![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
G Polymorphism Is Associated with Increased Plasma Homocysteine Concentration When Combined with the Homozygous Methylenetetrahydrofolate Reductase 677CT Variant1,2
Food Science and Human Nutrition Department and * General Clinical Research Center, University of Florida, Gainesville, FL 32611
3To whom correspondence should be addressed. E-mail: lbbailey{at}mail.ifas.ufl.edu.
 |
ABSTRACT |
|---|
 TOP ABSTRACT SUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
T, MTHFR 1298AC, and MTRR 66AG), folate, and vitamin B-12 status on plasma homocysteine in women (20–30 y; n = 362). Plasma homocysteine was inversely (P < 0.0001) associated with serum folate and plasma vitamin B-12 regardless of genotype. Plasma homocysteine was higher (P < 0.05) for women with the MTHFR 677 TT/1298 AA genotype combination compared with the CC/AA, CC/AC, and CT/AA genotypes. Women with the MTHFR 677 TT/MTRR 66 AG genotype had higher (P < 0.05) plasma homocysteine than all other genotype combinations except the TT/AA and TT/GG genotypes. There were 5.4-, 4.3-, and 3.8-fold increases (P < 0.001) in risk for plasma homocysteine in the top 5, 10, and 20%, respectively, of the homocysteine distribution for subjects with the MTHFR 677 TT compared with the CC and CT genotypes. Predicted plasma homocysteine was inversely associated with serum folate (P = 0.003) and plasma vitamin B-12 (P = 0.002), with the degree of correlation dependent on MTHFR 677CT genotype. These data suggest that coexistence of the MTHFR 677 TT genotype with the MTRR 66AG polymorphism may exacerbate the effect of the MTHFR variant alone. The potential negative effect of combined polymorphisms of the MTHFR and MTRR genes on plasma homocysteine in at-risk population groups with low folate and/or vitamin B-12 status, such as women of reproductive potential, deserves further investigation.
KEY WORDS: • folate • genetic polymorphisms • homocysteine • vitamin B-12
The importance of adequate folate status for reproductive health has prompted investigations to evaluate how genetic variations in key folate enzymes may influence one-carbon metabolism. The most widely studied polymorphism is a cytosine to thymine transition in the gene for 5,10-methylenetetrahydrofolate reductase (MTHFR)4 at bp 677, resulting in an alanine to valine substitution in the enzyme (1). MTHFR is required to catalyze the reduction of 5,10-methylenetetrahydrofolate (5,10-methyleneTHF) to 5-methyltetrahydrofolate (5-methylTHF), the primary methyl donor in the remethylation of homocysteine to methionine. The presence of the MTHFR 677 TT genotype is important in women of reproductive age because of its reported association with an increased risk for certain birth defects (2) and pregnancy complications (3,4). Another polymorphism of MTHFR occurs when adenine is replaced with cytosine at bp 1298, yielding a substitution of alanine for glutamate in the enzyme (5,6). Although the variant MTHFR 1298 CC genotype was not reported to affect birth defect risk, double heterozygosity for the 677 and 1298 MTHFR polymorphisms was associated with a significantly higher risk for neural-tube defects (NTDs) (5).
When MTHFR enzyme variants are coupled with other polymorphisms that may affect one-carbon metabolism, the combined metabolic effects may be additive. The methionine synthase (MS) reaction requires vitamin B-12 (cobalamin) as a cofactor for the remethylation of homocysteine to methionine. During the MS reaction, transfer of the methyl group from methylcob(III)alamin results in the formation of the highly reactive cob(I)alamin, which may become oxidized to cob(II)alamin, resulting in MS inactivation (7), an event that may occur every 100 methyl transfer cycles (8). Methionine synthase reductase (MTRR) is required for the reductive methylation of cob(II)alamin (with S-adenosylmethionine providing the methyl group), which reactivates MS. Wilson and colleagues (9) identified a common variant of MTRR (66AG) in which methionine replaces isoleucine in the enzyme with a reported population frequency of 
30% (9–11). Heterozygosity and homozygosity for this polymorphism were associated with an increased risk for NTDs (9,12,13). Of particular importance is that the MTRR 66 GG genotype, in association with the MTHFR 677 TT genotype, was associated with an increased risk for NTDs (9).
The MTHFR 677 TT genotype is associated with elevated plasma homocysteine when folate status is low (14). Although the MTHFR 1298AC polymorphism was not reported to affect homocysteine status, double heterozygosity for both MTHFR polymorphisms was cited as a risk factor for hyperhomocysteinemia (15). Polymorphisms at the MTRR 66AG loci also were associated with an increase in plasma homocysteine, with the GG genotype having a greater effect than the AG genotype (10); however, data are limited and additional research is warranted to further characterize this relation.
Although much of the emphasis has been on folate status, associations between genetic polymorphisms and vitamin B-12 status were reported. Our research group reported data on the effect of folate and vitamin B-12 status on plasma homocysteine in young, healthy women on the basis of their MTHFR 677CT and 1298AC genotypes (16). A significant inverse relation between plasma homocysteine concentration and vitamin B-12 status in women with the MTHFR 677 CT/1298 AC genotype combination was detected, which led to our hypothesis that the presence of the MTRR 66AG polymorphism may have contributed to this inverse relation because MTRR is required for normal vitamin B-12–dependent MS activity. Of interest is the fact that the MTRR 66 GG genotype was associated with an increased risk for having an NTD-affected pregnancy when maternal vitamin B-12 concentrations are low (9).
The objective of the present study was to investigate the combined influence of the MTRR 66AG and MTHFR 677CT and 1298AC polymorphisms and folate and vitamin B-12 status on plasma homocysteine concentration in young women of reproductive age.
|
SUBJECTS AND METHODS |
|---|
|
TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Specimen collections and analytical methods. Blood samples were collected from fasting subjects between October 2000 and January 2001 and immediately processed and stored at –20°C until analyzed. Serum folate concentration was determined using the Lactobacillus casei microbiological assay in a 96-well microplate system, adapted from Tamura (17) and Horne and Patterson (18). Plasma homocysteine was determined by a modification of a method by Pfeiffer et al. (19) using HPLC with fluorescence detection. Plasma vitamin B-12 concentration was determined using a radioligand binding kit (Bio-Rad Quantaphase II).
Genotype determinations.
DNA was extracted from freshly collected or stored blood (–20°C) using a commercially available kit (Bio-Rad Aqua-Pure). Polymorphisms at the MTHFR 677CT and 1298AC loci were detected using the multiplexed restriction fragment length polymorphism PCR protocols of Yi et al. (20). Briefly, using appropriate forward and reverse primer pairs bracketing both mutations, PCR-amplified DNA was digested separately with restriction enzymes, cleaving both products, which were combined and analyzed by agarose gel electrophoresis for band patterns characteristic of wild, heterozygous, or variant profiles for both loci.
Polymorphisms at the MTRR 66AG loci were detected using real-time PCR for allelic discrimination (21) with a commercially available validated kit (Assay-on-Demand, Applied Biosystems) containing optimized primers and Taqman probes. Briefly, PCR amplification reactions containing DNA sample, buffer, MgCl2, dNTPs, Taqman fluorogenic probes, and DNA polymerase (Taq) were performed as recommended. Fluorescence of each reporter dye is suppressed in the intact probe due to the close proximity of a quencher dye. During 5' extension by Taq, probe fluorochromes are cleaved and released from the quencher to provide separate fluorescent signals. Using an ABI 7700 Sequence detection system, the amplified PCR products were detected and data analyzed with GeneAmp 7700 Sequence Detection System software (Applied Biosystems) by monitoring the increase in fluorescence signal over time for each channel representing the matching alleles.
Statistical analysis.
Initial descriptive statistics were calculated and are expressed as means, SD, minimum, and maximum values. ANOVA was used to determine differences in mean plasma vitamin B-12, serum folate, and plasma homocysteine concentrations by genotype (MTRR 66AG, MTHFR 677CT, and MTHFR 1298AC). Pairwise t tests, using Bonferroni’s correction for multiple comparisons, were then performed to determine differences between specific genotype groups. One-way ANOVA was used to detect differences in plasma homocysteine between subjects with plasma vitamin B-12 above vs. below 221 pmol/L, which is considered marginal vitamin B-12 status (22). The strength of the relations between the dependent variables (plasma vitamin B-12, serum folate, and plasma homocysteine) was examined via Pearson’s correlations. Contingency tables were constructed and Fisher’s exact test used to evaluate differences in supplementation status by genotype.
Regression was used to model predicted plasma homocysteine as a function of the MTRR 66AG, MTHFR 677CT, and MTHFR 1298AC genotypes, plasma vitamin B-12, and serum folate concentrations. First-order (genotype by genotype) interactions were evaluated, and any interactions not significant at the 
= 0.10 level were eliminated in stepwise fashion.
Finally, logistic regression was used to calculate odds ratios (OR) and 95% CI in examining the likelihood of having plasma homocysteine in specific percentiles (top 5, 10, 20, and 50%) for the MTRR 66 AG genotype vs. AA and GG genotypes and the MTHFR 677 TT genotype vs. the CC and CT genotypes. For all comparisons, the level was set a priori to 0.05. All statistics were computed using SAS 8.00.
|
RESULTS |
|---|
|
TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Effect of supplement use on folate, vitamin B-12, and homocysteine. Multivitamin supplement use did not differ among any of the genotype groups (P > 0.05). Individuals who reported using multivitamin supplements (n = 160) had significantly higher serum folate (67.4 ± 31.6 vs. 50.5 ± 21.1 nmol/L; P < 0.0001) and plasma vitamin B-12 (350 ± 149 vs. 303 ± 123 pmol/L; P = 0.0016) concentrations than those who did not use supplements (n = 180) before the study, independent of genotype. There was no significant difference (P > 0.05) in plasma homocysteine concentration between supplement users and nonusers.
Folate, vitamin B-12, and homocysteine concentrations by genotype. Plasma homocysteine was inversely associated with both serum folate (P < 0.0001; r = –0.24) and plasma vitamin B-12 (P < 0.0001; r = –0.22) regardless of genotype. Subjects with plasma vitamin B-12 concentrations < 221 pmol/L had significantly (P = 0.005) higher plasma homocysteine concentrations than subjects with values > 221 pmol/L regardless of genotype (7.1 ± 2.1 vs. 6.4 ± 1.6 µmol/L). Serum folate and plasma vitamin B-12 concentrations did not differ among genotype groups for the MTHFR 677 and 1298 variants; however, subjects with the MTHFR 677 TT/1298 AA genotype combination had significantly (P < 0.05) higher homocysteine concentrations than the CC/AA, CC/AC, and CT/AA genotype groups (7.6 ± 2.3 vs. 6.3 ± 1.7, 6.3 ± 1.7, and 6.3 ± 1.5 µmol/L, respectively).
No differences were detected among MTRR 66AG genotype groups for serum folate, plasma vitamin B-12, or plasma homocysteine concentrations (Table 1). Subjects with the MTHFR 677 TT/MTRR 66 AG genotype combination had significantly (P < 0.05) higher plasma homocysteine concentration than subjects with all other genotype combinations (Table 2 and Fig. 1). Subjects with the MTHFR 677 TT genotype were significantly (P < 0.001) overrepresented in the top 5, 10, and 20 percentiles of the homocysteine distribution compared with the CC and CT genotypes (Table 3). A nonsignificant (P = 0.072) increase (1.9-fold) in risk of having homocysteine in the top 10% was detected for subjects with the MTRR 66 AG genotype compared with those with the AA and GG genotypes.
|
|
|
|
T polymorphism and a trend (P = 0.09) for the MTHFR 1298AC polymorphism were found. Within the MTHFR 677CT polymorphism, predicted plasma homocysteine concentration was negatively associated with serum folate (P = 0.003) and plasma vitamin B-12 (P = 0.002) (Fig. 2A and Fig. 2B, respectively).
|
|
DISCUSSION |
|---|
|
TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
G, MTHFR 677CT, and 1298AC polymorphisms and folate and vitamin B-12 status on plasma homocysteine concentration in women of childbearing age. The findings of this study indicate that when the homozygous variant for the MTHFR 677CT polymorphism coexists with the MTRR 66 AG genotype, plasma homocysteine is significantly elevated relative to the other genotype groups. When the MTHFR 677 TT genotype occurred with either the homozygous or heterozygous genotype for the MTRR 66AG variant, plasma homocysteine concentrations were 1.0–1.8 µmol/L higher than that of the other genotype groups. This difference in homocysteine may have physiologic relevance in individuals not consuming foods fortified with folic acid and/or vitamin B-12. The small sample sizes within the TT/AA (n = 9) and the TT/GG (n = 13) genotype groups limited the power to detect significant differences in plasma homocysteine concentration between these and other genotype groups. The results confirm previous reports, including studies by our research group (23,24), that the MTHFR 677 TT genotype is associated with an elevated plasma homocysteine concentration when folate status is low. These data also suggest that low vitamin B-12 status (< 221 pmol/L) negatively affects homocysteine concentration regardless of genotype in our population of healthy young women. Although the homocysteine concentrations above and below 221 pmol/L (6.4 and 7.1 µmol/L, respectively) observed in this study are well within the normal range, this finding may be important in population subgroups (such as vegans) chronically consuming low vitamin B-12 diets. The increasing trend in the consumption of vegetarian diets by young women (25) who do not supplement their diets with vitamin B-12 is a concern because of the association between elevated homocysteine concentration and birth defects (26).
Although the MTHFR 677CT polymorphism was the most extensively studied, a single nucleotide polymorphism occurring at bp 66 of the gene that encodes for MTRR emerged as a potential contributor to elevated homocysteine concentration (10) and birth defect risk (9). Of note is a report that the MTRR 66 GG variant was associated with an increased risk for an NTD-affected pregnancy when maternal vitamin B-12 status was low (9).
Findings from previous reports of the effect of allelic variations of the MTRR 66AG polymorphism on homocysteine status have not been consistent. Gaughan et al. (10) reported a significantly higher homocysteine concentration in men with the GG genotype compared with the AA and AG genotypes. Kluijtmans et al. (27) detected a trend toward higher homocysteine concentration with the presence of the G allele. In contrast, other investigations did not detect a difference in homocysteine concentration among the MTRR 66 genotypes (9,11,28), which is consistent with the findings from the present study.
van der Put et al. (5) reported that double heterozygosity for the MTHFR 677 and 1298 polymorphisms (CT and AC, respectively) was associated with a higher plasma homocysteine concentration than the CT/AA genotype. These data were not confirmed in the present study. In addition, young women with the MTHFR 677 TT/1298 AA genotype combination had significantly higher plasma homocysteine than the other MTHFR 677/1298 genotype combinations. These results are consistent with the findings of Kluijtmans et al. (27) and support the conclusion that the MTHFR 677CT polymorphism has a greater effect on plasma homocysteine than the MTHFR 1298 polymorphism (29).
Zhu et al. (12) found an increased risk for NTDs in infants with the MTRR 66 GG genotype compared with the AA genotype. Additionally, the G allele for the MTRR 66AG polymorphism was shown to increase the risk of having an NTD-affected offspring (12,30), but the role of vitamin B-12 status was not investigated. Wilson et al. (9) examined the effect of vitamin B-12 status and the MTRR 66 GG genotype in mothers and reported that the combination of the GG genotype and a vitamin B-12 concentration in the lowest quartile increased the risk for having an NTD-affected pregnancy 5-fold compared with mothers with the AA genotype with vitamin B-12 concentrations in the other 3 quartiles. Furthermore, the MTHFR 677 TT genotype in combination with the MTRR 66 GG genotype was associated with an increased risk for an NTD-affected pregnancy or of being born with an NTD compared with either genotype alone. Homocysteine concentrations for each of the MTHFR 677/MTRR 66 genotype combinations were not reported. In the present study, plasma homocysteine concentration was significantly higher in individuals with the MTHFR 677 TT/MTRR 66 AG genotype combination compared with all other genotype combinations. Because the MTHFR 677 TT/MTRR 66 AG genotype combination group had the highest homocysteine concentration, the effect of these genotypes on homocysteine was investigated individually. It was evident from the OR results that the MTHFR 677 polymorphism has a greater effect on plasma homocysteine concentration than the MTRR 66 polymorphism.
The findings from this study in healthy, well-nourished young women indicate that both folate and vitamin B-12 status influence predicted homocysteine concentrations regardless of genotype, and the presence of the MTHFR 677 polymorphism exacerbates the relations between predicted plasma homocysteine and folate and vitamin B-12 status. The data from this investigation suggest that coexistence of the MTHFR 677 TT genotype and either the AG or GG genotypes for the MTRR 66AG polymorphism may magnify the effect of the MTHFR TT genotype alone. These findings provide the impetus for future investigations of the combined effect of the MTHFR 677CT and the MTRR 66AG polymorphisms on plasma homocysteine concentration. A particular concern is that the combined presence of these polymorphisms in young women with low folate and/or vitamin B-12 status may increase reproductive health risks.
|
FOOTNOTES |
|---|
G/ methylenetetrahydrofolate reductase 677CT polymorphisms, vitamin B-12 and folate status on plasma homocysteine in young women. FASEB J. 17: 3912 (abs.)]. 
2 Supported by the Florida Agricultural Experiment Station and grants from U.S. Department of Agriculture-National Research Institute 00–35009102, USDA-NRI 00–35009113, National Institutes of Health DK56724, and NIH GCRC RR00082, and approved for publication as Journal Series No. R-10337.
4 Abbreviations used: MS, methionine synthase; MTHFR, methylenetetrahydrofolate reductase; MTRR, methionine synthase reductase; 5,10-methyleneTHF, 5,10-methylenetetrahydrofolate; 5-methylTHF, 5-methyltetrahydrofolate; NTD, neural-tube defect.
Manuscript received 30 June 2004. Initial review completed 4 August 2004. Revision accepted 18 August 2004.
|
LITERATURE CITED |
|---|
|
TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
1. Frosst, P., Blom, H. J., Milos, R., Goyette, P., Sheppard, C. A., Matthews, R. G., Boers, G. J., den Heijer, M., Kluijtmans, L. A. & van den Heuvel, L. P., et al (1995) A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase. Nat. Genet. 10:111-113.[Medline]
2. Shields, D. C., Kirke, P. N., Mills, J. L., Ramsbottom, D., Molloy, A. M., Burke, H., Weir, D. G., Scott, J. M. & Whitehead, A. S. (1999) The "thermolabile" variant of methylenetetrahydrofolate reductase and neural tube defects: An evaluation of genetic risk and the relative importance of the genotypes of the embryo and the mother. Am. J. Hum. Genet. 64:1045-1055.[Medline]
3. Sohda, S., Arinami, T., Hamada, H., Yamada, N., Hamaguchi, H. & Kubo, T. (1997) Methylenetetrahydrofolate reductase polymorphism and pre-eclampsia. J. Med. Genet. 34:525-526.[Abstract]
4. Lissak, A., Sharon, A., Fruchter, O., Kassel, A., Sanderovitz, J. & Abramovici, H. (1999) Polymorphism for mutation of cytosine to thymine at location 677 in the methylenetetrahydrofolate reductase gene is associated with recurrent early fetal loss. Am. J. Obstet. Gynecol. 181:126-130.[Medline]
5. van der Put, N. M., Gabreels, F., Stevens, E. M., Smeitink, J. A., Trijbels, F. J., Eskes, T. K., van den Heuvel, L. P. & Blom, H. J. (1998) A second common mutation in the methylenetetrahydrofolate reductase gene: an additional risk factor for neural-tube defects?. Am. J. Hum. Genet. 62:1044-1051.[Medline]
6. Weisberg, I., Tran, P., Christensen, B., Sibani, S. & Rozen, R. (1998) A second genetic polymorphism in methylenetetrahydrofolate reductase (MTHFR) associated with decreased enzyme activity. Mol. Genet. Metab. 64:169-172.[Medline]
7. Leclerc, D., Wilson, A., Dumas, R., Gafuik, C., Song, D., Watkins, D., Heng, H. H., Rommens, J. M., Scherer, S. W., Rosenblatt, D. S. & Gravel, R. A. (1998) Cloning and mapping of a cDNA for methionine synthase reductase, a flavoprotein defective in patients with homocystinuria. Proc. Natl. Acad. Sci. U.S.A. 95:3059-3064.
8. Fujii, K., Galivan, J. H. & Huennekens, F. M. (1977) Activation of methionine synthase: further characterization of flavoprotein system. Arch. Biochem. Biophys. 178:662-670.[Medline]
9. Wilson, A., Platt, R., Wu, Q., Leclerc, D., Christensen, B., Yang, H., Gravel, R. A. & Rozen, R. (1999) A common variant in methionine synthase reductase combined with low cobalamin (vitamin B-12) increases risk for spina bifida. Mol. Genet. Metab. 67:317-323.[Medline]
10. Gaughan, D. J., Kluijtmans, L.A.J., Barbaux, S., McMaster, D., Young, I. S., Yarnell, J.W.G., Evans, A. & Whitehead, A. S. (2001) The methionine synthase reductase (MTRR) A66G polymorphism is a novel genetic determinant of plasma homocysteine concentrations. Atherosclerosis 157:451-456.[Medline]
11. Brilakis, E. S., Berger, P. B., Ballman, K. V. & Rozen, R. (2003) Methylenetetrahydrofolate reductase (MTHFR) 677CT and methionine synthase reductase (MTRR) 66AG polymorphisms: association with serum homocysteine and angiographic coronary artery disease in the era of flour products fortified with folic acid. Atherosclerosis 168:315-322.[Medline]
12. Zhu, H., Wicker, N. J., Shaw, G. M., Lammer, E. J., Hendricks, K., Suarez, L., Canfield, M. & Finnell, R. H. (2003) Homocysteine remethylation enzyme polymorphisms and increased risks for neural tube defects. Mol. Genet. Metab. 78:216-221.[Medline]
13. Gueant-Rodriguez, R. M., Rendeli, C., Namour, B., Venuti, L., Romano, A., Anello, G., Bosco, P., Debard, R., Gerard, P., Viola, M., Salvaggio, E. & Gueant, J. L. (2003) Transcobalamin and methionine synthase reductase mutated polymorphisms aggravate the risk of neural tube defects in humans. Neurosci. Lett. 344:189-192.[Medline]
14. Jacques, P. F., Bostom, A. G., Williams, R. R., Ellison, R. C., Eckfeldt, J. H., Rosenberg, I. H., Selhub, J. & Rozen, R. (1996) Relation between folate status, a common mutation in methylenetetrahydrofolate reductase, and plasma homocysteine concentrations. Circulation 93:7-9.[Medline]
15. Weisberg, I. S., Jacques, P. F., Selhub, J., Bostom, A. G., Chen, Z., Curtis Ellison, R., Eckfeldt, J. H. & Rozen, R. (2001) The 1298AC polymorphism in methylenetetrahydrofolate reductase (MTHFR): in vitro expression and association with homocysteine. Atherosclerosis 156:409-415.[Medline]
16. Bailey, L. B., Duhaney, R. L., Maneval, D. R., Kauwell, G. P., Quinlivan, E. P., Davis, S. R., Cuadras, A., Hutson, A. D. & Gregory, J. F. (2002) Vitamin B-12 status is inversely associated with plasma homocysteine in young women with C677T and/or A1298C methylenetetrahydrofolate reductase polymorphisms. J. Nutr. 132:1872-1878.
17. Tamura, T. (1990) Microbiological assay of folate. Picciano, M. F. Stokstad, E. R. Gregory, J. F. eds. Folic Acid Metabolism in Health and Disease 1990:121-137 Wiley-Liss New York, NY. .
18. Horne, D. W. & Patterson, D. (1988) Lactobacillus casei microbiological assay of folic acid derivatives in 96-well microtiter plates. Clin. Chem. 34:2357-2359.
19. Pfeiffer, C. M., Huff, D. L. & Gunter, E. W. (1999) Rapid and accurate HPLC assay for plasma total homocysteine and cysteine in a clinical laboratory setting. Clin. Chem. 45:290-292.
20. Yi, P., Pogribny, I. P. & Jill James, S. (2002) Multiplex PCR for simultaneous detection of 677 CT and 1298 AC polymorphisms in methylenetetrahydrofolate reductase gene for population studies of cancer risk. Cancer Lett. 181:209-213.
21. Ulvik, A. & Ueland, P. M. (2001) Single nucleotide polymorphism (SNP) genotyping in unprocessed whole blood and serum by real-time PCR: application to SNPs affecting homocysteine and folate metabolism. Clin. Chem. 47:2050-2053.
22. Lindenbaum, J. & Allen, R. (1995) Clinical spectrum and diagnosis of folate deficiency. Bailey, L. eds. Folate in Health and Disease 1995:43-73 Marcel Dekker New York, NY. .
23. Kauwell, G. P., Wilsky, C. E., Cerda, J. J., Herrlinger-Garcia, K., Hutson, A. D., Theriaque, D. W., Boddie, A., Rampersaud, G. C. & Bailey, L. B. (2000) Methylenetetrahydrofolate reductase mutation (677CT) negatively influences plasma homocysteine response to marginal folate intake in elderly women. Metabolism 49:1440-1443.[Medline]
24. Shelnutt, K. P., Kauwell, G. P., Chapman, C. M., Gregory, J. F., Maneval, D. R., Browdy, A. A., Theriaque, D. W. & Bailey, L. B. (2003) Folate status response to controlled folate intake is affected by the methylenetetrahydrofolate reductase 677CT polymorphism in young women. J. Nutr. 133:4107-4111.
25. Barr, S. I. & Broughton, T. M. (2000) Relative weight, weight loss efforts and nutrient intakes among health-conscious vegetarian, past vegetarian and nonvegetarian women ages 18 to 50. J. Am. Coll. Nutr. 19:781-788.
26. Steegers-Theunissen, R. P., Boers, G. H., Blom, H. J., Nijhuis, J. G., Thomas, C. M., Borm, G. F. & Eskes, T. K. (1995) Neural tube defects and elevated homocysteine levels in amniotic fluid. Am. J. Obstet. Gynecol. 172:1436-1441.[Medline]
27. Kluijtmans, L. A., Young, I. S., Boreham, C. A., Murray, L., McMaster, D., McNulty, H., Strain, J. J., McPartlin, J., Scott, J. M. & Whitehead, A. S. (2003) Genetic and nutritional factors contributing to hyperhomocysteinemia in young adults. Blood 101:2483-2488.
28. Jacques, P. F., Bostom, A. G., Selhub, J., Rich, S., Ellison, R. C., Eckfeldt, J. H., Gravel, R. A. & Rozen, R. (2003) Effects of polymorphisms of methionine synthase and methionine synthase reductase on total plasma homocysteine in the NHLBI Family Heart Study. Atherosclerosis 166:49-55.[Medline]
29. Yamada, K., Chen, Z., Rozen, R. & Matthews, R. G. (2001) Effects of common polymorphisms on the properties of recombinant human methylenetetrahydrofolate reductase. Proc. Natl. Acad. Sci. U.S.A. 98:14853-14858.
30. Doolin, M. T., Barbaux, S., McDonnell, M., Hoess, K., Whitehead, A. S. & Mitchell, L. E. (2002) Maternal genetic effects, exerted by genes involved in homocysteine remethylation, influence the risk of spina bifida. Am. J. Hum. Genet. 71:1222-1226.[Medline]
This article has been cited by other articles:
|
|
 |
|
  M. J. Shrubsole, Y.-T. Gao, Q. Cai, X. O. Shu, Q. Dai, F. Jin, and W. Zheng MTR and MTRR Polymorphisms, Dietary Intake, and Breast Cancer Risk. Cancer Epidemiol. Biomarkers Prev., March 1, 2006; 15(3): 586 - 588. [Full Text] [PDF]
|
|
|
|
 |
|
 J.-L. Gueant, L. Xiaohong, S. Ortiou, P. Gerard, S. Shue, F. Namour, L. D. McCabe, G. P McCabe, and J H. Pratt The association between plasma homocysteine and holo-transcobalamin and the transcobalamin 776C->G polymorphism is influenced by folate in the absence of supplementation and fortified diet Am. J. Clinical Nutrition, January 1, 2006; 83(1): 171 - 172. [Full Text] [PDF]
|
|
|
|
 |
|
 B. Beagle, T. L. Yang, J. Hung, E. A. Cogger, D. J. Moriarty, and M. A. Caudill The Glycine N-Methyltransferase (GNMT) 1289 C->T Variant Influences Plasma Total Homocysteine Concentrations in Young Women after Restricting Folate Intake J. Nutr., December 1, 2005; 135(12): 2780 - 2785. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. M von Castel-Dunwoody, G. P. Kauwell, K. P Shelnutt, J. D Vaughn, E. R Griffin, D. R Maneval, D. W Theriaque, and L. B Bailey Transcobalamin 776C->G polymorphism negatively affects vitamin B-12 metabolism Am. J. Clinical Nutrition, June 1, 2005; 81(6): 1436 - 1441. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
