Maternal Serum α-Fetoprotein Screening for the Detection of Neural Tube Defects—Report of a Pilot Program

We tested 10,715 low-risk pregnancies in a voluntary maternal serum α-fetoprotein screening program for the detection of neural tube defects in California. In all, 5.3 percent of women had one elevated serum level, 3.3 percent were referred for sonography and 1.5 percent for amniocentesis. There were 12 cases of open neural tube defects (1.1 per 1,000); all of the mothers had one elevated serum αfetoprotein level: nine (75 percent) completed the protocol and the neural tube defects were correctly identified. No normal pregnancies were terminated. The risk of an open neural tube defect occurring was about 1 in 50 after the first abnormal serum level and 1 in 15 at amniocentesis. We found significantly increased risk for fetal death and low birth weight after one elevated serum α-fetoprotein level, though the likelihood of a normal pregnancy outcome was about 80 percent. Maternal serum screening was also useful in identifying twin pregnancies and correcting underestimated gestational dates.     

SNPs in the neural cell adhesion molecule 1 gene (NCAM1) may be associated with human neural tube defects

Neural tube defects (NTDs) are common birth defects, occurring in approximately 1/1,000 births; both genetic and environmental factors are implicated. To date, no major genetic risk factors have been identified. Throughout development, cell adhesion molecules are strongly implicated in cell–cell interactions, and may play a role in the formation and closure of the neural tube. To evaluate the role of neural cell adhesion molecule 1 (NCAM1) in risk of human NTDs, we screened for novel single-nucleotide polymorphisms (SNPs) within the gene. Eleven SNPs across NCAM1 were genotyped using TaqMan. We utilized a family-based approach to evaluate evidence for association and/or linkage disequilibrium. We evaluated American Caucasian simplex lumbosacral myelomeningocele families (n=132 families) using the family based association test (FBAT) and the pedigree disequilibrium test (PDT). Association analysis revealed a significant association between risk for NTDs and intronic SNP rs2298526 using both the FBAT test (P=0.0018) and the PDT (P=0.0025). Using the HBAT version of the FBAT to look for haplotype association, all pairwise comparisons with SNP rs2298526 were also significant. A replication study set, consisting of 72 additional families showed no significant association; however, the overall trend for overtransmission of the less common allele of SNP rs2298526 remained significant in the combined sample set. In addition, we analyzed the expression pattern of the NCAM1 protein in human embryos, and while NCAM1 is not expressed within the neural tube at the time of closure, it is expressed in the surrounding and later in differentiated neurons of the CNS. These results suggest variations in NCAM1 may influence risk for human NTDs.Other members of NTD Collaborative Group involved in this study are listed in the appendix     

A unique missense allele of BAF155, a core BAF chromatin remodeling complex protein,causes neural tube closure defects in mice

Failure of embryonic neural tube closure results in the second most common class of birth defects known as neural tube defects (NTDs). While NTDs are likely the result of complex multigenic dysfunction, it is not known whether polymorphisms in epigenetic regulators may be risk factors for NTDs. Here we characterized Baf155^msp3, a unique ENU‐induced allele in mice. Homozygous Baf155^mps3 embryos exhibit highly penetrant exencephaly, allowing us to investigate the roles of an assembled, but malfunctional BAF chromatin remodeling complex in vivo at the time of neural tube closure. Evidence of defects in proliferation and apoptosis were found within the neural tube. RNA‐Seq analysis revealed that surprisingly few genes showed altered expression in Baf155 mutant neural tissue, given the broad epigenetic role of the BAF complex, but included genes involved in neural development and cell survival. Moreover, gene expression changes between individual mutants were variable even though the NTD was consistently observed. This suggests that inconsistent gene regulation contributes to failed neural tube closure. These results shed light on the role of the BAF complex in the process of neural tube closure and highlight the importance of studying missense alleles to understand epigenetic regulation during critical phases of development. © 2013 Wiley Periodicals, Inc. Develop Neurobiol 74: 483–497, 2014     

Prevalence of neural tube defects in South Australia, 1966-91: effectiveness and impact of prenatal diagnosis.

OBJECTIVE--To determine trends in total prevalence of neural tube defects in South Australia during 1966-91, the impact of prenatal diagnosis on birth prevalence, and the effectiveness of prenatal screening for neural tube defects in 1986-91. DESIGN--All births and terminations of pregnancy affected by neural tube defects and information on prenatal screening were ascertained from multiple sources including the South Australian perinatal and abortion statistics collections, birth defects register, and state maternal serum alpha fetoprotein screening programme. SETTING--Southern Australia. SUBJECTS--All 1058 births and terminations of pregnancy affected by neural tube defects in 1966-91. MAIN OUTCOME MEASURES--Total prevalence and birth prevalence of individual and all neural tube defects. The proportion of screened cases detected prenatally. RESULTS--Total prevalence of neural tube defects during 1966-91 was 2.01/1000 births with no upward or downward trend. However, birth prevalence fell significantly (by 5.1% a year), with an 84% reduction from 2.29/1000 births in 1966 to 0.35/1000 in 1991 (relative risk = 0.16, 95% confidence interval 0.07 to 0.34). The fall was 96% for anencephaly and 82% for spina bifida. 85% of defects, both open and closed, were detected before 28 weeks'' gestation in women screened by serum alpha fetoprotein or mid-trimester ultrasonography, or both, in 1986-91 (99.0% for anencephaly and 75.7% for spina bifida). CONCLUSIONS--While the total prevalence of neural tube defects in South Australia remained stable, prenatal diagnosis and termination of pregnancy resulted in an 84% fall in birth prevalence during 1966-91. Screening detected over four fifths of cases in 1986-91.     

还原叶酸载体基因（RFC1）与神经管和颅面畸形病因学关系的研究进展

神经管畸形和颅面畸形是最常见的出生缺陷,由遗传和环境因素共同作用所致,大规模的人群流行病学研究已证实,叶酸能降低发生这类畸形的危险。叶酸缺乏是神经管和颅面畸形发生的主要环境因素,但其机制尚不清楚,通过对与叶酸代谢有关的还原叶酸载体（reduced folate carrier,RFC）的生化特点、生理功能、还原叶酸载体基因（RFC1）结构功能、调控、表达及其与叶酸水平和神经管颅面畸形的关系等研究进展进行综述,从而为神经管和颅面畸形的病因学研究提出可能的候选基因。 Abstract: Neural tube and craniofacial defects are common birth defects which are ascribed to the combination of genetic and environmental factors. The population epidemiological studies suggested that periconceptional use of multivitamins containing folic acid can reduce a woman’s risk of having a child with neural tube and craniofacial defects. It’s a major environmental factor that periconceptinal women with deficiency of folic acid may increase their risk for delivering babies with neural tube and craniofacial defects, but the mechanism by which folic acid facilitated this risk rediction is unknown. This paper reviews folate transport carrier, Reduced Folate Carrier(RFC)’s characteristics in biological chemistry, physiological function, the folate transport mechanism, structure, function, regulation and expression of reduced folate carrier gene(RFC1), and the relationship between RFC1 with plasm or erythrocyte folate level and neural tube defects, et al. It is suggested a etiologic hypothesis in investigation of candidate gene encoding specific folat-related pathways of neural tube and craniofacial defects.     

Population differences in vision acuity: A review,with speculative notes on selection relaxation

Abstract

The contrast between the lower frequencies of vision defects reported among several different samples of hunting populations and the higher frequencies found repeatedly among populations with relatively long histories of agriculture and settled habitations points strongly to the relaxation of natural selection. Two rough estimates of the heritability of that conglomeration of genetic entities comprising “vision defects” are found in studies of MZ versus DZ twins and in studies of offspring of consanguineous parents versus those of unrelated parents. The hypothesis of relaxation of natural selection is plausible as man developed culture habitats more tolerant of persons with slight refractive aberrations. One can reasonably imagine that hereditary deficiencies accumulated sufficiently under such conditions to make possible quantitative estimates of differential population frequencies.     

Folate status of the population in the Canadian Health Measures Survey

Background

Low folate concentrations are inversely associated with birth defects, including neural tube defects, congenital heart disease and oral clefts. Conversely, high folate concentrations may be associated with adverse outcomes, including increased risk of colorectal cancer among those with pre-existing neoplasms. The purpose of our study was to investigate the folate status of a nationally representative sample of Canadians, including a subset of women of childbearing age.

Methods

We examined red blood cell folate concentrations among members of the general population aged 6–79 years (n = 5248) and separately among women of childbearing age (15–45 yr, n = 1162), as recorded by the Canadian Health Measures Survey and measured by immunologic assay. We assessed the data for significant differences by age, sex and socioeconomic status.

Results

Less than 1% of Canadians showed folate deficiency (red blood cell folate < 305 nmol/L) and 40% showed high folate concentrations (> 1360 nmol/L). Among women of childbearing age, 22% showed concentrations below those considered optimal for maximal neural tube defect-risk reduction (< 906 nmol/L). Significant differences by age and socio-economic status, but not sex, were evident in median red blood cell folate concentrations, although concentrations in all groups exceeded recommended levels. No differences by age or income were found among women of child-bearing age.

Interpretation

Folate deficiency is virtually nonexistent in the Canadian population, although high folate concentrations are evident. Additional research is needed to better understand the determinants of red blood cell folate among women of childbearing age who have concentrations below levels that are maximally protective against neural tube defects. Ongoing monitoring of the folate status of Canadians and the relationship between red blood cell folate and health outcomes is warranted.Folic acid represents both a public health success and a controversial debate over associated health risks. Fortification with folic acid of Canadian white wheat flour (150 μg/100 g) and other selected grains in 1998 has been linked to a 46% reduction in the prevalence of neural tube defects.¹ Declines in rates of neural tube defects have also been documented in the United States and Chile after fortification of grains with folic acid.^2,3 To further reduce the risk of folate-dependent neural tube defects, women of childbearing age are encouraged to eat folate-rich foods and take a multivitamin supplement containing folic acid (0.4 mg/d).⁴ Higher-dose supplements (4–5 mg/d) are recommended for women at increased risk of giving birth to a baby with a neural tube defect (e.g., those who regularly use folic acid antagonist medications or have a family history of neural tube defects).⁵ Although biochemical assessment of the folate status of select subgroups of Canadians has been done, it has not been studied on a nationally representative sample in over 30 years.^6–9 The recent Canadian Health Measures Survey provides data to fill this gap.⁷ The purpose of our study was to describe the current folate status of Canadians, including a subgroup of Canadian women of childbearing age, and to assess whether folate concentrations vary by age, sex and socio-economic status.     

Birth Prevalence of Neural Tube Defects and Orofacial Clefts in India: A Systematic Review and Meta-Analysis

Background

In the last two decades, India has witnessed a substantial decrease in infant mortality attributed to infectious disease and malnutrition. However, the mortality attributed to birth defects remains constant. Studies on the prevalence of birth defects such as neural tube defects and orofacial clefts in India have reported inconsistent results. Therefore, we conducted a systematic review of observational studies to document the birth prevalence of neural tube defects and orofacial clefts.

Methods

A comprehensive literature search for observational studies was conducted in MEDLINE and EMBASE databases using key MeSH terms (neural tube defects OR cleft lip OR cleft palate AND Prevalence AND India). Two reviewers independently reviewed the retrieved studies, and studies satisfying the eligibility were included. The quality of included studies was assessed using selected criteria from STROBE statement.

Results

The overall pooled birth prevalence (random effect) of neural tube defects in India is 4.5 per 1000 total births (95% CI 4.2 to 4.9). The overall pooled birth prevalence (random effect) of orofacial clefts is 1.3 per 1000 total births (95% CI 1.1 to 1.5). Subgroup analyses were performed by region, time period, consanguinity, and gender of newborn.

Conclusion

The overall prevalence of neural tube defects from India is high compared to other regions of the world, while that of orofacial clefts is similar to other countries. The majority of studies included in the review were hospital based. The quality of these studies ranged from low to moderate. Further well-designed, high quality community-based observational studies are needed to accurately estimate the burden of neural tube defects and orofacial clefts in India.     

The Reissner's Fiber Termination in Some Lower Chordates

The caudal end of the neural tube of the tunicate Oikopleura, the cephalochordate Branchiostoma and newly hatched fry of the clupeiform teleosts Clupea, Engraulis and Sardinops was studied by means of the electron microscope. In Oikopleura and the teleost larvae either Reissner's fiber or an amorphous mass of fiber substance leaks out of the neural tube into the surrounding tissue spaces. In Branchiostoma the disintegrated fiber material is apparently engulfed by the caudal ependymal cells. A relationship seems to exist between the degree of fiber disintegration within the neural tube and the degree of specialization of the caudal neural tube ependymal cells, the two extremes being represented by Branchiostoma with a “closed” Reissner's fiber system with highly specialized caudal ependymal cells and a teleost fry with the intact fiber leaving the neural tube between almost undifferentiated ependymal cells. These observations on lower chordates are in accordance with the hypothesis that Reissner's fiber acts as a detoxicator for the neural tube fluid.     

Reproductive consequences of oral arsenate exposure during pregnancy in a mouse model

BACKGROUND: The second most common of all structural birth defects, neural tube defects (NTDs), affect approximately 2.6/1,000 births worldwide, and 1/1,000 births in the United States. Of the many environmental agents suspected of being teratogenic, arsenic (As) is capable of inducing NTDs in laboratory animals. METHODS: We evaluated the teratogenicity of oral exposure on embryonic day (E) 7.5 and E:8.5 to As 4.8, 9.6, or 14.4 mg/kg (as sodium arsenate) in an inbred mouse strain, LM/Bc/Fnn, that does not exhibit spontaneous neural tube malformations. Control and arsenic‐treated dams (20 per treatment group) were weighed daily, and evaluated for signs of maternal toxicity. Fetuses were evaluated for soft tissue and skeletal malformations. RESULTS: There was no maternal toxicity as evidenced by losses in maternal body weight following As treatment. However, liver weights were lower in all As‐treated groups, suggesting hepatotoxicity due to As exposure. The number of litters affected with an NTD (exencephaly) in each treatment group was: 0, 1, 5, and 9 for control, As 4.8, 9.6, or 14.4, respectively, which exhibited a positive linear trend. There was evidence for trends between As dose and the number of litters displaying vertebral (p<0.001) and calvarial (p<0.01) abnormalities, components of the axial skeleton. Mean fetal weight of all As‐treated groups was significantly less than in control. DISCUSSION: In our model, maternal oral treatment with As induced NTDs. It also significantly increased the frequency of axial skeletal anomalies in the offspring exposed in utero, and reduced mean fetal weight, without evidence of maternal toxicity. Birth Defects Res (Part B). © 2008 Wiley‐Liss, Inc.     

The emerging role of epigenetic mechanisms in the etiology of neural tube defects

The molecular requirements for neural tube closure are complex. This is illustrated by the occurrence of neural tube defects (NTDs) in many genetic mouse mutants, which implicate a variety of genes, pathways and cellular functions. NTDs are also prevalent birth defects in humans, affecting around 1 per 1,000 pregnancies worldwide. In humans the causation is thought to involve the interplay of fetal genes and the effect of environmental factors. Recent studies on the etiology of human NTDs, as well as analysis of mouse models, have raised the question of the possible involvement of epigenetic factors in determining susceptibility. A consideration of potential causative factors in human NTDs must now include both alterations in the regulation of gene expression, through mutation of promoter or regulatory elements and the additional analysis of epigenetic regulation. Alterations in the epigenetic status can be directly modified by various environmental insults or maternal dietary factors.Key words: neural tube defects, diet, folic acid, epigenome, epigenetic regulation, methylation, chromatin, histones, acetylation     

Grainyhead-like 2 regulates neural tube closure and adhesion molecule expression during neural fold fusion

Defects in closure of embryonic tissues such as the neural tube, body wall, face and eye lead to severe birth defects. Cell adhesion is hypothesized to contribute to closure of the neural tube and body wall; however, potential molecular regulators of this process have not been identified. Here we identify an ENU-induced mutation in mice that reveals a molecular pathway of embryonic closure. Line2F homozygous mutant embryos fail to close the neural tube, body wall, face, and optic fissure, and they also display defects in lung and heart development. Using a new technology of genomic sequence capture and high-throughput sequencing of a 2.5 Mb region of the mouse genome, we discovered a mutation in the grainyhead-like 2 gene (Grhl2). Microarray analysis revealed Grhl2 affects the expression of a battery of genes involved in cell adhesion and E-cadherin protein is drastically reduced in tissues that require Grhl2 function. The tissue closure defects in Grhl2 mutants are similar to that of AP-2α null mutants and AP-2α has been shown to bind to the promoter of E-cadherin. Therefore, we tested for a possible interaction between these genes. However, we find that Grhl2 and AP-2α do not regulate each other's expression, E-cadherin expression is normal in AP-2α mutants during neural tube closure, and Grhl2;AP-2α trans-heterozygous embryos are morphologically normal. Taken together, our studies point to a complex regulation of neural tube fusion and highlight the importance of comparisons between these two models to understand more fully the molecular pathways of embryonic tissue closure.     

Differentially expressed genes in embryonic cardiac tissues of mice lacking <Emphasis Type="Italic">Folr1</Emphasis>gene activity

Background  

Heart anomalies are the most frequently observed among all human congenital defects. As with the situation for neural tube defects (NTDs), it has been demonstrated that women who use multivitamins containing folic acid peri-conceptionally have a reduced risk for delivering offspring with conotruncal heart defects [1–3]. Cellular folate transport is mediated by a receptor or binding protein and by an anionic transporter protein system. Defective function of the Folr1 (also known as Folbp1; homologue of human FRα) gene in mice results in inadequate transport, accumulation, or metabolism of folate during cardiovascular morphogenesis.     

LINE-1 DNA methylation is inversely correlated with cord plasma homocysteine in man: A preliminary study

Folic acid supplementation during pregnancy has known beneficial effects. It reduces risk of neural tube defects and low birth weight. Folate and other one-carbon intermediates might secure these clinical effects via DNA methylation. However, most data on the effects of folate on the epigenome is derived from animal or in vitro models. We examined the relationship between cord blood methylation and maternal folic acid intake, cord blood folate and homocysteine using data from 24 pregnant women. Genome-wide methylation was determined by the level of methylation of LINE-1 repeats using Pyrosequencing. We show that cord plasma homocysteine (p = 0.001, r = -0.688), but not serum folate or maternal folic acid intake, is inverse correlated with LINE-1 methylation. This remained significant after correction for potential confounders (p = 0.004). These data indicate that levels of folate-associated intermediates in cord blood during late pregnancy have significant consequences for the fetal epigenome.     

Immaculate conceptions in sub‐Saharan Africa: Exploratory analysis of inconsistencies in the timing of first sexual intercourse and first birth

Abstract

Survey data from a number of developing countries show that a considerable proportion of parous women report that they had their first birth one or more years before they first had sexual intercourse. In this paper, I use data from eight African Demographic and Health Surveys to explore factors that contribute to cross‐national differentials in the prevalence of these “immaculate conceptions.” The results suggest that this data problem results not only from recall errors, but also from the fact that some respondents misinterpret the question on first sexual intercourse and report their age at the onset of intercourse with either their first or current husband rather than their age at sexual initiation.     

Effects‐initiated assessments are not risk assessments

True risk assessments address the probability of a future risk occurring given a certain set of circumstances. However, “effects‐initiated assessments”; or “retrospective assessments”; often are improperly included under the broad appellation of “risk assessment”; and are conducted when an apparently adverse effect is seen in some environmental component and the question of cause (i.e., etiology) is raised. Base line risk assessments at Superfund sites or for Natural Resource Damage Assessments are examples of effects‐initiated assessments. We argue here that this type of study is not a risk assessment, either by strict definition of terminology or by logical approach taken in answering the posed question (s), and should more properly be called “diagnostic ecology.”; Diagnostic ecology starts from the premise that ecological effects have occurred and exposure to a Stressor has taken place. The problem then is to pose all possible etiologies and utilize deductive logic to systematically eliminate each agent except for one as the actual cause. A risk assessment, on the other hand, employs inductive reasoning. That is, hypotheses are generated about the possible sources of a stressor and the possible outcome if exposure occurs. Both exercises require an understanding of the ecological relationships of the various components in the ecosystem, both need an understanding of die cause‐and‐effect relationships of agents, and both require a proper framing of the questions being asked. However, risk assessors should not try to fit all environmental impact assessments into a single framework, but rather should recognize that biomedical techniques are better suited for solving diagnostic riddles than are prospective risk assessment approaches.     

Maternal alpha-fetoprotein screening: two years' experience in a low-risk district.

Over a two-year period, 3479 pregnant women in the Kings'' Lynn Health District were screened for neural tube defects by estimation of maternal serum alpha-fetoprotein. Most pregnancies were scanned by sonar for fetal maturity. Eight women had fetuses with open neural tube defects; four with anencephaly were associated with very high alpha-fetoprotein values. Of the four with open neural tube defects without anencephaly, only one was detected by screening and confirmed after amniocentesis. One other had a raised serum alpha-fetoprotein but a normal amniotic fluid value. The other two affected fetuses were missed. This disappointing outcome was attributed to the poor predictive value of alpha-fetoprotein in detecting open neural tube defects (anencephaly apart) rather than to errors in its estimation or in assessment of fetal maturity by sonar scan. We question the validity of screening, particularly in areas of intermediate or low incidence.     

An insertion/deletion polymorphism of the dihydrofolate reductase (DHFR) gene is associated with serum and red blood cell folate concentrations in women

A low serum folate and high homocysteine phenotype is associated with an increased risk of neural tube defects (NTDs), cardiovascular diseases and other pathologies. Thus defining both genetic and non-genetic factors that may impact folate/homocysteine metabolism will enhance our understanding of the etiologic mechanisms underlying these conditions and facilitate risk assessment. Dihydrofolate reductase catalyzes the reduction of folic acid to dihydrofolate and thereafter to tetrahydrofolate. The impact of the dihydrofolate reductase (DHFR) c.86 + 60_78 insertion/deletion (ins/del) polymorphism on folate and homocysteine concentrations was analyzed using data from healthy young adults from Northern Ireland, collected as part of visit three of the Young Hearts Project. Among men the DHFR c.86 + 60_78 polymorphism was not significantly associated with serum or red blood cell folate concentrations, or with homocysteine concentrations. Among women the DHFR c.86 + 60_78 polymorphism explained 2% of the variation in RBC folate levels and 5% of the variation in serum folate levels, but did not appear to have an independent effect on homocysteine. Relative to women with the DHFR c.86 + 60_78 ins/ins and ins/del genotypes, del/del homozygotes had increased serum and red blood cell folate concentrations and may therefore be at decreased risk of having offspring affected by NTDs and of other adverse reproductive and health outcomes attributable to low folate.     

Transgenic mice expressing PAX3-FKHR have multiple defects in muscle development, including ectopic skeletal myogenesis in the developing neural tube

The t(2;13) chromosomal translocation is found in the majority of human alveolar rhabdomyosarcomas (RMS). The resulting PAX3-FKHR fusion protein contains PAX3 DNA-binding domains fused to the potent transactivation domain of FKHR, suggesting that PAX3-FKHR functions to deregulate PAX3-specific target genes and signaling pathways. We previously developed transgenic mice expressing PAX3-FKHR under the control of mouse Pax3 regulatory sequences to test this hypothesis. We reported that PAX3-FKHR interferes with normal Pax3 developmental functions, with mice exhibiting neural tube and neural crest abnormalities that mimic those found in Pax3-deficient Splotch mice. Here we expanded those studies to show that developmental expression of PAX3-FKHR results in aberrant myogenesis in the developing somites and neural tube, leading to ectopic skeletal muscle formation in the mature spinal cord. Gene expression profiling indicated that PAX3-FKHR expression in the developing neural tube induces a myogenic pattern of gene expression at the expense of the normal neurogenic program. Somite defects in PAX3-FKHR transgenic animals resulted in skeletal malformations that included rib fusions and mis-attachments. As opposed to the neural tube defects, the severity of the rib phenotype was rescued by reducing Pax3 levels through mating with Splotch mice. Embryos from the transgenic line expressing the highest levels of PAX3-FKHR had severe neural tube defects, including exencephaly, and almost half of the embryos died between gestational ages E13.5-E15.5. Nearly all of the embryos that survived to term died after birth due to severe spina bifida, rather than the absence of a muscular diaphragm. These studies reveal a prominent role for PAX3-FKHR in disrupting Pax3 functions and in deregulating skeletal muscle development, suggesting that this fusion protein plays a critical role in the pathogenesis of␣alveolar RMS by influencing the commitment␣and differentiation of the myogenic cell lineage.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .