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

Impaired Function of Solute Carrier Family 19 Leads to Low Folate Levels and Lipid Droplet Accumulation in Hepatocytes

Low serum folate levels are inversely related to metabolic associated fatty liver disease (MAFLD). The role of the folate transporter gene (SLC19A1) was assessed to clarify its involvement in lipid accumulation during the onset of MAFLD in humans and in liver cells by genomic, transcriptomic, and metabolomic techniques. Genotypes of 3 SNPs in a case-control cohort were initially correlated to clinical and serum MAFLD markers. Subsequently, the expression of 84 key genes in response to the loss of SLC19A1 was evaluated with the aid of an RT² profiler-array. After shRNA-silencing of SLC19A1 in THLE2 cells, folate and lipid levels were measured by ELISA and staining techniques, respectively. In addition, up to 482 amino acids and lipid metabolites were semi-quantified in SLC19A1-knockdown (KD) cells through ultra-high-performance liquid chromatography coupled with mass spectrometry. SNPs, rs1051266 and rs3788200, were significantly associated with the development of fatty liver for the single-marker allelic test. The minor alleles of these SNPs were associated with a 0.6/-1.67-fold decreased risk of developing MAFLD. When SLC19A1 was KD in THLE2 cells, intracellular folate content was four times lower than in wild-type cells. The lack of functional SLC19A1 provoked significant changes in the regulation of genes associated with lipid droplet accumulation within the cell and the onset of NAFLD. Metabolomic analyses showed a highly altered profile, where most of the species that accumulated in SLC19A1-KD-cells belong to the chemical groups of triacylglycerols, diacylglycerols, polyunsaturated fatty acids, and long chain, highly unsaturated cholesterol esters. In conclusion, the lack of SLC19A1 gene expression in hepatocytes affects the regulation of key genes for normal liver function, reduces intracellular folate levels, and impairs lipid metabolism, which entails lipid droplet accumulation in hepatocytes.

The Concept of Folic Acid in Health and Disease

Folates have a pterine core structure and high metabolic activity due to their ability to accept electrons and react with O-, S-, N-, C-bounds. Folates play a role as cofactors in essential one-carbon pathways donating methyl-groups to choline phospholipids, creatine, epinephrine, DNA. Compounds similar to folates are ubiquitous and have been found in different animals, plants, and microorganisms. Folates enter the body from the diet and are also synthesized by intestinal bacteria with consequent adsorption from the colon. Three types of folate and antifolate cellular transporters have been found, differing in tissue localization, substrate affinity, type of transferring, and optimal pH for function. Laboratory criteria of folate deficiency are accepted by WHO. Severe folate deficiencies, manifesting in early life, are seen in hereditary folate malabsorption and cerebral folate deficiency. Acquired folate deficiency is quite common and is associated with poor diet and malabsorption, alcohol consumption, obesity, and kidney failure. Given the observational data that folates have a protective effect against neural tube defects, ischemic events, and cancer, food folic acid fortification was introduced in many countries. However, high physiological folate concentrations and folate overload may increase the risk of impaired brain development in embryogenesis and possess a growth advantage for precancerous altered cells.

The effects of drug transporters on the efficacy of methotrexate in the treatment of rheumatoid arthritis

The ATP-binding cassette (ABC) and solute carrier (SLC) transporter families consist of common drug transporters that mediate the efflux and uptake of drugs, respectively, and play an important role in the absorption, distribution, metabolism and excretion of drugs in vivo. Rheumatoid arthritis (RA) is an autoimmune disease characterized by erosive arthritis, and there are many RA patients worldwide. Methotrexate (MTX), the first-choice treatment for RA, can reduce the level of inflammation, prevent joint erosion and functional damage, and greatly reduce pain in RA patients. However, many patients show resistance to MTX, greatly affecting the efficacy of MTX. Many factors, such as irrational drug use and heredity, are associated with drug resistance. Considering the effect of drug transporters on drugs, many studies have compared the expression of drug transporters in drug-resistant and drug-sensitive patients, and abnormal transporter expression and transport activity have been found in patients with MTX resistance. Thus, drug transporters are involved in drug resistance. This article reviews the effects of transporters on the efficacy of MTX in the treatment of RA.

Understanding how the concentration of neighborhood advantage and disadvantage affects spina bifida risk among births to non-Hispanic white and Hispanic women, Texas, 1999-2014

BACKGROUND

This is the first study to utilize the index of concentration at the extremes (ICE) to examine risk factors for spina bifida in Texas. The ICE is a useful measure for providing the degree to which residents in a certain area are concentrated into groups at the extremes of disadvantage and privilege. We introduce two novel ICE measures (language and nativity), and three existing ICE measures (race/ethnicity, income, and education), which we applied specifically to Texas residents.

METHODS

We used multivariable mixed-model Poisson regression analyses to estimate spina bifida birth prevalence and prevalence ratios among singleton live births in Texas, 1999-2014, for each of our ICE measures. Maternal census tract at delivery was included in the models as a random effect. Analyses were stratified by maternal race/ethnicity (Hispanics and non-Hispanic whites). Live births served as denominators for each category.

RESULTS

Among non-Hispanic white women, those in the most disadvantaged versus the advantaged census tract quintile had adjusted relative risk between 1.6 and 8.5 for having a baby affected by spina bifida. However, Hispanic women in the most disadvantaged versus advantaged census tract quintile for four ICE measures had a 33% to 87% lower risk of having an affected pregnancy.

CONCLUSIONS

Findings suggest spina bifida risk is associated with neighborhood disadvantage or advantage, and that relationship seems to vary by race-ethnicity. The varied associations between ICE measures and spina bifida by race/ethnicity highlights the importance of using targeted interventions in the prevention of spina bifida.

The study of association between reduced folate carrier 1 (RFC1) polymorphism and non-syndromic cleft lip/palate in Iranian population

Introduction: Cleft lip/palate is one of the most common congenital defects and is supposed to have multifactorial etiology, including a complex interaction between genetics and environment. Reduced folate carrier 1 (RFC1) gene takes part in folate transportation within the cells. In this study, the association of A80G polymorphism in the RFC1 gene with the non-syndromic cleft lip/palate (nsCL/P) was investigated in Iranian infants for the first time. Methods: In this case-control survey, 122 Iranian infants with nsCL/P and 164 healthy infants were investigated for RFC1 polymorphism by PCR and RFLP methods. The results were statistically compared with control group, odds ratios with 95% CI were estimated by univariate and multivariate logistic regression model and a P <0.05 was considered statistically significant. Results: The RFC1 G allele was significantly higher (P=0.001; OR=7, 95% CI: 4.7-10.2) in the cases (60.3%) compared with the controls (17.9%). Not only the RFC1 AG genotype was significantly higher (P<0.001; OR=44, 95% CI: 14.6-133) in cases (67.8%) than the controls (27.4%), but also GG genotype (P<0.001; OR=85, 95% CI: 20.5-352) was much higher in cases (26.4%) than the controls (4.3%). Conclusion: Our study indicated that the RFC1 (A80G) polymorphism was associated with the nsCL/P in Iranian population. Moreover, 80GG homozygosity was significant in the cases. The presence of G allele can be considered as a risk factor for the nsCL/P. Infants with the GG and AG genotypes were more prone to cleft lip/palate as compared to the AA ones. This finding emphasizes the role of RFC1 gene and the intracellular levels of folate.

Mutations in folate transporter genes and risk for human myelomeningocele

The molecular mechanisms linking folate deficiency and neural tube defect (NTD) risk in offspring remain unclear. Folate transporters (SLC19A1, SLC46A1, SLC25A32, and FOLH1) and folate receptors (FOLR1, FOLR2, and FOLR3) are suggested to play essential roles in transporting folate from maternal intestinal lumen to the developing embryo. Loss of function variants in these genes may affect folate availability and contribute to NTD risk. This study examines whether variants within the folate transporter and receptor genes are associated with an increased risk for myelomeningocele (MM). Exons and their flanking intron sequences of 348 MM subjects were sequenced using the Sanger sequencing method and/or next generation sequencing to identify variants. Frequencies of alleles of single nucleotide polymorphisms (SNPs) in MM subjects were compared to those from ethnically matched reference populations to evaluate alleles' associated risk for MM. We identified eight novel variants in SLC19A1 and twelve novel variants in FOLR1, FOLR2, and FOLR3. Pathogenic variants include c.1265delG in SLC19A1 resulting in an early stop codon, four large insertion deletion variants in FOLR3, and a stop_gain variant in FOLR3. No new variants were identified in SLC46A1, SLC25A32, or FOLH1. In SLC19A1, c.80A>G (rs1051266) was not associated with our MM cohort; we did observe a variant allele G frequency of 61.7%, higher than previously reported in other NTD populations. In conclusion, we discovered novel loss of function variants in genes involved in folate transport in MM subjects. Our results support the growing evidence of associations between genes involved in folate transport and susceptibility to NTDs.

Association between SLC19A1 Gene Polymorphism and High Dose Methotrexate Toxicity in Childhood Acute Lymphoblastic Leukaemia and Non Hodgkin Malignant Lymphoma: Introducing a Haplotype based Approach

Background

We investigated the clinical relevance of SLC 19A1 genetic variability for high dose methotrexate (HD-MTX) related toxicities in children and adolescents with acute lymphoblastic leukaemia (ALL) and non Hodgkin malignant lymphoma (NHML).

Patients and methods

Eighty-eight children and adolescents with ALL/NHML were investigated for the influence of SLC 19A1 single nucleotide polymorphisms (SNPs) and haplotypes on HD-MTX induced toxicities.

Results

Patients with rs2838958 TT genotype had higher probability for mucositis development as compared to carriers of at least one rs2838958 C allele (OR 0.226 (0.071–0.725), p < 0.009). Haplotype TGTTCCG (H4) statistically significantly reduced the risk for the occurrence of adverse events during treatment with HD-MTX (OR 0.143 (0.023–0.852), p = 0.030).

Conclusions

SLC 19A1 SNP and haplotype analysis could provide additional information in a personalized HD-MTX therapy for children with ALL/NHML in order to achieve better treatment outcome. However further studies are needed to validate the results.

Folic acid supplementation for pregnant women and those planning pregnancy: 2015 update

During the last decade critical new information has been published pertaining to folic acid supplementation in the prevention of neural tube defects (NTDs) and other folic acid-sensitive congenital malformations. These new data have important implications for women, their families, and health care professionals. We performed a review looking for the optimal dosage of folic acid that should be given to women of reproductive age who are planning or not avoiding conception to propose updated guidelines and thus help health care providers and patients. In addition to fortification of dietary staples with folic acid, women of reproductive age should supplement before conception with 0.4-1.0 mg of folic acid daily as part of their multivitamins. In the United States all enriched rice is also fortified with folic acid at 0.7 mg per pound of raw rice. However, this is not the case in many countries, and it has been estimated that only 1% of industrially milled rice is fortified with folic acid. In countries where rice is the main staple (eg, China), this does not allow effective folate fortification. Whereas the incidence of NTDs is around 1/1000 in the United States, it is 3- to 5-fold higher in Northern China and 3-fold higher in India. A recent population-based US study estimated that the reduction in NTD rates by folic acid is more modest than previously predicted. The potential of NTD prevention by folic acid is underutilized due to low adherence with folic acid supplementation, and calls for revising the policy of supplementation have been raised. We identified groups of women of reproductive age who may benefit from higher daily doses of folic acid, and this should be considered in current practice. These include women who have had previous pregnancies with NTDs, those who did not plan their pregnancy and hence did not supplement, and women with low intake or impaired adherence to daily folic acid supplementation. In addition, women with known genetic variations in the folate metabolic cycle, those exposed to medications with antifolate effects, smokers, diabetics, and the obese may benefit from higher doses of folic acid daily during the first trimester.

Evaluation of proton-coupled folate transporter (SLC46A1) polymorphisms as risk factors for neural tube defects and oral clefts

Many folate-related genes have been investigated for possible causal roles in neural tube defects (NTDs) and oral clefts. However, no previous reports have examined the major gene responsible for folate uptake, the proton-coupled folate transporter (SLC46A1). We tested for association between these birth defects and single nucleotide polymorphisms in the SLC46A1 gene. The NTD study population included 549 complete and incomplete case-family triads, and 999 controls from Ireland. The oral clefts study population comprised a sample from Utah (495 complete and incomplete case-family triads and 551 controls) and 221 Filipino multiplex cleft families. There was suggestive evidence of increased NTD case risk with the rs17719944 minor allele (odds ratio (OR): 1.29; 95% confidence intervals (CI): [1.00-1.67]), and decreased maternal risk of an NTD pregnancy with the rs4795436 minor allele (OR: 0.62; [0.39-0.99]). In the Utah sample, the rs739439 minor allele was associated with decreased case risk for cleft lip with cleft palate (genotype relative risk (GRR): 0.56 [0.32-0.98]). Additionally, the rs2239907 minor allele was associated with decreased case risk for cleft lip with cleft palate in several models, and with cleft palate only in a recessive model (OR: 0.41; [0.20-0.85]). These associations did not remain statistically significant after correcting for multiple hypothesis testing. Nominal associations between SLC46A1 polymorphisms and both Irish NTDs and oral clefts in the Utah population suggest some role in the etiology of these birth defects, but further investigation in other populations is needed.

The A1298C Methylenetetrahydrofolate Reductase Gene Variant as a Susceptibility Gene for Non-Syndromic Conotruncal Heart Defects in an Indian Population

Conotruncal heart defects (CTHDS) are a subgroup of congenital heart malformations that are considered to be a folate-sensitive birth defect. It has been hypothesized that polymorphisms in genes that code for key enzymes in the folate pathway may alter enzyme activity, leading to disruptions in folate metabolism and thus may influence the risk of such heart defects. This study was designed to investigate the association of six selected folate-metabolizing gene polymorphisms with the risk of non-syndromic CTHDs in an Indian population. This was a case-control study involving 96 cases of CTHDs and 100 control samples, ranging in age from birth to 18 years. Genotyping using Sanger sequencing was performed for six single nucleotide polymorphisms of genes involved in folate metabolism. Logistic regression analyses revealed that for the 5,10-methylenetetrahydrofolate (MTHFR) A1298C polymorphism, the CC variant homozygote genotype was associated with a significantly increased risk of CTHDs. The results of this study support an association between the inherited MTHFR A1298C genotype and the risk of CTHDs in an Indian population.

RFC-1 80G>A polymorphism in case-mother/control-mother dyads is associated with risk of nephroblastoma and neuroblastoma

AIM

Embryonic tumors are associated with an interruption during normal organ development; they may be related to disturbances in the folate pathway involved in DNA synthesis, methylation, and repair. Prenatal supplementation with folic acid is associated with a decreased risk of neuroblastoma, brain tumors, retinoblastoma, and nephroblastoma. The aim of this study was to investigate the association between MTHFR rs1801133 (C677T) and RFC-1 rs1051266 (G80A) genotypes with the risk of developing nephroblastoma and neuroblastoma.

MATERIALS AND METHODS

Case-mother/control-mother dyad study. Samples from Brazilian children with nephroblastoma (n=80), neuroblastoma (n=66), healthy controls (n=453), and their mothers (case n=93; control n=75) were analyzed. Genomic DNA was isolated from peripheral blood cells and/or buccal cells and genotyped to identify MTHFR C677T and RFC-1 G80A polymorphisms. Differences in genotype distribution between patients and controls were tested by multiple logistic regression analysis.

RESULTS

Risk for nephroblastoma and neuroblastoma was two- to fourfold increased among children with RFC-1 polymorphisms. An increased four- to eightfold risk for neuroblastoma and nephroblastoma was seen when the child and maternal genotypes were combined.

CONCLUSION

Our results suggest that mother and child RFC-1 G80A genotypes play a role on the risk of neuroblastoma and nephroblastoma since this polymorphism may impair the intracellular levels of folate, through carrying fewer folate molecules to the cell interior, and thus, the intracellular concentration is not enough to maintain regular DNA synthesis and methylation pathways.

Replication and exploratory analysis of 24 candidate risk polymorphisms for neural tube defects

Background

Neural tube defects (NTDs), which are among the most common congenital malformations, are influenced by environmental and genetic factors. Low maternal folate is the strongest known contributing factor, making variants in genes in the folate metabolic pathway attractive candidates for NTD risk. Multiple studies have identified nominally significant allelic associations with NTDs. We tested whether associations detected in a large Irish cohort could be replicated in an independent population.

Methods

Replication tests of 24 nominally significant NTD associations were performed in racially/ethnically matched populations. Family-based tests of fifteen nominally significant single nucleotide polymorphisms (SNPs) were repeated in a cohort of NTD trios (530 cases and their parents) from the United Kingdom, and case–control tests of nine nominally significant SNPs were repeated in a cohort (190 cases, 941 controls) from New York State (NYS). Secondary hypotheses involved evaluating the latter set of nine SNPs for NTD association using alternate case–control models and NTD groupings in white, African American and Hispanic cohorts from NYS.

Results

Of the 24 SNPs tested for replication, ADA rs452159 and MTR rs10925260 were significantly associated with isolated NTDs. Of the secondary tests performed, ARID1A rs11247593 was associated with NTDs in whites, and ALDH1A2 rs7169289 was associated with isolated NTDs in African Americans.

Conclusions

We report a number of associations between SNP genotypes and neural tube defects. These associations were nominally significant before correction for multiple hypothesis testing. These corrections are highly conservative for association studies of untested hypotheses, and may be too conservative for replication studies. We therefore believe the true effect of these four nominally significant SNPs on NTD risk will be more definitively determined by further study in other populations, and eventual meta-analysis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-014-0102-9) contains supplementary material, which is available to authorized users.

Interaction between the SLC19A1 gene and maternal first trimester fever on offspring neural tube defects

BACKGROUND

Many studies have indicated that the reduced folate carrier gene (SLC19A1) is associated with an increased risk of neural tube defects (NTDs). However, the interaction between the SLC19A1 gene variant and maternal fever exposure and NTD risk remains unknown. The aim of this study was to investigate whether the risk for NTDs was influenced by the interactions between the SLC19A1 (rs1051266) variant and maternal first trimester fever.

METHODS

We investigated the potential interaction between maternal first trimester fever and maternal or offspring SLC19A1 polymorphism through a population-based case-control study. One hundred and four nuclear families with NTDs and 100 control families with nonmal newborns were included in the study. SLC19A1 polymorphism was determined using polymerase chain reaction-restricted fragment length polymorphism.

RESULTS

Mothers who had the GG/GA genotype and first trimester fever had an elevated risk of NTDs (adjusted odds ratio, 11.73; 95% confidence interval, 3.02-45.58) as compared to absence of maternal first trimester fever and AA genotype after adjusting for maternal education, paternal education, and age, and had a significant interactive coefficient (γ = 3.17) between maternal GG/GA genotype and first trimester fever. However, there was no interaction between offspring's GG/GA genotype and maternal first trimester fever (the interactive coefficient γ = 0.97) after adjusting for confounding factors.

CONCLUSION

Our findings suggested that the risk of NTDs was potentially influenced by a gene-environment interaction between maternal SLC19A1 rs1051266 GG/GA genotype and first trimester fever. Maternal GG/GA genotype may strengthen the effect of maternal fever exposure on NTD risk in this Chinese population.

Reduced folate carrier-1 G80a gene polymorphism is associated with neuroblastoma's development

Neuroblastoma is a malignant embryonal tumor of neural crest cells that give rise to the sympathetic nervous system, responsible for 10-70% of all cases of childhood cancer. Because of its early appearance, it has been suggested that risk factors active in the prenatal can be associated with the pathogenesis of neuroblastoma. The aim of this study was to investigate whether the genetic polymorphisms MTHFR C677T and A1298C, MTR A2756G, TYMS 2R/3R and SLC19A1 G80A, involved in folate metabolism, increase the risk of neuroblastoma in Brazilian children. This study comprised 31 Brazilian children (0-14 years old) diagnosed with neuroblastoma compared with 92 controls. Investigation of polymorphisms MTHFR C677T, MTR A2756G and SLC19A1 A80G was performed using PCR-RFLP, the TYMS 2R/3R using PCR and MTHFR A1298C using AS-PCR. The SLC19A1 A80A genotype was significantly associated with the development of neuroblastoma, compared with the control group (Williams G-Test = 0.0286; OR = 5.1667; 95% CI = 1.4481-18.4338; p = 0.0175). When analyzed together, the 80AG+AA genotypes showed a trend toward association (OR = 3.3033; 95% CI = 1.0586-10.3080; p = 0.0563). Our results suggest that individuals carriers of genotype AA for the SLC19A1 gene present risk for the development of neuroblastoma and possibly have difficulty in absorption of folic acid by the cells, and this may adversely affect the metabolism of folate causing genomic instability and promoting the development of cancer. This is the first retrospective/prospective study to examine the relationship between polymorphisms of folate pathway genes and risk of neuroblastoma.

Neural tube defects, folic acid and methylation

Neural tube defects (NTDs) are common complex congenital malformations resulting from failure of the neural tube closure during embryogenesis. It is established that folic acid supplementation decreases the prevalence of NTDs, which has led to national public health policies regarding folic acid. To date, animal studies have not provided sufficient information to establish the metabolic and/or genomic mechanism(s) underlying human folic acid responsiveness in NTDs. However, several lines of evidence suggest that not only folates but also choline, B12 and methylation metabolisms are involved in NTDs. Decreased B12 vitamin and increased total choline or homocysteine in maternal blood have been shown to be associated with increased NTDs risk. Several polymorphisms of genes involved in these pathways have also been implicated in risk of development of NTDs. This raises the question whether supplementation with B12 vitamin, betaine or other methylation donors in addition to folic acid periconceptional supplementation will further reduce NTD risk. The objective of this article is to review the role of methylation metabolism in the onset of neural tube defects.

Risk of congenital heart defects is influenced by genetic variation in folate metabolism

Genetic disturbances in folate metabolism may increase risk for congenital heart defects. We examined the association of heart defects with four polymorphisms in folate-related genes (methylenetetrahydrofolate reductase (MTHFR) c.677C.T, MTHFR c.1298A.C, methionine synthase reductase (MTRR) c.66A.G, and reduced folate carrier (SLC19A1) c.80A.G) in a case-control study of children (156 patients, 69 controls) and mothers of children with heart defects (181 patients, 65 controls), born before folic acid fortification. MTRR c.66A.G in children modified odds ratios for overall heart defects, specifically ventricular septal defect and aortic valve stenosis (p-value below 0.05). The 66GG and AG genotypes were associated with decreased odds ratios for heart defects (0.42, 95% confidence interval (0.18-0.97) and 0.39 (0.18-0.84), respectively). This overall association was driven by decreased risk for ventricular septal defect for 66GG and AG (odds ratio 0.32 (0.11-0.91) and 0.25 (0.09-0.65)) and decreased odds ratio for aortic valve stenosis for 66AG (0.27 (0.09-0.79)). The association of ventricular septal defect and 66AG remained significant after correction for multiple testing (p = 0.0044, multiple testing threshold p = 0.0125). Maternal MTHFR 1298AC genotype was associated with increased odds ratio for aortic valve stenosis (2.90 (1.22-6.86), p = 0.0157), but this association did not meet the higher multiple testing threshold. No association between MTHFR c.677C.T or SLC19A1 c.80A.G and heart defect risk was found. The influence of folate-related polymorphisms may be specific to certain types of heart defects; larger cohorts of mothers and children with distinct sub-classes are required to adequately address risk.

Influence of Methylenetetrahydrofolate Reductase C677T, A1298C, and G80A Polymorphisms on the Survival of Pediatric Patients with Acute Lymphoblastic Leukemia

The influence of genic polymorphisms involved in metabolism of chemotherapeutic agents as the methotrexate (MTX) has been studied mainly in acute lymphoblastic leukemia (ALL) of childhood. Advances in treatment may be attributed to identification of prognostic factors added to chemotherapy protocol. The aim of this study was to analyze the association of the C677T, A1298C, and G80A polymorphisms on MTHFR gene and on the overall survival of pediatric patients (n = 126) with lymphoblastic leukemia treated with MTX according to the Brazilian protocol in 187 months. The C677T and G80A polymorphisms were genotyped by PCR-RFLP and A1298C polymorphism by allele-specific PCR. We observed that ALL patients presented rate (dead/alive) of 0.36 for the 677CC genotype, corresponding also to lower overall survival (P = 0.0013); on the other hand, the 677TT genotype showed a better survival (98%). Thus, we believe that patients with 80AA genotype presented a small reduction in MTX plasma level, suggesting that ALL children, carrying the 80AA genotype, showed a high toxicity to MTX (P < 0.0001).

Methylenetetrahydrofolate reductase C677T polymorphism and susceptibility to cervical cancer and cervical intraepithelial neoplasia: a meta-analysis

Background

A number of studies have explored the association between methyl enetetrahydrofolate reductase (MTHFR) C677T polymorphism and susceptibility to cervical cancer and cervical intraepithelial neoplasia (CIN). However, results remained controversial. To address this gap, we decided to conduct a meta-analysis of all available published studies.

Methods

Electronic literature searches of the PubMed, EmBase and Medline databases were performed up to April 30, 2012. Fixed-effects or random-effects model was used to calculate the pooled ORs for different genetic models.

Results

A total of 12 case-control studies were ultimately identified. No statistical correlation was found between C677T variants and cervical cancer for the overall population. However, subgroup analyses on the White women pointed to a significant protective effect for individuals heterozygous or homozygous for the T-allele (for CT vs. CC: OR = 0.72, 95% CI 0.59–0.88; for TT vs. CC: OR = 0.69, 95% CI = 0.49–0.97; for CT+TT vs. CC: OR = 0.71, 95% CI 0.59–0.86). C677T variants were associated with neither combined nor stratified CIN among the overall population.

Conclusions

This meta-analysis suggests that White women with mutant C677T genotypes might have a lower risk of cervical cancer, yet lacking enough statistical robustness. Further investigations are needed to get more insight into the role of this polymorphism in cervical carcinogenesis.

Reduced folate carrier A80G polymorphism and susceptibility to neural tube defects: a meta-analysis

The reduced folate carrier (RFC1) plays a crucial role in mediating folate delivery into a variety of cells. RFC1 polymorphism (A80G) has been reported to be associated with increased risk of neural tube defects (NTDs). However, results derived from individually underpowered studies are conflicting. We performed a systematic search of MEDLINE and EMBASE databases and carried out a meta-analysis on the association between RFC1 polymorphism (A80G) and NTDs risk. Overall, a significant correlation between RFC1 A80G polymorphism and NTDs risk was found neither in infants nor in maternal (allele contrast in infants: OR(RE)=1.15, 95% CI: 0.92-1.45; allele contrast in mothers: OR(RE)=1.24, 95% CI: 0.98-1.56). The present meta-analysis failed to support a positive association between RFC1 A80G polymorphism and susceptibility to NTDs. It is important to realize, however, that socio-economic factors, and gene-environment and gene-gene interactions, could have influenced the outcome of our meta-analysis. For this reason, a relationship between the A80G polymorphism and NTD risk cannot be entirely discounted.

Maternal and infant gene-folate interactions and the risk of neural tube defects

Neural tube defects (NTDs) are common, serious malformations with a complex etiology that suggests involvement of both genetic and environmental factors. The authors evaluated maternal or offspring folate-related gene variants and interactions between the gene variants and maternal intake of folates on the risk of NTDs in their offspring. A case-control study was conducted on mothers and/or their fetuses and infants who were born in California from 1999 to 2003 with an NTD (cases n = 222, including 24 mother-infant pairs) or without a major malformation (controls n = 454, including 186 mother-infant pairs). Maternal intake of folates was assessed by food frequency questionnaire and genotyping was performed on samples from mothers and infants. For mothers in the lowest folate-intake group, risk of NTDs in offspring was significantly decreased for maternal MTHFR SNPs rs1476413, rs1801131, and rs1801133 (odds ratio [OR] = 0.55, 80% confidence interval [CI]: 0.20, 1.48; OR = 0.58, 80% CI: 0.24, 1.43; OR = 0.69, 80% CI: 0.41, 1.17, respectively), and TYMS SNPs rs502396 and rs699517 (OR = 0.91, 80% CI: 0.53, 1.56; OR = 0.70, 80% CI: 0.38, 1.29). A gene-only effect was observed for maternal SHMT1 SNP rs669340 (OR = 0.69, 95% CI: 0.49, 0.96). When there was low maternal folate intake, risk of NTDs was significantly increased for infant MTHFD1 SNPs rs2236224, rs2236225, and rs11627387 (OR = 1.58, 80% CI: 0.99, 2.51; OR = 1.53, 80% CI: 0.95, 2.47; OR = 4.25, 80% CI: 2.33, 7.75, respectively) and SHMT1 SNP rs12939757 (OR = 2.01, 80% CI: 1.20, 3.37), but decreased for TYMS SNP rs2847153 (OR = 0.73, 80% CI: 0.37, 1.45). Although power to detect interaction effects was low for this birth defects association study, the gene-folate interactions observed in this study represent preliminary findings that will be useful for informing future studies on the complex etiology of NTDs.

Genetic polymorphisms in metabolic and cellular transport pathway of methotrexate impact clinical outcome of methotrexate monotherapy in Japanese patients with rheumatoid arthritis

The aim of this study was to investigate the impact of genetic polymorphisms in the metabolic and cellular transport pathway of methotrexate (MTX) on the clinical outcome of MTX monotherapy in Japanese rheumatoid arthritis (RA) patients. Fifty-five patients were treated with MTX monotherapy at a dose of 4-10 mg/week. The total concentration of MTX-polyglutamates (MTX-PGs) was measured at steady-state in red blood cells (RBCs) by high performance liquid chromatography. The genotype at 16 polymorphic sites in 11 genes (ABCB1, ABCG2, ABCC2, RFC1, PCFT, SLCO1B1, MTHFR, GGH, ATIC, MTR, and MTRR) was analyzed. No significant association between the total concentration of MTX-PGs in RBCs and clinical outcome was found. However, patients with the ABCB1 3435TT genotype had a significantly lower mean disease activity score (DAS) 28 than did patients with the ABCB1 3435CC genotype (p = 0.02). Similarly, patients with the ABCB1 2677AA/AT/TT genotypes had a significantly lower mean DAS28 than did patients with the ABCB1 2677GG/GA/GT genotypes (p = 0.04). The patients with the MTHFR 1298AA genotype had a significantly lower mean DAS28 than those with the MTHFR 1298AC/CC genotypes (p = 0.04). In conclusion, the ABCB1 3435C>T, ABCB1 2677G>A/T, and MTHFR 1298A>C polymorphisms influenced the efficacy of MTX monotherapy.

The role of MTHFR and RFC1 polymorphisms on toxicity and outcome of adult patients with hematological malignancies treated with high-dose methotrexate followed by leucovorin rescue

PURPOSE

In the last years, the influence of different genes involved in metabolism of chemotherapeutic agents has been studied. Methotrexate (MTX) is a key compound of chemotherapeutic regimens used in the treatment of acute lymphoblastic leukemia (ALL), primary central nervous system lymphoma (PCNSL) and Burkitt's lymphomas (BL). This study aims to evaluate the role of MTHFR C677T and A1298C polymorphisms and G80A reduced folate carrier gene (RFC1) in a cohort of adult patients with lymphoproliferative malignancies submitted to high-dose MTX followed by leucovorin rescue.

METHODS

We performed the analysis of these polymorphisms on genomic DNA with RFLP-PCR.

RESULTS

Patients carrying MTHFR A1298C variant showed decreased hepatic and hematological toxicity (P = 0.03). Overall survival (OS) and progression-free survival (PFS) between homozygous wild-type and variant patients for the RFC1 G(80)A were significantly different (P = 0.035 and P = 0.02, respectively). A significant correlation between hematological toxicity and age (P = 0.003) was observed. There was no significant influence of MTHFR C677T genotype on toxicity, OS and PFS.

CONCLUSIONS

Leucovorin rescue given after high-dose MTX probably accounts for the lack of influence of C677T polymorphism. To better define a role of RFC1 polymorphism on patients outcome, it would be worthwhile to perform a study on intracellular MTX level and RFC1 substrate binding affinities in different genotypes.

Pharmacogenetics of drug-induced birth defects: what is known so far?

A literature review was performed to collect information on the role of pharmacogenetics in six proposed teratogenic mechanisms associated with drug use during pregnancy: folate antagonism, oxidative stress, angiotensin-converting enzyme inhibition and angiotensin II receptor antagonism, cyclooxygenase-1 and -2 inhibition, 5-hydroxytryptamine-reuptake inhibition and drug transporters in the placenta. Data on the direct relationship between pharmacogenetics and drug-induced birth defects were found for folate metabolism, oxidative stress caused by phenytoin exposure and drug transporters in the placenta. Although no specific data to support pharmacogenetic-related birth defects were found for the NSAIDs, paroxetine and fluoxetine, it might be expected that polymorphisms modify their teratogenic effects. The usually low prevalence of drug-induced malformations impedes the demonstration of the contribution of pharmacogenetics. Large-scale studies, preferably case-control studies, are needed.

Variation in folate pathway genes contributes to risk of congenital heart defects among individuals with Down syndrome

Cardiac abnormalities are one of the most common congenital defects observed in individuals with Down syndrome. Considerable research has implicated both folate deficiency and genetic variation in folate pathway genes with birth defects, including both congenital heart defects (CHD) and Down syndrome (DS). Here, we test variation in folate pathway genes for a role in the major DS-associated CHD atrioventricular septal defect (AVSD). In a group of 121 case families (mother, father, and proband with DS and AVSD) and 122 control families (mother, father, and proband with DS and no CHD), tag SNPs were genotyped in and around five folate pathway genes: 5,10-methylenetetrahyrdofolate reductase (MTHFR), methionine synthase (MTR), methionine synthase reductase (MTRR), cystathionine beta-synthase (CBS), and the reduced folate carrier (SLC19A1, RFC1). SLC19A1 was found to be associated with AVSD using a multilocus allele-sharing test. Individual SNP tests also showed nominally significant associations with odds ratios of between 1.34 and 3.78, depending on the SNP and genetic model. Interestingly, all marginally significant SNPs in SLC19A1 are in strong linkage disequilibrium (r(2)> or = 0.8) with the nonsynonymous coding SNP rs1051266 (c.80A>G), which has previously been associated with nonsyndromic cases of CHD. In addition to SLC19A1, the known functional polymorphism MTHFR c.1298A was over-transmitted to cases with AVSD (P=0.05) and under-transmitted to controls (P=0.02). We conclude, therefore, that disruption of the folate pathway contributes to the incidence of AVSD among individuals with DS.

Nonsyndromic cleft lip and palate: CRISPLD genes and the folate gene pathway connection

BACKGROUND

Nonsyndromic cleft lip with or without cleft palate (NSCLP) is a common birth defect that has a multifactorial etiology. Despite having substantial genetic liability, <15% of the genetic contribution to NSCLP has been delineated. In our efforts to dissect the genetics of NSCLP, we found that variation in the CRISPLD2 (cysteine-rich secretory protein LCCL domain containing 2) gene is associated with NSCLP and that the protein is expressed in the developing murine craniofacies. In addition, we found suggestive linkage of NSCLP (LOD > 1.0) to the chromosomal region on 8q13.2-21.13 that contains the CRISPLD1 gene. The protein products of both CRISPLD1 and CRISPLD2 contain more cysteine residues than comparably sized proteins. Interestingly, the folic acid pathway produces endogenous cysteines, and variation in genes in this pathway is associated with NSCLP. Based on these observations, we hypothesized that variation in CRISPLD1 contributes to NSCLP and that both CRISPLD genes interact with each other and genes in the folic acid pathway.

METHODS

Single nucleotide polymorphisms (SNPs) in CRISPLD1 were genotyped in our non-Hispanic white and Hispanic multiplex and simplex NSCLP families.

RESULTS

There was little evidence for a role of variation for CRISPLD1 alone in NSCLP. However, interactions were detected between CRISPLD1/CRISPLD2 SNPs and variation in folate pathway genes. Altered transmission of one CRISPLD1 SNP was detected in the NHW simplex families. Importantly, interactions were detected between SNPs in CRISPLD1 and CRISPLD2 (15 interactions, 0.0031 ≤p < 0.05).

CONCLUSION

These novel findings suggest that CRISPLD1 plays a role in NSCLP through the interaction with CRISPLD2 and folate pathway genes.

Gene-environment interactions, folate metabolism and the embryonic nervous system

Formation of brain and spinal cord requires the successful closure of neural ectoderm into an embryonic neural tube. Defects in this process result in anencephaly or spina bifida, which together constitute a leading cause of mortality and morbidity in children, affecting all ethnic and socioeconomic groups. The subject of intensive research for decades, neural tube defects (NTDs), are understood to arise from complex interactions of genes and environmental conditions, though systems-level details are still elusive. Despite the variety of underlying causes, a single intervention, folic acid supplementation given in the first gestational month, can measurably reduce the occurrence of NTDs in a population. Evidence for and the scope of gene-environment interactions in the genesis of NTDs is discussed. A systems-based approach is now possible toward studies of genetic and environmental influences underlying NTDs that will enable the assessment of individual risk and personalized optimization of prevention.

Concentrations of unmetabolized folic acid and primary folate forms in pregnant women at delivery and in umbilical cord blood

BACKGROUND

The importance of unmetabolized folic acid in maternal and fetal blood is not known.

OBJECTIVE

We investigated total folate, tetrahydrofolate (THF), 5-methyltetrahydrofolate (5-MTHF), formyl-THF, 5,10-methenylTHF, and folic acid concentrations in women and in umbilical cord blood at delivery.

DESIGN

The study included 87 pregnant women and 29 cord blood samples, including 24 mother-infant pairs. We measured serum concentrations of folate forms by using ultraperformance liquid chromatography-tandem mass spectrometry.

RESULTS

Pregnant women who received 400 μg folic acid daily (n = 25) had higher total folate (P = 0.041), 5-MTHF (P = 0.049), and formyl-THF (P < 0.001) concentrations and slightly higher THF (P = 0.093) concentrations than did nonsupplemented pregnant women (n = 61). We measured folic acid concentrations >0.20 nmol/L in 38 (44%) pregnant women and in 55% of the cord serum samples, but these measurements were not explained by maternal supplement use. Concentrations of folic acid were nonsignificantly higher in cord blood from supplemented women than in cord blood from nonsupplemented women (P = 0.154). Proportions of folic acid to total folate in cord serum did not differ according to maternal supplement usage (0.54% compared with 0.43% in supplemented and nonsupplemented women, respectively). Concentrations of folic acid did not differ between maternal and cord serum. However, folic acid constituted a significantly lower proportion of total folate in cord serum than in maternal serum.

CONCLUSIONS

We detected unmetabolized folic acid in more than one-half of cord blood samples. Folic acid (400 μg/d) supplied during pregnancy is not likely to accumulate in the fetus, in contrast to 5-MTHF and THF, which accumulate in the fetus.

The SLC19A1 80G>A polymorphism is not associated with male infertility

Previous studies have revealed that genetic factors may be involved in regulating folate turnover, e.g. methylenetetrahydrofolate reductase polymorphism in the development of male infertility. Folate transporter, encoded by the SLC19A1 gene, commonly referred to as reduced folate carrier (RFC) is a transmembrane protein, which transfers hydrophilic folates across the cell membrane. It was hypothesized that common polymorphism within the SLC19A1 gene (rs1051266:G>A, 80G>A) may alter RFC function. The aim of this study was to investigate a potential association between the SLC19A1 80G>A polymorphism and male infertility in a case-control study. The SLC19A1 80G>A polymorphism was determined by means of a polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) assay in 213 infertile Caucasian men and 226 ethnically matched controls. The distribution of SLC19A1 genotypes in the infertile men was as follows: GG 26.8%, GA 51.2%, AA 22.1% and in fertile men: GG 24.8%, GA 50.4%, AA 24.8%, and was comparable in the both the evaluated groups. Odds ratios (95% confidence interval, CI): 0.90 (0.59-1.38) and 0.88 (0.56-1.36) for dominant and recessive models remained non-significant, also after adjustment for age: 0.89 (0.57-1.37) and 0.80 (0.51-1.25), respectively. Our study demonstrated that polymorphism 80G>A of the SLC19A1 gene is not associated with male infertility.

Serological differences in folate/vitamin B12 in pregnancies affected by neural tube defects

BACKGROUND

Laboratory evidence is presented of significant associations between reduced maternal serum folate and vitamin B12 levels and neural tube birth defects (NTD) compared to referents.

METHODS

This was an incident case-control study. Cases of neural tube defects (including anencephaly and open spina bifida) diagnosed in residents within 100 miles of the US-Mexico border from January 1993 to October 2000 were eligible. Most cases were diagnosed in utero upon visits to clinics, obstetrical or genetic expert offices. Cases identified upon hospital admission or at delivery were also eligible. Cases identified after discharge were not. Controls were matched on geographic region, maternal age, race/ethnicity, gestational age, and type of health insurance (including none).

RESULTS

Three hundred eighty-two border area residents (107 cases and 275 individually matched controls) provided biological specimens. Median folate concentrations for case mothers were 36% lower than controls (9.8 ng/mL vs. 15 ng/mL). Maternal serum folate concentrations in quartiles above 9.5 ng/mL indicated significantly reduced risk (OR = 0.4, OR = 0.3, and OR = 0.2). Likewise, the risk for NTD decreased (OR = 0.4, OR = 0.3, and OR = 0.2) in quartiles of sera B12 concentrations above 246 pg/mL.

CONCLUSIONS

Physician attention is invited to significantly lower concentrations of serum folate and vitamin B12 in women with NTD-affected pregnancies. This study assayed sera samples from women while still pregnant or immediately after delivery. The confounding effect of reduced folate and B12 levels with other biological and chemical exposures will be addressed in subsequent communications.

Knockout of the folate transporter folt-1 causes germline and somatic defects in C. elegans

BACKGROUND

The C. elegans gene folt-1 is an ortholog of the human reduced folate carrier gene. The FOLT-1 protein has been shown to transport folate and to be involved in uptake of exogenous folate by worms. A knockout mutation of the gene, folt-1(ok1460), was shown to cause sterility, and here we investigate the source of the sterility and the effect of the folt-1 knockout on somatic function.

RESULTS

Our results show that folt-1(ok1460) knockout hermaphrodites have a substantially reduced germline, generate a small number of functional sperm, and only rarely produce a functional oocyte. We found no evidence of increased apoptosis in the germline of folt-1 knockout mutants, suggesting that germline proliferation is defective. While folt-1 knockout males are fertile, their rate of spermatogenesis was severely diminished, and the males were very poor maters. The mating defect is likely due to compromised metabolism and/or other somatic functions, as folt-1 knockout hermaphrodites displayed a shortened lifespan and elongated defecation intervals.

CONCLUSIONS

The FOLT-1 protein function affects both the soma and the germline. folt-1(ok1460) hermaphrodites suffer severely diminished lifespan and germline defects that result in sterility. Germline defects associated with folate deficiency appear widespread in animals, being found in humans, mice, fruit flies, and here, nematodes.

Pharmacogenetics in reproductive and perinatal medicine

The clinical application of pharmacogenetics has been well accepted by some medical specialties, but not all. The aim of this review is to discuss the current use of pharmacogenetics in reproductive and perinatal medicine and to highlight areas where pharmacogenetics may be able to help in the future to predict response to medicines in terms of efficacy and safety. This applies to drugs that are specific to pregnancy and reproduction, as well as drugs prescribed for the treatment of medical disorders in pregnancy. Our review points out the need for well-designed clinical studies on the efficacy and safety of medicines used in women of childbearing age in order to define the additional utility provided by pharmacogenetic testing.

Cleft lip and palate genetics and application in early embryological development

The development of the head involves the interaction of several cell populations and coordination of cell signalling pathways, which when disrupted can cause defects such as facial clefts. This review concentrates on genetic contributions to facial clefts with and without cleft palate (CP). An overview of early palatal development with emphasis on muscle and bone development is blended with the effects of environmental insults and known genetic mutations that impact human palatal development. An extensive table of known genes in syndromic and non-syndromic CP, with or without cleft lip (CL), is provided. We have also included some genes that have been identified in environmental risk factors for CP/L. We include primary and review references on this topic.

Association of reduced folate carrier gene polymorphism and maternal folic acid use with neural tube defects

This study was designed to investigate whether the risk for neural tube defects (NTDs) was associated with reduced folate carrier gene (RFC1 A80G) polymorphism and/or with the interaction between the RFC1 gene and maternal periconceptional use of folic acid. One hundred four nuclear families with NTDs and 100 non-malformed control families were sampled to investigate the potential interaction between maternal or the offspring's RFC1 (A80G) genotypes and the maternal periconceptional use of folic acid through a population-based case-control study. RFC1 (A80G) genotypes were detected using PCR-restricted fragment length polymorphism (PCR-RFLP). Mother who had the GG genotype and did not take folic acid had an elevated risk for NTDs (OR = 5.43, 95% CI = 1.68-18.28) as compared to the mother who had AA or GA genotype and took maternal periconceptional folic acid. The interactive coefficient was 1.12 between maternal GG genotype and the periconceptional folic acid non-use. The risk for having an infant with NTDs was 8.80 (95% CI = 2.83-28.69) for offspring with the GG genotype, as compared to the offspring with AA or GA genotype among the mothers who did not take folic acid supplements. The interactive coefficient was 1.45 for offspring with the GG genotype and without maternal periconceptional supplementation of folic acid. Our findings suggest that there is a potential gene-environment interaction on the risk of NTDs between maternal or offspring RFC1 GG genotype and maternal periconceptional intake of folic acid. The RFC1 is likely to be an important candidate gene in folate transportation and RFC1 GG genotype (A80G) may be associated with an increased risk for NTDs in this Chinese population.

Genetic basis of neural tube defects

Neural tube defects (NTDs) represent a common group of severe congenital malformations of the central nervous system. They result from failure of neural tube closure during early embryonic life. Their etiology is complex, involving environmental and genetic factors that interact to modulate the incidence and severity of the developing phenotype. Despite a long history of etiologic studies, the molecular and cellular pathogenic mechanisms underlining NTDs remain poorly understood. The major epidemiologic finding in NTDs is the protective effect of perinatal folic acid supplementation that reduces their risk by 60%-70%. Genetic studies in NTDs have focused mainly on folate-related genes and identified a few significant associations between variants in these genes and an increased risk for NTDs. The candidate gene approach investigating genes involved in neurulation and inferred from animal models has faced limited success in identifying major causative genes predisposing to NTDs. However, we are witnessing a rapid and impressive progress in understanding the genetic basis of NTDs, based mainly on the development of whole genome innovative technologies and the powerful tool of animal models.

Importance of gene-environment interactions in the etiology of selected birth defects

It is generally understood that both genetic and environmental factors contribute to the highly complex etiology of structural birth defects, including neural tube defects, oral clefts and congenital heart defects, by disrupting highly regulated embryonic developmental processes. The intrauterine environment of the developing embryo/fetus is determined by maternal factors such as health/disease status, lifestyle, medication, exposure to environmental teratogens, as well as the maternal genotype. Certain genetic characteristics of the embryo/fetus also predispose it to developmental abnormalities. Epidemiologic and animal studies conducted over the last few decades have suggested that the interplay between genes and environmental factors underlies the etiological heterogeneity of these defects. It is now widely believed that the study of gene-environment interactions will lead to better understanding of the biological mechanisms and pathological processes that contribute to the development of complex birth defects. It is only through such an understanding that more efficient measures will be developed to prevent these severe, costly and often deadly defects. In this review, we attempt to summarize the complex clinical and experimental literature on current hypotheses of interactions between several select environmental factors and those genetic pathways in which they are most likely to have significant modifying effects. These include maternal folate nutritional status, maternal diabetes/obesity-related conditions, and maternal exposure to selected medications and environmental contaminants. Our goal is to highlight the potential gene-environment interactions affecting early embryogenesis that deserve comprehensive study.

Individualization of thiopurine therapy: thiopurine S-methyltransferase and beyond

The metabolism of a given drug depends, not solely on a particular enzyme, but rather on a complex metabolic network. Thiopurine S-methyltransferase (TPMT) catalyzes the methylation, and thus deactivation, of 6-mercaptopurine, a thiopurine used in the treatment of acute lymphoblastic leukemia. Low TPMT activity has been associated with severe toxicity of 6-mercaptopurine. Determination of mutations in the TPMT gene before starting 6-mercaptopurine therapy constitutes a quick, simple and cost-effective strategy to individualize thiopurine dosing. However, TPMT phenotype-to-genotype correlation is not complete, indicating a need for identification of novel biomarkers. Based on our recent findings and reviewing seemingly unrelated literature reports we present a synthesis of the current understanding of factors that influence TPMT activity and consequently modulate responsiveness to thiopurine treatment. Identification and understanding of these factors is crucial for improving the efficacy and safety of acute lymphoblastic leukemia treatment.

The reduced folate carrier (SLC19A1) c.80G>A polymorphism is associated with red cell folate concentrations among women

Low folate status may be a consequence of suboptimal intake, transport or cellular utilization of folate and, together with elevated homocysteine, is a recognized risk factor or marker for several human pathologies. As folate transport across cell membranes is mediated in part by the reduced folate carrier (RFC1), variants within SLC19A1, the gene that encodes RFC1, may influence disease risk via an effect on folate and/or homocysteine levels. The present study was undertaken to assess the association between the SLC19A1 c.80G>A polymorphism and folate/homocysteine concentrations in healthy young adults from Northern Ireland. The SLC19A1 c.80G>A polymorphism was not strongly associated with either serum folate or homocysteine concentrations in either men or women. However, in women, but not in men, this polymorphism explained 5% of the variation in red blood cell (RBC) folate levels (P= 0.02). Relative to women with the SLC19A1 c.80GG genotype, women with the GA and AA genotypes had higher RBC folate concentrations. Consequently, compared to women with the SLC19A1 c.80GA and AA genotypes, women who are homozygous for the 80G allele may be at increased risk of having a child affected with a neural tube defect and of developing pathologies that have been associated with folate insufficiency, such as cardiovascular disease.

Investigation of inter-individual variability of the one-carbon folate pathway: a bioinformatic and genetic review

Genetic polymorphisms in the one-carbon folate pathway have been widely studied in association with a number of conditions. Most of the research has focused on the 677C>T polymorphism in the coding region of the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene. However, there are a total of 25 genes in this pathway coding for enzymes, transporters and receptors, which can be investigated using 267 tagging single nucleotide polymorphisms (SNPs); using SNP database (dbSNP), 38 non-synonymous SNPs with a minor allele frequency of >5% are present in these genes. Most of these variants have not been investigated in relation to disease or drug response phenotypes. In addition, their functional consequences are largely unknown. Prediction of the functional effect using six publicly available programs (PolyPhen, SIFT BLink, PMut, SNPs3D, I-Mutant2.0 and LS-SNP) was limited to functionally well-characterized SNPs such as MTHFR c.677C>T and c.1298A>C ranking low. Epigenetic modifications may also be important with some of these genes. In summary, to date, investigation of the one-carbon folate pathway genes has been limited. Future studies should aim for a more comprehensive assessment of this pathway, while further research is also required in determining the functional effects of these genetic variants.

The search for genetic polymorphisms in the homocysteine/folate pathway that contribute to the etiology of human neural tube defects

In this paper, we trace the history of current research into the genetic and biochemical mechanisms that underlie folate-preventable neural tube defects (NTDs). The inspired suggestion by Smithells that common vitamins might prevent NTDs ignited a decade of biochemical investigations-first exploring the nutritional and metabolic factors related to NTDs, then onto the hunt for NTD genes. Although NTDs were known to have a strong genetic component, the concept of common genetic variance being linked to disease risk was relatively novel in 1995, when the first folate-related polymorphism associated with NTDs was discovered. The realization that more genes must be involved started a rush to find polymorphic needles in genetic haystacks. Early efforts entailed the intellectually challenging and time-consuming task of identifying and analyzing candidate single nucleotide polymorphisms (SNPs) in folate pathway genes. Luckily, human genome research has developed rapidly, and the search for the genetic factors that contribute to the etiology of human NTDs has evolved to mirror the increased level of knowledge and data available on the human genome. Large-scale candidate gene analysis and genome-wide association studies are now readily available. With the technical hurdles removed, the remaining challenge is to gather a sample large enough to uncover the polymorphisms that contribute to NTD risk. In some respects the real work is beginning. Although moving forward is exciting, it is humbling that the most important result-prevention of NTDs by maternal folic acid supplementation-was achieved years ago, the direct result of Smithells' groundbreaking studies.

Folic acid, methylation and neural tube closure in humans

This review provides a brief description of folate use and folic acid metabolism in relation to neural tube defect (NTD) risk. First, a meta-analysis of reduction in NTD recurrence and occurrence risk with periconceptional folic acid supplementation is presented. Second, an overview of the complex folate metabolism is given. Third, SNPs for genes involved in folate and homocysteine metabolism that have been studied in relation to NTD riskare discussed. Fourth, the questions whether folate receptor autoantibodies or hampered methylation are mechanisms underlying NTDs are briefly discussed.

Insights into metabolic mechanisms underlying folate-responsive neural tube defects: a minireview

Neural tube defects (NTDs), including anencephaly and spina bifida, arise from the failure of neurulation during early embryonic development. Neural tube defects are common birth defects with a heterogenous and multifactorial etiology with interacting genetic and environmental risk factors. Although the mechanisms resulting in failure of neural tube closure are unknown, up to 70% of NTDs can be prevented by maternal folic acid supplementation. However, the metabolic mechanisms underlying the association between folic acid and NTD pathogenesis have not been identified. This review summarizes our current understanding of the mechanisms by which impairments in folate metabolism might ultimately lead to failure of neural tube closure, with an emphasis on untangling the relative contributions of nutritional deficiency and genetic risk factors to NTD pathogenesis.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

118 SNPs of folate-related genes and risks of spina bifida and conotruncal heart defects

Background

Folic acid taken in early pregnancy reduces risks for delivering offspring with several congenital anomalies. The mechanism by which folic acid reduces risk is unknown. Investigations into genetic variation that influences transport and metabolism of folate will help fill this data gap. We focused on 118 SNPs involved in folate transport and metabolism.

Methods

Using data from a California population-based registry, we investigated whether risks of spina bifida or conotruncal heart defects were influenced by 118 single nucleotide polymorphisms (SNPs) associated with the complex folate pathway. This case-control study included 259 infants with spina bifida and a random sample of 359 nonmalformed control infants born during 1983–86 or 1994–95. It also included 214 infants with conotruncal heart defects born during 1983–86. Infant genotyping was performed blinded to case or control status using a designed SNPlex assay. We examined single SNP effects for each of the 118 SNPs, as well as haplotypes, for each of the two outcomes.

Results

Few odds ratios (ORs) revealed sizable departures from 1.0. With respect to spina bifida, we observed ORs with 95% confidence intervals that did not include 1.0 for the following SNPs (heterozygous or homozygous) relative to the reference genotype: BHMT (rs3733890) OR = 1.8 (1.1–3.1), CBS (rs2851391) OR = 2.0 (1.2–3.1); CBS (rs234713) OR = 2.9 (1.3–6.7); MTHFD1 (rs2236224) OR = 1.7 (1.1–2.7); MTHFD1 (hcv11462908) OR = 0.2 (0–0.9); MTHFD2 (rs702465) OR = 0.6 (0.4–0.9); MTHFD2 (rs7571842) OR = 0.6 (0.4–0.9); MTHFR (rs1801133) OR = 2.0 (1.2–3.1); MTRR (rs162036) OR = 3.0 (1.5–5.9); MTRR (rs10380) OR = 3.4 (1.6–7.1); MTRR (rs1801394) OR = 0.7 (0.5–0.9); MTRR (rs9332) OR = 2.7 (1.3–5.3); TYMS (rs2847149) OR = 2.2 (1.4–3.5); TYMS (rs1001761) OR = 2.4 (1.5–3.8); and TYMS (rs502396) OR = 2.1 (1.3–3.3). However, multiple SNPs observed for a given gene showed evidence of linkage disequilibrium indicating that the observed SNPs were not individually contributing to risk. We did not observe any ORs with confidence intervals that did not include 1.0 for any of the studied SNPs with conotruncal heart defects. Haplotype reconstruction showed statistical evidence of nonrandom associations with TYMS, MTHFR, BHMT and MTR for spina bifida.

Conclusion

Our observations do not implicate a particular folate transport or metabolism gene to be strongly associated with risks for spina bifida or conotruncal defects.

High prevalence of orofacial clefts in Shanxi Province in northern China, 2003-2004

Shanxi Province in northern China has been identified as an area with the highest prevalence of neural tube defects in the world; however, few reports exist on the prevalence of orofacial clefts (OFC). We examined the prevalence of OFC and their association with selected characteristics. Data came from a population-based birth defects surveillance system in four counties of Shanxi Province. The system captures information on all live births, stillbirths of at least 20 weeks gestation, and pregnancy terminations at any gestational age after prenatal diagnosis of a birth defect. Out of 25,355 births in 2003-2004, 83 cases with orofacial clefts were identified resulting in a birth prevalence of 3.27 per 1,000. Other major external birth defects were present in 12 (14.5%) OFC cases. Cleft lip with palate (CLP), cleft lip alone (CL) and cleft palate alone (CP) accounted for 62.0%, 29.6% and 8.4% of OFC cases without additional external defects, respectively. The male to female ratio was 1.04 (95%CI: 0.67-1.60) for all OFC, 1.46 (95%CI: 0.80-2.68) for CLP, 1.23 (95%CI: 0.52-2.91) for CL, 0.46 (95%CI: 0.08-2.51) for CP without additional major external defects, and 0.31(95%CI: 0.08-1.13) for OFC with additional external defects. The prevalence of OFC without additional external defects was increased with decreased maternal age (P < 0.05) and increased maternal education (P < 0.05). The birth prevalence of OFC in Shanxi Province of northern China is among the highest worldwide. Further studies are required to define the factors associated with excess risk of clefts.

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

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

Relationships between gene polymorphisms of folate-related proteins and vitamins and metabolites in pregnant women and neonates

BACKGROUND

The methylenetetrahydrofolate reductase (MTHFR), glutamate carboxypeptidase II (GCPII) and reduced folate carrier (RFC1) gene polymorphisms were associated with folate status. We investigated the effects of these polymorphisms on serum folate (SF) and folate-related metabolites in mothers and their neonates.

METHODS

Cobalamin (Cbl), SF, total homocysteine (tHcy), methylmalonic acid (MMA), S-adenosylmethionine (SAM), and S-adenosylhomocysteine (SAH) were measured in 275 healthy women and their neonates. MTHFR C677T, GCPII C1561T and RFC1 A80G polymorphisms were determined by PCR-RFLP.

RESULTS

Maternal tHcy was affected individually by MTHFR C677T and GCPII C1561T polymorphisms and by combined genotypes MTHFR 677TT/GCPII 1561CC and MTHFR 677TT/RFC1 80AG. The MTHFR and RFC1 polymorphisms were not associated with variations in vitamins or SAM, SAH and MMA in neonates. Neonatal tHcy was predicted directly by maternal tHcy and inversely by maternal SF, neonatal Cbl and neonatal RFC1 80G allele (AG+GG genotypes). Maternal MMA and SAM/SAH were predicted by creatinine and Cbl, respectively. Neonatal MMA was predicted by maternal MMA and GCPII 1561T allele (CT+TT genotypes) and by neonatal Cbl.

CONCLUSIONS

Maternal tHcy was affected by MTHFR C677T, RFC1 A80G and GCPII C1561T polymorphisms. Maternal GCPII C1561T variant was associated with neonatal MMA. Neonatal RFC1 A80G polymorphism influenced tHcy in neonates.