Q J Med 2003; 96: 297-303
© 2003 Association of Physicians
5,10-Methylenetetrahydrofolate reductase 677C
T and 1298AC mutations are genetic determinants of elevated homocysteine
From the 1 Centro de Patogénese Molecular, Faculdade de Farmácia da Universidade de Lisboa, and 2 Centro de Nutrição e Metabolismo, Faculdade de Medicina da Universidade de Lisboa, Lisboa, Portugal, 3 Metabolic Unit, Department of Clinical Chemistry, VU University Medical Centre, Amsterdam, and 4 Department of Paediatrics, University Medical Center St. Radboud, Nijmegen, The Netherlands
Received 16 October 2002 Accepted for publication 3 January 2003.
 |
Summary |
|---|
 Top Summary IntroductionMethodsResultsDiscussionReferences |
|---|
Background: Methylenetetrahydrofolate reductase (MTHFR) is one of the main regulatory enzymes of homocysteine metabolism. Elevated plasma total homocysteine (tHcy) is a major risk for cardiovascular disease. A common 677C
T mutation in the MTHFR gene results in decreased enzymic activity, and contributes to increased plasma tHcy, in association with low plasma folate. A recently described 1298AC mutation in the MTHFR gene clearly reduces MTHFR activity (although to a lesser extent than the 677CT) but its effect on plasma tHcy levels is not yet clear. Aim: To investigate the frequency of these two MTHFR polymorphisms in a Portuguese population, and to correlate the MTHFR genotype with the biochemical phenotype at the level of homocysteine and folate concentrations.
Design: Prospective population survey.
Methods: We studied 117 healthy volunteers (71 females, 46 males). The 677CT and 1298AC mutations were screened by PCR-RFLP. Levels of plasma tHcy and folate, and red blood cell folate, were determined.
Results: The allele frequencies of the 677CT and 1298AC mutations were 0.33 and 0.28, respectively. Homozygotes for the 677CT mutation had significantly elevated plasma tHcy and RBC folate levels and significantly lowered plasma folate concentrations than subjects without the mutation. The 1298AC mutation showed a significant effect on plasma tHcy, but not on plasma folate or RBC folate levels.
Discussion: The observed 677T allele frequency is not consistent with the idea of a north-south gradient as previously suggested. The 1298AC mutation is common in Portugal. Both MTHFR mutations showed effects on plasma tHcy levels.
|
Introduction |
|---|
|
TopSummaryIntroductionMethodsResultsDiscussionReferences |
|---|
Hyperhomocysteinemia is an established independent risk factor for cardiovascular disease, and may result from dietary deficiencies (especially folate) and/or genetic alterations in enzymes involved in the metabolism of methionine or homocysteine.1–3 5,10-methylenetetrahydrofolate reductase (MTHFR) catalyses the reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, the main circulating form of folate and the methyl donor for the vitamin B12-dependent remethylation of homocysteine to methionine.
A common 677CT transition in the MTHFR gene results in a thermolabile variant with specific decreased enzymic activity, and is well established as a genetic determinant of hyperhomocysteinemia. The molecular basis of this thermolability is a missense mutation in exon 4 of the MTHFR gene, a cytosine to thymine substitution at nucleotide 677, which converts an alanine to a valine codon. The protective effect of folate may be mediated by stabilization of FAD binding.4 This association of the MTHFR genotype with homocysteine is well known to be contingent on folate status.
Recently, a second polymorphism in the MTHFR gene, associated with decreased enzymic activity but not with thermolability, has been discovered.5 This genetic variant corresponds to an adenosine to cytosine transversion at nucleotide 1298, in exon 7, leading to a glutamate to alanine substitution in the MTHFR protein. Subjects with the 1298CC genotype have reduced enzyme activity, but to a lesser extent than those with the 677TT genotype.5 Double heterozygous (677CT/1298AC) individuals display lower MTHFR activity than subjects heterozygous for either single nucleotide polymorphism.5
The prevalence of the 677CT polymorphism varies greatly in different ethnic groups, while the 1298AC allele frequency, although less documented, seems more uniform in the majority of the studied populations.1,6–10 The aim of the present study was to investigate the frequency of these two MTHFR polymorphisms in the Portuguese population, and to correlate the MTHFR genotype with the biochemical phenotype at the level of homocysteine and folate concentrations.
|
Methods |
|---|
|
TopSummaryIntroductionMethodsResultsDiscussionReferences |
|---|
Subjects
We studied 117 healthy unrelated Portuguese Caucasian subjects, 71 females and 46 males, aged 20–69 years (mean age 41±13 years), who were volunteers from the Faculty of Pharmacy staff and students. Details of lifestyle (i.e. smoking, alcohol consumption, medication, physical exercise, as well as personal and family history) and routine biochemical measurements were established using standardized questionnaires and protocols. The criteria for inclusion were: routine biochemical values within the normal range, non-smokers, no history of metabolic, renal or vascular pathology and no supplementary intake of vitamins within the two previous months. A written informed consent was obtained from all participants, and the Local Ethical Committee approved the study.
Biochemical measurements
Overnight fasting (12 h) blood samples were drawn from all participants by venepuncture. Blood was collected either into EDTA-containing tubes, kept on ice, or into sodium citrate light-protected tubes. EDTA blood was used for tHcy and routine biochemical measurements, and for genomic DNA preparation. Sodium citrate blood was used for determination of haematocrit and plasma and red blood cell (RBC) folate levels. Plasma was promptly separated by centrifugation at 4 °C, divided into aliquots, and stored at -20 °C until analysis. Plasma tHcy (protein-bound plus free oxidized and reduced species) and folate, as well as RBC folate concentrations, were determined by specific immunoassays (IMX, Abbott Laboratories).
Genetic analysis
Genomic DNA was isolated from peripheral blood leucocytes according to standard methods.11,12 The MTHFR gene mutations, 677CT and 1298AC, were analysed by PCR-RFLP as previously described by others.5,13–15 Briefly, 500 ng of genomic DNA was incubated in a total reaction volume of 50 µl containing final concentrations of 500 nM of the forward and the reverse primers, 200 µM each dNTP, 10 mM Tris-HCl pH 8.3, 50 mM KCl, 2 mM MgCl2, 0.05% detergent and 1 unit Taq DNA polymerase (Life Technologies). PCR conditions were optimized for the Omnigene (Hybaid) apparatus and included denaturation at 94 °C, annealing at 70 °C for 677CT or 55 °C for 1298AC and extension at 72 °C. The 677CT variant creates a HinfI site, and the 1298AC variant abolishes a MboII site. After restriction enzyme digestion, PCR products were evaluated by gel electrophoresis analysis. A recent review of the human MTHFR mRNA sequence showed that the 1317TC mutation does not serve as restriction site for Mbo II.14 The presence of this silent mutation cannot therefore interfere with Mbo II restriction isotyping of the 1298AC mutation, as has been suggested.6
Statistical analysis
The tHcy and vitamin concentrations were expressed as median values and 95% confidence intervals (95% CI). The distributions of the tHcy and vitamin concentrations were positively skewed, and a logarithmic transformation was performed. One-way analysis of variance (ANOVA) was used to assess the differences in continuous variables between the different genotypes. For positive ANOVA results, the differences between mean values were detected by Student's t test corrected for multiple comparisons (Bonferroni/Dunn test). For all statistics, p values are two-tailed and significance was set at the 5% level. SPSS 10.0 and EPI–Info 2000 (CDC) were used for analyses.
|
Results |
|---|
|
TopSummaryIntroductionMethodsResultsDiscussionReferences |
|---|
The median plasma tHcy level was significantly (p<0.05) higher in males (9.9 µM, 95%CI 10.0–11.6) than in females (7.6 µM, 95%CI 7.5–8.4) (Table 1
). These results are in agreement with the well-documented sex difference in plasma tHcy. There were no significant differences in plasma folate or RBC folate concentrations between genders.
|
The distribution of the MTHFR genotypes for the 677C
T and 1298AC mutations is summarized in Table 2; both were in Hardy-Weinberg equilibrium. The relative frequencies of the 677T and 1298C alleles were 33.3% and 28.2%, respectively. Overall, 10.3% of the subjects carried the 677TT genotype and 6.0% had the 1298CC genotype. The heterozygous status for both mutations was similar, 46.2% for the 677CT mutation and 44.4% for the 1298AC mutation.
|
The separate effects of each MTHFR genotype (677C
T or 1298AC) on the tHcy and folate levels are shown in Table 3. Subjects were divided into three groups based on their independent status relative to each of the two studied polymorphic sites. For the 677CT transition, a linear progression was observed for the plasma tHcy and folate levels, but not for the RBC folate levels. In individuals homozygous for the 677T allele, compared to those with the wild-type genotype, median plasma tHcy and RBC folate levels were significantly higher and plasma folate concentration significantly lower (both p<0.05). Heterozygotes (677CT) for this mutation displayed slightly higher median tHcy levels than those with the 677CC genotype, but the difference was not significant. However, when we stratified heterozygote (677CT) subjects according to their plasma folate status, those with plasma folate under the median had significantly (p<0.05) higher tHcy (9.7 µM, 95%CI 8.4–10.8) than those with folate above the median (tHcy 7.0 µM, 95%CI 6.7–8.7). Regarding the 1298AC mutation, the 1298C allele had a significant effect on plasma tHcy levels. Homozygous mutant individuals displayed significantly (p<0.05) higher plasma tHcy levels than the individuals harbouring the other two genotypes. No significant effect was observed on plasma folate or RBC folate levels.
|
Examining the effect of the combination of both mutations (Table 4
), 21.4% of the individuals were double heterozygotes (677CT/1298AC). The 677TT genotype was always associated with the normal 1298AA genotype in all individuals but one (who had the 1298AC heterozygous genotype), and the 1298CC genotype was always associated with the normal 677CC genotype. Double mutant homozygous individuals were not observed. Significantly higher plasma median tHcy levels were associated with the 677TT/1298AA or the 677CC/1298CC genotypes, compared with the wild-type genotype (677CC/1298AA). In double heterozygotes (677CT/1298AC) there was a trend towards an increase in plasma tHcy levels, but this was not statistically significant (p<0.07).
|
|
Discussion |
|---|
|
TopSummaryIntroductionMethodsResultsDiscussionReferences |
|---|
Hyperhomocysteinemia is a known risk factor for cardiovascular disease. Increased homocysteine levels are the result of both genetic and epigenetic factors, such as population specificity of allelic association and vitamin status. We investigated the prevalence of two common MTHFR polymorphisms, the well-known 677C
T and the recently described 1298AC, in 117 normal subjects. These are the first such results in the Portuguese population. We also related MTHFR genotypes to plasma tHcy, folate and RBC folate levels. The European Atherosclerosis Research Study (EARS), based on pooled data from different European countries, showed a north-south gradient for plasma tHcy levels, with particularly high values for Italy and Greece.16 The results of the present study are not consistent with that observation; a median plasma tHcy concentration of 8.8 µM (95%CI 8.6–9.6) for all participants was observed, which is similar to results reported for middle or north European populations.16 It seems unlikely that this finding can be attributed to the use of different methods for the plasma tHcy determination. A good correlation between immunoassay and high-performance liquid chromatography (HPLC) was recently reported.17 As stated in several studies,18,19 the gender plasma tHcy level difference was also observed in the studied population.
In the whole sample, the relative frequency of the 677T allele was 33.3%, which is much lower than that reported for Mediterranean populations, Spanish (42%)20 and Italian (43.8%)8 (Table 5). Accordingly, the prevalence of the mutant homozygous 677TT (10.3%) was also lower than in those South European populations (15.8% and 18.0%, respectively),8,20 or in the French population (16.8% and 18.2%)7,21 (Table 5). With respect to these MTHFR polymorphisms, our Portuguese sample resembled the published North-European populations much more than those of South Europe.
|
Analysis of the combined genotypes showed that 21.4% of the subjects were compound heterozygotes for the two MTHFR single nucleotide polymorphisms (677CT/1298AC), which is similar to that in other studied populations.2,7,22,23 We found no double homozygotes (677TT/1298CC), but we found one individual with the 677TT/1298AC genotype. Although these findings concur with the general idea that these two polymorphisms rarely occur in cis,5,6,9,22 a recent report by Dekou et al.2 showed that the occurrence of these two polymorphisms in cis is not so rare as previously thought. More likely, the two mutations occurred independently, and have not had enough time for a recombination event to bring them together on the same chromosome.6 Homozygosity for the 677C
T mutation has been associated with moderately increased fasting tHcy levels, particularly in the presence of low plasma folate levels.8,24–26 Our data also confirmed this observation; tHcy levels were significantly higher in individuals with the 677TT genotype than in those with the wild-type genotype, and were associated with significantly lower plasma folate levels. In heterozygotes, this effect was only visible when the 677CT subjects were stratified according to their plasma folate status: those with plasma folate under the median had significantly higher tHcy levels than those with folate above the median.
MTHFR catalyses the reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate. The former is found mainly within cells, whereas the latter is the main circulating form of folate. Therefore, in the presence of decreased MTHFR activity, caused by the 677CT transition, one would expect not only a decrease in plasma folate concentration but an increase in RBC folate levels as well. Our results accord well with this expectation: RBC folate levels were significantly higher in individuals with the 677TT genotype than in those with the wild-type genotype. In the literature, there are conflicting data with respect to this issue. Increased5 and decreased27 RBC folate levels have both been reported in subjects mutant homozygous for the 677CT mutation when compared to the wild-type genotype. These discrepancies might be due to the different methods used for the RBC folate levels measurements.
Regarding the 1298AC mutation, our results were in agreement with those in the few published studies: the 1298C allele frequency was 28.2%, demonstrating that the mutation is also common in our population.
The association of the 1298AC mutation with decreased MTHFR specific activity is agreed, although its effect on plasma tHcy levels is not yet clear.1 Reports show either no effect of this mutation on plasma tHcy levels,1,5 or an association with even lower levels of plasma tHcy in homozygous individuals.28 We observed a significant effect of the 1298 AC mutation on plasma tHcy levels. Subjects bearing the 1298CC genotype had significantly higher tHcy levels than those bearing the wild-type genotype (1298AA) (Table 3
). This effect is visible when the 677CT mutation is not taken into account (Table 3) and, accordingly, is also present when both mutations are considered at once (Table 4).
It appears that 677CT and 1298AC polymorphisms can act synergistically, given that heterozygosity for both polymorphisms causes lower MTHFR activity than heterozygosity alone for either mutation5 and a trend to higher or significantly higher plasma tHcy levels, particularly in association with low folate levels, was described in double heterozygotes.1 Accordingly, our study showed a trend (p<0.07) towards higher plasma tHcy levels in individuals with double heterozygosity, comparing to those with the wild-type genotype (677CC/1298AA), although low folate levels were not observed (Table 4).
In summary, our results show relative frequencies of the 677T allele and of the 677TT genotype lower than those reported for the other two South European countries, Spain and Italy. These data are not consistent with the idea of a north-south gradient, and confirm the notion that local geographic population studies are necessary. We also confirmed that the 1298AC mutation is common in Portugal. However, these estimates of the MTHFR mutations frequencies in the Portuguese population are based on a small and possibly unrepresentative sample, and will require replication before they can be considered definitive. The effects of the different genotypes on the evaluated biochemical parameters were mostly consistent with previously published data. Both MTHFR mutations, either taken separately or together, showed effects on plasma tHcy concentrations. Further studies are still necessary to clarify the impact of these genetic variants in hyperhomocysteinemia.
|
Acknowledgments |
|---|
We thank Dr Adelaide Belo, Hosp. Distrital de Beja, for her collaboration and Carla Mendes for technical assistance. We also thank to Fernanda Ramalho, Elisa Alves and Amélia Pereira for the expert sampling and routine biochemical determinations. This study was partially supported by a grant awarded to Rita Azevedo e Castro (Praxis XXI/BD/11383/97) by the FCT (Fundação para a Ciência e Tecnologia). Henk Blom is supported by the Netherlands Heart Foundation (D97.021).
|
Notes |
|---|
Address correspondence to Professor I.T. de Almeida, Centro de Patogénese Molecular, Faculdade de Farmácia da Universidade de Lisboa, Av. Prof. Gama Pinto, 1649–039 Lisboa, Portugal. e-mail: italmeida{at}ff.ul.pt
|
References |
|---|
|
TopSummaryIntroductionMethodsResultsDiscussionReferences |
|---|
1. Lievers KJ, Boers GH, Verhoef P, den Heijer M, Kluijtmans LA, van der Put NM, Trijbels FJ, Blom HJ. A second common variant in the methylenetetrahydrofolate reductase (MTHFR) gene and its relationship to MTHFR enzyme activity, homocysteine, and cardiovascular disease risk. J Mol Med 2001; 79:522–8.
2. Dekou V, Whincup P, Papacosta O, Ebrahim S, Lennon L, Ueland PM, Refsum H, Humphries SE, Gudnason V. The effect of the C677T and A1298C polymorphisms in the methylenetetrahydrofolate reductase gene on homocysteine levels in elderly men and women from the British regional heart study. Atherosclerosis 2001; 154:659–66.
3. Blom HJ. Genetic determinants of hyperhomocysteinaemia: the roles of cystathionine beta-synthase and 5,10-methylenetetrahydrofolate reductase. Eur J Pediatr 2000; 159:S208–12.
4. Guenther BD, Sheppard CA, Tran P, Rozen R, Matthews RG, Ludwig ML. The structure and properties of methylenetetrahydrofolate reductase from Escherichia coli suggest how folate ameliorates human hyperhomocysteinemia. Nat Struct Biol 1999; 6:359–65.
5. van der Put NM, Gabreels F, Stevens EM, Smeitink JA, Trijbels FJ, Eskes TK, van den Heuvel LP, Blom HJ. A second common mutation in the methylenetetrahydrofolate reductase gene: an additional risk factor for neural-tube defects? Am J Hum Genet 1998; 62:1044–51.
6. Weisberg IS, Jacques PF, Selhub J, Bostom AG, Chen Z, Curtis Ellison R, Eckfeldt JH, Rozen R. The 1298A–>C polymorphism in methylenetetrahydrofolate reductase (MTHFR): in vitro expression and association with homocysteine. Atherosclerosis 2001; 156:409–15.
7. Chango A, Boisson F, Barbe F, Quilliot D, Droesch S, Pfister M, Fillon-Emery N, Lambert D, Fremont S, Rosenblatt DS, Nicolas JP. The effect of 677CT and 1298AC mutations on plasma homocysteine and 5,10-methylenetetrahydrofolate reductase activity in healthy subjects. Br J Nutr 2000; 83:593–6.
8. Botto LD, Yang Q. 5,10-Methylenetetrahydrofolate reductase gene variants and congenital anomalies: a HuGE review. Am J Epidemiol 2000; 151:862–77.
9. Rady PL, Tyring SK, Hudnall SD, Vargas T, Kellner LH, Nitowsky H, Matalon RK. Methylenetetrahydrofolate reductase (MTHFR): the incidence of mutations C677T and A1298C in the Ashkenazi Jewish population. Am J Med Genet 1999; 86:380–4.
10. Peng F, Labelle LA, Rainey BJ, Tsongalis GJ. Single nucleotide polymorphisms in the methylenetetrahydrofolate reductase gene are common in US Caucasian and Hispanic American populations. Int J Mol Med 2001; 8:509–11.
11. Miller SA, Dykes DD, Polesky HF. A simple salting out procedure for extracting DNA from human nucleated cells. Nucl Acids Res 1988; 16:1215.
12. Leadon SA, Cerutti PA. A rapid and mild procedure for the isolation of DNA from mammalian cells. Anal Biochem 1982; 120:282–8.
13. Frosst P, Blom HJ, Milos R, Goyette P, Sheppard CA, Matthews RG, Boers GJ, den Heijer M, Kluijtmans LA, van den Heuvel LP. A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase. Nat Genet 1995; 10:111–3.
14. Donnelly JG. The silent T1317C mutation of methylenetetrahydrofolate reductase should not interfere with MboII restriction isotyping of the reported A1298C mutation. Mol Genet Metab 1999; 68:511–2.
15. van der Put NM, Blom HJ. Reply to Donnelly. Am J Hum Genet 2000; 66:744–5.
16. Gudnason V, Stansbie D, Scott J, Bowron A, Nicaud V, Humphries S. C677T (thermolabile alanine/valine) polymorphism in methylenetetrahydrofolate reductase (MTHFR): its frequency and impact on plasma homocysteine concentration in different European populations. EARS group. Atherosclerosis 1998; 136:347–54.
17. Donnelly JG, Pronovost C. Evaluation of the Abbott IMx fluorescence polarization immunoassay and the bio-rad enzyme immunoassay for homocysteine: comparison with high-performance liquid chromatography. Ann Clin Biochem 2000; 37:194–8.
18. Selhub J, Jacques PF, Rosenberg IH, Rogers G, Bowman BA, Gunter EW, Wright JD, Johnson CL. Serum total homocysteine concentrations in the third National Health and Nutrition Examination Survey (1991–1994): population reference ranges and contribution of vitamin status to high serum concentrations. Ann Intern Med 1999; 131:331–9.
19. Jacques PF, Rosenberg IH, Rogers G, Selhub J, Bowman BA, Gunter EW, Wright JD, Johnson CL. Serum total homocysteine concentrations in adolescent and adult Americans: results from the third National Health and Nutrition Examination Survey. Am J Clin Nutr 1999; 69:482–9.
20. Guillen M, Corella D, Portoles, Gonzalez JI, Mulet F, Saiz C. Prevalence of the methylenetetrahydrofolate reductase 677C > T mutation in the Mediterranean Spanish population. Association with cardiovascular risk factors. Eur J Epidemiol 2001; 17:255–61.
21. Chango A, Potier De Courcy G, Boisson F, Guilland JC, Barbe F, Perrin MO, Christides JP, Rabhi K, Pfister M, Galan P, Hercberg S, Nicolas JP. 5,10-methylenetetrahydrofolate reductase common mutations, folate status and plasma homocysteine in healthy French adults of the Supplementation en Vitamines et Mineraux Antioxydants (SU.VI.MAX) cohort. Br J Nutr 2000; 84:891–6.
22. Hanson NQ, Aras O, Yang F, Tsai MY. C677T and A1298C polymorphisms of the methylenetetrahydrofolate reductase gene: incidence and effect of combined genotypes on plasma fasting and post-methionine load homocysteine in vascular disease. Clin Chem 2001; 47:661–6.
23. Meisel C, Cascorbi I, Gerloff T, Stangl V, Laule M, Muller JM, Wernecke KD, Baumann G, Roots I, Stangl K. Identification of six methylenetetrahydrofolate reductase (MTHFR) genotypes resulting from common polymorphisms: impact on plasma homocysteine levels and development of coronary artery disease. Atherosclerosis 2001; 154:651–8.
24. Brattstrom L, Wilcken DE, Ohrvik J, Brudin L. Common methylenetetrahydrofolate reductase gene mutation leads to hyperhomocysteinemia but not to vascular disease: the result of a meta-analysis. Circulation 1998; 98:2520–6.
25. Jacques PF, Bostom AG, Williams RR, Ellison RC, Eckfeldt JH, Rosenberg IH, Selhub J, Rozen R. Relation between folate status, a common mutation in methylenetetrahydrofolate reductase, and plasma homocysteine concentrations. Circulation 1996; 93:7–9.
26. van der Put NM, Steegers-Theunissen RP, Frosst P, Trijbels FJ, Eskes TK, van den Heuvel LP, Mariman EC, den Heyer M, Rozen R, Blom HJ. Mutated methylenetetrahydrofolate reductase as a risk factor for spina bifida. Lancet 1995; 346:1070–1.
27. Molloy AM, Mills JL, Kirke PN, Whitehead AS, Weir DG, Scott JM. Whole-blood folate values in subjects with different methylenetetrahydrofolate reductase genotypes: differences between the radioassay and microbiological assays. Clin Chem 1998; 44:186–8.
28. Friedman G, Goldschmidt N, Friedlander Y, Ben-Yehuda A, Selhub J, Babaey S, Mendel M, Kidron M, Bar-On H. A common mutation A1298C in human methylenetetrahydrofolate reductase gene: association with plasma total homocysteine and folate concentrations. J Nutr 1999; 129:1656–61.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  Q.-H. Yang, L. D Botto, M. Gallagher, J. Friedman, C. L Sanders, D. Koontz, S. Nikolova, J D. Erickson, and K. Steinberg Prevalence and effects of gene-gene and gene-nutrient interactions on serum folate and serum total homocysteine concentrations in the United States: findings from the third National Health and Nutrition Examination Survey DNA Bank Am. J. Clinical Nutrition, July 1, 2008; 88(1): 232 - 246. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 W. Zhang, O. A. Press, C. A. Haiman, D. Y. Yang, M. A. Gordon, W. Fazzone, A. El-khoueiry, S. Iqbal, A. E. Sherrod, G. Lurje, et al. Association of Methylenetetrahydrofolate Reductase Gene Polymorphisms and Sex-Specific Survival in Patients With Metastatic Colon Cancer J. Clin. Oncol., August 20, 2007; 25(24): 3726 - 3731. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R Castro, I Rivera, P Ravasco, M E Camilo, C Jakobs, H J Blom, and I T de Almeida 5,10-methylenetetrahydrofolate reductase (MTHFR) 677C->T and 1298A->C mutations are associated with DNA hypomethylation J. Med. Genet., June 1, 2004; 41(6): 454 - 458. [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||