DPYD is a pyrimidine catabolic enzyme and the initial and rate-limiting factor in the pathway of uracil and thymidine catabolism. DPYD plays a crucial role in the metabolism of pyrimidines, catalyzing the first rate-limiting step in the NADPH-dependent catabolism of uracil and thymine to dihydrouracil and dihydrothymine. DPYD deficiency can lead to the accumulation of uracil and thymine, potentially contributing to neurological disorders and posing significant risks for cancer patients undergoing treatment with certain pyrimidine analogs. DPYD is integral to the metabolic pathway of the anticancer drug 5-fluorouracil (5-FU), influencing both efficacy and potential toxicity. Variations in DPYD expression can occur due to transcriptional changes, such as hypermethylation of the DPYD promoter, which can downregulate enzyme expression.