Associations Between Single Nucleotide Polymorphisms in Folate Uptake and Metabolizing Genes with Blood Folate, Homocysteine, and DNA Uracil Concentrations

Background—Folate is an essential nutrient that supports nucleotide synthesis and biological methylation reactions. Diminished folate status results in chromosome breakage and is associated with several diseases, including colorectal cancer. Folate status is also inversely related to plasma homocysteine concentrations—a risk factor for cardiovascular disease. Objective—We sought to gain further understanding of the genetic determinants of plasma folate and homocysteine concentrations. Because folate is required for the synthesis of thymidine from uracil, the latter accumulating and being misincorporated into DNA during folate depletion, the DNA uracil content was also measured. Design—Thirteen single nucleotide polymorphisms (SNPs) in genes involved in folate uptake and metabolism, including folate hydrolase (FOLH1), folate polyglutamate synthase (FPGS), γ-glutamyl hydrolase (GGH), methylene tetrahydrofolate reductase (MTHFR), methionine synthase (MTR), proton-coupled folate transporter (PCFT), and reduced folate carrier (RFC1), were studied in a cohort of 991 individuals. Results—The MTHFR 677TT genotype was associated with increased plasma homocysteine and decreased plasma folate. MTHFR 1298A\u3eC and RFC1 intron 5A\u3eG polymorphisms were associated with significantly altered plasma homocysteine concentrations. The FOLH1 1561C\u3eT SNP was associated with altered plasma folate concentrations. The MTHFR 677TT genotype was associated with a ≈34% lower DNA uracil content (P = 0.045), whereas the G allele of the GGH – 124T\u3eG SNP was associated with a stepwise increase in DNA uracil content (P = 0.022). Conclusion—Because the accumulation of uracil in DNA induces chromosome breaks, mutagenic lesions, we suggest that, as for MTHFR C677T, the GGH – 124 T\u3eG SNP may modulate the risk of carcinogenesis and therefore warrants further attention