CLINICAL STUDIES
A common mutation in the methylenetetrahydrofolate reductase gene and risk of coronary heart disease: results among U.S. men
Petra Verhoef, PhD* ¶,
Eric B. Rimm, SCD*  ||,
David J. Hunter, MBBS ||,
Jia Chen, SCD ||,
Walter C. Willett, MD* ||,
Karl Kelsey, MD  and
Meir J. Stampfer, MD* ||
* Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts, USA
Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA
Department of Cancer Biology, Harvard School of Public Health, Boston, Massachusetts, USA
Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA
|| Channing Laboratory, Department of Medicine, Harvard Medical School and Brigham and Women’s Hospital, Boston, Massachusetts, USA
¶ Division of Human Nutrition and Epidemiology, Agricultural University, Wageningen, The Netherlands
Manuscript received August 13, 1997;
revised manuscript received March 30, 1998,
accepted April 16, 1998.
Address for correspondence: Dr. Eric B. Rimm, Department of Nutrition, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115
 |
Abstract
|
|---|
Objectives. We examined the risk of coronary heart disease associated with homozygosity for the C677T mutation in the methylenetetrahydrofolate reductase gene.
Background. The mutation increases plasma homocysteine levels by impairing its remethylation. Increased plasma homocysteine is an independent risk factor for cardiovascular disease.
Methods. This was a case-control study nested within the Health Professionals Follow-up Study. In 1986, 44,940 U.S. male health professionals, aged 40 to 75 years and free from diagnosed cardiovascular disease, provided detailed information on usual dietary intake, including intake of folate, vitamins B2, B6 and B12, and methionine. Between 1993 and 1995, blood samples were provided by approximately 40% of the participants. We compared data from 500 men with nonfatal coronary heart disease, diagnosed between 1986 and 1992, with data from 500 age-matched control subjects who were free of diagnosed cardiovascular disease at the time of the matched case subject’s diagnosis.
Results. Frequencies of homozygosity (+/+) and heterozygosity (+/–) for the mutation were 12.2% and 41.8% in case subjects and 14.4% and 40.0% in control subjects. With subjects homozygous (–/–) or heterozygous (+/–) for the wildtype allele as a reference and matched by age, the odds ratio of coronary heart disease was 0.83 (95% confidence interval, 0.57 to 1.19) for +/+ subjects. The odds ratio was unchanged after adjustment for smoking and other risk factors for coronary heart disease. Odds ratios were also calculated within strata for intake of vitamins involved in homocysteine metabolism or methionine, the metabolic precursor of homocysteine. The +/+ genotype was not directly associated with risk of coronary heart disease among men with low (that is, within the lowest quartile) intake (<301 µg/d) of folate, the substrate for methylenetetrahydrofolate reductase; low intake (<1.8 mg/d) of vitamin B2, the cofactor for methylenetetrahydrofolate reductase; low intake (<8.0 µg/d) of vitamin B12, the cofactor for remethylation; low intake (<2.1 mg/d) of vitamin B6, the cofactor in the catabolic pathway of homocysteine; or high intake (>2.4 g/d) of methionine.
Conclusions. In this generally well-nourished population, men with the +/+ genotype for the C677T mutation in the methylenetetrahydrofolate reductase gene have no increase in risk of coronary heart disease, even when intake of folate or other B vitamins is low.
|
Abbreviations and Acronyms
| | CABG | = coronary artery bypass grafting | | CHD | = coronary heart disease | | CI | = confidence interval | | CVD | = cardiovascular disease | | MTHFR | = methylenetetrahydrofolate reductase | | OR | = odds ratio |
|
The vitamin B2-dependent enzyme methylenetetrahydrofolate reductase (MTHFR) forms 5-methyltetrahydrofolate by reducing 5,10-methylenetetrahydrofolate, which is derived from dietary folate. 5-Methyltetrahydrofolate provides a methyl group for remethylation of the amino acid homocysteine to methionine, a vitamin B12-dependent reaction (1). Increased plasma total homocysteine level is associated with increased risk of vascular disease of the coronary, cerebral and peripheral vessels (2,3). Reduced activity of MTHFR increases homocysteine levels and consequently has been postulated to be a risk factor for vascular disease (4). Complete MTHFR deficiency is rare and results in hyperhomocysteinemia and premature cardiovascular disease (CVD) (5). A less severe genetic disorder that leads to thermolability of MTHFR was described by Kang et al. (6,7). The presence of thermolabile MTHFR was associated with increased total homocysteine levels and carries a higher risk of coronary artery disease (8–10). Recently, Frosst et al. (11) identified a missense mutation in which a cytosine residue at position 677 of the MTHFR gene is replaced by thymine. The mutation results in a substitution of alanine by valine, and persons homozygous for the mutation have decreased specific MTHFR activity and increased thermolability of the enzyme (11). Persons heterozygous for the gene have a specific MTHFR activity intermediate between the two homozygous groups (11). However, only +/+ homozygous subjects have increased total homocysteine levels, 20% to 30% higher than subjects with the homozygous normal genotype (11–14). This finding is most apparent in subjects with low folate status (12,13,15). Several epidemiologic studies investigated the association between the C677T mutation and risk of CVD; most used coronary heart disease (CHD) as an end point and obtained contradictory results (13,14,16–31).
In the present investigation among 500 case subjects and 500 control subjects in the Health Professionals Follow-up Study, we studied risk of CHD associated with homozygosity for the mutation. We investigated whether the effect of the mutation could be moderated by dietary folate and various other factors that might affect homocysteine or folate metabolism, including age, and intake of vitamins B2, B6, B12, methionine (the metabolic precursor of homocysteine), and alcohol. We hypothesized that homozygosity for the mutation would be a stronger risk factor for CHD in subgroups with low vitamin intake levels (particularly low folate intake), high methionine intake, and high alcohol consumption (because of its effects on folate metabolism).
|
Methods
|
|---|
The health professionals follow-up study.
In 1986 this study prospectively investigated 51,529 male health professionals, 40 to 75 years old, who completed a comprehensive mail ed questionnaire on dietary and exercise habits. Follow-up questionnaires were mail ed in 1988, 1990, and 1992 to ascertain newly diagnosed coronary events (32).
On the basis of a priori criteria we excluded 1,595 men whose reported daily energy intake was outside the range of 3,360 to 17,640 kJ or who left blank 70 or more items about food in the dietary questionnaire. Because men with CVD or related conditions may have recently changed their dietary pattern in response to diagnosis, we further excluded 4,994 men who reported CVD on the baseline 1986 questionnaire, leaving 44,940 men for follow-up.
Blood collection.
In 1992, we sent a blood collection kit to each participant who was willing to provide a specimen. Participants were asked to return three 10-ml vials of whole blood. Between 1993 and 1995 we received blood samples from 18,025 participants. Upon arrival, the specimens were centrifuged at 4°C to obtain plasma, serum, and buffy coat. These samples were stored at –150°C in liquid nitrogen.
Case ascertainment and control identification.
We selected subjects who had provided blood samples and in whom CHD had been diagnosed (either myocardial infarction, coronary artery bypass grafting [CABG], or percutaneous transluminal coronary angioplasty [PTCA]) after return of the baseline 1986 questionnaire but before January 31, 1992. The men reported the diagnosis on the follow-up questionnaires of 1988, 1990, or 1992. We requested medical records from a sample of participants who reported CABG or PTCA. In a sample of 102 self-reported events, 98 (96%) were confirmed by medical record, so we accepted self-report of all other CABGs or PTCAs as CHD end points. A myocardial infarction was confirmed by a study physician using the following World Health Organization criteria: compatible symptoms plus either typical electrocardiographic changes or elevation of cardiac enzymes (33). We identified 500 cases of nonfatal CHD, 220 with myocardial infarction and 280 with either CABG or PTCA. Because the blood samples were collected after diagnosis, we could not include fatal cases. One control subject was matched to each case subject by age (±1 year). Control subjects were randomly selected from participants who had also provided a blood sample, met the matching criteria and were free from clinical CHD at the time of diagnosis in the matched case subject.
Dietary assessment.
The 1986 questionnaire inquired about average intake of 131 foods during the previous year. In addition to the structured questions on food intake, we asked participants to identify specific brands of cold breakfast cereals, multivitamins, and cooking oils. Average intake of methionine, folate, and vitamins B2, B6 and B12 was computed by multiplying the frequency of consumption of each food item by the nutrient content of the listed portion size (34). Intake from vitamin supplements was factored into average intake. We used food composition tables from U.S. Department of Agriculture sources (35) with supplementary information provided by collaborating laboratories and other publications. We adjusted all dietary intakes for total energy intake by using regression analysis (36). In 1987, the precision of nutrient consumption measured by the questionnaire was evaluated in a subsample of 127 participants from the Boston area (34). In brief, these men completed two 1-week dietary records and provided a fasting blood sample. Mean daily intake of nutrients, including folate, vitamins B2, B6 and B12, as assessed by the questionnaire and the dietary records were very similar, and the correlations between the two methods were 0.71 for folate, 0.85 for vitamin B2, 0.82 for vitamin B6, and 0.50 for vitamin B12. Data on methionine intake were not available from diet records. The correlation between folate intake as determined by the questionnaire and erythrocyte folate from the blood samples was 0.55 (with deattenuation for within-person variability in the blood level) (37). In a subpopulation of elderly in the Framingham study (38), in which the same dietary questionnaire was used, the correlation between folate intake and plasma folate concentration was 0.63. In that same study, the correlation between intake of vitamin B6 and plasma pyridoxal-5'-phosphate was 0.39 (39) and the correlation between vitamin B12 intake and plasma vitamin B12 was 0.35 (38).
DNA analysis for MTHFR mutation.
We use the notations "+" and "–" to refer to alleles with and without the mutation, respectively. Thus, homozygosity for the mutation is denoted as +/+, heterozygosity as +/–, and homozygosity for the wild type as –/–.
We extracted DNA from the buffy coat specimens. Genotyping for MTHFR was carried out using a modification (40) of the polymerase chain reaction–restriction fragment length polymorphism assay of Frosst et al. (11). The sequence change of cytosine to thymine results in a gain of a Hinfl restriction site. Polymerase chain reaction amplification was followed by Hinfl digestion, and restriction fragments were size-fractioned on polyacrylamide gels. The 198-bp polymerase chain reaction fragment was digested into 175-bp and 23-bp fragments; the latter fragment ran off the gel. As a result, there was one 198-bp band for the –/– genotype, 198-bp and 175-bp bands for the +/– genotype and one 175-bp band for the +/+ genotype. Genotype results were scored without reference to case-control status. If there was any ambiguity, the polymerase chain reaction, Hinfl digestion, and scoring were repeated.
Approximately 10% of the samples were quality control specimens. We selected an equal number of samples known to be of the +/+ genotype, the +/– genotype and the –/– genotype (four of each) and randomly, repeatedly placed them throughout the batches to total 10% of the samples.
Statistical analysis.
Differences in coronary risk factors between case and control subjects were tested for significance by a paired Student’s t test for continuous variables and a McNemar paired chi-square test for categorical variables. The association of MTHFR genotype with risk of CHD was evaluated by calculating odds ratios (ORs) and 95% confidence intervals (CIs) for +/+ genotype, using conditional logistic regression analysis. Odds ratios were also calculated with unconditional logistic regression analysis, disregarding the pair matching for age, but with age as a covariate in the model. We present ORs for +/– and +/+ genotypes, with –/– genotype as the reference, and for +/+ subjects with both other genotypes as the reference. The unmatched risk analyses were repeated for cases of coronary artery disease (that is, all subjects with CABG or PTCA) and cases of myocardial infarction separately, because CABG and PTCA may represent atherosclerotic heart disease and myocardial infarction (athero)thrombotic heart disease. Furthermore, we performed risk analyses for CHD with presence or absence of one or more conventional risk factors for CHD (smoking, hypertension, hypercholesterolemia). In addition, we calculated ORs for +/+ subjects versus +/– or –/– subjects, within strata of dietary folate and other factors that may affect folate or homocysteine metabolism, such as age, alcohol consumption and dietary intake of methionine, and vitamins B2, B6 and B12. The three strata of each of these factors were based on quartile boundaries of the total population ( 25th percentile, 26th to 75th percentile and >76th percentile). All p values are two sided.
|
Results
|
|---|
Risk factors for coronary artery disease and other characteristics at baseline are shown in Table 1. Case subjects had a higher mean body mass index, were more often current smokers and had a higher frequency of history of hypertension, hypercholesterolemia, diabetes and familial history of myocardial infarction.
View this table:
[in this window]
[in a new window]
|
Table 1 Characteristics of 500 Cases of Nonfatal Coronary Heart Disease and 500 Age-matched Control Subjects in the Health Professionals Follow-Up Study
|
|
Table 2 shows genotype frequencies for case and control subjects separately. Frequencies of the various genotypes were similar and were in Hardy-Weinberg equilibrium in both case and control subjects. Compared to the other two genotypes combined, homozygosity for the mutation was slightly and nonsignificantly (p = 0.31) more common among control subjects than case subjects. When –/– genotype was considered as a reference, the age-matched OR for +/+ genotype was 0.84 (95% CI 0.57 to 1.23); +/– subjects had an OR of 1.04 (95% CI 0.80 to 1.37). When –/– and +/– subjects were considered as a single reference group, the age-matched OR for +/+ genotype was 0.83 (95% CI 0.57 to 1.19). The unmatched ORs (Table 2), with age as a covariate, were similar to the age-matched ORs.
View this table:
[in this window]
[in a new window]
|
Table 2 Frequency of Methylenetetrahydrofolate Reductase Genotype and Odds Ratios of Nonfatal Coronary Heart Disease Among 500 Case and 500 Control Subjects
|
|
There were no statistically significant differences in mean levels or frequencies of coronary risk factors among the genotypes or a trend of any kind. Thus, inclusion of smoking, hypertension, hypercholesterolemia, body mass index, alcohol intake, diabetes, multivitamin use and family history of myocardial infarction as covariates in the multivariately adjusted logistic regression model did not affect the ORs (Table 2). Controlling for family history of myocardial infarction may be considered over-controlling when studying a genetic risk factor, but exclusion of this factor from the multivariate model did not change results. Homozygosity for the mutation was not more common among subjects with a positive family history of myocardial infarction.
In all subsequent risk analyses, we considered –/– and +/– genotypes as one reference group, because the risk of CHD in subjects with +/– genotype was not higher and because +/– and –/– groups had plasma total homocysteine levels similar to those in other studies (11,13).
Because pathophysiologic mechanisms may differ between subjects with coronary artery disease (that is, persons who have undergone CABG or PTCA) and subjects who have had a myocardial infarction, we repeated the calculations of the ORs for +/+ genotype in these subgroups of cases, using all control subjects in both analyses and taking –/– and +/– genotypes as the reference group. The OR for coronary artery disease was 1.04 (95% CI 0.69 to 1.58) and for myocardial infarction was 0.55 (95% CI 0.32 to 0.95) after adjustment for age. When controlling for other risk factors of CHD, these ORs were 1.04 (95% CI 0.67 to 1.62) and 0.49 (96% CI 0.28 to 0.87), respectively.
Similarly, we conducted separate analyses for CHD with or without the presence of various risk factors for coronary artery disease (current smoking, hypertension, hypercholesterolemia), including all control subjects in both subanalyses. Controlling for age, the ORs for +/+ genotype versus +/– and –/– genotypes were 0.82 (95% CI 0.52 to 1.29) for nonfatal CHD without presence of current smoking, hypertension or hypercholesterolemia (256 cases) and 0.82 (95% CI 0.52 to 1.30) for nonfatal CHD with presence of one or more of the risk factors (244 cases). Additional adjustment for other factors, (body mass index, alcohol intake, diabetes, multivitamin use and family history of myocardial infarction) did not change the ORs.
Finally, we calculated ORs for the +/+ genotype versus the –/– or +/– genotypes within strata of dietary folate level and several other factors that might affect homocysteine or folate metabolism (Table 3). The OR for +/+ genotype was not higher in any of the strata where an increased risk for +/+ genotype might be expected, eg, low intake of folate or other vitamins, high intake of methionine, younger age or high alcohol consumption.
View this table:
[in this window]
[in a new window]
|
Table 3 Odds Ratios of Nonfatal Coronary Heart Disease for +/+ Methylenetetrahydrofolate Reductase Genotype versus +/– or –/– Genotype, Stratified by Age, Alcohol Consumption, Intake of Folate, Vitamins B12, B2, B6 and Methionine
|
|
|
Discussion
|
|---|
Strengths and limitations of present study.
In the Health Professionals Follow-up Study, we found no increased risk of nonfatal CHD among men homozygous for the C677T mutation in the MTHFR gene, even among those with low intake of folate. When myocardial infarction and coronary artery disease (CABG and PTCA) were considered as separate end points, we found a statistically significant inverse association for myocardial infarction and no association with CABG and PTCA, possibly a chance finding.
A limitation of the present study was that we did not measure plasma homocysteine concentrations. It is possible that men homozygous for the MTHFR C677T mutation had normal homocysteine concentrations, which would explain the absence of an association between genotype and risk of CHD. However, in the Physicians’ Health Study (13), a population comparable to the present one in age, gender, occupation and frequency of vitamin supplement use, mean plasma total homocysteine levels were 2 to 4 µmol/l higher in subjects with +/+ genotype than the –/– or +/– genotype. Differences of this magnitude were also observed in other studies (11,14). On the basis of a large meta-analysis (2), for this difference in plasma homocysteine levels, an OR of about 1.5 for CHD would be expected for the +/+ genotype compared with the other genotypes. The CI for our overall estimate excludes this value, but it is included in the CI for the coronary artery disease end point. Thus, our study suggests that the +/+ genotype for the C677T mutation does not confer an increased risk of CHD, although we cannot completely eliminate a small increase in risk of coronary atherosclerosis.
We considered that only men who survived until 1995 could provide blood samples. If CHD in subjects with +/+ genotype was more often fatal, then these subjects might be underrepresented in our population, which could in part explain an inverse association. However, fatality because of CHD was low (18%) in case subjects. Thus, only an extremely strong relationship between genotype and case fatality could obscure a true OR of 1.5. We have no reason to believe that the relationship between increased plasma homocysteine level differs for incident cases of fatal and nonfatal CHD; in the Physicians’ Health Study results were similar for fatal and nonfatal myocardial infarction (Ma J, personal communication, July 1997).
The +/+ genotype was not associated with risk of CHD in men with no conventional risk factors, men younger than 55 years, men with low intake of folate, vitamin B2, vitamin B12 (coenzyme for remethylation of homocysteine to methionine) or vitamin B6 (coenzyme in catabolic pathway of homocysteine metabolism). The present study examined the interaction between MTHFR genotype and prospectively measured folate intake. Homozygosity for the mutation was associated with reduced plasma folate concentration (13,41); therefore, examining dietary folate is directly advantageous. The detailed food frequency questionnaire measures dietary intake of folate and other B vitamins moderately accurately (35) and correlates with measures of folate status, such as erythrocyte (37) and plasma folate levels (38), thus reducing the chance that we missed any important effect modification. However, this study population is generally well nourished, and an association might be seen with folate intake level less than the lowest quartile of this group.
Comparison with results from other studies.
Several studies have investigated the relation between the MTHFR C677T mutation and risk of CVD, with most having CHD as the disease end point of interest (13,14,16–31). In five of these studies (14,17,18,24,29), a direct association was observed, with ORs for the +/+ genotype between 2 and 3, whereas the other studies found no association between this common mutation and risk of CVD. In the studies that observed direct association between the mutation and risk of CVD, patients with early-onset CVD (as expected for a genetically-determined risk factor) were more likely to be included, although other studies of premature cardiovascular disease did not find an association. Another possible explanation for the direct association in those five studies might be a lower status of vitamins involved in homocysteine metabolism, especially folate. In Europe as opposed to the United States, use of vitamin supplements and fortification of food products with folic acid is uncommon. For comparison, in a large population-based sample of Irish men (12), mean serum folate level was approximately 11 nmol/l, whereas mean plasma levels of 14 and 15 nmol/l are reported in U.S. populations (15,25). Similarly, the increased risk in the two Japanese studies (18,29) may be related to the relatively low intake of vitamin B2 (coenzyme for MTHFR) because of low consumption of milk and milk products.
Concluding remarks.
There are several possible explanations for the absence of a positive association between +/+ genotype and risk of CHD. It is possible that homocysteine concentrations were not increased in subjects with the +/+ genotype. However, homocysteine concentration is generally higher among those with the +/+ genotype, as well as in well-nourished populations, such as that of the Physicians’ Health Study (13). Therefore, our findings may also indicate that higher plasma total homocysteine level is not itself a risk factor for CHD but a marker of low folate status, which may independently affect risk of CHD. However, two factors weigh against this explanation, plausible atherothrombotic effects of homocysteine (42) and the possibility that the +/+ genotype increases risk in populations with a lower folate status.
We found no evidence that men with the +/+ genotype for the C677T mutation in the MTHFR gene are at increased risk of nonfatal CHD, even among those with folate or other B-vitamin intake lower than the 25th percentile. The well-nourished condition of the study population might contribute to this finding. Our results of a decreased risk of nonfatal myocardial infarction are most likely a chance finding but introduce the possibility of a beneficial effect of the mutation. If the results of all other epidemiologic studies are considered, it is unlikely that the C677T mutation is an important risk factor for CHD in particular and cardiovascular disease in general.
|
Acknowledgments
|
|---|
We thank the participants of the Health Professionals Follow-up Study. We are also indebted to Al Wing, MBA, Karen Corsano, Mira Kaufman, and Elaine Coughlan-Havas for computer assistance; Betsy Frost-Hawes, Kerry Demers, Mitzi Wolff, and Jan Vomacka for their assistance with compiling the data; Laura Sampson, RD, and Helaine Rockett for maintaining the accuracy of our food composition tables.
|
Footnotes
|
|---|
This study was supported by research grants CA55075 and HL35464 from the National Institutes of Health. Dr. Chen is supported by Training Grant ES07069 from the National Institute for Environmental Health Sciences. Dr. Kelsey is supported by Research Grant ES00002 from the National Institute for Environmental Health Sciences.
|
References
|
|---|
1. Selhub J, Miller JW. The pathogenesis of homocysteinemia: interruption of the coordinate regulation by S-adenosylmethionine of the remethylation and transsulfuration of homocysteine. Am J Clin Nutr. 1992;55:131–138[Abstract/Free Full Text]
2. Boushey CJ, Beresford SAA, Omenn GS, Motulsky AG. A quantitative assessment of plasma homocysteine as a risk factor for vascular disease. Probable benefits of increasing folic acid intakes. JAMA. 1995;274:1049–1057[Abstract/Free Full Text]
3. Stampfer MJ, Malinow MR, Willett WC, et al. A prospective study of plasma homocyst(e)ine and risk of myocardial infarction in US physicians. JAMA. 1992;268:877–881[Abstract/Free Full Text]
4. Rozen R. Molecular genetic aspects of hyperhomocysteinemia and its relation to folic acid. Clin Invest Med. 1996;19:171–178[Medline]
5. Ueland PM, Refsum H, Brattström L. Plasma homocysteine and cardiovascular disease. Francis RB Jr. Atherosclerotic Cardiovascular Disease, Hemostasis, and Endothelial Function. New York: Marcel Dekker; 1992. p. 183–236
6. Kang SS, Wong PWK, Zhou J, et al. Thermolabile methylenetetrahydrofolate reductase in patients with coronary artery disease. Metabolism. 1988;37:611–613[CrossRef][Medline]
7. Kang SS, Zhou J, Wong PWK, Kowalisyn J, Strokosch G. Intermediate homocysteinemia: a thermolabile variant of methylenetetrahydrofolate reductase. Am J Hum Genet. 1988;43:414–421[Medline]
8. Engbersen AMT, Franken DG, Boers GHJ, Stevens EMB, Trijbels FJM, Blom HJ. Thermolabile 5,10-methylenetetrahydrofolate reductase as a cause of mild hyperhomocysteinemia. Am J Hum Genet. 1995;56:142–150[Medline]
9. Kang SS, Wong PWK, Susmano A, Sora J, Norusis M, Ruggie N. Thermolabile methylenetetrahydrofolate reductase: an inherited risk factor for coronary artery disease. Am J Hum Genet. 1991;48:536–545[Medline]
10. Kang SS, Passen EL, Ruggie N, Wong PW, Sora H. Thermolabile defect of methylenetetrahydrofolate reductase in coronary artery disease. Circulation. 1993;88:1463–1469[Abstract/Free Full Text]
11. Frosst P, Blom HJ, Milos R, et al. A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase. Nat Genet. 1995;10:111–113[CrossRef][Medline]
12. Harmon DL, Woodside JV, Yarnell JWG, et al. The common ‘thermolabile’ variant of methylenetetrahydrofolate reductase is a major determinant of mild hyperhomocysteinemia. Q J Med. 1996;89:571–577
13. Ma J, Stampfer MJ, Hennekens CH, et al. Methylenetetrahydrofolate reductase polymorphism, plasma folate, homocysteine, and risk of myocardial infarction in US physicians. Circulation. 1996;94:2410–2416[Abstract/Free Full Text]
14. Kluijtmans LAJ, Van den Heuvel LPWJ, Boers GHJ, et al. Molecular genetic analysis in mild hyperhomocysteinemia: a common mutation in the methylenetetrahydrofolate reductase gene is a genetic risk factor for cardiovascular disease. Am J Hum Genet. 1996;58:35–41[Medline]
15. Jacques PF, Bostom AG, Williams RR, et al. Relation between folate status, a common mutation in methylenetetrahydrofolate reductase, and plasma homocysteine concentrations. Circulation. 1996;93:7–9[Abstract/Free Full Text]
16. Adams M, Smith PD, Martin D, Thompson JR, Lodwick D, Samani NJ. Genetic analysis of thermolabile methylenetetrahydrofolate reductase as a risk factor for myocardial infarction. Q J Med. 1996;89:437–444
17. Gallagher PM, Meleady R, Shields DC, et al. Homocysteine and risk of premature coronary heart disease. Evidence for a common gene mutation. Circulation. 1996;94:2154–2158[Abstract/Free Full Text]
18. Izumi M, Iwai N, Ohmichi N, Nakamura Y, Shimoike H, Kinoshita M. Molecular variant of 5,10-methylenetetrahydrofolate reductase is a risk factor of ischemic disease in the Japanese population. Atherosclerosis. 1996;121:293–294[CrossRef][Medline]
19. Narang R, Callaghan G, Haider AW, Davies GJ, Tuddenham EGD. Methylenetetrahydrofolate reductase and coronary artery disease. Circulation. 1996;94:2322–2323
20. Schmitz C, Lindpaintner K, Verhoef P, Gaziano JM, Buring J. Genetic polymorphism of methylenetetrahydrofolate reductase and myocardial infarction: a case-control study. Circulation. 1996;94:1812–1814[Abstract/Free Full Text]
21. Verhoef P, Kok FJ, Kluijtmans LAJ, Blom HJ, Refsum H, Ueland PM, et al. The 677C T mutation in the methylenetetrahydrofolate reductase gene: associations with plasma total homocysteine levels and risk of coronary atherosclerotic disease. Atherosclerosis 1997;132:105–3.
22. Wilcken DEL, Wang XL, Sim AS, McCredie RM. Distribution in healthy and coronary populations of the methylenetetrahydrofolate reductase (MTHFR) C667T mutation. Arterioscler Thromb Vasc Biol. 1996;16:877–882
23. Brulhart M-C, Dussoix P, Ruiz J, Passa P, Froguel Ph, James RW. The (Ala-Val) mutation of methylenetetrahydrofolate reductase as a genetic risk factor for vascular disease in non-insulin-dependent diabetic patients. Am J Hum Genet. 1997;60:228–229[Medline]
24. De Franchis R, Mancini FP, D’Angelo A, et al. Elevated total plasma homocysteine and 677CT mutation in 5,10-methylenetetrahydrofolate reductase gene in thrombotic vascular disease. Am J Hum Genet. 1996;59:262–264[Medline]
25. Deloughery TG, Evans A, Sadehgi A, et al. Common mutation in methylenetetrahydrofolate reductase. Correlation with homocysteine metabolism and late-onset vascular disease. Circulation. 1996;94:3074–3078[Abstract/Free Full Text]
26. Van Bockxmeer FM, Mamotte CD, Vasikaran SD, Taylor RR. Methylenetetrahydrofolate reductase gene and coronary artery disease. Circulation. 1997;95:21–23[Abstract/Free Full Text]
27. Brugada R, Marian AJ. A common mutation in methylenetetrahydrofolate reductase gene is not a major risk of coronary artery disease or mycocardial infarction. Atherosclerosis. 1997;128:107–112[CrossRef][Medline]
28. Cristensen B, Frosst P, Lussier-Cacan S, et al. Correlation of a common mutation in the methylenetetrahydrofolate reductase gene with plasma homocysteine in patients with premature coronary artery disease. Arterioscler Thromb Vasc Biol. 1997;17:569–573[Abstract/Free Full Text]
29. Morita H, Taguchi J, Kurihara H, et al. Genetic polymorphism of 5,10-methylenetetrahydrofolate reductase (MTHFR) as a risk factor for coronary artery disease. Circulation. 1997;95:2032–2036[Abstract/Free Full Text]
30. Anderson JL, King GJ, Thomson MJ, et al. A mutation in methylenetetrahydrofolate reductase is not associated with increased risk for coronary artery disease or myocardial infarction. J Am Coll Cardiol. 1997;30:1206–1211[Abstract]
31. Kluijtmans LAJ, Kastelein JJP, Lindemans J, et al. Thermolabile methylenetetrahydrofolate reductase in coronary artery disease. Circulation. 1997;96:2573–2577[Abstract/Free Full Text]
32. Rimm EB, Stampfer MJ, Ascherio A, Giovannucci E, Colditz GA, Willett WC. Vitamin E consumption and the risk of coronary heart disease in men. N Engl J Med. 1993;328:1450–1456[Abstract/Free Full Text]
33. Rose GA, Blackburn H. Cardiovascular survey methods. In: World Health Organization Monograph Series No. 58. Geneva, Switzerland: World Health Organization, 1982.
34. Rimm EB, Giovannucci EL, Stampfer MJ, Colditz GA, Litin LB, Willett WC. Reproducibility and validity of an expanded self-administered semiquantitative food frequency questionnaire among male health professionals. Am J Epidemiol. 1992;135:1114–1126[Abstract/Free Full Text]
35. US Department of Agriculture: Agricultural Handbook No. 8 series. Composition of Foods: Raw, Processed and Prepared. Washington, DC: US Govt Print Off: 1963–1988.
36. Willett WC, Stampfer MJ. Total energy intake: implications for epidemiologic analyses. Am J Epidemiol. 1986;124:17–27[Free Full Text]
37. Giovannucci E, Stampfer MJ, Colditz GA, et al. Folate, methionine and alcohol intake and risk of colorectal adenoma. J Natl Cancer Inst. 1993;85:875–884[Abstract/Free Full Text]
38. Jacques PF, Sulsky SI, Sadowski JA, Phillips JCC, Rush D, Willett WC. Comparison of micronutrient intake measured by a dietary questionnaire and biochemical indicators of micronutrient status. Am J Clin Nutr. 1993;57:182–189[Abstract/Free Full Text]
39. Willett WC. Nutritional Epidemiology. New York: Oxford University Press; 1990. p. 92–126
40. Chen J, Giovannucci E, Kelsey K, et al. A methylenetetrahydrofolate reductase polymorphism and the risk of colorectal cancer. Cancer Res. 1996;56:4862–4864[Abstract/Free Full Text]
41. Van der Put NMJ, Steegers-Theunissen RPM, Frosst P, et al. Mutated methylenetetrahydrofolate reductase as a risk factor for spina bifida. Lancet. 1995;346:1070–1071[CrossRef][Medline]
42. Rees MM, Rodgers GM. Homocysteinemia: association of a metabolic disorder with vascular disease and thrombosis. Thromb Res. 1993;71:337–359[CrossRef][Medline]
This article has been cited by other articles:
|
|
|
|
 
U. Lim, K. Peng, B. Shane, P. J. Stover, A. A. Litonjua, S. T. Weiss, J. M. Gaziano, R. L. Strawderman, F. Raiszadeh, J. Selhub, et al.
Polymorphisms in Cytoplasmic Serine Hydroxymethyltransferase and Methylenetetrahydrofolate Reductase Affect the Risk of Cardiovascular Disease in Men
J. Nutr.,
August 1, 2005;
135(8):
1989 - 1994.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D Castle
Clinical challenges posed by new biotechnology
Postgrad. Med. J.,
February 1, 2003;
79(928):
65 - 66.
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Klerk, P. Verhoef, R. Clarke, H. J. Blom, F. J. Kok, E. G. Schouten, and and the MTHFR Studies Collaboration Group
MTHFR 677C->T Polymorphism and Risk of Coronary Heart Disease: A Meta-analysis
JAMA,
October 23, 2002;
288(16):
2023 - 2031.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
H. McNulty, M. C McKinley, B. Wilson, J. McPartlin, J. Strain, D. G Weir, and J. M Scott
Impaired functioning of thermolabile methylenetetrahydrofolate reductase is dependent on riboflavin status: implications for riboflavin requirements
Am. J. Clinical Nutrition,
August 1, 2002;
76(2):
436 - 441.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Skoupy, M. Fodinger, M. Veitl, A. Perschl, H. Puttinger, C. Rohrer, K. Schindler, A. Vychytil, W. H. Horl, and G. Sunder-Plassmann
Riboflavin Is a Determinant of Total Homocysteine Plasma Concentrations in End-Stage Renal Disease Patients
J. Am. Soc. Nephrol.,
May 1, 2002;
13(5):
1331 - 1337.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M.C. Verhaar, E. Stroes, and T.J. Rabelink
Folates and Cardiovascular Disease
Arterioscler Thromb Vasc Biol,
January 1, 2002;
22(1):
6 - 13.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Roest, Y. T. van der Schouw, D. E. Grobbee, M. J. Tempelman, P. G. de Groot, J. J. Sixma, and J. D. Banga
Methylenetetrahydrofolate Reductase 677 C/T Genotype and Cardiovascular Disease Mortality in Postmenopausal Women
Am. J. Epidemiol.,
April 1, 2001;
153(7):
673 - 679.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
L. Brattstrom and D. E. Wilcken
Homocysteine and cardiovascular disease: cause or effect?
Am. J. Clinical Nutrition,
August 1, 2000;
72(2):
315 - 323.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
P. M. Ridker, J. E. Manson, J. E. Buring, J. Shih, M. Matias, and C. H. Hennekens
Homocysteine and Risk of Cardiovascular Disease Among Postmenopausal Women
JAMA,
May 19, 1999;
281(19):
1817 - 1821.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
Top
Abstract
Methods