Dihydropyrimidine dehydrogenase deficiency (DPD deficiency) is an inherited disorder caused by a deficiency of the enzyme dihydropyrimidine dehydrogenase (DPD). This enzyme is responsible for breaking down certain molecules called pyrimidines, which are found in many foods. Without enough DPD, these molecules build up in the body and can cause a variety of symptoms, including nausea, vomiting, abdominal pain, and fatigue. DPD deficiency can also lead to an increased risk of certain types of cancer, such as colorectal cancer. Treatment for DPD deficiency typically involves dietary changes and medications to reduce the levels of pyrimidines in the body.