Folate-related gene variants in Irish families affected by neural tube defects.

Fisk Green R, Byrne J, Crider KS, Gallagher M, Koontz D, Berry RJ. (2013) Folate-related gene variants in Irish families affected by neural tube defects. Frontiers in Genetics. 2013 Nov 6;4:223.

 

Periconceptional folic acid use can often prevent neural tube defects (NTDs). Variants of genes involved in folate metabolism in mothers and children have been associated with occurrence of NTDs. We identified Irish families with individuals affected by neural tube defects. In these families, we observed that neural tube defects and birth defects overall occurred at a higher rate in the maternal lineage compared with the paternal lineage. The goal of this study was to look for evidence for genetic effects that could explain the discrepancy in the occurrence of these birth defects in the maternal vs. paternal lineage. We genotyped blood samples from 322 individuals from NTD-affected Irish families, identified through their membership in spina bifida associations. We looked for differences in distribution in maternal vs. paternal lineages of five genetic polymorphisms: the DHFR 19 bp deletion, MTHFD1 1958G>A, MTHFR 1298A>C, MTHFR 677C>T, and SLC19A1 80A>G. In addition to looking at genotypes individually, we determined the number of genotypes associated with decreased folate metabolism in each relative ("risk genotypes") and compared the distribution of these genotypes in maternal vs. paternal relatives. Overall, maternal relatives had a higher number of genotypes associated with lower folate metabolism than paternal relatives (p = 0.017). We expected that relatives would share the same risk genotype as the individuals with NTDs and/or their mothers. However, we observed that maternal relatives had an over-abundance of any risk genotype, rather than one specific genotype. The observed genetic effects suggest an epigenetic mechanism in which decreased folate metabolism results in epigenetic alterations related to the increased rate of NTDs and other birth defects seen in the maternal lineage. Future studies on the etiology of NTDs and other birth defects could benefit from including multigenerational extended families, in order to explore potential epigenetic mechanisms.

 

 

doi: 10.3389/fgene.2013.00223.

 

Free PMC Article

Nucleotide precursors prevent folic acid-resistant neural tube defects in the mouse.

Leung KY, De Castro SC, Savery D, Copp AJ, Greene ND. (2013) Nucleotide precursors prevent folic acid-resistant neural tube defects in the mouse. Brain. 2013 Aug 8. [Epub ahead of print]

Closure of the neural tube during embryogenesis is a crucial step in development of the central nervous system. Failure of this process results in neural tube defects, including spina bifida and anencephaly, which are among the most common birth defects worldwide. Maternal use of folic acid supplements reduces risk of neural tube defects but a proportion of cases are not preventable. Folic acid is thought to act through folate one-carbon metabolism, which transfers one-carbon units for methylation reactions and nucleotide biosynthesis. Hence suboptimal performance of the intervening reactions could limit the efficacy of folic acid. We hypothesized that direct supplementation with nucleotides, downstream of folate metabolism, has the potential to support neural tube closure. Therefore, in a mouse model that exhibits folic acid-resistant neural tube defects, we tested the effect of specific combinations of pyrimidine and purine nucleotide precursors and observed a significant protective effect. Labelling in whole embryo culture showed that nucleotides are taken up by the neurulating embryo and incorporated into genomic DNA. Furthermore, the mitotic index was elevated in neural folds and hindgut of treated embryos, consistent with a proposed mechanism of neural tube defect prevention through stimulation of cellular proliferation. These findings may provide an impetus for future investigations of supplemental nucleotides as a means to prevent a greater proportion of human neural tube defects than can be achieved by folic acid alone.

PMID: 23935126

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

The scientific basis for eliminating folic acid-preventable spina bifida: a modern miracle from epidemiology.

Oakley GP Jr. The scientific basis for eliminating folic acid-preventable spina bifida: a modern miracle from epidemiology. Annals of Epidemiology. 2009 Apr;19(4):226-30.

Department of Epidemiology, Rollins School of Public Health of Emory University, Atlanta, GA, USA. gpoakley@mindspring.com

One of the most remarkable successes of epidemiology was the demonstration in the late twentieth century that spina bifida and anencephaly-two of the most common and severe birth defects-are caused primarily by folate deficiency. This article reviews the descriptive epidemiological studies that began when we did not have a clue about etiology. The paper tells the success story of the trials that proved that folic acid would prevent folic-acid-preventable spina bifida. Finally, it will tell how difficult it is to get prevention policy implemented, even when the scientific evidence is compelling. It concludes by noting that the inaction or inappropriate actions of food regulatory bodies in so many countries means that only 10% of folic-acid-preventable spina bifida is actually being prevented--a serious failure of public health policy.

PMID: 19344858

Autoantibodies to folate receptor during pregnancy and neural tube defect risk

Robert M. Cabrera, Gary M. Shaw, Johnathan L. Ballard, Suzan L. Carmichael, Wei Yang, Edward J. Lammer, Richard H. Finnell Autoantibodies to folate receptor during pregnancy and neural tube defect risk Journal of Reproductive Immunology, In Press, Corrected Proof, Available online 18 September 2008


Abstract
Periconceptional folic acid can reduce the occurrence of neural tube defects (NTDs) by up to 70%, and autoantibodies for folate receptors (FRs) have been observed in serum from women with a pregnancy complicated by an NTD. This population-based cohort
study has examined serum from pregnant mothers for autoantibodies to FRs, antibodies to bovine folate binding protein (FBP), and inhibition of folic acid binding to FR and FBP in association with NTD risk. The mid-gestational maternal serum specimens
used for this study were collected during the 15–18th week of pregnancy. Samples were obtained from the California Birth Defects Monitoring Program; 29 mothers had a pregnancy complicated by spina bifida and 76 mothers had unaffected children. The presence of IgG and IgM antibodies to human FR, bovine FBP, and inhibition of folic acid binding to FR and FBP was determined. Higher activity of IgM to FBP in cases verses controls was observed (P = 0.04). Higher activity of IgM and IgG autoantibodies to FR was observed (P < 0.001 and P = 0.04, respectively). Risk estimates at two standard deviations above average control antibody
concentrations were OR= 2.07 (CI = 1.02, 4.06) for anti-FBP IgM, OR= 2.15 (CI = 1.02, 4.69) for anti-FR IgG and OR= 3.19 (CI = 1.47, 6.92) for anti-FR IgM. These data support the hypothesis that high titers of antibodies and blocking of folic acid binding to FRs by maternal serum should be regarded as risk factors for NTDs.
© 2008 Elsevier Ireland Ltd. All rights reserved.

Keywords: Folate receptor; Autoantibodies; Pregnancy; Neural tube defects

Mouse mutants with neural tube closure defects and their role in understanding human neural tube defects

Harris MJ, Juriloff DM. Mouse mutants with neural tube closure defects and their role in understanding human neural tube defects. Birth Defects Research Part A: Clinical and Molecular Teratology. 2007 Mar;79(3):187-210. Review.

BACKGROUND: The number of mouse mutants and strains with neural tube closure defects (NTDs) now exceeds 190, including 155 involving known genes, 33 with unidentified genes, and eight "multifactorial" strains.

METHODS: The emerging patterns of mouse NTDs are considered in relation to the unknown genetics of the common human NTDs, anencephaly, and spina bifida aperta.

RESULTS: Of the 150 mouse mutants that survive past midgestation, 20% have risk of either exencephaly and spina bifida aperta or both, parallel to the majority of human NTDs, whereas 70% have only exencephaly, 5% have only spina bifida, and 5% have craniorachischisis. The primary defect in most mouse NTDs is failure of neural fold elevation. Most null mutations (>90%) produce syndromes of multiple affected structures with high penetrance in homozygotes, whereas the "multifactorial" strains and several null-mutant heterozygotes and mutants with partial gene function (hypomorphs) have low-penetrance nonsyndromic NTDs, like the majority of human NTDs. The normal functions of the mutated genes are diverse, with clusters in pathways of actin function, apoptosis, and chromatin methylation and structure. The female excess observed in human anencephaly is found in all mouse exencephaly mutants for which gender has been studied. Maternal agents, including folate, methionine, inositol, or alternative commercial diets, have specific preventative effects in eight mutants and strains.

CONCLUSIONS: If the human homologs of the mouse NTD mutants contribute to risk of common human NTDs, it seems likely to be in multifactorial combinations of hypomorphs and low-penetrance heterozygotes, as exemplified by mouse digenic mutants and the oligogenic SELH/Bc strain.

PMID: 17177317

The effect of C677T mutation of methylene tetrahydrofolate reductase gene and plasma folate level on hyperhomocysteinemia in patients with meningomyel

Lee BH, Cheong HI, Shin YS, Cho BK, Wang KC. The effect of C677T mutation of methylene tetrahydrofolate reductase gene and plasma folate level on hyperhomocysteinemia in patients with meningomyelocele. Child's Nervous System. 2000 Sep;16(9):559-63.

To evaluate the relationship between genotypes of methylene tetrahydrofolate reductase (MTHFR), and plasma folate and homocysteine (Hcy) levels in meningomyelocele, 21 Korean patients, 47 of their family members, and 43 healthy controls were recruited. The presence of C677T mutation in the MTHFR gene and plasma concentrations of folate/Hcy were investigated. The genotype frequency of C677T mutation was not higher in study groups (patients and family members). The plasma folate concentration showed no difference either between the study and the control groups or among MTHFR-genotypic groups. The plasma Hcy concentration in homozygotes in the study group was higher than that in the control group, and higher than that in heterozygotes when plasma folate levels were low (P=0.006). Although neither MTHFR genotype nor plasma folate/Hcy level plays a definite part on its own, they seem to have an additive effect on the occurrence of meningomyelocele. Our results support folate supplementation for the prevention of hyperhomocysteinemia and meningomyelocele.

PMID: 11048629

Homocysteine, folate, lipid profile and MTHFR genotype and disability in children with myelomeningocele

Rendeli C, Ausili E, Castorina M, Antuzzi D, Tabacco F, Caldarelli M. Homocysteine, folate, lipid profile and MTHFR genotype and disability in children with myelomeningocele. Child's Nervous System. 2006 Oct;22(10):1316-21. Epub 2006 Apr 7.

STUDY DESIGN: We performed a cross-sectional study in myelomeningocele children. OBJECTIVE: To investigate plasma total homocysteine, folate, lipid profile, 5,10- metylenetetrahydrofolate reductase genotype (MTHFR) and disability.

MATERIALS AND METHODS: Sixty patients aged between 2 and 14 years with myelomeningocele (18 ambulatory and 42 non-ambulatory) and 150 healthy children of same age, are investigated for lipid profile, homocysteine concentration and for the determination of MTHFR genotype.

RESULTS: Plasma homocysteine concentrations were significantly higher in myelomeningocele children than in the control group. In myelomeningocele female group, there were higher levels of total cholesterol and very-low-density lipoprotein cholesterol with respect to the control group. Myelomeningocele children walking with tutorial aid showed triglyceride levels significantly lower than those observed in myelomeningocele non-walking children.

CONCLUSION: Disability, insulin uptake, lipid, homocysteine, hormones plasma levels, and genetic factors such as allelic variants of MTHFR are possible for cardiovascular disease in myelomeningocele children. This study highlights the importance of a continuous surveillance of any changes in the lipid profile that should be corrected as soon as possible. Constant physical activity necessary to increase HDL levels should be planned in all susceptible children. Nonetheless, further investigations are necessary to identify new homocysteine susceptible genes for prevention of early atherosclerosis and consequent cardiovascular disease.

PMID: 16602021

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

Evaluation of genetic variants in the reduced folate carrier and in glutamate carboxypeptidase II for spina bifida risk

Morin I, Devlin AM, Leclerc D, Sabbaghian N, Halsted CH, Finnell R, Rozen R. Evaluation of genetic variants in the reduced folate carrier and in glutamate carboxypeptidase II for spina bifida risk. Molecular Genetics & Metabolism 2003 Jul;79(3):197-200.

Genetic variants in folate metabolism have been reported to increase risk for neural tube defects (NTD). The first such sequence change was the 677C-->T substitution in methylenetetrahydrofolate reductase (MTHFR), but additional sequence changes have been identified in enzymes or transporters for folates. Two recently identified variants are the 1561C-->T (H475Y) mutation in glutamate carboxypeptidase II (GCPII) and the 80A-->G (H27R) change in the reduced folate carrier RFC-1. We examined a group of mothers of spina bifida offspring, and a group of control women, for the above polymorphisms to assess their impact on NTD risk as well as on homocysteine and nutrient (RBC folate, serum folate, and serum cobalamin) levels. The GCPII variant (in the heterozygous state) did not influence NTD risk or metabolite levels; homozygous mutant (YY) women were not observed in our study group. The homozygous mutant (RR) genotype for the RFC-1 gene was not associated with a significant difference in NTD risk (OR=1.39, 95% CI=0.55-3.54), but there was a borderline significant (p=0.065) decrease in RBC folate levels, compared with the HH genotype. However, the combination of the RR genotype for RFC-1 and low RBC folate was associated with a significant 4.6-fold increase in NTD risk (OR=4.6, 95% CI=1.47-14.37). Since this small study is the first to demonstrate increased risk for women with the RFC-1 variant for having a child with a NTD, additional larger studies are required to confirm this change as another potential genetic modifier for spina bifida risk.

PMID: 12855225

Genetic susceptibility to neural tube defect pregnancy varies with offspring phenotype

Relton CL, Wilding CS, Jonas PA, Lynch SA, Tawn EJ, Burn J. Genetic susceptibility to neural tube defect pregnancy varies with offspring phenotype.
Clinical Genetics. 2003 Nov;64(5):424-8.

Neural tube defects (NTDs) have a well-established genetic basis, although no single genetic factor has been identified as a major risk factor in NTD susceptibility. A large number of association studies have been conducted to investigate the possibility that NTD susceptibility is linked to polymorphic variation in genes involved in early embryonic development or in the absorption or metabolism of folate, a nutrient that has been clearly associated with a reduction in the risk of NTD pregnancy. A study of three candidate gene polymorphisms at loci implicated in folate absorption and metabolism has been conducted on a population of 211 mothers of a heterogeneous mix of NTD phenotypes: 59% spina bifida aperta (SBA), 20.3% spina bifida occulta (SBO), 17% anencephaly, and 3.7% other NTD. Allele and genotype frequencies were stratified according to offspring NTD phenotype, and variation in the level of NTD risk was associated with different phenotypes. All the three variants (MTHFR 677C > T, GCPII 1561C > T, and RFC-1 80G > A) were shown to significantly influence the risk of anencephalic pregnancy. In addition, the MTHFR 677C > T variant conferred a modest protective effect in SBO mothers and the total NTD mother group, but not in SBA mothers. The RFC-1 80G > A variant elevated the risk of SBO and anencephalic pregnancy. The findings of this study suggest that NTD phenotypic heterogeneity may help explain the mixed findings of previous association studies and that different polymorphisms may hold differing degrees of significance for the various NTD phenotypes.

PMID: 14616766

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

Abnormal folate metabolism in foetuses affected by neural tube defects

Dunlevy LP, Chitty LS, Burren KA, Doudney K, Stojilkovic-Mikic T, Stanier P, Scott R, Copp AJ, Greene ND. Abnormal folate metabolism in foetuses affected by neural tube defects. Brain: A Journal of Neurology. 2007 Apr;130(Pt 4):1043-9.

Folic acid supplementation can prevent many cases of neural tube defects (NTDs), whereas suboptimal maternal folate status is a risk factor, suggesting that folate metabolism is a key determinant of susceptibility to NTDs. Despite extensive genetic analysis of folate cycle enzymes, and quantification of metabolites in maternal blood, neither the protective mechanism nor the relationship between maternal folate status and susceptibility are understood in most cases. In order to investigate potential abnormalities in folate metabolism in the embryo itself, we derived primary fibroblastic cell lines from foetuses affected by NTDs and subjected them to the dU suppression test, a sensitive metabolic test of folate metabolism. Significantly, a subset of NTD cases exhibited low scores in this test, indicative of abnormalities in folate cycling that may be causally linked to the defect. Susceptibility to NTDs may be increased by suppression of the methylation cycle, which is interlinked with the folate cycle. However, reduced efficacy in the dU suppression test was not associated with altered abundance of the methylation cycle intermediates, s-adenosylmethionine and s-adenosylhomocysteine, suggesting that a methylation cycle defect is unlikely to be responsible for the observed abnormality of folate metabolism. Genotyping of samples for known polymorphisms in genes encoding folate-associated enzymes did not reveal any correlation between specific genotypes and the observed abnormalities in folate metabolism. These data suggest that as yet unrecognized genetic variants result in embryonic abnormalities of folate cycling that may be causally related to NTDs.

PMID: 17438019