<prompt> The genetic variation in drug metabolism pathway that results in severe toxicity of fluorouracil is:CYP2C9Dihydropyrimidine dehydrogenaseThiopurine-S methyltransferaseCYP2D6  <response>: Genetic variation in drug metabolism pathway dihydropyrimidine dehydrogenase results in severe toxicity of capecitabine, fluorouracil. Ref: Harrison, Edition-18, Page-42. 