Nutrigenetics in cancer research--folate metabolism and colorectal cancer

The B vitamin folate is essential for one-carbon transfer reactions, including those related to the methylation of DNA or other substrates and nucleotide synthesis. Epidemiologic and experimental studies implicate low-folate intakes in elevated risk of colorectal neoplasia and suggest that biologic mechanisms underlying this relation include disturbances in DNA methylation patterns or adverse effects on DNA synthesis and repair. With the completion of the Human Genome Project, a vast amount of data on inherited genetic variability has become available. This genetic information can be used in studies of molecular epidemiology to provide information on multiple aspects of folate metabolism. First, studies linking polymorphisms in folate metabolism to an altered risk of cancer provide evidence for a causal link between this pathway and colorectal carcinogenesis. Second, studies on genetic characteristics can help clarify whether certain individuals may benefit from higher or lower intakes of folate or nutrients relevant to folate metabolism. Third, studies on genetic polymorphisms can generate hypotheses regarding possible biologic mechanisms that connect this pathway to carcinogenesis. Last, genetic variability in folate metabolism may predict survival after a cancer diagnosis, possibly via pharmacogenetic effects. To solve the puzzle of the folate-cancer relation, a transdisciplinary approach is needed that integrates knowledge from epidemiology, clinical studies, experimental nutrition, and mathematical modeling. This review illustrates knowledge that can be gained from molecular epidemiology in the context of nutrigenetics, and the questions that this approach can answer or raise.