High prevalence of the thermolabile methylenetetrahydrofolate reductase variant in Mexico: a country with a very high prevalence of neural tube defects

Study of C677T Methylene Tetrahydrofolate Reductase Gene Polymorphism as a Risk Factor for Neural Tube Defects

Introduction

Various genetic and environmental factors contribute to the development of neural tube defects (NTDs) which are a group of neurulation defects resulting from failure of closure of embryonic neural tube. Among genetic factors is polymorphism in methylene tetrahydrofolate reductase (MTHFR) gene, giving rise to a gene variant or mutant. However, in most studies directed at finding an association between MTHFR variants and NTD, there is no clear evidence of a cause-and-effect relationship.

Materials and Methods

Forty diagnosed cases of NTDs and forty healthy individuals were investigated in a case-control study for presence of C677T MTHFR gene polymorphism. Serum folate and Vitamin B12 levels were estimated and MTHFR gene polymorphism was detected by polymerase chain reaction-restriction fragment length polymorphism.

Results

It was found that 32 cases were homozygous with CC genotype and eight were heterozygous with CT genotype, whereas 35 controls had CC genotype and five had CT genotype. TT genotype was absent in both the groups. There was no statistically significant difference between both the groups. No evidence of association between MTHFR C677T polymorphism and NTDs was found.

Conclusion

Although there was no evidence of association between MTHFR C677T polymorphism and NTDs, our study does not rule out the impact of MTHFR gene mutation on folate metabolism. The reason for absence of TT genotype and no association could be a small sample size. Larger, comprehensive, and well-designed multicentric but feasible studies involving proper subjects and appropriate and adequate controls from several hospitals may provide more meaningful data.

Cystathionine β-synthase and methylenetetrahydrofolate reductase mutations in Mexican individuals with hyperhomocysteinemia

Background:

Hyperhomocysteinemia, a thrombotic risk factor, may have several causes. Among the genetic causes of hyperhomocysteinemia, there are polymorphisms in the enzymes methylenetetrahydrofolate reductase (C677T) and cystathionine β-synthase (C699T, C1080T, and 844ins68). Although the frequency of hyperhomocysteinemia in our country is high, there is no evidence about the frequencies of these polymorphisms.

Methods:

We analyzed 80 healthy individuals from several regions in our country. We evaluated the fasting and post-oral methionine load plasma Hcy and the genotypes in order to obtain the allele frequencies of the polymorphisms C677T of methylenetetrahydrofolate reductase and C699T, C1080T, and 844ins68 of the cystathionine β-synthase.

Results:

No individual had deficiency of folic acid, vitamins B12, or B6, but 80% had post-oral methionine load hyperhomocysteinemia. We found a significant increase in the Hcy plasma concentration associated with age and gender. Only the polymorphism C1080T was significantly associated with hyperhomocysteinemia.

Conclusion:

There is an association between fasting and post-oral methionine load plasma Hcy concentrations with the allelic frequencies of the polymorphisms C669T, 844ins68, and C1080T of the cystathionine β-synthase and C667T of the methylenetetrahydrofolate reductase in healthy Mexican individuals. As compared with individuals with normal fasting or post-oral methionine load Hcy plasma levels, only C1080T was significantly associated with hyperhomocysteinemia.

Intranasal perillyl alcohol therapy improves survival of patients with recurrent glioblastoma harboring mutant variant for MTHFR rs1801133 polymorphism

Background

Polymorphisms in MTHFR gene influence risk and overall survival of patients with brain tumor. Global genomic DNA (gDNA) methylation profile from tumor tissues is replicated in peripheral leukocytes. This study aimed to draw a correlation between rs1801133 MTHFR variants, gDNA methylation and overall survival of patients with recurrent glioblastoma (rGBM) under perillyl alcohol (POH) treatment.

Methods

gDNA from whole blood was extracted using a commercially available kit (Axygen) and quantified by spectrophotometry. Global gDNA methylation was determined by ELISA and rs1801133 polymorphism by PCR-RFLP. Statistical analysis of gDNA methylation profile and rs1801133 variants included Mann-Whitney, Kruskal-Wallis, Spearman point-biserial correlation tests (SPSS and Graphpad Prism packages; significant results for effect size higher than 0.4). Prognostic value of gDNA methylation and rs1801133 variants considered survival profiles at 25 weeks of POH treatment, having the date of protocol adhesion as starting count and death as the final event.

Results

Most rGBM patients showed global gDNA hypomethylation (median = 31.7%) and a significant, moderate and negative correlation between TT genotype and gDNA hypomethylation (median = 13.35%; rho = − 0.520; p = 0.003) compared to CC variant (median = 32.10%), which was not observed for CT variant (median = 33.34%; rho = − 0.289; p = 0.06). gDNA hypermethylated phenotype (median = 131.90%) exhibited significant, moderate and negative correlations between TT genotype (median = 112.02%) and gDNA hypermethylation levels when compared to CC (median = 132.45%; rho = − 0,450; p = 0.04) or CT (median = 137.80%; rho = − 0.518; p = 0.023) variants. TT variant of rs1801133 significantly decreased gDNA methylation levels for both patient groups, when compared to CC (d values: hypomethylated = 1.189; hypermethylated = 0.979) or CT (d values: hypomethylated = 0.597; hypermethylated = 1.167) variants. Positive prognostic for rGBM patients may be assigned to gDNA hypermethylation for survivors above 25 weeks of treatment (median = 88 weeks); and TT variant of rs1801133 regardless POH treatment length.

Conclusion

rGBM patients under POH-based therapy harboring hypermethylated phenotype and TT variant for rs1801133 had longer survival. Intranasal POH therapy mitigates detrimental effects of gDNA hypomethylation and improved survival of patients with rGBM harboring TT mutant variant for MTHFR rs1801133 polymorphism.

Trial registration

CONEP -9681- 25,000.009267 / 2004. Registered 12th July, 2004.

Methylenetetrahydrofolate reductase polymorphism in healthy volunteers and its correlation with homocysteine levels in patients with thrombosis

OBJECTIVE:

To determine prevalence of methylenetetrahydrofolate reductase (MTHFR) mutations in apparently healthy individuals residing in Mumbai and patients with deep vein thrombosis (DVT) and coronary artery disease (CAD) and to correlate these polymorphisms with homocysteine (Hcy) levels.

MATERIALS AND METHODS:

This case–control study was initiated after receiving ethical approval and following the participant's written consent. One hundred and twenty unmatched healthy volunteers and 240 patients with arterial and venous thrombosis were enrolled. The prevalence of C677T and A1298C MTHFR mutations was detected using polymerase chain reaction-restriction fragment length polymorphism technique. Serum Hcy concentration and lipid levels were determined using biochemical kits.

RESULTS:

Allele frequency of 677T was 7%, 15%, and 14% in healthy controls, DVT, and CAD patients, respectively, while for 1298C allele, it was 31%, 33%, and 29%, respectively. The lipid markers in CAD patients were significantly low in comparison to the controls while the Hcy level in patients with thrombosis was higher in comparison with the controls. Highest Hcy levels were observed in participants with TT genotype followed by CT genotype and CC genotype in all the three groups. A higher risk of raised Hcy levels was seen in the variants (CT + TT) as compared to CC genotype in DVT (odds ratio [OR] = 3.39, 95% confidence interval [CI] = 1.39–8.2,P < 0.01) and CAD (OR = 21.67, 95%CI = 4.87–96.47,P < 0.0001). The risk observed for A1298C was 2.28 and 2.12 times higher in variants (AC + CC) of both DVT and CAD (OR = 2.28, 95%CI = 1.09–4.75 and OR = 2.12, 95%CI = 1.02–4.40, respectively).

CONCLUSIONS:

The prevalence of variants was more in thrombosis patients as compared to unmatched controls. Our study highlights the fact that MTHFR C677T polymorphism as compared to A1298C significantly affects Hcy levels in patients with thrombosis indicating that patients with mutant variants are at higher risk of rapid progression of their disease condition.

MTHFR Gene Mutations Correlate with White Matter Disease Burden and Predict Cerebrovascular Disease and Dementia

The incidence of dementia is on the rise and expected to continue to increase in the foreseeable future. Two of the most common subtypes of dementia are Alzheimer's subtype and vascular dementia. Hyperhomocysteinemia has been shown to serve as a risk factor for dementia due to an associated blood-brain barrier dysfunction and subsequent small-vessel disease pathology. There are varying causes for hyperhomocysteinemia, including genetic and dietary, among others. We highlight the importance of identifying hyperhomocysteinemia as a potential etiologic and therapeutic target for the most common subtypes of dementia.

Whole Genome Sequence, Variant Discovery and Annotation in Mapuche-Huilliche Native South Americans

Whole human genome sequencing initiatives help us understand population history and the basis of genetic diseases. Current data mostly focuses on Old World populations, and the information of the genomic structure of Native Americans, especially those from the Southern Cone is scant. Here we present annotation and variant discovery from high-quality complete genome sequences of a cohort of 11 Mapuche-Huilliche individuals (HUI) from Southern Chile. We found approximately 3.1 × 106 single nucleotide variants (SNVs) per individual and identified 403,383 (6.9%) of novel SNVs events. Analyses of large-scale genomic events detected 680 copy number variants (CNVs) and 4,514 structural variants (SVs), including 398 and 1,910 novel events, respectively. Global ancestry composition of HUI genomes revealed that the cohort represents a sample from a marginally admixed population from the Southern Cone, whose main genetic component derives from Native American ancestors. Additionally, we found that HUI genomes contain variants in genes associated with 5 of the 6 leading causes of noncommunicable diseases in Chile, which may have an impact on the risk of prevalent diseases in Chilean and Amerindian populations. Our data represents a useful resource that can contribute to population-based studies and for the design of early diagnostics or prevention tools for Native and admixed Latin American populations.

Polymorphisms C677T and A1298C of MTHFR Gene: Homocysteine Levels and Prothrombotic Biomarkers in Coronary and Pulmonary Thromboembolic Disease

The activity of the enzyme methylenetetrahydrofolate reductase (MTHFR) determines homocysteine (Hcy) levels, and polymorphisms in its gene affect the activity of the enzyme. Changes in the enzyme's activity may lead to a higher susceptibility to develop arterial and venous thromboembolic disease. The aim was to analyze the relationship between the C677T and A1298C polymorphisms of MTHFR, Hcy levels, and prothrombotic biomarkers in pulmonary embolism (PE) and acute myocardial ischemia (AMI). Clinical files of patients with thromboembolic diseases having complete data and whose doctor had requested an assay to determine the polymorphisms of the MTHFR gene, Hcy levels, and prothrombotic biomarkers were studied to search for the correlation between mutations of the MTHFR gene and Hcy levels in the different diseases. We included 334 files: 158 were from women and 176 from men (51 [19 SD] years). Sixty-three percent have had thrombosis, 8% AMI, and 31% PE. Patients with thrombosis had elevated frequency of the C677T polymorphism. The CC genotype was higher than the TT genotype ( P = .003) and CT versus the TT ( P = .009). In patients with PE, the CC genotype was higher than the TT genotype ( P = .038). Pulmonary embolism with massive and submassive events had predominant genotypes 677 TT ( P = .003) and the AA 1298 ( P = .017). Elevated Hcy levels in the presence of the T allele in the C677T gene and of the A allele in the A1298C gene are associated with AMI and massive and submassive PE.

The Methylenetetrahydrofolate Reductase C677T (rs1801133) and Apolipoprotein A5-1131T>C (rs662799) Polymorphisms, and Anemia Are Independent Risk Factors for Ischemic Stroke

BACKGROUND

Although there is adequate knowledge as to the role of traditional cardiovascular risk factors on stroke incidence, knowledge of other risk factors, particularly genetic ones, is still incomplete.

METHODS

To assess the participation of some polymorphisms, along with other modifiable risk factors, a case-control study was conducted. A total of 253 cases were identified in the emergency room of a general regional hospital, with a clinical trait of stroke confirmed by a skull computerized axial tomography scan. In the surgery ward, 253 controls were identified, gender and age (±5 years) matched. Biochemical parameters were measured, and 4 polymorphisms were genotyped by polymerase chain reaction, rs1801133 (methylenetetrahydrofolate reductase [MTHFR]), rs1498373 (dimethylarginine dimethylaminohydrolase type 1 [DDAH1]), rs662799 (apolipoprotein A5 [APOA5]), and rs1799983 (endothelial nitric oxide). Odds ratios were estimated to assess the strength of association, with 95% confidence intervals, both in a matched case-control analysis and in a conditional regression analysis.

RESULTS

Cases had higher mean blood pressure and triglycerides and lower hemoglobin levels. Heterozygous and homozygous subjects to the rs1801133 variant of the MTHFR gene had a 3-fold higher risk of stroke. In the dominant model, those with the polymorphism rs662799 of the promoter region for APOA5 had twice the risk of stroke. Anemia increased the risk of stroke 4-fold.

CONCLUSIONS

Polymorphisms of the genes MTHFR (rs1801133) and APOA5 (rs662799), as well as anemia, are independent risk factors for stroke in Mexicans, together with traditional cardiovascular risk factors such as high triglycerides and high blood pressure.

Should vitamin B12 status be considered in assessing risk of neural tube defects?

There is a strong biological premise for including vitamin B₁₂ with folic acid in strategies to prevent neural tube defects (NTDs), due to the closely interlinked metabolism of these two vitamins. For example, reduction of B₁₂ deficiency among women of reproductive age could enhance the capacity of folic acid to prevent NTDs by optimizing the cellular uptake and utilization of natural folate cofactors. Vitamin B₁₂ might also have an independent role in NTD prevention, such that adding it in fortification programs might be more effective than fortifying with folic acid alone. Globally, there is ample evidence of widespread vitamin B₁₂ deficiency in low‐ and middle‐income countries, but there is also considerable divergence of vitamin B₁₂ status across regions, likely due to genetic as well as nutritional factors. Here, I consider the evidence that low vitamin B₁₂ status may be an independent factor associated with risk of NTDs, and whether a fortification strategy to improve B₁₂ status would help reduce the prevalence of NTDs. I seek to identify knowledge gaps in this respect and specify research goals that would address these gaps.

Tailoring Nutritional Advice for Mexicans Based on Prevalence Profiles of Diet-Related Adaptive Gene Polymorphisms

Diet-related adaptive gene (DRAG) polymorphisms identified in specific populations are associated with chronic disorders in carriers of the adaptive alleles due to changes in dietary and lifestyle patterns in recent times. Mexico’s population is comprised of Amerindians (AM) and Mestizos who have variable AM, European (EUR) and African genetic ancestry and an increased risk of nutrition-related chronic diseases. Nutritional advice based on the Mexican genome and the traditional food culture is needed to develop preventive and therapeutic strategies. Therefore, we aimed to provide a prevalence profile of several DRAG polymorphisms in the Mexican population, including Central West (CW) Mexico subpopulations. Geographic heat maps were built using ArcGIS10 (Esri, Redlands, CA, USA) software, based on the published data of the MTHFR C677T (rs1801133), ABCA1 Arg230Cys (rs9282541), APOE T388C (rs429358)/C526T (rs7412), LCT C-13910T (rs4988235) polymorphisms and AMY1 copy number variation (CNV). Also, new data obtained by allelic discrimination-real-time polymerase chain reaction (RT-PCR) assays for the MTHFR, ABCA1, and APOE polymorphisms as well as the AMY1 CNV in the CW Mexico subpopulations with different proportions of AM and EUR ancestry were included. In the CW region, the highest frequency of the MTHFR 677T, ABCA1 230C and APOE ε4 adaptive alleles was observed in the AM groups, followed by Mestizos with intermediate AM ancestry. The LCT-13910T allele frequency was highest in Mestizos-EUR but extremely low in AM, while the AMY1 diploid copy number was 6.82 ± 3.3 copies. Overall, the heat maps showed a heterogeneous distribution of the DRAG polymorphisms, in which the AM groups revealed the highest frequencies of the adaptive alleles followed by Mestizos. Given these genetic differences, genome-based nutritional advice should be tailored in a regionalized and individualized manner according to the available foods and Mexican traditional food culture that may lead to a healthier dietary pattern.

Interethnic variability of pharmacogenetic biomarkers in Mexican healthy volunteers: a report from the RIBEF (Ibero-American Network of Pharmacogenetics and Pharmacogenomics)

Mexico presents a complex population diversity integrated by Mexican indigenous (MI) (7% of Mexico's population) and Mexican mestizos (MMs). This composition highlights the importance of pharmacogenetic studies in Mexican populations. The aims of this study were to analyze the reported frequencies of the most relevant pharmacogenetic biomarkers and metabolic phenotypes in healthy volunteers from Mexican populations and to assess its interethnic variability across MI and MM populations. After a literature search in PubMed, and according to previously defined inclusion criteria, 63 pharmacogenetic studies performed in Mexican healthy volunteers up to date were selected. These reports comprised 56,292 healthy volunteers (71.58% MM). Allele frequencies in 31 pharmacogenetic biomarkers, from 121 searched, are described. Nine of these biomarkers presented variation within MM and MI groups. The frequencies of CYP2D6*3, *4, *5, *10, *17, *35 and *41 alleles in the MM group were different from those reported in the MI group. CYP2C9*2 and *3 alleles were more frequent in MM than in MI populations (χ2 test, p<0.05). CYP2C19*3 allele was not found in the MM or MI populations reported. For UGT1A1*28, only one study was found. HLA-A*31:01 and HLA-B*15:02 were present in some MM and MI populations. Poor metabolizers for CYP2D6 and CYP2C9 were more frequent in MM than in MI groups (χ2 test, p<0.05). Only 26% of the relevant pharmacogenetic biomarkers searched have been studied in Mexican healthy volunteers; therefore, further studies are warranted. The frequency variation of biomarkers in MM and MI populations could be important for the clinical implementation of pharmacogenetics in Mexico.

Distribution of MTHFR C677T Gene Polymorphism in Healthy North Indian Population and an Updated Meta-analysis

Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme of folate pathway. Several polymorphisms were reported in MTHFR gene but C677T polymorphism is most studied and it has been reported to be risk factor for several diseases/disorders. The present study was designed to explore the frequency of MTHFR C677T polymorphism in North Indian healthy population. In addition to this a meta-analysis of published articles was also performed to estimate the global prevalence of MTHFR C677T polymorphism. A total of 1000 unrelated healthy subjects were selected for MTHFR C677T polymorphism analysis. Different databases were searched for eligible articles. Prevalence proportion with 95 % CI was used to determine global prevalence of T allele and TT genotype. Meta-analysis was performed by Open meta-analyst. In 1000 blood samples analyzed, the frequency of T allele and TT genotype was 11 and 1 % respectively. Results of the meta-analysis showed that the global prevalence of T allele and TT genotype were 24.0 % (95 % CI 21.7-26.5) and 7.7 % (95 % CI 6.5-8.9) respectively. In sub-group meta-analysis, the lowest frequency of T allele was found in Africans (10.3 %; 95 % CI 3.8-16.8), and highest in Europeans (34.1 %; 95 % CI 31.9-36.3). The frequency of T allele in the North India is 11 %. The results of the meta-analysis showed that the frequency of the T allele and the TT genotype of C677T is highest in the Caucasian population.

Heterogenous Distribution of MTHFR Gene Variants among Mestizos and Diverse Amerindian Groups from Mexico

Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme in folate metabolism. Folate deficiency has been related to several conditions, including neural tube defects (NTDs) and cardiovascular diseases. Hence, MTHFR genetic variants have been studied worldwide, particularly the C677T and A1298C. We genotyped the C677T and A1298C MTHFR polymorphisms in Mexican Amerindians (MAs), from the largest sample included in a genetic study (n = 2026, from 62 ethnic groups), and in a geographically-matched Mexican Mestizo population (MEZ, n = 638). The 677T allele was most frequent in Mexican individuals, particularly in MAs. The frequency of this allele in both MAs and MEZs was clearly enriched in the South region of the country, followed by the Central East and South East regions. In contrast, the frequency of the 1298C risk allele in Mexicans was one of the lowest in the world. Both in MAs and MEZs the variants 677T and 1298C displayed opposite allele frequency gradients from southern to northern Mexico. Our findings suggest that in Mestizos the 677T allele was derived from Amerindians while the 1298C allele was a European contribution. Some subgroups showed an allele frequency distribution that highlighted their genetic diversity. Notably, the distribution of the frequency of the 677T allele was consistent with that of the high incidence of NTDs reported in MEZ.

Geographical and ethnic distribution of single nucleotide polymorphisms within genes of the folate/homocysteine pathway metabolism

High levels of plasma homocysteine are associated with an increased risk of many health conditions influenced by both environmental and genetic factors. The objective of this study was to provide the geographical distribution of folate pathway genetic polymorphisms in Mexico and the comparison with the reported frequencies in different continental populations. This study included the analysis of the genotypic frequencies of eight polymorphisms in genes of the folate/homocysteine metabolic pathway in 1,350 Mestizo and Amerindian subjects from different regions in Mexico and 836 individuals from European, African and Asian populations of the 1,000 Genomes Project. In Mexican Mestizo and Amerindian populations, the MTHFR C677T risk genotype (TT) was highly prevalent (frequency: 25 and 57 %, respectively). In Mestizos, the frequency showed clear regional variation related to ancestry; the Guerrero subpopulation with the highest Amerindian contribution had the highest TT frequency (33 %). The MTHFD1 G1958A AA risk genotype was also enriched in Mexican Mestizos and Amerindians (frequency: 34 and 58 %, respectively), whereas in African and Asian ancestry populations the frequency for AA was low (~4 %). All together risk genotypes showed regional differences, and Sonora had significantly different genetic frequencies compared with the other regions (P value <0.05). Our study illustrates differential geographical distribution of the risk variants in the folate/homocysteine metabolic pathway relative to ethnic background. This work supports that certain areas of the world have increased needs for folic acid and vitamin B supplementation, and this information needs to be considered in public health guidelines and eventually policies.

C677T mutation in methylenetetrahydrofolate reductase gene and neural tube defects: should Japanese women undergo gene screening before pregnancy?

We analyzed the role of maternal C677T mutation in methylenetetrahydrofolate reductase (MTHFR) gene on spina bifida development in newborns. A total of 115 mothers who had given birth to a spina bifida child (SB mothers) gave 10 mL of blood together with written informed consent. The genotype distribution of C677T mutation was assessed and compared with that of the 4517 control individuals. The prevalence of the homozygous genotype (TT) among SB mothers was not significantly different from that among the controls (odds ratio [OR] = 0.65; 95% confidence interval [CI] = 0.31-1.25; P = 0.182), suggesting that MTHFR 677TT genotype in Japan is not associated with spina bifida development in newborns. The T allele frequency was not increased in SB mothers (34.8%) as compared to that of the control individuals (38.2%). Further, the internationally reported association between the two groups was found to be similar in all 15 countries studied except the Netherlands, where the TT genotype was found to be a genetic risk factor for spina bifida. For the prevention of affected pregnancy every woman planning to conceive has to take folic acid supplements 400 μg a day and the government is asked to take action in implementing food fortification with folic acid in the near future. In conclusion, it is not necessary for Japanese women to undergo genetic screening C677T mutation of the MTHFR gene as a predictive marker for spina bifida prior to pregnancy, because the TT genotype is not a risk factor for having an affected infant.

Geographical distribution of MTHFR C677T, A1298C and MTRR A66G gene polymorphisms in China: findings from 15357 adults of Han nationality

Background

Methylenetetrahydrofolate reductase (MTHFR) C677T, A1298C and methionine synthase reductase (MTRR) A66G polymorphisms are important genetic determinants for homocysteine (Hcy) levels, and are associated with several disorders. These polymorphisms are heterogeneously distributed worldwide. Our objective was to explore the geographical distributions of these polymorphisms in China.

Methodologies

15357 healthy adults were recruited from 10 regions. Buccal samples were collected and genomic DNA was isolated. Genotyping was performed using the fluorogenic 5′-nuclease assay.

Principal Findings

The prevalence of the three polymorphisms among different populations from China varied significantly and showed apparent geographical gradients. For MTHFR C677T, the frequencies of the 677T allele and the 677TT genotype were significantly higher among northern populations and ranged from the lowest values (24.0% and 6.4%, respectively) in Hainan (southern) to the highest values (63.1% and 40.8%, respectively) in Shandong (northern). For MTHFR A1298C, the 1298C allele and the 1298CC genotype frequencies were significantly higher among southern populations and increased from low values (13.1% and 1.4%, respectively) in Shandong to high values (25.7% and 6.7%, respectively) in Hainan. For A66G, the 66G allele and the 66GG genotype frequencies increased from lower values (23.7% and 5.4%, respectively) in Shandong to higher values (29.2% and 8.6%, respectively) in Hainan. The overall frequency of the 677T allele, 677TT genotype, 1298C allele, 1298CC genotype, 66G allele and 66GG genotype in the Chinese Han population was 45.2%, 23.2%, 18.6%, 3.9%, 25.7%, and 6.6%, respectively. No gender differences were found in the prevalence of both the MTHFR C677T and MTRR A66G polymorphisms.

Conclusions

This study indicates that there are marked geographical variations in the prevalence of the three polymorphisms among Chinese Han populations. Our baseline data may be useful for future researches in related fields.

Polymorphism 677C → T MTHFR gene in Mexican mothers of children with complex congenital heart disease

Congenital heart defects (CHD) are the third leading cause of death in children <1 year of age in Mexico where there is a high prevalence of the 677C → T polymorphism of the MTHFR gene. This is important because the homozygous 677T/T MTHFR gene and deficiency of folic acid (FA) intake have been associated with CHD. Our objective was to analyze the possible association between the genotype 677T/T of the MTHFR gene and supplementation of FA in Mexican women with the presence of complex CHD in their children. We analyzed genotypes of 31 mothers of children with complex CHD (group I) and 62 mothers of healthy children (group II) and investigated FA supplementation during pregnancy in both study groups. Allele frequencies in group I were 41.9 % for C and 58.1 % for T and 22.6 % for genotype frequencies CC, 38.7 % for CT, and 38.7 % for TT. Allele frequencies in group II were 63.7 % for C and 36.3 % for T and 38.7 % for genotype frequencies CC, 50 % for CT and 11.3 % for TT. Both populations are in Hardy-Weinberg equilibrium. Odds ratio for having a child with a complex CHD was 5.9, p = 0.008 (95 % CI 1.67; 20.63) for the TT genotype. FA supplementation at any time during pregnancy was 90.3 and 87.9 % in groups II and I respectively (p > 0.05). Association was found between the maternal genotype (677/TT MTHFR) with the presence of complex CHD in their offspring. No differences in FA supplementation during any stage were found between groups.

Cervical cancer with polymorphism in MTHFR C677T gene: a systematic review and meta-analysis

To perform a meta-analysis investigating the association of MTHFR C677T polymorphism and susceptibility of cervical cancer. All case-control studies published in English and Chinese with estimates of the relationship between MTHFR C677T polymorphism and risk of cervical cancer were analyzed using odds ratio (OR) with 95 % confidence interval (CI). A total of 10 studies (2,023 cases and 2,570 controls) were included in the meta-analysis. No significant association was observed between T allele and C allele (OR = 0.90; 95 %CI = 0.70-1.17; P = 0.43), and for genotype TT versus CC (OR = 1.09; 95 %CI = 0.74-1.61; P = 0.67), CT versus CC (OR = 0.95; 95 %CI = 0.75-1.20; P = 0.65), CT + TT versus CC (OR = 0.91; 95 %CI = 0.66-1.24; P = 0.55). The current meta-analysis results suggest that the MTHFR C677T polymorphism may not be associated with cervical cancer.

Effect on risk of anencephaly of gene-nutrient interactions between methylenetetrahydrofolate reductase C677T polymorphism and maternal folate, vitamin B12 and homocysteine profile

OBJECTIVE

To evaluate the effects on anencephaly risk of the interaction between the maternal profile of folate, vitamin B12 and homocysteine and the 677C→T polymorphism in the gene encoding methylenetetrahydrofolate reductase (MTHFR).

DESIGN

Case-control study paired (1:1) on maternity clinic, date of birth and state of residence. Cases of anencephaly were identified using the Registry of the Mexican Neural Tube Defect Epidemiological Surveillance System. Case and control mothers were selected from the same maternity departments. All mothers completed a structured questionnaire and blood samples were obtained to determine the MTHFR 677C→T polymorphism and biochemical profile.

SETTING

Mexico, Puebla and Guerrero states, Mexico.

SUBJECTS

A total of 151 mothers of cases and controls were enrolled from March 2000 to February 2001. We had complete information on biochemical profile and MTHFR C677T polymorphism for ninety-eight mothers of cases and ninety-one mothers of controls.

RESULTS

The adjusted models show that the risk of anencephaly in mothers with 677TT genotype was reduced by 18 % (OR = 0·82; 95 % CI 0·72, 0·94) for each 1 ng/ml increment in serum folate. In terms of tertiles, mothers with 677TT genotype with serum folate levels in the upper tertile (>14·1 ng/ml) had a 95 % lower risk to have a child with anencephaly than mothers with serum folate levels in the first and second tertiles (P trend = 0·012).

CONCLUSIONS

Our data agree with the hypothesis of a gene-nutrient interaction between MTHFR 677C→T polymorphism and folate status. We observed a protective effect on anencephaly risk only in mothers with 677TT genotype as serum folate levels increased.

Genetic aspects of folate metabolism

The vitamin folate functions within the cell as a carrier of one-carbon units. The requirement for one-carbon transfers is ubiquitous and all mammalian cells carry out folate dependent reactions. In recent years, low folate status has been linked to risk of numerous 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 inadequate intake of folate seems to be the primary contributor but there is also evidence that an underlying genetic susceptibility can play a modest role by causing subtle alterations in the availability, metabolism or distribution of intermediates in folate related pathways. Folate linked one-carbon units are essential for DNA synthesis and repair and as a source of methyl groups for biological methylation reactions. The notion of common genetic variants being linked to risk of disease was relatively novel in 1995 when the first functional folate-related polymorphism was discovered. Numerous polymorphisms have now been identified in folate related genes and have been tested for functionality either as a modifier of folate status or as being associated with risk of disease. Moreover, there is increasing research into the importance of folate-derived one-carbon units for DNA and histone methylation reactions, which exert crucial epigenetic control over cellular protein synthesis. It is thus becoming clear that genetic aspects of folate metabolism are wide-ranging and may touch on events as disparate as prenatal imprinting to cancer susceptibility. This chapter will review the current knowledge in this area.

Methylenetetrahydrofolate reductase gene 677CT polymorphism and isolated congenital heart disease in a Mexican population

INTRODUCTION AND OBJECTIVES

The frequency of the 677C>T mutation in the methylenetetrahydrofolate reductase gene in Mexico is one of the highest worldwide. Some studies have shown that both the homozygous state of this mutation and a high homocysteine concentration are associated with congenital heart disease. The aim of this study was to determine whether this association exists in the Mexican population.

METHODS

Genotypes were analyzed in 60 patients with congenital heart disease and in their mothers, and the levels of homocysteine were determined in the latter group. The genotypes were compared with those of a control group (n=62) and of their mothers. All the possible mother-child genotype combinations were also compared.

RESULTS

There were no significant differences in allele or genotype frequencies between the patients with congenital heart disease and the controls or their respective mothers (P>.05). Although no significant differences were observed when the homocysteine concentrations in the presence of the CC or the TT genotype were compared, a clear trend was observed (P=.0621). We found no significant differences in homocysteine concentrations in relation to folic acid intake. The study cases and controls did not differ in terms of the possible combinations of mother-child genotypes.

CONCLUSIONS

The frequencies obtained were consistent with those reported for Mexico. No significant differences were found between groups. Nor did we find any association between TT mutations in both the mother and child and hyperhomocysteinemia. There was no evidence of an association between any of the mother-child genotype combinations and congenital heart disease. Similar studies with larger numbers of patients are required to confirm or refute some of the trends observed in this report.

Methylenetetrahydrofolate reductase (MTHFR) gene C677T, A1298C and G1793A polymorphisms: association with risk for clear cell renal cell carcinoma and tumour behaviour in men

AIMS

Methylenetetrahydrofolate reductase (MTHFR) plays a crucial role in regulating folate metabolism, which affects DNA synthesis and methylation. This study investigated whether MTHFR C677T, A1298C and G1793A polymorphisms modified clear cell renal cell carcinoma (CCRCC) risk independently as well as in combination with serum total homocysteine (Hcy) and folate levels.

MATERIALS AND METHODS

A case-control study of 152 cases (men) and 304 age-matched healthy controls was conducted in one geographical area of Iran. Genotyping of MTHFR gene polymorphisms was carried out using a polymerase chain reaction restriction fragment length polymorphism technique. Serum levels of total Hcy, folate and vitamin B12 were also determined.

RESULTS

The MTHFR 677T and 1298C allele frequencies were 42.8 and 47.4% in cases, compared with 33.7 and 33.1% in controls. After controlling for confounding factors, a significant increase in CCRCC risk was found among carriers of the 677CT genotype compared with those with the 677CC genotype (odds ratio 2.21, 95% confidence interval 1.31-3.76), with a significant trend (P=0.014). Statistically significant odds ratios were also found in patients homozygous for MTHFR C677T, who have a 1.58-fold higher risk of developing CCRCC (95% confidence interval=1.21-2.44; P=0.024). Compared with the MTHFR 677CC genotype, the odds ratio (95% confidence interval) for the MTHFR 677TT genotype was 6.18 (95% confidence interval=4.75-8.34) for stage IV cancer and 4.68 (95% confidence interval=2.72-6.54) for grade 3 CCRCC (both P=0.0001). After adjustment for selected variants, the MTHFR 1298AC genotype showed a significantly increased risk of CCRCC compared with the wild-type (odds ratio=3.71, 95% confidence interval=2.22-5.33; P=0.001), and the 1298C allele carrier showed a positive association with the risk of CCRCC compared with the wild-type (odds ratio=3.9, 95% confidence interval=2.55-6.02; P=0.001). Furthermore, subjects carrying at least one copy of the variant allele showed a 4.4 times increased risk of developing CCRCC than their control counterparts (odds ratio=4.40, 95% confidence interval=2.41-6.72; P=0.0001). There was not a significant interaction between MTHFR polymorphisms and serum levels of total Hcy and folate in increasing the risk of CCRCC.

CONCLUSIONS

Our results provide evidence that the MTHFR polymorphisms might contribute to increased CCRCC risk in men.

C677T polymorphism of the 5,10 MTHFR gene in young Mexican subjects with ST-elevation myocardial infarction

BACKGROUND AND AIMS

The C677T polymorphism of 5,10 methylenetetrahydrofolate reductase (MTHFR) gene has been associated with hypertension and coronary artery disease in several populations worldwide, but results are still controversial. The aim of this study was to examine the possible association of C677T polymorphism with ST-elevation myocardial infarction (STEMI) in young Mexican subjects.

METHODS

In a case-control study, 167 unrelated patients < or = 45 years of age with diagnosis of STEMI who were admitted to a cardiovascular intense care unit and 167 unrelated controls subjects matched by age and gender were recruited from January 2006 and June 2009. The C677T polymorphism was determined in all participants by a polymerase chain reaction-restriction fragment length polymorphism assay (PCR-RFLP).

RESULTS

There was no significant difference in the genotype distribution between groups (p = 0.69) or allele frequency (p = 0.40). There were independent factors for STEMI: smoking (OR 4.9, 95% CI 3.0-8.1, p = 0.001), hypertension (OR 1.8, 95% CI 1.0-3.3, p = 0.03), family history of atherothrombotic disease (OR 2.3, 95% CI 2.0-4.6, p = 0.02), and dyslipidemia (OR 3.2, 95% CI 1.8-5.6, p <0.001). Diabetes mellitus did not represent an independent risk factor for STEMI (OR 1.2, 95% CI 0.2-2.2, p = 0.82).

CONCLUSIONS

The TT genotype from the C677T of 5,10 MTHFR gene is not an independent risk factor for STEMI in the Mexican population. However, more studies are needed to determine the possible "protective effect" of the C677T polymorphism in our population.

Dietary folate and vitamin B12 intake before diagnosis decreases gastric cancer mortality risk among susceptible MTHFR 677TT carriers

OBJECTIVE

To assess gastric cancer survival in relation to dietary intake of methyl donors and the methylenetetrahydrofolate reductase 677C>T (MTHFR 677C>T) polymorphism.

METHODS

A prospective cohort of 257 incidental, histologically confirmed gastric cancer cases was assembled in January 2004 and followed until June 2006. Patients were recruited from the main oncology and/or gastroenterology units in Mexico City and were queried regarding their sociodemographic information, clinical history, and dietary habits 3 y before the onset of their symptoms. The intake of methyl donors was estimated with a food-frequency questionnaire and the MTHFR 677C>T polymorphisms were determined by polymerase chain reaction/restriction fragment length polymorphism analysis. Cox's multivariate regression models were used to estimate the mortality risk of gastric cancer.

RESULTS

MTHFR 677TT carriers with low folate and vitamin B12 intakes had the lowest survival rate in cases of gastric cancer. High intakes of folate and vitamin B12 before diagnosis was associated with decreased gastric cancer mortality risk in susceptible MTHFR 677TT carriers (mortality risk for folate 0.14, 95% confidence interval 0.04-0.46, P for trend=0.001; mortality risk for vitamin B12 0.23, 95% confidence interval 0.08-0.66, P for trend=0.008).

CONCLUSION

Folate and related B vitamins may be used as an intervention strategy to improve the survival outcome of gastric cancer.

The search for genetic polymorphisms in the homocysteine/folate pathway that contribute to the etiology of human neural tube defects

In this paper, we trace the history of current research into the genetic and biochemical mechanisms that underlie folate-preventable neural tube defects (NTDs). The inspired suggestion by Smithells that common vitamins might prevent NTDs ignited a decade of biochemical investigations-first exploring the nutritional and metabolic factors related to NTDs, then onto the hunt for NTD genes. Although NTDs were known to have a strong genetic component, the concept of common genetic variance being linked to disease risk was relatively novel in 1995, when the first folate-related polymorphism associated with NTDs was discovered. The realization that more genes must be involved started a rush to find polymorphic needles in genetic haystacks. Early efforts entailed the intellectually challenging and time-consuming task of identifying and analyzing candidate single nucleotide polymorphisms (SNPs) in folate pathway genes. Luckily, human genome research has developed rapidly, and the search for the genetic factors that contribute to the etiology of human NTDs has evolved to mirror the increased level of knowledge and data available on the human genome. Large-scale candidate gene analysis and genome-wide association studies are now readily available. With the technical hurdles removed, the remaining challenge is to gather a sample large enough to uncover the polymorphisms that contribute to NTD risk. In some respects the real work is beginning. Although moving forward is exciting, it is humbling that the most important result-prevention of NTDs by maternal folic acid supplementation-was achieved years ago, the direct result of Smithells' groundbreaking studies.

Maternal MTHFR 677C>T genotype and dietary intake of folate and vitamin B(12): their impact on child neurodevelopment

Using the Bayley test, the mental and psychomotor development in a cohort of 253 children were evaluated. Maternal dietary intake of vitamin B(12) and folate was assessed from a semiquantitative questionnaire administered during the first trimester of pregnancy. Maternal genotypes of MTHFR (677C>T and 1298A>C), were ascertained by PCR-RFLP. The 677T and 1298C variant alleles were present in 59% and 10% of participants, respectively. A dietary deficiency of vitamin B(12) was negatively associated with mental development (beta = -1.6; 95% CI = -2.8 to -0.3). In contrast, dietary intake of folate (< 400 mg/day) reduced the mental development index only among children of mothers who were carriers of the TT genotype (beta = -1.8; 95% CI = -3.6 to -0.04; P for interaction = 0.07). Vitamin B(12) and folate supplementation during pregnancy could have a favorable impact on the mental development of children during their first year of life, mainly in populations that are genetically susceptible.

Maternal MTHFR polymorphisms and risk of spontaneous abortion

OBJECTIVE

To asses the association between intake of folate and B vitamins and the incidence of spontaneous abortion (SA) according to the maternal methylenetetrahydrofolate reductase (MTHFR) polymorphisms (677 C>T and 1298 A>C).

MATERIAL AND METHODS

We conducted a nested case-control study within a perinatal cohort of women recruited in the state of Morelos, Mexico. Twenty-three women with SA were compared to 74 women whose pregnancy survived beyond week 20th. Intake of folate and B vitamins respectively, was estimated using a validated food frequency questionnaire. Maternal MTHFR polymorphisms were determined by PCR-RFLP and serum homocysteine levels by HPLC.

RESULTS

Carriers of MTHFR 677TT and 1298AC genotypes respectively showed an increased risk of SA (OR 677TT vs. CC/CT=5.0; 95% CI: 1.2, 20.9 and OR 1298 AC vs. AA=5.5; 95% CI: 1.1, 26.6).

CONCLUSIONS

Our results support the role of MTHFR polymorphisms as a risk factor for SA, regardless of dietary intake of B vitamins.

Human genetic selection on the MTHFR 677C>T polymorphism

Background

The prevalence of genotypes of the 677C>T polymorphism for the MTHFR gene varies among humans. In previous studies, we found changes in the genotypic frequencies of this polymorphism in populations of different ages, suggesting that this could be caused by an increase in the intake of folate and multivitamins by women during the periconceptional period. The aim was to analyze changes in the allelic frequencies of this polymorphism in a Spanish population, including samples from spontaneous abortions (SA).

Methods

A total of 1305 subjects born in the 20th century were genotyped for the 677C>T polymorphism using allele specific real-time PCR with Taqman^® probes. A section of our population (n = 276) born in 1980–1989 was compared with fetal samples (n = 344) from SA of unknown etiology from the same period.

Results

An increase in the frequency of the T allele (0.38 vs 0.47; p < 0.001) and of the TT genotype (0.14 vs 0.24; p < 0.001) in subjects born in the last quarter of the century was observed. In the 1980–1989 period, the results show that the frequency of the wild type genotype (CC) is about tenfold lower in the SA samples than in the controls (0.03 vs 0.33; p < 0.001) and that the frequency of the TT genotype increases in the controls (0.19 to 0.27) and in the SA samples (0.20 to 0.33 (p < 0.01)); r = 0.98.

Conclusion

Selection in favor of the T allele has been detected. This selection could be due to the increased fetal viability in early stages of embryonic development, as is deduced by the increase of mutants in both living and SA populations.

Discussion: Effects of Folate and Vitamin B12 Deficiencies During Pregnancy on Fetal, Infant, and Child Development

The essentiality of folate and vitamin B12 for the synthesis of DNA may interfere with a successful pregnancy outcome when the mother is deficient in these micronutrients. The objective of this paper is to assess the effects of folate and vitamin B12 deficiencies on pregnancy outcomes, other than neural tube defects (NTD), and the effects of these deficiencies on infant and child development.

Supplementation studies identified by two Cochran Reviews were selected to assess the impact of folate deficiency on pregnancy outcomes, and a systematic review of the literature was used to assess their effects on infant and child developments.

Folate supplementation consistently resulted in improvement of hematological and folate status indicators. Seven supplemental studies consistently found no differences in the risk of total fetal loss, early or late miscarriage, stillbirth, preeclampsia, perinatal death, neonatal death, preterm birth, small-for-gestational age, or infant death in supplemented women compared with their controls. Two of those studies found greater placental weights (difference 96 g; 95% CI, 30.7 to 161.2 g), birthweights (difference 312 g; 95% CI, 108.5 to 515.4 g), and a lower risk for newborns weighing < 2,500 g in supplemented women (RR = 0.94; 95% CI, 0.90 to 0.99). Abnormal vitamin B12 and homocysteine serum concentrations were more readily associated with poor pregnancy outcomes. The very few studies addressing the effects of folate and vitamin B12 deficiencies on infant and child development were inconclusive.

Early supplementation with folate to pregnant women improves hematological and folate status indicators, but has little or no effect on pregnancy outcomes, other than on NTD. Vitamin B12 deficiencies and low homocysteine are more readily associated with poor pregnancy outcomes.

Methylenetetrahydrofolate reductase (MTHFR) C677T and thymidylate synthase promoter (TSER) polymorphisms in Indonesian children with and without leukemia

Genetic variations in the polymorphic tandem repeat sequence of the enhancer region of the thymidylate synthase promoter (TSER), as well as in methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism, influence methotrexate sensitivity. We studied these polymorphisms in children with acute lymphoblastic leukaemia (ALL) and in subjects without malignancy in Indonesia and Holland. The frequencies of TT and CT genotypes were two-fold higher in Dutch children. The TSER 3R/3R repeat was three-fold more frequent in the Indonesian children, while the 2R/2R repeat was only 1% compared to 21% in the Dutch children. No differences of these polymorphisms were found between ALL cells and normal blood cells, indicating an ethnic rather than leukemic origin. These results may have implications for treatment of Indonesian children with ALL.

Methylenetetrahydrofolate reductase gene polymorphisms and the risk of anencephaly in Mexico

The precise etiology of neural tube defects (NTDs) is not known. There is some evidence that mutations in MTHFR gene provide susceptibility to NTDs in some populations; however, other studies have not found this association. One of the problems with previous studies is that they treat NTDs as a homogeneous group, when specific defects could have different etiologies. We conducted a case-control study specifically for anencephaly, based on the Mexican Epidemiological Surveillance System of Neural Tube Defects to evaluate its association with maternal MTHFR 677C > T and 1298A > C polymorphisms, in three states with high frequencies of NTDs: Puebla, Estado de México and Guerrero. We interviewed and collected blood samples from 118 case mothers and 112 control mothers. The questionnaire included information on their reproductive history, socioeconomic characteristics, prenatal care, tobacco and alcohol use, presence of chronic diseases, acute illnesses and fever, consumption of multivitamins and drugs during the periconceptional period. After adjusting for potential confounders, the risk from the mutated homozygous mothers (677TT genotype) was significantly higher than that from mothers with 677CC genotype (OR 3.16, 95% CI 1.29-7.73); in the case of the heterozygous mothers, an increased risk of anencephaly was observed, even though this was not statistically significant (OR 1.81 95% CI 0.78-4.25). The association found between maternal 677TT genotype and anencephaly and the elevated presence of the 677T allele among Mexican women of fertile age urges intensifying folic acid supplementation which has proved to modify this genetic risk in other populations.

Prevalence of methylenetetrahydrofolate reductase 677T and 1298C alleles and folate status: a comparative study in Mexican, West African, and European populations

BACKGROUND

Methylenetetrahydrofolate reductase (MTHFR) 677C-->T polymorphism is heterogeneously distributed worldwide, with the highest and lowest frequencies of the T allele in Mexico and Africa, respectively, and a south-to-north gradient in Europe. Distribution of MTHFR 1298A-->C is less well known. It has been hypothesized that 677T frequency could result in part from gene-nutrient interactions.

OBJECTIVE

The objective was to compare the association of 677T and 1298C alleles with plasma concentrations of homocysteine, folate, and vitamin B-12 in geographical areas with contrasting 677T allele frequencies.

DESIGN

Healthy young adults (n = 1277) were recruited in Mexico City, the West African countries of Bénin and Togo, France, and Sicily (Italy). Homocysteine, folate, and vitamin B-12 were measured in plasma, and MTHFR polymorphisms were measured in genomic DNA.

RESULTS

Mexico City and Sicily reported the highest and Bénin and Togo reported the lowest plasma concentrations of folate. Mexico City had the highest 677T allele prevalence and the lowest influence of 677TT genotype on homocysteine, whereas the opposite was observed in Africa. The prevalence of the 1298C allele was lowest in the Mexicans and Africans and highest in the French. The percentage of the 677T genotype was significantly associated with the folate concentrations in 677CC carriers in a univariate analysis (R = 0.976; 95% CI: 0.797, 0.996; P < 0.0002) and in a multiple regression model that included homocysteine, vitamin B-12, and age (P = 0.0002).

CONCLUSION

Our data agree with the hypothesis of a gene-nutrient interaction between MTHFR 677C-->T polymorphism and folate status that may confer a selective advantage of TT-homozygous genotype when dietary intake of folate is adequate, at least in the areas studied.

Exposure to fumonisins and the occurrence of neural tube defects along the Texas-Mexico border

Along the Texas-Mexico border, the prevalence of neural tube defects (NTDs) among Mexican-American women doubled during 1990-1991. The human outbreak began during the same crop year as epizootics attributed to exposure to fumonisin, a mycotoxin that often contaminates corn. Because Mexican Americans in Texas consume large quantities of corn, primarily in the form of tortillas, they may be exposed to high levels of fumonisins. We examined whether or not maternal exposure to fumonisins increases the risk of NTDs in offspring using a population-based case-control study. We estimated fumonisin exposure from a postpartum sphinganine:sphingosine (sa:so) ratio, a biomarker for fumonisin exposure measured in maternal serum, and from maternal recall of periconceptional corn tortilla intake. After adjusting for confounders, moderate (301-400) compared with low (< or = 100) consumption of tortillas during the first trimester was associated with increased odds ratios (ORs) of having an NTD-affected pregnancy (OR = 2.4; 95% confidence interval, 1.1-5.3). No increased risks were observed at intakes higher than 400 tortillas (OR = 0.8 for 401-800, OR = 1.0 for > 800). Based on the postpartum sa:so ratio, increasing levels of fumonisin exposure were associated with increasing ORs for NTD occurrences, except for the highest exposure category (sa:so > 0.35). Our findings suggest that fumonisin exposure increases the risk of NTD, proportionate to dose, up to a threshold level, at which point fetal death may be more likely to occur. These results also call for population studies that can more directly measure individual fumonisin intakes and assess effects on the developing embryo.

Influence of human genetic variation on nutritional requirements

Genetic variation is known to affect food tolerances among human subpopulations and may also influence dietary requirements, giving rise to the new field of nutritional genomics and raising the possibility of individualizing nutritional intake for optimal health and disease prevention on the basis of an individual's genome. However, because gene-diet interactions are complex and poorly understood, the use of genomic knowledge to adjust population-based dietary recommendations is not without risk. Whereas current recommendations target most of the population to prevent nutritional deficiencies, inclusion of genomic criteria may indicate subpopulations that may incur differential benefit or risk from generalized recommendations and fortification policies. Current efforts to identify gene alleles that affect nutrient utilization have been enhanced by the identification of genetic variations that have expanded as a consequence of selection under extreme conditions. Identification of genetic variation that arose as a consequence of diet as a selective pressure helps to identify gene alleles that affect nutrient utilization. Understanding the molecular mechanisms underlying gene-nutrient interactions and their modification by genetic variation is expected to result in dietary recommendations and nutritional interventions that optimize individual health.

Dietary and genetic determinants of homocysteine levels among Mexican women of reproductive age

OBJECTIVE

To evaluate the independent and joint effects of dietary folate, vitamin B(12) consumption and methylenetetrahydrofolate reductase (MTHFR) polymorphisms (677C>T and 1298A>C) on the circulating folate and homocysteine (Hcy) levels among Mexican women of reproductive age.

DESIGN

A cross-sectional, population-based study.

SUBJECTS

The first 130 healthy non-pregnant women (aged 16-34 years) who agreed to participate in a reproductive cohort in Morelos, Mexico.

MAIN OUTCOME MEASUREMENTS

Dietary intakes of vitamin B(12) and folate were estimated using a semiquantitative food frequency questionnaire. MTHFR 677C>T and 1298A>C polymorphisms were ascertained using the PCR-based method. Serum levels of Hcy and folate were determined using high-performance liquid chromatography and radioimmunoassay, respectively.

RESULTS

Genotype frequencies for the MTHFR 677C>T polymorphism were 21.5% (CC), 52.3% (CT) and 26.2% (TT) among Mexican women. Of the population, 22% had the MTHFR 1298AC genotype, while no individual carried the 1298CC genotype. We observed an increased level of Hcy among carriers of the 677TT genotype, compared to carriers of the 677CC genotype. The highest level of Hcy was observed among MTHFR 677TT carriers with low B(12) intake (<2.0 microg/day), which resulted with a significant interaction (P=0.01).

CONCLUSION

Vitamin B(12) is an important determinant of Hcy levels in Mexico. Supplementation of folic acid with vitamin B(12) may be preferable when the MTHFR 677T variant allele is prevalent.

Methylenetetrahydrofolate reductase 677C>T polymorphism and gastric cancer susceptibility in Mexico

This study investigated whether methylenetetrahydrofolate reductase MTHFR 677C>T polymorphism modified gastric cancer (GC) risk independently as well as in combination with folate intake and alcohol consumption. A hospital-based case-control study of 201 cases and 427 controls was conducted in three geographical areas of Mexico, between 1994 and 1996. The MTHFR 677T allele frequency was 51.0% in cases compared with 45.3% in controls. After controlling for dietary sources of folate, alcohol intake and other selected variables, a significant increase in GC risk was found among carriers of the 677TT genotype compared with those with the 677CC genotype (odds ratio (OR) 1.62, 95% confidence interval (CI) 1.00-2.59), with a significant trend (P = 0.048). There were no significant interactions between the MTHFR polymorphism and consumption of folate and alcohol. Our results suggest that the high prevalence of MTHFR 677T allele may be a contributor to the high rate of morbidity and mortality in GC in Mexico.

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.

Differences in the frequency of the C677T mutation in the methylenetetrahydrofolate reductase (MTHFR) gene among the Lebanese population

In view of its role in precipitating mild hyperhomocysteinemia as well as being a risk factor for vascular thrombosis, we investigated the frequency of the C677T mutation of the methylenetetrahydrofolate reductase (MTHFR) gene among 589 healthy Lebanese subjects by PCR-RFLP analysis (HinfI digestion) and compared them with those of other countries of Caucasian and non-Caucasian origin. The prevalence of the mutated homozygous (T/T) and heterozygous (C/T) C677T MTHFR genotype was 11.04% and 39.73%, respectively, giving an allele frequency of 0.309. While the prevalence of the T/T genotype was similar with respect to gender, higher prevalence was noted among Christian (13.08%) compared to Moslem (7.66%) subjects (P < 0.001), and heterogeneity in its distribution was seen in the different Lebanese provinces, and was directly related to the Christian/Moslem composition of each province. The distribution of the MTHFR C677T in Lebanon is unique with regard to its higher occurrence among Christians compared to Moslems, adding to the existing body of literature on the heterogeneity of its prevalence and distribution.

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.

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.