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.     

Lack of maternal folic acid supplementation is associated with heart defects in Down syndrome: a report from the National Down Syndrome Project

BACKGROUND: Maternal folic acid supplementation has been associated with a reduced risk for neural tube defects and may be associated with a reduced risk for congenital heart defects and other birth defects. Individuals with Down syndrome are at high risk for congenital heart defects and have been shown to have abnormal folate metabolism. METHODS: As part of the population‐based case‐control National Down Syndrome Project, 1011 mothers of infants with Down syndrome reported their use of supplements containing folic acid. These data were used to determine whether a lack of periconceptional maternal folic acid supplementation is associated with congenital heart defects in Down syndrome. We used logistic regression to test the relationship between maternal folic acid supplementation and the frequency of specific heart defects correcting for maternal race or ethnicity, proband sex, maternal use of alcohol and cigarettes, and maternal age at conception. RESULTS: Lack of maternal folic acid supplementation was more frequent among infants with Down syndrome and atrioventricular septal defects (odds ratio [OR], 1.69; 95% confidence interval [CI], 1.08–2.63; p = 0.011) or atrial septal defects (OR, 1.69; 95% CI, 1.11–2.58; p = 0.007) than among infants with Down syndrome and no heart defect. Preliminary evidence suggests that the patterns of association differ by race or ethnicity and sex of the proband. There was no statistically significant association with ventricular septal defects (OR, 1.26; 95% CI, 0.85–1.87; p = 0.124). CONCLUSIONS: Our results suggest that lack of maternal folic acid supplementation is associated with septal defects in infants with Down syndrome. Birth Defects Research (Part A), 2011. © 2011 Wiley‐Liss, Inc.     

A possible cause of non-disjunction of additional chromosome 21 in Down syndrome

Summary A possible cause of non-disjunction of chromosome 21 in Down Syndromes has been cytogenetically evaluated by examining the parents by Ag-staining technique. In all the cases studied so far, the contributing parents have active ribosomal cistrons on both chromosomes 21 i.e. both chromosomes are stained positively by silver staining. These results show that the active NORs might play an essential role in meiotic non-disjunction. Furthermore, the preliminary results demonstrate that the acrocentric associations of homologous and non-homologous nature involving chromosome 21 are the most frequent in the contributing parent which may further indicate the role of multiple cellular factors affecting the associations in promoting the non-disjunction in addition to active NORs. The possible mechanisms regarding the non-disjunction of chromosome 21 have been described.Presented at the 34th Annual Meeting of the American Society of Human Genetics, Norfolk, VA, USA     

Prevalence of methylenetetrahydrofolate reductase 677 C-T polymorphism among mothers of Down syndrome children

INTRODUCTION:

The relationship between chromosomal non-disjunction leading to aneuploidy and folate metabolism has drawn attention in the recent years. In this study, we examined the polymorphism in the gene encoding the folate metabolizing enzyme methylenetetrahydrofolate reductase (MTHFR), namely, 677 C-T in women having Down syndrome (DS) children.

MATERIALS AND METHODS:

The prevalence of these variant genotypes (MTHFR 677 C-T polymorphism) in women having DS children (case mothers) (n = 110) was compared with controls (n = 111) from Punjab. Genotyping was done using the polymerase chain reaction method followed by restriction fragment length polymorphism.

RESULTS:

In the present study, 1.8% of case mothers had TT genotype while none of the control mothers showed this genotype. T allele frequency among cases was 0.13 and 0.11 in controls. The Chi-square value showed a non-significant difference between cases and controls.

CONCLUSION:

No association has been observed between 677 C-T polymorphism and risk of non-disjunction in case mothers. Detection of polymorphisms in more genes of folate pathway is required to find out the exact cause of non-disjunction.     

Age-dependent dysregulation of brain amyloid precursor protein in the Ts65Dn Down syndrome mouse model

Individuals with Down syndrome develop β-amyloid deposition characteristic of early-onset Alzheimer's disease (AD) in mid-life, presumably because of an extra copy of the chromosome 21-located amyloid precursor protein ( App ) gene. App mRNA and APP metabolite levels were assessed in the brains of Ts65Dn mice, a mouse model of Down syndrome, using quantitative PCR, western blot analysis, immunoprecipitation, and ELISAs. In spite of the additional App gene copy, App mRNA, APP holoprotein, and all APP metabolite levels in the brains of 4-month-old trisomic mice were not increased compared with the levels seen in diploid littermate controls. However starting at 10 months of age, brain APP levels were increased proportional to the App gene dosage imbalance reflecting increased App message levels in Ts65Dn mice. Similar to APP levels, soluble amino-terminal fragments of APP (sAPPα and sAPPβ) were increased in Ts65Dn mice compared with diploid mice at 12 months but not at 4 months of age. Brain levels of both Aβ40 and Aβ42 were not increased in Ts65Dn mice compared with diploid mice at all ages examined. Therefore, multiple mechanisms contribute to the regulation towards diploid levels of APP metabolites in the Ts65Dn mouse brain.     

Protein expression in Down syndrome brain

Down syndrome (DS) is the most common chromosomal abnormality associated with early mental retardation and neurological abnormalities followed by precocious age dependent Alzheimer-type neurode generation later in life. Knowledge of the pathological mechanisms involved in DS is far from complete, but overexpression of genes residing in chromosome 21 was considered to be the central point for the DS phenotype. In this regard, beta amyloid precursor protein (APP), CuZn superoxide dismutase (SOD1) and S100beta have been implicated in causing apoptosis, a mechanism thought to be responsible for neuronal loss in DS, in one way or another. The gene dosage hypothesis has been challenged, however, and dysregulation of expression of genes located on other chromosomes has been described, which may well be secondary to chromosomal imbalance or a direct consequence of the disease process. The present review focuses on the protein expression profile in DS and we postulate that abnormalities in the coordinated expression, as well as interaction of proteins may be responsible for the neuropathology of DS. A series of candidate proteins are discussed that may be directly causing or reflecting the DS phenotype, in particular the brain abnormalities in DS.     

Quantitative proteomic analysis of amniocytes reveals potentially dysregulated molecular networks in Down syndrome

Background

Down syndrome (DS), caused by an extra copy of chromosome 21, affects 1 in 750 live births and is characterized by cognitive impairment and a constellation of congenital defects. Currently, little is known about the molecular pathogenesis and no direct genotype-phenotype relationship has yet been confirmed. Since DS amniocytes are expected to have a distinct biological behaviour compared to normal amniocytes, we hypothesize that relative quantification of proteins produced from trisomy and euploid (chromosomally normal) amniocytes will reveal dysregulated molecular pathways.

Results

Chromosomally normal- and Trisomy 21-amniocytes were quantitatively analyzed by using Stable Isotope Labeling of Amino acids in Cell culture and tandem mass spectrometry. A total of 4919 unique proteins were identified from the supernatant and cell lysate proteome. More specifically, 4548 unique proteins were identified from the lysate, and 91% of these proteins were quantified based on MS/MS spectra ratios of peptides containing isotope-labeled amino acids. A total of 904 proteins showed significant differential expression and were involved in 25 molecular pathways, each containing a minimum of 16 proteins. Sixty of these proteins consistently showed aberrant expression from trisomy 21 affected amniocytes, indicating their potential role in DS pathogenesis. Nine proteins were analyzed with a multiplex selected reaction monitoring assay in an independent set of Trisomy 21-amniocyte samples and two of them (SOD1 and NES) showed a consistent differential expression.

Conclusions

The most extensive proteome of amniocytes and amniotic fluid has been generated and differentially expressed proteins from amniocytes with Trisomy 21 revealed molecular pathways that seem to be most significantly affected by the presence of an extra copy of chromosome 21.     

Altered nucleosome spacing associated with down syndrome

Micrococcal nuclease digestions of human leukocytes were analyzed using gel electrophoresis. The relative size (or average number of nucleotides) of nucleosomes was determined. The mean nucleosome size of the normal 46 chromosome karyotype is 185±2 bp. There was no significant variation in nucleosome size within the normal population due to age, sex, or race. The mean nucleosome size of the Down syndrome samples is 173±3 bp. These two groups have separate normal distribution curves which do not overlap and are significantly different atP<0.1%.     

Systemic oxidative stress in children and teenagers with Down syndrome

Aims

The aim of this study was to evaluate the antioxidant status and oxidative stress biomarkers in the blood of children and teenagers with Down syndrome.

Main methods

The analysis of enzymatic antioxidant defenses, such as the activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione transferase (GST), non-enzymatic antioxidants, such as levels of reduced glutathione (GSH), uric acid (UA) and vitamin E, as well as oxidative damage indicators, such as protein carbonyls (PC) levels and lipoperoxidation (TBARS), of DS individuals (n = 20) compared to healthy controls (n = 18). Except the vitamin E was measured by HPLC, all other markers were measured spectrophotometrically.

Key Findings

Antioxidant enzymes analysis showed significant increases in the SOD (47.2%), CAT (24.7%) and GR (49.6%) activities in DS subjects. No significant difference in GPx activity was detected while GST activity (61.2%) was decreased, and both responses may be consequence of the depletion of GSH (24.9%) levels. There were no significant differences in TBARS levels, while PC levels showed decreased (31.7%) levels compared to healthy controls, which may be related to the increase (16.1%) found in serum UA. Levels of vitamin E showed no significant differences between DS individuals compared to controls.

Significance

The results revealed a systemic pro-oxidant status in DS individuals, evidenced by the increased activity of some important antioxidant enzymes, together with decreased GSH levels in whole blood and elevated UA levels in plasma, probably as an antioxidant compensation related to the redox imbalance in DS individuals.     

Mitochondrial alterations and tendency to apoptosis in peripheral blood cells from children with Down syndrome

Different types of cells from subjects with Down syndrome (DS) have an increased susceptibility to cell death. We have studied apoptosis and mitochondrial (mt) membrane potential (DeltaPsi(m)) in peripheral blood mononuclear cells (PBMC) from DS children and age-matched healthy donors after in vitro treatment with apoptogenic molecules, along with mtDNA content. We found that PBMC from DS and healthy controls had a similar tendency to undergo apoptosis and a similar amount of mtDNA. However, in cells from DS subjects, mitochondria showed a higher loss of DeltaPsi(m), underlying the presence of an increasing susceptibility of these organelles to damaging agents.     

Down syndrome candidate region-1 protein interacts with Tollip and positively modulates interleukin-1 receptor-mediated signaling

Background

The Down syndrome candidate region-1 gene (DSCR1, also known as RCAN1) is situated close to the Down Syndrome Critical Region (DSCR), which contains genes responsible for many features of Down syndrome. DSCR1 modulates calcineurin phosphatase activity, though its functional role is incompletely understood.

Methods

Here we investigated the role of DSCR1-1S isoform in IL-1 receptor (IL-1R)-mediated signaling by analyzing interaction between DSCR1-1S and the IL-1R pathway components Tollip, IRAK-1, and TRAF6.

Results

Co-immunoprecipitation analyses of HEK293 cells revealed that DSCR1-1S interacted with Tollip, an IRAK-1 inhibitor, leading to the dissociation of IRAK-1 from Tollip. Similarly, both DSCR1-1S and Tollip interacted with TRAF6, with DSCR1 reducing interaction between Tollip and TRAF6. DSCR1-1S also stimulated IL-1R-mediated signaling pathways, TAK1 activation, NF-κB transactivation, and IL-8 production, all downstream consequences of IL-1R activation.

General significance

Together, these results suggest that DSCR1-1S isoform positively modulates IL-1R-mediated signaling pathways by regulating Tollip/IRAK-1/TRAF6 complex formation.     

An investigation of the molecular mechanisms engaged before and after the development of Alzheimer disease neuropathology in Down syndrome: a proteomics approach

Down syndrome (DS) is one of the most common causes of intellectual disability, owing to trisomy of all or part of chromosome 21. DS is also associated with the development of Alzheimer disease (AD) neuropathology after the age of 40 years. To better clarify the cellular and metabolic pathways that could contribute to the differences in DS brain, in particular those involved in the onset of neurodegeneration, we analyzed the frontal cortex of DS subjects with or without significant AD pathology in comparison with age-matched controls, using a proteomics approach. Proteomics represents an advantageous tool to investigate the molecular mechanisms underlying the disease. From these analyses, we investigated the effects that age, DS, and AD neuropathology could have on protein expression levels. Our results show overlapping and independent molecular pathways (including energy metabolism, oxidative damage, protein synthesis, and autophagy) contributing to DS, to aging, and to the presence of AD pathology in DS. Investigation of pathomechanisms involved in DS with AD may provide putative targets for therapeutic approaches to slow the development of AD.