Modeling anterior development in mice: Diet as modulator of risk for neural tube defects.

Kappen C. (2013). Modeling anterior development in mice: Diet as modulator of risk for neural tube defects.  American Journal of Medical Genetics Part C Seminars in Medical Genetics. 163(4):333-56. doi: 10.1002/ajmg.c.31380. Epub 2013 Oct 4.

Abstract

Head morphogenesis is a complex process that is controlled by multiple signaling centers. The most common defects of cranial development are craniofacial defects, such as cleft lip and cleft palate, and neural tube defects, such as anencephaly and encephalocoele in humans. More than 400 genes that contribute to proper neural tube closure have been identified in experimental animals, but only very few causative gene mutations have been identified in humans, supporting the notion that environmental influences are critical. The intrauterine environment is influenced by maternal nutrition, and hence, maternal diet can modulate the risk for cranial and neural tube defects. This article reviews recent progress toward a better understanding of nutrients during pregnancy, with particular focus on mouse models for defective neural tube closure. At least four major patterns of nutrient responses are apparent, suggesting that multiple pathways are involved in the response, and likely in the underlying pathogenesis of the defects. Folic acid has been the most widely studied nutrient, and the diverse responses of the mouse models to folic acid supplementation indicate that folic acid is not universally beneficial, but that the effect is dependent on genetic configuration. If this is the case for other nutrients as well, efforts to prevent neural tube defects with nutritional supplementation may need to become more specifically targeted than previously appreciated. Mouse models are indispensable for a better understanding of nutrient-gene interactions in normal pregnancies, as well as in those affected by metabolic diseases, such as diabetes and obesity. © 2013 Wiley Periodicals, Inc.

 

PMID:24124024

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

Tinker SC, Devine O, Mai C, Hamner HC, Reefhuis J, Gilboa SM, Dowling NF, Honein MA. (2013) Estimate of the potential impact of folic acid fortification of corn masa flour on the prevention of neural tube defects. Birth Defects Res A Clin Mol Teratol.  97(10):649-57. doi: 10.1002/bdra.23158.

Abstract

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. Birth Defects Research (Part A) 97:649-657, 2013. © 2013 Wiley Periodicals, Inc.

PMID:24142499

http://onlinelibrary.wiley.com/doi/10.1002/bdra.23158/full

Evaluation of the levels of folate, vitamin B12, homocysteine and fluoride in the parents and the affected neonates with neural tube defect and their

Ratan SK, Rattan KN, Pandey RM, Singhal S, Kharab S, Bala M, Singh V, Jhanwar A. (2008) Evaluation of the levels of folate, vitamin B12, homocysteine and fluoride in the parents and the affected neonates with neural tube defect and their matched controls. Pediatric Surgery International. Jul;24(7):803-8.

Department of Pediatric Surgery, Pandit BD Sharma Post Graduate Institute of Medical Sciences, Rohtak, Haryana, India. drjohnsimmi@yahoo.com

The aim of this study is to evaluate the folate, vitamin B12, fluoride and homocysteine levels in newborns with neural tube defect (NTD) and their parents. The study included 35 neonates with NTD and their parents, 31 neonates with congenital anomalies other than NTD formed control 1, 24 neonates with no anomalies, with the highest birth order and normal siblings formed control 2. These groups matched for socio-economic and nutritional status. Demographic, antenatal history, parental habits, folate (RBC, whole blood and serum), serum vitamin B12 and homocysteine levels were estimated using chemiluminescence technology. Chi-square test was used to assess association between factors and the outcome. One-way ANOVA was used to compare means in the three groups. To determine the risk factors for NTD, odds ratios (95% CI) was computed using bivariate and multivariate logistic regression analysis (STATA 9.0). No difference was found between NTD group and 'control 1' group. The fathers in NTD group had significantly lower folate and vitamin B12 and a higher homocysteine, in comparison to 'control 2' group (i.e. with normal babies). The babies with NTD had higher homocysteine while their mothers had significantly low folate levels in comparison to 'control 2' mothers. Low RBC folate, low serum vitamin B12 and high plasma homocysteine in both the parents had an association with NTD. Multivariate logistic regression revealed high homocysteine of father as the only independent significant risk factor [OR(95% CI):2.6(2.6, 226)] for NTD and also for other anomalies. NTD (and other congenital anomalies) may not only be due to nutritional deficiency in the mothers but also due to more intricate gene-nutrient interaction defects in the affected families, probably some abnormal folate-homocysteine metabolism. These defects seem to be affect the fathers more severely and in all likelihood, get transmitted to the babies from either or both the parents. The emergence of father's serum homocysteine levels as an independent risk factor for NTD and also other congenital anomalies calls for further studies to evaluate if this can be taken as a marker for congenital anomalies in the fetus during antenatal screening.

PMID: 18463884

Vitamin B12 insufficiency and the risk of fetal neural tube defects.

Ray JG, Blom HJ. Vitamin B12 insufficiency and the risk of fetal neural tube defects. QJM. 2003 Apr;96(4):289-95. Review.

Division of Obstetrical Medicine, Department of Medicine, Sunnybrook and Women's College Health Sciences Centre, University of Toronto, Toronto, Ontario, Canada. jray515445@aol.com

BACKGROUND: Although maternal folate insufficiency is a risk factor for fetal neural tube defects (NTDs), there is controversy about whether vitamin B12 (B12) insufficiency is also associated with an increased risk of NTDs. AIM: To investigate whether low maternal B12 is associated with an increased risk of fetal NTDs. DESIGN: Systematic review.

METHODS: A systematic search of Medline between 1980 and October 2002, with an examination of the citations of all retrieved studies. Studies were included that: (i) used a cohort or case-control design; (ii) included case mothers with a prior or current NTD-affected pregnancy; (iii) assessed a group of unaffected 'controls'; and (iv) measured the vitamin B12 status of all participants.

RESULTS: Overall, 17 case-control studies were included, mean sample size 33 cases and 93 controls. In 5/6, mean amniotic fluid B12 concentration was significantly lower in case mothers than in controls. Of 11 that measured maternal serum or plasma B12, three observed a significantly lower mean concentration in case mothers vs. controls, while five others found a non-significant lower trend in the case group. One study observed a significantly higher mean concentration of maternal serum methylmalonic acid among the maternal cases, while another found a non-significant lower mean concentration of plasma holo-transcobalamin. Five studies estimated the risk of NTDs in relation to low B12 or B12-related metabolic markers: it was significantly increased in three studies, with a non-significant trend in the fourth.

DISCUSSION: There seems to be a moderate association between low maternal B12 status and the risk of fetal NTDs. However, several design limitations, and the inclusion of few study participants, may have under-represented this. A large observational study, using reliable and valid indicators of B12 status in early pregnancy, could best assess the association between B12 insufficiency and the risk of fetal NTDs.

PMID: 12651973

Maternal vitamin B12 and the risk of fetal neural tube defects in Egyptian patients.

Gaber KR, Farag MK, Soliman SE, El-Bassyouni HT, El-Kamah G. (2007) Maternal vitamin B12 and the risk of fetal neural tube defects in Egyptian patients.
Clinical Laboratory. 2007;53(1-2):69-75.

Prenatal Diagnosis and Fetal Medicine Department, National Research Centre, Cairo, Egypt.

OBJECTIVE: Folic acid insufficiency is a known risk factor for neural tube defects (NTDs), while the role of vitamin B12 is questionable. Thus, our purpose was to investigate whether low maternal serum vitamin B12 is associated with an increased risk of NTDs.

SETTING: Prenatal Diagnosis and Clinical Genetics Clinics, National Research Centre, in collaboration with the Radioisotope Department, Nuclear Research Centre, Cairo.

MATERIALS AND METHODS: The study groups included 36 women who were, or had been, pregnant with a NTD-affected fetus. The control groups comprised 35 healthy women with normal prior or current pregnancy and uncomplicated obstetric histories. Fasting plasma homocysteine, serum folate and cobalamin (vitamin B12) were determined. Odds ratio (OR) and 95% confidence intervals were calculated.

RESULTS: The fasting homocysteine was significantly higher in the study groups as compared to the controls. The median serum folate concentrations were similar in cases and controls, while the median vitamin B12 concentrations were significantly lower in the study groups compared to the controls. Low vitamin B12 concentration was associated with an approximately 2- to 3-fold increased risk for NTDs.

CONCLUSION: Low maternal serum values of vitamin B12 can be considered an important etiologic factor for the development of neural tube defects in our population. This may help in both genetic counseling for families with a history of NTD malformation, and as a pre-conceptional prophylactic measure by maternal supplementation of vitamin B12 and folic acid.

PMID: 17323828

Mouse models for neural tube closure defects.

Juriloff DM, Harris MJ. Mouse models for neural tube closure defects. Human Molecular Genetics. 2000 Apr 12;9(6):993-1000. Review.

Department of Medical Genetics, University of British Columbia, 6174 University Boulevard, Vancouver, British Columbia, Canada. juriloff@interchange.ubc.ca

Neural tube closure defects (NTDs), in particular anencephaly and spina bifida, are common human birth defects (1 in 1000), their genetics is complex and their risk is reduced by periconceptional maternal folic acid supplementation. There are > 60 mouse mutants and strains with NTDs, many reported within the past 2 years. Not only are NTD mutations at loci widely heterogeneous in function, but also most of the mutants demonstrate variable low penetrance and some show complex inheritance patterns (e.g. SELH/Bc, Abl / Arg, Mena / Profilin1 ). In most of these mouse models, the NTDs are exencephaly (equivalent to anencephaly) or spina bifida or both, reflecting failure of neural fold elevation in well defined, mechanistically distinct elevation zones. NTD risk is reduced in various models by different maternal nutrient supplements, including folic acid ( Pax3, Cart1, Cd mutants), inositol ( ct ) and methionine ( Axd ). Lack of de novo methylation in embryos ( Dnmt3b -null) leads to NTD risk, and we suggest a potential link between methylation and the observed female excess among cranial NTDs in several models. Some surprising NTD mutants ( Gadd45a, Terc, Trp53 ) suggest that genes with a basic mitotic function also have a function specific to neural fold elevation. The genes mutated in several mouse NTD models involve actin regulation ( Abl/Arg, Macs, Mena/Profilin1, Mlp, Shrm, Vcl ), support the postulated key role of actin in neural fold elevation, and may be a good candidate pathway to search for human NTD genes.

PMID: 10767323

Addressing a Folate Imbalance in Fetal Cerebrospinal Fluid Can Decrease the Incidence of Congenital Hydrocephalus

Cains S, Shepherd A, Nabiuni M, Owen-Lynch PJ, Miyan J. Addressing a Folate Imbalance in Fetal Cerebrospinal Fluid Can Decrease the Incidence of Congenital Hydrocephalus. Journal of Neuropathology and Experimental Neurology. 2009 Mar 12.

From the Faculty of Life Sciences, The University of Manchester, Manchester (SC, AS, MN, JM); and Division of Biomedical and Life Sciences, School of Health and Medicine, Lancaster University, Lancaster (PJOL), United Kingdom; and Department of Biology, Faculty of Basic Sciences, Tarbiat Moallem University (Kharazmi), Tehran, Iran (MN).

Fetal-onset hydrocephalus (HC), which affects between 1:500 and 1:5000 live human births, results from unequal production and drainage of cerebrospinal fluid (CSF) and is associated with abnormal development of the cerebral cortex leading to severe neurological deficits. We previously found that in the hydrocephalic Texas rat, the CSF of affected fetuses induced a cell cycle arrest in neural progenitor cells. Here, we show that alterations in folate metabolism in the CSF of the developing cerebrum are likely responsible for this effect. We identified 3 folate enzymes in the CSF and demonstrate that low levels of one of these, 10-formyltetrahydrofolate dehydrogenase, are associated with HC in the hydrocephalic Texas rat. Therefore, we tested whether supplementation with specific folate species would improve developmental outcome. After daily administration of a combination of tetrahydrofolic and 5-formyltetrahydrofolic acids to pregnant dams, there was a significant reduction in the incidence of HC and improved brain development. By contrast, supplementation with folic acid increased the incidence of congenital HC in this model. These results indicate the complexities of folate metabolism in the developing brain and suggest that folate imbalance leading to HC in the hydrocephalic Texas rat fetuses can be treated with maternal folate supplementation using specific folate metabolites and combinations thereof.

PMID: 19287311

Myelomeningocele: a review of the epidemiology, genetics, risk factors for conception, prenatal diagnosis, and prognosis for affected individuals

Shaer CM, Chescheir N, Schulkin J. Myelomeningocele: a review of the epidemiology, genetics, risk factors for conception, prenatal diagnosis, and prognosis for affected individuals. Obstetrical & Gynecological Survey. 2007 Jul;62(7):471-9. Review.

Although the use of folic acid before conception decreases the chance that a fetus will have an open neural tube defect, this condition still affects 0.5-1.0/1000 pregnancies in the United States. Results of a recent survey suggest that there are gaps in obstetrician-gynecologists' knowledge of risk factors for conception, strategies for prenatal diagnosis, and prognosis for affected individuals. To address these gaps this paper reviews the epidemiology, genetics, risk factors for conception, prenatal diagnosis, and prognosis for affected individuals, presents current information, and makes suggestions for expanding obstetrician-gynecologists' knowledge of myelomeningocele.

TARGET AUDIENCE: Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES: After completion of this article, the reader should be able to state that despite a large amount of professional and public education on the use of folic acid in prevention of open neural tube defects (ONTDs) the incidence still affects 0.5-1.0/1000 pregnancies and recall that a recent survey conducted by the ACOG shows substantial misunderstanding and misinformation on major categories of neural tube birth defects.

PMID: 17572919

CHKA and PCYT1A gene polymorphisms, choline intake and spina bifida risk in a California population

Enaw JO, Zhu H, Yang W, Lu W, Shaw GM, Lammer EJ, Finnell RH. CHKA and PCYT1A gene polymorphisms, choline intake and spina bifida risk in a California population. BMC Medicine. 2006 Dec 21;4:36.

BACKGROUND: Neural tube defects (NTDs) are among the most common of all human congenital defects. Over the last two decades, accumulating evidence has made it clear that periconceptional intake of folic acid can significantly reduce the risk of NTD affected pregnancies. This beneficial effect may be related to the ability of folates to donate methyl groups for critical physiological reactions. Choline is an essential nutrient and it is also a methyl donor critical for the maintenance of cell membrane integrity and methyl metabolism. Perturbations in choline metabolism in vitro have been shown to induce NTDs in mouse embryos.

METHODS: This study investigated whether single nucleotide polymorphisms (SNPs) in human choline kinase A (CHKA) gene and CTP:phosphocholine cytidylytransferase (PCYT1A) gene were risk factors for spina bifida. Fluorescence-based allelic discrimination analysis was performed for the two CHKA intronic SNPs hCV1562388 (rs7928739) and hCV1562393, and PCYT1A SNP rs939883 and rs3772109. The study population consisted of 103 infants with spina bifida and 338 non-malformed control infants who were born in selected California counties in the period 1989-1991.

RESULTS: The CHKA SNP hCV1562388 genotypes with at least one C allele were associated with a reduced risk of spina bifida (odds ratio = 0.60, 95%CI = 0.38-0.94). The PCYT1A SNP rs939883 genotype AA was associated with a twofold increased risk of spina bifida (odds ratio = 1.89, 95% CI = 0.97-3.67). These gene-only effects were not substantially modified by analytic consideration to maternal periconceptional choline intake.

CONCLUSION: Our analyses showed genotype effects of CHKA and PCYT1A genes on spina bifida risk, but did not show evidence of gene-nutrient interactions. The underlying mechanisms are yet to be resolved.

PMID: 17184542

Maternal periconceptional vitamin use, genetic variation of infant reduced folate carrier (A80G), and risk of spina bifida

Shaw GM, Lammer EJ, Zhu H, Baker MW, Neri E, Finnell RH. Maternal periconceptional vitamin use, genetic variation of infant reduced folate carrier (A80G), and risk of spina bifida.
American Journal of Medical Genetics. 2002 Feb 15;108(1):1-6. Erratum in: Am J Med Genet 2002 Dec 15;113(4):392.

Women who consume folic acid in early pregnancy reduced their risks for delivering offspring with neural tube defects (NTDs). The underlying process by which folic acid facilitated this risk reduction is unknown. Investigating genetic variation that influences cellular absorption, transport, and metabolism of folate will help fill this data gap. We focused our studies on a candidate gene that is involved in folate transport, the reduced folate carrier 1 (RFC1). Using data from a California population-based case control interview study (1989-1991 birth cohorts), we investigated whether spina bifida risk was influenced by an interaction between a polymorphism of infant RFC1 at nucleotide 80 (A80G) and maternal periconceptional use of vitamins containing folic acid. Allelic variants of RFC1 were determined by genotyping 133 live-born spina bifida case infants and 188 control infants. The percentages of case infants with the A80/A80, G80/G80, and G80/A80 genotypes were 27.2%, 28.0%, and 44.7%, respectively. The percentages of control infants were similar: 26.1%, 29.3%, and 44.7%. Odds ratios of 1.0 (95% confidence interval 0.5-2.0) for the G80/G80 genotype and 1.1 (0.6-2.0) for the G80/A80 genotype were observed relative to the A80/A80 genotype. Among mothers who did not use vitamins, spina bifida risk was 2.4 (0.8-6.9) for infants with genotype G80/G80 compared to those with A80/A80 genotype. Among mothers who did use vitamins, the risk was 0.5 (0.1-3.1) for infants with the G80/G80 genotype. Although this study did not find an increased spina bifida risk for infants who were heterozygous or homozygous for RFC1 A80G, it did reveal modest evidence for a gene-nutrient interaction between infant homozygosity for the RFC1 G80/G80 genotype and maternal periconceptional intake of vitamins containing folic acid on the risk of spina bifida. Copyright 2002 Wiley-Liss, Inc.

PMID: 11857541

The NAT1 C1095A polymorphism, maternal multivitamin use and smoking, and the risk of spina bifida

Jensen LE, Hoess K, Whitehead AS, Mitchell LE. The NAT1 C1095A polymorphism, maternal multivitamin use and smoking, and the risk of spina bifida.
Birth Defects Research Part A: Clinical and Molecular Teratology. 2005 Jul;73(7):512-6.

BACKGROUND: The risk of having a child with a neural tube defect (NTD) can be reduced by maternal, periconceptional supplementation with folic acid, but the underlying folate-dependent protective mechanism remains unclear. N-acetyltransferase 1 is involved in acetylation of aromatic and heterocyclic amines and the catabolism of folates. Hence, functional polymorphisms in NAT1, the gene encoding N-acetyltransferase 1, are plausible risk factors for NTDs. Such variants could exert an influence on the risk of NTDs via their role in acetylation or folate catabolism and could act through the maternal or the embryonic genotype.

METHODS: NAT1 C1095A genotypes and information on maternal, periconceptional multivitamin use and smoking were obtained as part of a family-based study of spina bifida. Associations between spina bifida and the embryonic and maternal NAT1 C1095A genotypes, and potential NAT1 C1095A genotype-exposure interactions were evaluated using log-linear modeling.

RESULTS: The analyses provided no evidence that the embryonic or maternal NAT1 C1095 genotypes influence the risk of spina bifida independently, or through interactions with maternal use of multivitamins. There was evidence that the embryonic, and possibly the maternal, NAT1 C1095A genotype influence the risk of spina bifida via interactions with maternal smoking status.

CONCLUSIONS: The genotype for the NAT1 C1095A polymorphism does not appear to be an independent risk factor for spina bifida. However, the results of these analyses provide preliminary evidence that this polymorphism may be associated with the risk of spina bifida in the offspring of women who smoke during early pregnancy. (c) 2005 Wiley-Liss, Inc.

PMID: 15959877

Loss of function polymorphisms in NAT1 protect against spina bifida.

Jensen LE, Hoess K, Mitchell LE, Whitehead AS. Loss of function polymorphisms in NAT1 protect against spina bifida. Human Genetics. 2006 Aug;120(1):52-7. Epub 2006 May 6.

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.

PMID: 16680433

The etiology of neural tube defects: the role of folic acid

McLone DG. The etiology of neural tube defects: the role of folic acid.
Child's Nervous System. 2003 Aug;19(7-8):537-9. Epub 2003 Aug 12.

DISCUSSION: While the cause of neural tube defects in humans is considered to be multifactorial, it is apparent that folic acid can prevent 70% of open neural tube defects. Even in laboratory animals with known genetic defects, folic acid can prevent the genetic expression.

CONCLUSION: While some of the metabolic pathways for folic acid are known, the true effects of folic acid on closure of the neural tube have yet to be discovered.

PMID: 12920544

Investigation of folate pathway gene polymorphisms and the incidence of neural tube defects in a Texas hispanic population

Barber R, Shalat S, Hendricks K, Joggerst B, Larsen R, Suarez L, Finnell R. Investigation of folate pathway gene polymorphisms and the incidence of neural tube defects in a Texas hispanic population. Molecular Genetics & Metabolism. 2000 May;70(1):45-52.

Neural tube defects (NTDs) are multifactorial in their etiology, having both genetic and environmental factors contributing to their development. Recent evidence demonstrates that periconceptional supplementation of the maternal diet with a multivitamin containing folic acid significantly reduces the occurrence and recurrence risk for having a pregnancy complicated by NTDs. Unfortunately, the mechanism underlying the beneficial effects of folic acid remains unknown. NTD surveillance data from the Texas-Mexico border show that the high NTD rate (28/10,000 live births) noted during the 1990-1991 Cameron county NTD cluster was superimposed on a background Cameron county NTD rate (16/10,000 live births) which is considerably higher than that generally noted in the United States (8-10/10,000 live births). These data suggest that genetic factors as well as transient environmental factors may contribute to the etiology of the NTDs. Furthermore, clinical and experimental evidence imply that allelic forms of genes involved with folate metabolism and/or transport may explain some of the observed variation in the NTD rates found across different populations. Two folate pathway genes were selected for evaluation in this study. The loci investigated included two known alleles of the 5, 10-methylenetetrahydrofolate reductase (MTHFR) gene, as well as the promoter region of the folate receptor-alpha (FR-alpha) gene. Odds ratios (ORs) for the C677T polymorphism in the MTHFR gene were 1.8 (CI 0.47-6.8) for heterozygosity and 1.8 (CI 0.35-9.4) for homozygosity for the mutant 677T allele, relative to wildtype homozygotes. The odds ratio for the heterozygosity for the A1298C polymorphism in the same gene was 1.1 (CI 0.09-14). No individuals homozygous for the 1298C allele were observed. The OR for heterozygosity of FR-alpha gene polymorphisms detected at nucleotide 762 and at nucleotides 610/631 was 1.4 and 0.7, respectively. Neither of the FR-alpha polymorphisms was observed in the homozygous condition. No statistically significant associations were observed for any of the polymorphisms examined, as the 95% confidence intervals for all of the ORs included one. However, the frequency of the MTHFR 677T allele in the largely Hispanic control group from Texas was significantly different from other populations (P < 0.005), and among the highest reported for any control populations examined. Copyright 2000 Academic Press.

PMID: 10833330

Polymorphisms in genes involved in folate metabolism as risk factors for NTDs.

De Marco P, Calevo MG, Moroni A, Arata L, Merello E, Cama A, Finnell RH, Andreussi L, Capra V. Polymorphisms in genes involved in folate metabolism as risk factors for NTDs. European Journal of Pediatric Surgery. 2001 Dec;11 Suppl 1:S14-7.

Moderate hyperhomocysteinemia in pregnant women has been associated with an increased risk of neural tube defects (NTDs). Periconceptional supplementation with multi-vitamins containing folic acid may normalize homocysteine metabolism and decrease the NTD risk. The C677 T variant of the MTHFR gene coding for a thermolabile enzyme has been described as the first genetic risk factor that accounts for a group of NTDs characterized by low maternal folate status and high homocysteine concentrations. Another common mutation of the same MTHFR gene, A1298 C, has also been described as an NTD risk factor. In addition to abnormal folate metabolism, anything that compromises the internalization of folate into the cell may be involved in the pathogenesis of NTDs. For this reason, a common polymorphism in the RFC-1 gene encoding the reduced folate carrier protein (A80 G) could also be an additional NTD risk factor. In the present study we examined the genotypic distributions and the allele frequencies of MTHFR A1298 C and RFC-1 A80 G polymorphisms in DNA samples from healthy Italian individuals and compared them to the frequencies observed in NTD cases and their parents. By means of restriction enzymatic analysis, we determined that the frequency of the mutated C allele of the A1298 C mutation was 0.25 among control individuals, which is in the range of that recently reported in other ethnic groups. However, we report that the mutant C allele frequencies are significantly higher among NTD cases and case mothers than among controls (0.39, 0.44, 0.25). Furthermore, for the RFC-1 A80 G mutation, we found that the frequency of the G allele of the RFC-1 mutation was 0.46 in the control population, suggesting that this is a common polymorphism in the Italian population. In spite of the high prevalence of the 80 G/G genotype among healthy subjects, we observed an increased frequency of the G allele in NTD-affected children, and their mothers and fathers. These preliminary results indicate that both the MTHFR and RFC-1 polymorphisms may play a role in NTD risk, at least in the Italian population. Further studies should be directed toward the evaluation of the level of risk conferred by the mutant MTHFR and RFC-1 genotypes, as well as the interaction between these genetic determinants and other nutritional and environmental factors.

PMID: 11813127

The 19-bp deletion polymorphism in intron-1 of dihydrofolate reductase (DHFR) may decrease rather than increase risk for spina bifida in the Irish pop

Parle-McDermott A, Pangilinan F, Mills JL, Kirke PN, Gibney ER, Troendle J, O'Leary VB, Molloy AM, Conley M, Scott JM, Brody LC. The 19-bp deletion polymorphism in intron-1 of dihydrofolate reductase (DHFR) may decrease rather than increase risk for spina bifida in the Irish population. American Journal of Medical Genetics A. 2007 Jun 1;143(11):1174-80.

Periconceptional maternal folic acid supplementation can prevent up to 70% of pregnancies affected with neural tube defects (NTDs), including spina bifida. This has focused attention on folate-related genes such as dihydrofolate reductase (DHFR) in a bid to identify the genetic factors that influence NTD risk through either the fetal or maternal genotype. We considered a novel intronic 19-bp deletion polymorphism and two polymorphisms within the 3' untranslated region (721A>T and 829C>T) of the DHFR gene as candidates for NTD risk. We studied NTD cases (n=283), mothers of cases (n=280), fathers of cases (n=279), and controls (n=256). We did not find the DHFR 829C>T polymorphism to be variable within the Irish population. The 19-bp intron deletion and the 721A>T polymorphisms were found to be in linkage disequilibrium. In contrast to a previous study, the 19-bp intron deletion allele did show a significant protective effect in mothers of NTD cases when present in one (relative risk 0.59 [95%CI: 0.39-0.89], P=0.01) or two copies (relative risk 0.52 [95%CI: 0.32-0.86], P=0.01). Analysis of mRNA levels revealed a small increase in expression ( approximately 1.5-fold) associated with the 19-bp intron deletion polymorphism, but this was not significant. In conclusion, the DHFR intron 19-bp deletion allele may be a protective NTD genetic factor by increasing DHFR mRNA levels in pregnant women. Copyright (c) 2007 Wiley-Liss, Inc.

PMID: 17486595

Survival of infants with neural tube defects in the presence of folic acid fortification.

Bol KA, Collins JS, Kirby RS;
Survival of infants with neural tube defects in the presence of folic acid fortification. Pediatrics. 2006 Mar;117(3):803-13.

OBJECTIVE: Neural tube defects (NTDs) are preventable through preconceptional and periconceptional folic acid intake. Although decreases in the prevalence of NTDs have been reported since folic acid fortification of United States grain products began, it is not known whether folic acid plays a role in reducing the severity of occurring NTDs. Our aim was to determine whether survival among infants born with spina bifida and encephalocele has improved since folic acid fortification and to measure the effects of selected maternal, pregnancy, and birth characteristics on first-year (infant) survival rates.

METHODS: A retrospective cohort study was conducted and included 2841 infants with spina bifida and 638 infants with encephalocele who were born between 1995 and 2001 and were registered in any of 16 participating birth defects monitoring programs in the United States. First-year survival rates for both spina bifida and encephalocele cohorts were measured with Kaplan-Meier estimation; factors associated with improved chances of first-year survival, including birth before or during folic acid fortification, were measured with Cox proportional-hazards regression analysis.

RESULTS: Infants with spina bifida experienced a significantly improved first-year survival rate of 92.1% (adjusted hazard ratio: 0.68; 95% confidence interval: 0.50-0.91) during the period of mandatory folic acid fortification, compared with a 90.3% survival rate for those born before fortification. Infants with encephalocele had a statistically nonsignificant increase in survival rates, ie, 79.1% (adjusted hazard ratio: 0.76; 95% confidence interval: 0.51-1.13) with folic acid fortification, compared with 75.7% for earlier births.

CONCLUSIONS: Folic acid may play a role in reducing the severity of NTDs in addition to preventing the occurrence of NTDs. This phenomenon contributes to our understanding of the efficacy of folic acid. Additionally, as survival of NTD-affected infants improves, health care, education, and family support must expand to meet their needs.

Reduction in neural-tube defects after folic acid fortification in Canada.

De Wals P, Tairou F, Van Allen MI, Uh SH, Lowry RB, Sibbald B, Evans JA, Van den Hof MC, Zimmer P, Crowley M, Fernandez B, Lee NS, Niyonsenga T.
Reduction in neural-tube defects after folic acid fortification in Canada. New England Journal of Medicine 2007 Jul 12;357(2):135-42.

BACKGROUND: In 1998, folic acid fortification of a large variety of cereal products became mandatory in Canada, a country where the prevalence of neural-tube defects was historically higher in the eastern provinces than in the western provinces. We assessed changes in the prevalence of neural-tube defects in Canada before and after food fortification with folic acid was implemented.

METHODS: The study population included live births, stillbirths, and terminations of pregnancies because of fetal anomalies among women residing in seven Canadian provinces from 1993 to 2002. On the basis of published results of testing of red-cell folate levels, the study period was divided into prefortification, partial-fortification, and full-fortification periods. We evaluated the relationship between baseline rates of neural-tube defects in each province and the magnitude of the decrease after fortification was implemented.

RESULTS: A total of 2446 subjects with neural-tube defects were recorded among 1.9 million births. The prevalence of neural-tube defects decreased from 1.58 per 1000 births before fortification to 0.86 per 1000 births during the full-fortification period, a 46% reduction (95% confidence interval, 40 to 51). The magnitude of the decrease was proportional to the prefortification baseline rate in each province, and geographical differences almost disappeared after fortification began. The observed reduction in rate was greater for spina bifida (a decrease of 53%) than for anencephaly and encephalocele (decreases of 38% and 31%, respectively).

CONCLUSIONS: Food fortification with folic acid was associated with a significant reduction in the rate of neural-tube defects in Canada. The decrease was greatest in areas in which the baseline rate was high. Copyright 2007 Massachusetts Medical Society.

Neural tube defects, micronutrient deficiencies, and Helicobacter pylori: A new hypothesis.

Felkner M, Suarez L, Liszka B, Brender JD, Canfield M. Neural tube defects, micronutrient deficiencies, and Helicobacter pylori: A new hypothesis. Birth defects research. Part A, Clinical and molecular teratology. 2007 Jul 11

BACKGROUND: Previous findings for the Texas Neural Tube Defects Project suggested that while maternal access to nutrients is adequate, bioavailability of nutrients to the fetus is compromised in NTD-affected pregnancies. Helicobacter pylori could cause nutrient loss to the fetus. Folate, B(12,) and ferritin are depleted in H. pylori infection; these same deficiencies are related to NTD risk.

METHODS: Using H. pylori IgG ELISA Test System, we tested for H. pylori serum antibodies in participants in the population-based case-control study component of the Texas Neural Tube Defect Project conducted along the Texas-Mexico border. Case-women had pregnancies affected by NTD (anencephalus, spina bifida, encephalocele) and resided and delivered in one of the 14 Texas-Mexico border counties from 1995 through 2000. Control-women were study area residents delivering normal live births during the same period.

RESULTS: Of 225 case- and 378 control-women, 103 cases and 156 controls provided questionnaire and H. pylori antibody data. H. pylori seropositivity was modestly associated with NTD-affected pregnancies (OR 1.4; 95% CI: 0.8-2.4). ORs of 2.0 or greater were seen in women younger than age 25 and with less than 7 years education.

CONCLUSIONS: Our findings intimate that H. pylori could play a role in NTD causation in certain populations. While results did not provide compelling support for this proposal, subgroup findings prompt us to advocate an evaluation of this hypothesis in developing nations among populations with higher prevalence of H. pylori, marginal nutrient intake, and young childbearing age. Birth Defects Research (Part A), 2007. (c) 2007 Wiley-Liss, Inc.