Association of seven functional polymorphisms of one-carbon metabolic pathway with total plasma homocysteine levels and susceptibility to Parkinson's disease among South Indians

This study from South India was performed to ascertain the impact of seven functional polymorphisms of one-carbon metabolic pathway on total plasma homocysteine levels and susceptibility to PD. A total of 151 cases of Parkinson's disease and 416 healthy controls were analyzed for fasting plasma homocysteine levels by reverse phase HPLC. PCR-RFLP approaches were used to analyze glutamate carboxypeptidase II (GCPII) 1561 C>T, reduced folate carrier 1 (RFC1) 80 G>A, cytosolic serine hydroxymethyl transferase (cSHMT) 1420 C>T, methylene tetrahydrofolate reductase (MTHFR) 677 C>T, methionine synthase (MTR) 2756 A>G and methionine synthase reductase (MTRR) 66 A>G polymorphisms. PCR-AFLP was used for the analysis of thymidylate synthase (TYMS) 5'-UTR 28bp tandem repeat. PD cases exhibited elevated plasma homocysteine levels compared to controls (men: 28.8 ± 6.9 vs. 16.4 ± 8.8 μmol/L; women: 25.4 ± 5.3 vs. 11.2 ± 5.1μmol/L). Homocysteine levels showed positive correlation with male gender (r=0.39, p<0.0001) and MTRR 66 A>G (r=0.31, p<0.0001) whereas an inverse correlation was observed with cSHMT 1420 C>T polymorphism. MTRR 66 A>G polymorphism showed independent risk for PD (OR: 3.42, 95% CI: 2.35-4.98) whereas cSHMT 1420 C>T conferred protection against PD (OR: 0.11, 95% CI: 0.07-0.17). Multifactor dimensionality reduction analysis showed synergistic interactions between MTHFR 677 C>T and MTRR 66 A>G, whereas cSHMT 1420 C>T exhibited counteracting interactions in altering susceptibility to PD. To conclude, PD cases exhibited hyperhomocysteinemia and MTRR 66 A>G and cSHMT 1420 C>T gene variants were shown to modulate PD risk by altering the homocysteine levels.