Nutrient-Gene Interactions Methionine Synthase Reductase 66A3 G Polymorphism Is Associated with Increased Plasma Homocysteine Concentration When Combined with the Homozygous Methylenetetrahydrofolate Reductase 677C3 T Variant 1,2 Jaimie D. Vaughn, Lynn B. Bailey, 3 Karla P. Shelnutt, Kristina M. von-Castel Dunwoody, David R. Maneval, Steven R. Davis, Eoin P. Quinlivan, Jesse F. Gregory, III, Douglas W. Theriaque,* and Gail P. A. Kauwell Food Science and Human Nutrition Department and *General Clinical Research Center, University of Florida, Gainesville, FL 32611 ABSTRACT Methylenetetrahydrofolate reductase (MTHFR) and methionine synthase reductase (MTRR) are im- portant for homocysteine remethylation. This study was designed to determine the influence of genetic variants (MTHFR 677C3 T, MTHFR 1298A3 C, and MTRR 66A3 G), folate, and vitamin B-12 status on plasma homocys- teine 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 677C3 T genotype. These data suggest that coexistence of the MTHFR 677 TT genotype with the MTRR 66A3 G 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. J. Nutr. 134: 2985–2990, 2004. 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 cyto- sine to thymine transition in the gene for 5,10-methylenetet- rahydrofolate 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-methylenetetrahy- drofolate (5,10-methyleneTHF) to 5-methyltetrahydrofolate (5-methylTHF), the primary methyl donor in the remethyla- tion of homocysteine to methionine. The presence of the MTHFR 677 TT genotype is important in women of repro- ductive age because of its reported association with an in- creased risk for certain birth defects (2) and pregnancy com- plications (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 methio- nine. 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 1 Presented in part at Experimental Biology ’04, April 2004, Washington, DC [Vaughn, J., Bailey, L. B., von-Castel Dunwoody, K., Shelnutt, K. P., Maneval, D. R., Davis, S. R., Quinlivan, E. P., Gregory, J. F., III & Kauwell, G.P.A. (2004) Combined influence of the methionine synthase reductase 66A3G/ methyl- enetetrahydrofolate reductase 677C3T 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. 3 To whom correspondence should be addressed. E-mail: lbbailey@mail.ifas.ufl.edu. 4 Abbreviations used: MS, methionine synthase; MTHFR, methylenetetrahy- drofolate reductase; MTRR, methionine synthase reductase; 5,10-methyleneTHF, 5,10-methylenetetrahydrofolate; 5-methylTHF, 5-methyltetrahydrofolate; NTD, neural-tube defect. 0022-3166/04 $8.00 © 2004 American Society for Nutritional Sciences. Manuscript received 30 June 2004. Initial review completed 4 August 2004. Revision accepted 18 August 2004. 2985 Downloaded from https://academic.oup.com/jn/article/134/11/2985/4688494 by guest on 28 August 2022