart (6.5%; 9/139). Genetic anomalies were diagnosed in 7 of the 74 conclusive results (9.5%; 7/74; trisomy 18, n = 5; triploidy, n = 1; duplication of Xq, n = 1). In univariate logistic regression models, male sex, limb anomalies and ventral body wall defects significantly increased the risk of genetic anomalies (OR 12.3; p = 0.024; OR 16.5; p = 0.002 and OR 10.4; p = 0.009, respectively).

CONCLUSIONS

A significant number of fetuses with AEAS have additional structural non-NTD anomalies, which are mostly consistent with limb body wall complex. Genetic abnormalities are diagnosed in almost 10% of affected fetuses and trisomy 18 is the most common aberration. Factors that significantly increased the odds of genetic anomalies in fetuses with AEAS comprise male sex, limb anomalies and ventral body wall defects.

An overview of PAX1: Expression, function and regulation in development and diseases

Transcription factors play multifaceted roles in embryonic development and diseases. PAX1, a paired-box transcription factor, has been elucidated to play key roles in multiple tissues during embryonic development by extensive studies. Recently, an emerging role of PAX1 in cancers was clarified. Herein, we summarize the expression and functions of PAX1 in skeletal system and thymus development, as well as cancer biology and outline its cellular and molecular modes of action and the association of PAX1 mutation or dysregulation with human diseases, thus providing insights for the molecular basis of congenital diseases and cancers.

Sacral Spina Bifida Occulta: A Frequency Analysis of Secular Change

Substantial relaxation of natural selection beginning around 1900 changed the mutation/selec­tion balance of modern genetic material, producing an increase in variable anatomical structures. While multiple structures have been affected, the temporal increase in variations of the sacrum, specifically, ‘Sa­cral Spina Bifida Occulta,’ have been reliably demonstrated on a localised scale. Calculation of largescale frequency has been hindered by the localised nature of these publications, the morphological variability of this variation, and potential pathological associations, which have produced divergent classifications, and conflicting reported rates of occurrence. A systematic review of the reported literature was conducted to provide an objective analysis of Sacral Spina Bifida Occulta frequency from 2500 BCE to the present. This review was designed to compensate for observed inconsistencies in reporting and to ascertain, for the first time, the temporal trajectory of this secular trend. A systematic review of Sacral Spina Bifida Occulta lit­erature was conducted through the strict use of clinical meta-analysis criteria. Publications were retrieved from four databases: PubMed, Embase, the Adelaide University Library database, and Google Scholar. Data were separated into three historical groups, (1 = <1900, 2 = 1900 to 1980 and 3 = >1980), and frequency outcomes compared, to determine temporal rates of occurrence. A total of 39/409 publications were included in the final analysis, representing data for 16,167 sacra, spanning a period of 4,500 years. Statistically significant results were obtained, with total open S1 frequen­cy increasing from 2.34%, (79 to 1900CE), to 4.80%, (1900 to 1980CE) and to 5.43% (>1980CE). These increases were significant at p<0.0001, with Chi-squared analysis. A clear secular increase in the global frequency of Sacral Spina Bifida Occulta has been demonstrated from 1900 to the present. This research provides a novel and adaptable framework for the future assessment of variation distribution, with impor­tant implications for the fields of biological anthropology and bioarchaeology.

Nutrigenomic Studies on the Ameliorative Effect of Enzyme-Digested Phycocyanin in Alzheimer's Disease Model Mice

Alzheimer’s disease (AD) is the most common form of dementia, and the cognitive impairments associated with this degenerative disease seriously affect daily life. Nutraceuticals for the prevention or delay of AD are urgently needed. It has been increasingly observed that phycocyanin (PC) exerts neuroprotective effects. AD model mice intracerebroventricularly injected with amyloid beta-peptide 25–35 (Aβ_25–35) at 10 nmol/head displayed significant cognitive impairment in the spontaneous alternation test. Cognitive impairment was significantly ameliorated in mice treated with 750 mg/kg of enzyme-digested (ED) PC by daily oral administration for 22 consecutive days. Application of DNA microarray data on hippocampal gene expression to nutrigenomics studies revealed that oral EDPC counteracted the aberrant expression of 35 genes, including Prnp, Cct4, Vegfd (Figf), Map9 (Mtap9), Pik3cg, Zfand5, Endog, and Hbq1a. These results suggest that oral administration of EDPC ameliorated cognitive impairment in AD model mice by maintaining and/or restoring normal gene expression patterns in the hippocampus.

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.

Association between dense PAX1 promoter methylation and HPV16 infection in cervical squamous epithelial neoplasms of Xin Jiang Uyghur and Han women

DNA methylation is an epigenetic alteration that may lead to carcinogenesis by silencing key tumor suppressor genes. Hypermethylation of the paired box gene 1 (PAX1) promoter is important in cervical cancer development. Here, PAX1 methylation levels were compared between Uyghur and Han patients with cervical lesions. Data on PAX1 methylation in different cervical lesions were obtained from the Gene Expression Omnibus (GEO) database, whereas data on survival and PAX1 mRNA expression in invasive cervical cancer (ICC) were retrieved from the Cancer Genome Atlas (TCGA) database. MassARRAY spectrometry was used to detect methylation of 19 CpG sites in the promoter region of PAX1, whereas gene mass spectrograms were drawn by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry. Human papillomavirus (HPV) 16 infection was detected by polymerase chain reaction. PAX1 methylation in high-grade squamous intraepithelial lesion (HSIL) and ICC was significantly higher than in normal tissues. PAX1 hypermethylation was associated with poor prognosis and reduced transcription. ICC-specific PAX1 promoter methylation involved distinct CpG sites in Uyghur and Han patients HPV16 infection in HSIL and ICC patient was significantly higher than in normal women (p < 0.05). Our study revealed a strong association between PAX1 methylation and the development of cervical cancer. Moreover, hypermethylation of distinct CpG sites may induce HSIL transformation into ICC in both Uyghur and Han patients. Our results suggest the existence of ethnic differences in the genetic susceptibility to cervical cancer. Finally, PAX1 methylation and HPV infection exhibited synergistic effects on cervical carcinogenesis.

The promising role of PAX1 (aliases: HUP48, OFC2) gene methylation in cancer screening

Background

Paired‐box gene 1 (PAX1), a member of the PAX family, plays a role in pattern formation during embryogenesis, and might be essential for development of the vertebral column.

Methods

PAX1 is silenced by methylation in several cancers and is considered a tumor suppressor gene. Our previous studies reported PAX1 as hypermethylated in cervical cancer tissues, thereby suggesting it as a potential screening marker. Recently, an increasing number of studies have confirmed PAX1 methylation as a promising biomarker in cervical cancer based on its excellent discriminatory ability between high‐grade cervical lesions and normal tissues, resulting in a reduced necessity for referral for colposcopy and biopsy. Additionally, PAX1 is also hypermethylated in other tumors, including those associated with epithelial ovarian cancer, esophageal squamous cell carcinoma, head and neck squamous cell carcinoma, and endometrial carcinoma, and shows relatively good sensitivity and specificity for the detection of these tumors.

Results

This review summarizes reports of PAX1 methylation and its promising role in cancer screening, especially that associated with cervical cancer.

Conclusion

According to current evidence, combined testing for human papillomavirus and PAX1 methylation analysis represents an efficacious cervical cancer‐screening protocol.

PAX genes in childhood oncogenesis: developmental biology gone awry?

Childhood solid tumors often arise from embryonal-like cells, which are distinct from the epithelial cancers observed in adults, and etiologically can be considered as 'developmental patterning gone awry'. Paired-box (PAX) genes encode a family of evolutionarily conserved transcription factors that are important regulators of cell lineage specification, migration and tissue patterning. PAX loss-of-function mutations are well known to cause potent developmental phenotypes in animal models and underlie genetic disease in humans, whereas dysregulation and/or genetic modification of PAX genes have been shown to function as critical triggers for human tumorigenesis. Consequently, exploring PAX-related pathobiology generates insights into both normal developmental biology and key molecular mechanisms that underlie pediatric cancer, which are the topics of this review.

Exon sequencing of PAX3 and T (brachyury) in cases with spina bifida

BACKGROUND

Based on studies in animals and humans, PAX3 and T (brachyury) are candidate genes for spina bifida. However, neither gene has been definitively identified as a risk factor for this condition.

METHODS

Sanger sequencing was used to identify variants in all PAX3 and T exons and promoter regions in 114 spina bifida cases. For known variants, allele frequencies in cases were compared with those from public databases using unadjusted odds ratios. Novel variants were genotyped in parents and assessed for predicted functional impact.

RESULTS

We identified common variants in PAX3 (n = 2) and T (n = 3) for which the allele frequencies in cases were significantly different from those reported in at least one public database. We also identified novel variants in both PAX3 (n = 11) and T (n = 1) in spina bifida cases. Several of the novel PAX3 variants are predicted to be highly conserved and/or impact gene function or expression.

CONCLUSION

These studies provide some evidence that common variants of PAX3 and T are associated with spina bifida. Rare and novel variants in these genes were also identified in affected individuals. However, additional studies will be required to determine whether these variants influence the risk of spina bifida.

A hypofunctional PAX1 mutation causes autosomal recessively inherited otofaciocervical syndrome

Otofaciocervical syndrome (OFCS) is an autosomal recessively inherited disorder characterized by facial dysmorphism, external ear anomalies with preauricular pits and hearing impairment, branchial cysts or fistulas, anomalies of the vertebrae and the shoulder girdle, and mild intellectual disability. In a large consanguineous family with OFCS from Turkey, we performed whole-exome sequencing (WES) of a single pooled DNA sample of four affected individuals. Filtering for variants with a percentage of alternate reads ≥ 90 % and a coverage of at least five reads identified only a single novel homozygous variant, c.497G>T, located in PAX1 that co-segregated with the disease in the family. PAX1 encodes a transcription factor with a critical role in pattern formation during embryogenesis in vertebrates. The mutation is predicted to substitute the glycine at position 166 to valine (p.G166V) within the highly conserved paired-box domain of the PAX1 protein. We performed a dual luciferase reporter assay to examine the transactivation of a regulatory sequence in the Nkx3-2 promoter region, which is a direct target of mouse Pax1 transcriptional regulation. We observed a significantly reduced transactivation in HEK293T cells overexpressing Pax1(G157V) in comparison to Pax1(WT) expressing cells, indicating a reduced DNA-binding affinity of the mutant protein. Taken together, our results show that the strategy of pooling DNA is a powerful, cost-effective application for WES in consanguineous families and establish PAX1 as a new disease-causing gene for OFCS and as part of the EYA-DACH-SIX-PAX network, important in early embryogenesis.

Delineation of a region responsible for panhypopituitarism in 20p11.2

We report on the case of a young woman with a de novo 20p11.21p11.23 deletion, discovered by array-CGH. She has behavioral troubles with autistic traits, intellectual disability, panhypopituitarism, severe hypoglycemia, epilepsy, and scoliosis. The majority of the reported 20p deletions are located on the 20p12 region, covering the JAG1 gene responsible for the Alagille syndrome. More proximal deletions are even rarer, with very few cases described in the literature to date. The deletion carried by our patient is, to our knowledge, the smallest described de novo proximal 20p11.2 deletion. It was first discovered by 0.5 Mb BAC array-CGH, further delineated using an oligonucleotide array, and finally confirmed by fluorescence in situ hybridization. The deletion is 4.22 Mb in size, with the exact location on chr20: 19.810.034-24.031.344 (Feb. 2009, GRCh37/hg19). In light of the other reported cases that display genomic and phenotypic overlap with our patient, we discuss the phenotype of our patient, in order to further delineate the 20p proximal deletion phenotype. We propose a minimal critical region responsible for panhypopituitarism with global developmental delay, intellectual disability, scoliosis and facial dysmorphism. Moreover, considering the deleted genes, we highlight the impact of the deletion of this minimal critical region on the Shh signaling pathway.

Mouse as a model for multifactorial inheritance of neural tube defects

Neural tube defects (NTDs) such as spina bifida and anencephaly are some of the most common structural birth defects found in humans. These defects occur due to failures of neurulation, a process where the flat neural plate rolls into a tube. In spite of their prevalence, the causes of NTDs are poorly understood. The multifactorial threshold model best describes the pattern of inheritance of NTDs where multiple undefined gene variants interact with environmental factors to cause an NTD. To date, mouse models have implicated a multitude of genes as required for neurulation, providing a mechanistic understanding of the cellular and molecular pathways that control neurulation. However, the majority of these mouse models exhibit NTDs with a Mendelian pattern of inheritance. Still, many examples of multifactorial inheritance have been demonstrated in mouse models of NTDs. These include null and hypomorphic alleles of neurulation genes that interact in a complex fashion with other genetic mutations or environmental factors to cause NTDs. These models have implicated several genes and pathways for testing as candidates for the genetic basis of NTDs in humans, resulting in identification of putative pathogenic mutations in some patients. Mouse models also provide an experimental paradigm to gain a mechanistic understanding of the environmental factors that influence NTD occurrence, such as folic acid and maternal diabetes, and have led to the discovery of additional preventative nutritional supplements such as inositol. This review provides examples of how multifactorial inheritance of NTDs can be modeled in the mouse.

Transcription factors in parathyroid development: lessons from hypoparathyroid disorders

Parathyroid developmental anomalies, which result in hypoparathyroidism, are common and may occur in one in 4,000 live births. Parathyroids, in man, develop from the endodermal cells of the third and fourth pharyngeal pouches, whereas, in the mouse they develop solely from the endoderm of the third pharyngeal pouches. In addition, neural crest cells that arise from the embryonic mid- and hindbrain also contribute to parathyroid gland development. The molecular signaling pathways that are involved in determining the differentiation of the pharyngeal pouch endoderm into parathyroid cells are being elucidated by studies of patients with hypoparathyroidism and appropriate mouse models. These studies have revealed important roles for a number of transcription factors, which include Tbx1, Gata3, Gcm2, Sox3, Aire1 and members of the homeobox (Hox) and paired box (Pax) families.

20p11 deletion in a female child with panhypopituitarism, cleft lip and palate, dysmorphic facial features, global developmental delay and seizure disorder

Deletions of 20p are rare with the majority of reported cases involving individuals with 20p12 deletions associated with Alagille syndrome. We report on a child with a de novo mosaic 20p11 deletion who presents with panhypopituitarism; hypoplastic pituitary gland and ectopic posterior pituitary gland on MRI of the brain; cleft lip and palate; kyphosis with anterior beaking of L1 and L2 vertebral bodies; pulmonic stenosis; dysmorphic facial features including flat nasal bridge, hypoplastic premaxilla, hypotelorism, preauricular pit, and cupped ears; seizure disorder; variable muscle tone; and global developmental delay. Array comparative genomic hybridization revealed this deletion to be approximately 5.4 Mb in size, containing 35 genes. Previously, an infant with 20p11.22 deletion who had panhypopituitarism, craniofacial, and genital abnormalities was reported, but the precise parameters of that deletion are unavailable. Several other reported cases of 20p11 deletions also have phenotypic overlap with our case. The similarities in clinical features of these patients suggest that the genes at 20p11 have a critical role in development of midline brain structures.

Genetic basis of neural tube defects

Neural tube defects (NTDs) represent a common group of severe congenital malformations of the central nervous system. They result from failure of neural tube closure during early embryonic life. Their etiology is complex, involving environmental and genetic factors that interact to modulate the incidence and severity of the developing phenotype. Despite a long history of etiologic studies, the molecular and cellular pathogenic mechanisms underlining NTDs remain poorly understood. The major epidemiologic finding in NTDs is the protective effect of perinatal folic acid supplementation that reduces their risk by 60%-70%. Genetic studies in NTDs have focused mainly on folate-related genes and identified a few significant associations between variants in these genes and an increased risk for NTDs. The candidate gene approach investigating genes involved in neurulation and inferred from animal models has faced limited success in identifying major causative genes predisposing to NTDs. However, we are witnessing a rapid and impressive progress in understanding the genetic basis of NTDs, based mainly on the development of whole genome innovative technologies and the powerful tool of animal models.

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.

Chromosomal abnormalities associated with neural tube defects (II): partial aneuploidy

Fetuses with neural tube defects (NTDs) carry a risk of chromosomal abnormalities. The risk varies with maternal age, gestational age at diagnosis, association with other structural abnormalities, and family history of chromosome aberrations. This article provides a comprehensive review of structural chromosomal abnormalities associated with NTDs, such as del(13q), r(13), dup(2p), del(2q), del(1p), del(1q), dup(1q), del(3p), dup(3p), del(3q), dup(3q), del(4p), dup(4p), del(4q), dup(4q), del(5p), del(6p), dup(6q), del(6q), dup(7p), del(7q), dup(8q), del(9p), del(10q), del(11q), dup(11q), dup(12p), dup(14q), del(14q), del(15q), dup(16q), del(18q), r(18), dup(20p), +i(20p), del(22q), del(Xp), and dup(Xq). NTDs may be associated with aneuploidy. Perinatal identification of NTDs should alert one to the possibility of chromosomal abnormalities and prompt a thorough cytogenetic investigation and genetic counseling.

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.

Screening for novel PAX3 polymorphisms and risks of spina bifida

BACKGROUND

PAX3 plays an important role in mammalian embryonic development. Known mutations in PAX3 are etiologically associated with Waardenburg syndrome and syndromic neural tube defects (NTDs). Mutations in the murine homologue, pax3, are responsible for the phenotype of splotch mice, in which nullizygotes are 100% penetrant for NTDs.

METHODS

The study sample included 74 infants with spina bifida (cases) and 87 nonmalformed infant controls. The conserved paired-box domain as well as the upstream genomic region of PAX3 were subjected to resequencing and those identified SNPs were evaluated as haplotypes. The associations of haplotypes for selected gene regions and the risks of spina bifida were further studied.

RESULTS

Nineteen SNPs were observed; 15 observed in controls had been submitted to the National Center for Biotechnology Information (NCBI) database with allele frequencies. The PAX3 gene variant T-1186C (rs16863657) and its related haplotype, TCTCCGCCC of nine SNPs, were found to be associated with an increased risk of spina bifida, with an OR of 3.5 (95% CI: 1.2-10.0) among Hispanic Whites.

CONCLUSIONS

Our analyses indicated that PAX3 SNPs were not strong risk factors for human spina bifida. However, additional follow-up of the PAX3 gene variant T-1186C (rs16863657) and its related haplotype, TCTCCGCCC, may be important in other populations.

Prenatal Diagnosis and Genetic Counseling in a Case of Spina Bifida in a Family with Waardenburg Syndrome Type I

OBJECTIVE

Waardenburg syndrome type I (WS I) is an autosomal dominant inherited disorder with an incidence of 1:45,000 in Europe. Mutations within the PAX3 gene are responsible for the clinical phenotype ranging from mild facial features to severe malformations detectable in prenatal diagnosis.

METHODS

Here, we report a four-generation family with several affected members showing various symptoms of WS I. We diagnosed the syndrome first in a pregnant young woman; she was referred because of a spina bifida in prenatal diagnosis. We performed clinical genetic investigations and molecular genetic analysis in all available family members.

RESULTS

The phenotype displays a wide intra-familial clinical variability of pigmentary disturbances, facial anomalies and developmental defects. Molecular studies identified a novel splice site mutation within the PAX3 gene in intron 5 in all affected family members, but in none of the unaffected relatives.

CONCLUSIONS

This case demonstrates the prenatal diagnosis of spina bifida in a fetus which leads to the initial diagnosis of WS I. Further studies could identify a private splice site mutation within the PAX3 gene responsible for the phenotype in this family.

Current perspectives on the genetic causes of neural tube defects

Neural tube defects (NTDs) are a group of severe congenital abnormalities resulting from the failure of neurulation. The pattern of inheritance of these complex defects is multifactorial, making it difficult to identify the underlying causes. Scientific research has rapidly progressed in experimental embryology and molecular genetics to elucidate the basis of neurulation. Crucial mechanisms of neurulation include the planar cell polarity pathway, which is essential for the initiation of neural tube closure, and the sonic hedgehog signaling pathway, which regulates neural plate bending. Genes influencing neurulation have been investigated for their contribution to human neural tube defects, but only genes with well-established role in convergent extension provide an exciting new set of candidate genes. Biochemical factors such as folic acid appear to be the greatest modifiers of NTDs risk in the human population. Consequently, much research has focused on genes of folate-related metabolic pathways. Variants of several such genes have been found to be significantly associated with the risk of neural tube defects in more studies. In this manuscript, we reviewed the current perspectives on the causes of neural tube defects and highlighted that we are still a long way from understanding the etiology of these complex defects.

Haplotype-dependent binding of nuclear proteins to the promoter of the neural tube defects-associated platelet-derived growth factor alpha-receptor gene

We have previously shown that polymorphisms in the promoter of the human platelet-derived growth factor alpha-receptor (PDGFRA) gene can be grouped into five distinct haplotypes, designated H1, H 2 alpha, H 2 beta, H 2 gamma and H 2 delta, and that specific combinations of these promoter haplotypes predispose to neural tube defects (NTDs). These promoter haplotypes differ strongly in their ability to drive reporter gene expression in various human cell lines, with highest activity for H 2 alpha and H 2 beta. Here, we show that the haplotype-linked PDGFRA promoter region extends to 3.6 kb upstream from the transcription start site, and contains a total of ten polymorphic sites. For two of these polymorphic sites, i.e. -909 C/A and +68 GAins/del, we observed differential binding of nuclear proteins from human osteosarcoma (HOS) cells. The protein complex binding specifically to -909 C, which is present in all haplotypes except the low activity haplotype H 2 gamma, contained members of the upstream stimulatory factor (USF) family of transcription factors. Furthermore, we identified a protein complex of 125 kDa which bound specifically to the low activity haplotype H1 at position +68 GAdel and may represent an H1-specific PDGFRA transcriptional repressor. The current identification of cis-acting elements in the PDGFRA promoter and the transcription factors that bind them, provides a new strategy for the identification of genes that are potentially involved in neural tube defects.

Using genomewide mutagenesis screens to identify the genes required for neural tube closure in the mouse

BACKGROUND

Neural tube closure is a critical embryological process that requires the coordination of many molecular and cellular events. Only recently has the molecular basis of the cell movements that drive neural tube closure begun to be elucidated. This has been accomplished in part due to the analysis of a growing number of genetically targeted and naturally occurring mouse mutant strains that have neural tube defects (NTDs). Currently there are more than 100 genes that when mutated result in NTDs in the mouse. Yet only approximately 10% of genes in the mouse genome have been mutated and their gross phenotype analyzed, suggesting that only a small percentage of the genes that can cause NTDs have been identified.

METHODS

In order to more systematically and fully understand the genetic basis of neural tube closure and to begin to define the molecular pathways that direct this key embryonic event, our laboratories have undertaken a forward genetic screen in mice. From this we hope to gain a better understanding of the regulation of this complex morphogenic processes.

CONCLUSIONS

The mouse provides a good model for human neural tube closure, and therefore the information gained from generating novel mouse models of NTDs will help to predict the genes responsible for human NTDs and provide experimental evidence for how they function.

An analysis of PAX1 in the development of vertebral malformations

An analysis of PAX1 in the development of vertebral malformations. Due to the sporadic occurrence of congenital vertebral malformations, traditional linkage approaches to identify genes associated with human vertebral development are not possible. We therefore identified PAX1 as a candidate gene in vertebral malformations and congenital scoliosis due to its mutation in the undulated mouse. We performed DNA sequence analysis of the PAX1 gene in a series of 48 patients with congenital vertebral malformations, collectively spanning the entire vertebral column length. DNA sequence coding variants were identified in the heterozygous state in exon 4 in two male patients with thoracic vertebral malformations. One patient had T9 hypoplasia, T12 hemivertebrae and absent T10 pedicle, incomplete fusion of T7 posterior elements, ventricular septal defect, and polydactyly. This patient had a CCC (Pro)-->CTC (Leu) change at amino acid 410. This variant was not observed in 180 chromosomes tested in the National Institute of Environmental Health Sciences (NIEHS) single nucleotide polymorphism (SNP) database and occurred at a frequency of 0.3% in a diversity panel of 1066 human samples. The second patient had a T11 wedge vertebra and a missense mutation at amino acid 413 corresponding to CCA (Pro)-->CTA (Leu). This particular variant has been reported to occur in one of 164 chromosomes in the NIEHS SNP database and was found to occur with a similar frequency of 0.8% in a diversity panel of 1066 human samples. Although each patient's mother was clinically asymptomatic and heterozygous for the respective variant allele, the possibility that these sequence variants have clinical significance is not excluded.

Candidate gene analysis in human neural tube defects

Biochemical and developmental pathways, mouse models, and positional evidence have provided numerous candidate genes for the study of human neural tube defects. In a survey of 80 studies on 38 candidate genes, few found significant results in human populations through case-control or family-based association studies. While the folate pathway has been explored extensively, only the MTHFR 677C > T polymorphism was significant, and only in an Irish population. Developmental pathways such as the Wnt signaling pathway and Hox genes have also been explored without positive results. More than 90 mouse candidates have been identified through spontaneous and knockout mutations, but only the T locus (mouse Brachyury gene) showed association in an initial study that was not confirmed on follow-up. Positional candidates have been derived from cytogenetic evidence, but preliminary genomic screens have limited power due to small sample sizes. Future studies would increase their power to detect association by using more samples. In addition a clarification of the phenotype would be beneficial as many studies used different inclusion criteria. Incorporating several types of data could highlight better candidates, as would looking beyond the traditional sources for candidate genes. Recent studies of an energy metabolism gene (UCP2) and vitamin B metabolism (Transcoalbumin) have produced promising results. Utilizing other model organisms may also be beneficial, as in a recent study from a chick model of NTDs in NCAM1. New approaches combined with traditional methods and increased sample sizes will help prioritize human NTD candidate genes and clarify the complex etiology of this condition.

Whole genomewide linkage screen for neural tube defects reveals regions of interest on chromosomes 7 and 10

Neural tube defects (NTDs) are the second most common birth defects (1 in 1000 live births) in the world. Periconceptional maternal folate supplementation reduces NTD risk by 50-70%; however, studies of folate related and other developmental genes in humans have failed to definitively identify a major causal gene for NTD. The aetiology of NTDs remains unknown and both genetic and environmental factors are implicated. We present findings from a microsatellite based screen of 44 multiplex pedigrees ascertained through the NTD Collaborative Group. For the linkage analysis, we defined our phenotype narrowly by considering individuals with a lumbosacral level myelomeningocele as affected, then we expanded the phenotype to include all types of NTDs. Two point parametric analyses were performed using VITESSE and HOMOG. Multipoint parametric and nonparametric analyses were performed using ALLEGRO. Initial results identified chromosomes 7 and 10, both with maximum parametric multipoint lod scores (Mlod) >2.0. Chromosome 7 produced the highest score in the 24 cM interval between D7S3056 and D7S3051 (parametric Mlod 2.45; nonparametric Mlod 1.89). Further investigation demonstrated that results on chromosome 7 were being primarily driven by a single large pedigree (parametric Mlod 2.40). When this family was removed from analysis, chromosome 10 was the most interesting region, with a peak Mlod of 2.25 at D10S1731. Based on mouse human synteny, two candidate genes (Meox2, Twist1) were identified on chromosome 7. A review of public databases revealed three biologically plausible candidates (FGFR2, GFRA1, Pax2) on chromosome 10. The results from this screen provide valuable positional data for prioritisation of candidate gene assessment in future studies of NTDs.

Investigations into the etiology of neural tube defects

Neural tube defects (NTDs) are serious malformations affecting approximately 1 per 1000 births, yet the mechanisms by which they arise are unknown. There have been consistent efforts in many fields of research to elucidate the etiology of this multifactorial condition. While no single gene has been identified as a major independent risk factor for NTDs, candidate genes have been proposed that may modify the effects of maternal and/or embryonic exposures. Folate supplementation effectively reduces the occurrence of NTDs and, consequently, has focused much research on metabolism of folate-related pathways during pregnancy and development. Further understanding of normal development and how teratogens can perturb these orchestrated processes also remains at the fore of modern scientific endeavors. The composite of these factors remains fragmented; the aim of this review is to provide the reader with a summary of sentinel and current works in the body of literature addressing NTD disease etiology.

Spina bifida

Spina bifida results from failure of fusion of the caudal neural tube, and is one of the most common malformations of human structure. The causes of this disorder are heterogeneous and include chromosome abnormalities, single gene disorders, and teratogenic exposures. However, the cause is not known in most cases. Up to 70% of spina bifida cases can be prevented by maternal, periconceptional folic acid supplementation. The mechanism underlying this protective effect is unknown, but it is likely to include genes that regulate folate transport and metabolism. Individuals with spina bifida need both surgical and medical management. Although surgical closure of the malformation is generally done in the neonatal period, a randomised clinical trial to assess in utero closure of spina bifida has been initiated in the USA. Medical management is a lifelong necessity for individuals with spina bifida, and should be provided by a multidisciplinary team.

Aberrant Pax1 and Pax9 expression in Jarcho-Levin syndrome: report of two Caucasian siblings and literature review

We report two consecutive Caucasian male siblings of nonconsanguineous parents autopsied at 22 and 13 weeks gestational age both with prenatal diagnosis of Jarcho-Levin syndrome (JLS). Segmentation anomalies of the vertebrae and ribs encompass a spectrum of syndromes with or without associated anomalies of other developmental fields, and include spondylothoracic dysostosis (STD), JLS, Casamassima-Morton-Nance (CMN) syndrome, and spondylocostal dysostosis (SCD), among others. In both these new JLS cases the autopsies confirmed that there were severe developmental alterations in the thoracic and vertebral skeleton (including "crab-like" thorax), accompanied in the older fetus by renal defects. Because vertebral development is controlled by a limited number of master genes including Pax1 and Pax9, we analyzed protein expression from these genes in these two cases compared to age-matched controls. Immunochemical analysis showed a significant reduction in levels of Pax1 and Pax9 protein expression in chondrocytes of the vertebral column. Implications for the etiology and pathogenesis of JLS and related disorders are discussed.

Mutations in PAX1 may be associated with Klippel-Feil syndrome

Pax genes are a highly conserved family of developmental control genes that encode transcription factors. In vertebrates, Pax genes play a role in pattern formation during embryogenesis. Mutations in Pax genes have been associated with both spontaneous mouse mutants and congenital human diseases. The mouse Pax1 mutant phenotype undulated is characterised by vertebral segmentation defects reminiscent of the human disorder Klippel-Feil syndrome (KFS). To determine whether PAX1 haploinsufficiency plays a role in KFS, we have defined the gene structure of the human PAX1 gene and screened 63 KFS patients for mutations in this gene. Differences in the PAX1 sequence were detected in eight patients. Two patients had a silent change within the paired box that was also seen in 2/303 control chromosomes. The other variants were missense, silent or intronic changes not represented in the control panel tested. The significance of these results and the possible role of PAX1 in the pathogenesis of KFS are discussed.

A regulating element essential for PDGFRA transcription is recognized by neural tube defect-associated PRX homeobox transcription factors

We have previously shown that deregulated expression of the platelet-derived growth factor alpha-receptor (PDGFRA) can be associated with neural tube defects (NTDs) in both men and mice. In the present study, we have investigated the transcription factors that control the up-regulation of PDGFRA expression during differentiation of early embryonic human cells in culture. In Tera-2 embryonal carcinoma cells, PDGFRA expression is strongly enhanced upon differentiation induced by retinoic acid and cAMP treatment. Here we show that the corresponding increase in promoter activity is controlled by an ATTA-sequence-containing element located near the transcription initiation site, which is bound by a transcriptional complex that includes PBX and PRX homeobox transcription factors. Mutation of the putative binding sites for these transcription factors results in strong impairment of PDGFRA promoter activity in differentiated cells. Since functional inactivation of Prx genes has been associated with NTDs in mice, these data support a model in which improper PDGFRA expression as a result of mutations in or altered binding of its upstream regulators may be causally related to NTDs.

Testing for genetic associations with the PAX gene family in a spina bifida population

Neural tube defects (NTDs) are among the most common severely disabling birth defects in the United States, affecting approximately 1-2 of every 1,000 live births. The etiology of NTDs is multifactorial, involving the combined action of both genetic and environmental factors. A nonparametric linkage method, the transmission disequilibrium test (TDT), was utilized to determine if the genes in the PAX family play a role in the formation of NTDs. DNA from 459 spina bifida (SB) patients and their parents (430 mothers and 239 fathers, for a total population of 1,128 subjects) was tested for linkage and association utilizing polymorphic markers from within or very close to the PAX genes of interest. Significant findings were obtained for the following markers: marker locus D20S101 flanking the PAX1 gene (P = 0.019), marker locus D1S228 within the PAX7 gene (P = 0.011), and marker locus D2S110 within the PAX8 gene (P = 0.013). Even though our findings are only mildly significant, given the known expression patterns of the PAX genes in development and the availability of their sequences, we elected to follow up these results by testing these genes directly for mutations utilizing single-strand conformational analysis (SSCA) and direct sequencing. Multiple variations were detected in each of the PAX genes with significant TDT results; however, these variations were not passed from parent to child in phase with the positively transmitted allele. Therefore, it is unlikely that these variations contribute to susceptibility for SB, but rather are previously unreported polymorphisms.

SNPs in the CpG island of NAP1L2: a possible link between DNA methylation and neural tube defects?

Deletion of the murine X-linked Nap1l2 gene causes lethality from midgestation onwards. The affected embryos exhibit neural tube defects (NTDs) closely resembling spina bifida and anencephaly in humans. X-linked familial and spontaneous cases of NTD were analyzed for sequence alterations in the human NAP1L2. No differences were found in the familial cases. However, a number of single nucleotide polymorphisms (SNPs) within the 5' region of NAP1L2 were identified both in cases of spontaneous NTD and in normal controls. Most of these SNPs lead to the replacement of guanidines or cytosines within a CpG island that is conserved between the human and the mouse promoter regions. Demethylation in vitro activates Nap1l2 transcriptional activity, suggesting the importance of the CpG island in regulating the activity of the Nap1l2/NAP1L2 genes, and the potential importance of the polymorphisms in modifying their transcriptional activity. NAP1L2/Nap1l2 expression may therefore depend on the genetic-environmental factors that are frequently associated with NTDs.

A screen for mutations in human homologues of mice exencephaly genes Tfap2alpha and Msx2 in patients with neural tube defects

BACKGROUND

Very little is known about the identity of genetic factors involved in the complex etiology of nonsyndromic neural tube defects (NTD). Potential susceptibility genes have emerged from the vast number of mutant mouse strains displaying NTD. Reasonable candidates are the human homologues of mice exencephaly genes Tfap2alpha and Msx2, which are expressed in the developing neural tube.

METHODS

A single-strand conformation analysis (SSCA) mutation screen of the coding sequences of TFAP2alpha and MSX2 was performed for 204 nonsyndromic NTD patients including cases of anencephaly (n = 10), encephalocele (n = 8), and spina bifida aperta, SBA (n = 183). A selected number of SBA patients was additionally tested for specific mutations in MTHFD, FRalpha, and PAX1 already shown to be related to NTD.

RESULTS

Two TFAP2alpha point mutations in individual SBA patients were silent on the amino acid level (C308C, T396T). On nucleic acid level, these mutations change evolutionary conserved codons and thus may influence mRNA processing and translation efficiency. One SBA patient displayed an exonic 9-bp deletion in MSX2 leading to a shortened and possibly less functional protein. None of these mutations was found in 222 controls. Seven polymorphisms detected in TFAP2alpha and MSX2 were equally distributed in patients and controls. Patients with combined heterozygosity of an exonic MSX2 and an intronic TFAP2alpha polymorphism were at a slightly increased risk of NTD (OR 1.71; 95% CI 0.57-5.39).

CONCLUSIONS

Although several new genetic variants were found in TFAP2 and MSX2, no statistically significant association was found between NTD cases and the new alleles or their combinations. Further studies are necessary to finally decide if these gene variants may have acted as susceptibility factors in our individual cases.

Promoter haplotype combinations of the platelet-derived growth factor alpha-receptor gene predispose to human neural tube defects

Neural tube defects (NTDs), including anencephaly and spina bifida, are multifactorial diseases that occur with an incidence of 1 in 300 births in the United Kingdom. Mouse models have indicated that deregulated expression of the gene encoding the platelet-derived growth factor alpha-receptor (Pdgfra) causes congenital NTDs (refs. 2-4), whereas mutant forms of Pax-1 that have been associated with NTDs cause deregulated activation of the human PDGFRA promoter. There is an increasing awareness that genetic polymorphisms may have an important role in the susceptibility for NTDs (ref. 6). Here we identify five different haplotypes in the human PDGFRA promoter, of which the two most abundant ones, designated H1 and H2 alpha, differ in at least six polymorphic sites. In a transient transfection assay in human bone cells, the five haplotypes differ strongly in their ability to enhance reporter gene activity. In a group of patients with sporadic spina bifida, haplotypes with low transcriptional activity, including H1, were under-represented, whereas those with high transcriptional activity, including H2 alpha, were over-represented. When testing for haplotype combinations, H1 homozygotes were fully absent from the group of sporadic patients, whereas H1/H2 alpha heterozygotes were over-represented in the groups of both sporadic and familial spina bifida patients, but strongly under-represented in unrelated controls. Our data indicate that specific combinations of naturally occurring PDGFRA promoter haplotypes strongly affect NTD genesis.

Spina bifida and other neural tube defects

NTDs, resulting from failure of the neural tube to close during the fourth week of embryogenesis, are the most common severely disabling birth defects in the United States, with a frequency of approximately 1 of every 2000 births. Neural tube malformations involving the spinal cord and vertebral arches are referred to as spina bifida, with severe types of spina bifida involving protrusion of the spinal cord and/or meninges through a defect in the vertebral arch. Depending on the level of the lesion, interruption of the spinal cord at the site of the spina bifida defect causes paralysis of the legs, incontinence of urine and feces, anesthesia of the skin, and abnormalities of the hips, knees, and feet. Two additional abnormalities often seen in children with spina bifida include hydrocephalus and the Arnold-Chiari type II malformation. Despite the physical and particular learning disabilities children with spina bifida must cope with, participation in individualized educational programs can allow these children to develop skills necessary for autonomy in adulthood. Advances in research to uncover the molecular basis of NTDs is enhanced by knowledge of the link between both the environmental and genetic factors involved in the etiology of NTDs. The most recent development in NTD research for disease-causing genes is the discovery of a genetic link to the most well-known environmental cause of neural tube malformation, folate deficiency in pregnant women. Nearly a decade ago, periconceptional folic acid supplementation was proven to decrease both the recurrence and occurrence of NTDs. The study of folate and its association with NTDs is an ongoing endeavor that has led to numerous studies of different genes involved in the folate metabolism pathway, including the most commonly studied thermolabile mutation (C677T) in the MTHFR gene. An additional focus for NTD research involves mouse models that exhibit both naturally occurring NTDs, as well as those created by experimental design. We hope the search for genes involved in the risk and/or development of NTDs will lead to the development of strategies for prevention and treatment. The most recent achievement in treatment of NTDs involves the repair of meningomyelocele through advancements in fetal surgery. Convincing experimental evidence exists that in utero repair preserves neurologic function, as well as resolving the hydrocephalus and Arnold-Chiari malformation that often accompany meningomyelocele defects. However, follow-up is needed to completely evaluate long-term neurologic function and overall improved quality of life. And in the words of Olutoye and Adzick, "until the benefits of fetal [meningomyelocele] repair are carefully elucidated, weighed against maternal and fetal risks, and compared to conventional postnatal therapy, this procedure should be restricted to a few centers that are committed (clinically and experimentally) to investigating these issues."

Syndromes associated with Homo sapiens pol II regulatory genes

The molecular basis of human characteristics is an intriguing but an unresolved problem. Human characteristics cover a broad spectrum, from the obvious to the abstract. Obvious characteristics may include morphological features such as height, shape, and facial form. Abstract characteristics may be hidden in processes that are controlled by hormones and the human brain. In this review we examine exaggerated characteristics presented as syndromes. Specifically, we focus on human genes that encode transcription factors to examine morphological, immunological, and hormonal anomalies that result from deletion, insertion, or mutation of genes that regulate transcription by RNA polymerase II (the Pol II genes). A close analysis of abnormal phenotypes can give clues into how sequence variations in regulatory genes and changes in transcriptional control may give rise to characteristics defined as complex traits.

Apparent lability of neural tube closure in laboratory animals and humans

Neural tube defects (NTDs), a set of structural abnormalities affecting the brain, spinal cord, and the skeletal and connective tissues that protect them, are common malformations among humans and laboratory animals. The embryogenesis of the neural tube is presented to convey the complexity of the phenomenon, the multiplicity of requisite cellular and subcellular processes, and the precise timing of events that must occur for successful neural tube development. Interruption, even transitory, of any of these intricate processes or disruption of an embryo's developmental schedule can lead to an NTD. The population distribution of human NTDs demonstrates that genetic predisposition functions in susceptibility to NTDs. Data from animal studies support these concepts. NTDs are common outcomes in developmental toxicity safety assessments, occurring among control and treated groups. Numerous agents have caused increased levels of NTDs in laboratory animals, and species with shorter gestational periods appear more prone to toxicant-induced NTDs than those with longer gestations. Data from post-implantation whole embryo culture, although not predictive of human risk, are useful in studying neurulation mechanisms and in demonstrating the importance of maintaining embryonic schedules of development. We conclude that the concept that NTDs are produced by only a few toxicants that selectively target the developing nervous system is untenable. Rather, the combination of the time in gestation that an agent is applied, its dose, and its ability to disrupt critical processes in neurulation leads to NTDs. We further conclude that, because of both the relatively high prevalence and the multifactorial nature of NTDs, the mere occurrence of an NTD is insufficient for inferring that the defect was caused by an exogenous agent.

Neural crest anomaly syndromes in children with spina bifida

A hereditary contribution to the etiology of neural tube defects (NTDs) has been suggested by clinical studies and animal models. To evaluate the hypothesis that common genes are important for both neural tube defects and neural crest anomalies, we examined children with developmental abnormalities of the spinal cord for anomalies of neural crest-derived structures. Neural crest anomalies, particularly auditory and pigmentary disorders, were identified and classified according to inheritance and type of anomaly. Of the 515 children screened, 44 (8.5%) had neural crest anomalies, 20 (3.9%) of which were apparently familial. Another 19 (3.7%) families had neural crest anomalies in two or more close relations, but the NTD subject was unaffected. Sixteen (3.1%) children with NTDs had a recognizable syndrome, including nine (1.7%) with a subtype of the Waardenburg syndromes. The coincidence of familial neural crest anomaly syndromes in subjects with spina bifida implies that defects in genes underlying neural crest development may contribute to the etiology of neural tube defects in a fraction of cases. The rate of anomalies and familial syndromes of neural crest-derived structures must be assessed in an adequate control sample to evaluate whether or not these abnormalities constitute risk factors for NTDs.

Human transcription factor SLUG: mutation analysis in patients with neural tube defects and identification of a missense mutation (D119E) in the Slug subfamily-defining region

Studies in mouse, chicken and Xenopus have shown that Slug is selectively expressed in the dorsal part of the developing neural tube. Ablation and antisense experiments in chicken suggest that Slug may be an important factor during neural tube closure. We therefore investigated the role of Slug as a possible candidate contributing to the aetiology of neural tube defects (NTD) in humans. We characterised the genomic structure of human SLUG including determination of the exon-intron boundaries. The coding sequence of SLUG was screened for mutations in 150 patients with NTD using single strand conformation analysis (SSCA). In one patient, we identified a missense mutation 1548C-->A in exon 2 causing an exchange of a conserved amino acid (D119E) in the Slug subfamily-defining region preceding the first zinc finger. This is the first description of a human mutation in the SLUG gene. In accordance with the findings in model organisms, the SLUG mutation may be causally related to the development of NTD in our patient and could be considered as a predisposing factor.

Altered regulation of platelet-derived growth factor receptor-alpha gene-transcription in vitro by spina bifida-associated mutant Pax1 proteins

Mouse models show that congenital neural tube defects (NTDs) can occur as a result of mutations in the platelet-derived growth factor receptor-alpha gene (PDGFRalpha). Mice heterozygous for the PDGFRalpha-mutation Patch, and at the same time homozygous for the undulated mutation in the Pax1 gene, exhibit a high incidence of lumbar spina bifida occulta, suggesting a functional relation between PDGFRalpha and Pax1. Using the human PDGFRalpha promoter linked to a luciferase reporter, we show in the present paper that Pax1 acts as a transcriptional activator of the PDGFRalpha gene in differentiated Tera-2 human embryonal carcinoma cells. Two mutant Pax1 proteins carrying either the undulated-mutation or the Gln --> His mutation previously identified by us in the PAX1 gene of a patient with spina bifida, were not or less effective, respectively. Surprisingly, Pax1 mutant proteins appear to have opposing transcriptional activities in undifferentiated Tera-2 cells as well as in the U-2 OS osteosarcoma cell line. In these cells, the mutant Pax1 proteins enhance PDGFRalpha-promoter activity whereas the wild-type protein does not. The apparent up-regulation of PDGFRalpha expression in these cells clearly demonstrates a gain-of-function phenomenon associated with mutations in Pax genes. The altered transcriptional activation properties correlate with altered protein-DNA interaction in band-shift assays. Our data provide additional evidence that mutations in Pax1 can act as a risk factor for NTDs and suggest that the PDGFRalpha gene is a direct target of Pax1. In addition, the results support the hypothesis that deregulated PDGFRalpha expression may be causally related to NTDs.

Epidemiology of spina bifida in Tottori Prefecture, Japan, 1976-1995

The authors studied the epidemiology of spina bifida in Tottori Prefecture, Japan, from 1976 to 1995. Thirty-four patients (16 men and 18 women) were registered in this study. Consanguineous marriages, familial occurrence, and abnormalities in prenatal history were not observed. The incidence rate in the entire prefecture and in the eastern, central, and western regions was 0.234, 0.148, 0.425, and 0.230 per 1,000 live births, respectively. The incidence rate in the central region was greater than that in the eastern region with statistical significance (P < 0.05), but the cause of the cluster is unknown. The incidence rate of 0.234 per 1,000 live births for 20 years is compatible with the previous two studies of 1922-1940 and 1948-1954 in Japan. Such apparently stable trends suggest that environmental factors have affected the Japanese less than genetic factors. Seasonal variations are not demonstrated.

Pax genes and organogenesis

Pax genes are a family of developmental control genes that encode nuclear transcription factors. They are characterized by the presence of the paired domain, a conserved amino acid motif with DNA-binding activity. Originally, paired-box-containing genes were detected in Drosophila melanogaster, where they exert multiple functions during embryogenesis. In vertebrates, Pax genes are also involved in embryogenesis. Mutations in four out of nine characterized Pax genes have been associated with either congenital human diseases such as Waardenburg syndrome (PAX3), Aniridia (PAX6), Peter's anomaly (PAX6), renal coloboma syndrome (PAX2) or spontaneous mouse mutants (undulated (Pax1), Splotch (Pax3), Small eye (Pax6), Pax2(1)Neu), which all show defects in development. Recently, analysis of spontaneous and transgenic mouse mutants has revealed that vertebrate pax genes are key regulators during organogenesis of kidney, eye, ear, nose, limb muscles, vertebral column and brain. Like their Drosophila counterparts, vertebrate Pax genes are involved in pattern formation during embryogenesis, possibly by determining the time and place of organ initiation or morphogenesis. For most tissues, however, the nature of the primary developmental action of Pax transcription factors remains to be elucidated. One predominant theme is signal transduction during tissue interactions, which may lead to a position-specific regulation of cell proliferation.