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.

 

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Genetic association analyses of nitric oxide synthase genes and neural tube defects vary by phenotype.

Soldano KL, Garrett ME, Cope HL, Rusnak JM, Ellis NJ, Dunlap KL, Speer MC, Gregory SG, Ashley-Koch AE. (2013) Genetic association analyses of nitric oxide synthase genes and neural tube defects vary by phenotype.  Birth defects research. Part B, Developmental and reproductive toxicology. Oct;98(5):365-73. 

Neural tube defects (NTDs) are caused by improper neural tube closure during the early stages of embryonic development. NTDs are hypothesized to have a complex genetic origin and numerous candidate genes have been proposed. The nitric oxide synthase 3 (NOS3) G594T polymorphism has been implicated in risk for spina bifida, and interactions between that single nucleotide polymorphism (SNP) and the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism have also been observed. To evaluate other genetic variation in the NO pathway in the development of NTDs, we examined all three NOS genes: NOS1, NOS2, and NOS3. Using 3109 Caucasian samples in 745 families, we evaluated association in the overall dataset and within specific phenotypic subsets. Haplotype tagging SNPs in the NOS genes were tested for genetic association with NTD subtypes, both for main effects as well as for the presence of interactions with the MTHFR C677T polymorphism. Nominal main effect associations were found with all subtypes, across all three NOS genes, and interactions were observed between SNPs in all three NOS genes and MTHFR C677T. Unlike the previous report, the most significant associations in our dataset were with cranial subtypes and the AG genotype of rs4795067 in NOS2 (p = 0.0014) and the interaction between the rs9658490 G allele in NOS1 and MTHFR 677TT genotype (p = 0.0014). Our data extend the previous findings by implicating a role for all three NOS genes, independently and through interactions with MTHFR, in risk not only for spina bifida, but all NTD subtypes.

doi: 10.1002/bdrb.21079. 

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

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

Gene-gene interaction in folate-related genes and risk of neural tube defects in a UK population.

Relton CL, Wilding CS, Pearce MS, Laffling AJ, Jonas PA, Lynch SA, Tawn EJ, Burn J. Gene-gene interaction in folate-related genes and risk of neural tube defects in a UK population. Journal of Medical Genetics. 2004 Apr;41(4):256-60.

OBJECTIVE: To investigate the contribution of polymorphic variation in genes involved in the folate-dependent homocysteine pathway in the aetiology of neural tube defects (NTD).

DESIGN: Case-control association study.

SUBJECTS: A total of 530 individuals from families affected by NTD, 645 maternal controls, and 602 healthy newborn controls from the northern UK.

MAIN OUTCOME MEASURES: Seven polymorphisms in six genes coding for proteins in the folate-dependent homocysteine pathway (MTHFR 677C-->T, MTHFR 1298A-->C, MTRR 66A-->G, SHMT 1420C-->T, CbetaS 844ins68, GCPII 1561C-->T, RFC-1 80G-->A). The impact of each polymorphism and the effect of gene-gene interactions (epistasis) upon risk of NTD were assessed using logistic regression analysis.

RESULTS: The MTHFR 677C-->T polymorphism was shown to represent a risk factor in NTD cases (CC v CT+TT odds ratio (OR) 2.03 [95% confidence interval (CI) 1.09, 3.79] p = 0.025) and the MTRR 66A-->G polymorphism was shown to exert a protective effect in NTD cases (AA v AG+GG OR 0.31 [95% CI 0.10, 0.94] p = 0.04). When statistical tests for interaction were conducted, three genotype combinations in cases (MTRR/GCPII; MTHFR 677/CbetaS; MTHFR 677/MTRR) and one combination in case mothers (CbetaS/RFC-1) were shown to elevate NTD risk. Maternal-fetal interaction was also detected when offspring carried the MTHFR 677C-->T variant and mothers carried the MTRR 66A-->G variant, resulting in a significantly elevated risk of NTD.

CONCLUSION: Both independent genetic effects and gene-gene interaction were observed in relation to NTD risk. Multi-locus rather than single locus analysis might be preferable to gain an accurate assessment of genetic susceptibility to NTD.

PMID: 15060097
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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 894G>T variant in the endothelial nitric oxide synthase gene and spina bifida risk

van der Linden IJ, Heil SG, den Heijer M, Blom HJ. The 894G>T variant in the endothelial nitric oxide synthase gene and spina bifida risk.
Journal of Human Genetics. 2007;52(6):516-20. Epub 2007 May 4.

The 894G>T single nucleotide polymorphism (SNP) in the endothelial NOS (NOS3) gene, has recently been associated with embryonic spina bifida risk. In this study, a possible association between the NOS3 894G>T SNP and spina bifida risk in both mothers and children in a Dutch population was examined using both a case-control design and a transmission disequilibrium test (TDT). Possible interactions between the NOS3 894G>T SNP and the MTHFR 677C>T SNP, elevated plasma homocysteine, and decreased plasma folate concentrations were also studied. The NOS3 894TT genotype did not increase spina bifida risk in mothers or children (OR 1.50, 95%CI 0.71-3.19 and OR 1.78, 95%CI 0.75-4.25, respectively). The TDT demonstrated no preferential transmission of the NOS3 894T allele (Chi2=0.06, P=0.81). In combination with the MTHFR 677TT genotype or elevated plasma homocysteine concentrations, the NOS3 894GT/TT genotype increased maternal spina bifida risk (OR 4.52, 95%CI 1.55-13.22 and OR 3.38, 95%CI 1.46-7.84, respectively). In our study population, the NOS3 894GT/TT genotype might be a risk factor for having a spina bifida affected child in mothers who already have an impaired homocysteine metabolism.

PMID: 17479212
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