MTHFR Polymorphism and B-Vitamin Levels

The association between the genotypes of the MTHFR polymorphism and allelic frequencies with the demographic variables was analyzed with Chi-square test. T-test was used to determine the association of homocysteine, vitamin B₁₂ and folic acid levels between cases and controls irregardless of the genotypes. The association between the plasma homocysteine, vitamin B₁₂ and folic acid levels and the MTHFR polymorphisms were analyzed using 3-way ANOVA. P values were considered statistically significant if they were less than 0.05. The sample size was determined using the power analysis, with the α error and β error set at 0.05 and 0.20 respectively. Approximately 40 subjects per group were sufficient for parametric test (Cohen, 1977) whilst for non-parametric test such as Chi-Square test, the expected frequency of a minimum 5 for each category was sufficient (Hays, 1994). The measure of skewness and kurtosis were used to assess the normality of the distribution of the parameters (homocysteine, vitamin B₁₂ and folic acid levels).