Genetics of neural tube defects

Awareness About Folic Acid Supplementation in First-Trimester Pregnant Women of Rural Raipur District, Chhattisgarh, and Its Determinants: A Cross-Sectional Study

BACKGROUND

Women are supplemented with folic acid (FA) during pregnancy as well as preconceptionally to prevent neural tube defects (NTDs) in newborns. To understand the importance of FA supplementation, women need to have awareness about the same, which in turn may be influenced by different factors. It is also known that both FA and vitamin B12 deficiency tend to cause NTDs in newborns and anemia. Very few studies have studied the relationship between hemoglobin, FA, and vitamin B12 levels. In this study, we aim to estimate the level of awareness of FA supplementation among pregnant women in the first trimester of pregnancy and the factors determining the presence of awareness regarding the same. Also, we aim to estimate any correlation between hemoglobin, FA, and vitamin B12 levels among a subset of pregnant women.

METHODS

A cross-sectional study was conducted in the Abhanpur Block of Raipur district in Chhattisgarh among 399 pregnant women in their first trimester of pregnancy, in which their knowledge was assessed using a pretested semistructured questionnaire. Each participant's knowledge score regarding FA supplementation was calculated and scored based on six indicators and classified as low, intermediate, and high scores. Logistic regression was applied to find out any significant association between knowledge about FA supplementation with any other sociodemographic variables. Scatter plots were used to assess the correlation of FA with hemoglobin, vitamin B12, and knowledge scores among 104 participants.

RESULTS

The majority (77.9%) of women had low knowledge scores with a mean score of 1.4 (0.15). It was found that only 45.6% of the participants knew the importance of FA supplementation, and the majority (23.1%) were informed by auxiliary nurse midwives (ANMs) followed by doctors. The majority (41.6%) of the study participants also did not know when to start FA, and only 1.3% knew that FA should be taken preconceptionally. On multivariable logistic regression, women who lived in joint families had significantly higher odds of having intermediate knowledge compared to those who lived in nuclear families. Although not statistically significant, there was a positive correlation between serum vitamin B12 and FA levels and also between hemoglobin and serum FA levels. However, a significant positive correlation was found between serum FA levels and the knowledge scores of the study participants.

CONCLUSION

The majority of study participants had poor knowledge and awareness regarding FA supplementation. So, health education, as well as information, education, and communication (IEC) activities, is required to improve the knowledge about FA supplementation among women of reproductive age in the community. A better understanding of FA supplementation can lead to adherence to FA consumption and prevent NTDs among newborns.

Evaluation of ganglion cell complex and retinal nerve fiber layer in children with spina bifida using optical coherence tomography

PURPOSE

Spina bifida (SB) is a congenital disorder caused by the incomplete fusion of the embryonic neural tube during spinal cord development. In this study, we used Spectral Domain Optic Coherence Tomography (SD-OCT) for retinal nerve fibre layer (RNFL) and ganglion cell complex (GCC) analyses and compared the results of healthy children and SB patients in a similar age group.

METHODS

Our study was planned prospectively and conducted between June 2017 and July 2019. One hundred eyes of 50 participants, consisting of 28 SB patients and 22 healthy children were included. In all cases, RNFL and GCC measurements were undertaken using SD-OCT. The circumpapillary RNFL analysis was conducted by examining the circular area of 3.45 mm in diameter around the centre of the optic disc. GCC parameters were determined with MM7 protocols by taking 15 vertical sections from a 7-mm macular square centred in the fovea.

RESULTS

The mean GCC thickness of the participants was 91.120 ± 5.224 µm in the control group and 91.696 ± 7.410 µm in the SB group. The difference between the two groups was not statistically significant (p > 0.05). The mean RNFL thickness was 102.499 ± 11.250 µm in the control group and 99.549 ± 15.235 µm in the SB group. The mean RNFL thickness of the patients in the SB group was lower than that of the control group, but the difference was not statistically significant (p > 0.05).

CONCLUSIONS

In this study, the lack of a statistically significant difference in the RNFL and GCC values between the SB and control groups can be attributed to successful clinical management.

The Role of Oxidative Stress in the Pathomechanism of Congenital Malformations

Congenital anomalies are significant causes of mortality and morbidity in infancy and childhood. Embryogenesis requires specific signaling pathways to regulate cell proliferation and differentiation. These signaling pathways are sensitive to endogenous and exogenous agents able to produce several structural changes of the developing fetus. Oxidative stress, due to an imbalance between the production of reactive oxygen species and antioxidant defenses, disrupts signaling pathways with a causative role in birth defects. This review provides a basis for understanding the role of oxidative stress in the pathomechanism of congenital malformations, discussing the mechanisms related to some congenital malformations. New insights in the knowledge of pathomechanism of oxidative stress-related congenital malformations, according to experimental and human studies, represent the basis of possible clinical applications in screening, prevention, and therapies.

Polymorphisms in MTHFD1 Gene and Susceptibility to Neural Tube Defects: A Case-Control Study in a Chinese Han Population with Relatively Low Folate Levels

Background

The polymorphism of methylenetetrahydrofolate dehydrogenase (MTHFD1) has been reported as a risk factor for neural tube defects (NTDs). In the present study, we aimed to investigate whether the single-nucleotide polymorphisms (SNPs) of MTHFD1 gene are associated with NTDs in a Chinese population and to determine their mechanism of action.

Material/Methods

MTHFD1 gene was scanned in a total of 270 NTDs cases and 192 healthy controls by using next-generation sequencing (NGS) method. After quality control procedures, 208 selected SNP sites in MTHFD1 gene were enrolled for follow-up statistical association analyses. Functional analyses were also performed for significant SNPs through bioinformatics analysis. Folic acid levels of brain tissue in available NTDs cases and healthy controls (113 and 123, respectively) were measured. Statistical and bioinformatics analyses were performed to investigate the relationship between SNPs in MTHFD1 and susceptibility to NTDs.

Results

Statistical analysis showed that 2 independent SNPs, rs1956545 and rs56811449, confer the risk of NTDs (P value=0.0195, OR (odds ratio)=1.41, 95% CI (confidence interval)=1.06–1.88; P value=0.0107, OR=0.56, 95% CI=0.36–0.87). The haplotype GGGG, which consists of 4 SNPs (rs2236225, rs2236224, rs1256146, and rs6573559), is also associated with risk of NTDs (P value=0.0438, OR=0.7180, 95% CI=0.5214–0.9888). The risk allele C of rs1956545 is also associated with decreased folic acid levels in the brain (P value=0.0222, standard beta=−0.2238, 95% CI=−0.4128 – −0.0349) according to analysis in the subset of NTDs cases and healthy controls. Bioinformatics analysis indicates that rs1956545 and rs56811449 are within ENCODE regulatory regions, the open chromatin regions of blastula Trophoblast cell line, and histone-marked region of brain astrocyte cell line.

Conclusions

The polymorphism of SNP loci rs1956545 and rs56811449 as well as a haplotype in MTHFD1 gene could serve as an indicator for the occurrence of NTDs in Chinese population and some specific genotypes of the loci may have lower risk of developing NTDs.

Dieting to lose weight and occurrence of neural tube defects in offspring of Mexican-American women

Lowered maternal weight gain and reduction in early pregnancy have been associated with risk of neural tube defects (NTDs) in offspring. We examined the association of self-reported maternal dieting behaviors on the occurrence of NTDs. We conducted a population based case-control study among Mexican-American women who were residents of the 14 Texas counties bordering Mexico. Case women had an NTD-affected pregnancy identified at birth or prenatally and had deliveries during the years 1995-2000. Control women were those who delivered live born infants without an apparent congenital malformation, randomly selected and frequency-matched to cases by year and facility. One hundred eighty-four case women and 225 control women were asked in person about the use of nutritional supplements, dieting to lose weight, and type of weight reduction supplements used during the 3 months before conception. Women who reported being on a diet to lose weight during the 3 months before conception had an NTD odds ratio (OR) of 1.9 (95% confidence interval (CI) = 1.1, 3.3) compared with those not reporting being on a diet. Neither consuming vitamin drinks (OR = 1.2) nor using diet pills (OR = 1.6) during the 3 months before conception had ORs that were different from the null, when compared to women not reporting those behaviors. The risk effect for dieting did not differ markedly among normal or underweight (OR = 2.0, 95% CI = 0.7, 5.6), overweight (OR = 1.9, 95% CI = 0.7, 5.0), or obese women (OR = 1.5, 95% CI = 0.6, 4.0). No effect was seen among dieting women who were consuming at least 1.0 mg/day of folate (OR = 1.1, CI = 0.3, 4.5). Maternal dieting prior to conception may increase the risk of NTDs in offspring.

Cats, frogs, and snakes: early concepts of neural tube defects

Disturbed neurulation fascinated scientists of all times. In Egypt, anencephalic infants were venerated as animal-headed gods. Roman law required them to be killed. The medieval world held the mother responsible, either because of assumed imagination or "miswatching," or because of suspected intercourse with animals or devils. Modern embryology and teratology began with the use of the microscope by Malpighi in 1672. Details of neural tube closure were described by Koelliker in 1861 and by His in 1874. From 1822, genetic disease and familial recurrence due to insufficient nutrition were discerned and lower social class identified as a risk factor. It took a century to define the malnutrition as insufficient folate intake. The mandatory supplementation of folate in staple foods successfully reduced the incidence of neural tube defects in the United States, Australia, Canada, and Chile, but it was not adopted by most European countries.

Gene-environment interactions, folate metabolism and the embryonic nervous system

Formation of brain and spinal cord requires the successful closure of neural ectoderm into an embryonic neural tube. Defects in this process result in anencephaly or spina bifida, which together constitute a leading cause of mortality and morbidity in children, affecting all ethnic and socioeconomic groups. The subject of intensive research for decades, neural tube defects (NTDs), are understood to arise from complex interactions of genes and environmental conditions, though systems-level details are still elusive. Despite the variety of underlying causes, a single intervention, folic acid supplementation given in the first gestational month, can measurably reduce the occurrence of NTDs in a population. Evidence for and the scope of gene-environment interactions in the genesis of NTDs is discussed. A systems-based approach is now possible toward studies of genetic and environmental influences underlying NTDs that will enable the assessment of individual risk and personalized optimization of prevention.

Importance of gene-environment interactions in the etiology of selected birth defects

It is generally understood that both genetic and environmental factors contribute to the highly complex etiology of structural birth defects, including neural tube defects, oral clefts and congenital heart defects, by disrupting highly regulated embryonic developmental processes. The intrauterine environment of the developing embryo/fetus is determined by maternal factors such as health/disease status, lifestyle, medication, exposure to environmental teratogens, as well as the maternal genotype. Certain genetic characteristics of the embryo/fetus also predispose it to developmental abnormalities. Epidemiologic and animal studies conducted over the last few decades have suggested that the interplay between genes and environmental factors underlies the etiological heterogeneity of these defects. It is now widely believed that the study of gene-environment interactions will lead to better understanding of the biological mechanisms and pathological processes that contribute to the development of complex birth defects. It is only through such an understanding that more efficient measures will be developed to prevent these severe, costly and often deadly defects. In this review, we attempt to summarize the complex clinical and experimental literature on current hypotheses of interactions between several select environmental factors and those genetic pathways in which they are most likely to have significant modifying effects. These include maternal folate nutritional status, maternal diabetes/obesity-related conditions, and maternal exposure to selected medications and environmental contaminants. Our goal is to highlight the potential gene-environment interactions affecting early embryogenesis that deserve comprehensive study.

Regulation of folate receptor 1 gene expression in the visceral endoderm

BACKGROUND

Nutrient supply to the developing mammalian embryo is a fundamental requirement. Before completion of the chorioallantoic placenta, the visceral endoderm plays a crucial role in nurturing the embryo. We have found that visceral endoderm cells express folate receptor 1, a high-affinity receptor for the essential micronutrient folic acid, suggesting that the visceral endoderm has an important function for folate transport to the embryo. The mechanisms that direct expression of FOLR1 in the visceral endoderm are unknown.

METHODS

Sequences were tested for transcriptional activation capabilities in the visceral endoderm utilizing reporter gene assays in a cell model for extraembryonic endoderm in vitro, and in transgenic mice in vivo.

RESULTS

With F9 embryo carcinoma cells as a model for extraembryonic endoderm, we demonstrate that the P4 promoter of the human FOLR1 gene is active during differentiation of the cells towards visceral endoderm. However, transgenic mouse experiments show that promoter sequences alone are insufficient to elicit reporter gene transcription in vivo. Using sequence conservation as guide to choose genomic sequences from the human FOLR1 gene locus, we demonstrate that the sequence termed F1CE2 exhibits specific enhancer activity in F9 cells in vitro, in the visceral endoderm, and later the yolk sac in transgenic mouse embryos in vivo. We further show that the transcription factor HNF4-alpha can activate this enhancer sequence.

CONCLUSIONS

We have identified a transcriptional enhancer sequence from the FOLR1 locus with specific activity in vitro and in vivo, and suggest that FOLR1 is a target for regulation by HNF4-alpha.

Prevalência de defeitos de fechamento de tubo neural no Vale do Paraíba, São Paulo

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.

The Hectd1 ubiquitin ligase is required for development of the head mesenchyme and neural tube closure

Closure of the cranial neural tube depends on normal development of the head mesenchyme. Homozygous-mutant embryos for the ENU-induced open mind (opm) mutation exhibit exencephaly associated with defects in head mesenchyme development and dorsal-lateral hinge point formation. The head mesenchyme in opm mutant embryos is denser than in wildtype embryos and displays an abnormal cellular organization. Since cells that originate from both the cephalic paraxial mesoderm and the neural crest populate the head mesenchyme, we explored the origin of the abnormal head mesenchyme. opm mutant embryos show apparently normal development of neural crest-derived structures. Furthermore, the abnormal head mesenchyme in opm mutant embryos is not derived from the neural crest, but instead expresses molecular markers of cephalic mesoderm. We also report the identification of the opm mutation in the ubiquitously expressed Hectd1 E3 ubiquitin ligase. Two different Hectd1 alleles cause incompletely penetrant neural tube defects in heterozygous animals, indicating that Hectd1 function is required at a critical threshold for neural tube closure. This low penetrance of neural tube defects in embryos heterozygous for Hectd1 mutations suggests that Hectd1 should be considered as candidate susceptibility gene in human neural tube defects.

Prevalência dos defeitos de fechamento do tubo neural em recém-nascidos do Centro de Atenção à Mulher do Instituto Materno Infantil Prof. Fernando Figueira, IMIP: 2000-2004

OBJETIVOS: conhecer a prevalência de defeito de fechamento do tubo neural (DFTN) em crianças nascidas na maternidade do Centro de Atenção à Mulher do Instituto Materno Infantil Prof. Fernando Figueira (IMIP) no período de 2000 a 2004. MÉTODOS: estudo descritivo, do tipo corte transversal, cujos dados foram coletados de um banco de dados do Sistema de Informações sobre Nascidos Vivos do qual foram selecionados todos os registros de recém-nascidos com malformação fetal. A partir daí selecionaram-se os recém-nascidos com DFTN ocorridos no período considerado. RESULTADOS: entre os 24.964 nascimentos, foram registrados 709 recém-nascidos apresentando alguma malformação ao nascer. Ao se considerar apenas os recém nascidos com DFTN, observaram-se 124 registros, representando uma prevalência de 0,5% entre nascimentos naquele período. Os recém-nascidos com DFTN apresentaram características semelhantes aos recém-nascidos com malformações, de uma forma geral. A maioria (68,5%) desses recém-nascidos era de parto cesariano e 37,7% apresentaram baixo peso ao nascer. CONCLUSÕES: a prevalência de DFTN entre os nascimentos registrados no Centro de Atenção à Mulher do Instituto Materno Infantil Prof. Fernando Figueira foi elevada (5/1000 nascimentos) e isso, provavelmente é reflexo do fato de a maternidade ser referência para gestações de alto-risco.

Evaluation of a methylenetetrahydrofolate-dehydrogenase 1958G>A polymorphism for neural tube defect risk

Genetic variants of enzymes involved in the folate pathway might be expected to have an impact on neural tube defect (NTD) risk. Given its key role in folate metabolism, the methylenetetrahydrofolate dehydrogenase 1 (MTHFD1) gene could represent an attractive candidate in NTD aetiology. In this study, the impact of the MTHFD1 1958G > A polymorphism on NTD risk in the Italian population was examined both by hospital-based case-control and family-based studies. The MTHFD1 1958G > A polymorphism was genotyped in 142 NTD cases, 125 mothers, 108 fathers and 523 controls. An increased risk was found for the heterozygous 1958G/A (OR = 1.69; P = 0.04) and homozygous 1958A/A (OR = 1.91; P = 0.02) genotypes in the children. Significant association was also found when combined 1958G/A and 1958A/A genotypes of cases were compared with the 1958G/G genotype (OR = 1.76; P = 0.02). The risk of an NTD-affected pregnancy of the mothers was increased 1.67-fold (P = 0.04) only when a dominant effect (1958G/A or 1958A/A vs 1958G/G) of the 1958A allele was analysed. The combined TDT/1-TDT (Z = 2.11; P = 0.03) and FBAT (Z = 2.4; P = 0.01) demonstrated a significant excess of transmission of the 1958A allele to affected individuals. In summary, our results indicate that heterozygosity and homozygosity for the MTHFD1 1958G > A polymorphism are genetic determinants of NTD risk in the cases examined.

Discrepancies between the effects of glutamine in cultures of preimplantation mouse embryos

A review of the literature shows divergent differences between laboratories of the effects of glutamine in mouse preimplantation embryo culture media. One laboratory reported several cases of exencephaly, which was attributed to ammonia produced by the breakdown of glutamine. Two other laboratories have found no such effects. It is suggested, but not proved, that the differences in results may have a genetic basis. Further, it is argued that studies on the toxicological actions of exogenous ammonium chloride on preimplantation development provide a biased model of the effects of glutamine as used in embryo culture protocols. The finding that ammonium can also cause exencephaly thus fosters undue concern about the teratological effects of glutamine.

Postmortem findings in term neonates

Neonatal deaths in infants born at term are relatively rare in the USA, occurring in 0.9/1000 live births. Congenital malformations, perinatal asphyxia, infections and inborn errors of metabolism are the leading causes. Chromosomal malformation syndromes, congenital heart disease, pulmonary hypoplasia and severe neural tube defects comprise the majority of lethal malformations. Several skeletal dysplasias are lethal in the newborn infant. Group B Streptococcus still plays a major role in neonatal mortality while deaths due to other infectious agents have decreased. Hypoxic ischaemic encephalopathy is a significant cause of neonatal death. Inborn errors of metabolism have variable presentations but some, such as the fatty acid oxidation disorders, may present in neonates and cause sudden death.

Genetic variants in ZIC1, ZIC2, and ZIC3 are not major risk factors for neural tube defects in humans

Neural tube defects (NTD) are congenital malformations arising from incomplete neural tube closure during early embryogenesis. Most NTD in humans show complex inheritance patterns, with both genetic and environmental factors involved in the etiology of this malformation. More than 120 mouse models for human NTD exist. NTD have been observed in mice deficient for the Zic family genes, Zic1, Zic2, and Zic3. We performed mutation analysis in the human orthologs of these genes using DNA material from a large panel of NTD patients. In ZIC2 we identified a deletion of one codon that encodes an alanine residue located in the amino terminal alanine stretch of the protein. The deletion was present in one patient, but not in 364 controls. That may suggest a role-albeit small-of this variant in the etiology of NTD in humans. Transmission disequilibrium testing of a frequent polymorphism in the ZIC2 gene (1059C > T, H353H) in parent-spina bifida aperta child triads showed no association with NTD. One silent polymorphism (858G > A, V286V) of unknown significance was identified in ZIC3. Neither mutations nor polymorphisms were found in the coding region or flanking sequences of ZIC1. Our data indicate that ZIC1, ZIC2, and ZIC3 are not major risk factors for NTD in humans.

Fumonisins disrupt sphingolipid metabolism, folate transport, and neural tube development in embryo culture and in vivo: a potential risk factor for human neural tube defects among populations consuming fumonisin-contaminated maize

Fumonisins are a family of toxic and carcinogenic mycotoxins produced by Fusarium verticillioides (formerly Fusarium moniliforme), a common fungal contaminant of maize. Fumonisins inhibit ceramide synthase, causing accumulation of bioactive intermediates of sphingolipid metabolism (sphinganine and other sphingoid bases and derivatives) as well as depletion of complex sphingolipids, which interferes with the function of some membrane proteins, including the folate-binding protein (human folate receptor alpha). Fumonisin causes neural tube and craniofacial defects in mouse embryos in culture. Many of these effects are prevented by supplemental folic acid. Recent studies in LMBc mice found that fumonisin exposure in utero increases the frequency of developmental defects and administration of folate or a complex sphingolipid is preventive. High incidences of neural tube defects (NTD) occur in some regions of the world where substantial consumption of fumonisins has been documented or plausibly suggested (Guatemala, South Africa, and China); furthermore, a recent study of NTD in border counties of Texas found a significant association between NTD and consumption of tortillas during the first trimester. Hence, we propose that fumonisins are potential risk factors for NTD, craniofacial anomalies, and other birth defects arising from neural crest cells because of their apparent interference with folate utilization.

Pharmacology of neural tube defects

The pharmacology of neural tube defects (NTDs) is a complex issue. Several theories regarding the etiology of NTDs emphasize the importance of interactions between genetic, environmental, and biochemical factors at a key point in time. One such factor is chronic drug therapy, a potential consequence of which is the formation of toxic drug metabolites, including free radicals (FRs), which have been implicated in the etiology of NTDs. Under normal physiological conditions, FRs are quickly destroyed by antioxidant defense systems. However, FR-mediated cellular damage can occur if these defense systems fail or are overburdened, such as in patients who are genetically deficient in FR scavenging enzyme activity (FRSEA) or who are receiving chronic drug therapy. Congenital defects, including NTDs, resulting from FR-induced damage have been reported in both experimental animals and humans. For example, the use of antiepileptic drugs (AEDs) during pregnancy that have the propensity to form FRs during their metabolism are associated with an increased risk of the development of congenital malformations, including NTDs. This article reviews the biochemistry of FRs, the factors regulating FR scavenging capacity, and the theories regarding the etiology of NTDs; presents a hypothesis of a unified mechanism for AED-induced NTDs and other congenital defects; and briefly discusses the roles of folate and selenium in the prevention of NTDs.

Pathobiology and genetics of neural tube defects

PURPOSE

Neural tube defects (NTDs), including spina bifida and anencephaly, are common congenital malformations that occur when the neural tube fails to achieve proper closure during early embryogenesis. Based on epidemiological and clinical data obtained over the last few decades, it is apparent that these multifactorial defects have a significant genetic component to their etiology that interacts with specific environmental risk factors. The purpose of this review article is to synthesize the existing literature on the genetic factors contributing to NTD risk.

RESULTS

To date, there is evidence that closure of the mammalian neural tube initiates and fuses intermittently at four discrete locations. Disruption of this process at any of these four sites may lead to an NTD, possibly arising through closure site-specific genetic mechanisms. Candidate genes involved in neural tube closure include genes of the folate metabolic pathway, as well as those involved in folate transport.

CONCLUSIONS

Although extensive efforts have focused on elucidating the genetic risk factors contributing to the etiology of NTDs, the population burden for these malformations remains unknown. One group at high risk for having children with NTDs is epileptic women receiving antiepileptic medications during pregnancy. Efforts to better understand the genetic factors that may contribute to their heightened risk, as well as the pathogenesis of neural tube closure defects, are reviewed herein.

A polymorphism, R653Q, in the trifunctional enzyme methylenetetrahydrofolate dehydrogenase/methenyltetrahydrofolate cyclohydrolase/formyltetrahydrofolate synthetase is a maternal genetic risk factor for neural tube defects: report of the Birth Defects Research Group

Women who take folic acid periconceptionally reduce their risk of having a child with a neural tube defect (NTD) by >50%. A variant form of methylenetetrahydrofolate reductase (MTHFR) (677C-->T) is a known risk factor for NTDs, but the prevalence of the risk genotype explains only a small portion of the protective effect of folic acid. This has prompted the search for additional NTD-associated variants in folate-metabolism enzymes. We have analyzed five potential single-nucleotide polymorphisms (SNPs) in the cytoplasmic, nicotinamide adenine dinucleotide phosphate-dependent, trifunctional enzyme methylenetetrahydrofolate dehydrogenase/methenyltetrahydrofolate cyclohydrolase/formyltetrahydrofolate synthetase (MTHFD1) for an association with NTDs in the Irish population. One SNP, R653Q, in this gene appears to be associated with NTD risk. We observed an excess of the MTHFD1 "Q" allele in the mothers of children with NTD, compared with control individuals. This excess was driven by the overrepresentation of QQ homozygotes in the mothers of children with NTD compared with control individuals (odds ratio 1.52 [95% confidence interval 1.16-1.99], P=.003). We conclude that genetic variation in the MTHFD1 gene is associated with an increase in the genetically determined risk that a woman will bear a child with NTD and that the gene may be associated with decreased embryo survival.

Gene expression profiling within the developing neural tube

The developing mammalian nervous system is subject to devastating congenital malformations with clinical significance that extends into the billions of health care dollars annually worldwide. Neural tube defects (NTDs) are among the most common of all human congenital defects, yet their etiology remains poorly understood. This is largely due to the complexity of the genetic factors regulating the intricate events involved in neurulation. Using mouse model systems and the application of modern molecular biological technologies, we have recently gained a greater appreciation for the factors that not only regulate normal neural tube closure (NTC), but those genetic factors that predispose an embryo to significant birth defects such as anencephaly or spina bifida. We have selected prominent murine mutants, both spontaneous and genetically modified, as well as the use of teratogenic agents, to examine the impact of altering the normal pattern of gene expression in the developing neural tube.