Association between C677T polymorphism of methylene tetrahydrofolate reductase and congenital heart disease: meta-analysis of 7697 cases and 13,125 controls

Association between MTHFR C677T variant and risk for congenital heart defects in Egyptian children: a case–control study including meta-analysis based on 147 cases and 143 controls

Background

Stratification analysis studies showed that ethnicity has a significant association regarding MTHFR C677T variant and congenital heart diseases (CHDs) risk, and many published studies have controversial conclusions toward this association.

Methods

In this study, the association between the MTHFR C677T variant and the risk for CHDs was evaluated in 91 children with CHD and 95 healthy controls, as new cases, by using restriction fragment length polymorphism (RFLP) technique. Besides that, 2 case–control studies in the Egyptian population published before 2021 were included in this meta-analysis. The association was assessed by the odds ratio (OR) with a 95% confidence interval (CI) based on 294 alleles in CHD cases and 286 alleles in controls.

Results

The overall meta-analysis showed a significant association between MTHFR C677T variant and CHDs risk in Egyptian children with heterogeneity (Heterogeneity = 0.001) in all the genetic models with the highly significant association in T versus C allele (pooled OR 1.89, 95% CI 1.31–2.74; p value < 0.0004). The consistency of the genotypes was detected by Hardy–Weinberg equilibrium (HWE).

Conclusions

Our results support the MTHFR -677T allele as a susceptibility factor for CHDs in the Egyptian pediatric patients.

Translational Genomic Research: The Association between Genetic Profiles and Cognitive Functioning or Cardiac Function Among Breast Cancer Survivors Completing Chemotherapy

Introduction: Emerging evidence suggests that Chemotherapy (CT) treated breast cancer survivors (BCS) who have "risk variants" in genes may be more susceptible to cognitive impairment (CI) and/or poor cardiac phenotypes. The objective of this preliminary study was to examine whether there is a relationship between genetic variants and objective/subjective cognitive or cardiac phenotypes. Methods and Analysis: BCS were recruited from Moffitt Cancer Center, Morsani College of Medicine, AdventHealth Tampa and Sarasota Memorial Hospital. Genomic DNA were collected at baseline for genotyping analysis. A total of 16 single nucleotide polymorphisms (SNPs) from 14 genes involved in cognitive or cardiac function were evaluated. Three genetic models (additive, dominant, and recessive) were used to test correlation coefficients between genetic variants and objective/subjective measures of cognitive functioning and cardiac outcomes (heart rate, diastolic blood pressure, systolic blood pressure, respiration rate, and oxygen saturation). Results: BCS (207 participants) with a mean age of 56 enrolled in this study. The majority were non-Hispanic white (73.7%), married (63.1%), and received both CT and radiation treatment (77.3%). Three SNPs in genes related to cognitive functioning (rs429358 in APOE, rs1800497 in ANKK1, rs10119 in TOMM40) emerged with the most consistent significant relationship with cognitive outcomes. Among five candidate SNPs related to cardiac functioning, rs8055236 in CDH13 and rs1801133 in MTHER emerged with potential significant relationships with cardiac phenotype. Conclusions: These preliminary results provide initial targets to further examine whether BCS with specific genetic profiles may preferentially benefit from interventions designed to improve cognitive and cardiac functioning following CT.

Probing the functional consequence and clinical relevance of CD320 p.E88del, a variant in the transcobalamin receptor gene

The biological and clinical significance of the p.E88del variant in the transcobalamin receptor, CD320, is unknown. This allele is annotated in ClinVar as likely benign, pathogenic, and of uncertain significance. To determine functional consequence and clinical relevance of this allele, we employed cell culture and genetic association studies. Fibroblasts from 16 CD320 p.E88del homozygotes exhibited reduced binding and uptake of cobalamin. Complete ascertainment of newborns with transiently elevated C3 (propionylcarnitine) in New York State demonstrated that homozygosity for CD320 p.E88del was over-represented (7/348, p < 6 × 10^-5 ). Using population data, we estimate that ~85% of the p.E88del homozygotes born in the same period did not have elevated C3, suggesting that cobalamin metabolism in the majority of these infants with this genotype is unaffected. Clinical follow-up of 4/9 homozygous individuals uncovered neuropsychological findings, mostly in speech and language development. None of these nine individuals exhibited perturbation of cobalamin metabolism beyond the newborn stage even during periods of acute illness. Newborns homozygous for this allele in the absence of other factors are at low risk of requiring clinical intervention, although more studies are required to clarify the natural history of various CD320 variants across patient populations.

Association analysis of maternal MTHFR gene polymorphisms and the occurrence of congenital heart disease in offspring

BACKGROUND

Although many studies showed that the risk of congenital heart disease (CHD) was closely related to genetic factors, the exact pathogenesis is still unknown. Our study aimed to comprehensively assess the association of single nucleotide polymorphisms (SNPs) of maternal MTHFR gene with risk of CHD and its three subtypes in offspring.

METHODS

A case-control study involving 569 mothers of CHD cases and 652 health controls was conducted. Thirteen SNPs were detected and analyzed.

RESULTS

Our study showed that genetic polymorphisms of maternal MTHFR gene at rs4846052 and rs1801131 were significantly associated with risk of CHD in the homozygote comparisons (TT vs. CC at rs4846052: OR = 7.62 [95%CI 2.95-19.65]; GG vs. TT at rs1801131: OR = 5.18 [95%CI 2.77-9.71]). And six haplotypes of G-C (involving rs4846048 and rs2274976), A-C (involving rs1801133 and rs4846052), G-T (involving rs1801133 and rs4846052), G-T-G (involving rs2066470, rs3737964 and rs535107), A-C-G (involving rs2066470, rs3737964 and rs535107) and G-C-G (involving rs2066470, rs3737964 and rs535107) were identified to be significantly associated with risk of CHD. Additionally, we observed that a two-locus model involving rs2066470 and rs1801131 as well as a three-locus model involving rs227497, rs1801133 and rs1801131 were significantly associated with risk of CHD in the gene-gene interaction analyses. For three subtypes including atrial septal defect, ventricular septal defect and patent ductus arteriosus, similar results were observed.

CONCLUSIONS

Our study indicated genetic polymorphisms of maternal MTHFR gene were significantly associated with risk of fetal CHD in the Chinese population. Additionally, there were significantly interactions among different SNPs on risk of CHD. However, how these SNPs affect the development of fetal heart remains unknown, and more studies in different ethnic populations and with a larger sample are required to confirm these findings.

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.

Study on Maternal SNPs of MTHFR Gene and HCY Level Related to Congenital Heart Diseases

The aim of this study is to evaluate the relationship between maternal single nucleotide polymorphisms (SNPs) of methylenetetrahydrofolate reductase (MTHFR) gene with plasma homocysteine (HCY) level and offspring congenital heart diseases (CHDs). 338 mothers with offspring CHDs as case group and 306 mothers of normal children as control group were recruited. Their pregnant histories were interviewed by questionnaire and the MTHFR rsl801133 and rsl801131 were genotyped. The case-control analysis was used to find out the relationship between maternal SNPs of MTHFR gene and offspring CHDs. And the plasma HCY concentration of the mothers of CHDs children was detected. This case-case study was intended to find out the relevance between maternal HCY level and SNPs of MTHFR gene. There were significant differences in the gender of children, occupation of mothers, family history with CHDs, history of abortion, history of adverse pregnancy, early pregnancy health, fetus during pregnancy, pesticide exposure and drug exposure in CHDs group and control group (P < 0.05). MTHFR rs1801133 was significantly associated with their offspring CHDs in mothers. The polymorphism of maternal MTHFR rs1801133 increased plasma HCY level, especially the homozygous mutation. Besides the environmental factors, our results suggested that the maternal MTHFR rs1801133 polymorphism might be a risk factor of their offspring CHDs, which may be due to the hyperhomocysteinemia by abnormal metabolism of HCY.

Mendelian randomisation approaches to the study of prenatal exposures: A systematic review

BACKGROUND

Mendelian randomisation (MR) designs apply instrumental variable techniques using genetic variants to study causal effects. MR is increasingly used to evaluate the role of maternal exposures during pregnancy on offspring health.

OBJECTIVES

We review the application of MR to prenatal exposures and describe reporting of methodologic challenges in this area.

DATA SOURCES

We searched PubMed, EMBASE, Medline Ovid, Cochrane Central, Web of Science, and Google Scholar.

STUDY SELECTION AND DATA EXTRACTION

Eligible studies met the following criteria: (a) a maternal pregnancy exposure; (b) an outcome assessed in offspring of the pregnancy; and (c) a genetic variant or score proposed as an instrument or proxy for an exposure.

SYNTHESIS

We quantified the frequency of reporting of MR conditions stated, techniques used to examine assumption plausibility, and reported limitations.

RESULTS

Forty-three eligible studies were identified. When discussing challenges or limitations, the most common issues described were known potential biases in the broader MR literature, including population stratification (n = 29), weak instrument bias (n = 18), and certain types of pleiotropy (n = 30). Of 22 studies presenting point estimates for the effect of exposure, four defined their causal estimand. Twenty-four studies discussed issues unique to prenatal MR, including selection on pregnancy (n = 1) and pleiotropy via postnatal exposure (n = 10) or offspring genotype (n = 20).

CONCLUSIONS

Prenatal MR studies frequently discuss issues that affect all MR studies, but rarely discuss problems specific to the prenatal context, including selection on pregnancy and effects of postnatal exposure. Future prenatal MR studies should report and attempt to falsify their assumptions, with particular attention to issues specific to prenatal MR. Further research is needed to evaluate the impacts of biases unique to prenatal MR in practice.

Effectiveness of community-based folate-oriented tertiary interventions on incidence of fetus and birth defects: a protocol for a single-blind cluster randomized controlled trial

BACKGROUND

Birth defects are the main cause of fetal death, infant mortality and morbidity worldwide. However, the etiology of birth defects remains largely unknown. Maternal folate status during periconception plays an important role in organogenesis and folic acid supplement reduces the risk of neural tube defects, congenital heart diseases, and several other birth defects. This trial seeks to evaluate the effectiveness of folate-oriented tertiary interventions during periconception on the incidence of fetus and birth defects.

METHODS

This is a single-blind, two-arm cluster randomized controlled trial in Shanghai, China. Eligible women from 22 clusters are recruited at pre-pregnancy physical examinations clinical settings. Compared to the routine perinatal care group (control arm), folate-oriented tertiary interventions will be provided to the intervention arm. The core interventions consist of assessments of folate status and metabolism, folate intake guidance, and re-evaluation of folate status to ensure red blood cell folate level above 400 ng/ml (906 nmol/L) before pregnancy. Screening and consulting of fetus and birth defects, and treatments of birth defects during pregnancy and afterward will be provided to both arms. The primary outcome is a composite incidence of fetus defects, stillbirth, and neonatal birth defects identified from the confirmation of pregnancy to 28 days after birth. Secondary outcomes include maternal and offspring adverse complications and cost-effectiveness of folate-oriented tertiary interventions. This protocol adheres to the SPIRIT Checklist.

DISCUSSION

To achieve the recommended folate status before or during pregnancy is still a challenge worldwide. This community-based cluster-randomized controlled intervention trial will evaluate the effectiveness of a package of interventions aiming at achieving recommended maternal folate status covering pre- and during pregnancy in reducing fetus and birth defects. Our study has the potential to improve the community-based practice of reducing modifiable risk factors of disease and improving primary prevention of the defects in China. The procedures would formulate the policy on folic acid supplementation during periconception against birth defects in primary care settings.

TRIAL REGISTRATION

Clinical Trial Registry, NCT03725878 . Prospectively registered on 31 October 2018.

Environmental Risk Factors for Congenital Heart Disease

Congenital heart disease (CHD) has many forms and a wide range of causes. Clinically, it is important to understand the causes. This allows estimation of recurrence rate, guides treatment options, and may also be used to formulate public health advice to reduce the population prevalence of CHD. The recent advent of sophisticated genetic and genomic methods has led to the identification of more than 100 genes associated with CHD. However, despite these great strides, to date only one-third of CHD cases have been shown to have a simple genetic cause. This is because CHD can also be caused by oligogenic factors, environmental factors, and/or gene-environment interaction. Although solid evidence for environmental causes of CHD have been available for almost 80 years, it is only very recently that the molecular mechanisms for these risk factors have begun to be investigated. In this review, we describe the most important environmental CHD risk factors, and what is known about how they cause CHD.

Placental epigenetics for evaluation of fetal congenital heart defects: Ventricular Septal Defect (VSD)

Ventricular Septal Defect (VSD), the most common congenital heart defect, is characterized by a hole in the septum between the right and left ventricles. The pathogenesis of VSD is unknown in most clinical cases. There is a paucity of data relevant to epigenetic changes in VSD. The placenta is a fetal tissue crucial in cardiac development and a potentially useful surrogate for evaluating the development of heart tissue. To understand epigenetic mechanisms that may play a role in the development of VSD, genome-wide DNA methylation assay on placentas of 8 term subjects with isolated VSD and no known or suspected genetic syndromes and 10 unaffected controls was performed using the Illumina HumanMethylation450 BeadChip assay. We identified a total of 80 highly accurate potential CpGs in 80 genes for detection of VSD; area under the receiver operating characteristic curve (AUC ROC) 1.0 with significant 95% CI (FDR) p-values < 0.05 for each individual locus. The biological processes and functions for many of these differentially methylated genes are previously known to be associated with heart development or disease, including cardiac ventricle development (HEY2, ISL1), heart looping (SRF), cardiac muscle cell differentiation (ACTC1, HEY2), cardiac septum development (ISL1), heart morphogenesis (SRF, HEY2, ISL1, HEYL), Notch signaling pathway (HEY2, HEYL), cardiac chamber development (ISL1), and cardiac muscle tissue development (ACTC1, ISL1). In addition, we identified 8 microRNAs that have the potential to be biomarkers for the detection of VSD including: miR-191, miR-548F1, miR-148A, miR-423, miR-92B, miR-611, miR-2110, and miR-548H4. To our knowledge this is the first report in which placental analysis has been used for determining the pathogenesis of and predicting VSD.

Association Between Maternal Folic Acid Supplementation and Congenital Heart Defects in Offspring in Birth Cohorts From Denmark and Norway

Background Evidence linking individual-level maternal folic acid supplementation to offspring risk of congenital heart defects is lacking. We investigated whether folic acid supplementation in early pregnancy reduces offspring risk of heart defects in 2 large birth cohort studies. Methods and Results Women recruited in early pregnancy within the DNBC (Danish National Birth Cohort), 1996-2003, and MoBa (Norwegian Mother and Child Cohort Study), 2000-2009, were followed until delivery. Information on periconceptional intake of folic acid and other supplements was linked with information on heart defects from national registers. Among 197 123 births, we identified 2247 individuals with heart defects (114/10 000). Periconceptional (4 weeks before through 8 weeks after conception) use of folic acid plus other supplements (54.8%), folic acid only (12.2%), and non-folic acid supplements (5.0%) were compared with no supplement use (28.0%); the adjusted relative risks of heart defects were 0.99 (95% CI, 0.80-1.22), 1.08 (95% CI , 0.93-1.25), and 1.07 (95% CI , 0.97-1.19), respectively. For initiation of folic acid in the preconception period weeks -4 to -1 (33.7%) and the postconception periods 0 to 4 weeks (15.5%), 5 to 8 weeks (17.8%), and 9 to 12 weeks (4.6%), compared with no or late folic acid intake (29.1%), relative risks of heart defect were 1.11 (95% CI , 1.00-1.25), 1.09 (95% CI , 0.95-1.25), 0.98 (95% CI , 0.86-1.12), and 0.97 (95% CI , 0.78-1.20), respectively. Relative risks of severe defects, conotruncal defects, and septal defects showed similar results. Conclusions Folic acid was not associated with offspring risk of heart defects, including severe defects, conotruncal defects, or septal defects.

Meta-Prediction of MTHFR Gene Polymorphism and Air Pollution on the Risks of Congenital Heart Defects Worldwide: A Transgenerational Analysis

Congenital heart disease (CHD) is the leading cause of death in children, and is affected by genetic and environmental factors. To investigate the association of air pollution with methylene-tetrahydrofolate reductase (MTHFR) polymorphisms and the risk of CHD, we included 58 study groups of children and parents, with 12,347 cases and 18,106 controls worldwide. Both MTHFR C677T (rs 1801133) and A1298C (rs 1801131) gene polymorphisms were risks for CHD in children with transgenerational effects from their parents. Countries with greater risks of CHD with a pooled risk ratio (RR) > 2 from MTHFR 677 polymorphisms included Germany, Portugal, China, and Egypt for children; and Brazil, Puerto Rico, Mexico, China, and Egypt for mothers. Whereas, countries with greater risk of CHD with RR > 2 from MTHFR 1298 polymorphisms included Taiwan, Turkey, and Egypt for children; and Brazil, China, and Egypt for mothers. Additionally, meta-prediction analysis revealed that the percentages of MTHFR 677TT and TT plus CT polymorphisms together were increased in countries with higher levels of air pollution, with a trend of increased CHD risks with higher levels of air pollution for children (p = 0.07). Our findings may have significant implications for inflammatory pathways in association with MTHFR polymorphisms and future intervention studies to correct for folate-related enzyme deficits resulted from MTHFR polymorphisms to prevent CHDs for future generations.

Recent Advances in Placenta-Heart Interactions

Congenital heart defects (CHD) occur in ∼1 in every 100 live births. In addition, an estimated 10% of fetal loss is due to severe forms of CHD. This makes heart defects the most frequently occurring birth defect and single cause of in utero fatality in humans. There is considerable evidence that CHD is heritable, indicating a strong contribution from genetic risk factors. There are also known external environmental exposures that are significantly associated with risk for CHD. Hence, the majority of CHD cases have long been considered to be multifactorial, or generally caused by the confluence of several risk factors potentially from genetic, epigenetic, and environmental sources. Consequently, a specific cause can be very difficult to ascertain, although patterns of associations are very important to prevention. While highly protective of the fetus, the in utero environment is not immune to insult. As the conduit between the mother and fetus, the placenta plays an essential role in maintaining fetal health. Since it is not a fully-formed organ at the onset of pregnancy, the development of the placenta must keep pace with the growth of the fetus in order to fulfill its critical role during pregnancy. In fact, the placenta and the fetal heart actually develop in parallel, a phenomenon known as the placenta–heart axis. This leaves the developing heart particularly vulnerable to early placental insufficiency. Both organs share several developmental pathways, so they also share a common vulnerability to genetic defects. In this article we explore the coordinated development of the placenta and fetal heart and the implications for placental involvement in the etiology and pathogenesis of CHD.

Genetic polymorphism of methylenetetrahydrofolate reductase as a potential risk factor for congenital heart disease: A meta-analysis in Chinese pediatric population

BACKGROUND

A meta-analysis of polymorphism C677T (rs1801133) of the methylene tetrahydrofolate reductase (MTHFR) gene as a potential risk factor for congenital heart disease (CHD) in Chinese paediatric population was studied in view of the previously reported controversial results.

METHODS

We searched literature including PubMed, Embase, Cochrane Library, CNKI, Wanfang, and VIP databases that resulted in the identification of a total of 21 separate studies with 6414 subjects that met the inclusion criteria in the Chinese population. The quality assessment of the included studies was preformed and relevant information was collected. We chose the fixed-effect model or random-effect model to calculate the pooled odds ratio (ORs) and its corresponding 95% confidence interval (95% CI) where appropriate. Begg test was used to measure publication bias and sensitivity analyses were done to ensure authenticity of the outcome.

RESULTS

We observed a significant association between MTHFR C677T polymorphism and CHD development in all the genetic models evaluated. The pooled ORs and 95% CIs in all genetic models indicated that children's MTHFR C677T polymorphism was significantly associated with CHD.

CONCLUSION

Our study results indicate that MTHFR gene 677T polymorphism is a genetic risk factor in the development of CHD in Chinese paediatric population.

'Mendelian randomization': an approach for exploring causal relations in epidemiology

OBJECTIVES

To assess the current status of Mendelian randomization (MR) approach in effectively influencing the observational epidemiology for examining causal relationships.

METHODS

Narrative review on studies related to principle, strengths, limitations, and achievements of MR approach.

RESULTS

Observational epidemiological studies have repeatedly produced several beneficiary associations which were discarded when tested by standard randomized controlled trials (RCTs). The technique which is more feasible, highly similar to RCTs, and has the potential to establish a causal relationship between modifiable exposures and disease outcomes is known as MR. The technique uses genetic variants related to modifiable traits/exposures as instruments for detecting causal and directional associations with outcomes.

CONCLUSIONS

In the last decade, the approach of MR has methodologically developed and progressed to a stage of high acceptance among the epidemiologists and is gradually expanding the landscape of causal relationships in non-communicable chronic diseases.

Maternal and infant genetic variants, maternal periconceptional use of selective serotonin reuptake inhibitors, and risk of congenital heart defects in offspring: population based study

Objective To evaluate whether the association between maternal periconceptional use of selective serotonin reuptake inhibitors (SSRIs) and increased risk of congenital heart defects in offspring is modified by maternal or infant genetic variants in folate, homocysteine, or transsulfuration pathways.Design Population based study. DNA from mothers, fathers, and infants was genotyped with an Illumina GoldenGate custom single nucleotide polymorphism panel. A hybrid design based on a log linear model was used to calculate relative risks and Bayesian false discovery probabilities (BFDP) to identify polymorphisms associated with congenital heart defects modified by SSRI use.Data sources Data from the US National Birth Defects Prevention Study on 1180 liveborn infants with congenital heart defects and 1644 controls, born 1997-2008.Main outcome measures Cases included infants with selected congenital heart defects and control infants had no major defects. SSRI use was obtained from telephone interviews with mothers.Results For women who reported taking SSRIs periconceptionally, maternal SHMT1 (rs9909104) GG and AGgenotypes were associated with a 5.9 and 2.4 increased risk of select congenital heart defects in offspring, respectively, versus the AA genotype (BFDP=0.69). Compared with the AA genotype, BHMT (rs492842 and rs542852) GG and AG genotypes were associated with twice the riskof congenital heart defects (BFDP=0.74 and 0.79, respectively). MGST1 (rs2075237) CC and ACgenotypes were associated with an increased risk compared with the GG genotype (8.0 and 2.8, respectively; BFDP=0.79). Single nucleotide polymorphism in infant genes in the folate (MTHFS rs12438477), homocysteine (TRDMT1 rs6602178 and GNMT rs11752813) and transsulfuration (GSTP1 rs7941395 and MGST1 rs7294985) pathways were also associated with an increased risk of congenital heart defects.Conclusions Common maternal or infant genetic variants in folate, homocysteine, or transsulfuration pathways are associated with an increased risk of certain congenital heart defects among children of women taking SSRIs during cardiogenesis.

Association of C677T MTHFR and G20210A FII prothrombin polymorphisms with susceptibility to myocardial infarction

Myocardial infarction (MI) is a common complex pathology, localized in the main leading causes of mortality worldwide. It is the result of the interaction of genetic and environmental factors. The aim of the present study was to investigate the potential association of C677T 5,10-methylenetetrahydrofolate reductase (MTHFR) (rs1801133) and G20210A factor II prothrombin (FII) (rs1799963) polymorphisms with the susceptibility of MI. Following extraction by the standard salting-out procedure, DNA samples of 100 MI patients and 182 apparently healthy controls were genotyped by polymerase chain reaction-restriction fragment length polymorphism using HinfI and HindIII restriction enzymes, respectively. The results show a significant association of the G20210T FII polymorphism with the MI risk. The frequencies of the heterozygote genotype GA, homozygous mutated AA and the G20210A allele was higher among patients compared to controls (GA: 59 vs. 5.5%, P<0.001; AA: 10 vs. 0%, P=0.003; and 20210A: 39.5 vs. 2.7%, P<0.003), suggesting that this polymorphism may be a potential genetic marker for MI. No significant association was observed between the C677T MTHFR and MI occurrence, and there was more heterozygote CT in the patient group compared to the controls. As a multifactorial disease, the development of MI may be the result of numerous factors that influence synergistically its occurrence. Thus, further studies are merited to try to better assess these associations (gene-gene and gene-environment interactions).

Obstructive heart defects associated with candidate genes, maternal obesity, and folic acid supplementation

Right-sided and left-sided obstructive heart defects (OHDs) are subtypes of congenital heart defects, in which the heart valves, arteries, or veins are abnormally narrow or blocked. Previous studies have suggested that the development of OHDs involved a complex interplay between genetic variants and maternal factors. Using the data from 569 OHD case families and 1,644 control families enrolled in the National Birth Defects Prevention Study (NBDPS) between 1997 and 2008, we conducted an analysis to investigate the genetic effects of 877 single nucleotide polymorphisms (SNPs) in 60 candidate genes for association with the risk of OHDs, and their interactions with maternal use of folic acid supplements, and pre-pregnancy obesity. Applying log-linear models based on the hybrid design, we identified a SNP in methylenetetrahydrofolate reductase (MTHFR) gene (C677T polymorphism) with a main genetic effect on the occurrence of OHDs. In addition, multiple SNPs in betaine-homocysteine methyltransferase (BHMT and BHMT2) were also identified to be associated with the occurrence of OHDs through significant main infant genetic effects and interaction effects with maternal use of folic acid supplements. We also identified multiple SNPs in glutamate-cysteine ligase, catalytic subunit (GCLC) and DNA (cytosine-5-)-methyltransferase 3 beta (DNMT3B) that were associated with elevated risk of OHDs among obese women. Our findings suggested that the risk of OHDs was closely related to a combined effect of variations in genes in the folate, homocysteine, or glutathione/transsulfuration pathways, maternal use of folic acid supplements and pre-pregnancy obesity.

Mendelian randomization studies: a review of the approaches used and the quality of reporting

BACKGROUND

Mendelian randomization (MR) studies investigate the effect of genetic variation in levels of an exposure on an outcome, thereby using genetic variation as an instrumental variable (IV). We provide a meta-epidemiological overview of the methodological approaches used in MR studies, and evaluate the discussion of MR assumptions and reporting of statistical methods.

METHODS

We searched PubMed, Medline, Embase and Web of Science for MR studies up to December 2013. We assessed (i) the MR approach used; (ii) whether the plausibility of MR assumptions was discussed; and (iii) whether the statistical methods used were reported adequately.

RESULTS

Of 99 studies using data from one study population, 32 used genetic information as a proxy for the exposure without further estimation, 44 performed a formal IV analysis, 7 compared the observed with the expected genotype-outcome association, and 1 used both the latter two approaches. The 80 studies using data from multiple study populations used many different approaches to combine the data; 52 of these studies used some form of IV analysis; 44% of studies discussed the plausibility of all three MR assumptions in their study. Statistical methods used for IV analysis were insufficiently described in 14% of studies.

CONCLUSIONS

Most MR studies either use the genotype as a proxy for exposure without further estimation or perform an IV analysis. The discussion of underlying assumptions and reporting of statistical methods for IV analysis are frequently insufficient. Studies using data from multiple study populations are further complicated by the combination of data or estimates. We provide a checklist for the reporting of MR studies.

The association of the MTHFR c.1625A>C genetic variant with the risk of congenital heart diseases in the Chinese

The purpose of this study is to investigate the association of methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms with the risk of congenital heart diseases (CHD). The genotypes of the MTHFR genetic variant were determined by the polymerase chain reaction-restriction fragment length polymorphism and DNA sequencing methods. Our data suggested that the allelic and genotypic frequencies of CHD patients were significantly different from non-CHD controls. The MTHFR c.1625A>C genetic variant was significantly associated with the increased risk of CHD (CC vs. AA: odds ratio [OR]=2.29, 95% confidence interval [CI] 1.15-4.53, p=0.016; C vs. A: OR=1.47, 95% CI 1.11-1.96, p=0.008). Results from this study indicate that the MTHFR c.1625A>C genetic variant influences the risk of CHD in the studied population.

Association between MTHFR polymorphisms and congenital heart disease: a meta-analysis based on 9,329 cases and 15,076 controls

The aim of our study was to evaluate the association between polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene and the risk for congenital heart disease (CHD). Electronic literature databases were searched to identify eligible studies published before Jun, 2014. The association was assessed by the odds ratio (OR) with a 95% confidence interval (CI). The publication bias was explored using Begg's test. Sensitivity analysis was performed to evaluate the stability of the crude results. A total of 35 studies were included in this meta-analysis. For the MTHFR C677T polymorphism, we detected significant association in all genetic models for Asian children and the maternal population. Significant association was also detected in T vs. C for a Caucasian paediatric population (OR = 1.163, 95% CI: 1.008–1.342) and in both T vs. C (OR = 1.125, 95% CI: 1.043–1.214) and the dominant model (OR = 1.216, 95% CI:b1.096–1.348) for a Caucasian maternal population. For the MTHFR A1298C polymorphism, the association was detected in CC vs. AC for the Caucasian paediatric population (OR = 1.484, 95% CI: 1.035–2.128). Our results support the MTHFR -677T allele as a susceptibility factor for CHD in the Asian maternal population and the -1298C allele as a risk factor in the Caucasian paediatric population.

Association analysis between MTHFR genetic polymorphisms and the risk of congenital heart diseases in Chinese Han population

OBJECTIVES

Congenital heart diseases (CHD) are common birth defects in the world. The methylenetetrahydrofolate reductase (MTHFR) gene is one of the most important candidate genes for the development of CHD. This case-control study aimed to evaluate the effect of MTHFR c.382A>G and c.1129C>T genetic polymorphisms as risk factors for the development of CHD.

METHODS

A total of 230 CHD patients and 237 non-CHD controls were included in the present study. The genotyping of MTHFR c.382A>G and c.1129C>T genetic polymorphisms were detected by the polymerase chain reaction-restriction fragment length polymorphism and created restriction site-polymerase chain reaction methods, respectively.

KEY FINDINGS

The alleles/genotypes distribution from these two genetic polymorphisms were statistically associated with the increased risk of CHD (for c.382A>G, GG versus AA: odds ratio (OR) = 2.39, 95% confidence interval (CI), 1.27 to 4.52, P = 0.006; for c.1129C>T, TT versus CC: OR = 2.73, 95% CI, 1.33 to 5.62, P = 0.005). The allele G and genotype GG of c.382A>G and allele T and genotype TT of c.1129C>T genetic polymorphisms might contribute to CHD susceptibility.

CONCLUSION

These preliminary findings indicate that these two MTHFR genetic polymorphisms are related with the risk of CHD in Chinese Han population, and might be potentially utilized as molecular markers.

The association between c.1333C > T genetic polymorphism of MTHFR gene and the risk of congenital heart diseases

This study aims to evaluate the influence of methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms on congenital heart diseases (CHD) risk. The frequencies of allelic and genotypic in CHD patients were significantly different from non-CHD controls. Our data suggested that the c.1333C > T genetic polymorphism of MTHFR gene was statistically associated with the increased risk of CHD [TT versus CC: odds ratio (OR) = 2.70, 95% confidence interval (CI) 1.34-5.45, p = 0.005; T versus C: OR = 1.38, 95% CI 1.03-1.86, p = 0.032]. Our findings indicate that the c.1333C > T genetic polymorphism influences CHD risk in the studied population.