DPYD(Dihydropyrimidine Dehydrogenase), also called DPD, is an enzyme that in humans is encoded by the DPYD gene. The protein encoded by this gene is a pyrimidine catabolic enzyme and the initial and rate-limiting factor in the pathway of uracil and thymidine catabolism. The structure of the DPYD gene contains 23 exons spanning about 950 kb. Using somatic cell hybrid strategies, the DPYD gene is mapped to the centromeric region of chromosome 1 between 1p22 and 1q21. By fluorescence in situ hybridization, the DPYD gene is mapped to 1p22. The highest level of DPD was found in monocytes followed by that in lymphocytes, granulocytes, and platelets, whereas no significant activity of DPD could be detected in erythrocytes. The activity of DPD in peripheral blood mononuclear cells was intermediate between that observed in monocytes and lymphocytes. By cDNA microarray, Western blot analysis, and luciferase reporter assay, the transcription factor LSF was identified as a positive regulator of DPYD.