Methylenetetrahydrofolate reductase (MTHFR) plays a central role in folate metabolism, regulating the flow of folate groups between two important biosynthetic pathways: DNA synthesis and DNA methylation (Figure 1) [1-4]. Methylenetetrahydrofolate reductase catalyzes the irreversible reduction of 5,10-methylenetetrahydrolate (5,10-methyleneTHF) to 5-methyltetrahydrofolate (5-methylTHF), the main circulating form of folate in plasma and provides methyl groups for de novo synthesis of methionine, the precursor of S-adenosylmethionine (SAM). S-adenosylmethionine is the universal methyl-group donor for methylation of a wide variety of biological substrates, including DNA methylation, and may thereby contribute to carcinogenesis.[5-9]. The substrate for MTHFR, 5,10-methyleneTHF, is an intracellular form of folate required for the conversion of deoxyuridylate (dUMP) to deoxythymidylate (dTMP) and is therefore vital for DNA synthesis. Depletion of this form of folate may produce deoxynucleotide pool imbalances, massive uracil incorporation into DNA and double-strand chromosome breaks, a feature commonly seen in colorectal cancer [10,11].

      The MTHFR gene is located on chromosome 1p36.3. A common C677T substitution (Ala222Val) in exon 4 has been linked with the risk of numerous diseases, including cancer [12]. The variant enzyme is associated with a reduced enzyme activity and increased thermolability [12,13]. Individuals homozygous for the variant allele (677TT) have approximately 30%, whereas heterozygotes (677CT) have 65% of the normal enzyme activity. Compared with the wild-type, heterozygotes and TT homozygotes have lower plasma folate levels, raised homocysteine levels and reduced global DNA methylation in peripheral leucocytes [13-16].

      Numerous studies have been made about the association between the C677T polymorphism and susceptibility to colorectal cancer (CRC). The majority point to a lower prevalence of CRC among individuals with the 677TT genotype [14,18-24], especially at high levels of folate intake [2,17]. However, some studies have implicated the C allele with increased CRC risk [25-27], while others have attributed no significant value to any allele of the C677T polymorphism [28,29]. Ethnicity, lifestyle, and pattern of diet may have introduced variability into different studies. To assess the MTHFR C677T polymorphism as a risk factor for CRC in the Macedonian population, we conducted a case-control study of 413 randomly selected CRC patients and 185 controls without a clinical diagnosis of CRC.