Common DPYD Mutation Associated with 5-Fluorouracil Toxicity Detected by PCR-mediated Site-directed Mutagenesis

The human dihydropyrimidine dehydrogenase gene (DPYD) encodes dihydropyrimidine dehydrogenase (DPD; EC 1.3.1.2), the first and rate-limiting enzyme in the three-step pathway of uracil and thymine catabolism. DPD is also the principal enzyme involved in detoxification of pyrimidine-based antimetabolic analogs, such as 5-fluorouracil (5-FU), a drug that is commonly used in the treatment of solid tumors (colon, breast, head, neck, ovary, and skin). Because >80% of the administered 5-FU is degraded by DPD (1), the DPD catalytic activity in cancer patients could affect the efficacy of 5-FU treatment. In cancer patients with very low DPD activity, toxic reactions (e.g., diarrhea, stomatitis, mucositis, myelosuppression, and neurotoxicity) were reported that in some cases were life-threatening and sometimes fatal (2). A frequency as high as 3% of putative heterozygotes for DPD deficiency was also estimated based on catalytic activities in population studies (3)(4). The identification and characterization of the human DPD cDNA (5) made possible the identification and molecular analysis of mutations that affect DPD expression and catalytic activity. The most common mutation (6) associated …