Methylenetetrahydrofolate reductase gene polymorphism, global DNA methylation and blood pressure: a population based study from North India

BACKGROUND: Hypertension is a complex disorder affected by gene-environment interactions. Methylenetetrahydrofolate reductase (MTHFR) gene is one of the genes in One Carbon Metabolic (OCM) pathway that affects both blood pressure and epigenetic phenomenon. MTHFR C677T gene polymorphism leads to reduced methylation capacity via increased homocysteine concentrations. Global DNA methylation (5mC%) also gets affected in conditions such as hypertension. However, no study is found to understand hypertension in terms of both genetics and epigenetics. The present study aims to understand the relation between methylation, MTHFR C677T gene polymorphism and hypertension. It also tries to understand relation (if any) between methylation and anti-hypertensive drugs. METHODS: This is a cross-sectional study where data were collected from a total of 1634 individuals of either sex in age group 35–65 years. Hypertensives (SBP ≥ 140 mm Hg and DBP ≥ 90 mm Hg) (on treatment/not on treatment) and absolute controls were 236 (cases) and 307 (controls), respectively. All the samples were subjected to MTHFR C677T gene polymorphism screening (PCR–RFLP) and global DNA methylation assay (ELISA based colorimetric assay). Results of both the analyses were obtained on 218 cases, 263 controls. RESULTS: Median 5mC% was relatively lower among cases (p > 0.05) compared to controls, despite controlling for confounders (age, sex, smoking, alcohol, diet) (r(2)-0.92, p-0.08). Cases not on medication had significantly reduced 5mC% compared to controls (p < 0.05), despite adjusting for confounders (r(2)-0.857, p-0.01). Among cases (irrespective of treatment), there was a significant variation in 5mC% across the three genotypes i.e. CC, CT and TT, with no such variation among controls. Cases (not on medication) with TT genotype had significantly lower methylation levels compared to the TT genotype controls and cases (on medication) (p < 0.01). CONCLUSION: Global DNA hypomethylation seems to be associated with hypertension and antihypertensive drugs seem to improve methylation. Hypertensive individuals with TT genotype but not on medication are more likely to be prone to global DNA hypomethylation. Important precursors in OCM pathway include micronutrients such as vitamin B-12, B-9 and B-6; their nutritional interventions (either dietary or supplement) may serve as strategies to prevent hypertension at population level. However, more epidemiological-longitudinal studies are needed for further validation.