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

MTHFR Polymorphisms and Risk of Chronic Lymphocytic Leukemia

Folate availability is critical for DNA integrity, required for the transfer of methyl groups in the biosynthesis of thymidilate. Reduction of 5,10-methylenetetrahydrofolate, a donor for methylating dUMP to dTMP in DNA synthesis, to 5-methyltetrahydrofolate, the primary methyl donor for methionine synthesis, is catalyzed by 5,10-methylenetetrahydrofolate reductase (MTHFR). The MTHFR polymorphisms C677T and A1298C have been shown in some studies to alter the risk of a range of different malignancies. We evaluated the role of the C677T and A1298C polymorphisms on chronic lymphocytic leukemia (CLL) risk by genotyping 832 patients and 886 healthy controls. The odds ratio of CLL associated with 677CT and 677TT genotypes were 1.02 [95% confidence interval (95% CI), 0.83-1.24] and 0.90 (95% CI, 0.66-1.24), respectively. The odds ratio of CLL associated with 1298AC and 1298CC genotypes were 0.97 (95% CI, 0.79-1.18) and 0.88 (95% CI, 0.62-1.24), respectively. This data indicate that the MTHFR polymorphisms C677T and A1298C do not significantly contribute to an inherited genetic susceptibility to CLL.

The MTHFR C677T polymorphism is associated with depressive episodes in patients from Northern Ireland

Low plasma folate and its derivatives have been linked with depressive disorders in studies dating back over 30 years. A thermolabile variant (677C>T) of the enzyme 5,10-methylenetetrahydrofolate reductase (MTHFR) is associated with low serum folate. The present study aimed to explore whether the thermolabile variant of MTHFR is associated with a vulnerability to depressive episodes. MTHFR C677T genotype frequencies in a cohort of patients (mean age 48 years) with depressive disorder (n = 100) were compared with those in age- and sex-matched controls. Serum levels of folate, homocysteine and vitamin B(12) were also compared between groups. The thermolabile variant of MTHFR was significantly more common in the group with a history of depressive disorder (P= 0.03). Serum levels of folate, homocysteine and vitamin B(12) did not differ significantly between groups. A MTHFR C677T genotype is associated with increased risk of depressive episodes in this homogenous patient population.

Spina bifida

Spina bifida results from failure of fusion of the caudal neural tube, and is one of the most common malformations of human structure. The causes of this disorder are heterogeneous and include chromosome abnormalities, single gene disorders, and teratogenic exposures. However, the cause is not known in most cases. Up to 70% of spina bifida cases can be prevented by maternal, periconceptional folic acid supplementation. The mechanism underlying this protective effect is unknown, but it is likely to include genes that regulate folate transport and metabolism. Individuals with spina bifida need both surgical and medical management. Although surgical closure of the malformation is generally done in the neonatal period, a randomised clinical trial to assess in utero closure of spina bifida has been initiated in the USA. Medical management is a lifelong necessity for individuals with spina bifida, and should be provided by a multidisciplinary team.

Medical genetics in developing countries

Since Watson & Crick's 1953 description of the structure of DNA, significant progress has been achieved in the control of congenital disorders, most of which has benefited industrialized countries. Little advantage accrued to developing nations, most of which in the same time frame achieved a significant epidemiological transition, resulting in congenital disorders attaining public health significance. The burden of congenital disorders in these lower-resource countries is high and they need to develop medical genetic services. We present a new pragmatic approach for the care and prevention of congenital disorders in these countries, pioneered initially by the World Health Organization.

Evidence that the risk of spina bifida is influenced by genetic variation at the NOS3 locus

BACKGROUND

There is substantial evidence that the risk of spina bifida, a malformation of the caudal neural tube, may be associated with maternal or embryonic disturbances in the folate-homocysteine metabolic axis. Hence, variants of genes that influence this pathway represent an intriguing group of candidate genes for spina bifida and other neural tube defects (NTD). A common variant of the gene for endothelial nitric oxide synthase (NOS3 G894T) was recently added to this group of NTD candidate genes, based on a report demonstrating that homozygosity for the T allele of this variant is associated with increased homocysteine levels in normal adult populations.

METHODS

The association between the risk of spina bifida and both the maternal and embryonic genotype for the NOS3 G894T variant was evaluated in data from 301 families by using the transmission disequilibrium test (TDT) and log-linear modeling.

RESULTS

Analyses of these data using the TDT provided no evidence that the risk of spina bifida was significantly related to either the maternal or embryonic NOS3 genotype. However, the log-linear analyses indicated that the risk of spina bifida was significantly associated with the embryonic, but not the maternal, genotype for the NOS3 G894T variant.

CONCLUSIONS

The results of the present analyses suggest that the embryonic NOS3 G894T genotype is associated with the risk of spina bifida. Moreover, these analyses highlight the importance of a detailed examination of the study data. Had these analyses been restricted to the methodologically simpler TDT, the association between the NOS3 G894T genotype and risk of spina bifida may well have been overlooked.

Diet, genes and disease: implications for nutrition policy

There is extensive evidence to show that there is considerable variation in diet and disease patterns in Europe and that many of the dietary patterns are predictive of chronic disease. Increasingly, there is evidence that this dietary effect is mediated by genetic background. The present paper examines the role of polymorphisms within three genes, those responsible for the synthesis of apoE, 5,10-methylenetetrahydrofolate reductase (MTHFR) and PPARgamma. There is clear evidence to support the concept that the diet-disease link is moderated by genetic variation. The paper then considers whether this moderating effect will have implications for dietary recommendations. In the formulation of dietary reference values it has long been recognized that these values cannot cover the needs of all individuals. By setting the upper level at the mean value +2 sd, the needs of 97.5% of the population are covered. Setting a hypothetical scenario of a nutrient requirement of 200 mg/d and a polymorphism with an allelic frequency in the general population in the range of 0, 10, 20 and 30% that causes an increased nutrient requirement of 25%, there was no evidence that the traditional approach requires revision. Whilst it is recognized that genetic variability may not influence population goals, genetic variability will have to be taken into account in the clinical nutrition management of disease. To knowingly assign a patient to life-long treatment with a diet that for genetic reasons will have no success is both unethical and uneconomical. Once accepted in clinical nutrition, the diet-gene interaction will filter into the prevention of disease in public health nutrition.

Polymorphisms and haplotypes in folate-metabolizing genes and risk of non-Hodgkin lymphoma

Folate metabolism plays an essential role in DNA synthesis and methylation processes. Deviations in the flux of folate due to genetic variation could result in selective growth and genomic instability and affect susceptibility to various cancers including lymphoma. To test this hypothesis, genetic polymorphisms in the folate metabolic pathway were investigated using DNA from a population-based case-control study of non-Hodgkin lymphoma (NHL) conducted in the San Francisco Bay Area between 1988 and 1995. The polymorphisms examined and haplotypes generated included thymidylate synthase (TYMS 28-bp triple repeat [3R] → double repeat [2R], 1494del6, IVS6 -68C>T, 1122A>G, and 1053C>T); 5,10-methylenetetrahydrofolate reductase (MTHFR 677C>T and 1298A>C); serine hydroxymethyltransferase (SHMT1 C1420T); reduced folate carrier (RFC G80A); and methionine synthase (MTR A2756G), making the present study the largest and most comprehensive to date to evaluate associations between genetic polymorphisms in folatemetabolizing genes and NHL risk. The TYMS 6 base pair (bp)-6bp- (homozygous for 6bp deletion), IVS6 -68C>T, and 1053C>T genotypes (all in complete linkage disequilibrium) were all inversely associated with NHL (TYMS; odds ratio [OR] = 0.57; 0.34-0.94), particularly with diffuse large cell lymphoma (DLCL; OR = 0.29; 0.10-0.82). Further, the MTR 2756AG/GG and the MTHFR 677TT genotypes were associated with increased risk for NHL (OR = 1.3; 0.99-1.7) and follicular lymphoma (FL; OR = 1.8; 0.98-3.1), respectively. We did not observe any significant differences in genotype frequencies of the SHMT1 and RFC polymorphisms between the cases and controls. The associations of DLCL and FL with TYMS 1494del6 and MTHFR 677TT genotypes, respectively, suggest that folate metabolism may play an important role in the pathogenesis of specific subtypes of NHL. (Blood. 2004;104: 2155-2162)

Epidemiologic approaches to identifying environmental causes of birth defects

Epidemiology can be used to elucidate environmental causes of birth defects. This paper discusses 1) different types of environmental causes; 2) the difficulties in comparing the prevalence of birth defects between populations, including the need for a population base and the implications of prenatal diagnosis; 3) the main study designs for observational epidemiological studies and the various sources of bias; 4) how statistical power can be increased by meta-analysis or multicentric studies, and improved grouping of birth defects into etiologically more homogeneous subgroups; 5) the distinction between association and causation; 6) the interpretation of clusters in time and space in relation to local environmental causes; and 7) the potential of genetic epidemiology to help elucidate environmental causes. While further research continues into the environmental causes of birth defects, the epidemiologic evidence base for policy making and clinical practice is poor in many areas. The epidemiologic approach is important not only to elucidate environmental causes but also to assess the implementation of existing research into policy and practice for the prevention of birth defects.

Drinking water contaminants, gene polymorphisms, and fetal growth

There are still many uncertainties regarding the risk of adverse pregnancy outcomes associated with exposure to drinking water disinfection by-products. In Montréal, Québec, Canada, we carried out a hospital-based case-control study including 493 cases of intrauterine growth restriction defined as birth weight below the 10th percentile for gestational age and sex, according to Canadian standards. Controls were babies (n = 472) delivered at the same hospital whose birth weight was at or above the 10th percentile, matched for gestational age, race, and sex. Exposure to total and specific trihalomethanes was measured using regulatory data collected by municipalities and the provincial Ministry of Environment. Residential history, water drinking, and shower habits during pregnancy, as well as known risk factors for intrauterine growth restriction, were measured with a face-to-face interview with all mothers. Mothers and newborns were characterized for two genetic polymorphisms, one in the CYP2E1 gene (G1259C), and another in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene (C677T). Exposure to specific and total trihalomethanes from drinking water, determined for 458 cases and 426 controls, did not result in an increased risk of intrauterine growth restriction. However, significant effect modification was observed between newborns with and without the CYP2E1 variant; among newborns with the variant, the adjusted odds ratio for intrauterine growth restriction associated with exposure to average total trihalomethanes above the 90th percentile (corresponding to 29.4 microg/L) was 13.20 (95% confidence interval, 1.19-146.72). These findings suggest that exposure to trihalomethanes at the highest levels can affect fetal growth but only in genetically susceptible newborns.

Parental employment status and neural-tube defects and folic acid/multivitamin supplementation in Hungary

OBJECTIVE

To study the role of parental employment status as indicator of socio-economic status (SES) in the origin of neural-tube defect (NTD) and in the use of periconceptional folic acid/multivitamin supplementation.

MATERIALS AND METHODS

One thousand two hundred and two cases with neural-tube defects, 38,151 population controls without any defects and 22,475 patient controls with other defects were compared in the population-based data set of the Hungarian case-control surveillance of congenital abnormalities, 1980-1996.

RESULTS

The proportion of professionals was lower, while the proportion of semi- and unskilled workers was higher in the neural-tube defect group compared with the population control group. However, the comparison of neural-tube defect and patient control groups showed a lower socio-economic status in the patient control group. In addition, the socio-economic status of fathers in the neural-tube defect group seemed to be better than in the population and patient control groups. The higher periconceptional folic acid supplementation and the higher use of multivitamins during pregnancy occurred in the professional and managerial categories in all the three study groups.

CONCLUSION

The occurrence of neural-tube defect shows a slight socio-economic dependence in the mothers at the comparison with population control group, however, patient control group had the lowest socio-economic status. The higher maternal education goes together with a higher proportion of periconceptional folic acid supplementation.

Genetic variants in ZIC1, ZIC2, and ZIC3 are not major risk factors for neural tube defects in humans

Neural tube defects (NTD) are congenital malformations arising from incomplete neural tube closure during early embryogenesis. Most NTD in humans show complex inheritance patterns, with both genetic and environmental factors involved in the etiology of this malformation. More than 120 mouse models for human NTD exist. NTD have been observed in mice deficient for the Zic family genes, Zic1, Zic2, and Zic3. We performed mutation analysis in the human orthologs of these genes using DNA material from a large panel of NTD patients. In ZIC2 we identified a deletion of one codon that encodes an alanine residue located in the amino terminal alanine stretch of the protein. The deletion was present in one patient, but not in 364 controls. That may suggest a role-albeit small-of this variant in the etiology of NTD in humans. Transmission disequilibrium testing of a frequent polymorphism in the ZIC2 gene (1059C > T, H353H) in parent-spina bifida aperta child triads showed no association with NTD. One silent polymorphism (858G > A, V286V) of unknown significance was identified in ZIC3. Neither mutations nor polymorphisms were found in the coding region or flanking sequences of ZIC1. Our data indicate that ZIC1, ZIC2, and ZIC3 are not major risk factors for NTD in humans.

Gene–nutrient interactions: importance of folates and retinoids during early embryogenesis

The role that nutritional factors play in mammalian development has received renewed attention over the past two decades, as the scientific literature exploded with reports of retinoid compounds disrupting craniofacial development, and with other reports that folic acid supplementation in the periconceptional period can protect embryos from highly significant malformations. As was often the case, the situation became far more complicated, as the interaction between nutritional factors with selected genes was recognized. In this review, we attempt to summarize a complex clinical and experimental literature of nutritional factors, their biological transport mechanisms, and the impact that they have during early embryogenesis. Although not exhaustive, our goal was to provide an overview of important gene-nutrient interactions and a framework for their investigation.

Associations between maternal methylenetetrahydrofolate reductase polymorphisms and adverse outcomes of pregnancy: the Hordaland Homocysteine Study

PURPOSE

Methylenetetrahydrofolate reductase (MTHFR) is involved in the metabolism of folate and homocysteine; a polymorphism in the MTHFR gene (677C-->T) has been associated with adverse outcomes of pregnancy. We studied whether two polymorphisms in the MTHFR gene (677C-->T and 1298A-->C) are associated with pregnancy complications, adverse outcomes, and birth defects.

METHODS

MTHFR polymorphisms were determined in blood collected in 1992 and 1993 from 5883 women aged 40 to 42 years, and linked with 14,492 pregnancies in the same women recorded in the Medical Birth Registry of Norway from 1967 to 1996.

RESULTS

The 677TT genotype in mothers was associated with increased risk of placental abruption (odds ratio [OR] = 2.6; 95% confidence interval [CI]: 1.4 to 4.8) compared with the CC variant. The risk of intrauterine growth restriction increased with number of T alleles (P for trend = 0.04). Compared with the 1298AA variant, the CC variant was associated with a reduced risk of very low birth weight infants (OR = 0.4; 95% CI: 0.2 to 0.8). No significant associations were found between MTHFR polymorphisms and birth defects.

CONCLUSION

The maternal MTHFR 677C-->T polymorphism was a risk factor for placental abruption. The unexpected protective effect of the 1298A-->C polymorphism on very low birth weight needs further study.

Thymidylate synthase repeat polymorphisms and risk of neural tube defects in a population from the northern United Kingdom

BACKGROUND

A 28-bp repeat polymorphism in the 5'UTR of the thymidylate synthase (TYMS) gene represents a candidate risk factor for neural tube defects (NTDs) due to involvement in folate-dependent homocysteine metabolism. Non-Hispanic, white, U.S. citizens carrying at least one 2x 28-bp repeat allele have recently been shown to be at a four-fold increased risk of spina bifida (SB). We investigated the association between this polymorphism and risk of NTD in families affected by NTDs and controls from the northern United Kingdom (UK).

METHODS

PCR was performed on genomic DNA extracted from blood or mouth swabs of family members affected by NTDs (mothers, fathers, and cases), and unaffected controls (mothers and infants) to determine the number of 28-bp repeat units within the promoter region of TYMS. Case-control and TDT analyses of the influence of TYMS genotype on risk of NTD, or NTD pregnancy, were conducted.

RESULTS

Odds ratio (OR) analysis indicated that individuals carrying the 2x 28-bp repeat allele either in homozygous or heterozygous form, are not at increased risk of NTDs, or of having an NTD affected pregnancy. Control population allele frequencies are seen to be markedly different between the U.S. controls and those in this study.

CONCLUSIONS

TYMS polymorphism appears to be not universally associated with NTD risk across Caucasian samples. The elevated risk of spina bifida in U.S. samples appears to be driven by an unusually low risk allele (2x 28 bp) frequency in control samples. Family based (TDT) testing of U.S. samples is therefore advocated.

Metabolic effects and the methylenetetrahydrofolate reductase (MTHFR) polymorphism associated with neural tube defects in southern Brazil

BACKGROUND

The importance of metabolic factors in neural tube defects (NTDs) has been the focus of many investigations. Several authors have suggested that abnormalities in homocysteine metabolism, such as hyperhomocysteinemia, folate deficiency, and low vitamin B12, may be responsible for these malformations and that both nutritional factors and genetic abnormalities are associated with them.

METHODS

We conducted a case-control study to investigate the influence of biochemical and genetic factors in NTDs in infants in southern Brazil. Levels of folate, vitamin B12, total homocysteine (t-Hcy) and the 677C>T and 1298A>C polymorphisms of the MTHFR gene were analyzed in 41 NTD child-mother pairs and 44 normal child-mother control pairs.

RESULTS

Subjects in the case group had a higher mean blood folate level than those in the control group. The level of vitamin B12 was lower in mothers in the NTD group than in control mothers (p = 0.004). The level of t-Hcy was not different in the two groups, but t-Hcy and vitamin B12 were correlated (p = 0.002). There was no difference in the genotype distribution for 677C>T and 1298A>C polymorphisms of MTHFR in the case and control pairs. The level of t-Hcy was correlated with 677TT.

CONCLUSIONS

Despite the small sample in this study, we suggest that low vitamin B12 and, consequently, hyperhomocysteinemia are important risk factors for NTDs in our population.

Characterization of a pseudogene for murine methylenetetrahydrofolate reductase

Methylenetetrahydrofolate reductase (MTHFR) reduces 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, the major carbon donor in the remethylation of homocysteine to methionine. Mild MTHFR deficiency, due to a common variant at nucleotide 677, has been reported to influence risk for several disorders including cardiovascular disease, neural tube defects, pregnancy complications and cancer. In recent work, we characterized the complete cDNA and gene sequences in the human and mouse genes, which had previously been mapped to chromosomes 1 and 4, respectively. During the course of this work, we observed that PCR primers in exons 1 and 2 of Mthfr generated amplicons of the expected size for the normal Mthfr transcript, using both reverse-transcribed RNA and genomic DNA as templates. These findings alluded to the existence of a pseudogene in the murine genome. Here, we report the characterization of this pseudogene. The absence of intron 1, the partial retention of intron 2, the location of this gene on chromosome 5, and the presence of sequences unrelated to Mthfr at the 5' and 3' ends of the 1259 bp fragment are features that are indicative of a partially-processed pseudogene, that we have designated Mthfr-ps. A Mthfr-ps transcript was not detectable by sensitive RT-PCR using assays designed to simultaneously detect the authentic Mthfr transcript. The structure of this paralogous gene and the identification of a repeat sequence at the 3' end of this pseudogene suggest that it arose by retrotransposition of a mis-spliced Mthfr transcript. Investigations of the Mthfr gene should take into account the presence of the non-functional Mthfr-ps to avoid misinterpretation of results.

A commonABCC2 promoter polymorphism is not a determinant of the risk of spina bifida

BACKGROUND

There is compelling evidence that the risk of spina bifida, a malformation of the caudal neural tube, is associated with maternal and/or embryonic disturbances in folate/homocysteine metabolism. Hence, functional variants of genes that influence folate/homocysteine metabolism constitute a biologically plausible group of candidate risk factors for spina bifida and other neural tube defects. One such candidate is ABCC2, the gene encoding ABCC2, (a.k.a. canalicular multispecific organic anion transporter [cMOAT], multidrug resistance related protein 2 [MRP2]), a member of the ABC transporter family that effluxes natural folates and anti-folate drugs such as methotrexate.

METHODS

The association between the risk of spina bifida and both the maternal and embryonic ABCC2 C(-24)T genotype was evaluated by using the transmission disequilibrium test and log-linear modeling.

RESULTS

These analyses provided no evidence that the risk of spina bifida was significantly related to either the maternal or embryonic ABCC2 C(-24)T genotype.

CONCLUSIONS

The results of the present analyses suggest that the C(-24)T variant of the ABCC2 gene is not a major determinant of spina bifida risk.

Gene-gene interaction in folate-related genes and risk of neural tube defects in a UK population

OBJECTIVE

To investigate the contribution of polymorphic variation in genes involved in the folate-dependent homocysteine pathway in the aetiology of neural tube defects (NTD).

DESIGN

Case-control association study.

SUBJECTS

A total of 530 individuals from families affected by NTD, 645 maternal controls, and 602 healthy newborn controls from the northern UK.

MAIN OUTCOME MEASURES

Seven polymorphisms in six genes coding for proteins in the folate-dependent homocysteine pathway (MTHFR 677C-->T, MTHFR 1298A-->C, MTRR 66A-->G, SHMT 1420C-->T, CbetaS 844ins68, GCPII 1561C-->T, RFC-1 80G-->A). The impact of each polymorphism and the effect of gene-gene interactions (epistasis) upon risk of NTD were assessed using logistic regression analysis.

RESULTS

The MTHFR 677C-->T polymorphism was shown to represent a risk factor in NTD cases (CC v CT+TT odds ratio (OR) 2.03 [95% confidence interval (CI) 1.09, 3.79] p = 0.025) and the MTRR 66A-->G polymorphism was shown to exert a protective effect in NTD cases (AA v AG+GG OR 0.31 [95% CI 0.10, 0.94] p = 0.04). When statistical tests for interaction were conducted, three genotype combinations in cases (MTRR/GCPII; MTHFR 677/CbetaS; MTHFR 677/MTRR) and one combination in case mothers (CbetaS/RFC-1) were shown to elevate NTD risk. Maternal-fetal interaction was also detected when offspring carried the MTHFR 677C-->T variant and mothers carried the MTRR 66A-->G variant, resulting in a significantly elevated risk of NTD.

CONCLUSION

Both independent genetic effects and gene-gene interaction were observed in relation to NTD risk. Multi-locus rather than single locus analysis might be preferable to gain an accurate assessment of genetic susceptibility to NTD.

NTP-CERHR Expert Panel report on the reproductive and developmental toxicity of methanol

The National Toxicology Program (NTP) and the National Institute of Environmental Health Sciences (NIEHS) established the NTP Center for the Evaluation of Risks to Human Reproduction (CERHR) in June 1998. The purpose of the Center is to provide timely, unbiased, scientifically sound evaluations of human and experimental evidence for adverse effects on reproduction, including development, caused by agents to which humans may be exposed. Methanol was selected for evaluation by the CERHR based on high production volume, extent of human exposure, and published evidence of reproductive or developmental toxicity. Methanol is used in chemical syntheses and as an industrial solvent. It is a natural component of the human diet and is found in consumer products such as paints, antifreeze, cleaning solutions, and adhesives. It is used in race car fuels and there is potential for expanded use as an automobile fuel. This evaluation is the result of a 10-month effort by a 12-member panel of government and non-government scientists that culminated in a public Expert Panel meeting. This report has been reviewed by CERHR staff scientists, and by members of the Methanol Expert Panel. Copies have been provided to the CERHR Core Committee, which is made up of representatives of NTP-participating agencies. This report is a product of the Expert Panel and is intended to (1). interpret the strength of scientific evidence that a given exposure or exposure circumstance may pose a hazard to reproduction and the health and welfare of children; (2). provide objective and scientifically thorough assessments of the scientific evidence that adverse reproductive/development health effects are associated with exposure to specific chemicals or classes of chemicals, including descriptions of any uncertainties that would diminish confidence in assessment of risks; and (3). identify knowledge gaps to help establish research and testing priorities. The expert panel report becomes a central part of the subsequent NTP-CERHR Monograph. Each monograph includes the NTP Brief on the chemical under evaluation, the expert panel report, and all public comments on the expert panel report. The NTP Brief contains the NTP's conclusions on the potential for exposure to result in adverse effects on human development and reproduction. It is based on the expert panel report, public comments on the report, and relevant data published after the expert panel report was completed. NTP-CERHR Monographs are publicly available and are transmitted to appropriate health and regulatory agencies.

A mutation in the 5,10-methylenetetrahydrofolate reductase gene is not associated with preeclampsia in women of southeast mexico

BACKGROUND

We investigated the possible association between C677T-5,10-methylenetetrahydrofolate (MTHFR) polymorphism and preeclampsia in women from the Yucatan Peninsula in Mexico.

METHODS

We performed a comparative study among three groups of subjects: 148 preeclamptic women; 177 women with normal pregnancies, and 313 healthy volunteers as control group. All subjects were genotyped for C677T polymorphism in MTHFR gene by PCR amplification and digestion of the product with Hinf I restriction enzyme. Genotypic and allelic frequencies were compared between affected women (preeclamptic) and nonaffected groups to determine the association using Fisher exact test. Odds ratios (ORs) were also calculated to obtain estimation of relative risk (RR) for developing preeclampsia.

RESULTS

Statistical analysis of intergroup comparisons among preeclamptic women, women with normal pregnancies, and control group showed no statistically significant differences for any genotype or for T allele (p >0.05).

CONCLUSIONS

Our results suggest that C677T-MTHFR polymorphism is not an associated risk factor for developing preeclampsia in southeast Mexico. Results also confirmed high prevalence of C677T mutation in Mexico.

Variable drug metabolism genes in Arab population

Cataloging interethnic differences in the distribution of genotypes of drug metabolic genes provides valuable information for profiling the pharmacogenetics of a population. We used PCR analysis to catalog the frequencies of alleles and genotypes for CYP1A1, NAT2, GSTs, MTHFR, MTR (MS) and NQO*1 in Arabs. The frequencies of alleles and/or genotypes for CYP1A1*2A, GSTT1 null, GSTT1 and GSTM1 double null, and GSTP1 A1578G in Arabs were significantly higher than those reported in Caucasians. However, the distribution of NAT2 acetylator phenotypes in both populations was similar. In contrast, the frequencies of MTHFR 677T allele and the combined (677+1298) genotypes for low activity were lower than those reported in Caucasians. Other alleles in Arabs, including CYP1A1 T3801C and GSTP1 A1578G were present in frequencies similar to Africans. The overall profile of variations in metabolism genes in Arabs is thus unique.

Increased transcription and activity of glutathione synthase in response to deficiencies in folate, vitamin E, and apolipoprotein E

Oxidative stress is a major contributing factor in neurodegeneration and can arise from dietary, environmental, and genetic sources. Here we examine the separate and combined impact of deprivation of folate and vitamin E, coupled with dietary iron as a prooxidant, on normal mice and transgenic mice lacking apolipoprotein E (ApoE-/- mice). Both mouse strains exhibited increased levels of glutathione when deprived of folate and vitamin E, but a substantial further increase was observed in ApoE-/- mice. To determine the mechanism(s) underlying this increase, we quantified transcription and activity of glutathione synthase (GS). Both normal and ApoE-/- mice demonstrated increased GS activity when deprived of folate and vitamin E. However, transcription was increased only in ApoE-/- mice deprived of folate and vitamin E. These findings demonstrate that deficiency in one gene can result in compensatory up-regulation in a second relevant gene and, furthermore, indicate that compensation for oxidative stress can occur in brain tissue at epigenetic and genetic levels depending on the nature and/or extent of oxidative stress.

Pharmacogenetic determinants of outcome in acute lymphoblastic leukaemia

Present day paediatric co-operative group acute lymphoblastic leukaemia (ALL) protocols cure approximately 80% of patients, a result achieved largely through the use of risk-stratified therapies that employ multiple chemotherapy agents. These risk-based therapies utilize host and leukaemia traits to select the most appropriate therapy. However, these risk-stratified approaches predict therapy response imperfectly and an important fraction of patients experience relapse or therapy-related toxicity. Pharmacogenetics, the study of genetic variations in drug-processing genes and individual responses to drugs, may enable the improved identification of patients at higher risk for either disease relapse or chemotherapy-associated side effects. While the impact of genetic variation in the thiopurine-S-methyltransferase gene on ALL treatment outcome and toxicity has been extensively studied, the role of other polymorphisms remains less well known. This review summarizes current research on the impact of genetic variation in drug-processing genes in paediatric ALL and reviews important methodological and statistical issues presently challenging the field of pharmacogenetics.

Effects of male age on the frequencies of germinal and heritable chromosomal abnormalities in humans and rodents

OBJECTIVE

To review evidence regarding the effects of male age on germinal and heritable chromosomal abnormalities using available human and rodent studies and to evaluate possible underlying mechanisms.

DESIGN

Review of English language-published research using MEDLINE database, excluding case reports and anecdotal data.

RESULT(S)

There was little evidence from offspring or germ cell studies for a generalized male age effect on autosomal aneuploidy, except in rodents. Sex chromosomal nondisjunction increased with age in both human and rodent male germ cells. Both human and rodent data showed age-related increases in the number of sperm with chromosomal breaks and fragments and suggest that postmeiotic cells are particularly vulnerable to the effects of aging. Translocation frequencies increased with age in murine spermatocytes, at rates comparable to mouse and human somatic cells. Age-related mechanisms of induction may include accumulation of environmental damage, reduced efficiency of DNA repair, increased genomic instability, genetic factors, hormonal influences, suppressed apoptosis, or decreased effectiveness of antioxidants and micronutrients.

CONCLUSION(S)

The weight of evidence suggests that the increasing trend toward fathering at older ages may have significant effects on the viability and genetic health of human pregnancies and offspring, primarily as a result of structural chromosomal aberrations in sperm.

Low erythrocyte folate status and polymorphic variation in folate-related genes are associated with risk of neural tube defect pregnancy

Previous studies have shown conflicting findings in linking polymorphic variation in folate-related genes to the risk of neural tube defect pregnancy. Recent evidence points to maternal genotype being important in determining NTD risk. A case-control study was undertaken in 97 mothers of NTD cases from the northern region of the UK. Pregnant controls (n = 190) from a regional DNA bank and non-pregnant controls (n = 100) from the same geographical area were recruited. MTHFR 677C >T, MTHFR 1298A >C, MTRR 66A >G, SHMT 1420C >T, CbetaS 844ins68, and RFC-1 80G >A allele and genotype frequencies were determined and odds ratios (OR) calculated. Erythrocyte folate levels for cases and controls were also measured and a comparison made of median erythrocyte folate levels stratified according to genotype. The MTHFR 677C >T variant was not shown to be an independent NTD risk factor in mothers of NTD-affected pregnancy. A second polymorphism in MTHFR, 1298A >C, was less frequently observed in mothers of NTD cases (OR [95% CI]=0.57 [0.33, 0.97]). Possession of compound 1298A >C and 677C >T variants elevated risk of NTD pregnancy considerably (TT/AC+TT/CC vs CC/AA OR [95% CI]=6.56 [1.10, 39.33]). Erythrocyte folate levels were persistently lower in NTD mothers (p = 0.001) despite assays being conducted many years after the index pregnancy (17.6+/-12.6 years). Erythrocyte folate levels were depressed in the presence of the MTHFR 677C >T variant.

High prevalence of hyperhomocysteinemia related to folate deficiency and the 677C-->T mutation of the gene encoding methylenetetrahydrofolate reductase in coastal West Africa

BACKGROUND

Moderate hyperhomocysteinemia is a risk for neural tube defect and neurodegenerative and vascular diseases and has nutritional, metabolic, and genetic determinants. Its prevalence in sub-Saharan Africa remains unknown.

OBJECTIVE

Our goal was to evaluate the prevalence of hyperhomocysteinemia and the influence of nutritional, metabolic, and genetic determinants in savanna and coastal regions of Togo and Benin.

DESIGN

Volunteers were recruited from coastal (C groups; n = 208) and savanna (S group; n = 68) regions. Vitamin B-12, folate, total homocysteine (tHcy), cystatin C (a marker of glomerular filtration), and inflammatory and nutritional protein markers were measured in plasma, and the methylenetetrahydrofolate reductase (MTHFR) 677C-->T and 1298A--> C polymorphisms and the methionine synthase 2756A-->G polymorphism were examined in genomic DNA.

RESULTS

Moderate hyperhomocysteinemia (tHcy > 15 micromol/L) was recorded in 62.3% and 29.4% of the subjects from the coast and savanna, respectively (P < 0.0001). A histogram distribution of tHcy in the coastal groups showed a distinct group, C2 (15% of the total group), with tHcy > 28 micro mol/L. Folate < 6.75 nmol/L (lower quartile) and MTHFRCT/TT genotype were the 2 main risk factors for moderate hyperhomocysteinemia in the whole population [odds ratios: 5.3 (95% CI: 2.5, 11.2; P < 0.0001) and 4.9 (1.6, 14.8; P = 0.0048), respectively] and in the C2 group [odds ratios: 15.9 (4.5, 56.8; P < 0.0001) and 9.0 (2.3, -35.2; P = 0.0017), respectively]. Cystatin C was another potent risk factor in the C2 group.

CONCLUSION

A high prevalence of hyperhomocysteinemia in coastal West Africa, related to folate concentrations and the MTHFR 677 T allele, suggests the need to evaluate the influence of hyperhomocysteinemia on disease in this area.

Methylenetetrahydrofolate reductase enzyme polymorphisms as maternal risk for down syndrome among Turkish women

Advanced maternal age is the only fully accepted risk factor for trisomy 21, while most children with Down syndrome (DS) are born to younger mothers (<35 years). The relationship between chromosomal nondisjunction leading to aneuploidy and folate metabolism has drawn attention in the recent years. In this study, we examined the two polymorphisms in genes encoding the folate metabolizing enzyme methylenetetrahydrofolate reductase (MTHFR), namely, 677C > T and 1298A > C. The prevalence of these variant genotypes in mothers of DS children (case mothers) (n = 152) was compared with controls (n = 91). Frequencies of MTHFR 677C > T genotypes (CC, CT, and TT) and also combination of heterozygous and homozygous variant genotypes (CT or TT) (P = 0.28) demonstrated no difference between the case and control groups. Genotype frequencies of MTHFR 1298A > C (AA, AC, and CC) were similar among the case and control mothers. Variant genotypes of MTHFR 1298A > C (AC or CC) were also insignificant when compared between the two groups. This is yet the largest case-control study conducted for MTHFR 677C > T and also the first to investigate a possible relation with MTHFR 1298A > C. The data presented in this study fail to support the relationship between MTHFR 677C > T and 1298A > C polymorphisms and risk of having a child with DS.

Antisense modulation of the coding or regulatory sequence of the folate receptor (folate binding protein-1) in mouse embryos leads to neural tube defects

BACKGROUND

Although folic acid decreases the incidence of neural tube defects (NTDs) in humans, the mechanism for this protection is unknown. We have employed antisense technology to alter expression of the gene for the folate receptor (folate binding protein-1 [Folbp1]) in mouse embryos cultured in vitro.

METHODS

Embryos were explanted on day 8 of gestation and cultured for 44 hr. Several oligodeoxyribonucleotides designed to modulate the coding region or a regulatory sequence in the 5'-untranslated region of Folbp1 were microinjected into the amniotic sac of embryos at the beginning of the culture period.

RESULTS

Two different antisense sequences to the 5' and 3' coding region in Folbp1 produced concentration-dependent increases in the number of embryos with NTDs. Coinjection of 5-methyltetrahydrofolate with these sequences decreased the frequency of abnormal embryos. A semi-quantitative RT-PCR technique used to measure the amount of Folbp1 mRNA in treated and control embryos confirmed that the mRNA level was decreased by treatment with the antisense sequences. An antisense oligodeoxyribonucleotide to a 17 base cis regulatory element also generated a concentration-dependent increase in the frequency of embryos with NTDs, and a decrease in the level of Folbp1 mRNA.

CONCLUSIONS

These results demonstrate that alterations in expression of Folbp1 by perturbing either the coding sequence or a critical regulatory cis-element can play a role in NTDs.

Association of a common polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene with bone phenotypes depends on plasma folate status

A study of a polymorphism in the MTHFR gene, plasma folate, and bone phenotypes in 1632 individuals revealed that the genotype effect on BMD and quantitative ultrasound was dependent on the level of folate. Our findings support the hypothesis that the association between an MTHFR polymorphism and bone phenotypes depends on folate status.

INTRODUCTION

Genome-wide screens using quantitative ultrasound (QUS) and BMD phenotypes have shown suggestive linkage on chromosome 1pter-1p36.3, a region containing the methylenetetrahydrofolate reductase (MTHFR) gene. Individuals homozygous (TT) for the MTHFR C677T polymorphism who have low plasma folate concentrations exhibit elevated plasma homocysteine (tHcy) concentrations that may compromise bone quality. We hypothesized that folate status might modify an association between the C677T polymorphism and bone, possibly by influencing homocysteine concentrations.

MATERIALS AND METHODS

QUS (broadband ultrasound attenuation [BUA], speed of sound, and quantitative ultrasound index) of the heel and BMD of the hip and spine were measured in 1632 male and female members of the Framingham Offspring Study (1996-2001). Participants were assessed for plasma folate concentration and genotyped for the MTHFR C677T polymorphism. TT participants were compared with individuals in the CC + CT group using analysis of covariance.

RESULTS

Adjusted mean QUS and BMD measures did not differ between C677T groups. Although all participants with plasma folate concentrations > or =4 ng/ml had approximately 2% higher QUS and BMD than those with folate <4 ng/ml, the association disappeared after controlling for tHcy. Suggestive interactions between folate status and the C677T group (CC + CT versus TT) were found for hip BMD (p < or = 0.05) and BUA (p = 0.11). Compared with CC + CT participants, TT individuals had lower mean BUA (p = 0.06) and Ward's area BMD (p = 0.08) within the folate <4 ng/ml group and significantly higher hip BMD (p < or = 0.05) within the folate > or =4 ng/ml group. For both folate groups, TT participants had higher age-adjusted mean plasma tHcy versus CC + CT participants. Controlling for tHcy in these models did not affect the statistical significance of the interaction effects.

CONCLUSIONS

Our findings support the hypothesis that the association between the C677T MTHFR polymorphism and bone phenotypes depends on folate status. The mechanism mediating the association, however, remains unclear, but may be partially caused by homocysteine effects on bone.

Prevalence of the C677T substitution of the methylenetetrahydrofolate reductase (MTHFR) gene in Wisconsin

PURPOSE

The objective of this study was to estimate the prevalence of the C677T substitution of the MTHFR gene in the State of Wisconsin.

METHODS

The MTHFR genotypes of 1059 randomly selected newborns were analyzed using PCR amplification, HinfI restriction enzyme digestion, and electrophoresis. The frequency of the substitution was calculated in different genders and statistically analyzed (Chi-square).

RESULTS

Among 1059 newborn infants, about 59% had a C/C homozygous genotype, 33% had a C/T heterozygous genotype, and the remaining 8% had a T/T homozygous genotype. The frequencies for the C and T alleles were 76% (p) and 24% (q), respectively. There were no significant differences between males and females.

CONCLUSION

The study provides a fair estimate for the prevalence of the C677T substitution of the MTHFR gene in the general population in Wisconsin, which will facilitate further investigations of the pathogenic effects of the gene.

Methylenetetrahydrofolate reductase and transcobalamin genetic polymorphisms in human spontaneous abortion: biological and clinical implications

The pathogenesis of human spontaneous abortion involves a complex interaction of several genetic and environmental factors. The firm association between increased homocysteine concentration and neural tube defects (NTD) has led to the hypothesis that high concentrations of homocysteine might be embryotoxic and lead to decreased fetal viability. There are several genetic polymorphisms that are associated with defects in folate- and vitamin B12-dependent homocysteine metabolism. The methylenetetrahydrofolate reductase (MTHFR) 677C>T and 1298A>C polymorphisms cause elevated homocysteine concentration and are associated with an increased risk of NTD. Additionally, low concentration of vitamin B12 (cobalamin) or transcobalamin that delivers vitamin B12 to the cells of the body leads to hyperhomocysteinemia and is associated with NTD. This effect involves the transcobalamin (TC) 776C>G polymorphism. Importantly, the biochemical consequences of these polymorphisms can be modified by folate and vitamin B12 supplementation. In this review, I focus on recent studies on the role of hyperhomocysteinemia-associated polymorphisms in the pathogenesis of human spontaneous abortion and discuss the possibility that periconceptional supplementation with folate and vitamin B12 might lower the incidence of miscarriage in women planning a pregnancy.

Folate and homocysteine interrelationships including genetics of the relevant enzymes

PURPOSE OF REVIEW

Inadequate folate status has been linked to risk of a wide range of adverse health conditions throughout life, from birth defects and complications of pregnancy to cardiovascular disease, cancer and cognitive dysfunction in the elderly. In many instances these risks are manifested through elevated plasma homocysteine. This review focuses on current research into the contribution of genetic variability to folate status and disease predisposition.

RECENT FINDINGS

Some dozen potentially important polymorphisms in folate-related genes have been examined for disease associations or for their role in determining the level of plasma homocysteine. In most instances, the effects are either modest, not significant, or undetectable. However, the mechanism by which the 677C-->T variant of methylenetetrahydrofolate reductase determines homocysteine status has become clearer with the elucidation of a critical role for riboflavin in modulating the plasma homocysteine of TT homozygotes. Moreover, several new metaanalyses have confirmed an association of this variant with vascular disease, probably through low folate status and elevated plasma homocysteine.

SUMMARY

There are enormous difficulties in attempting to assess the contribution of minor genetic variability to nutrient status, against major background differences due to ethnicity, age, gender, lifestyle, dietary habits and disease status. Nevertheless, this is an important goal in the future management of chronic multifactorial disease. The present research into the genetic components of folate and homocysteine variability is paving the way towards an eventual capacity to ensure optimal folate status in every individual and, consequently, to reduce their risk of developing such diseases.

Promoter haplotype combinations for the human PDGFRA gene are associated with risk of neural tube defects

Recent animal studies suggested that deregulated expression of the platelet-derived growth factor receptor alpha (PDGFRalpha) may contribute to the failure of normal neural tube closure (NTC). There is also suggestive evidence that the promoter haplotype of the PDGFRA is associated with genetic susceptibility in human neural tube defects (NTDs). The purpose of our study was to investigate the association between promoter haplotype combinations of the human PDGFRA gene and risk for NTDs in a Hispanic population from the Texas-Mexico border region. This population has a considerably higher prevalence of NTDs (16/10,000 live births) than that generally reported in the United States (8-10/10,000 live births). In the present study, NTDs were defined as spina bifida or anencephaly. The haplotype of PDGFRA gene promoter was determined by direct DNA sequence analysis. Two novel haplotypes, H2epsilon and H1beta, were found. We observed significant differences among variable haplotype groups from in vitro transient transfection studies in U2-OS osteosarcoma cell and two other cell lines (HeLa cell and MCF7 cell). Result from our case-control study demonstrated that the frequencies of haplotypes with low transcription activity were significantly higher in NTD mothers than that observed in control mothers (odds ratio=2.2, 95% CI=1.0-4.6). Infants with at least one low activity allele showed slightly higher risk (odds ratio=1.5, 95%=0.8-3.1). Our study suggests that the reduced transcriptional activity of PDGFRA gene could increase the risk of having an NTD-affected pregnancy.

Transmission disequilibrium test (TDT) for case–control studies

Genetic association, case-control studies are becoming a major instrument in the attempt to identify disease susceptibility markers of complex diseases. However, a major drawback of population-based studies of genetic association is the confounding effect of the population subdivision. We developed a statistic named T-value that estimates the differential transmission of marker alleles from heterozygous parents to the affected offspring, based on population data. Our method does not assume Hardy-Weinberg equilibrium and it can be used in very different population structures. A great advantage of this approach is that the genetic structure of the population can be assessed with a few unlinked loci and using classical population genetics theory (i.e. Wright's F-statistics). Four general models, assuming either one population with random mating, or one population without random mating, or several populations with random mating within them, or several populations without random mating within them, were developed to determine the behavior of the T-value under different mating conditions. Although a complete knowledge of the population structure is ideal to choose the best model, the simulations show that for a total inbreeding of 0.30 or less the last three models gave very similar estimates of the T-value. The model that assumed that total departure of Hardy-Weinberg proportions is due to population subdivision was the most robust under different scenarios of population structure. In sum, this study describes a novel procedure that can be used to identify the transmission of disease susceptibility markers in population-based studies.

Folate status response to controlled folate intake is affected by the methylenetetrahydrofolate reductase 677C-->T polymorphism in young women

This study was designed to evaluate the effect of the methylenetetrahydrofolate reductase (MTHFR) 677C-->T polymorphism on folate and homocysteine response in non-Hispanic women consuming a low folate diet followed by a diet providing the Recommended Dietary Allowance (RDA) for folate. Women (aged 20-30 y old) with either the TT (n = 19) or CC (n = 22) MTHFR 677C-->T genotype participated in a folate depletion-repletion study (7 wk, 115 microg dietary folate equivalents (DFE)/d; 7 wk, 400 microg DFE/d). Overall serum folate decreased (P < 0.0001) during depletion and increased (P < 0.0001) during repletion with lower (P = 0.03) postdepletion serum folate in women with the TT versus CC genotype. Folate status was low (serum folate < 13.6 nmol/L) in more women with the TT (59%) compared with the CC genotype (15%) postdepletion. Red blood cell folate for all subjects decreased during depletion (P < 0.0001) and repletion (P = 0.02) with lower (P = 0.04) red blood cell folate in women with the TT compared with the CC genotype postrepletion. Homocysteine increased (P < 0.0001) for both genotype groups postdepletion and decreased (P = 0.02) postrepletion for the CC genotype group only. Homocysteine concentrations tended to be higher (P = 0.09) in the TT versus CC genotype group postdepletion and postrepletion. These data suggest that the MTHFR 677C-->T polymorphism negatively affects the folate and homocysteine response in women consuming low folate diets followed by repletion with the RDA. These results may be important when evaluating the impact of the MTHFR 677C-->T polymorphism in countries in which low folate diets are chronically consumed.

Is there a familial link between Down's syndrome and neural tube defects? Population and familial survey

OBJECTIVE

To verify whether Down's syndrome and neural tube defects arise more often in the same family than expected by chance.

DESIGN

Population and familial survey.

SETTING

Network of maternity hospitals in the Latin American collaborative study of congenital malformations (ECLAMC) in Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Paraguay, Peru, Uruguay, and Venezuela between 1982 and 2000.

PROBANDS

2421 cases of neural tube defects, 952 of hydrocephalus, and 3095 of Down's syndrome registered from a total of 1 583 838 live births and stillbirths.

MAIN OUTCOME MEASURES

Observed number of cases of Down's syndrome among siblings of probands with a neural tube defect or hydrocephalus and number expected on the basis of maternal age; observed number of cases of neural tube defects or hydrocephalus among siblings of probands with Down's syndrome and number expected according to the prevalence in the same population.

RESULTS

Five cases of Down's syndrome occurred among 5404 pregnancies previous to a case of neural tube defect or hydrocephalus, compared with 5.13 expected after adjustment by maternal age. Twelve cases of neural tube defect or hydrocephalus occurred among 8066 pregnancies previous to a case of Down's syndrome, compared with 17.18 expected on the basis of the birth prevalence for neural tube defects plus hydrocephalus in the same population.

CONCLUSION

No association occurred between families at risk of neural tube defects and those at risk of Down's syndrome.

Abnormal folic acid-homocysteine metabolism as maternal risk factors for Down syndrome in Japan

BACKGROUND

Japan has been considered as "a folate sufficient area", since traditional Japanese food contains an adequate amount of folic acid. However, the recent westernized food style of young Japanese mothers may affect the intake of folic acid among them. This food style may contribute to the occurrence of Down syndrome, which has proved to be linked to abnormal folate and homocysteine metabolisms.

AIM OF THE STUDY

To preliminarily evaluate the levels of folic acid,homocysteine and other relevant factors which are associated with folate metabolism, among Japanese women who had pregnancies affected by Down syndrome.

METHODS

Blood samples from 31 women who had pregnancies affected by Down syndrome (DS) were obtained. 60 age-matched control blood samples were also obtained from mothers who had not experienced miscarriages or abnormal pregnancies (CONT). Plasma homocysteine and serum folic acid, vitamin B12, and B6 were measured and compared between DS and CONT. Furthermore, the frequency of MTHFR polymorphism (C677T) was also investigated.

RESULTS

Plasma levels of homocysteine were significantly increased in DS mothers (p = 0.004). In contrast, serum levels of folic acid were significantly decreased in DS mothers (p = 0.0001). There were no significant differences in the vitamin B12 and B6 levels between DS and CONT. Also, the frequency of 5,10-methylenetetrahydrofolate reductase gene (MTHFR) homozygous polymorphism showed no differences between DS and CONT.

CONCLUSION

Different levels of serum folic acid and plasma homocysteine between both groups may contribute to the occurrence of Down syndrome even in Japan. Although there was no significant difference in the frequency of MTHFR polymorphism between the groups, probably because of an inadequate number of samples, further studies may contribute to the understanding of the occurrence of Down syndrome in Japan.

Autosomal trisomy and maternal use of multivitamin supplements

Recent reports suggest that women carrying certain polymorphisms of folate genes associated with suboptimal folate status might be at increased risk for having a child with Down syndrome or other autosomal trisomies, and hypothesized that maternal use of multivitamin supplements might reduce such risk. To evaluate this hypothesis, we examined data from a population-based case-control study, and contrasted cases of Down syndrome, trisomy 18, and trisomy 13, with unaffected controls. Periconceptional multivitamin use, compared to no such use, was associated with an odds ratio (OR) of 0.9 (95% confidence interval [CI], 0.6-1.3) for having a pregnancy affected by an autosomal trisomy. The OR was 0.8 (95% CI, 0.5-1.3) for Down syndrome and 1.4 (95% CI, 0.5-3.6) for trisomies 13 and 18, with little variation by maternal race or age. Periconceptional multivitamin use was not associated with a major reduction in the risk for common autosomal trisomies.

Frecuencia de la mutación 677C-T del gen de la metilentetrahidrofolato reductasa en una muestra de 652 recién nacidos de toda España

BACKGROUND AND OBJECTIVE

An international study on the frequency of the mutation 677C-T of the methylenetetrahydrofolate reductase (MTHFR) gene and its genotypes has been performed on a sample of consecutive liveborn infants around the world. In that study Spain participated through the ECEMC group. Here we present the distribution of the frequency of the T-allele by Spanish Regions (Autonomic Comunities).

SUBJECTS AND METHOD

The ECEMC collaborating physicians gathered blood samples from 15 consecutive liveborn infants in 67 hospitals from all over the country during the same months, specifying the ethnicity and sex of each infant. The frequency of the mutation was estimated through the percentage with its confidence interval. The *2 of homogeneity (k-1 degrees of freedom) was used to confirm that the frequencies were not statistically different across the country.

RESULTS

The frequency distribution of the TT genotype does not differ significantly between Spanish Regions.

CONCLUSIONS

This seems to be the first nation-wide study on a homogeneous sample of individuals. The observed frequencies are in agreement with those observed in some published studies on specific Spanish geographic areas. The overall frequency is similar to that reported in Mediterranean countries.

Colon cancer and genetic variation in folate metabolism: the clinical bottom line

So far, evidence for the relation between folate intake and colorectal cancer has been insufficient to lead to specific public health interventions. In principle, data on the relation between genetic variation in folate metabolism and colorectal neoplasia could be used to corroborate the data on the relation between folate intake or status and the disease, strengthening the evidence base for primary prevention. Issues in considering the relation between a health outcome and genetic variation in metabolism of nutrients or other food components include knowledge of gene function, linkage disequilibrium, population stratification, study size and quality, and gene-environment interaction. Overall homozygosity for MTHFR variant genotypes is associated with a reduced risk of colorectal cancer, the opposite of what might have been expected a priori. This has led investigators to place greater emphasis on the functions of folate and methylenetetrahydrofolate reductase in DNA synthesis. Folate and related nutrients may be important after adenoma formation. A challenge for the future is to characterize the effects of multiple genes influencing folate metabolism. Limited data for colorectal cancer suggest that the effect of a low folate diet overrides the effect of genotype, but two studies of adenomas suggested the opposite. Another potential role of information on genetic variation in folate metabolism is in the management of colorectal cancer but most studies have been small, have included selected patient groups, and have made limited adjustment for potentially important factors.

Multiple single-nucleotide polymorphisms in the methylenetetrahydrofolate reductase and its truncated pseudogene of 23 inbred strains of mice

Reduced 5,10-methylenetetrahydrofolate reductase (MTHFR) results in a number of human diseases. To find a model mouse sensitive to these diseases, we analyzed single-nucleotide polymorphisms (SNPs) of the mouse Mthfr using 23 phylogenetically distant strains of mouse. We found five SNPs: two nonsynonymous and three synonymous. The CAST/Ei strain has the nonsynonymous SNP L350V and five strains (NMRI, KJR, SWN2, MSM, and JF1) have the nonsynonymous SNP S22G. The MTHFR activity of CAST/Ei and MSM showed no significant difference in activity or thermostability compared with that of C57BL/6J. We also found a pseudogene segment of the mouse Mthfr that was not present in human and was more frequently variable than the functional gene. These results suggest a possibility that the truncated pseudogene may buffer variations of the mouse Mthfr functional gene, and the mouse has evolved fewer variations of the gene than human.

Analysis of the MTHFR 1298A-->C and 677C-->T polymorphisms as risk factors for neural tube defects

The thermolabile variant (677TT) of methylenetetrahydrofolate reductase (MTHFR) is a known risk factor for neural tube defects (NTDs). The relationship between a second MTHFR polymorphism (1298A-->C) and NTD risk has been inconsistent between studies. We genotyped 276 complete NTD triads (mother, father and child affected with an NTD) and 256 controls for MTHFR 1298A-->C. Our findings do not support a role for the 1298A-->C polymorphism in NTDs (OR 0.85 (95% CI 0.49-1.47), p= 0.55), nor do we observe a combined effect with the 677C-->T polymorphism.

Polymorphisms within the vitamin B12 dependent methylmalonyl-coA mutase are not risk factors for neural tube defects

Methionine synthase and methylmalonyl-CoA mutase (mutase) are the only two known vitamin B(12) (B(12)) dependent enzymes in humans. A lower level of B(12) has been shown to be an independent maternal risk factor for neural tube defects (NTDs) prompting an investigation of common genetic variants within B(12) dependent enzymes. To investigate the role of methylmalonyl-CoA mutase variants we studied 279 complete NTD triads (NTD affected case and both parents) and 256 controls. Based on case-control and family based (transmission disequilibrium test) analyses we did not find an association between the mutase single nucleotide polymorphisms (SNPs) K212K (636A-->G), H532R (1595A-->G) and V671I (2011G-->A) and NTDs. However, there was a significant difference in the frequencies of these polymorphisms between a group of African Americans and American Caucasians (K212K, P=0.002; H532R, P</=0.001; V671I, P=0.006). In conclusion, common variants in the mutase gene do not appear to be risk factors for NTDs but their allele frequencies are significantly different between ethnic groups.