Dihydropyrimidine dehydrogenase (DPD) is an enzyme that plays a crucial role in the metabolism of pyrimidine compounds, which are essential building blocks of DNA and RNA. It catalyzes the first step in the breakdown of pyrimidines, specifically converting dihydropyrimidines into pyrimidine-5,6-diones. This process is vital for maintaining proper cellular function and regulating the levels of these compounds in the body. Deficiencies in DPD can lead to severe side effects when patients are treated with certain chemotherapy drugs, such as 5-fluorouracil, which rely on DPD for their metabolism. Understanding the function of DPD is important for optimizing cancer treatment and minimizing toxicity in patients with cancer.