Distribution of 5,10-methylenetetrahydrofolate reductase (C667T) polymorphism and its association with red blood cell 5-methyltetrahydrofolate in the healthy Iranians

Background and aims: Homozygosity for the thermolabile variant of 5, 10-methylenetetrahydrofolate reductase (C677T) that causes hyperhomocysteinemia has been reported in 5-15% of general populations. This mutation has also been suggested to be positively associated with the risk of vascular disease and neural tube defects. It has also been suggested that present dietary reference values may need to be altered for people heterozygote or homozygote for this mutation as tissue folate status has been reported to be compromised by these genetic variants. The aims of this study were to investigate the distribution of 5,10-methylenetetrahydrofolate reductase (C677T) polymorphism in a population of Shiraz, south west of Iran and to test the hypothesis that folate status is compromised by this mutation in our population. Methods: In this study age, body mass index, plasma and red blood cell 5-methytetrahydrofolate, plasma total homocysteine and vitamin B12 of 391 healthy Iranians (198 men and 193 women) together with methylenetetrahydrofolate reductase C667T genotypes were determined. The correlates of methytenetetrahydrofolate reductase polymorphism were determined using univariate and multi-variate statistical analysis. Results: The frequencies of CC, CT and TT genotypes were 56.2%, 38.7% and 5.1%, respectively. The C and T allele frequencies were determined to be 0.76 and 0.24, respectively and this polymorphism was compatible with Hardy-Weinberg equilibrium (X-2 = 1.54, df = 2, P = 0.46). Among all the variables examined, red blood cell 5-methyltetrahydrofolate (P = 0.007, ANOVA) and plasma 5-methyltetrahydrofolate (P = 0.012, ANOVA) were significantly lower in individuals with 17 genotype than those with either CC or CT genotype. Plasma total homocysteine was significantly higher in individuals with TT than those with either CC or CT genotype at below the median levels of red blood cell 5-methylterahydrofolate (P = 0.03, ANOVA) and plasma 5-methylterahydrofolate (P = 0.04, ANOVA). Univariate (r = -0.16, P = 0.002) and multivariate analysis (beta = -0.0005, P = 0,003) showed that red blood cell 5-methylterahydrofolate was the strongest correlates of methylenetetrahydrofolate reductase genotypes. Conclusions: Results from this study suggest that methyltetrahydrofoate reductase C667T genotypes are strongly and independently associated with low red blood cell 5-methylterahydrofolate that has been reported to be a more reliable and long-term marker for body's folate status among Iranians. These results may suggest that substantial minority of people in general populations may have increased folate needs and this may place doubts on the validity of assuming "normality" for nutrient requirements in any general population. (C) 2004 Elsevier Ltd. All rights reserved.