5,10-Methylenetetrahydrofolate reductase gene variants and congenital anomalies: a HuGE review

Neural tube closure depends on nitric oxide synthase activity

Neural tube (NT) closure is a multifactorial process that involves yet unresolved molecular mechanisms. It had been shown previously that high levels of nitric oxide (NO) block the process of NT closure in the chick embryo by inhibiting methionine synthase (MS). The MS inhibition and its effect on NT closure could be alleviated by folic acid, suggesting the involvement of the folate-methionine pathway in the process. Here we test the hypothesis that endogenous nitric oxide synthase (NOS) activity regulates the MS activity required in the process of NT closure. The experiments described here reveal that NOS activity per se, is indeed critical for NT closure in the chick embryo. Inhibition of NOS activity with either 2,4-diamino-6-hydroxypyrimidine (DAHP), which blocks biosynthesis of the NOS co-factor tetrahydrobiopterin (BH4), or with calmidazolium, which blocks calcium-calmodulin binding to NOS, resulted in reduced MS activity and consequently ablated NT closure. Addition of BH4 or the calcium ionophore A23187 restored NOS and MS activities, resulting in NT closure. The results described here imply that NOS and MS activities can serve as functional markers in this developmental process as they are essential in the process of NT closure.

Incorporating genetic analyses into birth defects cluster investigations: Strategies for identifying candidate genes

BACKGROUND

Incorporating genetic analyses into birth defect cluster investigations may increase understanding of both genetic and environmental risk factors for the defect. Current constraints of most birth defect cluster investigations make candidate gene selection the most feasible approach. Here, we describe strategies for choosing candidate genes for such investigations, which will also be applicable to more general gene-environment studies.

METHODS

We reviewed publicly available web-based resources for selection of candidate genes and identification of risk factors, as well as publications on different strategies for candidate gene selection.

RESULTS

Candidate gene selection requires consideration of available gene-disease databases, previous epidemiological studies, animal model research, linkage and expression studies, and other resources. We describe general considerations for utilizing available resources, as well as provide an example of a search for candidate genes related to gastroschisis.

CONCLUSIONS

Available web resources could facilitate selection of candidate genes, but selection of optimal candidates will still require a strong understanding of genetics and the pathogenesis of the defect, as well as careful consideration of previous epidemiological studies.

Emerging concepts in nutrigenomics: a preview of what is to come

This article provides an overview of the fundamental principles of genetics and emerging concepts related to the ways in which nutrients and bioactive food components may interact with the genome and subsequently affect human health. This exciting area of research is likely to have far-reaching implications for the assessment and treatment of critically and chronically ill individuals that will affect nutrition standards of care and practice. A brief overview of some of the ethical, legal, and social implications of genomic research and genome-based health care and a list of genetics resources also are provided.

Maternal and offspring MTHFR gene C677T polymorphism as predictors of congenital atrial septal defect and patent ductus arteriosus

To observe the association of MTHFR gene C677T locus polymorphism with occurrence of congenital heart defects (CHDs), 21 patients with atrial septal defect (ASD), 35 patients with patent ductus arteriosus (PDA), one patient with both conditions combined, and their biological parents were collected as the case group. Another 104 normal individuals and their biological parents without a family history of birth defects were selected as the control group. MTHFR C677T genotypes of each sample were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The results showed for the occurrence of ASD, the odds ratio (OR) of TT genotype was 4.08 [95% confidence interval (95% CI) = 1.28-13.24] compared with CT genotype. For the occurrence of PDA, the ORs of TT were 3.44 (95% CI = 0.89-16.13) and 2.38 (95% CI = 0.92-6.14) compared with CC and CT genotypes, respectively. Author as meant? Compared with CC + CT genotype combination, the ORs of TT were 3.95 (95% CI = 1.38-11.44) and 2.60 (95% CI = 1.02-6.36) for ASD and PSD respectively. The results also had sex differences and the statistical significance was only observed in male ASD and female PDA. The ORs of T allele carriers were 2.29 (95% CI = 1.08-4.92) and 1.88 (95% CI = 1.02-3.47) compared with C allele for the occurrences of ASD and PDA respectively. The analysis of parents genotype showed that the OR of TT mothers was 2.31 (95% CI = 0.96-5.59, P < 0.05) compared with (CC + CT) for the occurrence of PDA in offspring. So this study could give a clue that MTHFR C677T locus variation was related with occurrence of ASD and PDA, and the carriers of TT genotype and T allele had higher risk of diseases. The mother carrying TT genotype was associated with occurrence of PDA in offspring.

Prevalence of genetic risk factors for coronary artery disease in Corsica island (France)

We have investigated the frequencies of seven markers among 100 unrelated individuals with angiographically documented CAD (Coronary Artery Disease) and among 100 unrelated healthy blood donors in the central region of Corsica island (France). The seven polymorphisms analyzed were chosen from six candidate genes involved in (1) Renin-Angiotensin system: Angiotensin converting enzyme (ACE I/D), (2) Lipid metabolism: Cholesterol Ester Transfer Protein gene (CETP TAQ1B), (3) Platelet aggregation: alpha and beta subunits of the platelet GpIIb/GpIIIa integrin complex (GpIIb HPA3 and GpIIIa Pl(A1/A2)), (4) Coagulation fibrinolysis: Plasminogen Activator Tissue (PLAT TPA25 I/D) and Methylenetetrahydrofolate Reductase (MTHFR C677T and A1298C). The samples were genotyped using the polymerase chain reaction followed by restriction enzyme analysis for the RFLPs. No significant difference in allele frequencies between patient and control groups was observed. The occurrence of the MTHFR T677T genotype and of the T677T/A1298A compound genotype is higher in cases (20%) than in the controls (4%). Odds ratio seems to indicate that individuals with the MTHFR T677T genotype and the T677T/A1298A compound genotype had a 6-fold increased risk for developing CAD (ORs = 6; 95% CIs = 1.96-18.28) suggesting a possible association of MTHFR C677T with the risk of CAD in Corsican population.

Evaluation of a methylenetetrahydrofolate-dehydrogenase 1958G>A polymorphism for neural tube defect risk

Genetic variants of enzymes involved in the folate pathway might be expected to have an impact on neural tube defect (NTD) risk. Given its key role in folate metabolism, the methylenetetrahydrofolate dehydrogenase 1 (MTHFD1) gene could represent an attractive candidate in NTD aetiology. In this study, the impact of the MTHFD1 1958G > A polymorphism on NTD risk in the Italian population was examined both by hospital-based case-control and family-based studies. The MTHFD1 1958G > A polymorphism was genotyped in 142 NTD cases, 125 mothers, 108 fathers and 523 controls. An increased risk was found for the heterozygous 1958G/A (OR = 1.69; P = 0.04) and homozygous 1958A/A (OR = 1.91; P = 0.02) genotypes in the children. Significant association was also found when combined 1958G/A and 1958A/A genotypes of cases were compared with the 1958G/G genotype (OR = 1.76; P = 0.02). The risk of an NTD-affected pregnancy of the mothers was increased 1.67-fold (P = 0.04) only when a dominant effect (1958G/A or 1958A/A vs 1958G/G) of the 1958A allele was analysed. The combined TDT/1-TDT (Z = 2.11; P = 0.03) and FBAT (Z = 2.4; P = 0.01) demonstrated a significant excess of transmission of the 1958A allele to affected individuals. In summary, our results indicate that heterozygosity and homozygosity for the MTHFD1 1958G > A polymorphism are genetic determinants of NTD risk in the cases examined.

Methylenetetrahydrofolate reductase genetic polymorphisms in patients with cataract

PURPOSE

Hyperhomocysteinemia is commonly associated with polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene. The level of homocysteine can be lowered by dietary intake of folate. A protective effect of folate supplementation has been reported against cataract. Here we investigate MTHFR polymorphisms in human cataract.

DESIGN

Retrospective case-control association study.

METHODS

Patients with nuclear (n = 77), cortical (n = 155), posterior subcapsular (n = 119), and mixed (n = 151) cataract, and 187 controls were analyzed for the MTHFR 677C-->T and 1298A-->C polymorphisms using minisequencing technique.

RESULTS

The wild-type MTHFR 677CC/1298AA genotype was strongly overrepresented among cataract cases (P = .003). This effect was most pronounced in the mixed cataract group (P < .001). Hyperhomocysteinemia-associated genotypes had similar frequencies in cataract and control groups.

CONCLUSIONS

The previously reported protective effect of folate against cataract is not due to overrepresentation of hyperhomocysteinemia-associated MTHFR genotypes. Instead, the strong predominance of wild-type MTHFR in cataract may suggest impaired DNA synthesis as a cataractogenic factor.

Screening for new MTHFR polymorphisms and NTD risk

The enzyme, 5,10-methylenetetrahydrofolate reductase (MTHFR) plays a key role in cellular folate metabolism. The A222V (677C->T) polymorphism is a confirmed neural tube defect (NTD) risk factor within Irish and other populations. To search for other unknown single nucleotide polymorphisms (SNPs) that might play a role in the etiology of NTDs, we examined the entire MTHFR coding region in healthy individuals (n = 100). SNPs were identified using sequencing and database analysis and allele frequencies were determined in our Irish population. We identified P39P (116C->T; T allele frequency 0.13) and previously reported R594Q (1793G->A; Q allele frequency 0.07). We screened a large ethnically homogeneous Irish NTD cohort (n>1,300) for P39P and R594Q. A possible association between NTD cases and P39P (P = 0.034) was found but this was not confirmed by transmission disequilibrium testing. R594Q also showed some evidence of a NTD case association (P = 0.07). Further analysis indicated these observations are due to linkage disequilibrium with A222V (677C->T), and therefore these new SNPs are unlikely to be independent risk factors for NTDs. As rates of NTDs differ between ethnic groups, we examined allele and genotype frequencies of P39P and R594Q within African-American and American-Caucasian populations. This is the first NTD association study of both R594Q and the novel P39P. The association with NTD risk reported for these SNPs is driven by the linkage disequilibrium with the A222V (677C->T) NTD risk factor.

Regulatory studies of murine methylenetetrahydrofolate reductase reveal two major promoters and NF-kappaB sensitivity

Two promoters of the murine methylenetetrahydrofolate reductase gene (Mthfr), a key enzyme in folate metabolism, were characterized in Neuro-2a, NIH/3T3 and RAW 264.7 cells. Sequences of 189 bp and 273 bp were sufficient to achieve maximal activity of the upstream and downstream promoter, respectively. However, subtle differences in minimal promoter lengths and in promoter activities were observed between the cell lines. Both promoters demonstrated comparable activity in NIH/3T3 and RAW 264.7 cells, while in Neuro-2a cells, the upstream promoter was 15-fold more active than the downstream promoter. Alignment and data mining tools identified a candidate nuclear factor kappa B (NF-kappaB) binding site at the 3'end of the downstream promoter that is conserved throughout several species. NF-kappaB activation experiments in cultured cells were associated with increased Mthfr mRNA. Co-transfection of NF-kappaB and promoter constructs demonstrated Mthfr up-regulation by at least 2-fold through its downstream promoter in Neuro-2a cells; this increase was significantly reduced when the putative binding site was mutated. EMSA analysis demonstrated direct binding of NF-kappaB to this non-mutated site. This study, a first step into the elucidation of Mthfr regulation, demonstrates that two TATA-less, GC-rich promoters differentially drive transcription of Mthfr in a cell-specific manner, and provides a novel link of Mthfr to possible roles in the immune response and cell survival.

Evaluation of offspring and maternal genetic effects on disease risk using a family-based approach: the "pent" design

Diseases that develop during gestation may be influenced by the genotype of the mother and the inherited genotype of the embryo/fetus. However, given the correlation between maternal and offspring genotypes, differentiating between inherited and maternal genetic effects is not straightforward. The two-step transmission disequilibrium test was the first, family-based test proposed for the purpose of differentiating between maternal and offspring genetic effects. However, this approach, which requires data from "pents" comprising an affected child, mother, father, and maternal grandparents, provides biased tests for maternal genetic effects when the offspring genotype is associated with disease. An alternative approach based on transmissions from grandparents provides unbiased tests for maternal and offspring genetic effects but requires genotype information for paternal grandparents in addition to pents. The authors have developed two additional, pent-based approaches for the evaluation of maternal and offspring genetic effects. One approach requires the assumption of genetic mating type symmetry (pent-1), whereas the other does not (pent-2). Simulation studies demonstrate that both of these approaches provide valid estimation and testing for offspring and maternal genotypic effects. In addition, the power of the pent-1 approach is comparable with that of the approach based on data using all four grandparents.

Folates en période péri-conceptionnelle et prévention du risque de fente orofaciale : rôle des apports alimentaires en France

BACKGROUND

Orofacial clefts are among the most frequent congenital malformations at birth with a prevalence of 1 in 700 births in Europe. The implication of environmental factors in their etiology has been demonstrated. The role of folic acid, or folates, in the prevention of orofacial clefts is still debated although its efficacy has been demonstrated for the prevention of neural tube defects.

METHODS

A case-control study was conducted in 7 hospitals in 4 centers in France. Cases (N=240) were children with non-syndromic orofacial cleft referred to one of the study hospitals for initial surgical repair in 1998 and 1999. Controls (N=236) matched for gender, geographic origin, and age were chosen in paediatric departments of the same hospitals. Usual dietary intake of folates was estimated using a food frequency questionnaire submitted to the mother at hospital. During the same interview, data on sociodemographic characteristics, medical and obstetrical history, tobacco and alcohol consumption, and vitamin supplements, were obtained. Odds ratios associated with quintiles of dietary intake of folates were estimated using logistic regression adjusting for known confounders.

RESULTS

A significant dose-response relationship between the risk of orofacial clefts and a decrease in the intake of folates from diet was found, stronger for cleft palate without cleft lip. Only few women (<1%) declared having taken vitamin supplements containing folic acid when planning their pregnancy.

CONCLUSION

Our study further suggests that folates are useful for the prevention of orofacial clefts during the periconceptual period. In our study, the estimated average daily intake of folates (270 microg/day) was below French national recommendations for the prevention of neural tube defects (400 microg/day). Since those insufficient folate intakes during the periconceptual period are not presently met by vitamin supplementation, the solution may come from the food fortification program proposed and implemented by the National Agency for Food Safety (AFSSA).

Methylenetetrahydrofolate Reductase Polymorphisms and the Risk of Gestational Hypertension

BACKGROUND

Evidence on the association of 5,10 methylentetrahydrofolate reductase (MTHFR) C677T and A1298C polymorphisms in women with gestational hypertension is inconsistent. It is also unknown whether the fetal genotype is relevant, or whether folic acid supplementation modifies this association.

METHODS

The study population was composed of U.S. and Canadian white women with nonmalformed infants participating in the Slone Epidemiology Center Birth Defects Study between 1993 and 2000. Women were interviewed within 6 months after delivery regarding multivitamin use in pregnancy and the occurrence of gestational hypertension, among other factors. DNA was extracted from cheek swabs and gene alleles determined by restriction fragment length polymorphism analysis. We compared the prevalence of the 677TT/CT and 1298CC/AC genotypes between cases with gestational hypertension (54 mothers and their 51 offspring) and controls (100 mothers and their 99 offspring). We also estimated odds ratios (ORs) and 95% confidence intervals (CIs) using conditional logistic regression to control for geographic region and calendar year.

RESULTS

The T allele was present in 69% of women with gestational hypertension versus 57% of control women (compared with 677CC, OR = 1.9; 95% CI = 0.9-4.0). The offspring of case and control women had a 677TT/CT genotype prevalence of 68% and 47%, respectively (2.4; 1.1-5.0). Among women supplemented with folic acid during the first 5 months of pregnancy, the ORs for maternal and fetal 677TT/CT genotypes were 0.9 (0.3-2.5) and 2.1 (0.7-6.0), respectively. Neither maternal nor fetal 1298CC/AC genotypes were associated with an increased risk of gestational hypertension.

CONCLUSION

Maternal and fetal MTHFR C677T polymorphism may be associated with a moderately increased risk of gestational hypertension, and there is a suggestion that this association may be diminished among women receiving folate supplementation during pregnancy.

An investigation of folate-related genetic factors in the determination of birthweight

Recent evidence suggests that maternal folate status in early gestation is a significant determinant of infant birthweight. Folate metabolism is known to be controlled by genetic factors, with a number of polymorphic variations in folate metabolising genes identified, several of which have well-documented functional effects. The current study investigated whether folate-related polymorphic variation, in association with low maternal folate status, influences birthweight. Red blood cell (RBC) folate analysis and genotyping of five polymorphisms in folate-related genes [Methylenetetrahydrofolate reductase (MTHFR) 677C>T; MTHFR 1298A>C; cystathionine-beta-synthase (CbetaS) 844ins68bp; serine hydroxymethyltransferase (SHMT) 1420C>T; reduced folate carrier-1 (RFC-1) 80G>A] were undertaken in mothers and infants from 998 pregnancies. These data were analysed in relation to infant birthweight, adjusted for gender and gestational age (z-score). Low maternal RBC folate status was associated with reduced infant birthweight. None of the genetic variants studied showed an independent association with infant birthweight. However, two genetic variants were shown to have a significant effect on birthweight when found in association with low maternal RBC folate status. When individuals with variant genotypes and mothers with folate in the lowest quintile were compared with wild-type individuals and mothers with folate in the highest quintile, the following differences in mean birthweight (z-score) were observed; maternal MTHFR 677C>T (-0.56 [95% CI -1.00, -0.12]P=0.01) and infant CbetaS 844ins68bp (-0.71 [95% CI -1.97, -0.07]P=0.03). The findings of this study suggest that folate-related genetic polymorphisms do not directly influence infant birthweight. However, when placed on a background of deficient maternal nutritional status, they may detrimentally affect fetal growth.

Association of the C677T and A1298C polymorphisms of methylenetetrahydrofolate reductase gene with schizophrenia: association is significant in men but not in women

Schizophrenia is a complex and common psychiatric disorder with a polygenic inheritance. In our previous report, we showed an association between the methylenetetrahydrofolate reductase (MTHFR) gene C677T and A1298C polymorphisms and schizophrenia in patients from Bakirkoy in Istanbul, Turkey [Sazci, A., Ergul, E., Guzelhan, Y., Kaya, G., Kara, I., 2003. Methylenetetrahydrofolate reductase gene polymorphisms in patients with schizophrenia. Mol. Brain Res. 117, 104-107]. We wanted also independently to confirm this study in a gender-specific manner with schizophrenic patients from Erenkoy in Istanbul, Turkey. To investigate the role of the C677T and A1298C polymorphisms of methylenetetrahydrofolate reductase gene in schizophrenia in a gender-specific manner, we analyzed the genotypes of MTHFR677 and MTHFR1298 of 297 schizophrenic patients and 341 healthy controls, using a polymerase chain reaction restriction fragment length polymorphism method. The MTHFR 677T allele was significantly distributed (chi2=7.312; P=0.026), between schizophrenic patients and healthy controls. The T677T genotype was overrepresented in the total schizophrenic patients (OR=1.938; 95%CI=1.133-3.315; chi2=5.996; P=0.014). Similarly, the T677T/A1298A compound genotype was the most significant one in the total schizophrenic patients (OR=2.397; 95% CI=1.327-4.330; chi2=8.821; P=0.003). The C1298C genotype was overrepresented in the total schizophrenic patients (OR=1.706; 95%CI=1.014-2.870; chi2=4.126; P=0.042). Likewise, the C677C/C1298C compound genotype was significant in the total schizophrenic patients (OR=1.689; 95%CI=0.985-2.894; chi2=3.695; P=0.055). When schizophrenic patients and healthy controls were stratified according to gender difference, the T677T genotype and T677T/A1298A compound genotype were significantly overrepresented (OR=2.184; 95% CI=1.069-4.462; chi2=4.767; P=0.029; OR=2.748; 95% CI=1.215-6.214; chi2=6.301; P=0.012, respectively) in men schizophrenic patients. However, neither the MTHFR C677T nor the A1298C polymorphisms are associated with schizophrenia in women. In conclusion, the MTHFR 677T allele and T677T, C1298C genotypes, and T677T/A1298A, C677C/C1298C compound genotypes are genetic risk factors for schizophrenia in men but not in women in a gender-specific manner.

Decline in the prevalence of spina bifida and anencephaly by race/ethnicity: 1995-2002

OBJECTIVE

In an effort to reduce the occurrence of neural tube defects (NTDs), folic acid fortification of US enriched grain products was authorized by the Food and Drug Administration in March 1996 and required by January 1998. Fortification has been shown to result in an important decline in the prevalence of spina bifida and anencephaly in the general US population; however, fortification's impact on specific racial/ethnic groups has not been well described. We sought to characterize the decline in the prevalence of spina bifida and anencephaly among specific racial/ethnic groups during the transition to mandatory folic acid fortification in the United States.

METHODS

Data from 21 population-based birth defects surveillance systems were used to examine trends in prevalence of spina bifida and anencephaly for specific racial/ethnic groups for the years 1995-2002. These years were divided into 3 periods: prefortification, optional fortification, and mandatory fortification. Race/ethnicity was defined as Hispanic, non-Hispanic white, and non-Hispanic black. Prevalence ratios were calculated for each racial/ethnic group by dividing the prevalence from the mandatory fortification period by the prevalence in the prefortification period.

RESULTS

The study included data on 4468 cases of spina bifida and 2625 cases of anencephaly. The prevalence of spina bifida and anencephaly was highest among Hispanic births, followed by non-Hispanic white births, with the lowest prevalence among non-Hispanic black births. Significant declines in spina bifida and anencephaly were observed among Hispanic births and non-Hispanic white births. The prevalence ratio for non-Hispanic black births was of borderline significance for spina bifida and was not significant for anencephaly.

CONCLUSIONS

The results of this study suggest that folic acid fortification is associated with significant decreases in the prevalence of spina bifida and anencephaly among non-Hispanic white and Hispanic births. The magnitude of the reduction was similar between these 2 groups and was more pronounced for spina bifida than for anencephaly. The decline in the prevalence of spina bifida and anencephaly among non-Hispanic black births did not reach statistical significance. Efforts to increase folic acid consumption for the prevention of NTDs in pregnancies among women of all races/ethnicities should be continued, and studies to identify and elucidate other risk factors for NTDs are warranted.

Inhibition of transmethylation disturbs neurulation in chick embryos

Periconceptional folic acid supplementation can reduce the occurrence of neural tube defects. A low folate status will result in reduced remethylation of homocysteine (Hcy) to methionine and, subsequently, in a rise of Hcy levels. Indeed, elevated Hcy concentrations have been reported in mothers of children with neural tube defects. In our previous study, we showed that treatment of chick embryos with Hcy resulted in a delay of neural tube closure in an in vitro model. In the present study, we examined whether this effect of Hcy is due to inhibition of transmethylation via elevation of S-adenosylhomocysteine (AdoHcy). Transmethylation involves methylation of DNA, RNA and proteins by donation of a methyl group from S-adenosylmethionine (AdoMet). After application of inhibitors of S-adenosylhomocysteine hydrolase and of methionine adenosyltransferase, a delay of anterior neuropore closure, comparable to that observed after Hcy treatment, was observed. The changes in AdoMet and AdoHcy concentrations confirmed the inhibition of S-adenosylhomocysteine hydrolase or methionine adenosyltransferase, respectively, and the AdoMet/AdoHcy ratio was decreased in all cases, indicating reduced transmethylation. Moreover, the inhibition of methionine adenosyltransferase was prevented by pretreatment with methionine. This study, therefore, indicates that the Hcy-induced delay of the neural tube closure is caused by the inhibition of transmethylation via elevation of AdoHcy levels and a reduction of the AdoMet/AdoHcy ratio.

Maternal mutation 677C > T in the methylenetetrahydrofolate reductase gene associated with severe brain injury in offspring

A frequent polymorphism in the gene coding for 5,10-methylenetetrahydrofolate reductase is the substitution 677C > T which produces a thermolabile and inefficient enzyme. Homozygosity for the 677C > T allele is the most important determinant of hyperhomocys-teinemia, when folic acid intake is reduced. Most studies on the relationship between the 677C > T variant in the mother and defects in the offspring have focused on neural-tube defects. This study is a retrospective case-control investigation of hypoxic-ischemic encephalopathy of the newborn (HIEN) with reference to the 677C > T polymorphism as a genetic risk for this condition. The prevalence of the 677C > T allele was studied in 11 children with HIEN, their respective mothers, and 85 healthy individuals. Plasma homocysteine levels after fasting and methionine loading were determined in both mothers and controls. Ten of 11 patients were evaluated using magnetic resonance (MR) imaging, and all showed multicystic encephalomalacia and severe brain vasculopathy. Seven mothers were homozygous and four heterozygous for the 677C > T allele. Five of the children were homozygous and six heterozygous for this polymorphism. The variant allele frequency was higher in the group of mothers with affected children than in the controls and was associated with an increase in plasma homocysteine after methionine loading, in the group of mothers than in controls. The 677C > T mutation in mothers, either in a homozygous or heterozygous state, together with poor nutritional status (probable folate deficiency) may represent a risk factor for irreversible HIEN in the offspring.

Embryology of neural tube development

Neurulation is the process of forming the neural tube, which will become the brain and spinal cord. This article reviews the various cellular processes involved in neurulation and discusses possible roles of folate in this process.

Candidate gene analysis in human neural tube defects

Biochemical and developmental pathways, mouse models, and positional evidence have provided numerous candidate genes for the study of human neural tube defects. In a survey of 80 studies on 38 candidate genes, few found significant results in human populations through case-control or family-based association studies. While the folate pathway has been explored extensively, only the MTHFR 677C > T polymorphism was significant, and only in an Irish population. Developmental pathways such as the Wnt signaling pathway and Hox genes have also been explored without positive results. More than 90 mouse candidates have been identified through spontaneous and knockout mutations, but only the T locus (mouse Brachyury gene) showed association in an initial study that was not confirmed on follow-up. Positional candidates have been derived from cytogenetic evidence, but preliminary genomic screens have limited power due to small sample sizes. Future studies would increase their power to detect association by using more samples. In addition a clarification of the phenotype would be beneficial as many studies used different inclusion criteria. Incorporating several types of data could highlight better candidates, as would looking beyond the traditional sources for candidate genes. Recent studies of an energy metabolism gene (UCP2) and vitamin B metabolism (Transcoalbumin) have produced promising results. Utilizing other model organisms may also be beneficial, as in a recent study from a chick model of NTDs in NCAM1. New approaches combined with traditional methods and increased sample sizes will help prioritize human NTD candidate genes and clarify the complex etiology of this condition.

Genotype and allele frequencies of the polymorphic methylenetetrahydrofolate reductase gene in Turkey

The polymorphic methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms C677T and A1298C cause mild hyperhomocysteinemia, not only in homozygotes for C677T, but also in compound heterozygotes for C677T/A1298C. The aim of this study was to determine allelic frequencies of the polymorphic MTHFR gene C677T, A1298C. In this regard, we have investigated the allelic frequencies of C677T and A1298C polymorphisms of the MTHFR gene in 1684 randomized individuals around Turkey. DNA samples isolated from peripheral blood samples of randomized individuals were analysed. The study population consisted of 1004 females and 680 males. The frequency in Turkey of the C677T was 42.9 %; of C677C, 47.4 %; and of T677T, 9.6 %. The frequency in Turkey of A1298C was 43.7 %; of A1298A, 46.3 %; and of C1298C, 10.0 %. The allelic frequencies of the T allele of MTHFR 677 and the C allele of MTHFR 1298 were 33.34 and 33.16 %, respectively. The frequency of C677T/A1298C compound heterozygosity is highest in Turkey (21.6 %), as compared to Canada (15 %), the United States (17 %) and The Netherlands (20 %).

MTHFR genotypes and breast cancer survival after surgery and chemotherapy: a report from the Shanghai Breast Cancer Study

Methylenetetrahydrofolate reductase (MTHFR) regulates the intracellular folates pool for DNA synthesis and methylation. Sequence variations in MTHFR (nucleotides 677 (C-->T) and 1298 (A-->C)) result in allozymes with decreased activity. The 677TT genotype is associated with increased toxicity of methotrexate and increased clinical response to 5-fluorouracil in treatment of cancers including breast cancer. We evaluated MTHFR genotypes and breast cancer survival in a cohort of 1067 Chinese women diagnosed with breast cancer between 1996 and 1998 who received surgery and chemotherapy. Life table method was used to calculate 5-year survival rates. Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) after adjusting for potential confounding factors. Median follow-up time was 5.2 years; 5-year survival was 84.6%. Sixty-six percent carried a 677T allele and 31% carried a 1298 C allele. We found that overall 5-year breast cancer survival did not differ significantly across all genotypes (85.3% for 677 CC and 83.8% for 677TT; 83.8% for 1298 AA and 79.1% for 1298 CC). However, carrying the 677T allele was associated with non-significant increased risk of death for subjects with late stage disease (stages III-IV) (HR=1.80, 95% CI: 0.79-4.14 for TT vs. CC, p for trend=0.15), particularly among those who had survived past the second year (HR=2.97, 95% CI: 1.10-7.98, p for trend=0.04). The A1298C genotypes were not significantly associated with risk of death. This study suggests that the MTHFR C677T polymorphisms may affect long-term survival from advanced breast cancer.

Maternal methylenetetrahydrofolate reductase deficiency and low dietary folate lead to adverse reproductive outcomes and congenital heart defects in mice

BACKGROUND

Genetic or nutritional disturbances in folate metabolism may affect embryonic development because of the critical role of folate in nucleotide synthesis and methylation reactions. The possible role of a mild deficiency in methylenetetrahydrofolate reductase (MTHFR) and low dietary folate in pregnancy outcomes and heart morphogenesis requires further investigation.

OBJECTIVE

We investigated the effect of mild MTHFR deficiency, low dietary folate, or both on resorption rates, on length and weight, and on the incidence of heart malformations in murine embryos.

DESIGN

Female Mthfr +/+ and +/- mice were fed a control diet (CD) or a folic acid-deficient diet (FADD) before mating with male Mthfr +/- mice. On gestational day 14.5, implantation and resorption sites were recorded and viable embryos were examined for gross malformations, growth delay, and congenital heart defects.

RESULTS

Plasma homocysteine in Mthfr +/- dams and in FADD-treated dams was significantly higher than that in Mthfr +/+ dams and CD-treated dams, respectively. A significantly higher rate of resorption and greater developmental delay were observed in hyperhomocysteinemic mice than in CD-treated +/+ dams. Heart defects were identified in 4 of 11, 5 of 10, and 4 of 10 litters from CD-treated +/-, FADD-treated +/+, and FADD-treated +/- dams, respectively, but not in any of those from CD-treated +/+ dams (0/11 litters).

CONCLUSION

Our findings suggest that mild MTHFR deficiency, low dietary folate, or both in the dams increase the incidence of fetal loss, intrauterine growth retardation, and heart defects. These data support the benefit of folic acid supplementation in pregnant women, particularly in those with MTHFR deficiency.

Pharmacogenetics and Pediatric Cancer

The great advances in therapeutic success for childhood cancers have provided the impetus for strategies to avoid serious systemic toxicities from chemotherapy. This review describes the impact of genetic mutations in drug metabolism pathways on the toxicity of anticancer agents. Although many polymorphisms have been related to toxicity in adults, these associations are less well defined in children. The role of genetic polymorphisms in MTHFR, TYMS, TPMT, and UGT1A1 in influencing drug toxicity is reviewed. Better understanding of the pharmacogenetic determinants of drug metabolism or pharmacologic cofactors may allow for prospective identification of potential patients who are at increased risk for toxicity, allowing for dose optimization and resulting in a decrease in toxic risk while maximizing efficacy.

Hyperhomocysteinemia in acute Plasmodium falciparum malaria: an effect of host-parasite interaction

BACKGROUND

Plasmodium falciparum utilises the polyamine pathway, essential in proliferation and differentiation, and imposes an oxidative stress on host cell, enhancing the loss of glutathione.

METHODS

Standard hematological parameters were determined in 40 black African subjects with acute P. falciparum malaria, 30 aged 5-24 months, 5 aged 4-10 years and 5 aged 19-35 years. Plasma homocysteine, cysteine, glutathione and cysteinylglycine levels were measured by HPLC method. Twenty-eight healthy black children (15 aged 6-24 months and 13 aged 3-10 years) and 20 healthy black adults (aged 20-40 years) were also included as controls.

RESULTS

Plasma homocysteine levels were higher in all subjects with P. falciparum malaria and correlated positively with the disease severity and number of parasites, but negatively with Hb levels and patient ages. Cysteine level was found higher in all patients and markedly higher in 4-10 year old patients. Cysteinylglycine level was found lower particularly in 19-35 year old patients. Glutathione level was significantly lower in all patients.

CONCLUSIONS

The elevated level of homocysteine during acute P. falciparum infection suggests an imbalance in the folate cycle, which could be a consequence of the reduced availability of NADPH and Vit B12, caused by increased oxidative stress. This may suggest a selection for the C677T MTHFR allele, driven by P. falciparum in sub-Saharan regions. Hence Hcy level could be useful as a predictive parameter of severity, as well as of treatment efficacy.

Congenital heart defects and genetic variants in the methylenetetrahydroflate reductase gene

BACKGROUND

Most non-syndromic congenital heart defects (CHD) are caused by a complex interaction between maternal lifestyle factors, environmental exposures, and maternal and fetal genetic variants. Maternal periconceptional intake of folic acid containing vitamin supplements is reported to decrease the risk of CHD. The 677C-->T and 1298A-->C polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene decrease enzyme activity.

OBJECTIVE

To examine the relation between CHD and maternal and fetal MTHFR polymorphisms.

METHODS

375 nuclear families were studied. The transmission/disequilibrium test was used to test for transmission distortion in complete triads. A log-linear approach was used to test for associations between CHD and maternal and offspring polymorphisms, and to estimate independently the contributions of maternal and fetal variants to relative risks. Haplotype frequencies were estimated and a haplotype transmission disequilibrium test carried out.

RESULTS

The 1298C allele was transmitted less often than expected (p = 0.0013). There was no distortion in the transmission of the 677T allele, neither was there evidence of a parent of origin effect in the transmission of either of the single nucleotide polymorphisms. The 677C-1298C haplotype was also transmitted less often than expected (p = 0.0020). The relative risk associated with inheriting one copy of the 1298C allele was 0.64 (95% confidence interval, 0.48 to 0.87) and the that associated with inheriting two copies of the 1298C allele, 0.38 (0.21 to 0.70).

CONCLUSIONS

The apparent protective effect of the MTHFR 1298C allele against CHD could have several explanations and further study is needed.

Genetic risk factors associated with thrombosis in children with congenital neurologic disorders

Thromboembolic events during the perinatal period are responsible for irreversible brain damage owing to cerebral hypoxia and neuronal necrosis. We investigated the presence of thrombophilia risk factors in children with congenital neurologic disorders. Nineteen children (9 males and 10 females), aged 1 to 14 years (median 4.5 years), who had presented with symptoms and signs of congenital neurologic disorders were studied. Thirty-five age-matched healthy children recruited from the same geographic area served as controls. Three patients of 19 (15.8%) were carrying the factor V Leiden mutation compared with 2 children among the controls (5.7%). One patient was heterozygous for the prothrombin G20210A variant (5.2%) compared with one child who was heterozygous among the controls. Three patients were homozygous (15.8%) and 11 were heterozygous (57.9%) for the C677T 5,10-methylenetetrahydrofolate reductase gene mutation compared with 4 (11.5%) and 18 (51.4%), respectively, among the controls. Three patients of 19 (15.8%) were carrying more than one mutation. We found 18 mutations in 79% (15/19) of the patients and 25 mutations in 69% (24/35) of the healthy children. Among the individuals carrying the homozygous 677TT 5,10-methylenetetrahydrofolate reductase genotype, we found 7 mutations in 32% (6/19) of the patients and 7 mutations in 20% (7/35) of the healthy children (P > .05). In one patient, lupus anticoagulant and antiphospholipid antibodies of IgG isotype were detected. Reduced activities of protein C, protein S, or antithrombin III were not observed in either the patient or the control group. Although, among our cases, we found some well-known risk factors associated with thrombosis in adults, the pathogenesis of these clinical entities remains obscure.

Methylenetetrahydrofolate reductase genotype affects risk of relapse after hematopoietic cell transplantation for chronic myelogenous leukemia

PURPOSE

Methylenetetrahydrofolate reductase (MTHFR) directs intracellular folate toward homocysteine metabolism and away from nucleotide synthesis. Two common MTHFR polymorphisms, C677T and A1298C, are associated with reduced enzyme activity. We evaluated the association of these polymorphisms with risk of relapse and bcr-abl mRNA transcript detection among 336 Caucasian patients who underwent allogeneic hematopoietic cell transplantation for chronic myelogenous leukemia.

EXPERIMENTAL DESIGN

Data on the transplant course and folate-related exposures were abstracted from medical records. MTHFR C677T and A1298C genotypes were determined using polymerase chain reaction/restriction fragment length polymorphism and TaqMan assays. Qualitative bcr-abl mRNA testing was conducted using a two-step reverse transcription-polymerase chain reaction assay. Cox regression analysis was used to assess the association between MTHFR genotypes and time to relapse and bcr-abl mRNA detection.

RESULTS

A statistically significant decreased risk of relapse was observed in patients with the variant A1298C genotype [1298AC, hazard ratio (HR)=0.48 and 95% confidence interval (CI)=0.26-0.88; 1298CC, HR=0.28 and 95% CI=0.09-0.84; P-trend <0.01). For the joint C677T/A1298C genotype, variant genotypes were associated with a decreased risk of relapse when compared with the wild-type 677CC/1298AA genotype. This risk was lowest for the 677CC/1298CC genotype (HR, 0.23; 95% CI, 0.08-0.72). MTHFR genotypes were not associated with bcr-abl transcript detection.

CONCLUSIONS

These findings suggest that individuals with the 677CC/1298AA genotype are at higher risk of relapse after hematopoietic cell transplantation and that the balance of intracellular folate metabolites available for nucleotide synthesis (regulated by the relative activity of the MTHFR enzyme) may affect the progression from bcr-abl positivity to clinical relapse.

Assessment of tailor-made prevention of atherosclerosis with folic acid supplementation: randomized, double-blind, placebo-controlled trials in each MTHFR C677T genotype

This study aimed at assessing the effect of folic acid supplementation quantitatively in each MTHFR C677T genotype and considered the efficiency of tailor-made prevention of atherosclerosis. Study design was genotype-stratified, randomized, double-blind, placebo-controlled trials. The setting was a Japanese company in the chemical industry. Subjects were 203 healthy men after exclusion of those who took folic acid or drugs known to effect folic acid metabolism. Intervention was folic acid 1 mg/day p.o. for 3 months. The primary endpoint was plasma total homocysteine level (tHcy). In all three genotypes, there were significant tHcy decreases. The greatest decrease was in the TT homozygote [6.61 (3.47-9.76) micromol/l] compared with other genotypes [CC: 2.59 (1.81-3.36), CT: 2.64 (2.16-3.13)], and there was a significant trend between the mutated allele number and the decrease. The tHcy were significantly lowered in all the genotypes, but the amount of the decrease differed significantly in each genotype, which was observed at both 1 and 3 months. Using these time-series data, the largest benefit obtained by the TT homozygote was appraised as 2.4 times compared with the CC homozygote. Taking into account the high allele frequency of this SNP, this quantitative assessment should be useful when considering tailor-made prevention of atherosclerosis with folic acid.

What can mendelian randomisation tell us about modifiable behavioural and environmental exposures?

Using genetic variants as a proxy for modifiable environmental factors that are associated with disease can circumvent some of the problems of observational studies

Hyperhomocysteinemia, methylenetetrahydrofolate reductase 677TT genotype, and the risk for schizophrenia: a Dutch population based case-control study

Evidence for an involvement of aberrant homocysteine metabolism in the aetiology of schizophrenia is limited and controversial. A case-control study was performed to quantify the risk of schizophrenia in the presence of elevated homocysteine concentrations or homozygosity for the 677C --> T polymorphism (677TT) in the methylenetetrahydrofolate reductase (MTHFR) gene in subjects of Dutch ancestry. We determined the 677C --> T MTHFR genotype distribution in 254 well-defined patients and 414 healthy controls. Plasma homocysteine concentrations were measured in 62 patients with schizophrenia and 432 control subjects. When homocysteine concentrations were stratified into quartiles of the control distribution, we calculated an increased risk for schizophrenia in the fourth and third quartile versus the lowest quartile [odds ratio (OR) = 3.3; 95% confidence interval (CI): 1.2-9.2, and OR = 3.1; 95% CI: 1.2-8.0, respectively]. A significant dose-response relation of increasing homocysteine levels and increasing risk for schizophrenia was observed (P = 0.036). The 677TT genotype was associated with an OR of 1.6 [95% CI: 0.96-2.8] of having schizophrenia. Heterozygosity for the T allele compared to 677CC subjects accounted for an OR of 1.3 [95% CI: 0.91-1.8]. Elevated homocysteine levels and the MTHFR 677TT genotype are associated with an increased risk for schizophrenia. These observations support a causal relation between disturbed homocysteine metabolism and schizophrenia.

Distribution of 5,10-methylenetetrahydrofolate reductase (C667T) polymorphism and its association with red blood cell 5-methyltetrahydrofolate in the healthy Iranians

BACKGROUND AND AIMS

Homozygosity for the thermolabile variant of 5,10-methylenetetrahydrofolate reductase (C677T) that causes hyperhomocysteinemia has been reported in 5-15% of general populations. This mutation has also been suggested to be positively associated with the risk of vascular disease and neural tube defects. It has also been suggested that present dietary reference values may need to be altered for people heterozygote or homozygote for this mutation as tissue folate status has been reported to be compromised by these genetic variants. The aims of this study were to investigate the distribution of 5,10-methylenetetrahydrofolate reductase (C677T) polymorphism in a population of Shiraz, south west of Iran and to test the hypothesis that folate status is compromised by this mutation in our population.

METHODS

In this study age, body mass index, plasma and red blood cell 5-methytetrahydrofolate, plasma total homocysteine and vitamin B12 of 391 healthy Iranians (198 men and 193 women) together with methylenetetrahydrofolate reductase C667T genotypes were determined. The correlates of methylenetetrahydrofolate reductase polymorphism were determined using univariate and multivariate statistical analysis.

RESULTS

The frequencies of CC, CT and TT genotypes were 56.2%, 38.7% and 5.1%, respectively. The C and T allele frequencies were determined to be 0.76 and 0.24, respectively and this polymorphism was compatible with Hardy-Weinberg equilibrium (X2=1.54, df=2, P=0.46). Among all the variables examined, red blood cell 5-methyltetrahydrofolate (P=0.007, ANOVA) and plasma 5-methyltetrahydrofolate (P=0.012, ANOVA) were significantly lower in individuals with TT genotype than those with either CC or CT genotype. Plasma total homocysteine was significantly higher in individuals with TT than those with either CC or CT genotype at below the median levels of red blood cell 5-methylterahydrofolate (P=0.03, ANOVA) and plasma 5-methylterahydrofolate (P=0.04, ANOVA). Univariate (r=-0.16, P=0.002) and multivariate analysis (beta=-0.0005, P=0.003) showed that red blood cell 5-methylterahydrofolate was the strongest correlates of methylenetetrahydrofolate reductase genotypes.

CONCLUSIONS

Results from this study suggest that methyltetrahydrofoate reductase C667T genotypes are strongly and independently associated with low red blood cell 5-methylterahydrofolate that has been reported to be a more reliable and long-term marker for body's folate status among Iranians. These results may suggest that substantial minority of people in general populations may have increased folate needs and this may place doubts on the validity of assuming "normality" for nutrient requirements in any general population.

Human neural tube defects: developmental biology, epidemiology, and genetics

Birth defects (congenital anomalies) are the leading cause of death in babies under 1 year of age. Neural tube defects (NTD), with a birth incidence of approximately 1/1000 in American Caucasians, are the second most common type of birth defect after congenital heart defects. The most common presentations of NTD are spina bifida and anencephaly. The etiologies of NTDs are complex, with both genetic and environmental factors implicated. In this manuscript, we review the evidence for genetic etiology and for environmental influences, and we present current views on the developmental processes involved in human neural tube closure.

Polymorphisms of genes involved in homocysteine metabolism in preeclampsia and in uncomplicated pregnancies

OBJECTIVE

To evaluate the possible relationship between preeclampsia and polymorphisms in the main genes involved in folate-homocysteine metabolism.

STUDY DESIGN

Case-control study: 43 patients with preeclampsia and 122 controls without pregnancy complications. Laboratory studies: tHcy and other amino acids, folate and vitamin B(12) and polymorphisms: 677C > T and 1298A > C (MTHFR); 699C > T, 844ins68 and 1080C > T (CBS); 2756A > G (MTR); and 66G > A, IVS1+766G > A and IVS1+754A > C (MTRR).

RESULTS

Plasma tHcy and folate values were significantly higher (P = 0.004 and P = 0.019), while Met/tHcy ratios were lower (P < 0.001) in the patients compared with controls. No association was observed between polymorphisms tested and preeclampsia. In the control group, four such associations were found: the 1298A > C polymorphism (MTHFR) with the ratio Met/tHcy (P = 0.014); the 699C > T polymorphism (CBS) with the ratio tHcy/SigmaAA (P = 0.013); the 2756A > G polymorphism (MTR) with tHcy (P = 0.034); and the IVS1+766G > A polymorphism (MTRR) with hyperhomocysteinemia (P = 0.012).

CONCLUSION

An association between the polymorphisms analysed and preeclampsia could not be demonstrated.

A family-based association study of congenital left-sided heart malformations and 5,10 methylenetetrahydrofolate reductase

BACKGROUND

Aortic valve stenosis (AVS), coarctation of the aorta (CoA), and hypoplastic left heart syndrome (HLHS) are obstructive malformations of the left ventricular outflow tract that account for a significant proportion of infant mortality. Two previous small case-control studies suggested methylenetetrahydrofolate reductase (MTHFR) polymorphisms may be associated with this group of malformations.

METHODS

We used a family-based association design with inclusion criteria of nonsyndromic diagnosis of AVS, CoA, and HLHS, powered to detect an odds ratio for the heterozygote of <1.5. A total of 207 affected offspring-parent trios were genotyped by restriction fragment length polymorphisms at the two common polymorphic loci C677T and A1298C.

RESULTS

Error rate estimation based on replicate samples was 0.76%. Mendelian inconsistency at either polymorphism was noted in 10 trios, for a calculated undetected error rate of 1.95%. A total of 197 trios were analyzed using the transmission disequilibrium test. Significant association was not found between both the C677T or A1298C polymorphisms and presence of a heart defect, whether analyzed as a group, or by sex, ethnicity, or specific diagnosis. A log-linear analysis did not find increased relative risk based on the maternal genotype.

CONCLUSIONS

We were unable to replicate previous association studies and concluded that neither the affected nor the maternal MTHFR genotype, by itself, is a major risk factor for congenital left ventricular outflow tract malformations.

Association of the C677T and A1298C polymorphisms of methylenetetrahydrofolate reductase gene in patients with essential tremor in Turkey

Essential tremor (ET) is a most common human movement disorder of unknown etiology. Previous reports have shown that the C677T polymorphism of methylenetetrahydrofolate reductase gene has been associated with neurodegenerative disorders. To investigate the role of methylenetetrahydrofolate reductase gene polymorphisms in essential tremor, we analyzed the alleles and genotypes of methylenetetrahydrofolate reductase (MTHFR) C677T and MTHFR A1298C in a total of 158 unrelated essential tremor patients and compared them with those of 246 unrelated healthy control subjects, using a polymerase chain reaction restriction fragment length polymorphism method. The allele frequency of MTHFR 677T was 35.76% in the essential tremor cases and 30.08% in the controls. We obtained statistically significant results for MTHFR677 and also for MTHFR1298. The MTHFR T677T genotype was overrepresented and was statistically significant. The T677T/A1298A and C677C/C1298C compound genotypes were similarly statistically significant. The C677C/A1298A compound genotype provided protection for essential tremor. In conclusion, the MTHFR 677T, 1298C alleles and MTHFR T677T genotype and T677T/A1298A, and C677C/C1298C compound genotypes are genetic risk factors for essential tremor in Turkey.

Methylenetetrahydrofolate Reductase Polymorphisms and Therapy Response in Pediatric Acute Lymphoblastic Leukemia

A significant portion of patients treated for pediatric acute lymphoblastic leukemia (ALL) relapse. We hypothesized that common polymorphisms with moderate effect sizes and large attributive risks could explain an important fraction of ALL relapses. Methylenetetrahydrofolate reductase (MTHFR) is central to folate metabolism and has two common functional polymorphisms (C677T and A1298G). Methotrexate (MTX), which interrupts folate metabolism, is a mainstay of pediatric ALL therapy. MTX inhibits the synthesis of dTMP needed for DNA replication by blocking the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate by MTHFR. We hypothesized that a deactivating MTHFR allele would increase ALL relapse risk by potentially increasing 5,10-methylenetetrahydrofolate and dTMP, enhancing DNA synthesis and thus opposing MTX. To test this hypothesis, we genotyped 520 patients on the Children's Cancer Study Group ALL study, CCG-1891. The MTHFR C677T variant allele was statistically significantly associated with relapse (chi2 = 4.38, P = 0.036). This association remained significant (hazard ratio = 1.82, P = 0.008), controlling for important covariates, and was more predictive of relapse than other predictors, including day 7 bone marrow response. The MTHFR C677T variant allele was not associated with an increased risk of toxicity or infection. The MTHFR A1298G polymorphism was not associated with altered risks of relapse, toxicity, or infection. Haplotype analysis showed six common haplotypes that did not provide additional information predictive for relapse. These data provide evidence that the MTHFR C677T polymorphism is a common genetic variant conferring a moderate relative risk and a high attributable risk for relapse in pediatric ALL patients.

Folic acid - vitamin and panacea or genetic time bomb?

We live in a health-conscious age - many of us supplement our diet with essential micronutrients through the discretionary use of multivitamin pills or judicious selection of foods that have a health benefit beyond that conferred by the nutrient content alone - the so-called 'functional foods'. Indeed, the citizens of some nations have little choice, with a mandatory fortification policy in place for certain vitamins. But do we ever stop to consider the consequences of an increased exposure to micronutrients? We examine this issue in relation to the B-group vitamin folic acid, and ask whether supplementation with this vitamin could introduce a strong genetic selection pressure - one that has the side effect of increasing the prevalence of some of the most significant, human life-threatening diseases. Are we affecting our genetics - is this a case of human evolution in progress by altering our diet?

Gene-environment interactions: a review of effects on reproduction and development

Polymorphisms in genes can lead to differences in the level of susceptibility of individuals to potentially adverse effects of environmental influences, such as chemical exposure, on prenatal development or male or female reproductive function. We have reviewed the literature in this area, with the caveat that papers involving straight gene knock-outs in experimental animals, without a clear human relevance, were largely excluded. This review represents current knowledge in this rapidly moving field, presenting both human epidemiological and animal data, where available. Among the polymorphic genes and environmental interactions discussed with respect to prenatal development are those for P-glycoprotein (multidrug resistance protein) and the avermectins; methylenetetrahydrofolate reductase (MTHFR), an enzyme in folate metabolism, and dietary folic acid; transforming growth factor alpha (TGFalpha) and cigarette smoke; and alcohol dehydrogenase (ADH) and cytochrome P-450 (CYP) 2E1 in association with alcohol consumption. Effects on male reproduction attributable to gene-environment interaction involve infertility seen as a result of either organophosphorous (OP) pesticide interaction with the polymorphic paraoxonase (PON1) gene or antiandrogenic agent interaction with the androgen receptor (AR). MTHFR, folate metabolism, and dietary folic acid are also considered in conjunction with preeclampsia and early pregnancy loss, and the effect of the interaction of glutathione S-transferase (GST) with exposure to benzene or cigarette smoke on pregnancy maintenance is explored. As a conclusion, we offer a discussion of lessons learned and suggested research needs.

Methylenetetrahydrofolate reductase 677C-->T polymorphism affects DNA methylation in response to controlled folate intake in young women

DNA methylation is critical for normal genomic structure and function and is dependent on adequate folate status. A polymorphism (677C-->T) in a key folate enzyme, methylenetetrahydrofolate reductase (MTHFR), may impair DNA methylation when folate intake is inadequate and may increase the risk of reproductive abnormalities. The present study was designed to evaluate the effect of the MTHFR 677C-->T polymorphism on changes in global DNA methylation in young women consuming a low folate diet followed by repletion with the current Recommended Dietary Allowance (RDA). Women (age 20-30 years) with the TT (variant; n = 19) or CC (n = 22) genotype for the MTHFR 677C-->T polymorphism participated in a folate depletion-repletion study (7 weeks, 115 microg DFE/day; 7 weeks, 400 microg DFE/day). DNA methylation was measured at baseline, week 7, and week 14 using a [3H]methyl acceptance assay and a novel liquid chromatography tandem mass spectrometry assay of the DNA bases methylcytosine and cytosine. [3H]Methyl group acceptance tended to increase (P = 0.08) during depletion in all subjects, indicative of a decrease in global DNA methylation. During repletion, the raw change and the percent change in the methylcytosine/total cytosine ratio increased (P = 0.03 and P = 0.04, respectively) only in the subjects with the TT genotype. Moderate folate depletion in young women may cause a decrease in overall DNA methylation. The response to folate repletion suggests that following folate depletion women with the MTHFR 677 TT genotype have a greater increase in DNA methylation with folate repletion than women with the CC genotype.

Folate-related genes and omphalocele

Women who take folic acid in the periconceptional period greatly reduce their chances of having a child with a neural tube defect (NTD). Using multivitamins may also reduce the risk of having a child with an omphalocele. In this study, we tested single nucleotide polymorphisms in folate-related enzyme genes for association with omphalocele. Polymorphisms in methylenetetrahydrofolate reductase (MTHFR), methylenetetrahydrofolate dehydrogenase (MTHFD1), the reduced folate carrier (SLC19A1), and transcobalamin II (TCN2) were examined in 25 children with euploid omphalocele and 59 matched controls. Omphalocele cases were significantly more likely to carry the T allele of MTHFR 677C-->T, a known risk factor for NTDs (odds ratio 3.50, 95% confidence interval 1.07-11.47, P=0.035). The MTHFD1 R653Q, SLC19A1 R27H, and TCN2 P259R polymorphisms showed no significant association with omphalocele. In this small study, the thermolabile variant of MTHFR, 677C-->T, was associated with an increased risk for omphalocele. This variant causes reduced enzyme activity, thus suggesting a mechanism by which multivitamins with folic acid might prevent omphalocele. Additional investigation is required.

Investigations into the etiology of neural tube defects

Neural tube defects (NTDs) are serious malformations affecting approximately 1 per 1000 births, yet the mechanisms by which they arise are unknown. There have been consistent efforts in many fields of research to elucidate the etiology of this multifactorial condition. While no single gene has been identified as a major independent risk factor for NTDs, candidate genes have been proposed that may modify the effects of maternal and/or embryonic exposures. Folate supplementation effectively reduces the occurrence of NTDs and, consequently, has focused much research on metabolism of folate-related pathways during pregnancy and development. Further understanding of normal development and how teratogens can perturb these orchestrated processes also remains at the fore of modern scientific endeavors. The composite of these factors remains fragmented; the aim of this review is to provide the reader with a summary of sentinel and current works in the body of literature addressing NTD disease etiology.

The Epidemiologic Approach to Pharmacogenomics

The epidemiologic approach enables the systematic evaluation of potential improvements in the safety and efficacy of drug treatment which might result from targeting treatment on the basis of genomic information. The main epidemiologic designs are the randomized control trial, the cohort study, and the case-control study, and derivatives of these proposed for investigating gene-environment interactions. However, no one design is ideal for every situation, and methodological issues, notably selection bias, information bias, confounding and chance, all play a part in determining which study design is best for a given situation. There is also a need to employ a range of different designs to establish a portfolio of evidence about specific gene-drug interactions. In view of the complexity of gene-drug interactions, pooling of data across studies is likely to be needed in order to have adequate statistical power to test hypotheses. We suggest that there may be opportunities (i) to exploit samples from trials already completed to investigate possible gene-drug interactions; (ii) to consider the use of the case-only design nested within randomized controlled trials as a possible means of reducing genotyping costs when dichotomous outcomes are being investigated; and (iii) to make use of population-based disease registries that can be linked with tissue samples, treatment information and death records, to investigate gene-treatment interactions in survival.

Methylenetetrahydrofolate reductase gene polymorphisms and their association with trisomy 21

OBJECTIVES

To verify whether the frequencies of 5,10-methylenotetrahydrofolate reductase (MTHFR) polymorphisms at positions 677 and 1298 are higher in women with children affected by trisomy 21 than in those with chromosomally normal offspring.

METHODS

A case-control study was carried out with 70 women whose children had trisomy 21 and 88 controls whose children were chromosomally normal. The frequencies of polymorphisms of points C677T and A1298C of MTHFR gene coding were studied in these two groups. Odds ratios (OR) for having a child affected by trisomy 21 were estimated for homozygosis, heterozygosis or the absence of the above-mentioned MTHFR polymorphisms. Logistic regression models were used to control for the effect of confounding variables on these odds ratios.

RESULTS

The frequency of joint heterozygotic polymorphism (677 and 1298) was significantly higher in women with children affected by trisomy 21 than in those with chromosomally normal offspring (OR: 5.7).

CONCLUSIONS

The presence of joint heterozygotic polymorphism in the codifying gene for MTHFR was a risk factor for having a child with trisomy 21.

Pharmacogenetics of methotrexate

Methotrexate (MTX) has proven efficient in the treatment of a number of malignancies, as well as non-malignant disorders characterized by a rapid cellular growth. Yet some patients might develop resistance, while others could have toxic side effects. MTX achieves its cytotoxicity through the inhibition of folate-dependent enzymes, suggesting that the genes controlling their activity or the levels of folate cofactors can modulate drug efficacy and, thus, the sensitivity of a patient to MTX. Indeed, several studies, conducted mostly in leukemia and rheumatoid arthritis patients, have addressed the potential for tailoring MTX therapy based on a patient's genetics. Several genetic variants have been shown to have a predictive role, among which the most frequently studied are those of methylenetetrahydrofolate reductase and thymidylate synthase genes. The other candidates, as well as gene-gene interactions, which may be even more important for the prediction of disease outcomes than the individual gene effects, are also briefly discussed.