Polymorphisms of Key Enzymes in Homocysteine Metabolism Affect Diet Responsiveness of Plasma Homocysteine in Healthy Women

High plasma total homocysteine (tHcy), low dietary intake of folate and other B vitamins, and genetic polymorphisms related to metabolism of homocysteine may interactively contribute to the risk of cardiovascular disease. We investigated whether known mutations in genes regulating homocysteine metabolism affect the responsiveness of serum folate and plasma tHcy to high intake of natural folate from food. Healthy females (n 5 37) aged 22-57 y volunteered to participate in a crossover dietary intervention with two 5-wk diet periods (low and high folate diets). Concentrations of serum and RBC folate, serum vitamin B-12 and plasma tHcy were measured at baseline and at the end of each diet period. The prevalences of C677T transition of methylenetetrahydrofolate reductase (MTHFR) gene, 844ins68 of cystathionine b-synthase (CBS) gene and A2756G mutation of methionine synthase (MS) gene were determined. Compared with the low folate diet, the high folate diet increased the serum folate concentration by 85% (P , 0.001), 77% (P , 0.001) and 55% (P , 0.05) in the subjects with the genotypes C/C (n 5 19), C/T (n 5 13) and T/T (n 5 5), respectively, of the MTHFR gene. Also, the plasma tHcy of the subjects with the genotypes C/C, C/T and T/T was decreased by 11% (P , 0.001), 15% (P , 0.01) and 18% (P , 0.05), respectively, during the high folate diet period. The subjects carrying the G2756 allele of the MS gene (n 5 15) had a more extensive reduction (P , 0.05) of plasma tHcy during the high folate diet period than the subjects with the genotype A/A (n 5 22). The 844ins68 of CBS gene did not affect plasma tHcy concentrations or diet responsive- ness. In conclusion, diet responsiveness of plasma homocysteine may be genetically regulated. J. Nutr. 131: 2643-2647, 2001.