Genetic variation of infant reduced folate carrier (A80G) and risk of orofacial defects and congenital heart defects in China

Increased susceptibility for nonsyndromic cleft lip with or without cleft palate by SLC19A1 80G>A genetic variation

BACKGROUND

The disruption of craniofacial developmental pathways during early embryogenesis can lead to conditions such as nonsyndromic cleft lip with or without cleft palate (NSCL/P). Several lines of evidence indicate that inadequate maternal nutrition causes low folate levels during the periconceptional period, resulting in NSCL/P. Although substantial research has been conducted on the possible link between SLC19A1 genetic variants and NSCL/P, the association between SLC19A1 80G>A (rs1051266) and NSCL/P remains unclear. In the present study, the associations of SLC19A1 80G>A with NSCL/P risk were assessed by calculating the pooled odds ratios (ORs) and 95% confidence intervals (CIs) by meta-analyses.

METHODS

Following the PRISMA guidelines, a meta-analysis was conducted on 10 studies assessing the NSCL/P risk associated with SLC19A1 80G>A variant. To ascertain the degree of relationship between the SLC19A1 80G>A genetic variant and the risk of NSCL/P, data were analyzed in allelic, recessive and dominant genetic models. CI of OR for each study and the pooled data were obtained. All statistical analyses were conducted utilizing the MetaGenyo software tool, which integrates the adjustment of P values for multiple testing through the Bonferroni method.

RESULTS

The pooled analysis showed that SLC19A1 80G>A variant significantly increased the NSCL/P risk in the allelic model (OR 1.39; 95% CI 1.00-1.92), recessive model (OR 1.37; 95% CI 1.03-1.82) and dominant models (OR 1.7; 95% CI 1.05-2.90). Publication bias was not observed.

CONCLUSIONS

This study supports that the SLC19A1 80G>A genetic variant is associated with NSCL/P risk.

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.

A Common Polymorphism in the MTHFD1 Gene Is a Modulator of Risk of Congenital Heart Disease

Several environmental and genetic factors may influence the risk of congenital heart defects (CHDs), which can have a substantial impact on pediatric morbidity and mortality. We investigated the association of polymorphisms in the genes of the folate and methionine pathways with CHDs using different strategies: a case–control, mother–child pair design, and a family-based association study. The polymorphism rs2236225 in the MTHFD1 was confirmed as an important modulator of CHD risk in both, whereas polymorphisms in MTRR, FPGS, and SLC19A1 were identified as risk factors in only one of the models. A strong synergistic effect on the development of CHDs was detected for MTHFD1 polymorphism and a lack of maternal folate supplementation during early pregnancy. A common polymorphism in the MTHFD1 is a genetic risk factor for the development of CHD, especially in the absence of folate supplementation in early pregnancy.

Association of maternal folate use and reduced folate carrier gene polymorphisms with the risk of congenital heart disease in offspring

Although it is generally recognized that genetic and environmental factors are associated with the risk of congenital heart disease (CHD), the mechanism remains largely uncertain. This study aimed to investigate the association of maternal folate use, the time when folate use was started, and polymorphisms of the reduced folate carrier (RFC1) gene with the risk of CHD in offspring of Chinese descent, which can help provide new insight into the etiology of folate-related birth defects. A case-control study of 683 mothers of CHD patients and 740 mothers of healthy children was performed. The present study showed that mothers who did not use folate were at a significantly increased risk of CHD (OR=2.04; 95% CI: 1.42-2.93). When compared with those who started using folate prior to conception, mothers who started using folate from the first trimester of pregnancy (OR=1.90; 95% CI: 1.43-2.54) or from the second trimester of pregnancy (OR=8.92; 95% CI: 4.20-18.97) had a significantly higher risk of CHD. Maternal RFC1 gene polymorphisms at rs2236484 (AG vs AA: OR=1.79 [95% CI: 1.33-2.39]; GG vs AA: OR=1.64 [95% CI: 1.15-2.35]) and rs2330183 (CT vs CC: OR=1.54 [95% CI: 1.14-2.09]) were also significantly associated with CHD risk. Additionally, the risk of CHD was significantly decreased among mothers who had variant genotypes but used folate when compared with those who had variant genotypes and did not use folate.Conclusion: In those of Chinese descent, maternal folate use and the time when use started are significantly associated with the risk of CHD in offspring. Furthermore, maternal folate supplementation may help to offset some of the risks of CHD in offspring due to maternal RFC1 genetic variants. What is Known: • Folate use could help prevent CHD, but the relationship between the time when folate use is started and CHD has not received sufficient attention. • Studies have assessed the associations of folate metabolism-related genes with CHD, but genes involved in cellular transportation of folate, such as the RFC1 gene, have not garnered enough attention. What is New: • In those of Chinese descents, the time when folate use is started is significantly associated with the risk of CHD in offspring. • Maternal RFC1 polymorphisms were significantly associated with the risk of CHD. • Folate supplementation may help to offset some risks of CHD due to RFC1 genetic variants.

Orofacial Clefts in High Prevalence Area of Birth Defects - Five Counties, Shanxi Province, China, 2000-2020

WHAT IS ALREADY KNOWN ON THIS TOPIC?

The prevalence of structural birth defects, especially neural tube defects, decreased after national folic acid (FA) supplementation initiation.

WHAT IS ADDED BY THIS REPORT?

The prevalence of orofacial clefts (OFCs) in five counties of Shanxi Province in northern China, including most subtypes except cleft palate, showed a downward trend in the past two decades. In this study, pre-perinatal prevalence increased due to earlier detection.

WHAT ARE THE IMPLICATIONS FOR PUBLIC HEALTH PRACTICE?

Periconceptional supplementation with FA may contribute to the decline in OFCs prevalence, while the effect on the OFCs subtype needs further investigation. Continuing to advocate for earlier supplementation (3 months before conception) and increased supplementation frequency (daily consumption) could promote further reduction in the prevalence of OFCs. Specific surveillance of this effect in the era of universal three-child policy is warranted.

The Roles of Reduced Folate Carrier-1 (RFC1) A80G (rs1051266) Polymorphism in Congenital Heart Disease: A Meta-Analysis

Background

We performed the present study to better elucidate the correlation of reduced folate carrier-1 (RFC1) A80G (rs1051266) polymorphism with the risk of congenital heart disease (CHD).

Material/Methods

According to the designed search strategy, a systematic literature search was performed through the PubMed, Cochrane Library, Web of Science, EMBASE, CNKI, VIP, and Wan Fang databases to collect published case-control studies on the correlation between RFC1 A80G polymorphism and CHD. All relevant studies up to October 1, 2019 were identified. The odds ratio (OR) and 95% confidence interval (CI) of the genotype distribution were used as the effect indicators.

Results

A total of 6 eligible studies was finally included in our meta-analysis, including 724 children with CHD, 760 healthy children, 258 mothers of the children with CHD, and 334 mothers of healthy control children. The meta-analysis revealed that for fetal analysis, only in the heterozygous model (GA vs GG, OR=1.36, 95% CI [1.06, 1.75], P=0.02) was RFC1 A80G polymorphism associated with risk of CHD. In maternal analysis, 3 genetic models of RFC1 A80G polymorphism increased the risk of CHD: the allelic model (A vs G, OR=1.36, 95% CI [1.07, 1.71], P=0.01), the homozygote model (AA vs GG, OR=2.99, 95%CI [1.06, 8.41], P=0.04), and the dominance model (GA+AA vs GG, OR=1.53, 95%CI [1.08, 2.16], P=0.02).

Conclusions

The maternal RFC1 A80G polymorphism has a strong correlation with CHD. Compared with the G allele, the A allele increases the risk of CHD by 0.36-fold.

Association between RFC1 A80G polymorphism and the susceptibility to nonsyndromic cleft lip with or without cleft palate: a meta-analysis

Background

Reduced folate carrier 1 (RFC1) gene is a candidate for susceptibility to nonsyndromic cleft lip with or without cleft palate (NSCL/P). Association between RFC1 A80G polymorphism and NSCL/P have been studied. The published results are conflicting.

Methods

A meta-analysis of the association between RFC1 A80G polymorphism and NSCL/P was carried out using Stata13.0. A systematic literature search was performed through the PubMed, EMBASE, the Cochrane Library, Web of Science, ScienceDirect, EBSCOhost, China Biology Medicine databases, China National Knowledge Infrastructure and the Wanfang databases. All relevant studies up to 9 September 2019 were identified.

Results

Nine case-control studies including 4,229 total participants (1,334 NSCL/P children, 1,515 healthy children, 656 mothers of the NSCL/P children, and 724 mothers of healthy control children) were included in this study. The meta-analysis revealed that two genetic models of RFC1 A80G polymorphism in NSCL/P children increased risk of NSCL/P: the homozygote model (GG vs. AA, OR =2.346, 95% CI: 1.127-4.884) and the recessive model (GG vs. AG + AA, OR =1.503, 95% CI: 1.049-2.152). Further sensitivity analysis indicated that the frequency of G allele and GG genotype in NSCL/P children was significantly higher than those in the control. However, there was no significant statistical differences after Bonferroni correction. Subgroup analyses indicated the presence of the association of all the model with NSCL/P risk in the Indian children. RFC1 A80G polymorphism in the maternal population of NSCL/P children was not significantly associated with children NSCL/P.

Conclusions

The RFC1 A80G polymorphism was a candidate for susceptibility to NSCL/P in the Indian pediatric population. More studies with larger samples are necessary to reach more conclusive outcomes.

Folate and choline absorption and uptake: Their role in fetal development

SCOPE

In this review, we attempt to assess how choline and folate transporters affect fetal development. We focus on how the expression of these transporters in response to choline and folate intake affects transport effectiveness. We additionally describe allelic variants of the genes encoding these transporters and their phenotypic effects.

METHODS AND RESULTS

We made an extensive review of recent articles describing role of choline and folate - with particularly emphasize on their transporters - in fetal development. Folate and choline are necessary for the proper functioning of the cell and body. During pregnancy, the requirements of these nutrients increase because of elevated maternal demand and the rapid division of fetal cells. The concentrations of folate and choline in cells depend on food intake, the absorption of nutrients, and the cellular transport system, which is tissue-specific and developmentally regulated. Relatively few studies have investigated the role of choline transporters in fetal development.

CONCLUSIONS

In this review we show relations between functioning of folate and choline transporters and fetal development.

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.

Serum and red-blood-cell folate demonstrate differential associations with BMI in pregnant women

Objective

To examine the association between BMI and folate concentrations in serum and red blood cells (RBC) in pregnant women.

Design

A cross-sectional comparison of folate concentrations in serum and RBC sampled simultaneously from the same individual.

Setting

The Ottawa Hospital and Kingston General Hospital, Ontario, Canada.

Subjects

Pregnant women recruited between 12 and 20 weeks of gestation.

Results

A total of 869 pregnant women recruited from April 2008 to April 2009 were included in the final analysis. Serum folate was inversely associated and RBC folate positively associated with BMI, after adjusting for folic acid supplementation, age, gestational age at blood sample collection, race, maternal education, annual income, smoking and MTHFR 677C→T genotype. In stratified analyses, this differential association was significant in women with the MTHFR CC variant. In women with the CT and TT variants, the differential associations were in the same direction but not significant. Folic acid supplementation during pregnancy did not alter the differential association of BMI with serum and RBC folate concentration. This indicates that the current RBC folate cut-off approach for assessing risk of neural tube defects in obese women may be limited.

Conclusions

BMI is inversely associated with serum folate and positively associated with RBC folate in pregnant women, especially for those with the MTHFR CC variant.

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 association between RFC1 G80A polymorphism and cancer susceptibility: Evidence from 33 studies

Aberrant folate metabolism is closely related to tumorigenesis. Genetic variations in the Reduced folate carrier 1 (RFC1) may alter the progress of folate metabolism, and thereby cause the initiation and progress of the cancer. Considerable studies have performed to investigate the association between RFC1 G80A (rs1051266) polymorphism and cancer susceptibility, but the conclusions were conflicting. Therefore, we conducted a meta-analysis to reevaluate the association of RFC1 G80A polymorphism with cancer risk. PubMed and EMBASE were searched for eligible studies. The association of RFC1 G80A polymorphism and cancer risk was evaluated by the pooled odds ratios (ORs) and corresponding 95% confidence intervals (CIs). The significant association was found between RFC1 G80A polymorphism and hematological malignance susceptibility (A vs. G: OR=1.11, 95%CI=1.003-1.23, P=0.045; GA vs. GG: OR=1.18, 95%CI=1.06-1.31, P=0.002; AA+GA vs. GG: OR=1.18, 95%CI=1.07-1.29, P=0.001). Stratified analysis by ethnicity indicated that the association became more prominent among Caucasians (GA vs. GG: OR=1.28, 95%CI=1.12-1.45, P<0.001; AA+GA vs. GG: OR=1.21, 95%CI=1.08-1.36, P=0.001). In term of the cancer type, this polymorphism significantly increased the risk of acute lymphoblast leukemia (GA vs. GG: OR=1.13, 95%CI=1.001-1.28, P=0.048; AA+GA vs. GG: OR=1.28, 95%CI=1.13-1.46, P<0.001) and acute myeloid leukemia (GA vs. GG: OR=2.57, 95%CI=1.37-4.85, P=0.003). No significant association between RFC1 G80A polymorphism and overall solid cancer risk was observed, but a protective association with digestive cancer risk was found (GA vs. GG: OR=0.89, 95%CI= 0.81-0.99, P=0.030). The comprehensive meta-analysis encouraged the notion that RFC1 G80A polymorphism may play an important role in hematopoietic system malignance. These findings need further validation in the large multicenter investigations.

Association of reduced folate carrier-1 (RFC-1) polymorphisms with ischemic stroke and silent brain infarction

Stroke is the second leading cause of death in the world and in South Korea. Ischemic stroke and silent brain infarction (SBI) are complex, multifactorial diseases influenced by multiple genetic and environmental factors. Moderately elevated plasma homocysteine levels are a major risk factor for vascular diseases, including stroke and SBI. Folate and vitamin B12 are important regulators of homocysteine metabolism. Reduced folate carrier (RFC), a bidirectional anion exchanger, mediates folate delivery to a variety of cells. We selected three known RFC-1 polymorphisms (-43C>T, 80A>G, 696T>C) and investigated their relationship to cerebral infarction in the Korean population. We used the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method to analyze associations between the three RFC-1 polymorphisms, disease status, and folate and homocysteine levels in 584 ischemic stroke patients, 353 SBI patients, and 505 control subjects. The frequencies of the RFC-1 -43TT, 80GG, and 696CC genotypes differed significantly between the stroke and control groups. The RFC-1 80A>G substitution was also associated with small artery occlusion and SBI. In a gene-environment analysis, the RFC-1 -43C>T, 80A>G, and 696T>C polymorphisms in the ischemic stroke group had combined effects with all environmental factors. In summary, we found that the RFC-1 -43C>T, 80A>G, and 696T>C polymorphisms may be risk factors for ischemic stroke.

RFC1 and non-syndromic cleft lip with or without cleft palate: an association based study in Italy

The molecular basis of orofacial development is largely unknown and needs to be unravelled. Non-syndromic cleft lip with or without cleft palate (NSCL/P) is the most common craniofacial malformation, with an incidence of about 1/700 live births, although variable according to ethnicity. Being a multifactorial disease, it arises as a result of an interplay between genetic and environmental factors. Several approaches have been developed to identify susceptibility genes. Genes belonging to the folate/homocysteine pathway are attracting increasing interest because folate supplementation before and during early pregnancy can reduce the risk of NSCL/P. We performed a family based association study in order to assess if a genetic variant of RFC1 could be involved in NSCL/P onset. We genotyped 404 unrelated probands and their relatives for three biallelic polymorphic variants (rs1051266, rs4818789 and rs3788205), that were selected because they produced conflicting results on previous investigations. Evidence of association was found between the investigated polymorphisms and NSCL/P in our sample of the Italian population, albeit with weak significance levels. Results from this investigation provided a support of previous studies suggesting a role of RFC1 in NSCL/P aetiology, reinforcing the concept that genetic predisposition to NSCL/P varies enormously within different ethnic groups.

Relationship between reduced folate carrier gene polymorphism and non-syndromic cleft lip and palate in Indian population

OBJECTIVE

Folate metabolism involves absorption, transport, modifications and interconversions of folates. The reduced folate carrier does not participate directly in folate metabolism but plays a major role in intracellular transport of metabolically active 5-methyltetrahydrofolate and maintains the intracellular concentrations of folate. The purpose of this study was to identify the prevalence of reduced folate carrier 1 (RFC1) A80G polymorphism and to further delineate its association with non-syndromic cleft lip and palate (NSCLP) in a south Indian population.

METHODS

In the present case-control study, we studied RFC1 gene A80G polymorphism to evaluate its impact on NSCLP risk in south Indian population. Blood samples of 142 cases with NSCLP and 141 controls were collected and genotyped using PCR-RFLP.

RESULTS

The genotype distribution in the control group followed Hardy-Weinberg equilibrium (p = 0.633). The G allele frequency of cases was 64.8% (184/284) and was significantly lower than that found in the control group 56.4% (160/282). The genotype distributions between NSCLP cases and controls was not significantly different (p = 0.131). The allelic model significantly increased the risk of NSCLP (G versus A; OR = 1.40; 95% CI: 1.00-1.97; p = 0.050). In subgroup analysis, the A80G variant showed significant association for the CLP group in dominant and allelic models.

CONCLUSIONS

Altogether, our findings support the hypothesis that RFC1 A80G variant may contribute to NSCLP susceptibility in a south Indian population.

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.

Oral cleft prevention program (OCPP)

Background

Oral clefts are one of the most common birth defects with significant medical, psychosocial, and economic ramifications. Oral clefts have a complex etiology with genetic and environmental risk factors. There are suggestive results for decreased risks of cleft occurrence and recurrence with folic acid supplements taken at preconception and during pregnancy with a stronger evidence for higher than lower doses in preventing recurrence. Yet previous studies have suffered from considerable design limitations particularly non-randomization into treatment. There is also well-documented effectiveness for folic acid in preventing neural tube defect occurrence at 0.4 mg and recurrence with 4 mg. Given the substantial burden of clefting on the individual and the family and the supportive data for the effectiveness of folic acid supplementation as well as its low cost, a randomized clinical trial of the effectiveness of high versus low dose folic acid for prevention of cleft recurrence is warranted.

Methods/design

This study will assess the effect of 4 mg and 0.4 mg doses of folic acid, taken on a daily basis during preconception and up to 3 months of pregnancy by women who are at risk of having a child with nonsyndromic cleft lip with/without palate (NSCL/P), on the recurrence of NSCL/P. The total sample will include about 6,000 women (that either have NSCL/P or that have at least one child with NSCL/P) randomly assigned to the 4 mg and the 0.4 mg folic acid study groups. The study will also compare the recurrence rates of NSCL/P in the total sample of subjects, as well as the two study groups (4mg, 0.4 mg) to that of a historical control group.

The study has been approved by IRBs (ethics committees) of all involved sites. Results will be disseminated through publications and presentations at scientific meetings.

Discussion

The costs related to oral clefts are high, including long term psychological and socio-economic effects. This study provides an opportunity for huge savings in not only money but the overall quality of life. This may help establish more specific clinical guidelines for oral cleft prevention so that the intervention can be better tailored for at-risk women.

ClinicalTrials.gov Identifier

NCT00397917

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Maternal Mthfd1 disruption impairs fetal growth but does not cause neural tube defects in mice

BACKGROUND

MTHFD1 encodes C1-tetrahydrofolate synthase, which is a folate-dependent enzyme that catalyzes the formation and interconversion of folate-activated one-carbon groups for nucleotide biosynthesis and cellular methylation. A polymorphism in MTHFD1 (1958G→A) impairs enzymatic activity and is associated with increased risk of adverse pregnancy outcomes, but the mechanisms are unknown.

OBJECTIVE

The objective of this study was to determine whether disruption of the embryonic or maternal Mthfd1 gene or both interacts with impaired folate and choline status to affect neural tube closure, fetal growth, and fertility in mice and to investigate the underlying metabolic disruptions.

DESIGN

Dams with a gene-trapped (gt) allele in Mthfd1 and wild-type dams were fed a control or folate- and choline-deficient AIN93G diet (Dyets Inc). Litters were examined for gross morphologic defects, crown-rump length, and resorptions. Folate status and amounts of folate-related metabolites were determined in pregnant dams.

RESULTS

Reduced folate and choline status resulted in severe fetal growth restriction (FGR) and impaired fertility in litters harvested from Mthfd1(gt/+) dams, but embryonic Mthfd1(gt/+) genotype did not affect fetal growth. Gestational supplementation of Mthfd1(gt/+) dams with hypoxanthine increased FGR frequency and caused occasional neural tube defects (NTDs) in Mthfd1(gt/+) embryos. Mthfd1(gt/+) dams exhibited lower red blood cell folate and plasma methionine concentrations than did wild-type dams.

CONCLUSIONS

Maternal Mthfd1(gt/+) genotype impairs fetal growth but does not cause NTDs when dams are maintained on a folate- and choline-deficient diet. Mthfd1(gt/+) mice exhibit a spectrum of adverse reproductive outcomes previously attributed to the human MTHFD1 1958G→A polymorphism. Mthfd1 heterozygosity impairs folate status in pregnant mice but does not significantly affect homocysteine metabolism.

Lack of maternal folic acid supplementation is associated with heart defects in Down syndrome: a report from the National Down Syndrome Project

BACKGROUND

Maternal folic acid supplementation has been associated with a reduced risk for neural tube defects and may be associated with a reduced risk for congenital heart defects and other birth defects. Individuals with Down syndrome are at high risk for congenital heart defects and have been shown to have abnormal folate metabolism.

METHODS

As part of the population-based case-control National Down Syndrome Project, 1011 mothers of infants with Down syndrome reported their use of supplements containing folic acid. These data were used to determine whether a lack of periconceptional maternal folic acid supplementation is associated with congenital heart defects in Down syndrome. We used logistic regression to test the relationship between maternal folic acid supplementation and the frequency of specific heart defects correcting for maternal race or ethnicity, proband sex, maternal use of alcohol and cigarettes, and maternal age at conception.

RESULTS

Lack of maternal folic acid supplementation was more frequent among infants with Down syndrome and atrioventricular septal defects (odds ratio [OR], 1.69; 95% confidence interval [CI], 1.08-2.63; p = 0.011) or atrial septal defects (OR, 1.69; 95% CI, 1.11-2.58; p = 0.007) than among infants with Down syndrome and no heart defect. Preliminary evidence suggests that the patterns of association differ by race or ethnicity and sex of the proband. There was no statistically significant association with ventricular septal defects (OR, 1.26; 95% CI, 0.85-1.87; p = 0.124).

CONCLUSIONS

Our results suggest that lack of maternal folic acid supplementation is associated with septal defects in infants with Down syndrome. Birth Defects Research (Part A), 2011. © 2011 Wiley-Liss, Inc.

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.

NAT1, NOS3, and TYMS genotypes and the risk of conotruncal cardiac defects

BACKGROUND

Although congenital heart defects (CHDs) are a common and serious group of birth defects, relatively little is known about the causes of these conditions, and there are no established prevention strategies. There is, however, evidence suggesting that the risk of CHDs in general, and conotruncal and related defects (CTRDs) in particular, may be associated with maternal folate status and genetic variants of folate-related genes. Although several folate-related genes have been studied as they relate to CHDs and CTRDs (e.g., MTHFR), others have not been adequately assessed.

METHODS

Case-parent triads were examined using log-linear analyses to assess the associations between CTRDs and both the genotype inherited by the case and the maternal genotype for the following variants: NAT1 1095C>A, NOS3 894G>T, and TYMS 1494del6. Subgroup analyses were also conducted among cases with classic conotruncal defects and cases with normally related great arteries.

RESULTS

The results provided little evidence that CTRD risk was associated with the genotype inherited by the case for any of the analyzed variants. However, our results suggest that CTRD risk may be associated with the maternal genotype for NOS3 894G>T (p = 0.024 in the subgroup with normally related great arteries) and TYMS 1494del6 (p = 0.048 in the subgroup with classic conotruncal defects). However, these results were not significant after correcting for multiple comparisons.

CONCLUSION

This study provides further evidence that CTRD risk may be related to variation within folate-pathway genes and suggests that these associations are, at least in part, mediated through the maternal genotype.

Folic acid and orofacial clefts: a review of the evidence

Orofacial clefts are common and burdensome birth defects with a complex genetic and environmental etiology. The contribution of nutritional factors and supplements to the etiology of orofacial clefts has long been theorized and studied. Multiple studies have evaluated the role of folic acid in the occurrence and recurrence of orofacial clefts, using observational and non-randomized interventional designs. While preventive effects of folic acid on orofacial clefts are commonly reported, the evidence remains generally inconsistent. This paper reviews the findings of the main studies of the effects of folic acid on orofacial clefts, summarizes study limitations, and discusses research needs with a focus on studying the effects of high dosage folic acid on the recurrence of oral clefts using a randomized clinical trial design. The role of folic acid in the prevention of neural tube defects is also briefly summarized and discussed as a reference model for orofacial clefts.

Genetic factors in non-syndromic congenital heart malformations

The genetic defect in most patients with non-syndromic congenital heart malformations (CHM) is unknown, although more than 40 different genes have already been implicated. Only a minority of CHM seems to be due to monogenetic mutations, and the majority occurs sporadically. The multifactorial inheritance hypothesis of common diseases suggesting that the cumulative effect of multiple genetic and environmental risk factors leads to disease, might also apply for CHM. We review here the monogenic disease genes with high-penetrance mutations, susceptibility genes with reduced-penetrance mutations, and somatic mutations implicated in non-syndromic CHM.

Variants of folate metabolism genes and risk of left-sided cardiac defects

BACKGROUND

Congenital heart defects (CHDs) are the most common, serious group of birth defects. Although relatively little is known about the causes of these conditions and there are no established prevention strategies, evidence suggests that the risk of CHDs may be related to maternal folate status as well as genetic variants in folate-related genes. Efforts to establish the relationships between these factors and CHD risk have, however, been hampered by a number of factors, including small study sample sizes and phenotypic heterogeneity.

METHODS

The present study examined the relationship between nine genetic variants in eight folate-related genes and a relatively homogeneous group of left-sided cardiac defects in a cohort of 386 case-parent triads. Log-linear analyses were used to assess both maternal and inherited genetic effects.

RESULTS

Analyses of the study data provided marginal evidence that the maternal MTR A2756G (unadjusted p = 0.01) and the inherited BHMT G742A (unadjusted p = 0.06) genotypes influence the risk of this subset of CHDs. However, neither association achieved significance when the false-discovery rate was controlled at 0.05.

CONCLUSIONS

These results, which are based on the largest study sample and most comprehensive assessment of the relationship between left-sided cardiac defects and folate-related genes reported to date, provide little evidence that this subset of CHDs is folate related. However, even larger studies and more comprehensive evaluations of the folate pathway genes are required to fully explore the relationship between folate and left-sided cardiac defects.

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.

The MTHFD1 p.Arg653Gln variant alters enzyme function and increases risk for congenital heart defects

Methylenetetrahydrofolate dehydrogenase)methenyltetrahydrofolate cyclohydrolase)formyltetrahydrofolate synthetase (MTHFD1) is a trifunctional enzyme that interconverts tetrahydrofolate (THF) derivatives for nucleotide synthesis. A common variant in MTHFD1, p.Arg653Gln (c.1958G>A), may increase the risk for neural tube defects (NTD). To examine the biological impact of this variant on MTHFD1 function, we measured enzyme activity and stability in vitro and assessed substrate flux in transfected mammalian cells. The purified Arg653Gln enzyme has normal substrate affinity but a 36% reduction in half)life at 42 degrees C. Thermolability is reduced by magnesium adenosine triphosphate and eliminated by the substrate analog folate pentaglutamate, suggesting that folate status may modulate impact of the variant. The mutation reduces the metabolic activity of MTHFD1 within cells: formate incorporation into DNA in murine Mthfd1 knockout cells transfected with Arg653Gln is reduced by 26%+/-7.7% (P<0.05), compared to cells transfected with wild)type protein, indicating a disruption of de novo purine synthesis. We assessed the impact of the variant on risk for congenital heart defects (CHD) in a cohort of Quebec children (158 cases, 110 controls) and mothers of children with heart defects (199 cases, 105 controls). The 653QQ genotype in children is associated with increased risk for heart defects (odds ratio [OR], 2.11; 95% confidence interval [CI], 1.01-4.42), particularly Tetralogy of Fallot (OR, 3.60; 95% CI, 1.38-9.42) and aortic stenosis (OR, 3.13; 95% CI, 1.13-8.66). There was no effect of maternal genotype. Our results indicate that the Arg653Gln polymorphism decreases enzyme stability and increases risk for CHD. Further evaluation of this polymorphism in folate)related disorders and its potential interaction with folate status is warranted.

Variants of folate metabolism genes and the risk of conotruncal cardiac defects

BACKGROUND

Although congenital heart defects (CHD) are the most common and serious group of birth defects, relatively little is known about the causes of these conditions and there are no established prevention strategies. There is evidence suggesting that the risk of CHD in general, and conotruncal and ventricular septal defects in particular, may be related to maternal folate status as well as genetic variants in folate-related genes. However, efforts to establish the relationships between these factors and CHD risk have been hampered by a number of factors including small study sample sizes and phenotypic heterogeneity.

METHODS AND RESULTS

The present study examined the relationships between variation in 9 folate-related genes and a subset of CHD phenotypes (ie, conotruncal defects, perimembranous and malalignment type ventricular septal defects, and isolated aortic arch anomalies) in a cohort of >700 case-parent triads. Further, both maternal and embryonic genetic effects were considered. Analyses of the study data confirmed an earlier reported association between embryonic genotype for MTHFR A1298C and disease risk (unadjusted P=0.002).

CONCLUSIONS

These results represent the most comprehensive and powerful analysis of the relationship between CHD and folate-related genes reported to date, and provide additional evidence that, similar to neural tube defects, this subset of CHD is folate related.

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.

Embryonic development in the reduced folate carrier knockout mouse is modulated by maternal folate supplementation

BACKGROUND

The reduced folate carrier (RFC1) is a ubiquitously expressed integral membrane protein that mediates delivery of 5-methyltetrahydrofolate into mammalian cells. In this study, embryonic/fetal development is characterized in an RFC1 knockout mouse model in which pregnant dams receive different levels of folate supplementation.

METHODS

RFC1(+/-) males were mated to RFC1(+/-) females, and pregnant dams were treated with vehicle (control) or folic acid (25 or 50 mg/kg) by daily subcutaneous injection (0.1 mL/10 g bwt), beginning on E0.5 and continuing throughout gestation until the time of sacrifice.

RESULTS

Without maternal folate supplementation, RFC1 nullizygous embryos die shortly postimplantation. Supplementation of pregnant dams with 25 mg/kg/day folic acid prolongs survival of mutant embryos until E9.5-E10.5, but they are developmentally delayed relative to wild-type littermates, display a marked absence of erythropoiesis, severe neural tube and limb bud defects, and failure of chorioallantoic fusion. Fgfr2 protein levels are significantly reduced or absent in the extraembryonic membranes of RFC1 nullizygous embryos. Maternal folate supplementation with 50 mg/kg/day results in survival of 22% of RFC1 mutants to E18.5, but they develop with multiple malformations of the eyelids, lungs, heart, and skin.

CONCLUSIONS

High doses of daily maternal folate supplementation during embryonic/fetal development are necessary for early postimplantation embryonic viability of RFC1 nullizygous embryos, and play a critical role in chorioallantoic fusion, erythropoiesis, and proper development of the neural tube, limbs, lungs, heart, and skin.

Folate intake, markers of folate status and oral clefts: is the evidence converging?

BACKGROUND

The ability of folic acid in the periconceptional period to prevent the occurrence of neural tube defects has stimulated tremendous interest in its effects on other health outcomes. Its possible effect on oral clefts has generated considerable debate. The purpose of this systematic review and meta-analysis was to assemble evidence on the role of folate in the aetiology of cleft lip with or without cleft palate (CL/P) and cleft palate only (CPO).

METHODS

Medline, PubMed, Embase, Science Citation Index and the HuGE Published Literature Database were searched to February 2007 for articles related to oral clefts and multivitamin use, dietary folate, folic acid fortification, biochemical markers of folate status and polymorphisms in 5,10-methylenetetrahydrofolate reductase (MTHFR) and other genes involved in folate metabolism. Random effects meta-analysis was conducted when appropriate.

RESULTS

Maternal multivitamin use was inversely associated with CL/P [odds ratio (OR) 0.75, 95% CI 0.65-0.88, based on 5717 cases and 59 784 controls] but to a lesser extent CPO (OR 0.88, 95% CI 0.76-1.01, 2586 cases and 59 684 controls). The volume of evidence on dietary folate, fortification and biochemical and genetic measures of folate status is substantially less; in aggregate, the evidence suggests that no association exists but there is substantial heterogeneity between studies.

CONCLUSIONS

The evidence is not converging and there is no strong evidence for an association between oral clefts and folic acid intake alone. Multivitamin use in early pregnancy, however, may protect against oral clefts, especially CL/P although this association may be confounded by other lifestyle factors associated with multivitamin use.

Microarray analysis of E9.5 reduced folate carrier (RFC1; Slc19a1) knockout embryos reveals altered expression of genes in the cubilin-megalin multiligand endocytic receptor complex

BACKGROUND

The reduced folate carrier (RFC1) is an integral membrane protein and facilitative anion exchanger that mediates delivery of 5-methyltetrahydrofolate into mammalian cells. Adequate maternal-fetal transport of folate is necessary for normal embryogenesis. Targeted inactivation of the murine RFC1 gene results in post-implantation embryolethality, but daily folic acid supplementation of pregnant dams prolongs survival of homozygous embryos until mid-gestation. At E10.5 RFC1-/- embryos are developmentally delayed relative to wildtype littermates, have multiple malformations, including neural tube defects, and die due to failure of chorioallantoic fusion. The mesoderm is sparse and disorganized, and there is a marked absence of erythrocytes in yolk sac blood islands. The identification of alterations in gene expression and signaling pathways involved in the observed dysmorphology following inactivation of RFC1-mediated folate transport are the focus of this investigation.

RESULTS

Affymetrix microarray analysis of the relative gene expression profiles in whole E9.5 RFC1-/- vs. RFC1+/+ embryos identified 200 known genes that were differentially expressed. Major ontology groups included transcription factors (13.04%), and genes involved in transport functions (ion, lipid, carbohydrate) (11.37%). Genes that code for receptors, ligands and interacting proteins in the cubilin-megalin multiligand endocytic receptor complex accounted for 9.36% of the total, followed closely by several genes involved in hematopoiesis (8.03%). The most highly significant gene network identified by Ingenuitytrade mark Pathway analysis included 12 genes in the cubilin-megalin multiligand endocytic receptor complex. Altered expression of these genes was validated by quantitative RT-PCR, and immunohistochemical analysis demonstrated that megalin protein expression disappeared from the visceral yolk sac of RFC1-/- embryos, while cubilin protein was widely misexpressed.

CONCLUSION

Inactivation of RFC1 impacts the expression of several ligands and interacting proteins in the cubilin-amnionless-megalin complex that are involved in the maternal-fetal transport of folate and other nutrients, lipids and morphogens such as sonic hedgehog (Shh) and retinoids that play critical roles in normal embryogenesis.

Folate and one-carbon metabolism gene polymorphisms and their associations with oral facial clefts

Folate metabolism plays a critical role in embryonic development. Prenatal folate supplementation reduces the risk of neural tube defects and probably oral facial clefts. Previous studies of related metabolic genes have associated polymorphisms in cystathionine-beta-synthase (CBS) and 5,10-methylenetetrahydrofolate reductase (MTHFR) with cleft risk. We explored associations between genes related to one-carbon metabolism and clefts in a Norwegian population-based study that included 362 families with cleft lip with or without cleft palate (CL/P) and 191 families with cleft palate only (CPO). We previously showed a 39% reduction in risk of CL/P with folic acid supplementation in this population. In the present study we genotyped 12 polymorphisms in nine genes related to one-carbon metabolism and looked for associations of clefting risk with fetal polymorphisms, maternal polymorphisms, as well as parent-of-origin effects, using combined likelihood-ratio tests (LRT). We also stratified by maternal periconceptional intake of folic acid (>400 microg) to explore gene-exposure interactions. We found a reduced risk of CL/P with mothers who carried the CBS C699T variant (rs234706); relative risk was 0.94 with one copy of the T allele (95% CI 0.63-1.4) and 0.50 (95% CI 0.26-0.96) with two copies (P = 0.008). We found no evidence of interaction of this variant with folate status. We saw no evidence of risk from the MTHFR C677T variant (rs1801133) either overall or after stratifying by maternal folate intake. No associations were found between any of the polymorphisms and CPO. Genetic variations in the nine metabolic genes examined here do not confer a substantial degree of risk for clefts.

Cardiovascular abnormalities inFolr1 knockout mice and folate rescue

BACKGROUND

Periconceptional folic acid supplementation is widely believed to aid in the prevention of neural tube defects (NTDs), orofacial clefts, and congenital heart defects. Folate-binding proteins or receptors serve to bind folic acid and 5-methyltetrahydrofolate, representing one of the two major mechanisms of cellular folate uptake.

METHODS

We herein describe abnormal cardiovascular development in mouse fetuses lacking a functional folate-binding protein gene (Folr1). We also performed a dose-response study with folinic acid and determined the impact of maternal folate supplementation on Folr1 nullizygous cardiac development.

RESULTS

Partially rescued preterm Folr1(-/-) (formerly referred to as Folbp1) fetuses were found to have outflow tract defects, aortic arch artery abnormalities, and isolated dextracardia. Maternal supplementation with folinic acid rescued the embryonic lethality and the observed cardiovascular phenotypes in a dose-dependant manner. Maternal genotype exhibited significant impact on the rescue efficiency, suggesting an important role of in utero folate status in embryonic development. Abnormal heart looping was observed during early development of Folr1(-/-) embryos partially rescued by maternal folinic acid supplementation. Migration pattern of cardiac neural crest cells, genetic signals in pharyngeal arches, and the secondary heart field were also found to be affected in the mutant embryos.

CONCLUSIONS

Our observations suggest that the beneficial effect of folic acid for congenital heart defects might be mediated via its impact on neural crest cells and by gene regulation of signaling pathways involved in the development of the pharyngeal arches and the secondary heart field.