Methylenetetrahydrofolate reductase (MTHFR): the incidence of mutations C677T and A1298C in the Ashkenazi Jewish population.

The polymorphic mutation C677T in the gene of MTHFR is considered a risk mutation for spina bifida and vascular disease. Another common mutation on the MTHFR gene, A1298C, has also been described as another risk mutation. We studied the frequencies of these two mutations on DNA samples from healthy Jewish individuals and compared them to the frequency of these mutations in DNA samples obtained from healthy individuals in South Texas. The presence of the C677T allele was determined by PCR and Hinf I digestion, and mutation A1298C by PCR and Mbo II digestion. A total of 310 alleles was examined for C677T in the Ashkenazi samples and 400 alleles in the non-Jewish samples. The rate of C677T among the Ashkenazi Jewish alleles was 47.7% as compared to 28.7% among the alleles from the non-Jewish population. The difference is statistically significant, P < 0.0005. Mutation A1298C was examined in 298 alleles of Jewish individuals and 374 alleles of non-Jewish counterparts from Texas. The rate of the A1298C mutation in the Jewish samples was 27.2% whereas in the non-Jewish was 35%. This was also statistically significant, P < 0.031. No individuals were homozygous for both mutations or were found to be homozygous for one mutation with heterozygosity of the other mutation, and that the C677T and the A1298C alleles did not occur in cis position. This study shows a unique distribution of C677T and the A1298C alleles among the Ashkenazi Jews. In spite of high frequency of C677T mutation, spina bifida is less common among Ashkenazi Jews. Further studies are needed to establish whether the C677T and the A1298C mutations have an impact on vascular disease in the Ashkenazi Jewish population.     

Decreased methylene tetrahydrofolate reductase activity due to the 677C→T mutation in families with spina bifida offspring

 Periconceptional folate intake reduces both the occurrence and recurrence risk of neural tube defects. Plasma homocysteine levels can be elevated in mothers of a child with a neural tube defect, suggesting a dysfunctional folate metabolism. Very recently we showed that a common 677C→T mutation in the 5,10-methylene tetrahydrofolate reductase gene, causing thermolability of the enzyme, is a risk factor for spina bifida offspring. Restriction enzyme analysis of the genomic 5,10-methylene tetrahydrofolate reductase polymerase chain reaction fragment revealed a significantly higher prevalence of a +/+ genotype among spina bifida patients and their mothers. The risk for spina bifida offspring is the strongest if both the mother and her child have the mutation in the homozygous state. Enzymatic analysis showed that homozygosity for the 677C→T mutation causes a decreased 5,10-methylene tetrahydrofolate reductase activity, resulting in elevated plasma homocysteine and red blood cell folate levels and lowered plasma folate and cysteine values. This extended study demonstrates that a nucleotide substitution in the coding region of 5,10-methylene tetrahydrofolate reductase, resulting in reduced activity and an impaired homocysteine and folate metabolism, is a genetic risk factor for spina bifida. Received: 24 May 1996 / Accepted: 14 August 1996     

Methylenetetrahydrofolate reductase (MTHFR): The incidence of mutations C677T and A1298C in the Ashkenazi Jewish population

The polymorphic mutation C677T in the gene of MTHFR is considered a risk mutation for spina bifida and vascular disease. Another common mutation on the MTHFR gene, A1298C, has also been described as another risk mutation. We studied the frequencies of these two mutations on DNA samples from healthy Jewish individuals and compared them to the frequency of these mutations in DNA samples obtained from healthy individuals in South Texas. The presence of the C677T allele was determined by PCR and Hinf I digestion, and mutation A1298C by PCR and Mbo II digestion. A total of 310 alleles was examined for C677T in the Ashkenazi samples and 400 alleles in the non-Jewish samples. The rate of C677T among the Ashkenazi Jewish alleles was 47.7% as compared to 28.7% among the alleles from the non-Jewish population. The difference is statistically significant, P < 0.0005. Mutation A1298C was examined in 298 alleles of Jewish individuals and 374 alleles of non-Jewish counterparts from Texas. The rate of the A1298C mutation in the Jewish samples was 27.2% whereas in the non-Jewish was 35%. This was also statistically significant, P < 0.031. No individuals were homozygous for both mutations or were found to be homozygous for one mutation with heterozygosity of the other mutation, and that the C677T and the A1298C alleles did not occur in cis position. This study shows a unique distribution of C677T and the A1298C alleles among the Ashkenazi Jews. In spite of high frequency of C677T mutation, spina bifida is less common among Ashkenazi Jews. Further studies are needed to establish whether the C677T and the A1298C mutations have an impact on vascular disease in the Ashkenazi Jewish population. Am. J. Med. Genet. 86:380–384, 1999. © 1999 Wiley-Liss, Inc.     

A second common variant in the methylenetetrahydrofolate reductase (MTHFR) gene and its relationship to MTHFR enzyme activity, homocysteine, and cardiovascular disease risk

Molecular defects in genes encoding enzymes involved in homocysteine metabolism may account for mild hyperhomocysteinemia, an independent and graded risk factor for cardiovascular disease (CVD). We examined the relationship of two polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene, the 677C-->T and 1298A-->C variants, to MTHFR activity, homocysteine concentrations, and risk of CVD in a population of 190 vascular disease patients and 601 apparently healthy controls. The mean specific and residual MTHFR activities were significantly lower in 677CT and 677TT individuals (both P<0.001). The 1298A-->C mutation alone showed no effect on MTHFR activities. However, when the 677C-->T genotype was taken into account, the 1298A-->C mutation also caused a significant decrease in MTHFR activities, which was observed in both the homozygous 1298CC (P<0.001) and the heterozygous 1298AC states (P=0.005). Both the 677TT as the 677CT genotypes were associated with significantly higher fasting and postload homocysteine levels than 677CC (P<0.001 and P=0.003, respectively). The 1298A-->C mutation had no effect on fasting or postload homocysteine levels. Since homocysteine itself is considered to be positively associated with the risk of CVD, these findings indicate that the 1298A-->C mutation cannot be considered a major risk factor for CVD.     

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.     

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.     

Folate gene polymorphisms and the risk of Down syndrome pregnancies in young Italian women

Maternal impairments in folate metabolism and elevated homocysteinemia are known risk factors for having a child with Down syndrome (DS) at a young age. The 80G>A polymorphism of the reduced folate carrier gene (RFC-1) has been recently demonstrated to affect plasma folate and homocysteine levels, alone or in combination with the 677C>T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene. We performed the present study on 80 Italian mothers of DS individuals, aged less than 35 at conception, and 111 Italian control mothers, to study the role of the RFC-1 80G>A, MTHFR 677C>T, and MTHFR 1298A>C genotypes to the risk of a DS offspring at a young maternal age. When polymorphisms were considered alone, both allele and genotype frequencies did not significantly differ between DS mothers and control mothers. However, the combined MTHFR677TT/RFC-1 80GG genotype was borderline associated with an increased risk (OR 6 (CI 95%: 1.0-35.9), P = 0.05), and to be MTHF1298AA/RFC-1 80(GA or AA) was inversely associated with the risk (OR 0.36 (CI 95%: 0.14-0.96), P = 0.04). Present results seem to indicate that none of the RFC-1 80G>A, MTHFR 677C>T, and MTHFR 1298A>C polymorphisms is an independent risk factor for a DS offspring at a young maternal age; however, a role for the combined MTHFR/RFC-1 genotypes in the risk of DS pregnancies among young Italian women cannot be excluded.     

Single nucleotide polymorphisms in the methylenetetrahydrofolate reductase gene are common in US Caucasian and Hispanic American populations

To investigate the prevalence of the C677T and A1298C single nucleotide polymorphisms (SNPs) in the methylenetetrahydrofolate reductase (MTHFR) gene in Caucasian and Hispanic populations, EDTA-anticoagulated whole blood specimens were collected from a total of 100 random patients, 50 Caucasians and 50 Hispanics of Puerto Rican dissent. The prevalence of the two MTHFR SNPs was determined by polymerase chain reaction (PCR) mediated restriction fragment length polymorphism analysis. In the Caucasian population, homozygosity for the MTHFR A1298C SNP was detected in 4% (2/50) of the individuals tested, while 42% (21/50) were heterozygous for this SNP. Among Hispanics, 4% (2/50) were homozygous and 38% (19/50) heterozygous for the A1298C SNP. Homozygosity for the C677T MTHFR SNP was detected in 16% (8/50) and 10% (5/50) of Caucasians and Hispanics, respectively. In this study, the frequency of the C677T heterozygotes was very high at 56% (28/50) and 52% (26/50) Caucasians and Hispanics, respectively. C677T and A1298C are common SNPs in the MTHFR gene. The high prevalence of these SNPs in both Caucasian and Hispanic populations demonstrates the possibility of compounding effects of these SNPs in the pathogenesis of human diseases. While subgroups of patients may exhibit some clinical phenotype linked to these SNPs, our analysis demonstrates the need for careful interpretation of SNP data in the context of population screening.     

Molecular genetic analysis of human folate receptors in neural tube defects

Neural tube defects (NTDs) are the most common congenital malformations and are considered to have a multifactorial origin, having both genetic and environmental components. Periconceptional folate administration reduces the recurrence and occurrence risk by 70-100%. Recently we discovered the first genetic risk factors for NTDs: the 677 C-->T and the 1298 A-->C mutations in the methylenetetrahydrofolate reductase gene explaining at the most 35-50% of the protective effect of folate. In this study we further explored the genetic component of NTDs by analysing the coding region, including the intron-exon boundaries and signal sequences of the folate receptor genes by SSCP analysis. Among 39 patients with spina bifida (SB), 47 mothers with a child with SB, and 10 controls, no polymorphism was present in the folate receptor alpha (FR-alpha) gene or in the folate receptor beta (FR-beta) gene.     

Polymorphisms in the CBS gene and homocysteine, folate and vitamin B12 levels: association with polymorphisms in the MTHFR and MTRR genes in Brazilian children

Polymorphisms in the methylenetetrahydrofolate reductase (MTHFR), methionine synthase reductase (MTRR) and cystathionine beta-synthase (CBS) genes, involved in the intracellular metabolism of homocysteine (Hcy), can result in hyperhomocysteinemia. The objective of this study was to evaluate prevalence estimates of CBS T833C, G919A and the insertion of 68-bp (844ins68) polymorphisms and their correlation with Hcy, folate and B(12) in 220 children previously genotyped for MTHFR C677T, A1298C, and MTRR A66G. The prevalence of heterozygote children for 844ins68 was 19.5%. The T833C CBS mutation was identified in association with 844ins68 in all the carriers of the insertion. Genotyping for CBS G919A mutation showed that all the children presented the GG genotype. Analysis of Hcy, B(12) and folate, according to the combination of the different genotypes of the C677T and A1298C MTHFR, A66G MTRR, and 844ins68 CBS showed that the 677TT/1298AA/68WW genotype is associated with an increase in Hcy, when compared to the 677CC/1298AC/68WW (P = 0.033) and the 677CT/1298AA/68WW genotypes (P = 0.034). Since B(12) and folate were not different between these groups, a genetic interaction between diverse polymorphisms probably influences Hcy. Our results emphasize the role of genetic interactions in Hcy levels.     

The C677T mutation of the 5,10-methylenetetrahydrofolate reductase gene is a moderate risk factor for spina bifida in Italy.

OBJECTIVE: To estimate the risk for spina bifida associated with the common mutation C677T of the MTHFR gene in a country with a relatively low prevalence of NTDs. DESIGN: Case-control study. SUBJECTS: Cases: 203 living patients affected with spina bifida (173 myelomeningocele and 30 lipomeningocele); controls: 583 subjects (306 young adults and 277 unselected newborns) from northern and central-southern Italy. SETTING: Cases: three spina bifida centres; young adult controls: DNA banks; newborn controls: regional neonatal screening centres. MAIN OUTCOME MEASURES: Prevalence of the C677T genotypes in cases and controls by place of birth; odds ratios for spina bifida and estimated attributable fraction. RESULTS: The prevalence of T/T, T/C, and C/C genotype was 16.6%, 53.7%, and 29.7% in controls and 25.6%, 43.8%, and 30.6% in cases, respectively. We found no differences between type of defect or place of birth. The odds ratio for spina bifida associated with the T/T genotype v C/C plus T/C was 1.73 (95% CI 1.15, 2.59) and the corresponding attributable fraction was 10.8%. No increased risk was found for heterozygous patients (OR=0.79, 95% CI 0.53-1.18). CONCLUSION: This study, as well as the meta-analysis we updated, shows that homozygosity for the MTHFR C677T mutation is a moderate risk factor in Europe, and even in Italy where there is a relatively low prevalence of spina bifida. The estimated attributable fraction associated with this risk factor explains only a small proportion of cases preventable by periconceptional folic acid supplementation. Thus, other genes involved in folate-homocysteine metabolism, their interaction, and the interaction between genetic and environmental factors should be investigated further.     

MTHFR genetic polymorphism as a risk factor in Egyptian mothers with Down syndrome children

Recent reports linking Down syndrome (DS) to maternal polymorphisms at the methylenetetrahydrofolate reductase (MTHFR) gene locus have generated great interest among investigators in the field. The present study aimed at evaluation of MTHFR 677C/T and 1298A/C polymorphisms in the MTHFR gene as maternal risk factors for DS. Forty two mothers of proven DS outcomes and forty eight control mothers with normal offspring were included. Complete medical and nutritional histories for all mothers were taken with special emphasis on folate intake. Folic acid intake from food or vitamin supplements was significantly low (below the Recommended Daily Allowance) in the group of case mothers compared to control mothers. Frequencies of MTHFR 677T and MTHFR 1298C alleles were significantly higher among case mothers (32.1% and 57.1%, respectively) compared to control mothers (18.7% and 32.3%, respectively). Heterozygous and homozygous genotype frequencies of MTHFR at position 677 (CT and TT) were higher among case mothers than controls (40.5% versus 25% and 11.9% versus 6.2%, respectively) with an odds ratio of 2.34 (95% confidence interval [CI] 0.93-5.89) and 2.75 (95% CI 0.95-12.77), respectively. Interestingly, the homozygous genotype frequency (CC) at position 1298 was significantly higher in case mothers than in controls (33.3% versus 2.1% respectively) with an odds ratio of 31.5 (95% CI 3.51 to 282.33) indicating that this polymorphism may have more genetic impact than 677 polymorphism. Heterozygous genotype (AC) did not show significant difference between the two groups. We here report on the first pilot study of the possible genetic association between DS and MTHFR 1298A/C genotypes among Egyptians. Further extended studies are recommended to confirm the present work.     

A1298C methylenetetrahydrofolate reductase mutation and coronary artery disease: relationships with C677T polymorphism and homocysteine/folate metabolism

5, 10-Methylenetetrahydrofolate reductase (MTHFR) is a crucial enzyme in homocysteine/methionine metabolism. The most-studied C677T polymorphism in the MTHFR gene results in a thermolabile variant with reduced activity, and is associated with increased levels of total plasma homocysteine, a risk factor for coronary artery disease. A new mutation in the MTHFR gene (A1298C) has also been reported to lower enzyme activity. Whether A1298C is a risk factor for coronary artery disease, separately or in combination with C677T, and/or relative to total plasma homocysteine and folate status, is unclear to date. We evaluated this hypothesis in 470 angiographically characterized subjects, 302 with coronary artery disease, and 168 with normal coronary arteries. The frequency of the 1298C allele was 0.33 and that of combined heterozygosity 0.315. No difference was found in the frequency of the genotypes or when analyzed for combined heterozygosity between patients with coronary artery disease and normals. Independent of folate status, the 1298C allele was not associated with increased total plasma homocysteine. No additional effect of A1298C on total plasma homocysteine was observed in 148 combined heterozygotes compared with 98 heterozygotes for the C677T alone. These findings do not support a major role for the A1298C mutation in homocysteine metabolism and emphasize the hypothesis that MTHFR genotypes may interfere with coronary artery disease risk only when an unbalanced nutritional status leads to raised total plasma homocysteine levels.     

Genetic polymorphisms in methylenetetrahydrofolate reductase and methionine synthase,folate levels in red blood cells,and risk of neural tube defects

Folic acid administration to women in the periconceptional period reduces the occurrence of neural tube defects (NTDs) in their offspring. A polymorphism in the gene encoding methylenetetrahydrofolate reductase (MTHFR), 677C→12;T, is the first genetic risk factor for NTDs in man identified at the molecular level. The gene encoding another folate-dependent enzyme, methionine synthase (MTR), has recently been cloned and a common variant, 2756A→12;G, has been identified. We assessed genotypes and folate status in 56 patients with spina bifida, 62 mothers of patients, 97 children without NTDs (controls), and 90 mothers of controls, to determine the impact of these factors on NTD risk. Twenty percent of cases and 18% of case mothers were homozygous for the MTHFR polymorphism, compared to 11% of controls and 11% of control mothers, indicating that the mutant genotype conferred an increased risk for NTDs. The risk was further increased if both mother and child had this genotype. The MTR polymorphism was associated with a decreased O.R. (O.R.); none of the cases and only 10% of controls were homozygous for this variant. Red blood cell (RBC) folate was lower in cases and in case mothers, compared to their respective controls. Having a RBC folate in the lowest quartile of the control distribution was associated with an O.R. of 2.56 (95% CI 1.28–5.13) for being a case and of 3.05 (95% CI 1.54–6.03) for being a case mother. The combination of homozygous mutant MTHFR genotype and RBC folate in the lowest quartile conferred an O.R. for being a NTD case of 13.43 (CI 2.49–72.33) and an O.R. for having a child with NTD of 3.28 (CI 0.84–12.85). We propose that the genetic-nutrient interaction—MTHFR polymorphism and low folate status—is associated with a greater risk for NTDs than either variable alone. Am. J. Med. Genet. 84:151–157, 1999. © 1999 Wiley-Liss, Inc.     

A Common Variant in Methionine Synthase Reductase Combined with Low Cobalamin (Vitamin B12) Increases Risk for Spina Bifida

Impairment of folate and cobalamin (vitamin B(12)) metabolism has been observed in families with neural tube defects (NTDs). Genetic variants of enzymes in the homocysteine remethylation pathway might act as predisposing factors contributing to NTD risk. The first polymorphism linked to increased NTD risk was the 677C-->T mutation in methylenetetrahydrofolate reductase (MTHFR). We now report a polymorphism in methionine synthase reductase (MTRR), the enzyme that activates cobalamin-dependent methionine synthase. This polymorphorism, 66A-->G (I22M), has an allele frequency of 0.51 and increases NTD risk when cobalamin status is low or when the MTHFR mutant genotype is present. Genotypes and cobalamin status were assessed in 56 patients with spina bifida, 58 mothers of patients, 97 control children, and 89 mothers of controls. Cases and case mothers were almost twice as likely to possess the homozygous mutant genotype when compared to controls, but this difference was not statistically significant. However, when combined with low levels of cobalamin, the risk for mothers increased nearly five times (odds ratio (OR) = 4.8, 95% CI 1.5-15.8); the OR for children with this combination was 2.5 (95% CI 0.63-9.7). In the presence of combined MTHFR and MTRR homozygous mutant genotypes, children and mothers had a fourfold and threefold increase in risk, respectively (OR = 4.1, 95% CI 1.0-16.4; and OR = 2.9, 95% CI 0.58-14.8). This study provides the first genetic link between vitamin B(12) deficiency and NTDs and supports the multifactorial origins of these common birth defects. Investigation of this polymorphism in other disorders associated with altered homocysteine metabolism, such as vascular disease, is clearly warranted.     

Evaluation of genetic variants in the reduced folate carrier and in glutamate carboxypeptidase II for spina bifida risk

Genetic variants in folate metabolism have been reported to increase risk for neural tube defects (NTD). The first such sequence change was the 677C-->T substitution in methylenetetrahydrofolate reductase (MTHFR), but additional sequence changes have been identified in enzymes or transporters for folates. Two recently identified variants are the 1561C-->T (H475Y) mutation in glutamate carboxypeptidase II (GCPII) and the 80A-->G (H27R) change in the reduced folate carrier RFC-1. We examined a group of mothers of spina bifida offspring, and a group of control women, for the above polymorphisms to assess their impact on NTD risk as well as on homocysteine and nutrient (RBC folate, serum folate, and serum cobalamin) levels. The GCPII variant (in the heterozygous state) did not influence NTD risk or metabolite levels; homozygous mutant (YY) women were not observed in our study group. The homozygous mutant (RR) genotype for the RFC-1 gene was not associated with a significant difference in NTD risk (OR=1.39, 95% CI=0.55-3.54), but there was a borderline significant (p=0.065) decrease in RBC folate levels, compared with the HH genotype. However, the combination of the RR genotype for RFC-1 and low RBC folate was associated with a significant 4.6-fold increase in NTD risk (OR=4.6, 95% CI=1.47-14.37). Since this small study is the first to demonstrate increased risk for women with the RFC-1 variant for having a child with a NTD, additional larger studies are required to confirm this change as another potential genetic modifier for spina bifida risk.     

Genetic polymorphisms in methylenetetrahydrofolate reductase and methionine synthase, folate levels in red blood cells, and risk of neural tube defects.

Folic acid administration to women in the periconceptional period reduces the occurrence of neural tube defects (NTDs) in their offspring. A polymorphism in the gene encoding methylenetetrahydrofolate reductase (MTHFR), 677C-->T, is the first genetic risk factor for NTDs in man identified at the molecular level. The gene encoding another folate-dependent enzyme, methionine synthase (MTR), has recently been cloned and a common variant, 2756A-->G, has been identified. We assessed genotypes and folate status in 56 patients with spina bifida, 62 mothers of patients, 97 children without NTDs (controls), and 90 mothers of controls, to determine the impact of these factors on NTD risk. Twenty percent of cases and 18% of case mothers were homozygous for the MTHFR polymorphism, compared to 11% of controls and 11% of control mothers, indicating that the mutant genotype conferred an increased risk for NTDs. The risk was further increased if both mother and child had this genotype. The MTR polymorphism was associated with a decreased O.R. (O.R.); none of the cases and only 10% of controls were homozygous for this variant. Red blood cell (RBC) folate was lower in cases and in case mothers, compared to their respective controls. Having a RBC folate in the lowest quartile of the control distribution was associated with an O.R. of 2.56 (95% CI 1.28-5.13) for being a case and of 3.05 (95% CI 1.54-6.03) for being a case mother. The combination of homozygous mutant MTHFR genotype and RBC folate in the lowest quartile conferred an O.R. for being a NTD case of 13.43 (CI 2.49-72.33) and an O.R. for having a child with NTD of 3.28 (CI 0.84-12.85). We propose that the genetic-nutrient interaction--MTHFR polymorphism and low folate status--is associated with a greater risk for NTDs than either variable alone.     

Maternal homozygosity for the common MTHFR mutation as a potential risk factor for offspring with limb defects

A common mutation, C677T, in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene leads to altered homocysteine metabolism, and has been associated with the occurrence of neural tube defects (NTD). Administration of folic acid decreases this risk. There is also evidence that periconceptional supplementation of mothers with folic acid can decrease the risk of limb defects in the offspring. Here we describe a child with a transverse terminal defect of one hand, whose mother is homozygous for the C677T MTHFR mutation. We suggest that homozygosity for the MTHFR mutation may be a risk factor for transverse terminal limb defect/s by an effect mediated through altered folate and homocysteine metabolism. Further studies of mothers of infants with limb reduction defects for the MTHFR mutation may be of help in establishing this association. A simple intervention in the form of folic acid supplementation would be protective, should an association be established.     

Association of methylenetetrahydrofolate reductase C677T and A1298C polymorphisms with myocardial infarction in Tunisian young patients

Myocardial infarction (MI) is an important clinical problem because of its large contribution to mortality. The objective of this study is to assess whether two methylenetetrahydrofolate reductase (MTHFR) polymorphisms, C677T and A1298C, were associated with MI among Tunisian patients. One hundred young patients (<47 years old) with MI were recruited and compared with 200 control subjects with no history of MI. The most common MI risk factors were investigated. Fasting plasma homocysteine levels were measured. Genotypes of the MTHFR C677T and A1298 polymorphisms were studied by polymerase chain reaction. The mean plasma homocysteine level in the study group was raised when compared with the control group. Homozygous MTHFR C677T mutation was observed in 2 (2 %) patients and in 17 (8.5 %) control subjects, whereas heterozygous MTHFR C677T mutation was detected in 82 (82 %) patients versus only 79 (39.5 %) in control subjects. The mean total homocysteine concentrations were significantly higher in individuals with the 677TT and CT genotypes. Our results indicate that C677T and A1298C MTHFR mutations and hyperhomocysteinemia contributed to the risk factors for MI.     

Increased frequency of combined methylenetetrahydrofolate reductase C677T and A1298C mutated alleles in spontaneously aborted embryos

The pathogenesis of spontaneous abortion is complex, presumably involving the interaction of several genetic and environmental factors. The methylenetetrahydrofolate reductase (MTHFR) gene C677T and A1298C polymorphisms are commonly associated with defects in folate dependent homocysteine metabolism and have been implicated as risk factors for recurrent embryo loss in early pregnancy. In the present study we have determined the prevalence of combined MTHFR C677T and A1298C polymorphisms in DNA samples from spontaneously aborted embryos (foetal death between sixth and twentieth week after conception) and adult controls using solid-phase minisequencing technique. There was a significant odds ratio of 14.2 (95% CI 1.78-113) in spontaneously aborted embryos comparing the prevalence of one or more 677T and 1298C alleles vs the wild type combined genotype (677CC/1298AA), indicating that the MTHFR polymorphisms may have a major impact on foetal survival. Combined 677CT/1298CC, 677TT/1298AC or 677TT/1298CC genotypes, which contain three or four mutant alleles, were not detected in any of the groups, suggesting complete linkage disequilibrium between the two polymorphisms. The present finding of high prevalence of mutated MTHFR genotypes in spontaneously aborted embryos emphasises the potential protective role of periconceptional folic acid supplementation.