The genetics of folate metabolism and maternal risk of birth of a child with Down syndrome and associated congenital heart defects

Association of maternal methionine synthase reductase gene polymorphisms with the risk of congenital heart disease in offspring: a hospital-based case-control study

BACKGROUND

Evidence suggests that periconceptional folic acid supplementation may prevent congenital heart disease (CHD). Methionine synthase reductase (MTRR) is one of the key regulatory enzymes in the folate metabolic pathway. This study aimed to comprehensively evaluate the association of single nucleotide polymorphisms (SNPs) in the maternal MTRR gene with CHD risk in offspring.

METHODS

A hospital-based case-control study involving 740 mothers of CHD cases and 683 health controls was conducted.

RESULTS

The study showed that maternal MTRR gene polymorphisms at rs1532268 (C/T vs. C/C: aOR = 1.524; T/T vs. C/C: aOR = 3.178), rs1802059 (G/A vs. G/G: aOR = 1.410; A/A vs. G/G: aOR = 3.953), rs2287779 (G/A vs. G/G: aOR = 0.540), rs16879334 (C/G vs. C/C: aOR = 0.454), and rs2303080 (T/A vs. T/T: aOR = 0.546) were associated with the risk of CHD. And seven haplotypes were observed to be associated with the risk of CHD, T-G-A haplotype (OR = 1.298), C-A-C-C (OR = 4.824) and A-G haplotype (OR = 1.751) were associated with increased risk of CHD in offspring; A-A-A (OR = 0.773), T-A-A (OR = 0.557), G-A-C-C (OR = 0.598) and G-C (OR = 0.740) were associated with decreased risk of CHD in offspring.

CONCLUSIONS

Maternal MTRR gene polymorphisms were associated with CHD in offspring, and its haplotypes have affected the occurrence of CHD. Furthermore, given the complexity and heterogeneity of CHD, the mechanisms by which these factors influence offspring cardiac development remain unknown, and studies in larger samples in an ethnically diverse population are needed.

Association of TP53 rs1042522 G > C, MDM2 rs2279744 T > G, and miR-34b/c rs4938723 T > C polymorphisms with aneuploidy pregnancy susceptibility

BACKGROUND

Aneuploidy pregnancy is a severe major birth defect and causes about 50% spontaneous miscarriages with unknown etiology. To date, only a few epidemiological studies with small sample sizes have investigated the risk factors for aneuploidy pregnancy. TP53, MDM2, and miR-34b/c genes are implicated in tumorigenesis with aneuploidy, yet the function of their polymorphisms in aneuploidy pregnancy susceptibility needs to be clarified.

OBJECTIVE

To elucidate the association of TP53 rs1042522 G > C, MDM2 rs2279744 309 T > G, and miR-34b/c rs4938723 T > C specific polymorphisms with aneuploidy pregnancy.

METHODS

In the retrospective case-control study, 330 aneuploidies pregnancy women and 813 normal pregnancy controls were recruited between January 2018 and April 2022 at the First People's Hospital of Yunnan Province, Kunming, China. Three functional polymorphisms, the TP53 rs1042522 G > C (Arg72Pro), MDM2 rs2279744 309 T > G, and miR-34b/c rs4938723 T > C, were genotyped using the snapshot method.

RESULTS

The frequency distribution of three genotypic variants was not different between case and control pregnant women and was similar to with Hardy-Weinberg Equilibrium (HWE). However, in the younger subgroup (less than 35 years old), a significant difference was detected in allele and recessive model (p = 0.01). In the advanced age subgroup (more than or equal to 35 years old), G of MDM2 rs2279744 T > G revealed a significantly higher frequency in cases than controls (p = 0.045), and miR-34b/c rs4938723 T > C revealed a significant difference under the dominant model (p = 0.03), but no significant differences were observed in other models and in both younger and older subgroup (p > 0.05, respectively). These results suggest that individual polymorphisms were not associated with aneuploidy pregnancy, combined with age, they may serve as a risk factor for aneuploidy pregnancy.

CONCLUSION

Combination of TP53 rs1042522 G > C, MDM2 rs2279744 T > G, and miR-34b/c rs4938723 T > C polymorphisms with maternal age may be related to aneuploidy pregnancy susceptibility. These findings might elaborate on the genetic etiology of aneuploidy pregnancy.

Effect of Low Dietary Folate on Mouse Spermatogenesis and Spindle Assembly Checkpoint Dysfunction May Contribute to Folate Deficiency-Induced Chromosomal Instability in Cultured Mouse Spermatogonia

Folate, as the initial substrate in one-carbon metabolism, is involved in the synthesis of important substances such as DNA, RNA, and protein. Folate deficiency (FD) is associated with male subfertility and impaired spermatogenesis, yet the underlying mechanisms are poorly understood. In the present study, we established an animal model of FD to investigate the effect of FD on spermatogenesis. GC-1 spermatogonia were used as a model to investigate the effect of FD on proliferation, viability, and chromosomal instability (CIN). Furthermore, we explored the expression of core genes and proteins of spindle assembly checkpoint (SAC), a signaling cascade ensuring accurate chromosome segregation and preventing CIN during mitosis. Cells were maintained in medium containing 0, 20, 200, or 2000 nM folate for 14 days. CIN was measured by using a cytokinesis-blocked micronucleus cytome assay. We found that sperm counts decreased significantly (p < 0.001) and the rate of sperm with defects in the head increased significantly (p < 0.05) in FD diet mice. We also found, relative to the folate-sufficient conditions (2000 nM), cells cultured with 0, 20, or 200 nM folate exhibited delayed growth and increased apoptosis in an inverse dose-dependent manner. FD (0, 20, or 200 nM) significantly induced CIN (p < 0.001, p < 0.001, and p < 0.05, respectively). Moreover, FD significantly and inverse dose dependently increased the mRNA and protein expression of several key SAC-related genes. The results indicate that FD impairs SAC activity, which contributes to mitotic aberrations and CIN. These findings establish a novel association between FD and SAC dysfunction. Thus, FD-impaired spermatogenesis may be partly due to genomic instability and proliferation inhibition of spermatogonia.

Association of C677T and A1298C polymorphisms of the MTHFR gene with maternal risk for Down syndrome: A meta-analysis of case-control studies

BACKGROUND

Several studies around the world support the hypothesis that genetic polymorphisms involved in folate metabolism could be related to the maternal risk for Down syndrome (DS). Most of them investigated the role of MTHFR C677T and/or A1298C polymorphisms as maternal risk factors for DS, but their results are often conflicting and still inconclusive.

METHODS

We conducted a systematic review and meta-analysis to clarify the association of MTHFR C677T and/or A1298C polymorphisms with the maternal risk of DS. Our search strategy selected 42 eligible case control studies for a total of 4131 case mothers and 5452 control mothers. The Newcastle-Ottawa Scale was used to assess the methodological quality of the selected studies. To assess the confidence of statistically significant associations we applied false positive report probability test, and we performed the trial sequential analysis to minimize the type I error and random error.

RESULTS

We observed significant associations between the MTHFR C677T polymorphism and maternal risk for DS for each of the genetic models investigated (dominant, recessive, codominant, and allelic contrast). Subgroup analysis by region revelated significant association in the Asian population for all the genetic models investigated. Significant associations were also found for certain genetic models in North American, South American, and Middle Eastern populations, while no association was observed in Europeans. The MTHFR A1298C polymorphism did not show any association with the maternal risk of DS, either alone or in combination with the C677T one. The results of false positive report probability to verify the confidence of a significant association suggest that the association between the MTHFR C677T polymorphism and the maternal risk for DS is noteworthy, with high confidence in Asians.

CONCLUSION

The results of this meta-analysis support that the MTHFR C677T polymorphism, but not the A1298C one, is associated with the maternal risk for DS. Further studies are required to better characterize the contribution of gene-gene and gene-nutrient interactions as well as those of other regional or ethnic factors that could explain the observed different effect size in different populations.

Early developmental profiles among infants with Down syndrome

BACKGROUND

Down syndrome (DS) generally predisposes children to a pattern of relative developmental strengths and challenges, but within-syndrome heterogeneity is also commonly observed across many dimensions. The present research examines whether heterogeneity in developmental presentation can be detected during infancy in DS and whether factors associated with differing profiles can be identified.

METHODS

Infants with DS (n = 75; age range: 3.9-17.6 months) were administered the Bayley Scales of Infant Development III (Bayley-III). A primary caregiver provided information regarding developmental history and family demographics. Latent profile analysis was conducted to identify whether early profiles were present across the five Bayley-III domains.

RESULTS

Three developmental profiles were observable within the sample: a 'Mild Delay' Profile, an 'Moderate Delay' Profile and a 'Pronounced Delay' Profile. In addition, chronological age, having received heart surgery and having received occupational therapy were associated with probability of profile membership.

CONCLUSIONS

Findings from this study contribute to the growing knowledgebase regarding heterogenous presentations associated with DS and can inform early intervention planning.

Molecular mechanism of substrate recognition by folate transporter SLC19A1

Folate (vitamin B₉) is the coenzyme involved in one-carbon transfer biochemical reactions essential for cell survival and proliferation, with its inadequacy causing developmental defects or severe diseases. Notably, mammalian cells lack the ability to de novo synthesize folate but instead rely on its intake from extracellular sources via specific transporters or receptors, among which SLC19A1 is the ubiquitously expressed one in tissues. However, the mechanism of substrate recognition by SLC19A1 remains unclear. Here we report the cryo-EM structures of human SLC19A1 and its complex with 5-methyltetrahydrofolate at 3.5-3.6 Å resolution and elucidate the critical residues for substrate recognition. In particular, we reveal that two variant residues among SLC19 subfamily members designate the specificity for folate. Moreover, we identify intracellular thiamine pyrophosphate as the favorite coupled substrate for folate transport by SLC19A1. Together, this work establishes the molecular basis of substrate recognition by this central folate transporter.

Different effects of maternal homocysteine concentration, MTHFR and MTRR genetic polymorphisms on the occurrence of fetal aneuploidy

RESEARCH QUESTION

Do maternal homocysteine (Hcy) concentrations, MTHFR and MTRR genes have effects on the occurrence of fetal aneuploidy?

DESIGN

A total of 619 aneuploidy mothers and 192 control mothers were recruited in this study. Differences in distributions of maternal MTHFR 677C>T, MTHFR 1298A>C and MTRR 66A>G genetic polymorphisms and maternal Hcy concentrations between aneuploidy mothers and control mothers were analysed.

RESULTS

The maternal MTHFR 677C>T polymorphism was found to be a risk factor for the occurrence of many fetal non-mosaic aneuploidies studied here, including trisomies 13, 15, 16, 18, 21, 22, TRA and TS. The maternal MTHFR 1298A>C polymorphism was found to be a risk factor specifically associated with the occurrence of fetal trisomy 15 and fetal TS. The maternal MTRR 66A>G polymorphism was found to be a risk factor only specifically associated with the occurrence of fetal trisomy 21. The Hcy concentrations of mothers of trisomies 22, 21, 18, 16, 15 and TS fetuses were significantly higher than the Hcy concentrations of control mothers.

CONCLUSIONS

Overall, data suggested an association between these maternal polymorphisms and the susceptibility of fetal non-mosaic trisomy and Turner syndrome. However, these three maternal polymorphisms had different associations with the susceptibility of different fetal aneuploidies, and the elevated maternal Hcy concentration appeared to be a likely risk factor for fetal Turner syndrome and fetal trisomies.

Blood levels of circulating methionine components in Alzheimer’s disease and mild cognitive impairment: A systematic review and meta-analysis

Background

Circulating methionine components have been reported to be associated with Alzheimer’s disease (AD) and mild cognitive impairment (MCI), although outcomes are not always consistent.

Materials and methods

Database searching was conducted using PubMed, Embase, Cochrane Library, and Web of Science from inception to 26 December 2021. In this study, two reviewers independently identified eligible articles and extracted the data. We used Joanna Briggs Institute (JBI) Critical Appraisal tools to assess the overall quality of the included studies. STATA software was employed to perform meta-analysis evaluating the standardized mean difference (SMD) with its 95% confidence intervals (CIs) using random-effects models. Evidence quality was assessed using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) criteria.

Results

Totally, 30 observational studies were eligible for inclusion. Compared with cognitively normal controls, patients with AD had increased homocysteine (Hcy) levels in the blood [standardized mean difference (SMD) = 0.59, 95% confidence interval [CI]: 0.36–0.82, P = 0.000], plasma (SMD = 0.39, 95% CI: 0.23–0.55, P = 0.000), and serum (SMD = 1.56, 95% CI: 0.59–2.95, P = 0.002). Patients with MCI were not significantly different from controls (SMD = 0.26, 95% CI: –0.07–0.58, P = 0.127). Patients with AD or MCI did not significantly differ from controls of blood vitamin B12 levels, AD (SMD = –0.05, 95% CI: –0.19–0.08, P = 0.440), or MCI (SMD = 0.01, 95% CI: –0.16–0.17, P = 0.94). Some cohort studies have suggested that higher Hcy, methionine, and S-adenosylmethionine levels may accelerate cognitive decline in patients with MCI or AD, and vitamin B12 deficiency is a risk factor for the disease; however, the results of other studies were inconsistent. According to the GRADE system, all these outcomes scored very low to low quality, and no high-quality evidence was found.

Conclusion

Only Hcy levels in the plasma and serum were found to be inversely related to the risk of AD. However, due to the low quality of supporting these results, high-quality studies are needed to verify these findings.

Systematic Review Registration

http://www.crd.york.ac.uk/PROSPERO/, identifier CRD42022308961.

Maternal MTHFR 677C>T, 1298A>C gene polymorphisms and risk of offspring aneuploidy

OBJECTIVE

The objective was to investigate the association between maternal methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms, crucial for DNA methylation, and risk of offspring aneuploidy.

METHODS

MTHFR gene polymorphisms 677C>T and 1298A>C were determined by polymerase chain reaction based method, in 163 women with offspring aneuploidy and 155 women with healthy children. Five genetic models were used to assess risk, according to the type of aneuploidy and the age of women at conception.

RESULTS

MTHFR 677TT genotype and T allele were significantly more prevalent among women with offspring aneuploidy, with an increased risk of aneuploidy demonstrated under a recessive (OR 3.499), homozygote (OR 3.456) and allele contrast model (OR 1.574). The more prominent association was found with sex chromosome aneuploidies and trisomy 13/18, and also in women ≤35 years at conception. No association was observed between 1298A>C polymorphism and risk of offspring aneuploidy, although synergistic effect of two polymorphisms increase the risk of aneuploidy, primarily amplifying the 677T allele effects (p<0.001).

CONCLUSION

Maternal MTHFR 677C>T gene polymorphism, alone or in combination with another 1298A>C polymorphism, appears to be a substantial risk factor for offspring aneuploidy in Montenegro population, especially for sex chromosome aneuploidies and trisomy 13/18, and among younger women. This article is protected by copyright. All rights reserved.

Association between MTR A2756G polymorphism and susceptibility to congenital heart disease: A meta-analysis

The association between methionine synthase (MTR) A2756G (rs1805087) polymorphism and the susceptibility to congenital heart disease (CHD) has not been fully determined. A meta-analysis of case-control studies was performed to systematically evaluate the above association. Studies were identified by searching the PubMed, Embase, Web of Science, China National Knowledge Infrastructure, and WanFang databases from inception to June 20, 2021. Two authors independently performed literature search, data extraction, and quality assessment. Predefined subgroup analyses were carried out to evaluate the impact of the population ethnicity, source of healthy controls (community or hospital-based), and methods used for genotyping on the outcomes. A random-effects model was used to combine the results, and 12 studies were included. Results showed that MTR A2756G polymorphism was not associated with CHD susceptibility under the allele model (odds ratio [OR]: 0.96, 95% confidence interval [CI]: 0.86 to 1.07, P = 0.43, I² = 4%), heterozygote model (OR: 0.95, 95% CI: 0.84 to 1.07, P = 0.41, I² = 0%), homozygote model (OR: 1.00, 95% CI: 0.64 to 1.55, P = 0.99, I² = 17%), dominant genetic model (OR: 0.95, 95% CI: 0.84 to 1.07, P = 0.41, I² = 0%), or recessive genetic model (OR: 0.94, 95% CI: 0.62 to 1.43, P = 0.32, I² = 13%). Consistent results were found in subgroup analyses between Asian and Caucasian populations in studies with community and hospital-derived controls as well as in studies with PCR-RFLP and direct sequencing (all P values for subgroup differences > 0.05). In conclusion, current evidence does not support an association between MTR A2756G polymorphism and CHD susceptibility.

Down-regulation of circPTTG1IP induces hepatocellular carcinoma development via miR-16-5p/RNF125/JAK1 axis

Circular RNAs are known to regulate the biological processes of hepatocellular carcinoma (HCC), and humans with Down syndrome are at low risk of developing solid tumors due to the amplification of several tumor suppressor genes on human chromosome 21 (HSA21). Here, we aimed to investigate the potential role of circRNAs originating from HSA21 in the progression of HCC. CircRNA-sequencing was performed to analyze differentially expressed circRNAs in 4 HCC and peritumor tissues, and circRNAs originating from HSA21 were further analyzed. Circ_0061984 (circPTTG1IP) was chosen for further study because it showed the lowest expression in HCC tissues, and qRT-PCR was used to confirm the expression of circPTTG1IP in HCC patient tissues. The biological function of circPTTG1IP was detected in HCC cells both in vivo and in vitro. Moreover, luciferase reporter assays, circRNA immunoprecipitation, and fluorescence in situ hybridization (FISH) were used to investigate the potential mechanism of circPTTG1IP. Finally, the possible mechanisms of filgotinib in circPTTG1IP-driven HCC were assessed. CircPTTG1IP expression was decreased in HCC compared to peritumoral tissues. Moreover, low circPTTG1IP expression was revealed to be associated with a poor prognosis of HCC patients. Elevation of circPTTG1IP was revealed to inhibit HCC development both in vitro and in vivo. Mechanistically, circPTTG1IP was shown to function as a competing endogenous RNA (ceRNA) of RNF125 by binding miR-16-5p to increase the level of the E3 ubiquitin ligase RNF125, which further ubiquitinated and degraded JAK1 protein. Finally, we demonstrated that administration of filgotinib, a JAK1 inhibitor, restricted HCC progression induced by low circPTTG1IP expression. Thus, we revealed that circPTTG1IP is a novel tumor suppresser circRNA in HCC and that a low circPTTG1IP level promotes HCC development via the miR-16-5p/RNF125/JAK1 axis. Patients with low circPTTG1IP may benefit from filgotinib treatment.

Red cell folate status among a subset of Canadian children with Down Syndrome post-fortification

BACKGROUND

Trisomy 21 or Down Syndrome (DS) is associated with altered methylation pathways. Children with DS may therefore represent a population subgroup with vulnerability to increased exposures to folic acid, which is involved in one-carbon metabolism. Folic acid (FA) fortification of flour and maternal FA supplementation are intended to reduce neural tube defects related to folate deficiency. The interventions have been widely successful in Canada. Emerging evidence suggests that higher FA exposures may also have potential negative consequences, including implications for DNA methylation. This retrospective chart review provides insight on the red blood cell (RBC) folate status of a subset of Canadian children and infants with DS, post-fortification.

METHODS

Children with DS in two Canadian provinces were assessed in the community. Access to RBC folate testing was variable, limiting sample size to 39 (n = 27 for children ≤6 years; n = 12 for children 6-18 years). All children with DS and an RBC folate result were included. The use of FA-containing supplements and formula was documented.

RESULTS

Among children 6-18 years, 100% had RBC folates >1000 nmol/L, 50% were >2000 nmol/L and 25% had levels above the upper laboratory reporting limit. Among the younger children (<6 years), 52% had RBC folates >2000 nmol and 2 children exceeded 3000 nmol/L. Among exclusively breast-fed infants (<12 months), 100% had RBC folates >1000 nmol/L and 50% had levels >2000 nmol/L, suggestive of in-utero or maternal exposures. RBC folate status among this subset of Canadian children with DS is higher than documented for the larger Canadian population, and higher than among US children with DS.

CONCLUSIONS

Young Canadian children with DS demonstrated high post-fortification RBC folate status. RBC folate status was higher than reported for the larger Canadian population, and higher than for US children with Down Syndrome. Consumption of folic acid-containing formula and/or supplements was relatively low among these Canadian children with DS, suggesting maternal FA supplements and/or FA-fortified foods may be important etiological factors. A larger, prospective study is needed to validate these results, and to explore potential health implications among this vulnerable population.

Health economic evaluation of noninvasive prenatal testing and serum screening for down syndrome

Background

Down syndrome (DS), also known as trisomy 21 (T21), is the most common genetic disorder associated with intellectual disability. There are two methods commonly used for prenatal testing of DS: serum screening (SS) for biomarkers in maternal serum and noninvasive prenatal testing (NIPT) for aneuploidy by cell-free DNA (cfDNA) in maternal plasma. However, cost-effectiveness analyses of these two methods are mostly based on data derived from simulations with various models, with theoretical values calculated. In this study, we statistically analyzed clinical DS screening data and pregnancy outcomes during the follow-up of pregnant women in Zhuhai City, China. The economics of the two mainstream prenatal DS screening methods was evaluated from a public health perspective.

Methods

A retrospective analysis was performed on the data of 17,363 pregnant women who received SS and NIPT during gestation in Zhuhai from 2018 to 2019, and a cost-effectiveness analysis was performed with four screening strategies. In strategy I, all pregnant women received SS, and those with T21 risk ≥1/270 had invasive prenatal diagnosis (IPD). In strategy II, all pregnant women received SS, those with T21 risk ≥ 1/270 had IPD, and those with 1/270 > T21 risk ≥ 1/1,000 had NIPT; then, women at high risk based on NIPT also had IPD. In strategy III, all pregnant women received SS, and those with T21 risk ≥1,000 had NIPT; then, women at high risk based on NIPT results had IPD. In strategy IV, all pregnant women received NIPT and those at high risk based on NIPT results had IPD. Finally, to assess the cost and effectiveness of DS screening, the total costs were calculated as the sum of screening and diagnosis as well as the direct and indirect economic burden during the average life cycle of DS patients.

Results

A total of 22 of the 17,363 (1/789) pregnant women had DS, of which only one woman was over 35 years of age. SS detected 1,024 cases at high risk of T21 (≥1/270), 8 cases were true positive, with a positive predictive value of 0.78% and a detection rate of 36.4%. NIPT detected 27 cases at high risk of T21 (Z ≥ 3) and 22 cases of DS, with a positive predictive value of 81.5% and a detection rate of 100%. Strategy I had the largest total cost of 65.54 million CNY, strategy II and III had similar total costs of 40 million CNY, and strategy IV had the lowest total cost of 14.91 million CNY. By comparison, the screening strategy with NIPT alone had the highest health economic value for DS.

Conclusions

SS was greatly affected by nuchal translucency and the accuracy of gestational age measured by ultrasonography. Unstandardized ultrasonography was an important reason for the low DS detection rate with SS. The influence of interfering factors on NIPT was much lower than in SS. NIPT can be used as an alternative to SS and as a primary screening strategy of prenatal DS screening for secondary prevention and control of birth defects. NIPT greatly decreased the frequency of IPD and the miscarriages associated with IPD, saved the limited medical and health resources, and greatly increased DS detection rate. Therefore, NIPT has great social and economic benefits.

Maternal Risk Factors Triggering Congenital Heart Defects in Down Syndrome: A Case-Control Study

OBJECTIVES

Maternal MTHFR and MTRR polymorphisms as a risk of CHD in DS fetus were studied along with maternal folic acid supplementation, which could influence the folate metabolism along with other risk factors.

MATERIAL AND METHODS

A case-control study comprising of mothers of DS with and without CHD along with controls were recruited from a tertiary care center since 2018-2019. Genomic DNA was isolated followed by PCR-RFLP.

RESULTS

Mothers with age ≥35 years and having history of miscarriages have a higher risk of giving birth to DS with CHD (n = 35% and 42%, respectively). Mothers who carried the MTHFR 677CT/TT and MTRR 524CT/TT genotypes combination in the folic acid nonusers group during pregnancies had six-fold (OR = 6.909, p-value = 0.027; 95% CI-1.23 ± 38.51) and four-fold (OR = 4.75, p-value = 0.040; 95% CI-1.067 ± 21.44) increased odds of having a DS child with CHD, respectively, as compared to folic acid users.

CONCLUSION

Maternal age, folic acid supplementation, and previous history of miscarriages is involved in the etiology of CHD in DS fetus in Indian population. Maternal MTHFR and MTRR polymorphisms are also involved in the occurrence of CHD and DS in Indian population when controlling for periconceptional folic acid supplementation.

LIMITATIONS

Single-Centered Study.

An Assessment of Selected Molecular and Biochemical Markers of the Folate Pathway as Potential Risk Factors for Fetal Trisomy 21 during the First Trimester of Pregnancy in the Polish Population

Are the maternal gene variants MTHFR: c.665C>T, MTHFR: c.1286A>C, MTR: c.2756A>G, MTRR: c.66A>G, RFC1: c.80C>T and TCN2: c.776G>C and blood markers of the folate pathway important factors in assessing the risk of fetal trisomy 21 (fetal-T21)? Twenty pregnant women with a high risk and twenty with a low risk of fetal-T21 underwent prenatal examination. Selected gene variants and folate pathway markers and pregnancy-associated plasma protein A (PAPP-A) and free β-subunit of human chorionic gonadotropin β (free-β-hCG) multiple of the medians (MoMs) were determined. The distributions of the alternative alleles and genotypes of the gene variants did not differ between the studied groups. There was no relationship between PAPP-A and β-hCG MoM values and the presence of allele alternative genotype variants. The occurrence of alternative variants of the selected genes and concentrations of most of the studied folate pathway markers may not play a crucial role in the risk of fetal-T21 in pregnant women. However, the relationships between erythrocyte folate concentrations and the occurrence of alternative variants: c.665C>T MTHFR and c.776G>C TCN2, as well as the methylmalonic acid concentration and the occurrence of alternative variant c.776G>C TCN2 in pregnant women with fetal-T21, encourage further research. So far, of the biochemical markers, maternal PAPP-A and β-hCG MoM values remain independent risk factors for fetal-T21.

Correlation among maternal risk factors, gene methylation and disease severity in females with autism spectrum disorder

Aim: To detect early-life environmental factors leading to DNA methylation changes of autism spectrum disorder (ASD)-related genes in young ASD females and reveal epigenetic biomarkers of disease severity. Materials & methods: We investigated blood methylation levels of MECP2, OXTR, BDNF, RELN, BCL2, EN2 and HTR1A genes in 42 ASD females. Results: Maternal gestational weight gain correlated with BDNF methylation levels (Bonferroni-corrected p = 0.034), and lack of folic acid supplementation at periconception resulted in higher disease severity in the ASD children (Bonferroni-corrected p = 0.048). RELN methylation levels were inversely correlated with disease severity (Bonferroni corrected p = 0.042). Conclusion: The present study revealed gene-environment interactions and potential epigenetic biomarkers of disease severity in ASD females.

Association between MTHFR C677T and A1298C gene polymorphisms and maternal risk for Down syndrome: A protocol for systematic review and/or meta-analysis

BACKGROUND

Down syndrome (DS) is one of the most common chromosomal abnormalities among live-born babies and one of the best-known intellectual disability disorders in humans. Errors leading to trisomy 21 are primarily arising from defects in chromosomal segregation during maternal meiosis (about 88% of cases), and the focus of many investigations has been to identify maternal risk factors favoring chromosome 21 malsegregation during oogenesis. Maternal polymorphisms of genes required for folate metabolism are the most investigated risk factors for the birth of children with DS. Through this review, we sought to investigate the association of the polymorphisms "C677T" and "A1298C" of the MTHFR gene with maternal risk for DS.

METHODS

We will use the databases PubMed, Embase, Scopus and Web of Science to search for case-control studies published from 1999 up to September 2021 without language restriction. Results will be presented as relative risks and 95% confidence intervals for dichotomous outcomes and mean differences, or standardized mean differences along with 95% confidence intervals, for continuous outcomes. The all data synthesis will be analyzed on the Review Manager 5.2 version software.

RESULTS

This study will be able to clarify all the doubts we seek and that it will be able to provide accurate data that will be able to describe how these polymorphisms can act to increase the predisposition for the birth of children with DS in different populations and under different dietary conditions.

CONCLUSIONS

This study will clarify the relationship between C677T and A1298C polymorphisms MTHFR gene with increased the maternal risk for Down syndrome.

REGISTRATION

This systematic review and meta-analysis protocol has been registered on the Prospective Registry of International Systematic Review and Meta-analyses: CRD42021269338.

One-carbon metabolism pathway genes and their non-association with the development of amyotrophic lateral sclerosis

Although of unknown etiology, some mechanisms associated with the metabolic cycle of folate are speculated to be related to the genesis of amyotrophic lateral sclerosis (ALS). Thus, the aim of the study was to analyze the role of genetic polymorphisms rs1051266 in SLC19A1 gene and rs1805087 in MTR gene and their associations with ALS development. A case-control study was conducted with 101 individuals with ALS and 119 individuals without diagnosis of neurodegenerative diseases, from the Brazilian central population. The polymorphisms were determined using the polymerase chain reaction-restriction fragment length polymorphism technique. The results showed no statistically significant differences, even when genotypes were analyzed by the dominant, recessive, codominant, and overdominant inheritance models. It was observed a statistical significance relating alcohol consumption with individuals in the case group (p = 0.01). Therefore, the need for more studies to evaluate the influence of genetic variants is highlighted, seeking to provide information on the etiopathogenesis of ALS.

Understanding etiology of chromosome 21 nondisjunction from gene × environment models

Maternal risk factors and their interactions with each other that associate chromosome 21 nondisjunction are intriguing and need incisive study to be resolved. We determined recombination profile of nondisjoined chromosome 21 and maternal genotypes for four selected polymorphic variants from the folate regulators genes stratifying the women according to the origin of segregation error and age at conception. We conducted association study for genotype and maternal addiction to smokeless chewing tobacco, usually chopped tobacco leaves or paste of tobacco leaves with the incidence of Down syndrome birth. Additionally, we designed various logistic regression models to explore the effects of maternal genotype, maternal habit of smokeless chewing tobacco, maternal age at conception and all possible interactions among them on chromosome 21 nondisjunction. We found folate regulator gene mutations are associated with maternal meiosis II error. Regression models revealed smokeless chewing tobacco and folate polymorphic/mutant risk genotype interact with each other to increase the risk of reduced and single peri-centromeric recombination events on chromosome 21 that nondisjoined at meiosis II in the oocytes and the effect is maternal age independent. We inferred maternal folate polymorphic/mutant risk genotypes and habit of smokeless chewing tobacco interact with each other and increase the risk of meiosis II error in oocytes in maternal age-independent manner.

Molecular Cytogenetic Classification of Down Syndrome and Screening of Somatic Aneuploidy in Mothers

Down Syndrome (DS) caused by trisomy 21 results in various congenital and developmental complications in children. It is crucial to cytogenetically diagnose the DS cases early for their proper health management and to reduce the risk of further DS childbirths in mothers. In this study, we performed a cytogenetic analysis of 436 suspected DS cases using karyotyping and fluorescent in situ hybridization. We detected free trisomies (95.3%), robertsonian translocations (2.4%), isochromosomes (0.6%), and mosaics (1.2%). We observed a slightly higher incidence of DS childbirth in younger mothers compared to mothers with advanced age. We compared the somatic aneuploidy in peripheral blood of mothers having DS children (MDS) and control mothers (CM) to identify biomarkers for predicting the risk for DS childbirths. No significant difference was observed. After induced demethylation in peripheral blood cells, we did not observe a significant difference in the frequency of aneuploidy between MDS and CM. In conclusion, free trisomy 21 is the most common type of chromosomal abnormality in DS. A small number of DS cases have translocations and mosaicism of chromosome 21. Additionally, somatic aneuploidy in the peripheral blood from the mother is not an effective marker to predict DS childbirths.

One-carbon epigenetics and redox biology of neurodegeneration

One-carbon metabolism provides the methyl groups for both DNA and histone tail methylation reactions, two of the main epigenetic processes that tightly regulate the chromatin structure and gene expression levels. Several enzymes involved in one-carbon metabolism, as well as several epigenetic enzymes, are regulated by intracellular metabolites and redox cofactors, but their expression levels are in turn regulated by epigenetic modifications, in such a way that metabolism and gene expression reciprocally regulate each other to maintain homeostasis and regulate cell growth, survival, differentiation and response to environmental stimuli. Increasing evidence highlights the contribution of impaired one-carbon metabolism and epigenetic modifications in neurodegeneration. This article provides an overview of DNA and histone tail methylation changes in major neurodegenerative disorders, namely Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis, discussing the contribution of oxidative stress and impaired one-carbon and redox metabolism to their onset and progression.

Epigenetic regulation in Alzheimer's disease: is it a potential therapeutic target?

Introduction: Alzheimer's disease (AD) is the most common neurodegenerative disorder and the primary form of dementia in the elderly. Changes in DNA methylation and post-translational modifications of histone tails are increasingly observed in AD tissues, and likely contribute to disease onset and progression. The reversibility of these epigenetic marks offers the potential for therapeutic interventions.Areas covered: After a concise and updated overview of DNA methylation and post-translational modifications of histone tails in AD tissues, this review provides an overview of the animal and cell culture studies investigating the potential of targeting these modifications to attenuate AD-like features. PubMed was searched for relevant literature between 2003 and 2021.Expert opinion: Methyl donor compounds and drugs acting on histone tail modifications attenuated the AD-like features and improved cognition in several transgenic AD mice; however, there are concerns about safety and tolerability for long-term treatment in humans. The challenges will be to take advantage of recent epigenome-wide investigations to identify the principal targets for future interventions, and to design novel, selective and safer agents. Natural compounds exerting epigenetic properties could represent a promising opportunity to delay disease onset in middle-aged individuals at increased AD risk.

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.

Methylenetetrahydrofolate Reductase Dimer Configuration as a Risk Factor for Maternal Meiosis I-Derived Trisomy 21

BACKGROUND

Evidence suggests that the dimer configuration of methylenetetrahydrofolate reductase (MTHFR) enzyme might be destabilized by polymorphisms in monomers at the positions C677T and A1298C. It has been observed that these polymorphisms may lead to stable (CCAA, CCAC, CCCC) and unstable (CTAA, CTAC, TTAA) enzyme dimer configurations.

OBJECTIVE

The aim of this study was to evaluate the association of the MTHFR enzyme dimer configuration and folate dietary intake with the stage of meiotic nondisjunction in mothers of children with maternally derived trisomy 21.

METHODS

A total of 119 mothers of children with maternally derived free trisomy 21 were included in the study. The mean maternal age at the time of the birth of the child with trisomy 21 was 32.3 ± 6.4 (range 16-43) years. All mothers were Caucasian. Parental origin of trisomy 21 and meiotic stage of nondisjunction was determined using short tandem repeat markers spanning from the centromere to the telomere of chromosome 21q. The MTHFR C677T and A1298C polymorphism was evaluated by PCR-RFLP.

RESULTS

Increased frequency of the MTHFR genotype combinations CTAA, CTAC, and TTAA was found in the group of mothers with meiosis I (MI) nondisjunction (p = 0.007). No differences were found between study participants regarding dietary and lifestyles habits.

CONCLUSION

The risk for MI nondisjunction of chromosome 21 was 4.6-fold higher in cases who had CTAA, CTAC, and TTAA MTHFR genotype combinations and who did not used folic acid supplements in the preconception period.

De novo mutations in folate-related genes associated with common developmental disorders

Folate deficiency is an environmental risk factor for several developmental disorders. De novo mutations (DNMs) also play important etiological roles in various developmental disorders. However, it remains unclear whether DNMs in folate-related genes (FRGs) contribute to developmental disorders. We obtained a list of 1,821 FRGs from folate metabolism pathways and the Comparative Toxicogenomics Database, along with data concerning DNMs in 15,404 cases and 3,391 controls from the Gene4Denovo database. We used a TADA-Denovo model to prioritize candidate disease-associated FRGs, and characterized these genes in terms of genic intolerance, functional networks, and expression patterns. Compared with the controls, FRGs were significantly enriched in likely damaging DNMs (ldDNMs) in patients with developmental disorders (1.54 ≤ odds ratio ≤ 3.39, P_adj ≤ 0.0075). Furthermore, FRGs with ldDNMs rather than with likely non-damaging DNMs (lndDNMs) overlapped significantly among the five developmental disorders included in the datasets. The TADA-Denovo model prioritized 96 candidate disease-associated FRGs, which were intolerant to genetic variants. Their functional networks mainly involved pathways associated with chromatin modification, organ development, and signal transduction pathways. DNMT3A, KMT2B, KMT2C, and YY1 emerged as hub FRGs from the protein–protein interaction network. These candidate disease-associated FRGs are preferentially expressed in the excitatory neurones during embryonic development, and in the cortex, cerebellum, striatum, and amygdala during foetal development. Overall, these findings show that DNMs in FRGs are associated with the risk of developmental disorders. Further research on these DNMs may facilitate the discovery of developmental disorder biomarkers and therapeutic targets, enabling detailed, personalized, and precise folate treatment plan.

Folate System Gene Variant rs1801394 66A>G may have a Causal Role in Down Syndrome in the Eastern Indian Population

Down syndrome (DS) is associated with trisomy of the 21^st chromosome in more than 95% cases. The extra chromosome mostly derives due to abnormal chromosomal segregation, i.e. non-disjunction, during meiosis. Earlier reports showed that abnormal folate metabolism can lead to DNA hypomethylation and abnormal chromosomal segregation. We analyzed three functional folate gene variants, namely 5-methyltetrahydrofolate-homocysteine methyltransferase rs1805087, 5-methyltetrahydrofolate-homocysteine methyltransferase reductase rs1801394, and reduced folate carrier 1 rs1051266, for contribution in the etiology of DS. Ethnically matched subjects including DS probands (N=183), their parents (N=273), and controls (N=286) were recruited after obtaining informed written consent for participation. Karyotype analysis confirmed trisomy 21 in DS patients recruited. Genomic DNA, purified from peripheral blood leukocytes was used for genotyping of the target sites by PCR based methods, and data obtained was subjected to population- as well as family-based association analysis. Frequency of rs1801394 ‘G’ allele and ‘GG’ genotype was higher in DS probands (P < 0.0001). Statistically significant higher occurrence of the ‘G’ allele in parents of DS probands (P < 0.0001) and maternal bias in transmission of the “G” allele was also noticed (P < 0.0001). Genetic model analysis demonstrated rs1801394 “G” as a risk allele under both dominant and recessive models. DS probands also showed higher occurrence of rs1051266 “G” (P = 0.05). Quantitative trait analysis revealed significant negative influence of rs1805087 “A” on birth weight. Screening for rs1801394 “G” could be useful in monitoring the risk of DS, at least in the studied population.

Review of epidemiological factors (other than maternal age) that determine the prevalence of common autosomal trisomies

The birth prevalence of each common autosomal trisomy (21, 18 and 13) increases with advancing maternal age and this is the most important epidemiological risk factor. Prevalence during pregnancy is also dependent on gestational age. Other factors claimed to influence prevalence include paternal age, ethnicity, family history, premature reproductive aging, parity, twinning, smoking, environmental exposures, maternal medical conditions, and predispositions. We review the evidence for these associations since they may provide insights into causal mechanisms. When investigating potential co-factors it is important to adequately allow for maternal age and minimize its confounding contribution. This is well illustrated by reports of an inverse paternal age effect where there is strong correlation between parental ages. Gestational age at diagnosis, availability of prenatal screening, diagnostic testing, and elective termination of affected pregnancies and healthcare disparities also confound the studies on ethnicity, medical conditions, and predispositions or environmental factors. Data from twin zygosity studies demonstrate the importance of differences in fetal viability for affected pregnancies. We conclude that existing epidemiological evidence for most of the co-factors discussed should currently be considered tenuous; history of Down syndrome, albeit biased, may be an exception. The co-factors may yet provide clues to hitherto poorly understood causal pathways.

Polymorphisms of genes required for methionine synthesis and DNA methylation influence mitochondrial DNA methylation

Aim: Impaired methylation of the mitochondrial DNA and particularly in the regulatory displacement loop (D-loop) region, is increasingly observed in patients with neurodegenerative disorders. The present study aims to investigate if common polymorphisms of genes required for one-carbon metabolism (MTHFR, MTRR, MTR and RFC-1) and DNA methylation reactions (DNMT1, DNMT3A and DNMT3B) influence D-loop methylation levels. Materials & methods: D-loop methylation data were available from 133 late-onset Alzheimer's disease patients and 130 matched controls. Genotyping was performed with PCR-RFLP or high resolution melting techniques. Results: Both MTRR 66A > G and DNMT3A -448A > G polymorphisms were significantly associated with D-loop methylation levels. Conclusion: This exploratory study suggests that MTRR and DNMT3A polymorphisms influence mitochondrial DNA methylation; further research is required to better address this issue.

Genetics of Congenital Heart Disease

Congenital heart disease (CHD) is one of the most common birth defects. Studies in animal models and humans have indicated a genetic etiology for CHD. About 400 genes have been implicated in CHD, encompassing transcription factors, cell signaling molecules, and structural proteins that are important for heart development. Recent studies have shown genes encoding chromatin modifiers, cilia related proteins, and cilia-transduced cell signaling pathways play important roles in CHD pathogenesis. Elucidating the genetic etiology of CHD will help improve diagnosis and the development of new therapies to improve patient outcomes.

Plasma Homocysteine and Polymorphisms of Genes Involved in Folate Metabolism Correlate with DNMT1 Gene Methylation Levels

DNA methyltransferase 1 (DNMT1) is responsible for the maintenance of DNA methylation patterns during cell division. Several human diseases are characterized by impaired DNMT1 gene methylation, but less is known about the factors that regulate DNMT1 promoter methylation levels. Dietary folates and related B-vitamins are essential micronutrients for DNA methylation processes, and we performed the present study to investigate the contribution of circulating folate, vitamin B12, homocysteine, and common polymorphisms in folate pathway genes to the DNMT1 gene methylation levels. We investigated DNMT1 gene methylation levels in peripheral blood DNA samples from 215 healthy individuals. All the DNA samples were genotyped for MTHFR 677C > T (rs1801133) and 1298A > C (rs1801131), MTRR 66A > G (rs1801394), MTR 2756A > G (rs1805087), SLC19A1 (RFC1) 80G > A (rs1051266), TYMS 28-bp tandem repeats (rs34743033) and 1494 6-bp insertion/deletion (indel) (rs34489327), DNMT3A -448A > G (rs1550117), and DNMT3B -149C > T (rs2424913) polymorphisms. Circulating homocysteine, folate, and vitamin B12 levels were available from 158 of the recruited individuals. We observed an inverse correlation between plasma homocysteine and DNMT1 methylation levels. Furthermore, both MTR rs1805087 and TYMS rs34743033 polymorphisms showed a statistically significant effect on DNMT1 methylation levels. The present study revealed several correlations between the folate metabolic pathway and DNMT1 promoter methylation that could be of relevance for those disorders characterized by altered DNA methylation.

Association of Polymorphisms in Genes Involved in One-Carbon Metabolism with MTHFR Methylation Levels

Methylenetetrahydrofolate reductase (MTHFR) is a pivotal enzyme in the one-carbon metabolism, a metabolic pathway required for DNA synthesis and methylation reactions. MTHFR hypermethylation, resulting in reduced gene expression, can contribute to several human disorders, but little is still known about the factors that regulate MTHFR methylation levels. We performed the present study to investigate if common polymorphisms in one-carbon metabolism genes contribute to MTHFR methylation levels. MTHFR methylation was assessed in peripheral blood DNA samples from 206 healthy subjects with methylation-sensitive high-resolution melting (MS-HRM); genotyping was performed for MTHFR 677C>T (rs1801133) and 1298A>C (rs1801131), MTRR 66A>G (rs1801394), MTR 2756A>G (rs1805087), SLC19A1 (RFC1) 80G>A (rs1051266), TYMS 28-bp tandem repeats (rs34743033) and 1494 6-bp ins/del (rs34489327), DNMT3A -448A>G (rs1550117), and DNMT3B -149C>T (rs2424913) polymorphisms. We observed a statistically significant effect of the DNMT3B -149C>T polymorphism on mean MTHFR methylation levels, and particularly CT and TT carriers showed increased methylation levels than CC carriers. The present study revealed an association between a functional polymorphism of DNMT3B and MTHFR methylation levels that could be of relevance in those disorders, such as inborn defects, metabolic disorders and cancer, that have been linked to impaired DNA methylation.

Molecular mechanisms of congenital heart disease in down syndrome

Down syndrome (DS), as a typical genomic aneuploidy, is a common cause of various birth defects, among which is congenital heart disease (CHD). 40-60% neonates with DS have some kinds of CHD. However, the molecular pathogenic mechanisms of DS associated CHD are still not fully understood. This review summarizes available studies on DS associated CHD from seven aspects so as to provide a crucial and updated overview of what we known so far in this domain.

Maternal LINE-1 DNA Methylation and Congenital Heart Defects in Down Syndrome

Background: Down syndrome (DS) is one of the most common chromosomal abnormalities associated with congenital heart defects (CHD), with approximately 40 to 60% of cases showing cardiac defects. This study assessed (i) the association between maternal LINE-1 methylation and the occurrence of CHDs in children with DS and (ii) the impact of endogenous maternal factors (MTHFR C677T polymorphism and maternal age) and exogenous maternal factors (cigarette smoking, alcohol intake, medication use, body mass index and dietary habits such as folate intake) on maternal LINE-1 methylation and on the occurrence of CHD in children with DS.

Patients and Methods: The study included 90 mothers of children with DS of maternal origin (49% DS-CHD⁺ mothers/51% DS-CHD⁻ mothers). LINE-1 DNA methylation was analyzed in peripheral blood lymphocytes by quantification of LINE-1 methylation using the MethyLight method. MTHFR C677T polymorphism genotyping was performed using PCR-RFLP.

Results: LINE-1 methylation was not significantly different between DS-CHD⁺ and DS-CHD⁻ mothers (P = 0.997). Combination of MTHFR C677T genotype/diet and BMI were significant independent predictors of LINE-1 DNA methylation in DS-CHD⁺ mothers (β −0.40, P = 0.01 and β −0.32, P = 0.03, respectively). In the analyzed multivariate model (model P = 0.028), these two factors explained around 72% of the variance in LINE-1 DNA methylation in mothers of children with DS and CHD. The group with the highest BMI (≥30 kg/m2) had significantly lower LINE-1 methylation than the group with normal BMI (Bonferroni post hoc P = 0.03) and the overweight group (Bonferroni post hoc P = 0.04). The lowest LINE-1 DNA methylation values were found in DS-CHD⁺ mothers with the CT+TT genotype and a low-folate diet; the values were significantly lower than the values in mothers with the CC genotype and a folate-rich diet (Bonferroni post hoc P = 0.04).

Conclusion: Association between maternal LINE-1 methylation and CHD in children with DS was not found. Study showed that the MTHFR genotype/diet combination and BMI were significantly associated with LINE-1 methylation in mothers of children with DS-CHD⁺. These results highlight the need for a multifactorial approach to assess the roles of endogenous and exogenous maternal factors in maternal LINE-1 DNA methylation and the consequent pathologies in children. More extensive studies in a larger sample may help elucidate these relationships.

Computational analysis for the determination of deleterious nsSNPs in human MTHFR gene

Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme involved in folate metabolism and plays a central role in DNA methylation and biosynthesis. MTHFR mutations may alter the cellular folate supply which in turn affects nucleic acid synthesis, DNA methylation and chromosomal damage. The identification of number of SNPs in the human genome growing nowadays and hence, the evaluation of functional & structural consequences of these SNPs is very laborious by means of experimental analysis. Therefore, in the present study, recently developed various computational algorithms have been used which can predict the functional and structural consequences of the SNPs. Various computational tools like SIFT, PolyPhen2, PROVEAN, SNAP2, nsSNPAnalyzer, SNPs&GO, PhD-SNP, PMut, I-Mutant, iPTREE-STAB and MUpro were used to predict most deleterious SNPs. Additionally, ConSurf was used to find amino acids conservation and NCBI conserved domain search tool to find conserved domains in MTHFR. Post translational modification sites were predicted using ModPred. SPARKS-X was used to generate 3D structure of the native and mutant MTHFR protein, ModRefiner for further refinement, Varify3D and RAMPAGE to validate structure. Ligand binding sites were predicted using FTsite, RaptorX binding and COACH. Three SNPs i.e. R157Q, L323P and W500C predicted the most deleterious in all the tools used for functional and stability analysis. Moreover, both residues R157, L323 and W500 were predicted highly conserved, buried and structural residues by ConSurf. Post translational modification sites were also predicted at R157 and W500. The ligand binding sites were predicted at R157, L323 and W500.

The thymidylate synthase enhancer region (TSER) polymorphism increases the risk of thymic lymphoid hyperplasia in patients with Myasthenia Gravis

BACKGROUND

Myasthenia Gravis (MG) is caused, in approximately 80% of the patients, by autoantibodies against the nicotinic acetylcholine receptor (AChR). The disease is often associated with pathological changes of the thymus: thymic epithelial tumours are present in about 10-20% of the patients, while up to 80% of the patients with early disease onset have thymic hyperplasia. Folate metabolism is required for the production of DNA precursors and for proper DNA methylation reactions, and impaired folate metabolism has been often associated with cellular growth and cancer.

METHODS

We investigated if major polymorphisms of folate-related genes, namely MTHFR c.677C>T, MTR c.2756A>G, MTRR c.66A>G and TYMS TSER (a 28-bp tandem repeat in the 5' promoter enhancer region of TYMS) increase the risk of pathological changes of the thymus in AChR+ MG patients. A total of 526 AChR+ MG patients, including 132 patients with normal (involuted) thymus, 146 patients with thymic hyperplasia, and 248 patients with a thymoma were included in the study. Allele and genotype comparisons were performed among the three study groups, after correcting for multiple testing.

RESULTS

The frequency of the TYMS TSER 3R allele was significantly higher in MG patients with thymic hyperplasia (P=0.004), and the TYMS TSER 3R3R genotype was significantly associated with increased risk of thymic hyperplasia [OR 2.71 (95% CI: 1.34-5.47)].

CONCLUSIONS

The 3R allele in the thymidylate synthase promoter enhancer region results in increased protein production, required for the synthesis of DNA precursors. The present study suggests that the TYMS TSER 3R allele increases the risk of thymic lymphoid hyperplasia in AChR+ MG patients.

MTHFR promoter hypermethylation may lead to congenital heart defects in Down syndrome

Altered global methylation levels revealed LINE-1 methylation in young mothers of Down syndrome (DS) compared to controls suggesting the possibility of impaired DNA methylation causing abnormal segregation of chromosome 21. Methylene Tetrahydrofolate Reductase (MTHFR) is one of the major enzymes of the folate metabolism pathway. MTHFR gene polymorphism has been associated with maternal risk for DS. Studies have revealed that increased MTHFR promoter methylation results in the reduction of MTHFR protein activity further leading to increased risk of various diseases. The aim of this study is to compare the levels of MTHFR promoter methylation in all three study groups. A total of 120 subjects were recruited for the study and was divided into the following three groups: Group I (mothers of DS without Congenital Heart Defects (CHD), n = 40); Group II (mothers of DS with CHD, n = 40); and Group III (age matched control mothers, n = 40). Genomic DNA was isolated from 2 ml peripheral blood and bisulfite treatment was done to convert all unmethylated cytosines into uracil followed by PCR amplification for MTHFR promoter region and Sanger's sequencing. Results showed that there was a two fold increase in methylated promoter region of MTHFR gene in group II compared to other groups. None of the methylation pattern was observed in the control group. MTHFR promoter methylation affects folate metabolism which is known to play a role in chromosomal breakage, abnormal chromosomal segregation and genomic instability and therefore a developmental defect in the form of congenital cardiac anomaly.

Computational analysis for the determination of deleterious nsSNPs in human MTHFD1 gene

Single nucleotide polymorphisms (SNPs) are the most common genetic polymorphisms and play a major role in many inherited diseases. Methylenetetrahydrofolate dehydrogenase 1 (MTHFD1) is one of the enzymes involved in folate metabolism. In the present study, the functional and structural consequences of nsSNPs of human MTHFD1 gene was analyzed using various computational tools like SIFT, PolyPhen2, PANTHER, PROVEAN, SNAP2, nsSNPAnalyzer, PhD-SNP, SNPs&GO, I-Mutant, MuPro, ConSurf, InterPro, NCBI Conserved Domain Search tool, ModPred, SPARKS-X, RAMPAGE, FT Site and PyMol. Out of 327 nsSNPs form human MTHFD1 gene, total 45 SNPs were predicted as functionally most significant SNPs, among which 17 were highly conserved and functional, 17 were highly conserved and structural residues. Among 45 most significant SNPs, 15 were predicted to be involved in post translational modifications. The p.Gly165Arg may interfere in homodimer interface formation. The p.Asn439Lys and p.Asp445Asn may interfere in binding interactions of MTHFD1 protein with cesium cation and potassium. The two SNPs (p.Asp562Gly and p.Gly637Cys) might interfere in interactions of MTHFD1 with ligand.

Genotype-phenotype correlation for congenital heart disease in Down syndrome through analysis of partial trisomy 21 cases

Among Down syndrome (DS) children, 40-50% have congenital heart disease (CHD). Although trisomy 21 is not sufficient to cause CHD, three copies of at least part of chromosome 21 (Hsa21) increases the risk for CHD. In order to establish a genotype-phenotype correlation for CHD in DS, we built an integrated Hsa21 map of all described partial trisomy 21 (PT21) cases with sufficient indications regarding presence or absence of CHD (n=107), focusing on DS PT21 cases. We suggest a DS CHD candidate region on 21q22.2 (0.96Mb), being shared by most PT21 cases with CHD and containing three known protein-coding genes (DSCAM, BACE2, PLAC4) and four known non-coding RNAs (DSCAM-AS1, DSCAM-IT1, LINC00323, MIR3197). The characterization of a DS CHD candidate region provides a useful approach to identify specific genes contributing to the pathology and to orient further investigations and possibly more effective therapy in relation to the multifactorial pathogenesis of CHD.

Folic Acid Deficiency Does Not Adversely Affect Oocyte Meiosis in Mice

Spindle defect and chromosome misalignment occuring in oocyte meiosis induce nondisjunction. Nondisjunction causes Down syndrome, also known as trisomy 21. Folic acid (FA) is an essential nutrient composition for fetal growth and development. It has been reported that FA nutritional status is associated with the risk of Down syndrome. However, to our knowledge, little is known about the effect of FA deficiency on abnormal oocytes (spindle defects, chromosome misalignments and immature oocyte) in vivo. In the present study, we investigate the effects of FA deficiency on oocyte meiosis in female mice. In order to induce FA deficiency in mice, female Crl:CD1 mice were fed a FA-free diet for 58 d. The diet also contained an antibiotic which has functions on limiting FA formation by intestinal microorganisms. The level of FA deficiency was determined by measuring the concentration of FA in the liver, hemocyte, uterus, ovary, and urine. FA concentrations in these samples from the FA-deficient group were 50-90% lower. Despite this, the frequency of abnormal oocytes was no different between the FA-deficient and control groups (20.0% vs 14.6%). According to the past research, FA transporter was strongly expressed in oocytes. Hence, it is possible that FA-free diets may not affect the concentration of oocyte FA in mice. To sum up these data, our study concluded that FA deficiency did not adversely affect oocyte meiosis.

Transgenerational cardiology: One way to a baby's heart is through the mother

Despite decades of progress, congenital heart disease remains a major cause of mortality and suffering in children and young adults. Prevention would be ideal, but formidable biological and technical hurdles face any intervention that seeks to target the main causes, genetic mutations in the embryo. Other factors, however, significantly modify the total risk in individuals who carry mutations. Investigation of these factors could lead to an alternative approach to prevention. To define the risk modifiers, our group has taken an "experimental epidemiologic" approach via inbred mouse strain crosses. The original intent was to map genes that modify an individual's risk of heart defects caused by an Nkx2-5 mutation. During the analysis of >2000 Nkx2-5(+/-) offspring from one cross we serendipitously discovered a maternal-age associated risk, which also exists in humans. Reciprocal ovarian transplants between young and old mothers indicate that the incidence of heart defects correlates with the age of the mother and not the oocyte, which implicates a maternal pathway as the basis of the risk. The quantitative risk varies between strain backgrounds, so maternal genetic polymorphisms determine the activity of a factor or factors in the pathway. Most strikingly, voluntary exercise by the mother mitigates the risk. Therefore, congenital heart disease can in principle be prevented by targeting a maternal pathway even if the embryo carries a causative mutation. Further mechanistic insight is necessary to develop an intervention that could be implemented on a broad scale, but the physiology of maternal-fetal interactions, aging, and exercise are notoriously complex and undefined. This suggests that an unbiased genetic approach would most efficiently lead to the relevant pathway. A genetic foundation would lay the groundwork for human studies and clinical trials.

Genetics of Congenital Heart Disease: Past and Present

Congenital heart disease is the most common congenital anomaly, representing an important cause of infant morbidity and mortality. Congenital heart disease represents a group of heart anomalies that include septal defects, valve defects, and outflow tract anomalies. The exact genetic, epigenetic, or environmental basis of congenital heart disease remains poorly understood, although the exact mechanism is likely multifactorial. However, the development of new technologies including copy number variants, single-nucleotide polymorphism, next-generation sequencing are accelerating the detection of genetic causes of heart anomalies. Recent studies suggest a role of small non-coding RNAs, micro RNA, in congenital heart disease. The recently described epigenetic factors have also been found to contribute to cardiac morphogenesis. In this review, we present past and recent genetic discoveries in congenital heart disease.