Folic acid alone prevents neural tube defects: evidence from the China study

Analysis of Gut Characteristics and Microbiota Changes with Maternal Supplementation in a Neural Tube Defect Mouse Model

Adequate nutrient supply is crucial for the proper development of the embryo. Although nutrient supply is determined by maternal diet, the gut microbiota also influences nutrient availability. While currently there is no cure for neural tube defects (NTDs), their prevention is largely amenable to maternal folic acid and inositol supplementation. The gut microbiota also contributes to the production of these nutrients, which are absorbed by the host, but its role in this context remains largely unexplored. In this study, we performed a functional and morphological analysis of the intestinal tract of loop-tail mice (Vangl2 mutants), a mouse model of folate/inositol-resistant NTDs. In addition, we investigated the changes in gut microbiota using 16S rRNA gene sequencing regarding (1) the host genotype; (2) the sample source for metagenomics analysis; (3) the pregnancy status in the gestational window of neural tube closure; (4) folic acid and (5) D-chiro-inositol supplementation. We observed that Vangl2+/Lp mice showed no apparent changes in gastrointestinal transit time or fecal output, yet exhibited increased intestinal length and cecal weight and gut dysbiosis. Moreover, our results showed that the mice supplemented with folic acid and D-chiro-inositol had significant changes in their microbiota composition, which are changes that could have implications for nutrient absorption.

Maternal Periconceptional Folic Acid Supplementation and DNA Methylation Patterns in Adolescent Offspring

BACKGROUND

Folate, including the folic acid form, is a key component of the one-carbon metabolic pathway used for DNA methylation. Changes in DNA methylation patterns during critical development periods are associated with disease outcomes and are associated with changes in nutritional status in pregnancy. The long-term impact of periconceptional folic acid supplementation on DNA methylation patterns is unknown.

OBJECTIVES

To determine the long-term impact of periconceptional folic acid supplementation on DNA methylation patterns, we examined the association of the recommended dosage (400 μg/d) and time period (periconceptional before pregnancy through first trimester) of folic acid supplementation with the DNA methylation patterns in the offspring at age 14-17 y compared with offspring with no supplementation.

METHODS

Two geographic sites in China from the 1993-1995 Community Intervention Program of folic acid supplementation were selected for the follow-up study. DNA methylation at 402,730 CpG sites was assessed using saliva samples from 89 mothers and 179 adolescents (89 male). The mean age at saliva collection was 40 y among mothers (range: 35-54 y) and 15 y among adolescents (range: 14-17 y). Epigenome-wide analyses were conducted to assess the interactions of periconceptional folic acid exposure, the 5,10-methylenetetrahydrofolate reductase (MTHFR)-C677T genotype, and epigenome-wide DNA methylation controlling for offspring sex, geographic region, and background cell composition in the saliva.

RESULTS

In the primary outcome, no significant differences were observed in epigenome-wide methylation patterns between adolescents exposed and those non-exposed to maternal periconceptional folic acid supplementation after adjustment for potential confounders [false discovery rate (FDR) P values < 0.05]. The MTHFR-C677T genotype did not modify this lack of association (FDR P values < 0.05).

CONCLUSIONS

Overall, there were no differences in DNA methylation between adolescents who were exposed during the critical developmental window and those not exposed to the recommended periconceptional/first-trimester dosage of folic acid.

Recent Developments in Folate Nutrition

The term folate (vitamin B9) refers to a group of water-soluble compounds that are nutritionally essential for the support of optimal human health and development. Folates participate in numerous one-carbon transfer reactions, including the methylation of important biomolecules (lipids, amino acids, DNA). A deficiency of folate leads to pathological outcomes including anemia and impairments in reproductive health and fetal development. Due to the linkage of impaired folate status with an increased prevalence of neural tube defects (NTDs) in babies, several jurisdictions required the fortification of the food supply with folic acid, a synthetic and stable form of folate. Data from the postfortification era have provided strong evidence for the reduction of NTDs due to folic acid fortification. However, concern is now growing with respect to the amount of synthetic folic acid within the human food supply. Excess folic acid intake has been linked to a masking of vitamin B12 deficiency, and concerns regarding the promotion of folate-sensitive cancers, including colorectal cancer. New strategies to ensure the supply of optimal folate to at-risk populations may be needed, including the use of biofortification approaches, in order to address recent concerns.

Are concentrations of alkaline earth elements in maternal hair associated with risk of neural tube defects?

The relationship between maternal intake of alkaline earth elements (AEEs) during the period of neural tube closure and the risk of neural tube defects (NTDs) is still unclear. We propose that AEE deficiency during the early period of pregnancy is associated with an elevated risk of NTDs in the offspring. In this study, we recruited 191 women with NTD-affected pregnancies (cases) and 261 women who delivered healthy infants (controls). The concentrations of four AEEs (Ca, Mg, Sr, Ba) in maternal hair sections that grew during early pregnancy were analyzed. Information on the dietary habits of the mothers was also collected by questionnaire. Higher concentrations of the four AEEs in hair had protective effects against the risk of total NTDs, with odds ratios with 95% confidence interval (comparing groups separated by each median level) of 0.44 (0.28-0.68) for Mg, 0.56 (0.36-0.87) for Ca, 0.45 (0.28-0.70) for Sr, and 0.41 (0.26-0.65) for Ba. Significant negative dose-response trends were identified for the relationships between the four AEE concentrations in maternal hair and the risks of anencephaly and spina bifida, but not for encephalocele. The frequencies of maternal consumption of fresh green vegetables, fresh fruit, and meat or fish were positively correlated with the concentrations of AEEs in hair. We concluded that the maternal intake of AEEs may play an important role in preventing NTD formation in offspring, and that this intake is related to maternal dietary habits of consuming fresh green vegetables, fresh fruit, and fish or meat.

Folic acid supplementation and fecundability: a Danish prospective cohort study

BACKGROUND/OBJECTIVES

Periconceptional folic acid (FA) supplementation reduces the risk of neural tube defects and has been associated with ovulatory function. However, only two studies have associated supplementation with multivitamins (MVs) that contained FA with increased pregnancy rates. We aimed to examine the association between FA supplementation (obtained either through single FA tablets or through MVs) and fecundability.

SUBJECTS/METHODS

A prospective cohort study of 3895 Danish women who were planning a pregnancy between 2007 and 2011. We estimated fecundability ratios (FRs) and 95% confidence intervals (CIs) in relation to FA supplementation (either through single FA tablets or MV) using a proportional probabilities regression model, with adjustment for potential socio-demographic, reproductive and lifestyle confounders. In stratified analyses, we also estimated FR with 95% CI in relation to FA supplementation for women with regular and irregular cycles, respectively, and for women with short (<27 days), medium (27-29 days) and long cycles (⩾30 days), respectively.

RESULTS

FA supplementation was associated with increased fecundability (FR=1.15, 95% CI=1.06-1.25), compared with non-use. The adjusted FRs for FA supplement use relative to non-use were 1.35 (95% CI=1.12-1.65) and 1.11 (95% CI=1.01-1.22) for women with irregular and regular cycles, respectively, and 1.36 (95% CI=0.95-1.95), 1.10 (95% CI=0.98-1.22) and 1.24 (95% CI=1.10-1.41) for women with short (<27 days), medium (27-29 days) and long cycles (⩾30 days), respectively.

CONCLUSIONS

FA supplementation was associated with increased fecundability, and this association appeared to be stronger among women with irregular cycles and among women with either short or long cycle length.

Bigger babies born to women survivors of the 1959-1961 Chinese famine: a puzzle due to survival selection?

The Chinese Famine of 1959-1961 caused up to 30 million deaths. It varied in intensity across China and affected rural areas disproportionately. Data from the China-U.S. Collaborative Project for Neural Tube Defect Prevention on 31, 449 women (born 1957-1963) and their offspring birth size were recorded in 1993-1996. We used a measure of famine intensity at county level based on the size of famine-born cohorts relative to cohorts preceding and following the famine in a difference-in-difference model that compared offspring birth size of pre-famine (1957-1958; exposed between 0.5 and 4.5 years), famine (1959-1961; prenatal and up to 2.5 years) and post-famine (1962; some exposed in early pregnancy) cohort groups to that of the unexposed 1963 cohort. The model corrected for age and cohort trends and estimated associations between maternal famine exposure and offspring birth size for the average level of famine intensity across counties, and included adjustment for clustering. In rural areas and in pre-famine and famine cohorts, exposure to famine was associated with larger weight (69 g; 95% CI 30, 108), length (0.3 cm; 95% CI -0.0, 0.5) and birth body mass index (0.1 kg/m2; 95% CI 0.0, 0.2). In urban areas, however, exposure to famine was not associated with offspring birth size. Our findings in rural areas suggest that severe and prolonged famine leads to larger newborn size in the offspring of mothers exposed to famine in utero and during the first few years of life; less severe famine in urban areas however, appeared to have no impact. The markedly increased mortality in rural areas may have resulted in the selection of hardier mothers with greater growth potential, which becomes expressed in their offspring.

A critical role of noggin in developing folate-nonresponsive NTD in Fkbp8 -/- embryos

PURPOSE

Maternal folate intake has reduced the incidence of human neural tube defects by 60-70 %. However, 30-40 % of cases remain nonresponsive to folate intake. The main purpose of this study was to understand the molecular mechanism of folate nonresponsiveness in a mouse model of neural tube defect.

METHODS

We used a folate-nonresponsive Fkbp8 knockout mouse model to elucidate the molecular mechanism(s) of folate nonresponsiveness. Neurospheres were grown from neural stem cells isolated from the lumbar neural tube of E9.5 Fkbp8 (-/-) and wild-type embryos. Immunostaining was used to determine the protein levels of oligodendrocyte transcription factor 2 (Olig2), Nkx6.1, class III beta-tubulin (TuJ1), O4, glial fibrillary acidic protein (GFAP), histone H3 Lys27 trimethylation (H3K27me3), ubiquitously transcribed tetratricopeptide repeat (UTX), and Msx2, and quantitative real-time (RT)-PCR was used to determine the message levels of Olig2, Nkx6.1, Msx2, and noggin in neural stem cells differentiated in the presence and absence of folic acid.

RESULTS

Fkbp8 (-/-)-derived neural stem cells showed (i) increased noggin expression; (ii) decreased Msx2 expression; (iii) premature differentiation--neurogenesis, oligodendrogenesis (Olig2 expression), and gliogenesis (GFAP expression); and (iv) increased UTX expression and decreased H3K27me3 polycomb modification. Exogenous folic acid did not reverse these markers.

CONCLUSIONS

Folate nonresponsiveness could be attributed in part to increased noggin expression in Fkbp8 (-/-) embryos, resulting in decreased Msx2 expression. Folate treatment further increases Olig2 and noggin expression, thereby exacerbating ventralization.

A question of balance: achieving appropriate nutrient levels in biofortified staple crops

The biofortification of staple crops with vitamins is an attractive strategy to increase the nutritional quality of human food, particularly in areas where the population subsists on a cereal-based diet. Unlike other approaches, biofortification is sustainable and does not require anything more than a standard food-distribution infrastructure. The health-promoting effects of vitamins depend on overall intake and bioavailability, the latter influenced by food processing, absorption efficiency and the utilisation or retention of the vitamin in the body. The bioavailability of vitamins in nutritionally enriched foods should ideally be adjusted to achieve the dietary reference intake in a reasonable portion. Current vitamin biofortification programmes focus on the fat-soluble vitamins A and E, and the water-soluble vitamins C and B9 (folate), but the control of dosage and bioavailability has been largely overlooked. In the present review, we discuss the vitamin content of nutritionally enhanced foods developed by conventional breeding and genetic engineering, focusing on dosage and bioavailability. Although the biofortification of staple crops could potentially address micronutrient deficiency on a global scale, further research is required to develop effective strategies that match the bioavailability of vitamins to the requirements of the human diet.

Estimate of the potential impact of folic acid fortification of corn masa flour on the prevention of neural tube defects

BACKGROUND

Hispanics in the US have a higher prevalence of neural tube defect (NTD) -affected pregnancies than non-Hispanic whites, and lower median total folic acid (FA) intake. FA fortification of corn masa flour (CMF) is a policy-level intervention for NTD prevention; however, the impact on NTD prevalence has not been estimated.

METHODS

We developed a model to estimate the percentage reduction in prevalence of spina bifida and anencephaly (NTDs) that could occur with FA fortification of CMF. Model inputs included estimates of the percentage reduction in United States NTD prevalence attributed to FA fortification of enriched cereal grain products (1995-1996 vs. 1998-2002), the increase in median FA intake after enriched cereal grain product fortification, and the estimated increase in median FA intake that could occur with CMF fortification at the same level as enriched cereal grain products (140 μg/100 g). We used Monte Carlo simulation to quantify uncertainty. We stratified analyses by racial/ethnic group and rounded results to the nearest 10.

RESULTS

We estimated CMF fortification could prevent 30 Hispanic infants from having spina bifida (95% uncertainty interval: 0, 80) and 10 infants from having anencephaly (95% uncertainty interval: 0, 40) annually. The estimated impact among non-Hispanic whites and blacks was smaller.

CONCLUSION

CMF fortification with FA could prevent from 0 to 120 infants, with the most likely value of approximately 40, from having spina bifida or anencephaly among Hispanics, the population most likely to benefit from the proposed intervention. While this estimated reduction is unlikely to be discernible using current birth defect surveillance methods, it still suggests an important benefit to the target population.

Folic acid use and nonsyndromic orofacial clefts in China: a prospective cohort study

BACKGROUND

Questions remain about the effectiveness, dose, and timing of folic acid in preventing orofacial clefts. Case-control studies report conflicting results. There have been no cohort studies of orofacial clefts and the use of folic acid without other vitamins.

METHODS

In a prospective cohort of 240,244 women enrolled between 1993 and 1995 in 1 northern and 2 southern provinces in China, we examined the risk of nonsyndromic cleft lip with or without cleft palate (CL/P) and cleft palate alone (CP) in relation to maternal use of 400 μg of folic acid without other vitamins.

RESULTS

Daily use of 400 μg of folic acid without other vitamins, started before the last menstrual period (LMP), was associated with reduced risk of CL/P with adjusted rate ratio (aRR) of 0.69 (95% confidence interval = 0.55-0.87). The greatest reduction in risk was observed in the north among daily users who began taking folic acid pills before LMP (aRR = 0.21 [0.10-0.44]); in the south there was marginal reduction in risk (aRR = 0.81 [0.63-1.05]). No evidence of reduced CL/P risk was observed among women who started folic acid pills on or after their LMP. No persuasive evidence for reduction in CP risk was seen with folic acid pill use at any time.

CONCLUSION

Daily maternal consumption of 400 μg of folic acid without other vitamins, started before mother's LMP, was associated with a reduced risk of CL/P in babies born in a high-prevalence region of China.

Nutrition deficiency increases the risk of stomach cancer mortality

BACKGROUND

The purpose of the study is to determine whether exposure to malnutrition during early life is associated with increased risk of stomach cancer in later life.

METHODS

The design protocol included analyzing the trend of gastric cancer mortality and nutrition and evaluating the association between nutrient deficiency in early life and the risk of gastric cancer by hierarchical age-period-birth cohort (APC) analysis using general log-linear Poisson models and to compare the difference between birth cohorts who were exposed to the 1959-1961 Chinese famine and those who were not exposed to the famine. Data on stomach cancer mortality from 1970 to 2009 and the dietary patterns from 1955 to 1985 which included the 1959-1961 Chinese famine period in the Zhaoyuan County population were obtained. The nutrition information was collected 15 years prior to the mortality data as based on the latest reference of disease incubation.

RESULTS

APC analysis revealed that severe nutrition deficiency during early life may increase the risk of stomach cancer. Compared with the 1960-1964 birth cohort, the risk for stomach cancer in all birth cohorts from 1900 to 1959 significantly increased; compared with the 1970-1974 cohort, the risk for stomach cancer in the 1975-1979 cohort significantly increased, whereas the others had a steadily decreased risk; compared with 85-89 age group in the 2005-2009 death survey, the ORs decreased with younger age and reached significant levels for the 50-54 age group after adjusting the confounding factors. The 1930 to 1964 group (exposed to famine) had a higher mortality rate than the 1965 to 1999 group (not exposed to famine). For males, the relative risk (RR) was 2.39 and the 95% confidence interval (CI) was 1.51 to 3.77. For females, RR was 1.64 and 95% CI was 1.02 to 2.62.

CONCLUSION

The results of the present study suggested that prolonged malnutrition during early life may increase the risk of stomach cancer mortality in later life.

Folic Acid Supplementation for Women of Childbearing Age versus Supplementation for the General Population: A Review of the Known Advantages and Risks

This paper focuses on the current best-evidence-based clinical practices and controversies surrounding folic acid supplementation/fortification for the prevention of neural tube defects (NTDs) during early pregnancy. The paper also discusses the controversies surrounding the effect of folic acid on the prevention as well as the promotion of cancer. Sufficient data is available to safely conclude that folic acid reduces the risk of NTDs during pregnancy; however, a safe dosage has not yet been calculated for the rest of the population. More research is necessary to study the complete role of folic acid in human growth and development.

Association between inhibited binding of folic acid to folate receptor alpha in maternal serum and folate-related birth defects in Norway

BACKGROUND

Folic acid intake during pregnancy can reduce the risk of neural tube defects (NTDs) and perhaps also oral facial clefts. Maternal autoantibodies to folate receptors can impair folic acid binding. We explored the relationship of these birth defects to inhibition of folic acid binding to folate receptor α (FRα), as well as possible effects of parental demographics or prenatal exposures.

METHODS

We conducted a nested case-control study within the Norwegian Mother and Child Cohort Study. The study included mothers of children with an NTD (n = 11), cleft lip with or without cleft palate (CL/P, n= 72), or cleft palate only (CPO, n= 27), and randomly selected mothers of controls (n = 221). The inhibition of folic acid binding to FRα was measured in maternal plasma collected around 17 weeks of gestation. On the basis of prior literature, the maternal age, gravidity, education, smoking, periconception folic acid supplement use and milk consumption were considered as potential confounding factors.

RESULTS

There was an increased risk of NTDs with increased binding inhibition [adjusted odds ratio (aOR) = 1.4, 95% confidence interval (CI) 1.0-1.8]. There was no increased risk of oral facial clefts from inhibited folic acid binding to FRα (CL/P aOR = 0.7, 95% CI 0.6-1.0; CPO aOR = 1.1, 95% CI 0.8-1.4). No association was seen between smoking, folate supplementation or other cofactors and inhibition of folic acid binding to FRα.

CONCLUSIONS

Inhibition of folic acid binding to FRα in maternal plasma collected during pregnancy was associated with increased risk of NTDs but not oral facial clefts.

Maternal intake of folic acid and neural crest stem cells

Maternal folic acid (FA) intake has beneficial effects in preventing neural tube defects and may also play a role in the prevention of adult onset diseases such as Alzheimer's disease, dementia, neuropsychiatric disorders, cardiovascular diseases, and cerebral ischemia. This review will focus on the effects of maternal FA intake on neural crest stem cell proliferation and differentiation. Although FA is generally considered beneficial, it has the potential of promoting cell proliferation at the expense of differentiation. In some situations, this may lead to miscarriage or postnatal developmental abnormalities. Therefore, a blind approach such as "FA for everyone" is not necessarily the best course of action. Ultimately, the best approach for FA supplementation, and potentially other nutritional supplements, will include customized patient genomic profiles for determining dose and duration.

Early life exposure to the 1959-1961 Chinese famine has long-term health consequences

The Chinese famine of 1959-1961 was the largest in human history. We used data on 35,025 women born in 1957-1963 to assess the impact of famine exposure on height, BMI, and hypertension at ~32 y of age. The data were from the China-U.S. Collaborative Project for Neural Tube Defect Prevention. The famine varied in intensity across provinces and counties and affected rural areas disproportionately. We used a measure of famine intensity at the county level based on the size of birth year cohorts in a difference-in-difference model, which compared each cohort to the unexposed 1963 cohort, after correcting for age and time trends, and estimated impact for the average level of intensity across counties. The impact was confined to rural areas, but this could be due to small sample sizes in urban areas. Height was reduced in the 1958 and 1959 cohorts by 1.7 and 1.3 cm, respectively. This corresponded to exposures during 0.5-3.5 y for the 1958 cohort and late pregnancy and 0-2.5 y for the 1959 cohort. BMI increased by 0.92 kg/m(2) in the 1957 cohort, exposed from 1.5 to 4.5 y, but decreased by 0.3 kg/m(2) in the 1960-1961 cohorts, exposed during pregnancy and infancy. Famine exposure was associated with a 3-fold increase in the odds of hypertension for the 1958 cohort. In general, postnatal exposure during the first 2-3 y of life reduced height and increased BMI and hypertension, whereas exposure during pregnancy and infancy reduced BMI.

Maize: A Paramount Staple Crop in the Context of Global Nutrition

  The maize plant (Zea mays), characterized by an erect green stalk, is one of the 3 great grain crops of the world. Its kernels, like other seeds, are storage organs that contain essential components for plant growth and reproduction. Many of these kernel constituents, including starch, protein, and some micronutrients, are also required for human health. For this reason, and others, maize has become highly integrated into global agriculture, human diet, and cultural traditions. The nutritional quality and integrity of maize kernels are influenced by many factors including genetic background, environment, and kernel processing. Cooking procedures, including nixtamalization and fermentation, can increase accessibility of micronutrients such as niacin. However, man cannot live on maize alone. For one-third of the world's population, namely in sub-Saharan Africa, Southeast Asia, and Latin America, humans subsist on maize as a staple food but malnutrition pervades. Strategies to further improve kernel macronutrient and micronutrient quality and quantities are under intense investigation. The 2 most common routes to enhance grain nutritional value are exogenous and endogenous fortification. Although exogenous fortification, such as addition of multivitamin premixes to maize flour, has been successful, endogenous fortification, also known as "biofortification," may provide a more sustainable and practical solution for chronically undernourished communities. Recent accomplishments, such as low-phytate, high-lysine, and multivitamin maize varieties, have been created using novel genetic and agronomic approaches. Investigational studies related to biofortified maize are currently underway to determine nutrient absorption and efficacy related to human health improvement.

Adherence and costs of micronutrient supplementation in pregnancy in a double-blind, randomized, controlled trial in rural western China

BACKGROUND

Efforts to determine the impact of prenatal multivitamin supplementation on birth outcome have been carried out in several developing countries. A review of factors that would impact the effectiveness of prenatal supplementation under normal field conditions is currently lacking and will be required for expanded supplementation programs. An efficacy trial of a multiple micronutrient supplement for pregnant women was conducted in rural western China, and additional information on side effects, rates of adherence, program inputs, and cost was also gathered.

OBJECTIVES

To examine reports of side effects and rates of adherence to prenatal multiple micronutrient supplementation in comparison with supplementation with folic acid and with iron-folic acid, and to describe inputs and costs associated with prenatal supplementation in China.

METHODS

A cluster-randomized, double-blind, controlled trial was conducted in two rural counties in northwest China. All pregnant women in villages were randomly assigned to take daily supplements of folic acid, iron-folic acid, or a recommended daily allowance of 15 vitamins and minerals from enrollment until delivery. Information was collected from the women on side effects and adherence. Program inputs and costs of supplementation were tracked. Descriptive statistics were used for the analysis. The biological effectiveness of prenatal multiple micronutrient supplements is reported elsewhere.

RESULTS

Less than 4% of women withdrew from the study because of side effects. Adherence to supplementation was high: the supplements were consumed on more than 90% of the days on which they were available for consumption. The mean number of supplements consumed was high at 165 capsules, and about 40% consumed the recommended 180 supplements during pregnancy.

CONCLUSIONS

High adherence to a prenatal supplement schedule can be achieved when mothers have frequent contact with trained health workers and a reliable supply of supplements.

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.

An association study of 45 folate-related genes in spina bifida: Involvement of cubilin (CUBN) and tRNA aspartic acid methyltransferase 1 (TRDMT1)

BACKGROUND

Spina bifida is a class of neural tube defects, which are congenital malformations of the central nervous system with a prevalence of 0.5 to 12 per 1000 births globally. In this article we attempt to identify genes related to folate and its metabolic pathways that are involved in the etiology of spina bifida.

METHODS

We selected 50 folate metabolism-related genes and genotyped polymorphisms in those genes. Eighty-seven polymorphisms in 45 genes passed quality controls. Associations with spina bifida were investigated in 180 patients and 190 controls. For those polymorphisms that were nominally associated with spina bifida risk, the relation with serum and red blood cell folate, vitamin B(12), and homocysteine was evaluated in controls.

RESULTS

A polymorphism in CUBN was significantly associated with decreased spina bifida risk, after correction for multiple testing, and was related to increased vitamin B(12) (p = 0.039) and red blood cell folate (p = 0.001). The CUBN gene encodes the intrinsic factor-cobalamin receptor (or cubilin), a peripheral membrane protein that acts as a receptor for intrinsic factor-vitamin B(12) complexes. Vitamin B(12) is an important cofactor in the folate metabolism, and low B(12) status in mothers has been linked to neural tube defects in children. Other interesting findings include nominally significant associations with polymorphisms in TRDMT1, ALDH1L1, SARDH, and SLCA19A1 (RFC1).

CONCLUSION

Our study indicates interesting new candidate genes and functional pathways for further study and confirms earlier findings. None of the genes CUBN, TRDMT1, ALDH1L1, or SARDH have been investigated previously for association with spina bifida.

Nutrient pathways and neural tube defects: a semi-Bayesian hierarchical analysis

BACKGROUND

We used conventional and hierarchical logistic regression to examine the association of neural tube defects (NTDs) with intake of 26 nutrients that contribute to the mechanistic pathways of methylation, glycemic control, and oxidative stress, all of which have been implicated in NTD etiology. The hierarchical approach produces more plausible, more stable estimates than the conventional approach, while adjusting for potential confounding by other nutrients.

METHODS

Analyses included 386 cases and 408 nonmalformed controls with complete data on nutrients and potential confounders (race/ethnicity, education, obesity, and intake of vitamin supplements) from a population-based case-control study of deliveries in California from 1989 to 1991. Nutrients were specified as continuous, and their units were standardized to have a mean of zero and standard deviation (SD) of 1 for comparability of units across pathways. ORs reflect a 1-SD increase in the corresponding nutrient.

RESULTS

Among women who took vitamin supplements, semi-Bayesian hierarchical modeling results suggested no associations between nutrient intake and NTDs. Among women who did not take supplements, both conventional and hierarchical models (HM) suggested an inverse association between lutein intake and NTD risk (HM odds ratio [OR] = 0.6; 95% confidence interval = 0.5-0.9) and a positive association with sucrose (HM OR 1.4; 1.1-1.8) and glycemic index (HM OR 1.3; 1.0-1.6).

CONCLUSIONS

Our findings for lutein, glycemic index, and sucrose suggest that further study of NTDs and the glycemic control and oxidative stress pathways is warranted.

Gene-nutrient interactions: importance of folic acid and vitamin B12 during early embryogenesis

The role that nutritional factors play in mammalian development has received renewed attention over the past two decades as the scientific literature has exploded with reports that folic acid supplementation in the periconceptional period can protect embryos from a number of highly significant malformations. As is often the case, the relationship between B vitamin supplementation and improved pregnancy outcomes is more complicated than initially perceived, as the interaction between nutritional factors and selected genes must be considered. In this review, we attempt to summarize the complex clinical and experimental literature on nutritional factors, their biological transport mechanisms, and interactions with genetic polymorphisms that impact early embryogenesis. While not exhaustive, our goal was to provide an overview of important gene-nutrient interactions, focusing on folic acid and vitamin B12, to serve as a framework for understanding the multiple roles they play in early embryogenesis.

Folate biofortification in food plants

Folate deficiency is a global health problem affecting many people in the developing and developed world. Current interventions (industrial food fortification and supplementation by folic acid pills) are effective if they can be used but might not be possible in less developed countries. Recent advances demonstrate that folate biofortification of food crops is now a feasible complementary strategy to fight folate deficiency worldwide. The genes and enzymes of folate synthesis are sufficiently understood to enable metabolic engineering of the pathway, and results from pilot engineering studies in plants (and bacteria) are encouraging. Here, we review the current status of investigations in the field of folate enhancement on the eve of a new era in food fortification.

Folate fortification of rice by metabolic engineering

Rice, the world's major staple crop, is a poor source of essential micronutrients, including folates (vitamin B9). We report folate biofortification of rice seeds achieved by overexpressing two Arabidopsis thaliana genes of the pterin and para-aminobenzoate branches of the folate biosynthetic pathway from a single locus. We obtained a maximal enhancement as high as 100 times above wild type, with 100 g of polished raw grains containing up to four times the adult daily folate requirement.

Loss of function polymorphisms in NAT1 protect against spina bifida

Periconceptional folic acid supplementation reduces the risk of having a child with spina bifida. N-acetyltransferase 1 (NAT1) participates in the catabolism of folates and the acetylation of aromatic and heterocyclic amines. Hence, functional polymorphisms in NAT1, the gene encoding NAT1, could influence the risk of spina bifida via either folate catabolism or acetylation of exogenous agents. Individuals with spina bifida and their parents were genotyped for six NAT1 single nucleotide polymorphisms (SNPs) for which the less common allele is associated with reduced or absent enzyme activity (i.e. 97C>T, 190C>T, 559C>T/560G>A, 640T>G and 752A>T). In addition, a "composite" NAT1 genotype was defined as a function of the genotyped SNPs. Descriptive analyses of the SNPs and of the composite genotype indicated that heterozygous parents were more likely to transmit the common allele than the rare allele to their affected offspring. Furthermore, matings of mothers homozygous for the common allele and heterozygous fathers were more common than the reciprocal matings. Log-linear analyses confirmed that both the maternal (P = 0.008) and offspring (P = 0.003) composite NAT1 genotypes were significantly related to the risk of spina bifida. NAT1 variants that reduce or abolish enzyme activity appear to protect against spina bifida, and to exert their influence via both the maternal and the offspring genotypes. These associations may be attributable to a decrease in either folate catabolism or the conversion of exogenous agents to teratogenic derivatives in women and/or developing embryos with a NAT1 genotype that includes a loss of function allele relative to those who do not.

Folate supplementation in three genetic models: implications for understanding folate-dependent developmental pathways

Supplementation of a pregnant mother's diet with folate has been shown to protect the developing embryo from birth defects in humans as well as rodent animal models. Folate supplementation not only reverses a potential nutritional deficiency; folate effectively prevents defects even when the mother's nutritional status is normal. These findings indicate that folate is able to interact with the molecular pathways that control normal embryonic development. Supplementation studies in animals provide the experimental starting point for the identification of such folate-responsive pathways. This review summarizes the progress to date in understanding the folate response in genetic models of birth defects in the mouse.

Developmental consequences of in utero sodium arsenate exposure in mice with folate transport deficiencies

Previous studies have demonstrated that mice lacking a functional folate binding protein 2 gene (Folbp2-/-) were significantly more sensitive to in utero arsenic exposure than were the wild-type mice similarly exposed. When these mice were fed a folate-deficient diet, the embryotoxic effect of arsenate was further exacerbated. Contrary to expectations, studies on 24-h urinary speciation of sodium arsenate did not demonstrate any significant difference in arsenic biotransformation between Folbp2-/- and Folbp2+/+ mice. To better understand the influence of folate pathway genes on arsenic embryotoxicity, the present investigation utilized transgenic mice with disrupted folate binding protein 1 (Folbp1) and reduced folate carrier (RFC) genes. Because complete inactivation of Folbp1 and RFC genes results in embryonic lethality, we used heterozygous animals. Overall, no RFC genotype-related differences in embryonic susceptibility to arsenic exposure were observed. Embryonic lethality and neural tube defect (NTD) frequency in Folbp1 mice was dose-dependent and differed from the RFC mice; however, no genotype-related differences were observed. The RFC heterozygotes tended to have higher plasma levels of S-adenosylhomocysteine (SAH) than did the wild-type controls, although this effect was not robust. It is concluded that genetic modifications at the Folbp1 and RFC loci confers no particular sensitivity to arsenic toxicity compared to wild-type controls, thus disproving the working hypothesis that decreased methylating capacity of the genetically modified mice would put them at increased risk for arsenic-induced reproductive toxicity.

Folate modulates Hox gene-controlled skeletal phenotypes

Hox genes are well-known regulators of pattern formation and cell differentiation in the developing vertebrate skeleton. Although skeletal variations are not uncommon in humans few mutations in human HOX genes have been described. If such mutations are compatible with life, there may be physiological modifiers for the manifestation of Hox gene-controlled phenotypes, masking underlying mutations. Here we present evidence that the essential nutrient folate modulates genetically induced skeletal defects in Hoxd4 transgenic mice. We also show that chondrocytes require folate for growth and differentiation and that they express folate transport genes, providing evidence for a direct effect of folate on skeletal cells. To our knowledge, this is the first report of nutritional influence on Hox gene-controlled phenotypes, and implicates gene-environment interactions as important modifiers of Hox gene function. Taken together, our results demonstrate a beneficial effect of folate on skeletal development that may also be relevant to disorders and variations of the human skeleton.

Embryonic development of folate binding protein-1 (Folbp1) knockout mice: Effects of the chemical form, dose, and timing of maternal folate supplementation

Inactivation of folate binding protein-1 (Folbp1) adversely impacts murine embryonic development, as nullizygous embryos (Folbp1(-/-)) die in utero. Administration of folinic acid (N5-formyl-tetrahydrofolate) to Folbp1-deficient dams before and throughout gestation rescues the majority of embryos from premature death; however, a portion of surviving embryos develop structural malformations, including neural tube defects. We examined whether maternal supplementation with L-N5-methyl-tetrahydrofolate (L-5M-THF) has superior protective effects on embryonic development of Folbp1(-/-) fetuses compared with L-N5-formyl-tetrahydrofolate (L-5F-THF). We also examined the critical period during gestation when folate supplementation is most beneficial to the developing Folbp1(-/-) embryos. Folbp1(-/-) pups presented with a range of malformations involving the neural tube, craniofacies, eyes, and abdominal wall. The frequencies of these malformations decreased with increasing folate dose, regardless of the form used. There was no additional benefit provided by L-5M-THF compared with L-5F-THF. Despite rescuing the phenotype in Folbp1(-/-) embryos, no significant elevation of Folbp1(-/-) maternal folate levels was observed with supplementation.

Evidence that the risk of spina bifida is influenced by genetic variation at the NOS3 locus

BACKGROUND

There is substantial evidence that the risk of spina bifida, a malformation of the caudal neural tube, may be associated with maternal or embryonic disturbances in the folate-homocysteine metabolic axis. Hence, variants of genes that influence this pathway represent an intriguing group of candidate genes for spina bifida and other neural tube defects (NTD). A common variant of the gene for endothelial nitric oxide synthase (NOS3 G894T) was recently added to this group of NTD candidate genes, based on a report demonstrating that homozygosity for the T allele of this variant is associated with increased homocysteine levels in normal adult populations.

METHODS

The association between the risk of spina bifida and both the maternal and embryonic genotype for the NOS3 G894T variant was evaluated in data from 301 families by using the transmission disequilibrium test (TDT) and log-linear modeling.

RESULTS

Analyses of these data using the TDT provided no evidence that the risk of spina bifida was significantly related to either the maternal or embryonic NOS3 genotype. However, the log-linear analyses indicated that the risk of spina bifida was significantly associated with the embryonic, but not the maternal, genotype for the NOS3 G894T variant.

CONCLUSIONS

The results of the present analyses suggest that the embryonic NOS3 G894T genotype is associated with the risk of spina bifida. Moreover, these analyses highlight the importance of a detailed examination of the study data. Had these analyses been restricted to the methodologically simpler TDT, the association between the NOS3 G894T genotype and risk of spina bifida may well have been overlooked.

The human T locus and spina bifida risk

The transcription factor T is essential for mesoderm formation and axial development during embryogenesis. Embryonic genotype for a single-nucleotide polymorphism in intron 7 of T ( TIVS7 T/C) has been associated with the risk of spina bifida in some but not all studies. We developed a novel genotyping assay for the TIVS7 polymorphism using heteroduplex generator methodology. This assay was used to genotype spina bifida case-parent trios and the resulting data were analyzed using the transmission disequilibrium test and log-linear analyses. Analyses of these data demonstrated that heterozygous parents transmit the TIVS7-C allele to their offspring with spina bifida significantly more frequently than expected under the assumption of Mendelian inheritance (63 vs 50%, P=0.02). Moreover, these analyses suggest that the TIVS7-C allele acts in a dominant fashion, such that individuals carrying one or more copies of this allele have a 1.6-fold increased risk of spina bifida compared with individuals with zero copies. In silico analysis of the sequence surrounding this polymorphism revealed a potential target site for olfactory neuron-specific factor-1, a transcription factor expressed in the neural tube during development, spanning the polymorphic site. Several other putative, developmentally important and/or environmentally responsive transcription factor-binding sites were also identified close to the TIVS7 polymorphism. The TIVS7 polymorphism or a variant that is in linkage disequilibrium with the TIVS7 polymorphism may, therefore, play a role in T gene expression and influence the risk of spina bifida.

A commonABCC2 promoter polymorphism is not a determinant of the risk of spina bifida

BACKGROUND

There is compelling evidence that the risk of spina bifida, a malformation of the caudal neural tube, is associated with maternal and/or embryonic disturbances in folate/homocysteine metabolism. Hence, functional variants of genes that influence folate/homocysteine metabolism constitute a biologically plausible group of candidate risk factors for spina bifida and other neural tube defects. One such candidate is ABCC2, the gene encoding ABCC2, (a.k.a. canalicular multispecific organic anion transporter [cMOAT], multidrug resistance related protein 2 [MRP2]), a member of the ABC transporter family that effluxes natural folates and anti-folate drugs such as methotrexate.

METHODS

The association between the risk of spina bifida and both the maternal and embryonic ABCC2 C(-24)T genotype was evaluated by using the transmission disequilibrium test and log-linear modeling.

RESULTS

These analyses provided no evidence that the risk of spina bifida was significantly related to either the maternal or embryonic ABCC2 C(-24)T genotype.

CONCLUSIONS

The results of the present analyses suggest that the C(-24)T variant of the ABCC2 gene is not a major determinant of spina bifida risk.

Valproate-induced neural tube defects in folate-binding protein-2 (Folbp2) knockout mice

BACKGROUND

Folate is an important B vitamin that is transported into cells by way of folate-binding proteins and transporters. Folate-binding protein-2 nullizygous (Folbp2(-/-)) mice develop normally; however, we have found them to be more susceptible to the teratogenic effects of arsenate exposure than wild-type control mice.

METHODS

In the current study, we wanted to extend our findings and test the hypothesis that Folbp2(-/-) mice are more susceptible to the teratogenic effects of valproic acid (VPA), a commonly used antiepileptic drug that is known to induce neural tube defects (NTDs) in both humans and laboratory animals.

RESULTS

Folbp2(-/-) mice had higher VPA-induced frequencies of embryonic lethality and exencephaly than did the wild-type control mice during folate supplementation and a control diet, respectively. All other differences in response between the two genotypes were short of reaching statistical significance. Folate supplementation of wild-type, but not Folbp2(-/-) dams reduced embryonic lethality of VPA-treated wild-type embryos compared to the folate-deficient diet.

CONCLUSIONS

Unlike our previous findings with arsenate, enhanced susceptibility of Folbp2(-/-) mice to in utero VPA exposure was demonstrated in some dietary folate regimens. Thus, our data indicate a relatively frail relationship between Folbp2 and VPA-induced NTDs.

Epidemiology of neural tube defects

Neural tube defects (NTDs)-malformations secondary to abnormal neural tube closure between the third and fourth weeks of gestational age-have a complex and imperfectly understood etiology in which both genetic and environmental factors appear to be involved. A number of specific chromosomal or single-gene disorders, presumably not affected by environmental influences, are associated with the development of NTDs, but such syndromal cases account for a small proportion of NTDs in live-born infants. Analysis of recurrence patterns within families and of twin-concordance data provides evidence of a genetic influence in nonsyndromal cases, but factors such as socioeconomic status and geographic area (independent of race or ethnicity) are also associated with variations in the incidence of NTDs. The prevalence at birth of both anencephaly and spina bifida has decreased, but the advent of antenatal diagnosis and elective termination of affected pregnancies has undermined the reliability of birth prevalence rate as an estimate of incidence. Some occupational and other exposures, including maternal use of antiepileptic drugs (AEDs), are associated with increased risk for NTDs. Among women who have had an NTD-affected pregnancy, recurrence risk is markedly higher than the risk for a first NTD-affected pregnancy in the general population. There is strong evidence, overall, for a protective effect of adequate folate consumption. In some high-risk groups, however, such as women taking AEDs, folate supplementation has not been proven to reduce NTD risk.

Strenuous work, nutrition and adverse pregnancy outcomes: a brief review

This brief review explores the available epidemiologic data to investigate the question of whether strenuous work by women during pregnancy in developing countries influences micronutrient status and thereby increase risks of adverse pregnancy outcomes. Some data exist on the potential relationship between strenuous work or physical activity and nutrient compromise, strenuous work or physical activity and adverse reproductive outcomes and micronutrient intakes or status and adverse reproductive outcomes. No substantial body of data exists that has directly investigated the potential causal path of whether strenuous work during pregnancy alters micronutrient status leading to adverse reproductive outcome. Search of the literature identified only a few papers from developing countries that provided even remotely related data on the topic. Thus, the available data are insufficient for drawing firm inferences that strenuous work, in a developing country, alters a pregnant woman's nutritional status and therefore affects her risk of an adverse pregnancy outcome. Effects on nutritional status, micronutrients in particular, of pregnant women from strenuous physical activities at work or in other lifestyle events require further study in developing countries.

Folic acid supplements during early pregnancy and likelihood of multiple births: a population-based cohort study

BACKGROUND

Folic acid supplements are recommended for women of childbearing age to prevent neural tube defects in their offspring. Results of some studies, however, suggest an increase in multiple births associated with use of vitamin supplements that contain folic acid during pregnancy. Our aim was to assess this association.

METHODS

We used data from a population-based cohort study from which we assessed the occurrence of multiple births in women (n=242015) who had participated in a campaign to prevent neural tube defects with folic acid supplements (400 microg per day) in China. Folic acid use was ascertained before pregnancy outcome was known. We studied the relation between multiple births and any use of folic acid pills before or during early pregnancy; additionally, we investigated mechanisms by which folic acid could potentially affect the occurrence of multiple births by examining pill-taking at three time periods: before ovulation, around the time of fertilisation, and after conception.

FINDINGS

1496 (0.62%) multiple births occurred in a cohort of 242015 women who had registered with the study between October, 1993, and September, 1995, and who had a pregnancy not affected by a birth defect; the rate of multiple births in women who did and did not take folic acid before or during early pregnancy was 0.59% and 0.65%, respectively (rate ratio 0.91; 95% CI 0.82-1.00).

INTERPRETATION

Our findings suggest that consumption of folic acid supplements during pregnancy is not associated with an increased occurrence of multiple births.