Gene-gene interactions in the folate metabolic pathway and the risk of conotruncal heart defects

A gene-based association test of interactions for maternal-fetal genotypes identifies genes associated with nonsyndromic congenital heart defects

The risk of congenital heart defects (CHDs) may be influenced by maternal genes, fetal genes, and their interactions. Existing methods commonly test the effects of maternal and fetal variants one-at-a-time and may have reduced statistical power to detect genetic variants with low minor allele frequencies. In this article, we propose a gene-based association test of interactions for maternal-fetal genotypes (GATI-MFG) using a case-mother and control-mother design. GATI-MFG can integrate the effects of multiple variants within a gene or genomic region and evaluate the joint effect of maternal and fetal genotypes while allowing for their interactions. In simulation studies, GATI-MFG had improved statistical power over alternative methods, such as the single-variant test and functional data analysis (FDA) under various disease scenarios. We further applied GATI-MFG to a two-phase genome-wide association study of CHDs for the testing of both common variants and rare variants using 947 CHD case mother-infant pairs and 1306 control mother-infant pairs from the National Birth Defects Prevention Study (NBDPS). After Bonferroni adjustment for 23,035 genes, two genes on chromosome 17, TMEM107 (p = 1.64e-06) and CTC1 (p = 2.0e-06), were identified for significant association with CHD in common variants analysis. Gene TMEM107 regulates ciliogenesis and ciliary protein composition and was found to be associated with heterotaxy. Gene CTC1 plays an essential role in protecting telomeres from degradation, which was suggested to be associated with cardiogenesis. Overall, GATI-MFG outperformed the single-variant test and FDA in the simulations, and the results of application to NBDPS samples are consistent with existing literature supporting the association of TMEM107 and CTC1 with CHDs.

"Association of MTHFR and MS/MTR gene polymorphisms with congenital heart defects in North Indian population (Jammu and Kashmir): a case-control study encompassing meta-analysis and trial sequential analysis"

Background

The risk of Congenital Heart Defects (CHD) is greatly influenced by variants within the genes involved in folate-homocysteine metabolism. Polymorphism in MTHFR (C677T and G1793A) and MS/MTR (A2756G) genes increases the risk of developing CHD risk, but results are controversial. Therefore, we conducted a case–control association pilot study followed by an up-dated meta-analysis with trial sequential analysis (TSA) to obtain more precise estimate of the associations of these two gene variants with the CHD risk.

Methods

For case–control study, we enrolled 50 CHD patients and 100 unrelated healthy controls. Genotyping was done by PCR–RFLP method and meta-analysis was performed by MetaGenyo online Statistical Analysis System software. For meta-analysis total number of individuals was as follows: for MTHFR C677T 3450 CHD patients and 4447 controls whereas for MS A2756G 697 CHD patients and 777 controls.

Results

Results of the original pilot study suggested lack of association for MTHFR C677T and MS A2756G polymorphism with risk of CHD whereas MTHFR G1793A was significantly associated with the disease. On performing meta-analysis, a significant association was observed with MTHFR C677T polymorphism but not with MS A2756G. Trial sequential Analysis also confirmed the sufficient sample size requirement for findings of meta-analysis.

Conclusions

The results of the meta-analysis suggested a significant role of MTHFR in increased risk of CHD.

Maternal gene-micronutrient interactions related to one-carbon metabolism and the risk of myelomeningocele among offspring

BACKGROUND

Few studies have evaluated interactions between maternal genetic variation in 5,10-methylenetetrahydrofolate reductase (MTHFR) and micronutrient intake on the risk of myelomeningocele (MM) in offspring. Therefore, we sought to determine if the role of maternal MTHFR C677T and A1298C on MM risk is altered by maternal intake of micronutrients related to one-carbon metabolism.

METHODS

The study consisted of 220 MM case-parent trios recruited from 1996 to 2006. A dietary questionnaire was used to obtain information on maternal dietary intake on eight micronutrients including folate and cobalamin. TaqMan assays were used to generate MTHFR C677T and A1298C genotypes. Log-linear models were used to evaluate the joint effects of maternal genotype and micronutrient intake dichotomized as at or above versus below the United States Recommended Dietary Allowance (US RDA) on MM.

RESULTS

There was little evidence to suggest maternal MTHFR genotypes interacted with micronutrient intake to influence the risk of MM. For instance, the effect of MTHFR 677T was similar for mothers with cobalamin intake below US RDA (relative risk [RR] = 0.97) versus at or above US RDA cobalamin intake (RR = 0.81, interaction p = 0.87). However, some differences were noted. For example, the effect of MTHFR 1298C appeared to be different between those mothers below US RDA folate intake (RR = 0.98) versus those at or above US RDA folate intake (RR = 0.68), but the interaction was not statistically significant (interaction p = 0.27).

CONCLUSION

There did not appear to be strong effects of maternal micronutrient intake on the role of maternal genetic polymorphisms in MTHFR C677T and A1298C on MM risk. Birth Defects Research 109:99-105, 2017. © 2016 Wiley Periodicals, Inc.

Risk factors and methylenetetrahydrofolate reductase gene in congenital heart disease

Background

Congenital heart disease (CHD), which involve congenital cardiovascular malformations that occur during an embryo stage, may be the result of a complex interaction between genetic factors and environmental factors. The homozygous 677 T/T MTHFR gene and potential factors have been associated with CHD. Our objective was to study associations between potential environmental risk factors and methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms in CHD.

Methods

A total of 346 children with CHD and 237 healthy children were recruited. Their parents were also enlisted in the study and interviewed face-to-face to identify potential environmental risk factors. The MTHFR genotype was analyzed by restriction fragment length polymorphism (RFLP). Interactions between environmental risk factors and MTHFR gene polymorphisms were evaluated by the relative excess risk due to interaction (RERI), the attributable proportion due to interaction (AP), and the synergy index (S).

Results

There were significant differences in the occupational statuses of the mothers and their levels of drug exposure during gestation between the controls and the cases (P<0.05). These differences significantly increased offspring CHD risk (occupation: OR =5.45, 95% CI: 3.46-8.58; drug exposure: OR =4.91, 95% CI: 2.18-11.09). The frequency of the MTHFR gene 677 TT polymorphism in the mothers who had offspring with CHD was significantly different from that in the non-CHD controls (P<0.05). The frequency of this polymorphism also significantly differed between the children with CHD and the control group (P<0.05). An interaction was identified between the presence of the homozygous 677 TT genotype in the children and the mothers' occupational statuses (RERI =9.43, CI: 0.06-18.91).

Conclusions

A significant interaction was found between the homozygous 677 T/T MTHFR gene in children and the maternal occupational status and level of drug exposure during gestation. Avoiding or reducing the exposure of the risk factors mentioned above, strengthening pre-pregnancy checkups and guidance might help to reduce the risk of CHD.

Folate, vitamin B12, homocysteine and polymorphisms in folate metabolizing genes in children with congenital heart disease and their mothers

BACKGROUND/OBJECTIVES

The objective of the study was to assess the role of variations in serum folate, vitamin B12, homocysteine and the presence of genetic polymorphisms as risk factors for congenital heart disease (CHD) in children.

SUBJECTS/METHODS

A total of 32 children with CHD, and their mothers and 32 normal children and their mothers formed the study and control groups, respectively. Serum folate, vitamin B12 and homocysteine as well as genetic polymorphisms MTHFR C677→︀T, MTHFR A1298→︀C, MTR A2756→︀G and MTRR A66→︀G were assessed.

RESULTS

Low serum folate and genetic polymorphisms MTHFR C677→︀T and MTRR A66→︀G among children and their mothers and high homocysteine among mothers were noted as risk factors for CHD (P<0.05). Vitamin B12 levels were normal and showed no association. Presence of MTHFR C677→︀T and MTRR A66→︀G, both concurrently among children as well as mothers and simultaneously among mother-child pairs, showed several fold increase in the risk for CHD. On multivariate analysis, the risk factors noted for CHD were presence of MTHFR C677→︀T among children and their mothers and MTRR A66→︀G among mothers. Analyses for nutrient-gene interaction revealed significant associations between low serum folate and high serum homocysteine levels, and the presence of selected genetic polymorphisms.

CONCLUSIONS

Low serum folate, high homocysteine and presence of selected genetic polymorphisms among children and their mothers were noted as risk factors for CHD. Nutrient-gene interaction being a modifiable risk factor, the study recommends the use of peri-conceptional folate supplementation with vitamin B12 sufficiency for primary prevention of CHD.

A Three-Way Interaction among Maternal and Fetal Variants Contributing to Congenital Heart Defects

Congenital heart defects (CHDs) develop through a complex interplay between genetic variants, epigenetic modifications, and maternal environmental exposures. Genetic studies of CHDs have commonly tested single genetic variants for association with CHDs. Less attention has been given to complex gene-by-gene and gene-by-environment interactions. In this study, we applied a recently developed likelihood-ratio Mann-Whitney (LRMW) method to detect joint actions among maternal variants, fetal variants, and maternal environmental exposures, allowing for high-order statistical interactions. All subjects are participants from the National Birth Defect Prevention Study, including 623 mother-offspring pairs with CHD-affected pregnancies and 875 mother-offspring pairs with unaffected pregnancies. Each individual has 872 single nucleotide polymorphisms encoding for critical enzymes in the homocysteine, folate, and trans-sulfuration pathways. By using the LRMW method, three variants (fetal rs625879, maternal rs2169650, and maternal rs8177441) were identified with a joint association to CHD risk (nominal P-value = 1.13e-07). These three variants are located within genes BHMT2, GSTP1, and GPX3, respectively. Further examination indicated that maternal SNP rs2169650 may interact with both fetal SNP rs625879 and maternal SNP rs8177441. Our findings suggest that the risk of CHD may be influenced by both the intragenerational interaction within the maternal genome and the intergenerational interaction between maternal and fetal genomes.

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.

B vitamins, homocysteine and bone health

Nutrition is one of the most important modifiable factors involved in the development and maintenance of good bone health. Calcium and Vitamin D have confirmed and established roles in the maintenance of proper bone health. However, other nutritional factors could also be implicated. This review will explore the emerging evidence of the supporting role of certain B Vitamins as modifiable factors associated with bone health. Individuals with high levels of homocysteine (hcy) exhibit reduced bone mineral density (BMD), alteration in microarchitecture and increased bone fragility. The pathophysiology caused by high serum homocysteine is not completely clear regarding fractures, but it may involve factors, such as bone mineral density, bone turnover, bone blood flow and collagen cross-linking. It is uncertain whether supplementation with B Vitamins, such as folate, Vitamin B1, and Vitamin B6, could decrease hip fracture incidence, but the results of further clinical trials should be awaited before a conclusion is drawn.

Folate pathway gene polymorphisms, maternal folic acid use, and risk of childhood acute lymphoblastic leukemia

BACKGROUND

Several studies suggest that maternal folic acid supplementation before or during pregnancy protects against childhood acute lymphoblastic leukemia (ALL). We investigated associations between ALL risk and folate pathway gene polymorphisms, and their modification by maternal folic acid supplements, in a population-based case-control study (2003-2007).

METHODS

All Australian pediatric oncology centers provided cases; controls were recruited by national random digit dialing. Data from 392 cases and 535 controls were included. Seven folate pathway gene polymorphisms (MTHFR 677C>T, MTHFR 1298A>C, MTRR 66A>G, MTR 2756 A>G, MTR 5049 C>A, CBS 844 Ins68, and CBS 2199 T>C) were genotyped in children and their parents. Information on prepregnancy maternal folic acid supplement use was collected. ORs were estimated with unconditional logistic regression adjusted for frequency-matched variables and potential confounders. Case-parent trios were also analyzed.

RESULTS

There was some evidence of a reduced risk of ALL among children who had, or whose father had, the MTRR 66GG genotype: ORs 0.60 [95% confidence interval (CI) 0.39-0.91] and 0.64 (95% CI, 0.40-1.03), respectively. The ORs for paternal MTHFR 677CT and TT genotypes were 1.41 (95% CI, 1.02-1.93) and 1.81 (95% CI, 1.06-3.07). ORs varied little by maternal folic acid supplementation.

CONCLUSIONS

Some folate pathway gene polymorphisms in the child or a parent may influence ALL risk. While biologically plausible, underlying mechanisms for these associations need further elucidation.

IMPACT

Folate pathway polymorphisms may be related to risk of childhood ALL, but larger studies are needed for conclusive results.

Maternal obesity and tobacco use modify the impact of genetic variants on the occurrence of conotruncal heart defects

Conotruncal heart defects (CTDs) are among the most severe birth defects worldwide. Studies of CTDs indicate both lifestyle behaviors and genetic variation contribute to the risk of CTDs. Based on a hybrid design using data from 616 case-parental and 1645 control-parental triads recruited for the National Birth Defects Prevention Study between 1997 and 2008, we investigated whether the occurrence of CTDs is associated with interactions between 921 maternal and/or fetal single nucleotide polymorphisms (SNPs) and maternal obesity and tobacco use. The maternal genotypes of the variants in the glutamate-cysteine ligase, catalytic subunit (GCLC) gene and the fetal genotypes of the variants in the glutathione S-transferase alpha 3 (GSTA3) gene were associated with an elevated risk of CTDs among obese mothers. The risk of delivering infants with CTDs among obese mothers carrying AC genotype for a variant in the GCLC gene (rs6458939) was 2.00 times the risk among those carrying CC genotype (95% confidence interval: 1.41, 2.38). The maternal genotypes of several variants in the glutathione-S-transferase (GST) family of genes and the fetal genotypes of the variants in the GCLC gene interacted with tobacco exposures to increase the risk of CTDs. Our study suggests that the genetic basis underlying susceptibility of the developing heart to the adverse effects of maternal obesity and tobacco use involve both maternal and embryonic genetic variants. These results may provide insights into the underlying pathophysiology of CTDs, and ultimately lead to novel prevention strategies.

A genetic association study detects haplotypes associated with obstructive heart defects

The development of congenital heart defects (CHDs) involves a complex interplay between genetic variants, epigenetic variants, and environmental exposures. Previous studies have suggested that susceptibility to CHDs is associated with maternal genotypes, fetal genotypes, and maternal-fetal genotype (MFG) interactions. We conducted a haplotype-based genetic association study of obstructive heart defects (OHDs), aiming to detect the genetic effects of 877 SNPs involved in the homocysteine, folate, and transsulfuration pathways. Genotypes were available for 285 mother-offspring pairs with OHD-affected pregnancies and 868 mother-offspring pairs with unaffected pregnancies. A penalized logistic regression model was applied with an adaptive least absolute shrinkage and selection operator (lasso), which dissects the maternal effect, fetal effect, and MFG interaction effects associated with OHDs. By examining the association between 140 haplotype blocks, we identified 9 blocks that are potentially associated with OHD occurrence. Four haplotype blocks, located in genes MGMT, MTHFS, CBS, and DNMT3L, were statistically significant using a Bayesian false-discovery probability threshold of 0.8. Two blocks in MGMT and MTHFS appear to have significant fetal effects, while the CBS and DNMT3L genes may have significant MFG interaction effects.

Genome-wide association study of maternal and inherited loci for conotruncal heart defects

Conotruncal and related heart defects (CTDs) are a group of serious and relatively common birth defects. Although both maternal and inherited genotypes are thought to play a role in the etiology of CTDs, few specific genetic risk factors have been identified. To determine whether common variants acting through the genotype of the mother (e.g. via an in utero effect) or the case are associated with CTDs, we conducted a genome-wide association study of 750 CTD case-parent triads, with follow-up analyses in 358 independent triads. Log-linear analyses were used to assess the association of CTDs with the genotypes of both the mother and case. No association achieved genomewide significance in either the discovery or combined (discovery+follow-up) samples. However, three loci with p-values suggestive of association (p<10⁻⁵) in the discovery sample had p-values <0.05 in the follow-up sample and p-values in the combined data that were lower than in the discovery sample. These included suggestive association with an inherited intergenic variant at 20p12.3 (rs6140038, combined p = 1.0×10⁻⁵) and an inherited intronic variant in KCNJ4 at 22q13.1 (rs2267386, combined p = 9.8×10⁻⁶), as well as with a maternal variant in SLC22A24 at 11q12.3 (rs11231379, combined p = 4.2×10⁻⁶). These observations suggest novel candidate loci for CTDs, including loci that appear to be associated with the risk of CTDs via the maternal genotype, but further studies are needed to confirm these associations.

Detecting maternal-fetal genotype interactions associated with conotruncal heart defects: a haplotype-based analysis with penalized logistic regression

Nonsyndromic congenital heart defects (CHDs) develop during embryogenesis as a result of a complex interplay between environmental exposures, genetics, and epigenetic causes. Genetic factors associated with CHDs may be attributed to either independent effects of maternal or fetal genes, or the intergenerational interactions between maternal and fetal genes. Detecting gene-by-gene interactions underlying complex diseases is a major challenge in genetic research. Detecting maternal-fetal genotype (MFG) interactions and differentiating them from the maternal/fetal main effects has presented additional statistical challenges due to correlations between maternal and fetal genomes. Traditionally, genetic variants are tested separately for maternal/fetal main effects and MFG interactions on a single-locus basis. We conducted a haplotype-based analysis with a penalized logistic regression framework to dissect the genetic effect associated with the development of nonsyndromic conotruncal heart defects (CTD). Our method allows simultaneous model selection and effect estimation, providing a unified framework to differentiate maternal/fetal main effect from the MFG interaction effect. In addition, the method is able to test multiple highly linked SNPs simultaneously with a configuration of haplotypes, which reduces the data dimensionality and the burden of multiple testing. By analyzing a dataset from the National Birth Defects Prevention Study (NBDPS), we identified seven genes (GSTA1, SOD2, MTRR, AHCYL2, GCLC, GSTM3, and RFC1) associated with the development of CTDs. Our findings suggest that MFG interactions between haplotypes in three of seven genes, GCLC, GSTM3, and RFC1, are associated with nonsyndromic conotruncal heart defects.

Maternal-fetal metabolic gene-gene interactions and risk of neural tube defects

Single-gene analyses indicate that maternal genes associated with metabolic conditions (e.g., obesity) may influence the risk of neural tube defects (NTDs). However, to our knowledge, there have been no assessments of maternal-fetal metabolic gene-gene interactions and NTDs. We investigated 23 single nucleotide polymorphisms among 7 maternal metabolic genes (ADRB3, ENPP1, FTO, LEP, PPARG, PPARGC1A, and TCF7L2) and 2 fetal metabolic genes (SLC2A2 and UCP2). Samples were obtained from 737 NTD case-parent triads included in the National Birth Defects Prevention Study for birth years 1999-2007. We used a 2-step approach to evaluate maternal-fetal gene-gene interactions. First, a case-only approach was applied to screen all potential maternal and fetal interactions (n = 76), as this design provides greater power in the assessment of gene-gene interactions compared to other approaches. Specifically, ordinal logistic regression was used to calculate the odds ratio (OR) and 95% confidence interval (CI) for each maternal-fetal gene-gene interaction, assuming a log-additive model of inheritance. Due to the number of comparisons, we calculated a corrected p-value (q-value) using the false discovery rate. Second, we confirmed all statistically significant interactions (q < 0.05) using a log-linear approach among case-parent triads. In step 1, there were 5 maternal-fetal gene-gene interactions with q < 0.05. The "top hit" was an interaction between maternal ENPP1 rs1044498 and fetal SLC2A2 rs6785233 (interaction OR = 3.65, 95% CI: 2.32-5.74, p = 2.09×10(-8), q=0.001), which was confirmed in step 2 (p = 0.00004). Our findings suggest that maternal metabolic genes associated with hyperglycemia and insulin resistance and fetal metabolic genes involved in glucose homeostasis may interact to increase the risk of NTDs.

Mthfr gene ablation enhances susceptibility to arsenic prenatal toxicity

BACKGROUND

In utero exposure to arsenic is known to adversely affect reproductive outcomes. Evidence of arsenic teratogenicity varies widely and depends on individual genotypic differences in sensitivity to As. In this study, we investigated the potential interaction between 5,10-methylenetetrahydrofolate reductase (Mthfr) genotype and arsenic embryotoxicity using the Mthfr knockout mouse model.

METHODS

Pregnant dams were treated with sodium arsenate, and reproductive outcomes including: implantation, resorption, congenital malformation and fetal birth weight were recorded at E18.5.

RESULTS

When the dams in Mthfr(+/-)×Mthfr(+/-) matings were treated with 7.2 mg/kg As, the resorption rate increased to 43.4%, from a background frequency of 7.2%. The As treatment also induced external malformations (40.9%) and significantly lowered the average fetal birth weight among fetuses, without any obvious toxic effect on the dam. When comparing the pregnancy outcomes resulting from different mating scenarios (Mthfr(+/+)×Mthfr(+/-), Mthfr(+/-)×Mthfr(+/-) and Mthfr(-/-)×(Mthfr+/-)) and arsenic exposure; the resorption rate showed a linear relationship with the number of null alleles (0, 1 or 2) in the Mthfr dams. Fetuses from nullizygous dams had the highest rate of external malformations (43%) and lowest average birth weight. When comparing the outcomes of reciprocal matings (nullizygote×wild-type versus wild-type×nullizygote) after As treatment, the null dams showed significantly higher rates of resorptions and malformations, along with lower fetal birth weights.

CONCLUSIONS

Maternal genotype contributes to the sensitivity of As embryotoxicity in the Mthfr mouse model. The fetal genotype, however, does not appear to affect the reproductive outcome after in utero As exposure.

Folic acid fortification and the birth prevalence of congenital heart defect cases in Alberta, Canada

BACKGROUND

Congenital heart defects (CHDs) are the most common type of congenital anomaly. The precise etiology is unknown and the development of successful primary prevention strategies is challenging. Folic acid may have a protective role; however published results have been inconsistent. This study examines the impact of mandatory folic acid fortification (FAF) on the prevalence of CHDs.

METHODS

CHD cases were ascertained using the Alberta Congenital Anomalies Surveillance System, Pediatric Cardiology Clinics, Pathology, and hospital records. The birth prevalence and odds ratios (OR) of isolated CHD cases (i.e., without noncardiac anomalies) were calculated comparing pre-FAF (1995-1997) with post-FAF (1999-2002).

RESULTS

The prevalence of isolated CHD cases remained relatively unchanged when pre-FAF (9.34, 95% confidence interval [CI] 8.79-9.92) was compared with post-FAF (9.41, 95% CI, 8.93-9.91). Left ventricular outflow tract obstruction (LVOTO) decreased post-FAF (OR, 0.76; 95% CI, 0.61-0.94). Coarctation of the aorta contributed to this decline (OR, 0.55; 95% CI, 0.32-0.92). Atrial septal defect (ASD) (OR, 1.42; 95% CI, 1.13-1.80) and ASD with ventricular septal defect (OR, 1.52; 95% CI, 1.10-2.10) increased post-FAF. The remaining types of CHDs were unchanged.

CONCLUSION

FAF alone does not have an impact on the prevalence of CHDs as a group and the majority of selected types of CHDs in Alberta. The decrease in LVOTO, particularly coarctation of the aorta, may be due to FAF or other environmental factors. The increase in ASD and ASD with ventricular septal defect may reflect an increase in diagnosis and ascertainment.

Associations between maternal genotypes and metabolites implicated in congenital heart defects

BACKGROUND

The development of non-syndromic congenital heart defects (CHDs) involves a complex interplay of genetics, metabolism, and lifestyle. Previous studies have implicated maternal single nucleotide polymorphisms (SNPs) and altered metabolism in folate-related pathways as CHD risk factors.

OBJECTIVE

We sought to discover associations between maternal SNPs and metabolites involved in the homocysteine, folate, and transsulfuration pathways, and determine if these associations differ between CHD cases and controls.

DESIGN

Genetic, metabolic, demographic, and lifestyle information was available for 335 mothers with CHD-affected pregnancies and 263 mothers with unaffected pregnancies. Analysis was conducted on 1160 SNPs, 13 plasma metabolites, and 2 metabolite ratios. A two-stage multiple linear regression was fitted to each combination of SNP and metabolite/ratio.

RESULTS

We identified 4 SNPs in the methionine adenosyltransferase II alpha (MAT2A) gene that were associated with methionine levels. Three SNPs in tRNA aspartic acid methyltransferase 1 (TRDMT1) gene were associated with total plasma folate levels. Glutamylcysteine (GluCys) levels were associated with multiple SNPs within the glutathione peroxidase 6 (GPX6) and O-6-methylguanine-DNA methyltransferase (MGMT) genes. The regression model revealed interactions between genotype and case-control status in the association of total plasma folate, total glutathione (GSH), and free GSH, to SNPs within the MGMT, 5,10-methenyltetrahydrofolate synthetase (MTHFS), and catalase (CAT) genes, respectively.

CONCLUSIONS

Our study provides further evidence that genetic variation within folate-related pathways accounts for inter-individual variability in key metabolites. We identified specific SNP-metabolite relationships that differed in mothers with CHD-affected pregnancies, compared to controls. Our results underscore the importance of multifactorial studies to define maternal CHD risk.

Gene variants in the folate-mediated one-carbon metabolism (FOCM) pathway as risk factors for conotruncal heart defects

We evaluated 35 variants among four folate-mediated one-carbon metabolism pathway genes, MTHFD1, SHMT1, MTHFR, and DHFR as risk factors for conotruncal heart defects. Cases with a diagnosis of single gene disorders or chromosomal aneusomies were excluded. Controls were randomly selected from area hospitals in proportion to their contribution to the total population of live-born infants. Odds ratios (OR) and the 95% confidence intervals (CI) were computed for each genotype (homozygous variant or heterozygote, vs. homozygous wildtype) and for increase of each less common allele (log-additive model). Interactions between each variant and three folate intake variables (maternal multivitamin use, maternal dietary folate intake, and combined maternal folate intake) were also evaluated under the log-additive model. In general, we did not identify notable associations. The A allele of MTHFD1 rs11627387 was associated with a 1.7-fold increase in conotruncal defects risk in both Hispanic mothers (OR = 1.7, 95% CI = 1.1-2.5) and Hispanic infants (OR = 1.7, 95% CI = 1.2-2.3). The T allele of MTHFR rs1801133 was associated with a 2.8-fold increase of risk among Hispanic women whose dietary folate intake was ≤ 25th centile. The C allele of MTHFR rs1801131 was associated with a two-fold increase of risk (OR = 2.0, 95% CI = 1.0-3.9) only among those whose dietary folate intake was >25th centile. Our study suggested that MTHFD1 rs11627387 may be associated with risk of conotruncal defects through both maternal and offspring genotype effect among the Hispanics. Maternal functional variants in MTHFR gene may interact with dietary folate intake and modify the conotruncal defects risk in the offspring.

Evaluation of heterogeneity in the association between congenital heart defects and variants of folate metabolism genes: conotruncal and left-sided cardiac defects

BACKGROUND

Genetic variation in the folate metabolic pathway may influence the risk of congenital heart defects. This study was undertaken to assess the associations between the inherited and maternal genotypes for variants in folate-related genes and the risk of a composite heart phenotype that included two component phenotypes: conotruncal heart defects (CTDs) and left-sided cardiac lesions (LSLs).

METHODS

Nine folate-related gene variants were evaluated using data from 692 case-parent triads (CTD, n = 419; LSL, n = 273). Log-linear analyses were used to test for heterogeneity of the genotype-phenotype association across the two component phenotypes (i.e., CTD and LSLs) and, when there was no evidence of heterogeneity, to assess the associations of the maternal and inherited genotypes with the composite phenotype.

RESULTS

There was little evidence of heterogeneity of the genotype-phenotype association across the two component phenotypes or of an association between the genotypes and the composite phenotype. There was evidence of heterogeneity in the association of the maternal MTR A2756G genotype (p = 0.01) with CTDs and LSLs. However, further analyses suggested that the observed associations with the maternal MTR A2756G genotype might be confounded by parental imprinting effects.

CONCLUSIONS

Our analyses of these data provide little evidence that the folate-related gene variants evaluated in this study influence the risk of this composite congenital heart defect phenotype. However, larger and more comprehensive studies that evaluate parent-of-origin effects, as well as additional folate-related genes, are required to more fully explore the relation between folate and congenital heart defects.

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.

Folate protection from congenital heart defects linked with canonical Wnt signaling and epigenetics

PURPOSE OF REVIEW

Environmental factors, such as drugs, chemicals, or abnormal concentrations of natural metabolites, induce birth defects. Environmental effects on cardiogenesis have been little studied in contrast to neurogenesis. This review presents evidence on three environmental factors: alcohol, the drug lithium, and the metabolite homocysteine, impacting the Wnt/β-catenin pathway during cardiac development and folate protection.

RECENT FINDINGS

Animal and epidemiological studies have shown that folate protects the embryo from birth defects. New animal studies demonstrate that folate prevents cardiovascular defects induced by the drug lithium, homocysteine, or alcohol, but protection occurs at a higher concentration than currently used in vitamin supplements. The data indicate that folate in combination with myo-inositol may further reduce the risk of birth defects. Discussion is presented of the cell specification stages that are impacted resulting in cardiac defects, how Wnt/β-catenin signaling is involved, and how folate and myo-inositol additively may protect embryonic pathways. The possible epigenetic role of folate in Wnt/β-catenin signaling is described.

SUMMARY

This review will enable better counseling of women by defining, during early pregnancy, a susceptible window of embryonic exposure leading to a high risk of cardiac defects, and provides a therapeutic means and the necessary timing for prevention of environmentally induced birth defects.

Epidemiology of nonsyndromic conotruncal heart defects in Texas, 1999-2004

INTRODUCTION

Congenital heart defects (CHDs) are the most common structural birth defects, yet their etiology is poorly understood. As there is heterogeneity within the group of CHDs, epidemiologic studies often focus on subgroups, of conditions, such as conotruncal heart defects (CTDs). However, even within these subgroups there may be etiologic heterogeneity. The aim of the present study was to identify and compare maternal and infant characteristics associated with three CTDs: truncus arteriosus (TA), dextro-transposition of the great arteries (d-TGA), and tetralogy of Fallot (TOF).

METHODS

Data for cases with nonsyndromic TA (n = 78), d-TGA (n = 438), and TOF (n = 529) from the Texas Birth Defects Registry, 1999-2004, were used to estimate crude and adjusted prevalence ratios, separately for each condition, using Poisson regression. Polytomous logistic regression was used to determine whether the observed associations were similar across the two largest case groups (d-TGA and TOF).

RESULTS

In Texas, 1999-2004, the prevalence of nonsyndromic TA, d-TGA, and TOF was 0.35, 1.98, and 2.40 per 10,000 live births, respectively. There was evidence of a significant linear increase in the risk of each condition with advancing maternal age (p < 0.01). Significant associations were observed for TA and maternal residence on the Texas-Mexico border; d-TGA and infant sex, maternal race/ethnicity, history of previous live birth, and birth year; and TOF and maternal race/ethnicity and education. Further, the associations with some, but not all, of the study variables were significantly different for d-TGA and TOF.

CONCLUSION

These findings add to our limited understanding of the epidemiology of CTDs.

Frequency of the Methylenetetrahydrofolate REDUCTASE 677CT and 1298AC mutations in an Iranian Turkish female population

INTRODUCTION

Gene-environmental interactions in the pathway of folate metabolism influence greatly the embryonic development. Individual specific MTHFR 677C/T and 1298A/C mutations are known as risk factors for predisposition to human disorders. Therefore, we studied the frequencies of the MTHFR 677CT and 1298AC mutations in a female general population from Iranian Azeri Turkish.

MATERIAL AND METHODS

We studied 108 unrelated women from Iranian Azeri Turkish general population. Genomic DNA was extracted using standard procedure. The MTHFR 677CT and 1298AC mutations determined by PCR-RFLP method.

OUTCOMES

The frequencies (percent) at position 677 for C and T alleles were 159(74%), 57(26%), and for CC, CT, and TT genotypes were 59(54.6%), 41(38%), and 8(7.41%) respectively. The frequencies (percent) at position 1298 for A and C alleles were 136(63%), 80(37%), and for AA, AC, and CC genotypes were 43(39.8%), 50(46.3%), and 15(13.9%) respectively.

CONCLUSIONS

The frequency of MTHFR 677 C and T alleles were 0.74 and 0.26 while that of MTHFR 1298 A and C alleles were 0.63 and 0.37 in present study, respectively. This is the first report in its own kind in Iranian Azeri Turkish women.