Factors Of Neural Tube Defects Research Articles

A Polymorphism, R653Q, in the Trifunctional Enzyme Methylenetetrahydrofolate Dehydrogenase/Methenyltetrahydrofolate Cyclohydrolase/Formyltetrahydrofolate Synthetase Is a Maternal Genetic Risk Factor for Neural Tube Defects: Report of the Birth Defects Research Group

Women who take folic acid periconceptionally reduce their risk of having a child with a neural tube defect (NTD) by >50%. A variant form of methylenetetrahydrofolate reductase (MTHFR) (677C-->T) is a known risk factor for NTDs, but the prevalence of the risk genotype explains only a small portion of the protective effect of folic acid. This has prompted the search for additional NTD-associated variants in folate-metabolism enzymes. We have analyzed five potential single-nucleotide polymorphisms (SNPs) in the cytoplasmic, nicotinamide adenine dinucleotide phosphate-dependent, trifunctional enzyme methylenetetrahydrofolate dehydrogenase/methenyltetrahydrofolate cyclohydrolase/formyltetrahydrofolate synthetase (MTHFD1) for an association with NTDs in the Irish population. One SNP, R653Q, in this gene appears to be associated with NTD risk. We observed an excess of the MTHFD1 "Q" allele in the mothers of children with NTD, compared with control individuals. This excess was driven by the overrepresentation of QQ homozygotes in the mothers of children with NTD compared with control individuals (odds ratio 1.52 [95% confidence interval 1.16-1.99], P=.003). We conclude that genetic variation in the MTHFD1 gene is associated with an increase in the genetically determined risk that a woman will bear a child with NTD and that the gene may be associated with decreased embryo survival.

Frequency of the thermolabile variant C677T in the MTHFR gene and lack of association with neural tube defects in the State of Yucatan, Mexico.

The C677T variant in the MTHFR gene is considered to be an associated risk factor for neural tube defects. However, the association has not been found in some ethnic groups. In order to assess the association between neural tube defects and the C677T variant, we determined the frequency of this variant in the MTHFR gene in the State of Yucatan, Mexico, where neural tube defects are highly prevalent. The study was performed on 65 subjects with spine bifida, 60 of their mothers and 110 control subjects. The presence of the C677T variant was determined by amplification and digestion with HinF1 of each subject's DNA. Genotypic and allelic frequencies were calculated for all groups. We did not observe any statistically significant difference in the genotypic or allelic frequencies between cases and controls for any of the groups studied (p > 0.05), suggesting that the thermolabile variant C677T is not an associated risk factor neither for the development of neural tube defects nor for mothers to have affected offspring in the population from Yucatan. Interestingly, the frequency of the C677T variant (54%) obtained in the Yucatan population is one of the highest reported (p < 0.01) and confirmed the high frequency of this allele throughout Mexico.

Study of MTHFR and MS polymorphisms as risk factors for NTD in the Italian population.

Homozygosity for the C677T mutation in the methylenetetrahydrofolate reductase ( MTHFR) gene is a risk factor for neural tube defects (NTDs) in many populations, including Italians. Another common mutation on the MTHFR gene, A1298C, has also been described as a risk mutation. Furthermore, several studies have suggested that a defective methionine synthase ( MS) enzyme could be a critical defect in folate-related NTDs. An A-to-G transition at bp 2756 on the MS gene has also been reported. In this case-control study, we studied the frequencies of these two polymorphisms in 203 Italian probands with non-syndromic NTDs: 98 mothers, 67 fathers, and 210 control individuals. Although the A1298C polymorphism is common in the Italian population (0.25), the allelic frequency was significantly higher among NTD cases and their parents. Heterozygous patients and mothers have an odds ratio (OR) of 1.98 and 2.11, respectively. The risk associated with the 1298CC genotype was higher for cases (OR = 3.67), for fathers (OR = 3.28), and, above all, for mothers (OR = 6.23). The prevalence of the A2756G polymorphism of the MS gene was determined (0.15). No increased prevalence of the mutated G allele was found in NTD families. This study shows that the MTHFRA1298C polymorphism is a genetic determinant for NTD risk in Italy. No association between the MSA2756G and NTD susceptibility was found.

Die Bedeutung von Vitamin B12 in der Schwangerschaft und daraus resultierende Empfehlungen für die Schwangerschaftsvorsorge

Die Versorgung mit Vitamin B12 in der Schwangerschaft gilt als unabhängiger Risikofaktor für die Entstehung von Neuralrohrdefekten. Ein Vitamin-B12-Mangel wird bei etwa 5 % aller Schwangerschaften beobachtet. Nicht nur die Vitamin-B12-Speicher, sondern auch die momentane Vitamin-B12-Zufuhr ist für die fetale Versorgung von Bedeutung. Während der ersten Phase der Schwangerschaft besteht häufig eine anhaltende Übelkeit, die zu Erbrechen verbunden mit einem einseitigen oder verminderten Lebensmittelverzehr führt. Es kann zu besonderen Aversionen gegen Lebensmittel tierischen Ursprungs kommen, welche die wichtigsten Vitamin-B12-Quellen darstellen. Aus diesem Grund benötigt die Vitamin-B12-Versorgung von schwangeren Vegetarierinnen - insbesondere von Veganerinnen - besondere Aufmerksamkeit. Zur Vermeidung eines sekundären Folatmangels als Folge eines Vitamin-B12-Mangels muss eine Supplementation mit Vitamin B12 in Erwägung gezogen werden.

Presence of the 5,10-methylenetetrahydrofolate reductase C677T mutation in Puerto Rican patients with neural tube defects.

Folic acid supplementation can reduce the incidence of neural tube defects. The first reported genetic risk factor for neural tube defects is a C677T mutation in the 5,10-methylenetetrahydrofolate reductase gene, resulting in decreased activity of the enzyme. We examined the enzyme mutation role of methylenetetrahydrofolate reductase in the etiology of neural tube defects in our population. The study group consisted of 204 Puerto Rican individuals including 37 pregnant females with a prenatal diagnosis of neural tube defects in their fetuses, 31 newborns, 36 fathers, and 100 healthy adults. The prevalence of the C677T mutation was examined. Homozygosity for the alanine to valine substitution (TT) was observed in 9% of the controls and 19% of the mothers with children with neural tube defects. Our results indicate that the presence of the T allele at the methylenetetrahydrofolate reductase 677 position may increase the risk of giving birth to an infant with a neural tube defect.

Metabolic effects of C677T and A1298C mutations at the MTHFR gene in Brazilian children with neural tube defects

Background: Methylenetetrahydrofolate reductase (MTHFR) deficiency leads to impairment in folate metabolism and is implicated as a risk factor for neural tube defects (NTDs). Both C677T and A1298C MTHFR mutations are associated with NTDs, in some populations. Methods: The frequencies of the C677T and A1298C MTHFR mutations were determined in 25 children with NTDs, case mothers and 75 healthy individuals from Sao Paulo City. Both C677T and A1298C mutations were analyzed by PCR-FLRP. The effects of MTHFR mutations on folate, vitamin B12 and homocysteine concentrations were also evaluated. Results: C677T and A1298C allele frequencies in NTDs children and mothers were similar to that found in controls. Eleven in 23 NTDs patients and 10 in 21 NTDs mothers had folate or vitamin B12 concentrations in the lower end of the normal range. In NTDs children, C677T MTHFR genotypes did not affect vitamins and homocysteine concentrations, but plasma homocysteine was higher ( p=0.028) in patients with 1298AA MTHFR genotype. Moreover, 677CT/1298AA haplotype was associated with lower vitamin B12 concentrations ( p<0.05) in NTDs children. Conclusions: MTHFR gene mutations may affect vitamin B12 and homocysteine metabolism in Brazilian children with NTDs.

Effects of hyperinsulinemia and obesity on risk of neural tube defects among Mexican Americans.

Although both maternal obesity and diabetes mellitus increase the risk for neural tube defects, it is unknown whether they are independent risk factors or manifestations of an underlying prediabetic state such as hyperinsulinemia. We investigated whether hyperinsulinemia was a risk factor for neural tube defects independent of obesity and hyperglycemia in Mexican-American women. We identified case and control women from residents delivering or terminating pregnancies in hospitals or birthing centers in any of the 14 Texas-Mexico border counties during 1995-2000. Case women had a pregnancy affected by anencephaly, spina bifida, or encephalocele; randomly selected control women had normal births, frequency matched by year and birth facility. Questionnaire and laboratory values obtained 5-6 weeks postpartum were available for 149 case and 178 control women. Both hyperinsulinemia and obesity were related to increased neural tube defect risk [odds ratio (OR) = 1.91, 95% confidence interval (CI) = 1.21-3.01 and OR = 1.73, 95% CI = 1.03-2.92, respectively]. Adjustment for obesity only slightly reduced the effect of hyperinsulinemia (OR = 1.75, 95% CI = 1.09-2.82). Alternatively, a modest effect remained for obesity after adjustment for hyperinsulinemia (OR = 1.45, 95% CI = 0.84-2.51). Hyperinsulinemia is a strong risk factor for neural tube defects and may be the driving force for the observed risk in obese women.

Efecto del ácido levofolínico sobre las concentraciones de homocisteína plasmática en la mujer joven y sana en la consulta preconcepcional

Increases in total plasmatic homocysteine (tHcy) represents a risk factor for neural tube defects. We studied the effects of levofolinic acid (l,5-formyl-tetrahydrofolic) on the plasmatic tHcylevels in women of child-bearing age. Healthy women aged 18-35 years (n = 30) received levofolinic acid, 5 mg/day,orally for 30 days. Both tHcy and intraerythrocytic folate levels were measured before treatment (day 0), on days 2, 5, 10 and 30 within the treatment period and on days 30 (day 60) and 60 (day 90) after the treatment was finished. Plasmatic tHcy was measured by fluorescence polarisation immunoassay and intraerythrocyticfolates by chemiluminescent immunoassay. Plasmatic tHcy decreased from the second day of treatment onwards (day 0 vs. 2: mean of difference: -1.24 micromol/l; CI 95% = -0.84 to -1.63; p < 0.001). The maximum decline (32.3%) was observed after 30 days (mean of difference = -2.72 micromol/l; CI 95% = -2.20 to -3.24; p < 0.001).After finishing the treatment, the hypohomocysteinic effect persisted up to days 60 (mean of difference = -2.67 micromol/l; CI 95% = -2.07 to -3.26; p < 0.001)and 90 (mean of difference = -1.49 micromol/l; CI 95% = -0.94 to -2.03; p < 0.001). The response was greater when the plasmatic tHcy concentration was >= 9 micromol/l. Levofolinic acid leads to a earlier, intense and persistent drop of the plasmatictHcy levels.

Homocysteine-Lowering Effect of 500 μg Folic Acid Every Other Day versus 250 μg/Day

Background/Aims: Elevated plasma total homocysteine (tHcy) concentrations are a risk factor for neural tube defects and vascular diseases. Supplementation with folic acid decreases tHcy. We investigated whether supplementation with 500 µg folic acid every other day is as effective in lowering tHcy as 250 µg folic acid each day. Methods: In a 4-week intervention study, 22 healthy young women (18–40 years old) took either 500 µg folic acid every other day (500-µg/2d group) or 250 µg folic acid each day (250-µg/d group). Fasting blood was collected on days 0 and 28. Results: Plasma folate concentrations increased by 11.4 nmol/l (6.8–15.9) in the 250-µg/d group and by 9.1 nmol/l (95% Cl 1.9–16.3) in the 500-µg/2d group. These increases were not significantly different from each other. THcy concentrations decreased by 1.52 µmol/l (95% Cl –2.09 to –0.95; p < 0.001) in the 250-µg/d group and by 0.88 µmol/l (–1.53 to –0.23; p < 0.05) in the 500-µg/2d group. The difference in decrease between the 250-µg/d group and the 500-µg/2d group was 0.64 µmol/l (p = 0.11). Conclusion: Although not conclusive, this study suggests that supplying subjects with folic acid each day decreases tHcy more effectively than a double dose every other day.

Lead levels in domestic water supplies and neural tube defects in Glasgow

OBJECTIVETo study the association between “pregnancy” prevalence (affected births and terminations) of neural tube defects in postcode districts of Glasgow and lead concentrations in domestic water.SETTINGPostcode districts of Glasgow supplied...

Dietary Folate from Vegetables and Citrus Fruit Decreases Plasma Homocysteine Concentrations in Humans in a Dietary Controlled Trial

Elevated total plasma homocysteine (tHcy) concentrations are considered a risk factor for neural tube defects (NTD) and cardiovascular disease. Supplementation with folic acid decreases the risk of women having children with NTD. In both sexes, it decreases tHcy levels. We investigated the efficacy of natural dietary folate in improving folate and homocysteine status. We performed a 4-wk dietary controlled, parallel design intervention trial with 66 healthy subjects (18–45 y) divided into 3 treatment groups: the dietary folate group, the folic acid group and the placebo group. Each day each group was fed a different diet. The dietary folate group received a diet high in vegetables and citrus fruit (total folate content ∼560 μg) plus a placebo tablet. The folic acid group received a diet naturally low in folate (∼210 μg) plus 500 μg folic acid and placebo tablet on alternate days, i.e., 250 μg folic acid/d. And the placebo group received the same low-folate diet as the folic acid group plus a placebo tablet. After 4 wk of intervention, folate status improved, and tHcy concentrations decreased in both the dietary folate and the folic acid groups. From the amount of additional folate (350 μg/d) and folic acid (250 μg/d) consumed, the relative bioavailability of dietary folate compared to folic acid was calculated to be 60–98%, depending on the endpoint used. In conclusion, increasing the consumption of vegetables and citrus fruit, both good sources of folate, will improve folate status and decrease tHcy concentrations. This may contribute to the prevention of cardiovascular disease and NTD in the general population

Genetic risk factor for unexplained recurrent early pregnancy loss

mutation in the methylenetetrahydrofolate reductase gene a risk factor for neural tube defects? A meta-analysis. Q J Med 1997; 90: 111–15. 3 Kluijtmans LAJ, Kastelein JJP, Lindemans J, et al. Thermolabile methylenetetrahydrofolate reductase in coronary artery disease. Circulation (in press). 4 Wouters MGAJ, Boers GHJ, Blom HJ, et al. Hyperhomocysteinemia: a risk factor in women with unexplained recurrent early pregnancy loss. Fertil Steril 1993; 60: 820–25. 5 Frosst P, Blom HJ, Milos R, et al. A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase. Nat Genet 1995; 10: 111–13.

Is the common 677C-->T mutation in the methylenetetrahydrofolate reductase gene a risk factor for neural tube defects? A meta-analysis.

The common 677C-->T mutation (+) in the 5,10-methylenetetrahydrofolate reductase gene, resulting in decreased activity of the enzyme, has been associated with spina bifida neural tube defects (NTD). We combined all known Dutch control groups, a total of 1273 individuals, and found a prevalence of the 677C-->T mutation of 8.4%. When compared with the frequencies in 55 SB patients and to mothers with a child with SB their parents, this gave an OR of 1.9 [95% CI 1.1-3.3] for mothers and an OR of 1.5 [95% CI 0.74-3.1] for patients. The frequency of this mutation and its associated risk for NTD may be population-dependent. However, the frequencies of the 677C-->T mutation in different national and international control groups are almost all in the same range. We therefore combined the observed frequencies of the 677C-->T mutation in all reported studies. The mutation was present in 9.2% of controls, resulting in ORs for all reported NTD patients and their parents of: 1.7 [95% CI: 1.1-2.6]; 1.8 [95% CI: 1.1-3.1] and 1.9 [95% CI: 1.3-2.8] for mothers (combined prevalence 14.5%), fathers (combined prevalence 15.5%) and NTD patients (combined prevalence 16.4%), respectively, vs. all international controls. This meta-analysis confirms that the 677C-->T mutation is a genetic risk factor for NTD.

The methylenetetrahydrofolate reductase (Mthfr) gene maps to distal mouse chromosome 4.

Species: Mouse Locus name: 5,10-Methylenetetrahydrofolate reductase Locus symbol: Mthfr Map position: Distal Chromosome (Chr) 4, Cen t romere D4Mit13-1.06 cM _+ 0.75-Mthfr-l.06 +_ 1.06-D4Mit42 Method of mapping: Mthfr was localized by RFLP analysis of 94 animals from an interspecific backcross panel ((C57BL/6JEi x SPRET/Ei)F 1 x SPRET/Ei) provided by The Jackson Laboratory, Bar Harbor, Me. (BSS panel) [1]. To verify the localization, RFLP analysis was performed on 94 animals from the reciprocal cross ((C57BL/6J x Mus spretus)F 1 x C57BL/6J) (BSB panel) (Fig. 1) [1]. Database deposit information: The data are available from the Mouse Genome Database, accession number MGD-CREX-672. Molecular reagents: A 727-bp mouse cDNA was obtained by reverse transcription/PCR of mouse brain RNA, with primer sequences based on sequence data of a mouse genomic clone (Pai et al. unpublished). The 5' primer (5 ' -ATGGTGAACGAGGCCAGAGGAA-3' ) began at the ATG translation initiation start site, and the 3' primer (5 ' -GCAGGCCTTCACAAAGCTGAAGA-3' ) ended at bp 727 of the mouse cDNA. Sequence analysis verified the identity of the PCR product (Frosst, results not shown). The mouse cDNA was labeled by random priming and hybridized to Southern blots of TaqI-digested mouse genomic DNA. Allele detection: Allele detection was performed by RFLP analysis of a TaqI polymorphism. The C57BL/6J strain has an allele of approximately 6.5 kb, while the Mus spretus strain has an allele of approximately 4.2 kb. A constant band of approximately 3.3 kb was seen in both strains. Previously identified homologs: Human MTHFR has been mapped to the p36.3-p36.2 region of Chr 1 by in situ hybridization [2]. Discussion: M T H F R cata lyzes the conve r s ion of 5,10methylenetetrahydrofolate to 5-methyltetrahydrofolate, the primary circulatory form of folate. 5-Methyltetrahydrofolate serves as the carbon donor for homocysteine remethylation to methionine. Recently, a common mutation in MTHFR (a C ~ T substitution at bp 677 resulting in an alanine to valine missense mutation) was proposed as a genetic risk factor for neural tube defects in man [3,4,5]. This mutation requires low folate status in plasma for the development of mild hyperhomocysteinemia [6]. This genetic-nutrient interactive effect is consistent with the multifactorial model for neural tube defects and with the established role of folic acid in reducing the recurrence and occurrence of this developmental anomaly. The curly-tail (cO mouse is a mouse model for neural tube defects; it is thought to closely mimic the human disorder with

5,10 Methylenetetrahydrofolate reductase genetic polymorphism as a risk factor for neural tube defects

Persons with a thermolabile form of the enzyme 5,10 methylenetetrahydrofolate reductase (MTHFR) have reduced enzyme activity and increased plasma homocysteine which can be lowered by supplemental folic acid. Thermolability of the enzyme has recently been shown to be caused by a common mutation (677C-->T) in the MTHFR gene. We studied 41 fibroblast cultures from NTD-affected fetuses and compared their genotypes with those of 109 blood specimens from individuals in the general population. 677C-->T homozygosity was associated with a 7.2 fold increased risk for NTDs (95% confidence interval: 1.8-30.3; p value: 0.001). These preliminary data suggest that the 677C-->T polymorphism of the MTHFR gene is a risk factor for spina bifida and anencephaly that may provide a partial biologic explanation for why folic acid prevents these types of NTD.

Elevated midtrimester serum methylmalonic acid levels as a risk factor for neural tube defects

The role of folic acid in the primary prevention of neural tube defects (NTDs) is well established. However, questions related to the protective mechanism remain unanswered. To help answer these questions, we designed a case-control study to assess the role of folate- and cobalamin-related metabolites in the pathogenesis of NTDs. Concentrations of folate, cobalamin, and 14 other related metabolites were measured by gas chromatography/mass spectrometry in midtrimester serum specimens from 32 women with an NTD-affected pregnancy and from 132 control women, and in serum specimens from 46 nonpregnant women who had a history of NTD-affected pregnancy and from 43 nonpregnant control women. Log-transformed means of metabolites were compared between case and control women for both the midtrimester and nonpregnant groups. In the pregnant group, serum methylmalonic acid (MMA) concentrations were higher among case women than among control women (130 vs 105 nM). There was a strong dose-response relationship between midtrimester serum MMA level and the risk for an NTD-affected pregnancy, with the relative risk increasing 13-fold for women with MMA levels > 90th percentile. In the nonpregnant group, there was no difference in serum MMA levels between case and control women (140 vs 140 nM). Thus, the serum MMA levels of women in the midtrimester of pregnancies unaffected by NTDs were significantly lower than the levels of nonpregnant women, whereas the levels of women whose pregnancies were affected by NTDs were similar to those of nonpregnant women. The finding of elevated MMA serum concentrations among women in the midtrimester of NTD-affected pregnancies suggests that cobalamin may be involved in the etiology of NTDs. The possible role of cobalamin in relation to the protective effect of folic acid needs further evaluation.

Spontaneous abortion--high risk factor for neural tube defects in subsequent pregnancy.

An increased spontaneous abortion rate has been observed in pregnancies preceding that of fetuses or newborn infants with neural tube defects (NTDs). There are 2 suggested explanations for this observation. One is that a trophoblastic cell rest, remaining from a previous aborted pregnancy, interferes with normal embryogenesis. The second is that the previous lost fetus was affected with NTD. We studied the obstetric history of mothers of newborn infants with NTDs compared to those with other birth defects, in low and high risk groups for NTD (Jew and Bedouins). A significantly higher spontaneous abortion rate (48%) in the preceding pregnancy was found in the NTD group compared to the group with other birth defects (20%). This was especially remarkable for spina bifida cases in the Jewish study population. A significantly higher rate of preceding spontaneous abortion was also found in congenital heart defects (CHD) when compared to other congenital malformations. A hypothesis based on the multifactorial threshold model is put forward to explain these findings. Based on the realization that spontaneous abortion constitutes a high risk factor for NTD and possibly also CHD, we recommend a delay of subsequent pregnancy and periconceptional treatment with folic acid following spontaneous abortion.

Stereospecific in vitro embryotoxicity of l-homocysteine in pre- and post-implantation rodent embryos

Recently a derangement of homocysteine metabolism has been suggested as a possible risk factor for neural tube defects and recurrent spontaneous abortion. To investigate a possible role of homocysteine in the aetiology of neural tube defects we tested the in vitro embryotoxicity of l-homocysteine by culturing day 10 post coitum post-implantation rat embryos in whole embryo culture (WEC) for 24 hr and day 2 post coitum pre-implantation mouse embryos for 48 hr. With an area under curve (AUC) of 6.3 m m/hr, l-homocysteine significantly reduced the percentage of mouse embryos that developed into blastocysts. In rat WEC, an AUC for l-homocysteine of 3.6 m m/hr reduced the mitotic index of the neural epithelium of the rhombencephalon and the cell density of the mesenchyme adjacent to it, while at an AUC of 7.2 m m/hr l-homocysteine reduced the total morphological score and the number of malformations was increased. Malformations most often seen were transparent rhombencephalon, no or delayed formation of forelimb buds, dysmorphogenesis of the somites, and blister formation dorso-laterally of the place of forelimb bud formation. The embryotoxicity of l-homocysteine was stereospecific since d-homocysteine caused no embryotoxic effects. Also the oxidation product l-homocystine (AUC, 72 m m/hr) and the metabolite l-methionine (AUC, 144 m m/hr) were not embryotoxic. Both stereoisomers of homocysteinethiolactone were embryotoxic at an AUC of 72 m m/hr. The results are discussed in relation to the metabolism of homocysteine and methionine and their possible role in the neurulation process.