Folate gene polymorphisms and the risk of Down syndrome pregnancies in young Italian women

MTHFR 677C>T and 1298A>C Variants in Mothers of Infants with Down Syndrome from Western Mexico

Background: Several studies in mothers of infants with Down syndrome (DS) (MoIDS) have suggested that the 677C>T and 1298A>C variants of the 5,10-methylentetrahydrofolate reductase (MTHFR) gene can increase the risk of having a child with DS. Aim: This study aimed to evaluate the MTHFR 677C>T and 1298A>C variants as potential maternal risk factors for DS. Materials and Methods: Using TaqMan allelic discrimination assay, we genotyped 95 MoIDS and 164 control mothers from western Mexico. Data were analyzed using logistic regression analysis. Results: We found that MoIDS had a significantly higher risk for the MTHFR 677TT genotype (adjusted odds ratio [aOR] = 3.4, 95% confidence interval [95% CI]: 1.1-10.6), and the MTHFR 677T allele (aOR = 1.5, 95% CI: 1.0-2.3), particularly in MoIDS <35 years of age. Conclusions: Our findings indicate that the presence of the 677TT genotype and 677T allele of the MTHFR 677C>T variant are maternal risk factors for DS in Mexican MoIDS.

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.

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.

Polyphenol-Rich Aronia melanocarpa Juice Consumption Affects LINE-1 DNA Methylation in Peripheral Blood Leukocytes in Dyslipidemic Women

Cardiovascular disease (CVD) is associated with alterations in DNA methylation and polyunsaturated fatty acid (PUFA) profile, both modulated by dietary polyphenols. The present parallel, placebo-controlled study (part of the original clinical study registered as NCT02800967 at www.clinicaltrials.gov) aimed to determine the impact of 4-week daily consumption of polyphenol-rich Aronia melanocarpa juice (AMJ) treatment on Long Interspersed Nucleotide Element-1 (LINE-1) methylation in peripheral blood leukocytes and on plasma PUFAs, in subjects (n = 54, age range of 40.2 ± 6.7 years) at moderate CVD risk, including an increased body mass index, central obesity, high normal blood pressure, and/or dyslipidemia. The goal was also to examine whether factors known to affect DNA methylation (folate intake levels, MTHFR C677T gene variant, anthropometric and metabolic parameters) modulated the LINE-1 methylation levels upon the consumption of polyphenol-rich aronia juice. Experimental analysis of LINE-1 methylation was done by MethyLight method. MTHFR C677T genotypes were determined by the polymerase chain reaction–restriction fragment length polymorphism method, and folate intake was assessed by processing the data from the food frequency questionnaire. PUFAs were measured by gas–liquid chromatography, and serum lipid profile was determined by using Roche Diagnostics kits. The statistical analyses were performed using Statistica software package. In the comparison after vs. before the treatment period, in dyslipidemic women (n = 22), we observed significant decreases in LINE-1 methylation levels (97.54 ± 1.50 vs. 98.39 ± 0.86%, respectively; P = 0.01) and arachidonic acid/eicosapentaenoic acid ratio [29.17 ± 15.21 vs. 38.42 (25.96–89.58), respectively; P = 0.02]. The change (after vs. before treatment) in LINE-1 methylation directly correlated with the presence of MTHFR 677T allele, average daily folate intake, and the change in serum low-density lipoprotein cholesterol but inversely correlated with the change in serum triacylglycerols (R = 0.72, R² = 0.52, adjusted R² = 0.36, P = 0.03). The current results imply potential cardioprotective effects of habitual polyphenol-rich aronia juice consumption achieved through the modifications of DNA methylation pattern and PUFAs in subjects at CVD risk, which should be further confirmed. Hence, the precision nutrition-driven modulations of both DNA methylation and PUFA profile may become targets for new approaches in the prevention of CVD.

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.

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.

Can the genetic polymorphisms of the folate metabolism have an influence in the polycystic ovary syndrome?

OBJECTIVE

To investigate the association of the genetic variants of the folate metabolism genes (MTHFR C677T; MTHFR A1298C; MTR A2756G; MTRR A66G and RFC-1 A80G) with the development of polycystic ovary syndrome (PCOS).

SUBJECTS AND METHODS

This study included 203 women (99 women with PCOS and 104 controls). The genotyping was performed by PCR-RFLP. Chi-squared test and multiple logistic regression were used in the statistical analysis. Haplotype analysis was conducted using the SNPstat program. The results were presented in odds ratio (OR) and confidence interval of 95% (CI-95%), with a significance level of 5% (p ≤ 0.05).

RESULTS

The genotypic distribution of the RFC-1 A80G polymorphism showed significant difference between the two groups, showing that the heterozygous genotype (AG genotype) was most frequent in controls. The polymorphic homozygous (GG genotype) of MTRR A66G polymorphism were most frequent in controls. The T-C haplotype MTHFR C677T and A1298C polymorphisms were more frequent in the control group (OR = 0.19; CI 95% - 0.04 to 0.93 e p = 0.042). The multivariate analysis evidenced that family history of PCOS was more frequent in the PCOS group (OR = 3.29; CI 95% - 1.48 to 7.31; p = 0.003).

CONCLUSION

In our casuistry, the polymorphic homozygous of MTRR A66G polymorphism gene and heterozygous of RFC-1 A80G polymorphism gene, the haplotype T-C C677T and A1298C polymorphisms of MTHFR gene, can be associated with protective factors for the disease.

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.

Association between polymorphisms in folate metabolism genes and maternal risk for Down syndrome: A meta-analysis

Previous studies have focused on the association between polymorphisms of the genes involved in folate metabolism and Down syndrome (DS); however, the results remain inconclusive. The present meta-analysis was conducted to assess the association between RFC-1 A80G/MTR A2756G/CBS 844ins68 polymorphisms and the maternal risk of DS. Published studies were retrieved from PubMed, Embase, China National Knowledge Infrastructure and Chinese Biomedicine databases. Pooled odds ratios (ORs) with 95% confidence interval (CIs) were calculated using the fixed- or random-effects model. Additionally, test of heterogeneity, cumulative meta-analysis, sensitivity analysis and assessment of bias were also performed. Finally, 11, 11 and 6 studies were deemed eligible for meta-analyses of RFC-1 A80G, MTR A2756G and CBS 844ins68, respectively. A significant association between RFC-1 A80G polymorphism and DS risk was observed for G vs. A (OR=1.19, 95% CI: 1.004-1.40, P=0.04) and the recessive model (OR=1.28, 95% CI: 1.05-1.56, P=0.01). In the stratified analysis by source of control or sample size, a significantly increased risk was observed among hospital-based studies and large-sample groups (>200 subjects), respectively. In addition, the cumulative meta-analysis of the RFC-1 A80G variant revealed a trend toward an association as the amount of data increased. However, for the MTR A2756G and CBS 844ins68 polymorphisms, no obvious association was found for all genetic models. In summary, the present meta-analysis demonstrated that RFC-1 A80G, but not MTR A2756G or CBS 844ins68, was considered as a maternal risk factor for DS in the offspring.

Evaluation of c677t and a1298c polymorphism of the methylenetetrahydrofolate reductase gene as a maternal risk factor for trisomy 21 (a monocentric study)

Aim: To assess the risk for trisomy 21 in children, depending on the polymorphisms C677T and A1298C of the methylenetetrahydrofolate reductase (MTHFR) gene in mothers.

Methods: For 93 mothers who have children with trisomy 21 and 202 mothers of healthy children (control group), genotyping of MTHFR polymorphisms C677T and A1298C was performed.

Results: For each polymorphism, three genotypes were identified (normal homozygous, heterozygous and mutant homozygous). For the polymorphism C677T, the frequencies of the three genotypes (CC, CT and TT) were 50.5%, 40.8% and 8.6% in mothers of children with trisomy 21, versus 42.6%, 46% and 11.4% in mothers of healthy children, with no statistically significant differences. The frequency of the polymorphism A1298C was not statistically significant between the two groups for the genotype (AA) (48.4% vs 56.4%) or the genotype (AC) (39.8% vs 38.6%), but the genotype TT was more frequent in mothers of children with trisomy 21 (11.8% vs 4.9%; p = 0.033; OR = 2.57).

Conclusion: Women with genotype CC for the polymorphism A1298C of the MTHFR gene have a 2.57 times higher risk of offspring with trisomy 21.

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.

Altered LINE-1 Methylation in Mothers of Children with Down Syndrome

Down syndrome (DS, also known as trisomy 21) most often results from chromosomal nondisjunction during oogenesis. Numerous studies sustain a causal link between global DNA hypomethylation and genetic instability. It has been suggested that DNA hypomethylation might affect the structure and dynamics of chromatin regions that are critical for chromosome stability and segregation, thus favouring chromosomal nondisjunction during meiosis. Maternal global DNA hypomethylation has not yet been analyzed as a potential risk factor for chromosome 21 nondisjunction. This study aimed to asses the risk for DS in association with maternal global DNA methylation and the impact of endogenous and exogenous factors that reportedly influence DNA methylation status. Global DNA methylation was analyzed in peripheral blood lymphocytes by quantifying LINE-1 methylation using the MethyLight method. Levels of global DNA methylation were significantly lower among mothers of children with maternally derived trisomy 21 than among control mothers (P = 0.000). The combination of MTHFR C677T genotype and diet significantly influenced global DNA methylation (R2 = 4.5%, P = 0.046). The lowest values of global DNA methylation were observed in mothers with MTHFR 677 CT+TT genotype and low dietary folate. Although our findings revealed an association between maternal global DNA hypomethylation and trisomy 21 of maternal origin, further progress and final conclusions regarding the role of global DNA methylation and the occurrence of trisomy 21 are facing major challenges.

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.

Maternal methylenetetrahydrofolate reductase C677T polymorphism and down syndrome risk: a meta-analysis from 34 studies

BACKGROUND

Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme of folate metabolic pathway which catalyzes the irreversible conversion of 5, 10-methylenetetrahydrofolate to 5-methyltetrahydrofolate. 5-methyltetrahydrofolate donates methyl group for the methylation of homocysteine to methionine. Several studies have investigated maternal MTHFR C677T polymorphism as a risk factor for DS, but the results were controversial and inconclusive. To come into a conclusive estimate, authors performed a meta-analysis.

AIM

A meta-analysis of published case control studies was performed to investigate the association between maternal MTHFR C677T polymorphism and Down syndrome.

METHODS

PubMed, Google Scholar, Elsevier, Springer Link databases were searched to select the eligible case control studies using appropriate keywords. The pooled odds ratio (OR) with 95%confidence interval were calculated for risk assessment.

RESULTS

Thirty four studies with 3,098 DS case mothers and 4,852 control mothers were included in the present meta-analysis. The pooled OR was estimated under five genetic models and significant association was found between maternal MTHFR 677C>T polymorphism and Down syndrome under four genetic models except recessive model (for T vs. C, OR = 1.26, 95% CI = 1.09-1.46, p = 0.001; for TT vs. CC, OR = 1.49, 95% CI = 1.13-1.97, p = 0.008; for CT vs. CC, OR = 1.29, 95% CI = 1.10-1.51, p = 0.001; for TT+CT vs. CC, OR = 1.35, 95% CI = 1.13-1.60, p = 0.0008; for TT vs. CT+CC, OR = 0.76, 95% CI = 0.60-0.94, p = 0.01).

CONCLUSION

The results of the present meta-analysis support that maternal MTHFR C677T polymorphism is a risk factor for DS- affected pregnancy.

A pilot study evaluating the contribution of SLC19A1 (RFC-1) 80G>a polymorphism to Alzheimer's disease in Italian Caucasians

Alzheimer's disease (AD) is the most common neurodegenerative disorder and the primary form of dementia in the elderly. Polymorphisms of genes involved in folate metabolism have been frequently suggested as risk factors for sporadic AD. A common c.80G>A polymorphism (rs1051266) in the gene coding for the reduced folate carrier (SLC19A1 gene, commonly known as RFC-1 gene) was investigated as AD risk factor in Asian populations, yielding conflicting results. We screened a Caucasian population of Italian origin composed of 192 sporadic AD patients and 186 healthy matched controls, for the presence of the RFC-1 c.80G>A polymorphism, and searched for correlation with circulating levels of folate, homocysteine, and vitamin B12. No difference in the distribution of allele and genotype frequencies was observed between AD patients and controls. No correlation was observed among the genotypes generated by the RFC-1 c.80G>A polymorphism and circulating levels of folate, homocysteine, and vitamin B12 either in the whole cohort of subjects or after stratification into clinical subtypes. Present results do not support a role for the RFC-1 c.80G>A polymorphism as independent risk factor for sporadic AD in Italian Caucasians.

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.

The reduced folate carrier (RFC-1) 80A>G polymorphism and maternal risk of having a child with Down syndrome: a meta-analysis

A common polymorphism (c.80A>G) in the gene coding for the reduced folate carrier (SLC19A1, commonly known as RFC-1) has been associated with maternal risk of the birth of a child with Down Syndrome (DS), but results are controversial. We searched major online databases to identify available case-control studies, and performed a meta-analysis to summarize the data concerning this association. Nine independent case-control studies were identified for a total of 930 DS mothers (MDS) and 1240 control mothers. Odds ratios (OR) and 95% confidence intervals (CI) were calculated using both fixed and random effects models. An increase in the risk of having a birth with DS was observed for carriers of the homozygous GG genotype (OR 1.27, 95% CI 1.04-1.57; p = 0.02, fixed effects model), even after removal from the meta-analysis of published data with deviations from Hardy-Weinberg equilibrium (HWE) in controls (OR 1.26, 95% CI 1.02-1.55; p = 0.03, fixed effects model). Moreover, the pooled OR under the fixed effects model showed an increase in the maternal risk for the G allele (OR 1.14, 95% CI 1.01-1.30; p = 0.03). Present results suggest that the maternal RFC-1 80A>G polymorphism might be associated with an increased risk of having a birth with DS, particularly among carriers of the GG genotype.

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.

Folate metabolism gene polymorphisms MTHFR C677T and A1298C and risk for Down syndrome offspring: a meta-analysis

OBJECTIVES

MTHFR C677T and A1298C have been associated with the risk of having an infant with Down syndrome (DS), but results were conflicting. We performed this meta-analysis to derive a more precise estimation of the association between maternal MTHFR polymorphisms and DS.

STUDY DESIGN

An electronic search of PubMed and Chinese Biomedicine database was conducted to select studies for meta-analysis. Twenty-eight case-control studies containing MTHFR C677T and A1298C gene polymorphisms were chosen, and odds ratio (OR) with confidence interval (CI) was used to assess the strength of this association.

RESULTS

Case-control studies including 2806 cases and 4597controls for MTHFR C677T were identified. The overall results suggested that the variant genotypes MTHFR C677T were associated with DS risk (TT+CT vs. CC: OR=1.305, 95% CI: 0.125-1.514, p=0). In the stratified analysis, individuals with the T-carriers genotype in the dominant model had increased risk of DS (OR=1.171, 95% CI: 0.976-1.405, p=0.09) in Caucasian subjects and in Asian subjects (OR=1.749, 95% CI: 1.084-2.824, p=0.022). In addition, case-control studies including 1854 cases and 2364 controls for MTHFR A1298C were chosen. Associations between MTHFR A1298C and the risk of having a child with DS were not found. A symmetric funnel plot, the Egger's test (p=0.126) suggested a lack of publication bias.

CONCLUSION

This meta-analysis supports the idea that MTHFR C677T genotype is associated with increased risk for DS offspring.

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.

One-carbon metabolism and Alzheimer's disease: focus on epigenetics

Alzheimer’s disease (AD) represents the most common form of dementia in the elderly, characterized by progressive loss of memory and cognitive capacity severe enough to interfere with daily functioning and the quality of life. Rare, fully penetrant mutations in three genes (APP, PSEN1 and PSEN2) are responsible for familial forms of the disease. However, more than 90% of AD is sporadic, likely resulting from complex interactions between genetic and environmental factors. Increasing evidence supports a role for epigenetic modifications in AD pathogenesis. Folate metabolism, also known as one-carbon metabolism, is required for the production of S-adenosylmethionine (SAM), which is the major DNA methylating agent. AD individuals are characterized by decreased plasma folate values, as well as increased plasma homocysteine (Hcy) levels, and there is indication of impaired SAM levels in AD brains. Polymorphisms of genes participating in one-carbon metabolism have been associated with AD risk and/or with increased Hcy levels in AD individuals. Studies in rodents suggest that early life exposure to neurotoxicants or dietary restriction of folate and other B vitamins result in epigenetic modifications of AD related genes in the animal brains. Similarly, studies performed on human neuronal cell cultures revealed that folate and other B vitamins deprivation from the media resulted in epigenetic modification of the PSEN1 gene. There is also evidence of epigenetic modifications in the DNA extracted from blood and brains of AD subjects. Here I review one-carbon metabolism in AD, with emphasis on possible epigenetic consequences.

MTHFR Gene variants C677T, A1298C and association with Down syndrome: A Case-control study from South India

BACKGROUND

The 5,10-methylenetetrahydrofolate reductase (MTHFR) polymorphisms and low folate levels are associated with inhibition of DNA methyltransferase and consequently DNA hypomethylation. The expanding spectrum of common conditions linked with MTHFR polymorphisms includes certain adverse birth outcome, pregnancy complications, cancers, adult cardiovascular diseases and psychiatric disorders, with several of these associations remaining still controversial. Trisomy 21 or Down syndrome (DS) is the most common genetic cause of mental retardation. It stems predominantly from the failure of chromosome 21 to segregate normally during meiosis. Despite substantial research, the molecular mechanisms underlying non-disjunction leading to trisomy 21 are poorly understood.

MATERIALS AND METHODS

Two common variants C677T and A1298C of the MTHFR gene were screened in 36 parents with DS children and 60 healthy couples from Tamil Nadu and Karnataka. The MTHFR genotypes were studied by RFLP analysis of PCR-amplified products and confirmed by sequencing.

RESULTS

The CT genotype was seen in three each (8.3%) of case mothers and fathers. One case father showed TT genotype. All the control individuals exhibited the wild type CC genotype. A similar frequency for the uncommon allele C of the second polymorphism was recorded in case mothers (0.35) and fathers (0.37) in comparison with the control mothers (0.39) and fathers (0.37).

CONCLUSION

This first report on MTHFR C677T and A1298C polymorphisms in trisomy 21 parents from south Indian population revealed that MTHFR 677CT polymorphism was associated with a risk for Down syndrome.

Polymorphism C1420T of Serine hydroxymethyltransferase gene on maternal risk for Down syndrome

Recent researches have investigated the factors that determine the maternal risk for Down syndrome (DS) in young woman. In this context, some studies have demonstrated the association between polymorphisms in genes involved on folate metabolism and the maternal risk for DS. These polymorphisms may result in abnormal folate metabolism and methyl deficiency, which is associated with aberrant chromosome segregation leading to trisomy 21. In this study, we analyzed the influence of the polymorphism C1420T in Serine hydroxymethyltransferase (SHMT) gene on maternal risk for DS and on metabolites concentrations of the folate pathway (serum folate and plasma homocysteine and methylmalonic acid). The study group was composed by 105 mothers with DS children (case group) and 185 mothers who had no children with DS (control group). The genotype distribution did not show significant statistical difference between case and control mothers (P = 0.24) however a protective effect between genotypes CC (P = 0.0002) and CT (P < 0.0001) and maternal risk for DS was observed. Furthermore, the SHMT C1420T polymorphism (rs1979277) does not affect the concentration of metabolites of folate pathway in our DS mothers. In conclusion, our data showed a protective role for the genotypes SHMT CC and CT on maternal risk for DS. The concentrations of metabolites of folate pathway did not differ significantly between the genotypes SHMT.

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.

19-base pair deletion polymorphism of the dihydrofolate reductase (DHFR) gene: maternal risk of Down syndrome and folate metabolism

CONTEXT AND OBJECTIVE

Polymorphisms in genes involved in folate metabolism may modulate the maternal risk of Down syndrome (DS). This study evaluated the influence of a 19-base pair (bp) deletion polymorphism in intron-1 of the dihydrofolate reductase (DHFR) gene on the maternal risk of DS, and investigated the association between this polymorphism and variations in the concentrations of serum folate and plasma homocysteine (Hcy) and plasma methylmalonic acid (MMA).

DESIGN AND SETTING

Analytical cross-sectional study carried out at Faculdade de Medicina de São José do Rio Preto (Famerp).

METHODS

105 mothers of individuals with free trisomy of chromosome 21, and 184 control mothers were evaluated. Molecular analysis on the polymorphism was performed using the polymerase chain reaction (PCR) through differences in the sizes of fragments. Folate was quantified by means of chemiluminescence, and Hcy and MMA by means of liquid chromatography and sequential mass spectrometry.

RESULTS

There was no difference between the groups in relation to allele and genotype frequencies (P = 0.44; P = 0.69, respectively). The folate, Hcy and MMA concentrations did not differ significantly between the groups, in relation to genotypes (P > 0.05).

CONCLUSIONS

The 19-bp deletion polymorphism of DHFR gene was not a maternal risk factor for DS and was not related to variations in the concentrations of serum folate and plasma Hcy and MMA in the study population.

Polymorphisms in genes involved in folate metabolism as maternal risk factors for Down syndrome — meta-analysis

Folate metabolism deficiency has been related to increased occurrence of maternal non-disjunction resulting in trisomy 21. Several polymorphisms in genes coding for folate metabolism enzymes have been investigated for association with the maternal risk of Down syndrome (DS) yielding variable results. We performed a meta-analysis of case-control studies obtained through the PubMed database. The studies on polymorphisms in the MTHFR, MTRR, MTR, RFC1 and CBS genes were included. The summary OR demonstrated a statistically significant increased risk of giving birth to a child with DS in mothers carrying the mutant allele of the MTHFR/C677T gene polymorphism (both genetic models) and in mothers homozygous for the mutant allele of the MTRR/A66G polymorphism (recessive genetic model). Analyses of other polymorphisms, MTHFR/A1298C, MTR/A2756G, RFC1/A80G, and CBS/844ins68, resulted in borderline or no statistical significance. In conclusion, our meta-analysis showed the significance of genetic alterations in the folate metabolism genes in maternal susceptibility to DS offspring. Our results suggest that the importance of folate supplementation to women in reproductive age in prevention of non-disjunction be revised. Further genetic studies on a combined effect of multiple folate metabolism genes is recommended. Additionally, more thorough studies on the haplotype analyses of genes is recommended as well, especially in populations that have not yet been investigated thus far.

Thrombotic genetic risk factors and warfarin pharmacogenetic variants in São Miguel's healthy population (Azores)

SUMMARY

BACKGROUND

The Azorean population presents the highest standardized mortality rate for cardiovascular diseases (CVD) when compared to mainland Portugal and other populations. Since thrombosis is a common cause of CVD, we assessed four polymorphisms in three thrombotic risk genes - F5 (G1691A), F2 (G20210A) and MTHFR (C677T, A1298C), in 469 healthy blood donors from São Miguel Island (Azores). We also analysed the CYP2C9 (C430T, A1075C) and VKORC1 (G1639A) variants in fifty-eight individuals with predisposition to thrombosis (possessing at least one variation in F5 or F2 genes and one in MTHFR) to evaluate their warfarin drug response genetic profiles.

RESULTS

Among the 469 individuals, the data showed that thrombotic risk allele frequencies - 1691A (4.9%), 20210A (1.8%), 677T (41.7%) and 1298C (24.8%) - were similar to other Caucasians, but significantly different from mainland Portuguese (chi2, p < 0.001). The combined analysis of these variants identified twenty-two different genetic profiles (genotype order: F5, F2, MTHFR C677T and A1298C). Complete homozygosity for all wild-type alleles (GG GG CC AA) was present in 11.7%, being GG GG CT AA (22.4%) the most frequent profile. The results also demonstrated that 12.4% (58 out of 469) of São Miguel islanders have increased genetic predisposition to thrombosis. Subsequently, we evaluated these individuals for their warfarin response genetic profiles. The data showed that seven out of fifty-eight individuals are poor metabolizers (two with CYP2C9*2/*2 and five with CYP2C9*2/*3 genotypes). VKORC1 polymorphism analysis identified twelve individuals (20.7%) with AA genotype, who probably will require lower doses of warfarin. The joint analysis of CYP2C9 and VKORC1 revealed that 79.3% (46 out of 58) of the individuals carry at least one polymorphism in these genes. Within these, twenty-five individuals (43.1%) need intermediate and/or low doses of warfarin, if treatment is started.

CONCLUSION

The present study demonstrated, for the first time, that São Miguel, and possibly the Azores population, shows significant differences on allele frequencies of thrombotic risk factors when compared to mainland Portugal. This research constitutes a primary approach for future studies on CVD, as well as for the implementation of warfarin dosing protocols using the patient's genotypic information.

Maternal polymorphisms for methyltetrahydrofolate reductase and methionine synthetase reductase and risk of children with Down syndrome

OBJECTIVE

The purpose of this research was to study factors that are involved in centromeric hypomethylation in the pathogenesis of Down syndrome (DS).

STUDY DESIGN

This was a case-control study to evaluate the association between methyltetrahydrofolate reductase (MTHFR) C677T and methionine synthetase-reductase (MTRR) A66G polymorphisms and the risk of DS; we compared mothers in Italy who had children with DS and matched control subjects.

RESULTS

Seventy-four cases of DS caused by an error in maternal meiosis were compared with 184 matched control subjects. The frequencies of the MTHFR C677T polymorphism were similar between the 2 groups. As regards the MTRR A66G polymorphism, the presence of the mutated G allele either in the heterozygous or homozygous form was significantly more common among mothers of children with DS than among control subjects (odds ratio, 2.21; 95% CI, 1.11-4.40).

CONCLUSION

In a population with a high prevalence of the mutated T allele, maternal MTRR A66G, but not MTHFR, polymorphisms are associated with Down syndrome.

Polymorphisms in folate-related genes and risk of pediatric acute lymphoblastic leukemia

Polymorphisms in folate pathway genes may influence the susceptibility to acute lymphoblastic leukemia (ALL). DNA was isolated from 245 pediatric ALL patients (cases) and from 500 blood bank donors (controls). Polymorphisms in methylene-tetrahydrofolate reductase (MTHFR 677C>T, 1298A>C), methionine synthase (MTR 2756A>G), methionine synthase reductase (MTRR 66A>G), methylenetetrahydrofolate dehydrogenase (MTHFD1 1958G>A), nicotinamide N-methyltransferase (NNMT IVS −151C>T), serine hydroxymethyl transferase (SHMT1 1420C>T), thymidylate synthase (TS 2R3R), and the reduced folate carrier (RFC1 80G>A) were detected. In ALL patients, an increased occurrence was observed of the RFC1 80AA variant (odds ratio [OR] = 2.1; 95% confidence interval [CI] = 1.3-3.2; P = .002) and the RFC1 80A allele (OR = 1.5; 95% CI, 1.1-2.1; P = .02). Likewise, the NNMT IVS −151TT genotype showed a 2.2-fold increased ALL risk (OR = 2.2; 95% CI, 1.1-4.6; P = .04). A 1.4-fold reduction in ALL risk was observed for (heterozygous or homozygous) carriers of the TS 2R allele and the MTHFR 677T allele (OR = 0.7; 95% CI, 0.5-1.0; P < .05). Furthermore, interactions between NNMT and MTHFR 677C>T and RFC1 were observed. NNMT IVS −151CC/MTHFR 677CT + TT patients exhibited a 2-fold reduction in ALL risk whereas RFC1 80AA/NNMT IVS −151CT + TT subjects had a 4.2-fold increase in ALL risk (P = .001). For the first time, we associate the RFC1 80G>A and NNMT IVS −151C>T variants to an increased ALL susceptibility.

Pharmacogenetics of the neurodevelopmental impact of anticancer chemotherapy

Pharmacogenetics holds the promise of minimizing adverse neurodevelopmental outcomes of cancer patients by identifying patients at risk, enabling the individualization of treatment and the planning of close follow-up and early remediation. This review focuses first on methotrexate, a drug often implicated in neurotoxicity, especially when used in combination with brain irradiation. The second focus is on glucocorticoids that have been found to be linked to adverse developmental effects in relation with the psychosocial environment. For both examples, we review how polymorphisms of genes encoding enzymes involved in specific mechanisms of action could moderate adverse neurodevelopmental consequences, eventually through common final pathways such as oxidative stress. We discuss a multiple hit model and possible strategies required to rise to the challenge of this integrative research.

Screening for methylenetetrahydrofolate reductase C677T and A1298C polymorphisms in Indian patients with idiopathic mental retardation

Although genetic, nutritional, and environmental factors have been found to aggravate mental retardation in approximately 1% of individuals, no cause is known till date. In this study, two genetic polymorphisms in methylenetetrahydrofolate reductase (MTHFR), C677T (rs#1801133) and A1298C (rs#1801131), have been investigated in idiopathic mental retardation (IMR) subjects. Significantly higher frequency of the C677 allele was observed in IMR (n = 155; chi(2) = 5.5; P = 0.019) and moderate IMR (n = 67; chi(2) = 6.16; P = 0.013) groups as compared to controls (n = 126); for A1298C, no significant difference was noticed. TDT analysis revealed preferential transmission of C677 allele to a small group of mild IMR probands (chi(2) = 5.545; P = 0.018). Higher frequency of CA haplotype was also noticed in IMR cases as compared to controls (chi(2) = 6.28; P = 0.012). We infer from the present investigation that these polymorphisms are not contributing to the aetiology of IMR in this population since both case-control and family-based analysis revealed no significant transmission of the mutated allele.

A80G polymorphism of reduced folate carrier 1 (RFC1) and C776G polymorphism of transcobalamin 2 (TC2) genes in Down's syndrome etiology

CONTEXT AND OBJECTIVE

There is evidence that polymorphisms of genes involved in folate metabolism may be associated with higher risk that mothers may bear a Down's syndrome (DS) child. This study therefore had the objective of investigating the A80G polymorphism of the reduced folate carrier 1 (RFC1) gene and the C776G polymorphism of the transcobalamin 2 (TC2) gene as maternal risk factors for DS among Brazilian women.

DESIGN AND SETTING

Analytical cross-sectional study with control group, at Faculdade de Medicina de São José do Rio Preto (Famerp).

METHODS

Sixty-seven mothers of DS individuals with free trisomy 21, and 113 control mothers, were studied. Molecular analysis of the polymorphisms was performed by means of the polymerase chain reaction with restriction fragment length polymorphism (PCR-RFLP), followed by electrophoresis on 2% agarose gel.

RESULTS

The frequencies of the polymorphic alleles were 0.51 and 0.52 for RFC1 80G, and 0.34 and 0.34 for TC2 776G, in the case and control groups, respectively. Thus, there were no differences between the groups in relation to either the allele or the genotype frequency, for both polymorphisms (P = 0.696 for RFC1 A80G; P = 0.166 for TC2 C776G; P = 0.268 for combined genotypes).

CONCLUSION

There was no evidence of any association between the RFC1 A80G and TC2 C776G polymorphisms and the maternal risk of DS in the sample evaluated.

Prevalence of the polymorphism MTHFR A1298C and not MTHFR C677T is related to chromosomal aneuploidy in Brazilian Turner Syndrome patients

BACKGROUND: Dysfunctions in the folate metabolism can result in DNA hypomethylation and abnormal chromosome segregation. Two common polymorphisms of this enzyme (C677T and A1298C) reduce its activity, but when associated with aneuploidy studies the results are conflicting. The objective of the present study is to analyze the MTHFR gene polymorphisms in women with Turner Syndrome and in a control group, correlating the findings to the chromosomal aneuploidy. METHODS: The study comprised 140 patients with Turner Syndrome, of which 36 with chromosome mosaicism and 104 non-mosaics, and a control group of 209 fertile and healthy women without a history of any offspring with aneuploidy. Polymorphisms C677T and A1298C were studied by RFLP-PCR and the results were statistically analyzed. RESULTS: The frequency of genotypes MTHFR 677CC, 677CT and 677TT in the patients with Turner Syndrome and chromosome mosaicism was, respectively, 58.3%, 38.9% and 2.8%. Among the patients with non-mosaic Turner Syndrome, 47.1% presented genotype 677CC, 45.2% genotype 677CT, and 7.7% genotype 677TT. Among the 209 individuals of the control group, genotypes 677CC, 677CT and 677TT were found at the following frequencies: 48.3%, 42.1% and 9.6%, respectively. As for polymorphism A1298C, the patients with Turner Syndrome and chromosome mosaicism presented genotypes 1298AA, 1298AC and 1298CC at the following frequencies: 58.3%, 27.8% and 13.9%, respectively. Among the non-mosaic Turner Syndrome patients, genotype 1298AA was found in 36.5%, genotype 1298AC in 39.4%, and genotype 1298CC in 22.1%. In the control group, genotypes 1298AA, 1298AC and 1298CC were present at the following frequencies: 52.6%, 40.7% and 6.7%, respectively. CONCLUSION: No correlation was observed between the MTHFR gene polymorphism 677 and chromosomal aneuploidy in the Turner Syndrome patients. However, the MTHFR gene polymorphism at position 1298, mainly genotype 1298CC that reduces the enzyme efficiency, was more frequent in the group of Turner Syndrome patients, suggesting its involvement in mechanisms related to chromosomal imbalances.

The biochemical structure and function of methylenetetrahydrofolate reductase provide the rationale to interpret the epidemiological results on the risk for infants with Down syndrome

Studies on the structure of the methylenetetrahydrofolate reductase (MTHFR) gene and the mechanisms by which folate may reduce homocysteine levels in bacteria and in humans have provided a rationale to understand the conflicting epidemiological observations between the studies on the 677C-T and 1298A-C MTHFR polymorphic variants, and the risk of having an infant with Down syndrome (DS). However, three of the combined genotypes (CTCC, TTAC, and TTCC) are very infrequent in the human population. In fact, these three rare genotypes were only observed in two of the eight epidemiological studies that analyzed these genotype combinations and the risk of DS. In a study of the Indian population these three genotypes were identified in mothers of DS children but not in control mothers demonstrating a statistically significant increase in the risk of giving birth to DS infants. Conversely, the CTCC and TTAC genotypes were only observed in control mothers and not in mothers of DS infants in the Spanish study, while the TTCC genotype was not observed in any Spanish mother analyzed. These results were not related to the frequency of the T allele, since this was lower in the Indian population (21.4% among case mothers and 12.4% in control mothers) than in the Spanish population (33.9%). At present, several important biological aspects on the Hcy cycle are known, including: (a) the biochemical structure and function of the MTHFR enzyme, (b) the biological basis for the effect of the different 677C-T and 1298A-C MTHFR genotype combinations on Hcy levels, (c) that folate is not synthesized by the organism that obtained it from the diet, (d) that TT homozygotes will be at particular risk when their folate status is low because the mutant enzyme requires much higher levels of folate than the physiological one to stabilize the binding of flavin-adenosine-dinucleotide (FAD), (e) that the release of flavin is prevented by increasing the levels of folate, and (f) that the cystathionine-beta-synthase gene is located on chromosome 21. Together, these facts suggest that destabilization of the Hcy cycle in function of the levels of S-adenosylmethionine (SAM), may be modified by some embryonic and maternal genotypes, as well as by maternal nutritional status and life style. This may also influence the probability that some embryos survive to birth, but in different way for those with and without trisomy 21, as is discussed in this article.

[Analysis of the frequencies of genotype combinations of 4 polymorphisms of genes acting on the folate cycle in the Spanish population]

BACKGROUND AND OBJECTIVE

Studies on different populations have shown a great variability of the frequencies of different polymorphisms in genes acting in the folate cycle. The present study was aimed to analyze the frequency in the Spanish population of each genotype combination of four polymorphisms, one of them -1561C-T of the glutamate carboxypeptidase II (GCPII) gene- being the first time that is studied in Spain. The study included a meta-analysis of the published data.

SUBJECTS AND METHOD

Using the Spanish Collaborative Study of Congenital Malformations (ECEMC) Network, blood samples of 190 mother-child couples with newborns without any congenital defect, were obtained from 15 Spanish autonomous regions. The study polymorphisms were the 677C-T and 1298A-C polymorphisms of the methylenetetrahydrofolate reductase (MTHFR), the 66A-G of the methionine synthase reductase (MTRR), and the 1561C-T polymorphism of the GCPII gene. To estimate the range for the population frequencies, 99% confidence intervals were calculated.

RESULTS

The frequencies observed in our country were significantly different from others, being similar to those obtained in countries of the Mediterranean European area. The 1561C-T polymorphism of the GCPII gene has a frequency in Spain of 5.11%, which is also similar to the values observed in France (5%) and in Italy (6%). On the other hand, the frequency of the genotypes CTCC, TTAC is quite few, while the genotype TTCC was not observed in any mother or infants. A meta-analysis was performed for a big sample (23,612 individuals) and the results showed that with a 99% of probability the values for the genotype combinations CTCC, TTAC, and TTCC were within 0.10-0.24; 0.20-0.36; and 0.003-0.05, respectively.

CONCLUSIONS

Our results are important to further analyze the relationship with some health problems and individual susceptibilities. Indeed, considering the published observations of the structure and function of the MTHFR enzyme, it is understandable that those genotype combinations that are quite little frequent, may be related to the embryo-fetal viability, and to the life style of each population.

Mice transgenic for reduced folate carrier: an animal model of Down syndrome?

In a previous publication we observed aberrant levels of the human reduced folate carrier (hRFC) in cortex from fetal Down syndrome (DS) subjects. Immunoreactivity for hRFC was increased as the only chromosome 21 gene product studied. We, therefore, analyzed mice transgenic for hRFC (TghRFC1) and wild-type (WT) mice for cognitive functions, behavior and in an observational neurological battery (FOB). Cognitive functions were evaluated by the Morris water maze (MWM), the open field (OF) was used for exploratory behavior, locomotor activity and anxiety-related behavior. The elevated plus maze (EPM) was used to confirm findings in the OF testing anxiety-related behavior and the rota rod (RR) to evaluate motor function. In the MWM TghRFC1 mice performed significantly worse (P < 0.0003) on the probe trial than WT mice. In the FOB visual placing was significantly reduced inTghRFC1 mice. In the OF TghRFC1 mice crossed twice as often (P < 0.029) and in the EPM individuals from this group showed a reduced number of exits from the closed arm (P < 0.044) compared to WT mice. TghRFC1 mice showed impaired performance on the RR, spending one-fourth of the time of WT on the revolving rod (P < 0.0003). Cognitive impairment is an obligatory symptom of DS and this deficiency corresponds to findings in the MWM of mice transgenic for hRFC. Findings of visual placing and failure on the RR may reflect impaired motor performance including muscular hypotonia in DS subjects. Increased crossings in the OF may indicate modulated anxiety-related behavior observed in patients with DS.

Epidemiology of Down syndrome

Down syndrome (DS) is the most commonly identified genetic form of mental retardation and the leading cause of specific birth defects and medical conditions. Traditional epidemiological studies to determine the prevalence, cause, and clinical significance of the syndrome have been conducted over the last 100 years. DS has been estimated to occur in approximately 1 in 732 infants in the United States, although there is some evidence that variability in prevalence of estimates exist among racial/ethnic groups. Progress has been made in characterizing the specific types of chromosome errors that lead to DS and in identifying associated factors that increase the risk of chromosome 21 malsegregation, i.e., advanced maternal age and recombination. Studies to examine the variability of the presence of specific DS-associated birth defects and medical conditions provide evidence for genetic and environmental modifiers. Here, we provide a brief survey of studies that address the current state of the field and suggest gaps in research that can soon be filled with new multidisciplinary approaches and technological advances.