Genetics of human neural tube defects

Neural tube defects (NTDs) are common, severe congenital malformations whose causation involves multiple genes and environmental factors. Although more than 200 genes are known to cause NTDs in mice, there has been rather limited progress in delineating the molecular basis underlying most human NTDs. Numerous genetic studies have been carried out to investigate candidate genes in cohorts of patients, with particular reference to those that participate in folate one-carbon metabolism. Although the homocysteine remethylation gene MTHFR has emerged as a risk factor in some human populations, few other consistent findings have resulted from this approach. Similarly, attention focused on the human homologues of mouse NTD genes has contributed only limited positive findings to date, although an emerging association between genes of the non-canonical Wnt (planar cell polarity) pathway and NTDs provides candidates for future studies. Priorities for the next phase of this research include: (i) larger studies that are sufficiently powered to detect significant associations with relatively minor risk factors; (ii) analysis of multiple candidate genes in groups of well-genotyped individuals to detect possible gene–gene interactions; (iii) use of high throughput genomic technology to evaluate the role of copy number variants and to detect ‘private’ and regulatory mutations, neither of which have been studied to date; (iv) detailed analysis of patient samples stratified by phenotype to enable, for example, hypothesis-driven testing of candidates genes in groups of NTDs with specific defects of folate metabolism, or in groups of fetuses with well-defined phenotypes such as craniorachischisis

Prenatal alcohol exposure triggers ceramide-induced apoptosis in neural crest-derived tissues concurrent with defective cranial development

Fetal alcohol syndrome (FAS) is caused by maternal alcohol consumption during pregnancy. The reason why specific embryonic tissues are sensitive toward ethanol is not understood. We found that in neural crest-derived cell (NCC) cultures from the first branchial arch of E10 mouse embryos, incubation with ethanol increases the number of apoptotic cells by fivefold. Apoptotic cells stain intensely for ceramide, suggesting that ceramide-induced apoptosis mediates ethanol damage to NCCs. Apoptosis is reduced by incubation with CDP-choline (citicoline), a precursor for the conversion of ceramide to sphingomyelin. Consistent with NCC cultures, ethanol intubation of pregnant mice results in ceramide elevation and increased apoptosis of NCCs in vivo. Ethanol also increases the protein level of prostate apoptosis response 4 (PAR-4), a sensitizer to ceramide-induced apoptosis. Prenatal ethanol exposure is concurrent with malformation of parietal bones in 20% of embryos at day E18. Meninges, a tissue complex derived from NCCs, is disrupted and generates reduced levels of TGF-β1, a growth factor critical for bone and brain development. Ethanol-induced apoptosis of NCCs leading to defects in the meninges may explain the simultaneous presence of cranial bone malformation and cognitive retardation in FAS. In addition, our data suggest that treatment with CDP-choline may alleviate the tissue damage caused by alcohol

Identification of Inappropriately Reprogrammed Genes by Large-Scale Transcriptome Analysis of Individual Cloned Mouse Blastocysts

Although cloned embryos generated by somatic/embryonic stem cell nuclear transfer (SECNT) certainly give rise to viable individuals, they can often undergo embryonic arrest at any stage of embryogenesis, leading to diverse morphological abnormalities. In an effort to gain further insights into reprogramming and the properties of SECNT embryos, we performed a large-scale gene expression profiling of 87 single blastocysts using GeneChip microarrays. Sertoli cells, cumulus cells, and embryonic stem cells were used as donor cells. The gene expression profiles of 87 blastocysts were subjected to microarray analysis. Using principal component analysis and hierarchical clustering, the gene expression profiles were clearly classified into 3 clusters corresponding to the type of donor cell. The results revealed that each type of SECNT embryo had a unique gene expression profile that was strictly dependent upon the type of donor cells, although there was considerable variation among the individual profiles within each group. This suggests that the reprogramming process is distinct for embryos cloned from different types of donor cells. Furthermore, on the basis of the results of comparison analysis, we identified 35 genes that were inappropriately reprogrammed in most of the SECNT embryos; our findings demonstrated that some of these genes, such as Asz1, Xlr3a and App, were appropriately reprogrammed only in the embryos with a transcriptional profile that was the closest to that of the controls. Our findings provide a framework to further understand the reprogramming in SECNT embryos

Folic Acid Exposure Rescues Spina Bifida Aperta Phenotypes in Human Induced Pluripotent Stem Cell Model

Neural tube defects (NTDs) are severe congenital abnormalities, caused by failed closure of neural tube during early embryonic development. Periconceptional folic acid (FA) supplementation greatly reduces the risk of NTDs. However, the molecular mechanisms behind NTDs and the preventive role of FA remain unclear. Here, we use human induced pluripotent stem cells (iPSCs) derived from fetuses with spina bifida aperta (SBA) to study the pathophysiology of NTDs and explore the effects of FA exposure. We report that FA exposure in SBA model is necessary for the proper formation and maturation of neural tube structures and robust differentiation of mesodermal derivatives. Additionally, we show that the folate antagonist methotrexate dramatically affects the formation of neural tube structures and FA partially reverts this aberrant phenotype. In conclusion, we present a novel model for human NTDs and provide evidence that it is a powerful tool to investigate the molecular mechanisms underlying NTDs, test drugs for therapeutic approaches

Prevalência de defeitos de fechamento de tubo neural no Vale do Paraíba, São Paulo Prevalence of neural tube defects in Vale do Paraíba, São Paulo, Brazil

OBJETIVO: Estimar a prevalência de defeitos de fechamento do tubo neural no Vale do Paraíba paulista e identificar possíveis fatores maternos e neonatais associados a tais defeitos. MÉTODOS: Realizou-se um estudo transversal com dados secundários obtidos na Secretaria Estadual da Saúde referentes aos nascimentos ocorridos em 2004 no Vale do Paraíba paulista, que compreende 35 municípios e conta com população de 2 milhões de habitantes. Anencefalia, encefalocele e espina bífida (mielocele e mielomeningocele) foram considerados defeitos de fechamento do tubo neural. As variáveis maternas foram: idade, escolaridade, cor da pele, número de consultas no pré-natal, número de filhos vivos e relato de óbito fetal prévio. As variáveis relativas ao recém-nascido foram: peso, idade gestacional e escore de Apgar. Realizou-se comparação das médias por meio do teste t de Student e obtiveram-se os valores das razões de chance com intervalos de confiança de 95%. RESULTADOS: Foram analisados 33.653 nascidos vivos. Trinta e oito recém-nascidos com o defeito foram encontrados (1,13/1.000 nascidos vivos), sendo 23 casos de espina bífida. Houve associação com baixo peso ao nascimento, prematuridade e menores escores de Apgar de cinco minutos. CONCLUSÕES: A prevalência desta anomalia foi inferior à de outros estudos nacionais e sua presença esteve associada ao baixo peso, à prematuridade e à baixa vitalidade ao nascer.<br>OBJECTIVE: To estimate the prevalence of neural tube defects in Vale do Paraíba, São Paulo, Brazil, and to identify possible maternal and neonatal variables associated with these defects. METHODS: This cross-sectional study used secondary records of the Health Department of São Paulo State related live births during 2004 in Vale do Paraíba, São Paulo, Brazil. This region has 35 cities and 2 million inhabitants. Anencephaly, encephalocele and spina bifida (myelocele and myelomeningocele) were considered as neural tube defects. The following maternal variables were analyzed: age, educational level, race, number of born alive and stillborn infants and prenatal visits. Neonatal variables were: birth weight, gestational age and Apgar score. Numerical variables were compared by Student t test, and Odds Ratio values were obtained with the 95% confidence interval. RESULTS: The analysis was performed based on 33,653 records of born alive infants. Twenty-three infants with spina bifida were identified, with an estimated prevalence of 1.13 cases for each 1,000 live births. The presence of neural tube defects was associated to low birth weight, prematurity and low Apgar score. CONCLUSIONS: The estimated prevalence of neural tube defects in this region of São Paulo was lower than others reported in previous Brazilian studies. These defects were associated with low birth weight, prematurity and respiratory depression at birth