Major genetic determinants of hepatotoxicity due to altered drug metabolism include DPYD polymorphisms and 5-fluorouracil toxicity in treatment of solid carcinomas [27], variants in TPMT and hematological toxicity of 6-mercaptopurines for treatment of leukemia and morbus Crohn [28,29], gene duplications of CYP2D6 and codeine toxicity [30] as well as the toxicity of the oncology compound irinotecan linked to indels in the UGT1A1 promoter (UGT1A1*28) [31]. This evidence concerns the gene UGT1A1 and leukemia.