MTHFR and colorectal carcinoma: Therefore, the frequencies of genotype and allele distributions for five SNPs in three major genes involved in capecitabine metabolism [Lys27Gln and Ala70Thr in cytidine deaminase (CDA), S471L in thymidine phosphorylase (TP), and C677T and A1298C in 5,10-methylenetetrahydrofolate reductase (MTHFR)] were examined in CRC patients and compared with control subjects to elucidate their contributions to CRC development risk.