Methionine synthase (MTR) 2756 (A --> G) polymorphism, double heterozygosity methionine synthase 2756 AG/methionine synthase reductase (MTRR) 66 AG, and elevated homocysteinemia are three risk factors for having a child with Down syndrome

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.

Genetic aetiology of Down syndrome birth: novel variants of maternal DNMT3B and RFC1 genes increase risk of meiosis II nondisjunction in the oocyte

The aim of the present work was to explore the intriguing association of maternal folate regulator gene polymorphisms and mutations with the incidence of chromosome 21 nondisjunction and Down syndrome birth. We tested polymorphisms/mutations of DNMT3B and RFC1 genes for their association with meiotic errors in oocyte among the 1215 Down syndrome child-bearing women and 900 controls. We observed that 23 out of 31 variants of DNMT3B and RFC1 exhibited an association with meiosis II nondisjunction in maternal age-independent manner. Additionally, we have reported 17 novel mutations and 1 novel polymorphic variant that are unique to the Indian Bengali speaking cohort and increased odds in favour of meiosis II nondisjunction. We hypothesize that the risk variants and mutations of DNMT3B and RFC1 genes may cause reduction in two or more recombination events and also cause peri-centromeric single exchange that increases the risk of nondisjunction at any age of women. In silico analyses predicted the probable damages of the transcripts or proteins from the respective genes owing to the said polymorphisms. These findings from the largest population sample tested ever revealed that mutations/polymorphisms of the genes DNMT3B and RFC1 impair recombination that leads to chromosome 21 nondisjunction in the oocyte at meiosis II stage and bring us a significant step closer towards understanding the aetiology of chromosome 21 nondisjunction and birth of a child with Down syndrome to women at any age.

Profiling the Influence of Gene Variants Related to Folate-Mediated One-Carbon Metabolism on the Outcome of In Vitro Fertilization (IVF) with Donor Oocytes in Recipients Receiving Folic Acid Fortification

Nutritional status and gene polymorphisms of one-carbon metabolism confer a well-known interaction that in pregnant women may affect embryo viability and the health of the newborn. Folate metabolism directly impacts nucleotide synthesis and methylation, which is of increasing interest in the reproductive medicine field. Studies assessing the genetic influence of folate metabolism on IVF treatments have currently been performed in women using their own oocytes. Most of these patients seeking to have a child or undergoing IVF treatments are advised to preventively intake folate supplies that restore known metabolic imbalances, but the treatments could lead to the promotion of specific enzymes in specific women, depending on their genetic variance. In the present study, we assess the influence of candidate gene variants related to folate metabolism, such as Serine Hydroxymethyltransferase 1 SHMT1 (rs1979276 and rs1979277), Betaine-Homocysteine S-Methyltransferase BHMT (rs3733890), Methionine synthase reductase MTRR (rs1801394), Methylenetetrahydrofolate reductase MTHFR (rs1801131 and rs1801133), methionine synthase MTR (rs12749581), ATP Binding Cassette Subfamily B Member 1 ABCB1 (rs1045642) and folate receptor alpha FOLR1 (rs2071010) on the success of IVF treatment performed in women being recipients of donated oocytes. The implication of such gene variants seems to have no direct impact on pregnancy consecution after IVF; however, several gene variants could influence pregnancy loss events or pregnancy maintenance, as consequence of folic acid fortification.

Problem in the Recent American Heart Association Guideline on Secondary Stroke Prevention: B Vitamins to Lower Homocysteine Do Prevent Stroke

In this article, we discuss a problem in the most recent American Heart Association guideline on secondary stroke prevention that apparently arose from the rules of evidence imposed on the guideline panel. We are told by the cochair of the panel that American Heart Association rules about guidelines for secondary prevention prohibited consideration of primary prevention studies and secondary analyses of secondary prevention studies. However, evidence-based medicine should consider all the best external evidence available and also clinical judgement. The most important problem in the guideline was the recommendation that B vitamins to lower homocysteine do not prevent recurrent stroke. When considering all the best external evidence, it is clear that B vitamins do prevent stroke, but in the early secondary stroke prevention studies, the benefit of B vitamins in participants with good renal function was apparently offset by harm from cyanocobalamin among participants with renal failure (level B-R evidence). We review the evidence that B vitamins should be used to prevent stroke, both in primary and secondary stroke prevention (class 2a recommendation). We also review issues in folate metabolism that require further study, with regard to the form of folate to be used for stroke prevention. We recommend that the guideline be revised to say that B vitamins to lower homocysteine prevent stroke and that methylcobalamin or hydroxycobalamin should be used instead of cyanocobalamin.

Role of folate metabolizing genes and homocysteine in mothers of Down syndrome children

Objectives

Folates are essential nutrients required for the synthesis of DNA/RNA in cell division and segregation. Folates are reduced and methylated in the liver with the help of enzymes such as methylenetetrahydrofolate reductase (MTHFR), MTR MTRR, reduced folate carrier 1, and cystathionine-β-synthase. Variants in the genes encoding these enzymes may lead to hypomethylation, resulting in nondisjunction which in turn increases the risk for Down syndrome (DS). The present study was conducted to genotype these genes and to see their association with homocysteine levels.

Materials and Methods

A total of 213 mothers having DS children and 220 mothers having normal children were enrolled in the study. Genomic DNA was isolated from lymphocytes followed by polymerase chain reaction/Restriction Fragment Length Polymorphism for genotyping. Homocysteine levels were checked by chemoassay utilizing coumarin-based fluorescent probe.

Results

Genotypic frequency of MTHFR 1298 A > C polymorphism was significantly different among cases and controls (χ ² = 5.83, P = 0.01), presence of C instead of A allele provided protection against DS in mothers (odds ratios = 0.57, 95% confidence interval = 0.35-0.91, P = 0.01). Higher levels of homocysteine were independently associated with the risk of having DS child (P = 0.0001).

Conclusion

Homocysteine acted as an independent risk factor in the present study and was not associated with folate metabolizing gene variants.

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.

MTHFR C677T Polymorphism and Serum Homocysteine Level as Risk Factors of Coronary Heart Disease in Patients with Androgenetic Alopecia: A Case Control Study

BACKGROUND

Androgenetic alopecia (AGA) is associated with a risk of coronary heart disease (CHD), although the causes underlying this association are not clear. Serum homocysteine (SH) is a known risk factor for CHD, and methylene tetrahydrofolate reductase enzyme (MTHFR) plays a crucial role in the remethylation of homocysteine to methionine. The polymorphism C677T that affects the catalytic domain of the MTHFR protein leads to a high levels of SH. Our hypothesis was that this polymorphism and SH level are risk factors for CHD in Patients with AGA.

METHODS

A total of 106 patients with AGA and 100 well-matched healthy controls were enrolled in the study. SH levels were estimated. DNA was extracted and polymerase chain reaction amplification, followed by restriction enzyme digestion for MTHFR (C677T) gene, was conducted.

RESULTS

SH levels were significantly higher in the patient group and highest in those with the TT genotype. The mutant T allele was associated with hyperhomocysteinemia and an increased risk of CHD in patients with AGA.

CONCLUSIONS

AGA is associated with a higher risk of developing CHD due to the associated higher level of SH that, in turn, depends on and is correlated with mutant MTHFR genotypes. Cardiac evaluation and follow-up of patients with AGA is recommended for early detection and treatment of CHD to avoid an overall detrimental course.

Genetic and molecular biology of autism spectrum disorder among Middle East population: a review

BACKGROUND

Autism spectrum disorder (ASD) is a neurodevelopmental disease, characterized by impaired social communication, executive dysfunction, and abnormal perceptual processing. It is more frequent among males. All of these clinical manifestations are associated with atypical neural development. Various genetic and environmental risk factors are involved in the etiology of autism. Genetic assessment is essential for the early detection and intervention which can improve social communications and reduce abnormal behaviors. Although, there is a noticeable ASD incidence in Middle East countries, there is still a lack of knowledge about the genetic and molecular biology of ASD among this population to introduce efficient diagnostic and prognostic methods.

MAIN BODY

In the present review, we have summarized all of the genes which have been associated with ASD progression among Middle East population. We have also categorized the reported genes based on their cell and molecular functions.

CONCLUSIONS

This review clarifies the genetic and molecular biology of ASD among Middle East population and paves the way of introducing an efficient population based panel of genetic markers for the early detection and management of ASD in Middle East countries.

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.

The N-terminus of MTRR plays a role in MTR reactivation cycle beyond electron transfer

In eucaryotic cells, methionine synthase reductase (MSR/MTRR) is capable of dominating the folate-homocysteine metabolism as an irreplaceable partner in electron transfer for regeneration of methionine synthase. The N-terminus of MTRR containing a conserved domain of FMN_Red is closely concerned with the oxidation-reduction process. Maternal substitution of I22M in this domain can bring about pregnancy with high risk of spina bifida. A new variation of Arg2del was identified from a female conceiving a fetus with spina bifida cystica. Although the deletion is far from the N-terminal FMN_Red domain, the biochemical features of the variant had been seriously investigated. Curiously, the deletion of arginine(s) of MTRR could not affect the electron relay, if only the FMN_Red domain was intact, but by degrees reduced the ability to promote MTR catalysis in methionine formation. Confirmation of the interaction between the isolated MTRR N-terminal polypeptide and MTR suggested that the native MTRR N-terminus might play an extra role in MTR function. The tandem arginines at the end of MTRR N-terminus conferring high affinity to MTR were indispensable for stimulating methyltransferase activity perhaps via triggering allosteric effect that could be attenuated by removal of the arginine(s). It was concluded that MTRR could also propel MTR enzymatic reaction relying on the tandem arginines at N-terminus more than just only implicated in electron transfer in MTR reactivation cycle. Perturbance of the enzymatic cooperation due to the novel deletion could possibly invite spina bifida in clinics.

Global Burden Related to Nitrous Oxide Exposure in Medical and Recreational Settings: A Systematic Review and Individual Patient Data Meta-Analysis

The risk of adverse effects of nitrous oxide (N₂O) exposure is insufficiently recognized despite its widespread use. These effects are mainly reported through case reports. We conducted an individual patient data meta-analysis to assess the prevalence of clinical, laboratory, and magnetic resonance findings in association with N₂O exposure in medical and recreational settings. We calculated the pooled estimates for the studied outcomes and assessed the potential bias related to population stratification using principal component analysis. Eighty-five publications met the inclusion criteria and reported on 100 patients with a median age of 27 years and 57% of recreational users. The most frequent outcomes were subacute combined degeneration (28%), myelopathy (26%), and generalized demyelinating polyneuropathy (23%). A T2 signal hyperintensity in the spinal cord was reported in 68% (57.2–78.8%) of patients. The most frequent clinical manifestations included paresthesia (80%; 72.0–88.0%), unsteady gait (58%; 48.2–67.8%), and weakness (43%; 33.1–52.9%). At least one hematological abnormality was retrieved in 71.7% (59.9–83.4%) of patients. Most patients had vitamin B12 deficiency: vitamin B12 <150 pmol/L (70.7%; 60.7–80.8%), homocysteine >15 µmol/L (90.3%; 79.3–100%), and methylmalonic acid >0.4 µmol/L (93.8%; 80.4–100%). Consistently, 85% of patients exhibited a possibly or probably deficient vitamin B12 status according to the cB12 scoring system. N₂O can produce severe outcomes, with neurological or hematological disorders in almost all published cases. More than half of them are reported in the setting of recreational use. The N₂O-related burden is dominated by vitamin B12 deficiency. This highlights the need to evaluate whether correcting B12 deficiency would prevent N₂O-related toxicity, particularly in countries with a high prevalence of B12 deficiency.

Biomarkers of Nutrition for Development (BOND): Vitamin B-12 Review

This report on vitamin B-12 (B12) is part of the Biomarkers of Nutrition for Development (BOND) Project, which provides state-of-the art information and advice on the selection, use, and interpretation of biomarkers of nutrient exposure, status, and function. As with the other 5 reports in this series, which focused on iodine, folate, zinc, iron, and vitamin A, this B12 report was developed with the assistance of an expert panel (BOND B12 EP) and other experts who provided information during a consultation. The experts reviewed the existing literature in depth in order to consolidate existing relevant information on the biology of B12, including known and possible effects of insufficiency, and available and potential biomarkers of status. Unlike the situation for the other 5 nutrients reviewed during the BOND project, there has been relatively little previous attention paid to B12 status and its biomarkers, so this report is a landmark in terms of the consolidation and interpretation of the available information on B12 nutrition. Historically, most focus has been on diagnosis and treatment of clinical symptoms of B12 deficiency, which result primarily from pernicious anemia or strict vegetarianism. More recently, we have become aware of the high prevalence of B12 insufficiency in populations consuming low amounts of animal-source foods, which can be detected with ≥1 serum biomarker but presents the new challenge of identifying functional consequences that may require public health interventions.

Genetic variants of the folate metabolic system and mild hyperhomocysteinemia may affect ADHD associated behavioral problems

An etiologically complex disorder, Attention Deficit Hyperactivity Disorder (ADHD), is often associated with various levels of cognitive deficit. Folate/vitamin B₉ is crucial for numerous biochemical pathways including neural stem cell proliferation and differentiation, regulation of gene expression, neurotransmitter synthesis, myelin synthesis and repair, etc. and a scarcity has often been linked to cognitive deficit. Our pilot study in the field revealed significant association of few genetic variants with ADHD. Mild hyperhomocysteinemia and vitamin B₁₂ deficiency was also noticed in the probands. In the present study additional genetic variants, folate and vitamin B₆, which may affect folate-homocysteine metabolic pathway, were investigated in 866 individuals including nuclear families with ADHD probands (N=221) and ethnically matched controls (N=286) to find out whether ADHD associated traits are affected by these factors. Population based analysis revealed significant over representation of MTRR rs1801394 "G" allele and "GG" genotype in all as well as male probands. Stratified analysis showed significantly higher frequency of RFC1 rs1051266 and BHMT rs3733890 "AG" genotypes in full term and prematurely delivered ADHD probands respectively. Probands with rs1801394 "GG" genotype and BHMT rs3733890 "G" allele showed association with hyperhomocysteinemia. MTHFR rs1801131, MTR rs1805087 and BHMT rs3733890 also showed association with ADHD index. While rs1051266, rs1801131, and rs1805087 showed association with behavioral problems, rs3733890 was associated with ODD score. Conduct problem exhibited association with RFC1 rs1051266, MTHFR rs1801133 and MTRR rs1801394. Gene-gene interaction analysis revealed positive synergistic interactions between rs1051266, rs1801131 and rs1801394 in the probands as compared to the controls. It can be inferred from the data obtained that folate system genetic variants and mild hyperhomocysteimenia may affect ADHD associated traits by attenuating folate metabolism.

Genetic polymorphisms in folate metabolism as risk for Down syndrome in the southern China

OBJECTIVE

To assess the association between maternal gene polymorphisms of the enzymes involved in folate metabolism and the risk of having a Down syndrome (DS) offspring in southern China mothers.

METHODS

Gene polymorphisms in folate metabolizing and the levels of homocysteine (HCY) were analyzed in 84 southern China mothers with DS babies (the case group) and 120 healthy mothers (the control group). Methylenetetrahydrofolate reductase (MTHFR) C677T (rs1801133) and A1298C (rs1801131), methionine synthase (MTR) A2756G (rs1805087), and methionine synthase reductase (MTRR) A66G (rs1801394) were studied.

RESULTS

We found no significant differences (p > .05) in the frequencies of four genetic polymorphisms between the two groups. We found gene-gene interactions had a 1.997-fold increased risk in MTHFR 677 CT with MTR AA (OR: 1.997, 95% CI: 1.038-3.841, p = .038) and a 2.588-fold increased risk in MTHFR 677 CT with MTRR AG (OR: 2.588, 95% CI: 1.111-6.031, p = .028) in the case group than control. The levels of HCY were significantly higher in MTHFR 677 TT than MTHFR 677 CC in the case group (TT 17.2167±5.1051, CC 12.1969±5.0299, F = 2.194, p < .05), and it was significantly higher in MTHFR 677 TT in the case group than control (TT 17.2167±5.1051 in the case group, TT 10.2286±1.4373 in the control group, F = 2.546, p < .05).

CONCLUSION

These results suggest that genetic polymorphisms involved in folate metabolism may have population specificity in determining the susceptibility of having DS offsprings. The gene-nutrition, gene-gene interactions and ethnicity are important variables to be considered in periconceptional nutritional supplementation and antenatal care for reducing the risk of DS babies.

Synthetic combinations of missense polymorphic genetic changes underlying Down syndrome susceptibility

Single nucleotide polymorphisms (SNPs) are important biomolecular markers in health and disease. Down syndrome, or Trisomy 21, is the most frequently occurring chromosomal abnormality in live-born children. Here, we highlight associations between SNPs in several important enzymes involved in the one-carbon folate metabolic pathway and the elevated maternal risk of having a child with Down syndrome. Our survey highlights that the combination of SNPs may be a more reliable predictor of the Down syndrome phenotype than single SNPs alone. We also describe recent links between SNPs in p53 and its related pathway proteins and Down syndrome, as well as highlight several proteins that help to associate apoptosis and p53 signaling with the Down syndrome phenotype. In addition to a comprehensive review of the literature, we also demonstrate that several SNPs reside within the same regions as these Down syndrome-linked SNPs, and propose that these closely located nucleotide changes may provide new candidates for future exploration.

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

Almost 15 years ago it was hypothesized that polymorphisms of genes encoding enzymes involved in folate metabolism could lead to aberrant methylation of peri-centromeric regions of chromosome 21, favoring its abnormal segregation during maternal meiosis. Subsequently, more than 50 small case-control studies investigated whether or not maternal polymorphisms of folate pathway genes could be risk factors for the birth of a child with Down syndrome (DS), yielding conflicting and inconclusive results. However, recent meta-analyses of those studies suggest that at least three of those polymorphisms, namely MTHFR 677C>T, MTRR 66A>G, and RFC1 80G>A, are likely to act as maternal risk factors for the birth of a child with trisomy 21, revealing also complex gene-nutrient interactions. A large-cohort study also revealed that lack of maternal folic acid supplementation at peri-conception resulted in increased risk for a DS birth due to errors occurred at maternal meiosis II in the aging oocyte, and it was shown that the methylation status of chromosome 21 peri-centromeric regions could favor recombination errors during meiosis leading to its malsegregation. In this regard, two recent case-control studies revealed association of maternal polymorphisms or haplotypes of the DNMT3B gene, coding for an enzyme required for the regulation of DNA methylation at centromeric and peri-centromeric regions of human chromosomes, with risk of having a birth with DS. Furthermore, congenital heart defects (CHD) are found in almost a half of DS births, and increasing evidence points to a possible contribution of lack of folic acid supplementation at peri-conception, maternal polymorphisms of folate pathway genes, and resulting epigenetic modifications of several genes, at the basis of their occurrence. This review summarizes available case-control studies and literature meta-analyses in order to provide a critical and up to date overview of what we currently know in this field.

Role of folate-homocysteine pathway gene polymorphisms and nutritional cofactors in Down syndrome: A triad study

STUDY QUESTION

Do gene-gene and gene-environment interactions in folate-homocysteine (Hcy) pathway have a predisposing role for Down syndrome (DS)?

SUMMARY ANSWER

The study provides evidence that in addition to advanced age, maternal genotype, micronutrient deficiency and elevated Hcy levels, individually and in combination, are risk factors for Down syndrome.

WHAT IS KNOWN ALREADY

Polymorphisms in certain folate-Hcy-pathway genes (especially the T allele of MTHFR C677T), elevated Hcy and poor folate levels in mothers during pregnancy have been shown to be risk factors for Down syndrome in certain Asian populations (including the eastern region of India), while the same SNPs are not a risk factor in European populations. This conflicting situation alludes to differential gene-environment (nutrition) interactions in different populations which needs to be explored.

STUDY DESIGN, SIZE, DURATION

Between 2008 and 2012, 151 Down syndrome triads and 200 age-matched controls (Control mothers n = 186) were included in the study. Seven polymorphisms in six genes of folate-Hcy metabolic pathway, along with Hcy, cysteine (Cys), vitamin B12 (vit-B12) and folate levels, were analysed and compared among the case and control groups.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Genotyping was performed by the PCR-RFLP technique. Levels of homocysteine and cysteine were measured by HPLC while vitamin B12 and folate were estimated by chemiluminescence.

MAIN RESULTS AND THE ROLE OF CHANCE

We demonstrate that polymorphisms in the folate-Hcy pathway genes in mothers collectively constitute a genotypic risk for DS which is effectively modified by interactions among genes and by the environment affecting folate, Hcy and vitamin B12 levels. The study also supports the idea that these maternal risk factors provide an adaptive advantage during pregnancy supporting live birth of the DS child.

LIMITATIONS AND REASONS FOR CAUTION

Our inability to obtain genotype and nutritional assessments of unaffected siblings of the DS children was an important limitation of the study. Also, its confinement to a specific geographic region (the eastern part) of India, and relatively small sample size is a limitation. A parallel investigation on another population could add greater authenticity to the data.

WIDER IMPLICATIONS OF THE FINDINGS

For mothers genetically susceptible to deliver a DS child (particularly in South Asia), peri-conceptional nutritional supplementation and antenatal care could potentially reduce the risk of a DS child. Additionally, nutritional strategies could possibly be used for better management of the symptoms of DS children.

STUDY FUNDING/COMPETING INTERESTS

The work is funded through Programme support for Genetic disorders by Department of Biotechnology, Government of India to R.R. The authors declare no conflict of interest.

Polymorphisms in folate pathway genes are not associated with somatic nondisjunction in turner syndrome

Folate metabolism dysfunction can lead to DNA hypomethylation and abnormal chromosomal segregation. Previous investigations of this association have produced controversial results. Here we performed a case-control study in patients with Turner syndrome (TS) to determine the effects of genetic polymorphisms of folate pathway genes as potential risk factors for somatic chromosomal nondisjunction. TS is a useful model for this investigation because patients with TS show a high frequency of chromosome mosaicism. Here we investigated the possible association of polymorphisms of the MTHFR gene with TS risk, which has been previously investigated with controversial results. We also examined the effects of MTR, RFC1, and TYMS gene polymorphisms in TS for the first time. The risk was evaluated according to allelic and genotype (independent and combined) frequencies among 70 patients with TS and 144 age-matched healthy control subjects. Polymorphism genotyping was performed by PCR, PCR-RFLP, and PCR-ASA. The polymorphisms MTHFR 677C>T and 1298A>C, MTR 2756A>G, RFC1 80G>A, and TYMS 2R/3R-alone or in combinations-were not associated with the risk of chromosomal aneuploidy in TS. In conclusion, our present findings did not support a link between impaired folate metabolism and abnormal chromosome segregation leading to somatic nondisjunction in TS patients.

Folate metabolism gene polymorphisms and risk for down syndrome offspring in Turkish women

AIMS

Down syndrome (DS) is the most common chromosomal abnormality. Many studies have assessed the association between maternal gene polymorphisms involved in folate metabolism and the risk of having a DS offspring, but data are conflicting. Six common polymorphisms in folate-metabolizing genes were analayzed to determine possible risk factors for a child to be born having DS (DS mothers); these samples were taken from 47 Turkish mothers having DS children (case group) and 49 control mothers. Investigated polymorphisms include methylenetetrahydrofolate reductase (MTHFR) C677T (rs1801133), A1298C (rs1801131), methionine synthase reductase (MTRR) A66G (rs1801394), methylenetetrahydrofolate dehydrogenase (MTHFD1) G1958A (rs2236225), reduced folate carrier (RFC1) A80G (rs1051266), and cystathionine β-synthase (CBS) 844ins68.

RESULTS

The frequency of the MTHFR 677C allele in DS mothers (79.8%) was significantly higher than in controls (66.3%), with a 0.499-fold increased risk of having a DS offspring (p=0.038 and 95% confidence interval [CI], 0.259-0.961). Mothers with the MTHFD1 1958A allele had a 1.880-fold increased risk of having a child with DS (p=0.031 and 95% CI, 1.060-3.335). No significant association was found for the other polymorphic variants in this study. Gene-gene interactions were not statistically significant.

CONCLUSION

Polymorphic variants of the enzymes involved in folate metabolism may play an important role in determining the susceptibility of having a DS offspring. The gene-nutrition, gene-gene interactions and ethnicity are important variables to be considered in future studies.

Genetic polymorphisms involved in folate metabolism and maternal risk for down syndrome: a meta-analysis

Inconclusive results of the association between genetic polymorphisms involved in folate metabolism and maternal risk for Down syndrome (DS) have been reported. Therefore, this meta-analysis was conducted. We searched electronic databases through May, 2014, for eligible studies. Pooled odds ratios with 95% confidence intervals were used to assess the strength of the association, which was estimated by fixed or random effects models. Heterogeneity among studies was evaluated using Q-test and I (2) statistic. Subgroup and sensitivity analyses were also conducted. Publication bias was estimated using Begg's and Egger's tests. A total of 17 case-controls studies were included. There was evidence for an association between the MTRR c.66A>G (rs1801394) polymorphism and maternal risk for DS. In the subgroup analysis, increased maternal risk for DS was found in Caucasians. Additionally, the polymorphic heterozygote MTHFD1 1958GA genotype was associated significantly with maternal risk for DS, when we limit the analysis by studies conformed to Hardy-Weinberg equilibrium. Finally, considering MTR c.2756A>G (rs1805087), TC2 c.776C>G (rs1801198), and CBS c.844ins68, no significant associations have been found, neither in the overall analyses nor in the stratified analyses by ethnicity. In conclusion, our meta-analysis suggested that the MTRR c.66A>G (rs1801394) polymorphism and MTHFD1 c.1958G>A (rs2236225) were associated with increased maternal risk for DS.

Methylenetetrahydrofolate reductase polymorphism is not risk factor for Down syndrome in North India

BACKGROUND

Down syndrome (DS) is the most common cause of mental retardation of genetic etiology with the prevalence rate of 1/700 to 1/1000 live births worldwide. Several polymorphisms in folate/homocysteine metabolism pathways genes have been reported as a risk factor in women for bearing DS child, but very few studies investigated these polymorphisms in DS cases whether there are a risk factor for being DS or not.

OBJECTIVE

We have investigated the association of methylenetetrahydrofolate reductase (MTHFR) with the occurrence of DS in Indian population. MTHFR is one of the key regulatory enzymes involved in the metabolic pathway of homocysteine responsible for the reduction of methyltetrahydrofolate. A total of 32 DS cases and 64 age, sex matched controls were genotyped for MTHFR C677T polymorphism by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

The observed genotype frequencies were CC = 0.81; CT = 0.17 and TT = 0.02 in controls and CC = 0.81 and CT = 0.19 in DS cases. Frequency of T allele in DS and controls were 0.09 and 0.1, respectively. Significant difference in the distribution of mutant 677T allele was not observed between DS cases and controls (odds ratio = 0.915; 95% confidence intervals: 0.331-2.53; P = 0.864).

CONCLUSION

Results of this study indicate that MTHFR C677T polymorphism is not risk factor for DS.

Hyperhomocysteinemia: related genetic diseases and congenital defects, abnormal DNA methylation and newborn screening issues

Homocysteine, a sulfur-containing amino acid derived from the methionine metabolism, is located at the branch point of two pathways of the methionine cycle, i.e. remethylation and transsulfuration. Gene abnormalities in the enzymes catalyzing reactions in both pathways lead to hyperhomocysteinemia. Hyperhomocysteinemia is associated with increased risk for congenital disorders, including neural tube closure defects, heart defects, cleft lip/palate, Down syndrome, and multi-system abnormalities in adults. Since hyperhomocysteinemia is known to affect the extent of DNA methylation, it is likely that abnormal DNA methylation during embryogenesis, may be a pathogenic factor for these congenital disorders. In this review we highlight the importance of homocysteinemia by describing the genes encoding for enzymes of homocysteine metabolism relevant to the clinical practice, especially cystathionine-β-synthase and methylenetetrahydrofolate reductase mutations, and the impairment of related metabolites levels. Moreover, a possible correlation between hyperhomocysteine and congenital disorders through the involvement of abnormal DNA methylation during embryogenesis is discussed. Finally, the relevance of present and future diagnostic tools such as tandem mass spectrometry and next generation sequencing in newborn screening is highlighted.

B vitamin polymorphisms and behavior: evidence of associations with neurodevelopment, depression, schizophrenia, bipolar disorder and cognitive decline

The B vitamins folic acid, vitamin B12 and B6 are essential for neuronal function, and severe deficiencies have been linked to increased risk of neurodevelopmental disorders, psychiatric disease and dementia. Polymorphisms of genes involved in B vitamin absorption, metabolism and function, such as methylene tetrahydrofolate reductase (MTHFR), cystathionine β synthase (CβS), transcobalamin 2 receptor (TCN2) and methionine synthase reductase (MTRR), have also been linked to increased incidence of psychiatric and cognitive disorders. However, the effects of these polymorphisms are often quite small and many studies failed to show any meaningful or consistent associations. This review discusses previous findings from clinical studies and highlights gaps in knowledge. Future studies assessing B vitamin-associated polymorphisms must take into account not just traditional demographics, but subjects' overall diet, relevant biomarkers of nutritional status and also analyze related genetic factors that may exacerbate behavioral effects or nutritional status.

The MTR 2756A>G polymorphism and maternal risk of birth of a child with Down syndrome: a case-control study and a meta-analysis

Methionine synthase (MTR) is required for the conversion of homocysteine (hcy) to methionine in the one-carbon metabolic pathway. Previous studies investigating a common MTR 2756A>G polymorphism as a maternal risk factor for the birth of a child with Down syndrome (DS) are conflicting and limited by small case-control cohorts, and its contribution to circulating hcy levels is still debated. We performed a large case-control study and a meta-analysis of the literature to further address the role of MTR 2756A>G as a maternal risk factor for the birth of a child with DS. 286 mothers of a DS child (MDS) and 305 control mothers of Italian origin were included in the case-control study. Genotyping was performed by means of PCR/RFLP technique. Data on circulating levels of hcy, folates, and vitamin B12 were available for 189 MDS and 194 control mothers. The meta analysis of previous and present data involved a total of 8 studies (1,171 MDS and 1,402 control mothers). Both the case-control study and the meta-analysis showed no association of MTR 2756A>G with the maternal risk of birth of a child with DS (OR = 1.15; 95 % CI 0.85-1.55, and OR = 1.08; 95 % CI 0.93-1.25, respectively), even after stratification of the overall data available for the meta-analysis into ethnic groups. No association of the studied polymorphism with circulating levels of hcy, folates, and vitamin B12 was observed. Present data do not support a role for MTR 2756A>G as independent maternal risk factor for a DS birth.

Effects of methionine synthase and methylenetetrahydrofolate reductase gene polymorphisms on markers of one-carbon metabolism

Genetic and nutritional factors play a role in determining the functionality of the one-carbon (1C) metabolism cycle, a network of biochemical reactions critical to intracellular processes. Genes encoding enzymes for methylenetetrahydrofolate reductase (MTHFR) and methionine synthase (MTR) may determine biomarkers of the cycle including homocysteine (HCY), S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH). MTHFR C677T is an established genetic determinant of HCY but less is known of its effect on SAM and SAH. Conversely, the relationship between MTR A2756G and HCY remains inconclusive, and its effect on SAM and SAH has only been previously investigated in a female-specific population. Folate and vitamin B12 are essential substrate and cofactor of 1C metabolism; thus, consideration of gene-nutrient interactions may clarify the role of genetic determinants of HCY, SAM and SAH. This cross-sectional study included 570 healthy volunteers from Kingston, Ontario, Ottawa, Ontario and Halifax, Nova Scotia, Canada. Least squares regression was used to examine the effects of MTR and MTHFR polymorphisms on plasma HCY, SAM and SAH concentrations; gene-gene and gene-nutrient interactions were considered with the inclusion of cross-products in the model. Main effects of MTR and MTHFR polymorphisms on HCY concentrations were observed; however, no gene-gene or gene-nutrient interactions were found. No association was observed for SAM. For SAH, interactions between MTR and MTHFR polymorphisms, and MTHFR polymorphism and serum folate were found. The findings of this research provide evidence that HCY and SAH, biomarkers of 1C metabolism, are influenced by genetic and nutritional factors and their interactions.

Analysis of methionine synthase reductase polymorphism (A66G) in Indian Muslim population

BACKGROUND AND OBJECTIVES:

Methionine synthase reductase (MTRR) is a vital enzyme of homocysteine/methionine metabolic pathway and is required for the conversion of inactive form of methionine synthase (MTR) to its active form. A clinically important allelic variant of MTRR A66G, with less enzymatic activity is reported with worldwide prevalence rate of ~ 30%. The present study was designed to determine the frequency of MTRR A66G polymorphism in rural Sunni Muslim population of Eastern Uttar Pradesh.

MATERIALS AND METHODS:

Total 56 subjects were analyzed for MTRR A66G polymorphism. A66G mutation analysis was carried out according to the polymerase chain reaction-restriction fragment length polymorphism method of Wilson et al. [1] amplification with MTRR specific primers followed by amplicon digestion with NdeI enzyme was used for the identification of different MTRR genotypes in subjects.

RESULTS AND DISCUSSION:

The AA genotype was found in 5 subjects, AG in 23 subjects, and GG genotype in 28 subjects. Genotype frequencies of AA, AG, and GG were 0.089, 0.41, and 0.5 respectively. The allele frequency of A allele was found to be 0.298 and G allele was 0.705.

CONCLUSION:

It is evident from the present study that the percentage of homozygous genotype GG and frequency of G allele is high in the target Muslim population.

DNMT3B promoter polymorphisms and maternal risk of birth of a child with Down syndrome

STUDY QUESTION

Are DNMT3B promoter polymorphisms among maternal risk factors for the birth of a child with Down syndrome (DS)?

SUMMARY ANSWER

Present results suggest that combinations of functional DNMT3B promoter polymorphisms might modulate maternal risk of birth of a child with DS.

WHAT IS KNOWN ALREADY

The DNMT3B gene codes for DNA methyltransferase 3b (DNMT3b), a protein required for genome-wide de novo methylation, for the establishment of DNA methylation patterns during development and for regulating the histone code and DNA methylation at centromeric regions. Two common functional DNMT3B promoter polymorphisms, namely -149 C > T (rs2424913) and -579 G > T (rs1569686), have been extensively investigated in cancer genetic association studies but less is known about their role in non-cancer diseases. Early in 1999, it was supposed that impaired DNA methylation of pericentromeric regions might represent a maternal risk factor for having a baby with DS.

STUDY DESIGN, SIZE AND DURATION

We aimed to investigate DNMT3B -149 C > T and -579 G > T polymorphisms as maternal risk factors for the birth of a child with DS. The study was performed on DNA samples from 172 mothers of DS individuals (135 aged <35 years when they conceived) and 157 age-matched mothers of unaffected individuals.

PARTICIPANTS/MATERIALS, SETTING AND METHODS

Genotyping was performed by means of the PCR-RFLP technique.

MAIN RESULTS AND THE ROLE OF CHANCE

The DNMT3B -579T allele [odds ratio (OR) = 0.68; 95% confidence interval (CI) = 0.48-0.94, P = 0.02], the DNMT3B -579 GT genotype (OR = 0.55; 95% CI = 0.35-0.87 , P = 0.01) and the combined DNMT3B -579 GT + TT genotype (OR = 0.55; 95% CI = 0.36-0.86 , P = 0.008) were associated with reduced risk of birth of a child with DS. A joint effect of the two polymorphisms was observed and the combined -579 GT/-149 CC genotype resulted in decreased DS risk (OR = 0.22; 95% CI = 0.08-0.64, P = 0.003). The effect remained statistically significant after Bonferroni's correction for multiple comparisons. Similar results were obtained when the analysis was restricted to women who conceived a DS child before 35 years of age.

LIMITATIONS AND REASONS FOR CAUTION

To the best of our knowledge, this is the first genetic association study aimed at evaluating DNMT3B polymorphisms as maternal risk factors for DS. Replication of the findings in other populations is required.

WIDER IMPLICATIONS OF THE FINDINGS

If confirmed in subsequent studies, DNMT3B promoter polymorphisms might be additional markers to be taken into account when evaluating the contribution of one-carbon (folate) metabolism to the maternal risk of birth of a child with DS.

Association of methylenetetrahydrofolate reductase gene 677C > T polymorphism and Down syndrome

The association between Down syndrome (DS) and maternal polymorphisms in genes encoding folic acid metabolizing enzymes remains a controversial issue. A meta-analysis was performed to evaluate the association of maternal MTHFR 677C > T polymorphism and the risk of having a child with DS. Case-control studies were screened from major literature databases. Twenty articles from 13 countries worldwide, with a total of 2,101 DS and 2,702 control mothers, attended the inclusion criteria. We found a 50 % increase for the association of maternal homozygous TT genotype and DS in both fixed (OR = 1.51; 95 % CI 1.22-1.87) and random effects models (OR 1.54; 95 % 1.15-2.05). Similarly, a significant pooled OR was found for the heterozygote CT, with an OR 1.26; 95 % CI 1.10-1.43 (fixed effects model) and OR 1.28; 95 % 1.08-1.51 (random effects model). As ultra-violet B solar radiation highly depends on latitude, and can promote, in less pigmented skin, intravascular folate photolysis, we stratified the analysis by latitude region, defining as Tropical (between 23.5(°) S and 23.5(°) N), Sub-Tropical (between 23.5(°) and 40(°) N and S), and Northern (≥ 40(o) N). Significant association was only found for Sub-Tropical area, both using fixed and random effect models. In conclusion, MTHFR 677C > T polymorphism is a moderate risk factor for DS for some populations, and populations located in Sub-Tropical region seem to be at greater risk. Latitude, ethnicity, skin pigmentation, and red blood cell folate are important variables to be considered in future studies.

Association Study between Folate Pathway Gene Single Nucleotide Polymorphisms and Gastric Cancer in Koreans

Gastric cancer is ranked as the most common cancer in Koreans. A recent molecular biological study about the folate pathway gene revealed the correlation with a couple of cancer types. In the folate pathway, several genes are involved, including methylenetetrahydrofolate reductase (MTHFR), methyltetrahydrofolate-homocysteine methyltransferase reductase (MTRR), and methyltetrahydrofolate-homocysteine methyltransferase (MTR). The MTHFR gene has been reported several times for the correlation with gastric cancer risk. However, the association of the MTRR or MTR gene has not been reported to date. In this study, we investigated the association between the single nucleotide polymorphisms (SNPs) of the MTHFR, MTRR, and MTR genes and the risk of gastric cancer in Koreans. To identify the genetic association with gastric cancer, we selected 17 SNPs sites in folate pathway-associated genes of MTHFR, MTR, and MTRR and tested in 1,261 gastric cancer patients and 375 healthy controls. By genotype analysis, estimating odds ratios and 95% confidence intervals (CI), rs1801394 in the MTRR gene showed increased risk for gastric cacner, with statistical significance both in the codominant model (odds ratio [OR], 1.39; 95% CI, 1.04 to 1.85) and dominant model (OR, 1.34; 95% CI, 1.02 to 1.75). Especially, in the obese group (body mass index ≥ 25 kg/m²), the codominant (OR, 9.08; 95% CI, 1.01 to 94.59) and recessive model (OR, 3.72; 95% CI, 0.92 to 16.59) showed dramatically increased risk (p < 0.05). In conclusion, rs1801394 in the MTRR gene is associated with gastric cancer risk, and its functional significance need to be validated.

Genetic polymorphisms modulate the folate metabolism of Brazilian individuals with Down syndrome

Individuals with Down syndrome (DS) carry three copies of the Cystathionine β-synthase (CβS) gene. The increase in the dosage of this gene results in an altered profile of metabolites involved in the folate pathway, including reduced homocysteine (Hcy), methionine, S-adenosylhomocysteine (SAH) and S-adenosylmethionine (SAM). Furthermore, previous studies in individuals with DS have shown that genetic variants in genes involved in the folate pathway influence the concentrations of this metabolism's products. The purpose of this study is to investigate whether polymorphisms in genes involved in folate metabolism affect the plasma concentrations of Hcy and methylmalonic acid (MMA) along with the concentration of serum folate in individuals with DS. Twelve genetic polymorphisms were investigated in 90 individuals with DS (median age 1.29 years, range 0.07-30.35 years; 49 male and 41 female). Genotyping for the polymorphisms was performed either by polymerase chain reaction (PCR) based techniques or by direct sequencing. Plasma concentrations of Hcy and MMA were measured by liquid chromatography-tandem mass spectrometry as previously described, and serum folate was quantified using a competitive immunoassay. Our results indicate that the MTHFR C677T, MTR A2756G, TC2 C776G and BHMT G742A polymorphisms along with MMA concentration are predictors of Hcy concentration. They also show that age and Hcy concentration are predictors of MMA concentration. These findings could help to understand how genetic variation impacts folate metabolism and what metabolic consequences these variants have in individuals with trisomy 21.

Polymorphisms in 1-carbon metabolism, epigenetics and folate-related pathologies

Folate-mediated 1-carbon metabolism is a network of interconnected metabolic pathways necessary for the synthesis of purine nucleotides, thymidylate and the remethylation of homocysteine to methionine. Disruptions in this pathway influence both DNA synthesis and stability and chromatin methylation, and result from nutritional deficiencies and common gene variants. The mechanisms underlying folate-associated pathologies and developmental anomalies have yet to be established. This review focuses on the relationships among folate-mediated 1-carbon metabolism, chromatin methylation and human disease, and the role of gene-nutrient interactions in modifying epigenetic processes.

Polymorphisms in the folate-metabolizing genes MTR, MTRR, and CBS and breast cancer risk

Alterations in the nucleotide sequences of folate-metabolizing genes can increase the risk of malignant transformation. The aim of our study was to investigate the association of three single-nucleotide polymorphisms (SNPs) in the folate-metabolizing genes - A2756G MTR, A66G MTRR, and 844ins68 CBS - which have putative functional significance in breast cancer risk. The allele and genotype frequencies of the SNPs were determined in a case group (840 women with sporadic breast cancer) and a control group (770 women). No statistically significant association of studied SNPs with breast cancer was revealed. A meta-analysis, which included data obtained from the literature and the present research, did not reveal any statistically significant associations of these SNPs with breast cancer. The results obtained provide evidence that these SNPs are not involved in the development of breast cancer.

MTHFR C677T and MTR A2756G polymorphisms and the homocysteine lowering efficacy of different doses of folic acid in hypertensive Chinese adults

BACKGROUND

This study aimed to investigate if the homocysteine-lowering efficacy of two commonly used physiological doses (0.4 mg/d and 0.8 mg/d) of folic acid (FA) can be modified by individual methylenetetrahydrofolate reductase (MTHFR) C677T and/or methionine synthase (MTR) A2756G polymorphisms in hypertensive Chinese adults.

METHODS

A total of 480 subjects with mild or moderate essential hypertension were randomly assigned to three treatment groups: 1) enalapril only (10 mg, control group); 2) enalapril-FA tablet [10:0.4 mg (10 mg enalapril combined with 0.4 mg of FA), low FA group]; and 3) enalapril-FA tablet (10:0.8 mg, high FA group), once daily for 8 weeks.

RESULTS

After 4 or 8 weeks of treatment, homocysteine concentrations were reduced across all genotypes and FA dosage groups, except in subjects with MTR 2756AG /GG genotype in the low FA group at week 4. However, compared to subjects with MTHFR 677CC genotype, homocysteine concentrations remained higher in subjects with CT or TT genotype in the low FA group (P < 0.05 for either of these genotypes) and TT genotype in the high FA group (P < 0.05). Furthermore, subjects with TT genotype showed a greater homocysteine-lowering response than did subjects with CC genotype in the high FA group (mean percent reduction of homocysteine at week 8: CC 10.8% vs. TT: 22.0%, P = 0.005), but not in the low FA group (CC 9.9% vs. TT 11.2%, P = 0.989).

CONCLUSIONS

This study demonstrated that MTHFR C677T polymorphism can not only affect homocysteine concentration at baseline and post-FA treatment, but also can modify therapeutic responses to various dosages of FA supplementation.

Genetic aspects of folate metabolism

The vitamin folate functions within the cell as a carrier of one-carbon units. The requirement for one-carbon transfers is ubiquitous and all mammalian cells carry out folate dependent reactions. In recent years, low folate status has been linked to risk of numerous adverse health conditions throughout life from birth defects and complications of pregnancy to cardiovascular disease, cancer and cognitive dysfunction in the elderly. In many instances inadequate intake of folate seems to be the primary contributor but there is also evidence that an underlying genetic susceptibility can play a modest role by causing subtle alterations in the availability, metabolism or distribution of intermediates in folate related pathways. Folate linked one-carbon units are essential for DNA synthesis and repair and as a source of methyl groups for biological methylation reactions. The notion of common genetic variants being linked to risk of disease was relatively novel in 1995 when the first functional folate-related polymorphism was discovered. Numerous polymorphisms have now been identified in folate related genes and have been tested for functionality either as a modifier of folate status or as being associated with risk of disease. Moreover, there is increasing research into the importance of folate-derived one-carbon units for DNA and histone methylation reactions, which exert crucial epigenetic control over cellular protein synthesis. It is thus becoming clear that genetic aspects of folate metabolism are wide-ranging and may touch on events as disparate as prenatal imprinting to cancer susceptibility. This chapter will review the current knowledge in this area.

MTHFR C677T and A1298C polymorphisms as a risk factor for congenital heart defects in Down syndrome

BACKGROUND

Congenital heart defects (CHD) are present in most, but not all, cases of Down syndrome (DS). The presence of methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C polymorphisms has been reported as a risk factor for CHD in DS. The aims of the present study were to assess (i) the frequency of MTHFR C677T and A1298C polymorphisms in DS individuals in the Croatian population; (ii) the relationship between the two maternal MTHFR polymorphisms and CHD-affected DS children; and (iii) the transmission frequencies of the variant alleles of the two MTHFR polymorphisms in CHD-affected DS.

METHODS

The study population included 112 DS subjects and 221 controls. CHD were present in 48% of the DS subjects (54/112). The mothers of 107 DS individuals were available for the study; none was a periconceptional folic acid user. Allele transmission was analyzed in 34 complete parent-offspring triads.

RESULTS

The frequencies of the allele, individual, and combined genotypes of MTHFR C677T and A1298C in DS subjects were not statistically different compared to the normal healthy Croatian controls. The maternal MTHFR polymorphisms were not found to be a risk factor for DS-related CHD. The allele transmission of the two MTHFR polymorphisms showed no deviations from random segregation.

CONCLUSIONS

Because the fetus is lost in a great proportion of trisomy 21 pregnancies, both maternal and fetal, not only live-born MTHFR C677T and A1298C, as well as maternal nutrition and lifestyle during pregnancy, should be analyzed to asses the impact on CHD in DS.

Polymorphisms in folate-metabolizing genes, chromosome damage, and risk of Down syndrome in Italian women: identification of key factors using artificial neural networks

BACKGROUND

Studies in mothers of Down syndrome individuals (MDS) point to a role for polymorphisms in folate metabolic genes in increasing chromosome damage and maternal risk for a Down syndrome (DS) pregnancy, suggesting complex gene-gene interactions. This study aimed to analyze a dataset of genetic and cytogenetic data in an Italian group of MDS and mothers of healthy children (control mothers) to assess the predictive capacity of artificial neural networks assembled in TWIST system in distinguish consistently these two different conditions and to identify the variables expressing the maximal amount of relevant information to the condition of being mother of a DS child.The dataset consisted of the following variables: the frequency of chromosome damage in peripheral lymphocytes (BNMN frequency) and the genotype for 7 common polymorphisms in folate metabolic genes (MTHFR 677C>T and 1298A>C, MTRR 66A>G, MTR 2756A>G, RFC1 80G>A and TYMS 28bp repeats and 1494 6bp deletion). Data were analysed using TWIST system in combination with supervised artificial neural networks, and a semantic connectivity map.

RESULTS

TWIST system selected 6 variables (BNMN frequency, MTHFR 677TT, RFC1 80AA, TYMS 1494 6bp +/+, TYMS 28bp 3R/3R and MTR 2756AA genotypes) that were subsequently used to discriminate between MDS and control mothers with 90% accuracy. The semantic connectivity map provided important information on the complex biological connections between the studied variables and the two conditions (being MDS or control mother).

CONCLUSIONS

Overall, the study suggests a link between polymorphisms in folate metabolic genes and DS risk in Italian women.