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1.  Maternal Vitamin B12 Status and Risk of Neural Tube Defects in a Population With High Neural Tube Defect Prevalence and No Folic Acid Fortification 
Pediatrics  2009;123(3):917-923.
OBJECTIVE
Folic acid fortification has reduced neural tube defect prevalence by 50% to 70%. It is unlikely that fortification levels will be increased to reduce neural tube defect prevalence further. Therefore, it is important to identify other modifiable risk factors. Vitamin B12 is metabolically related to folate; moreover, previous studies have found low B12 status in mothers of children affected by neural tube defect. Our objective was to quantify the effect of low B12 status on neural tube defect risk in a high-prevalence, unfortified population.
METHODS
We assessed pregnancy vitamin B12 status concentrations in blood samples taken at an average of 15 weeks’ gestation from 3 independent nested case-control groups of Irish women within population-based cohorts, at a time when vitamin supplementation or food fortification was rare. Group 1 blood samples were from 95 women during a neural tube defect–affected pregnancy and 265 control subjects. Group 2 included blood samples from 107 women who had a previous neural tube defect birth but whose current pregnancy was not affected and 414 control subjects. Group 3 samples were from 76 women during an affected pregnancy and 222 control subjects.
RESULTS
Mothers of children affected by neural tube defect had significantly lower B12 status. In all 3 groups those in the lowest B12 quartiles, compared with the highest, had between two and threefold higher adjusted odds ratios for being the mother of a child affected by neural tube defect. Pregnancy blood B12 concentrations of <250 ng/L were associated with the highest risks.
CONCLUSIONS
Deficient or inadequate maternal vitamin B12 status is associated with a significantly increased risk for neural tube defects. We suggest that women have vitamin B12 levels of >300 ng/L (221 pmol/L) before becoming pregnant. Improving B12 status beyond this level may afford a further reduction in risk, but this is uncertain.
doi:10.1542/peds.2008-1173
PMCID: PMC4161975  PMID: 19255021
vitamin B12; cobalamin; neural tube defects; folic acid fortification; folate
2.  Lack of Association between Folate-Receptor Autoantibodies and Neural-Tube Defects 
The New England journal of medicine  2009;361(2):152-160.
BACKGROUND
A previous report described the presence of autoantibodies against folate receptors in 75% of serum samples from women with a history of pregnancy complicated by a neural-tube defect, as compared with 10% of controls. We sought to confirm this finding in an Irish population, which traditionally has had a high prevalence of neuraltube defects.
METHODS
We performed two studies. Study 1 consisted of analysis of stored frozen blood samples collected from 1993 through 1994 from 103 mothers with a history of pregnancy complicated by a neural-tube defect (case mothers), 103 mothers with a history of pregnancy but no complication by a neural-tube defect (matched with regard to number of pregnancies and sampling dates), 58 women who had never been pregnant, and 36 men. Study 2, conducted to confirm that the storage of samples did not influence the folate-receptor autoantibodies, included fresh samples from 37 case mothers, 22 control mothers, 10 women who had never been pregnant, and 9 men. All samples were assayed for blocking and binding autoantibodies against folate receptors.
RESULTS
In Study 1, blocking autoantibodies were found in 17% of case mothers, as compared with 13% of control mothers (odds ratio, 1.54; 95% confidence interval [CI], 0.70 to 3.39), and binding autoantibodies in 29%, as compared with 32%, respectively (odds ratio, 0.82; 95% CI, 0.44 to 1.50). Study 2 showed similar results, indicating that sample degradation was unlikely.
CONCLUSIONS
The presence and titer of maternal folate-receptor autoantibodies were not significantly associated with a neural-tube defect–affected pregnancy in this Irish population.
doi:10.1056/NEJMoa0803783
PMCID: PMC4149290  PMID: 19587340
3.  A Common Variant in MTHFD1L is Associated with Neural Tube Defects and mRNA Splicing Efficiency 
Human mutation  2009;30(12):1650-1656.
Polymorphisms in folate-related genes have emerged as important risk factors in a range of diseases including neural tube defects (NTDs), cancer and coronary artery disease (CAD). Having previously identified a polymorphism within the cytoplasmic folate enzyme, MTHFD1, as a maternal risk factor for NTDs; we considered the more recently identified mitochondrial paralogue, MTHFD1L as a candidate gene for NTD association. We identified a common deletion/insertion polymorphism, rs3832406, c.781-6823ATT(7-9), that influences splicing efficiency and is strongly associated with NTD risk. Three alleles of rs3832406 were detected in the Irish population with varying number of ATT repeats; Allele 1 consists of ATT7, while Alleles 2 and 3 consist of ATT8 and ATT9 respectively. Allele 2 of this triallelic polymorphism showed a decreased case risk as demonstrated by case-control logistic regression (P= 0.002) and by transmission disequilibrium test (TDT) (P= 0.001); while Allele 1 showed an increased case risk. Allele 3 showed no influence on NTD risk and represents the lowest frequency allele (0.15). Additional SNP genotyping in the same genomic region provides additional supportive evidence of an association. We demonstrate that two of the three alleles of rs3832406 are functionally different and influence the splicing efficiency of the alternate MTHFD1L mRNA transcripts.
doi:10.1002/humu.21109
PMCID: PMC2787683  PMID: 19777576
MTHFD1L; NTD; Splicing; Polymorphism; Association; Folate; Mitochondria
4.  Analysis of the MTHFD1 promoter and risk of neural tube defects 
Human genetics  2009;125(3):247-256.
Genetic variants in MTHFD1 (5,10-methylenetetrahydrofolate dehydrogenase/ 5,10-methenyltetrahydrofolate cyclohydrolase/ 10-formyltetrahydrofolate synthetase), an important folate metabolic enzyme, are associated with a number of common diseases, including neural tube defects (NTDs). This study investigates the promoter of the human MTHFD1 gene in a bid to understand how this gene is controlled and regulated. Following a combination of in silico and molecular approaches, we report that MTHFD1 expression is controlled by a TATA-less, Initiator-less promoter and transcription is initiated at multiple start sites over a 126bp region. We confirmed the presence of three database polymorphisms (dbSNP) by direct sequencing of the upstream region (rs1076991 C>T, rs8010584 G>A, rs4243628 G>T), with a fourth (dbSNP rs746488 A>T) not found to be polymorphic in our population and no novel polymorphisms identified. We demonstrate that a common SNP rs1076991 C>T within the window of transcriptional initiation exerts a significant effect on promoter activity in vitro. We investigated this SNP as a potential risk factor for NTDs in a large homogenous Irish population and determined that it is not an independent risk factor, but, it does increase both case (χ2 = 11.06, P = 0.001) and maternal (χ2 = 6.68, P = 0.01) risk when allele frequencies were analysed in combination with the previously identified disease-associated p.R653Q (c.1958 G>A; dbSNP rs2236225) polymorphism. These results provide the first insight into how MTHFD1 is regulated and further emphasise its importance during embryonic development.
doi:10.1007/s00439-008-0616-3
PMCID: PMC2732995  PMID: 19130090
MTHFD1; NTD; Functional; SNP; R653Q; Promoter
5.  Testing for Genetic Association With Constrained Models Using Triads 
Annals of human genetics  2009;73(2):225-230.
Wang and Sheffield (2005) showed that it is preferable to use a robust model that incorporated constraints on the genotype relative risk rather than rely on a model that assumes the disease operates in a recessive or dominant fashion. Wang and Sheffield’s method is applicable to case-control studies, but not to family based studies of case children along with their parents (triads). We show here how to implement analogous constraints while analyzing triad data. The likelihood, conditional on the parents genotype, is maximized over the appropriately constrained parameter space. The asymptotic distribution for the maximized likelihood ratio statistic is found and used to estimate the null distribution of the test statistics. The properties of several methods of testing for association are compared by simulation. The constrained method provides higher power across a wide range of genetic models with little cost when compared to methods that restrict to a dominant, recessive, or multiplicative model, or make no modeling restriction. The methods are applied to two SNPs on the methylenetetrahy-drofolate reductase (MTHFR) gene with neural tube defect (NTD) triads.
doi:10.1111/j.1469-1809.2008.00494.x
PMCID: PMC2657230  PMID: 19178434
conditional distribution; genetic risk model; likelihood ratio test; power
6.  Uncoupling Protein 2 Polymorphisms as Risk Factors for Neural Tube Defects 
BACKGROUND:
Both environmental and genetic factors are involved in the etiology of neural tube defects (NTDs). Inadequate folate intake and obesity are important environmental risk factors. Several folate-related genetic variants have been identified as risk factors; however, little is known about how genetic variants relate to the increased risk seen in obese women. Uncoupling Protein 2 (UCP2) is an attractive candidate to screen for NTD risk because of its possible role in obesity as well as energy metabolism, type-2 diabetes, and the regulation of reactive oxygen species. Interestingly, a previous study found that a common UCP2 compound homozygous genotype was associated with a threefold increase in NTD risk.
METHODS:
We evaluated three polymorphisms, −866G>A, A55V, and the 3′UTR 45bp insertion/deletion, as risk factors for NTDs in Irish NTD cases (N=169), their mothers (N=163), their fathers (N=167) and normal control subjects (N=332).
RESULTS:
Allele and genotype frequencies were not significantly different when comparing NTD mothers, NTD fathers, or affected children to controls. Additionally, the previously reported risk genotype (combined homozygosity of 55VV and 3′UTR 45bp deletion/deletion) was not present at a higher frequency in any NTD group when compared to controls.
CONCLUSIONS:
In our Irish study population, UCP2 polymorphisms do not influence NTD risk. Moreover, the prevalence of this allele in other populations was similar to the Irish prevalence but far lower than reported in the previous NTD study, suggesting that this previous finding of an association with NTDs might have been due to an unrepresentative study sample.
doi:10.1002/bdra.20520
PMCID: PMC2724655  PMID: 19137581
neural tube defects; spina bifida; UCP2; obesity

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