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

Analysis of association between components of the folate metabolic pathway and autism spectrum disorder in eastern Indian subjects

BACKGROUND

Folate has a pivotal role in maintaining different cellular processes including DNA integrity and neurotransmitter levels. Further, folate deficiency was reported in subjects with neuropsychiatric disorders including autism spectrum disorder (ASD).

METHODS AND RESULTS

We recruited ASD probands following the Diagnostic and Statistical Manual of Mental Disorder-IV/-5. Severity was assessed by the Childhood Autism Rating Scale2-Standard Test (CARS2-ST). Functional SNPs in reduced folate carrier1 (rs1051266), methylenetetrahydrofolate dehydrogenase (rs2236225), methylenetetrahydrofolate methyltransferase (rs1805087), methylenetetrahydrofolate reductase (rs1801133 and rs1801131), cystathionine-beta- synthase (rs5742905), and serine hydroxymethyltransferase (rs1979277) genes were analyzed in the ASD probands (N = 203), their parents and controls (N = 250) by PCR/TaqMan based methods. Plasma homocysteine and vitamin B12 levels were examined by Enzyme-Linked ImmunoSorbent Assay. Statistical analysis revealed higher frequencies of rs1051266 and rs1805087 "A" alleles (P = 8.233e-005 and P = 0.010 respectively) and rs1051266 "AA" genotype (P = 0.02) in the ASD probands. Gender based stratified analysis revealed higher frequency of rs1051266 "AA" in the male probands (P = 0.001) while frequencies of rs1805087 "A" (P = 0.001) and "AA" (P < 0.05), and rs2236225 "CC" (P = 0.03) were higher in the females. The case-control analysis also exhibited a significant difference in the occurrence of biallelic and triallelic haplotypes. rs1051266 "A", rs1979277 "T" and rs5742905 "C" alleles showed biased parental transmission (P = 0.02). CARS2-ST scores were higher in the presence of rs5742905 "T" while scores were lower in the presence of rs1979277 "T" and rs1051266 "A". ASD probands showed vitamin B12 deficiency.

CONCLUSION

Based on these observations, we infer that components needed for proper folate metabolism may influence ASD severity in this population.

One-carbon metabolism and global DNA methylation in mothers of individuals with Down syndrome

Down syndrome (DS) is the most common chromosomal disorder, resulting from the failure of normal chromosome 21 segregation. Studies have suggested that impairments within the one-carbon metabolic pathway can be of relevance for the global genome instability observed in mothers of individuals with DS. Based on the association between global DNA hypomethylation, genome instability, and impairments within the one-carbon metabolic pathway, the present study aimed to identify possible predictors, within the one-carbon metabolism, of global DNA methylation, measured by methylation patterns of LINE-1 and Alu repetitive sequences, in mothers of individuals with DS and mothers of individuals without the syndrome. In addition, we investigated one-carbon genetic polymorphisms and metabolites as maternal predisposing factors for the occurrence of trisomy 21 in children. Eighty-three samples of mothers of children with DS with karyotypically confirmed free trisomy 21 (case group) and 84 of mothers who had at least one child without DS or any other aneuploidy were included in the study. Pyrosequencing assays were performed to access global methylation. The results showed that group affiliation (case or control), betaine-homocysteine methyltransferase (BHMT) G742A and transcobalamin 2 (TCN2) C776G polymorphisms, and folate concentration were identified as predictors of global Alu DNA methylation values. In addition, thymidylate synthase (TYMS) 28-bp repeats 2R/3R or 3R/3R genotypes are independent maternal predisposing factors for having a child with DS. This study adds evidence that supports the association of impairments in the one-carbon metabolism, global DNA methylation, and the possibility of having a child with DS.

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.

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.

DHFR 19-bp deletion and SHMT C1420T polymorphisms and metabolite concentrations of the folate pathway in individuals with Down syndrome

BACKGROUND

Down syndrome (DS) results from the presence and expression of three copies of the genes located on chromosome 21. Studies have shown that, in addition to overexpression of the Cystathionine β-synthase (CBS) gene, polymorphisms in genes involved in folate/homocysteine (Hcy) metabolism may also influence the concentrations of metabolites of this pathway.

AIM

Investigate the association between Dihydrofolate reductase (DHFR) 19-base pair (bp) deletion and Serine hydroxymethyltransferase (SHMT) C1420T polymorphisms and serum folate and plasma Hcy and methylmalonic acid (MMA) concentrations in 85 individuals with DS.

METHODS

Molecular analysis of the DHFR 19-bp deletion and SHMT C1420T polymorphisms was performed by polymerase chain reaction (PCR) by difference in the size of fragments and real-time PCR allelic discrimination, respectively. Serum folate was quantified by chemiluminescence and plasma Hcy and MMA by liquid chromatography-tandem mass spectrometry.

RESULTS

Individuals with DHFR DD/SHMT TT genotypes presented increased folate concentrations (p=0.004) and the DHFR II/SHMT TT genotypes were associated with increased MMA concentrations (p=0.008). In addition, the MMA concentrations were negatively associated with age (p=0.04).

CONCLUSION

There is an association between DHFR DD/SHMT TT and DHFR II/SHMT TT combined genotypes and folate and MMA concentrations in individuals with DS.