Genetic Risk Factors for Folate-Responsive Neural Tube Defects

Fundamental origins of neural tube defects with a basis in genetics and nutrition

Neural tube defects (NTDs) are leading congenital malformations. Its global prevalence is one in 1000 pregnancies and it has high morbidity and mortality. It has multiple risk factors like genetic errors and environmental stressors like maternal malnutrition and in utero exposure to pollutants like chemicals. The genetic program determines neural tube development based on timely expression of many genes involved in developmental signaling pathways like BMP, PCP and SHH. BMP expression defines ectoderm. SOX represses BMP in ectoderm and convertes to the neuroectoderm. Subsequently, PCP molecules define the tissue patterning for convergent-extension, a critical step in neural tube genesis. Further, SHH sets spatial patterning of the neural tube. Nutrients are the essential major environmental input for embryogenesis. But it may also carry risk factors. Malnutrition, especially folate deficiency, during embryogenesis is a major cause for NTDs. Folate is integral in the One Carbon metabolic pathway. Its deficiency and error in the pathway are implicated in NTDs. Folate supplementation alone is insufficient to prevent NTDs. Thus, a comprehensive understanding of the various risk factors is necessary to strategize reduction of NTDs. We review the current knowledge of various risk factors, like genetic, metabolic, nutritional, and drugs causing NTDs and discuss the steps required to identify them in the early embryogenesis to avoid NTDs.

DHFR2 RNA directly regulates dihydrofolate reductase and its expression level impacts folate one carbon metabolism

Dihydrofolate reductase activity is required in One Carbon Metabolism to ensure that the biologically active form of folate, tetrahydrofolate, is replenished and available as an enzyme cofactor for numerous cellular reactions, including purine and pyrimidine synthesis. Most cellular enzyme activity was thought to arise from the product of the DHFR gene on chromosome 5, with its paralogue DHFR2 (formerly known as DHFRL1; [chromosome 3]), believed to be responsible for mitochondrial dihydrofolate activity based on recombinant versions of the enzyme. In this paper, we confirm our earlier findings that dihydrofolate reductase activity in mitochondria is derived from the DHFR gene rather than DHFR2 and that endogenous DHFR2 protein is not detectable in most cells and tissues. Using HepG2 cell lines with modulated expression of either DHFR or DHFR2, we observed an impact of DHFR2 RNA on One Carbon Metabolism mediated through an influence on DHFR expression and activity. Knockout of DHFR2 results in a drop in dihydrofolate reductase activity, lowered 10-formyltetrahydrofolate abundance, downregulation of DHFR mRNA, and diminished DHFR protein abundance. We also observed downregulation of Serine Hydroxymethyltransferase and Thymidylate Synthase, two One Carbon Metabolism enzymes that work with DHFR to support de novo thymidylate synthesis. The expression of recombinant DHFR2 resulted in restoration of DHFR mRNA and protein levels while a DHFR knockdown cell line showed upregulation of DHFR2 RNA. We propose that the DHFR2 gene encodes an RNA molecule that regulates cellular dihydrofolate reductase activity through its impact on DHFR mRNA and protein.

Folic Acid and Methyltetrahydrofolate Supplementation in the Mthfr677C>T Mouse Model with Hepatic Steatosis

BACKGROUND/OBJECTIVES

The MTHFR677C>T gene variant results in a thermolabile MTHFR enzyme associated with elevated plasma homocysteine in TT individuals. Health risks associated with the TT genotype may be modified by dietary and supplemental folate intake. Supplementation with methyltetrahydrofolate (methylTHF) may be preferable to folic acid because it is the MTHFR product, and does not require reduction by DHFR to enter one-carbon folate metabolism. In the Mthfr677C>T mouse model for this variant, female 677TT (TT) mice have an increased incidence of hepatic steatosis. The objective of this study was to compare the effects of methylTHF and folic acid supplementation on hepatic steatosis and one-carbon metabolism in this model.

METHODS

Male and female C57BL/6J 677CC (CC) and TT mice were fed control (CD), 5xmethylTHF-supplemented (MFSD), or 5xfolic-acid-supplemented (FASD) diets for 4 months. Liver sections were assessed for steatosis by Oil Red O staining. One-carbon metabolites were measured in the liver and plasma. MTHFR protein expression was evaluated in the liver.

RESULTS

MFSD had no significant effect on plasma homocysteine, liver SAM/SAH ratios, or hepatic steatosis in males or females as compared to CD. MTHFR protein increased in MFSD TT female liver, but remained <50% of the CC. FASD had no effect on plasma homocysteine but it decreased the liver MTHFR protein and SAM/SAH ratios, and increased hepatic steatosis in CC females.

CONCLUSIONS

MethylTHF and folic acid supplementation had limited benefits for TT mice, while folic acid supplementation had negative effects on CC females. Further investigation is required to determine if these effects are relevant in humans.

Congenital syndromic Chiari-like malformation (CSCM) in Holstein cattle: towards unravelling of possible genetic causes

BACKGROUND

Chiari malformation type II (CMII) was originally reported in humans as a rare disorder characterized by the downward herniation of the hindbrain and towering cerebellum. The congenital brain malformation is usually accompanied by spina bifida, a congenital spinal anomaly resulting from incomplete closure of the dorsal aspect of the spinal neural tube, and occasionally by other lesions. A similar disorder has been reported in several animal species, including cattle, particularly as a congenital syndrome. A cause of congenital syndromic Chiari-like malformation (CSCM) in cattle has not been reported to date. We collected a series of 14 CSCM-affected Holstein calves (13 purebred, one Red Danish Dairy F1 cross) and performed whole-genome sequencing (WGS). WGS was performed on 33 cattle, including eight cases with parents (trio-based; group 1), three cases with one parent (group 2), and three single cases (solo-based; group 3).

RESULTS

Sequencing-based genome-wide association study of the 13 Holstein calves with CSCM and 166 controls revealed no significantly associated genome region. Assuming a single Holstein breed-specific recessive allele, no region of shared homozygosity was detected suggesting heterogeneity. Subsequent filtering for protein-changing variants that were only homozygous in the genomes of the individual cases allowed the identification of two missense variants affecting different genes, SHC4 in case 4 in group 1 and WDR45B in case 13 in group 3. Furthermore, these two variants were only observed in Holstein cattle when querying WGS data of > 5,100 animals. Alternatively, potential de novo mutational events were assessed in each case. Filtering for heterozygous private protein-changing variants identified one DYNC1H1 frameshift variant as a candidate causal dominant acting allele in case 12 in group 3. Finally, the presence of larger structural DNA variants and chromosomal abnormalities was investigated in all cases. Depth of coverage analysis revealed two different partial monosomies of chromosome 2 segments in cases 1 and 7 in group 1 and a trisomy of chromosome 12 in the WDR45B homozygous case 13 in group 3.

CONCLUSIONS

This study presents for the first time a detailed genomic evaluation of CSCM in Holstein cattle and suggests an unexpected genetic and allelic heterogeneity considering the mode of inheritance, as well as the type of variant. For the first time, we propose candidate causal variants that may explain bovine CSCM in a certain proportion of affected calves. We present cattle as a large animal model for human CMII and propose new genes and genomic variants as possible causes for related diseases in both animals and humans.

Vitamin B12 status and folic acid supplementation influence mitochondrial heteroplasmy levels in mice

One-carbon metabolism is a complex network of metabolic reactions that are essential for cellular function including DNA synthesis. Vitamin B12 and folate are micronutrients that are utilized in this pathway and their deficiency can result in the perturbation of one-carbon metabolism and subsequent perturbations in DNA replication and repair. This effect has been well characterized in nuclear DNA but to date, mitochondrial DNA (mtDNA) has not been investigated extensively. Mitochondrial variants have been associated with several inherited and age-related disease states; therefore, the study of factors that impact heteroplasmy are important for advancing our understanding of the mitochondrial genome's impact on human health. Heteroplasmy studies require robust and efficient mitochondrial DNA enrichment to carry out in-depth mtDNA sequencing. Many of the current methods for mtDNA enrichment can introduce biases and false-positive results. Here, we use a method that overcomes these limitations and have applied it to assess mitochondrial heteroplasmy in mouse models of altered one-carbon metabolism. Vitamin B12 deficiency was found to cause increased levels of mitochondrial DNA heteroplasmy across all tissues that were investigated. Folic acid supplementation also contributed to elevated mitochondrial DNA heteroplasmy across all mouse tissues investigated. Heteroplasmy analysis of human data from the Framingham Heart Study suggested a potential sex-specific effect of folate and vitamin B12 status on mitochondrial heteroplasmy. This is a novel relationship that may have broader consequences for our understanding of one-carbon metabolism, mitochondrial-related disease and the influence of nutrients on DNA mutation rates.

Genome-wide analysis of spina bifida risk variants in a case-control study from Bangladesh

BACKGROUND

Human studies of genetic risk factors for neural tube defects, severe birth defects associated with long-term health consequences in surviving children, have predominantly been restricted to a subset of candidate genes in specific biological pathways including folate metabolism.

METHODS

In this study, we investigated the association of genetic variants spanning the genome with risk of spina bifida (i.e., myelomeningocele and meningocele) in a subset of families enrolled from December 2016 through December 2022 in a case-control study in Bangladesh, a population often underrepresented in genetic studies. Saliva DNA samples were analyzed using the Illumina Global Screening Array. We performed genetic association analyses to compare allele frequencies between 112 case and 121 control children, 272 mothers, and 128 trios.

RESULTS

In the transmission disequilibrium test analyses with trios only, we identified three novel exonic spina bifida risk loci, including rs140199800 (SULT1C2, p = 1.9 × 10-7), rs45580033 (ASB2, p = 4.2 × 10-10), and rs75426652 (LHPP, p = 7.2 × 10-14), after adjusting for multiple hypothesis testing. Association analyses comparing cases and controls, as well as models that included their mothers, did not identify genome-wide significant variants.

CONCLUSIONS

This study identified three novel single nucleotide polymorphisms involved in biological pathways not previously associated with neural tube defects. The study warrants replication in larger groups to validate findings and to inform targeted prevention strategies.

Advances in Fetal Surgical Repair of Open Spina Bifida

Spina bifida remains a common congenital anomaly of the central nervous system despite national fortification of foods with folic acid, with a prevalence of 2-4 per 10,000 live births. Prenatal screening for the early detection of this condition provides patients with the opportunity to consider various management options during pregnancy. Prenatal repair of open spina bifida, traditionally performed by the open maternal-fetal surgical approach through hysterotomy, has been shown to improve outcomes for the child, including decreased need for cerebrospinal fluid diversion surgery and improved lower neuromotor function. However, the open maternal-fetal surgical approach is associated with relatively increased risk for the patient and the overall pregnancy, as well as future pregnancies. Recent advances in minimally invasive prenatal repair of open spina bifida through fetoscopy have shown similar benefits for the child but relatively improved outcomes for the pregnant patient and future childbearing.

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.

Pediatric Spina Bifida and Spinal Cord Injury

Pediatric spina bifida (SB) and spinal cord injury (SCI) are unfortunately common in our society, and their unique findings and comorbidities warrant special consideration. This manuscript will discuss the epidemiology, pathophysiology, prevention, and management strategies for children growing and developing with these unique neuromuscular disorders. Growth and development of the maturing child places them at high risk of spinal cord tethering, syringomyelia, ascending paralysis, pressure injuries, and orthopedic abnormalities that must be addressed frequently and judiciously. Similarly, proper neurogenic bladder and neurogenic bowel management is essential not just for medical safety, but also for optimal psychosocial integration into the child’s expanding social circle.

Maternal folic acid and multivitamin supplementation: International clinical evidence with considerations for the prevention of folate-sensitive birth defects

More evidence is available for maternal intake, absorption, distribution, tissue specific concentrations, and pregnancy outcomes with folic acid (fortification/supplementation) during preconception - first trimester. This Quality Improvement prevention review used expert guidelines/opinions, systematic reviews, randomized control trials/controlled clinical trials, and observational case control/case series studies, published in English, from 1990 to August 2021. Optimization for an oral maternal folic acid supplementation is difficult because it relies on folic acid dose, type of folate supplement, bio-availability of the folate from foods, timing of supplementation initiation, maternal metabolism/genetic factors, and many other factors. There is continued use of high dose pre-food fortification 'RCT evidenced-based' folic acid supplementation for NTD recurrence pregnancy prevention. Innovation requires preconception and pregnancy use of 'carbon one nutrient' supplements (folic acid, vitamin B12, B6, choline), using the appropriate evidence, need to be considered. The consideration and adoption of directed personalized approaches for maternal complex risk could use serum folate testing for supplementation dosing choice. Routine daily folic acid dosing for low-risk women should consider a multivitamin with 0.4 mg of folic acid starting 3 months prior to conception until completion of breastfeeding. Routine folic acid dosing or preconception measurement of maternal serum folate (after 4-6 weeks of folate supplementation) could be considered for maternal complex risk group with genetic/medical/surgical co-morbidities. These new approaches for folic acid oral supplementation are required to optimize benefit (decreasing folate sensitive congenital anomalies; childhood morbidity) and minimizing potential maternal and childhood risk.

[Expert consensus on diagnosis and treatment of spina bifida]

Spina bifida and tethered spinal cord are congenital diseases that can lead to severe disability. At present, most doctors in relevant specialties in China still have insufficient understanding of spina bifida, resulting in high incidence and aggravation of its complications. To provide guidance for the diagnosis and treatment of spina bifida and tethered spinal cord in China, experts from neurosurgery, urology, orthopedics, spine surgery, and rehabilitation departments who have experiences in the diagnosis and treatment of spina bifida discussed and summarized their experiences, and referred to the relevant literature on the diagnosis and treatment of spina bifida at home and abroad. Expert consensus was formed in the following aspects: concept, classification, and pathological changes of spina bifida; diagnosis; treatment process and operation timing; principles and methods of treatment; rehabilitation; and follow up. This expert consensus can provide reference for relevant care providers of spina bifida in China.

Study of C677T Methylene Tetrahydrofolate Reductase Gene Polymorphism as a Risk Factor for Neural Tube Defects

Introduction

Various genetic and environmental factors contribute to the development of neural tube defects (NTDs) which are a group of neurulation defects resulting from failure of closure of embryonic neural tube. Among genetic factors is polymorphism in methylene tetrahydrofolate reductase (MTHFR) gene, giving rise to a gene variant or mutant. However, in most studies directed at finding an association between MTHFR variants and NTD, there is no clear evidence of a cause-and-effect relationship.

Materials and Methods

Forty diagnosed cases of NTDs and forty healthy individuals were investigated in a case-control study for presence of C677T MTHFR gene polymorphism. Serum folate and Vitamin B12 levels were estimated and MTHFR gene polymorphism was detected by polymerase chain reaction-restriction fragment length polymorphism.

Results

It was found that 32 cases were homozygous with CC genotype and eight were heterozygous with CT genotype, whereas 35 controls had CC genotype and five had CT genotype. TT genotype was absent in both the groups. There was no statistically significant difference between both the groups. No evidence of association between MTHFR C677T polymorphism and NTDs was found.

Conclusion

Although there was no evidence of association between MTHFR C677T polymorphism and NTDs, our study does not rule out the impact of MTHFR gene mutation on folate metabolism. The reason for absence of TT genotype and no association could be a small sample size. Larger, comprehensive, and well-designed multicentric but feasible studies involving proper subjects and appropriate and adequate controls from several hospitals may provide more meaningful data.

Folic acid deficiency damages male reproduction via endoplasmic reticulum stress-associated PERK pathway induced by Caveolin-1 in mice

Folic acid is critical to maintaining normal male reproductive function. Endoplasmic reticulum (ER) stress plays a crucial role in folic acid deficiency. Studies have shown that Caveolin-1 (Cav-1) is involved in ER stress, but the specific mechanism in male reproduction is still unclear. This study aimed to investigate the effects of folic acid deficiency on spermatogenesis and elucidate the underlying mechanisms. C57BL/6 mice fed with folic acid deficiency induced diet(0.3 mg/kg) were used. A significant decrease in the sperm concentration in the folic acid deficiency group was observed. Meanwhile, folic acid deficiency decreased Cav-1 expression in the testis tissue and increased endoplasmic reticulum stress-related PERK, eIF2α, ATF4, CHOP gene expression. Our results suggest that folic acid deficiency can affect male reproduction through the Cav-1-PERK-eIFα-ATF4-CHOP pathway.Abbreviations: ATF4: activating transcription factor 4; Ca2+: calcium ion; Cav-1: Caveolin-1; CCK-8: cell counting kit-8; CHOP: CCAAT-enhancer-binding protein homologous protein; DNA: Deoxyribonucleic acid; DSB: double strand breakage; eIF2α: eukaryotic Initiation Factor 2 alpha; ER: endoplasmic reticulum; FD: folic acid deficiency; FITC: fluorescein isothiocyanate; HE: hematoxylin and eosin; H3K4me3: histone H3 lysine 4 trimethylation; PERK: protein kinase RNA-like endoplasmic reticulum kinase; PI: propidium iodide; RT-qPCR: quantitative reverse transcription PCR; TUNEL: TdT mediated dUTP Nick End Labeling.

Maternal ethnicity and the prevalence of British pregnancies affected by neural tube defects

BACKGROUND

Few data are available on the prevalence of neural tube defects (NTDs) within different ethnic communities of the United Kingdom. This study aimed to calculate prevalence estimates for NTD-affected pregnancies, classified by maternal ethnicity, and to explore why variations in prevalence might exist.

METHODS

A cross-sectional study was performed with data from regional congenital anomaly registers in England and Wales, for NTD-affected pregnancies between 2006 and 2011. Using binomial regression models, we examined NTD-affected pregnancy prevalence estimates and rate ratios (PRRs), by maternal ethnicity.

RESULTS

The prevalence of NTDs was 12.14 per 10,000 births, with no differences between study years. Anencephaly, encephalocele and spina bifida occurred at 4.98, 1.37 and 5.80 per 10,000 births respectively. Mothers of Indian ethnicity were 1.84 times more likely (95% CI: 1.24, 2.73) and Bangladeshi mothers 2.86 times more likely (95% CI: 1.48, 5.53) than White mothers to have an NTD-affected pregnancy, after adjusting for maternal deprivation and maternal age. The excess prevalence in Indian mothers was specifically for anencephaly (PRR 2.57; 95% CI: 1.52, 4.34), and in Bangladeshi mothers the trend was for increased spina bifida (PRR 3.86; 95% CI: 0.72, 8.69). Anencephaly in Indian mothers was especially associated with other congenital anomalies (non-isolated NTDs).

CONCLUSIONS

Different British ethnic groups vary in NTD prevalence. The excess prevalence of anencephaly as a non-isolated NTD in pregnancies of Indian mothers could indicate involvement of genetic or other unmeasured behavioral factors. Future work is needed to seek etiological explanations for the ethnicity differences and to develop improved methods for primary prevention.

First trimester mechanisms of gestational sac placental and foetal teratogenicity: a framework for birth cohort studies

BACKGROUND

The function of the gestational sac (GS) and the placenta in the closely related processes of embryogenesis and teratogenicity in the first trimester has been minimally described. The prevailing assumption is that direct teratogenic effects are mediated by the critical extraembryonic organ, the placenta, which either blocks or transfers exposures to the foetus. Placental transfer is a dominant mechanism, but there are other paradigms by which the placenta can mediate teratogenic effects. Knowledge of these paradigms and first trimester human developmental biology can be useful to the epidemiologist in the conduct of biomarker-based studies of both maternal and child health.

OBJECTIVE AND RATIONALE

Our aim is to provide a causal framework for modelling the teratogenic effects of first trimester exposures on child health outcomes mediated by the GS and placenta using biomarker data collected in the first trimester. We initially present first trimester human developmental biology for the sake of informing and strengthening epidemiologic approaches. We then propose analytic approaches of modelling placental mechanisms by way of causal diagrams using classical non-embryolethal teratogens (diethylstilboestrol [DES], folic acid deficiency and cytomegalovirus [CMV]) as illustrative examples. We extend this framework to two chronic exposures of particular current interest, phthalates and maternal adiposity.

SEARCH METHODS

Information on teratogens was identified by a non-systematic, narrative review. For each teratogen, we included papers that answered the five following questions: (i) why were these exposures declared teratogens? (ii) is there a consensus on biologic mechanism? (iii) is there reported evidence of a placental mechanism? (iv) can we construct a theoretical model of a placental mechanism? and (v) can this knowledge inform future work on measurement and modelling of placental-foetal teratogenesis? We prioritized literature specific to human development, the organogenesis window in the first trimester and non-embryolethal mechanisms.

OUTCOMES

As a result of our review of the literature on five exposures considered harmful in the first trimester, we developed four analytic strategies to address first trimester placental mechanisms in birth cohort studies: placental transfer and direct effects on the foetus (DES and maternal adiposity), indirect effects through targeted placental molecular pathways (DES and phthalates), pre-placental effects through disruptions in embryonic and extraembryonic tissue layer differentiation (folic acid deficiency), and multi-step mechanisms that involve maternal, placental and foetal immune function and inflammation (DES and CMV).

WIDER IMPLICATIONS

The significance of this review is to offer a causal approach to classify the large number of potentially harmful exposures in pregnancy when the exposure occurs in the first trimester. Our review will facilitate future research by advancing knowledge of the first trimester mechanisms necessary for researchers to effectively associate environmental exposures with child health outcomes.

Prevalence of open neural tube defects and risk factors related to isolated anencephaly and spina bifida in live births from the "Dr. Juan I. Menchaca" Civil Hospital of Guadalajara (Jalisco, Mexico)

We determine the prevalence and trends of open neural tube defects (ONTDs) during 1991 to 2019 at the "Dr. Juan I. Menchaca" Civil Hospital of Guadalajara (Mexico). Also, details of potential risks were obtained in 662 newborns, including those 143 patients with anencephaly and open spina bifida (OSB) classified as isolated (cases) and 519 controls. Data were analyzed using multivariable logistic regression. Among 267 201 live births during the study period, 336 were born with ONTDs, yielding an overall prevalence of 12.6 per 10 000. After folic acid (FA)-related programs began in Mexico (2003-2019), only OSB showed a decline of 20.6%. For anencephaly, associated risks included relatives with neural tube defects (NTDs) (adjusted odds ratio [aOR]: 67.9, 95% confidence interval [95% CI]: 11.3-409.8), pre-pregnancy body mass index (BMI) ≥25 kg/m² (aOR: 2.6, 95% CI: 1.1-6.0), insufficient gestational weight gain (aOR: 3.0, 95% CI: 1.3-7.1), parity ≥4 (aOR: 3.2, 95% CI: 1.3-7.7), and exposure to analgesic/antipyretic drugs (aOR: 9.0; 95% CI: 2.5-33.0). For OSB, associated risks included consanguinity (aOR: 14.0, 95% CI: 3.5-55.9), relatives with NTDs (aOR: 22.4, 95% CI: 4.5-112.9), BMI ≥25 kg/m² (aOR: 2.5, 95% CI: 1.6-4.2), insufficient gestational weight gain (aOR: 1.9, 95% CI: 1.1-3.1), and exposures to hyperthermia (aOR: 2.3, 95% CI: 1.2-4.3), common cold (aOR: 6.8, 95% CI: 3.6-12.7), and analgesic/antipyretic drugs (aOR: 3.6, 95% CI: 1.3-10.0). Our high rate probably results from exposures to preventable risks, most related to FA, indicating a need for strengthening existing FA-related programs in Mexico.

Diet Alters Micronutrient Pathways in the Gut and Placenta that Regulate Fetal Growth and Development in Pregnant Mice

Maternal malnutrition and micronutrient deficiencies can alter fetal development. However, the mechanisms underlying these relationships are poorly understood. We used a systems physiology approach to investigate diet-induced effects on maternal gut microbes and folate/inositol transport in the maternal/fetal gut and placenta. Female mice were fed a control diet (CON) diet, undernourished (UN, restricted by 30% of CON intake) or a high-fat diet (HF, 60% kcals fat) during pregnancy to model normal pregnancy, fetal growth restriction or maternal metabolic dysfunction, respectively. At gestational day 18.5, we assessed circulating folate levels by microbiological assay, relative abundance of gut lactobacilli by G3PhyloChip™, and folate/inositol transporters in placenta and maternal/fetal gut by qPCR/immunohistochemistry. UN and HF-fed mothers had lower plasma folate concentrations vs. CON. Relative abundances of three lactobacilli taxa were higher in HF vs. UN and CON. HF-fed mothers had higher gut proton coupled folate transporter (Pcft) and reduced folate carrier 1 (Rfc1), and lower sodium myo-inositol co-transporter 2 (Smit2), mRNA expression vs. UN and CON. HF placentae had increased folate receptor beta (Frβ) expression vs. UN. mRNA expression of Pcft, folate receptor alpha (Frα), and Smit2 was higher in gut of HF fetuses vs. UN and CON. Transporter protein expression was not different between groups. Maternal malnutrition alters abundance of select gut microbes and folate/inositol transporters, which may influence maternal micronutrient status and delivery to the fetus, impacting pregnancy/fetal outcomes.

Myelomeningocele genotype-phenotype correlation findings in cilia, HH, PCP, and WNT signaling pathways

BACKGROUND

Myelomeningocele (MMC) is the most severe and frequent type of spina bifida. Its etiology remains poorly understood. The Hedgehog (Hh), Wnt, and planar cell polarity (PCP) signaling pathways are essential for normal tube closure, needing a structural-functional cilium for its adequate function. The present study aimed to investigate the impact of different gene variants (GV) from those pathways on MMC genotype-subphenotype correlations.

METHODS

The study comprised 500 MMC trios and 500 controls, from 16 Telethon centers of 16 Mexican states. Thirty-four GVs of 29 genes from cilia, Hh, PCP, and Wnt pathways, were analyzed, by an Illumina on design microarray. The total sample (T-MMC) was stratified in High-MMC (H-MMC) when thoracic and Low-MMC (L-MMC) when lumbar-sacral vertebrae affected. STATA/SE-12.1 and PLINK software were used for allelic association, TDT, and gene-gene interaction (GGI) analyses, considering p value <.01 as statistically significant differences (SSD).

RESULTS

Association analysis showed SSD for COBL-rs10230120, DVL2-rs2074216, PLCB4-rs6077510 GVs in T-MMC and L-MMC, and VANGL2-rs120886448 in T-MMC and H-MMC, and INVS-rs7024375 exclusively in L-MMC. TDT assay showed SSD preferential transmissions of C2CD3-rs826058 in H-MMC, and LRP5-rs3736228, and BBS2-rs1373 in L-MMC. Statistically significant GGI was observed in four in T-MMC, four completely different in L-MMC, and one in H-MMC. Interestingly, no one repeated in subphenotypes.

CONCLUSIONS

Our results support an association of GVs in Hh, Wnt, PCP, and cilia pathways, with MMC occurrence location, although further validation is needed. Furthermore, present results show a distinctive panel of gene-variants in H-MMC and LMMC subphenotypes, suggesting a feasible genotype-phenotype correlation.

Key Modules and Hub Genes Identified by Coexpression Network Analysis for Revealing Novel Biomarkers for Spina Bifida

Spina bifida is a common neural tube defect (NTD) accounting for 5–10% of perinatal mortalities. As a polygenic disease, spina bifida is caused by a combination of genetic and environmental factors, for which the precise molecular pathogenesis is still not systemically understood. In the present study, we aimed to identify the related gene module that might play a vital role in the occurrence and development of spina bifida by using weighted gene co-expression network analysis (WGCNA). Transcription profiling according to an array of human amniocytes from patients with spina bifida and healthy controls was downloaded from the Gene Expression Omnibus database. First, outliers were identified and removed by principal component analysis (PCA) and sample clustering. Then, genes in the top 25% of variance in the GSE4182 dataset were then determined in order to explore candidate genes in potential hub modules using WGCNA. After data preprocessing, 5407 genes were obtained for further WGCNA. Highly correlated genes were divided into nineteen modules. Combined with a co-expression network and significant differentially expressed genes, 967 candidate genes were identified that may be involved in the pathological processes of spina bifida. Combined with our previous microRNA (miRNA) microarray results, we constructed an miRNA–mRNA network including four miRNAs and 39 mRNA among which three key genes were, respectively, linked to two miRNA-associated gene networks. Following the verification of qRT-PCR and KCND3 was upregulated in the spina bifida. KCND3 and its related miR-765 and miR-142-3p are worthy of further study. These findings may be conducive for early detection and intervention in spina bifida, as well as be of great significance to pregnant women and clinical staff.

Comparison of inherited neural tube defects in companion animals and livestock

Neural tube defects (NTDs) are congenital malformations resulting from the improper or incomplete closure of the neural tube during embryonic development. A number of similar malformations of the protective coverings surrounding the central nervous system are also often included under this umbrella term, which may not strictly fit this definition. A range of NTD phenotypes exist and have been reported in humans and a wide range of domestic and livestock species. In the veterinary literature, these include cases of anencephaly, encephalocele, dermoid sinus, spina bifida, and craniorachischisis. While environmental factors have a role, genetic predisposition may account for a significant part of the risk of NTDs in these animal cases. Studies of laboratory model species (fish, birds, amphibians, and rodents) have been instrumental in improving our understanding of the neurulation process. In mice, over 200 genes that may be involved in this process have been identified and variant phenotypes investigated. Like laboratory mouse models, domestic animals and livestock species display a wide range of NTD phenotypes. They remain, however, a largely underutilized population and could complement already established laboratory models. Here we review reports of NTDs in companion animals and livestock, and compare these to other animal species and human cases. We aim to highlight the potential of nonlaboratory animal models for mutation discovery as well as general insights into the mechanisms of neurulation and the development of NTDs.

Prevention of Neural Tube Defects by Folic Acid Supplementation: A National Population-Based Study

Folic acid supplementation is recommended for neural tube defect prevention during pregnancy. We conducted an observational, retrospective national registry study to determine the rate of dispensing of periconceptional folic acid after prescription in a sample of French women representative of the general population. Our study population (n = 186,061) was a representative sample of the French population, recorded in the Health Data System database on pharmacy dispensing of medication and mandatory reporting of pregnancy. Between 2006 and 2016, 14.3% of pregnant women had a prescription for folic acid supplementation during the month preceding conception and for the first 12 weeks of pregnancy. Of these prescriptions, 30.9% were issued before the start of pregnancy. This percentage was lower for first pregnancies. The rate of pharmacy dispensing during the preconception period increased progressively from 3.8% to 8.3% between 2006 and 2016. In France, the rate of pharmacy dispensing of periconceptional folic acid after medical prescription is very low and does not follow international recommendations. It seems essential to implement awareness-raising policies targeting the general population and physicians regarding effective periconceptional supplementation, particularly starting in the preconception period. Clarification of international recommendations and fortification of flour could improve the efficacy of folate supplementation at population level.

Effect of periconceptional folic acid supplementation on the risk of neural tube defects associated with a previous spontaneous abortion or maternal first-trimester fever

STUDY QUESTION

Does maternal periconceptional no folic acid supplementation have an increased risk of neural tube defects (NTDs) associated with previous spontaneous abortion or first-trimester fever?

SUMMARY ANSWER

Maternal periconceptional no folic acid supplementation can increase the risk of NTDs associated with previous spontaneous abortion or first-trimester fever, independent of known confounding factors.

WHAT IS KNOWN ALREADY

Maternal periconceptional folic acid deficiency can increase the risk of NTDs. However, whether an interaction between periconceptional no folic acid supplementation and history of spontaneous abortion or first-trimester fever may have an increased risk of NTDs remains unknown.

STUDY DESIGN, SIZE, DURATION

A population-based case-control study was performed including 104 nuclear families with offspring with NTDs and 100 control families with normal offspring between 1993 and 2002.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We investigated the potential interaction between periconceptional no folic acid use and a maternal history of spontaneous abortion or first-trimester fever in the risk for NTDs. Information on exposure factors was obtained at the onset of pregnancy, and pregnancy outcomes were collected during the first week after delivery or at the time of termination of the pregnancy. A multivariate logistic regression analysis was performed.

MAIN RESULTS AND THE ROLE OF CHANCE

The interaction between periconceptional no folic acid use and a maternal history of spontaneous abortion markedly increased the risk of NTDs (adjusted odds ratio (aOR) 18.68, 95% CI, 4.43-78.76) after adjusting for potential confounding factors. The interaction coefficient was found to be 2.08, higher than 1, indicating that there is a significant interaction between two factors. Mothers who did not take periconceptional folic acid and had first-trimester fever had an increased risk of NTDs (aOR 21.81, 95% CI, 8.81-80.73). However, the interaction coefficient was found to be 0.62, less than 1, indicating that there is no significant interaction between two factors.

LIMITATIONS, REASONS FOR CAUTION

A potential limitation was that the interval between the previous spontaneous abortion and the beginning of the subsequent pregnancy could not be estimated accurately, but was at least 1 year or more.

WIDER IMPLICATIONS OF THE FINDINGS

We emphasize that a previous spontaneous abortion may represent a first occurrence of NTDs rather than be the cause of NTDs. Our findings indicate that mothers with a history of spontaneous abortion are ideal candidates for periconceptional folic acid supplementation.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by National Natural Science Foundation of China (41871360) and Danone Nutrition Center for Dietary Nutrition Research and Education Foundation (DIC2015-05). There are no competing interests to declare.

Valproate and folate: Congenital and developmental risks

Increasing awareness of the congenital and developmental risks associated with the use of sodium valproate (VPA) has led to recent European guidelines designed to avoid the use of this drug in pregnancy if effective alternative treatments are available. In the general population, it is well established that periconceptual folic acid reduces the risk of neural tube defects (NTDs) and possibly other congenital abnormalities. We here review the evidence 1) that VPA interferes with one-carbon metabolism, including the transport of methylfolate into the brain and the placenta by targeting folate receptors; 2) that VPA effects on the folate metabolic system contribute to congenital and developmental problems associated with VPA exposure; and 3) that genetic factors, notably polymorphisms related to one-carbon metabolism, contribute to the vulnerability to these VPA-induced risks. Based on these facts, we propose that the standard periconceptual use of 400 μg of folic acid may not adequately protect against VPA or other antiepileptic drug (AED)-induced congenital or developmental risks. Pending definitive studies to determine appropriate dose, we recommend up to 5 mg of folic acid periconceptually in at-risk women with the caveat that the addition of supplementary vitamin B12 may also be prudent because vitamin B12 deficiency is common in pregnancy in some countries and is an additional risk factor for developmental abnormalities.

Closing in on Mechanisms of Open Neural Tube Defects

Neural tube defects (NTDs) represent a failure of the neural plate to complete the developmental transition to a neural tube. NTDs are the most common birth anomaly of the CNS. Following mandatory folic acid fortification of dietary grains, a dramatic reduction in the incidence of NTDs was observed in areas where the policy was implemented, yet the genetic drivers of NTDs in humans, and the mechanisms by which folic acid prevents disease, remain disputed. Here, we discuss current understanding of human NTD genetics, recent advances regarding potential mechanisms by which folic acid might modify risk through effects on the epigenome and transcriptome, and new approaches to study refined phenotypes for a greater appreciation of the developmental and genetic causes of NTDs.

Maternal, paternal, and neonatal risk factors for neural tube defects: A systematic review and meta-analysis

OBJECTIVE

Neural tube defects [NTDs] are severe congenital anomalies. The etiology of NTDs is not fully known, and studies on the potential risk factors of NTDs present inconsistent results. Thus, we conducted a systematic review and meta-analysis to investigate the maternal, paternal, and neonatal risk factors for NTDs.

STUDY DESIGN

We systematically reviewed relative original studies published through October 6, 2018 available in Pubmed, Embase and the Cochrane Library without restrictions for language. The selected studies measured maternal, paternal, and neonatal risk factors and examined their associations with NTDs. A meta-analysis, including subgroup analysis and sensitivity analysis, was conducted to estimate the pooled effect measures. Two reviewers independently extracted data using a predesigned data collection form.

RESULTS

Forty-five studies were eligible for inclusion in the meta-analysis, and twelve potential risk factors were analyzed. The factors that were associated with NTDs risk included stressful life events [odds ratio [OR],1.61; 95% confidence interval [CI], 1.24-2.08; p < 0.001; I2 = 59.2%], low maternal education level [OR, 1.42; 95% CI, 1.19-1.70; p < 0.001; I2 = 47.7%], pregestational diabetes [OR, 2.24; 95% CI, 1.21-4.12; p < 0.010; I2 = 56.3%], low paternal age [OR, 1.41; 95% CI, 1.10-1.81; p = 0.007; I2 = 0.0%], low birth weight [OR, 5.53; 95% CI, 1.95-15.70; p = 0.001; I2 = 98.5%], and neonatal female gender [OR, 1.54; 95% CI, 1.10-2.14; p = 0.012; I2 = 67.8%].

CONCLUSION

Stressful life events, pregestational diabetes, low birth weight, and neonatal female gender are risk factors associated with NTDs. Low maternal education level and low paternal age are factors that are moderately associated with NTDs. Further cohort studies are required to verify the factors associated with NTDs and control the risk of this severe birth defect.

The VACTERL association: mosaic mitotic aneuploidy as a cause and a model

While mitotic errors commonly cause aneuploid clones soon after conception, the embryos often normalize as clones are rapidly eliminated. Although generally considered benign, evidence suggests clone elimination as the primary cause of the vertebral, ano-rectal, cardiac, tracheo-esophageal, renal, and limb (VACTERL) association of anomalies, and possibly other adverse outcomes as well. Here, clone elimination-related development disruption at specific locations is used as the basis of a comprehensive theoretical VACTERL association model that also elucidates mitotic mosaic aneuploidy effects. For the association, the model explains random temporal and spatial origins during a limited time frame and overlapping clusters of component anomalies. It supports early developmental effects involving the stage of determination, where the position in a specific morphogen field controls what a cell will become and where it will be located. Developmental properties related to determination also create specific vulnerabilities to the midline and distal defects, the latter explaining exclusively radial and tibial defects with duplications and deficiencies. The model also supports isolated anomalies as part of the association and, for mosaic mitotic aneuploidy, indicates that clone elimination nears completion at the time of lower limb determination. Although mosaic clone elimination may cause other defects, occurrences in different developmental fields separate them from VACTERL anomalies. Clone elimination may also be related to risks for a single umbilical artery and for non-structural adverse pregnancy outcomes such as losses, prematurity, and growth delays, while a paucity of clone lethality in non-humans explains the rarity of the association and of single umbilical arteries in animals.

Molecular Basis of Spina Bifida: Recent Advances and Future Prospectives

Background:

Spina bifida (SB) (spinal neural tube [NT] defects) is basically caused by an abnormality at the closure of the NT.

Materials and Methods:

Molecular researchers have now got new etiopathogenesis of the defective neural tube closure. Although molecular mechanisms in the SB is really important taxation for further work. We understand through the unique novel mutant responsible genes and modifying genes and included the different molecular aspects of SB from the available tools and databases and excluded the case reports.

Statistical Analysis:

We use here simple statistics (percentage, mean, median, and average) through the Statistical Package for the Social Sciences (SPSS), version 14, and found P > 0.0001 to be significant.

Results:

We have reported that the majority of 90% genes are responsible in SB and their associated diseases. These innovative unique patterns of responsible genes attached with the result abnormalities at the neuronal and non neuronal tissues are equally important for the SB and NTC.

Conclusion:

Our present ideology is aiming to understand the inductive and direct interactions of the downstream target sites among responsible regulating genes (RRGs). It is an unique pattern of genetic roadmap to control and guides the neurulation and may provide further insights into the causes of SB and may help to develop new molecular-targeted therapy (MTT).

Abnormal level of CUL4B-mediated histone H2A ubiquitination causes disruptive HOX gene expression

Background

Neural tube defects (NTDs) are common birth defects involving the central nervous system. Recent studies on the etiology of human NTDs have raised the possibility that epigenetic regulation could be involved in determining susceptibility to them.

Results

Here, we show that the H2AK119ub1 E3 ligase CUL4B is required for the activation of retinoic acid (RA)-inducible developmentally critical homeobox (HOX) genes in NT2/D1 embryonal carcinoma cells. RA treatment led to attenuation of H2AK119ub1 due to decrease in CUL4B, further affecting HOX gene regulation. Furthermore, we found that CUL4B interacted directly with RORγ and negatively regulated its transcriptional activity. Interestingly, knockdown of RORγ decreased the expression of HOX genes along with increased H2AK119ub1 occupancy levels, at HOX gene sites in N2/D1 cells. In addition, upregulation of HOX genes was observed along with lower levels of CUL4B-mediated H2AK119ub1 in both mouse and human anencephaly NTD cases. Notably, the expression of HOXA10 genes was negatively correlated with CUL4B levels in human anencephaly NTD cases.

Conclusions

Our results indicate that abnormal HOX gene expression induced by aberrant CUL4B-mediated H2AK119ub1 levels may be a risk factor for NTDs, and highlight the need for further analysis of genome-wide epigenetic modifications in NTDs.

Electronic supplementary material

The online version of this article (10.1186/s13072-019-0268-7) contains supplementary material, which is available to authorized users.

Association of main folate metabolic pathway gene polymorphisms with neural tube defects in Han population of Northern China

PURPOSE

Neural tube defects (NTDs) are one of the most prevalent and the most severe congenital malformations worldwide. Studies have confirmed that folic acid supplementation could effectively reduce NTDs risk, but the genetic mechanism remains unclear. In this study, we explored association of single nucleotide polymorphisms (SNP) within folate metabolic pathway genes with NTDs in Han population of Northern China.

METHODS

We performed a case-control study to compare genotype and allele distributions of SNPs in 152 patients with NTDs and 169 controls. A total of 16 SNPs within five genes were genotyped by the Sequenom MassARRAY assay.

RESULTS

Our results indicated that three SNPs associated significantly with NTDs (P<0.05). For rs2236225 within MTHFD1, children with allele A or genotype AA had a high NTDs risk (OR=1.500, 95%CI=1.061~2.120; OR=2.862, 95%CI=1.022~8.015, respectively). For rs1801133 within MTHFR, NTDs risk markedly increased in patients with allele T or genotype TT (OR=1.552, 95%CI=1.130~2.131; OR=2.344, 95%CI=1.233~4.457, respectively). For rs1801394 within MTRR, children carrying allele G and genotype GG had a higher NTDs risk (OR=1.533, 95%CI=1.102~2.188; OR=2.355, 95%CI=1.044~5.312, respectively).

CONCLUSIONS

Our results suggest that rs2236225 of MTHFD1 gene, rs1801133 of MTHFR gene and rs1801394 of MTRR gene were associated with NTDs in Han population of Northern China.

Should vitamin B12 status be considered in assessing risk of neural tube defects?

There is a strong biological premise for including vitamin B₁₂ with folic acid in strategies to prevent neural tube defects (NTDs), due to the closely interlinked metabolism of these two vitamins. For example, reduction of B₁₂ deficiency among women of reproductive age could enhance the capacity of folic acid to prevent NTDs by optimizing the cellular uptake and utilization of natural folate cofactors. Vitamin B₁₂ might also have an independent role in NTD prevention, such that adding it in fortification programs might be more effective than fortifying with folic acid alone. Globally, there is ample evidence of widespread vitamin B₁₂ deficiency in low‐ and middle‐income countries, but there is also considerable divergence of vitamin B₁₂ status across regions, likely due to genetic as well as nutritional factors. Here, I consider the evidence that low vitamin B₁₂ status may be an independent factor associated with risk of NTDs, and whether a fortification strategy to improve B₁₂ status would help reduce the prevalence of NTDs. I seek to identify knowledge gaps in this respect and specify research goals that would address these gaps.