UGT1A1 and neutropenia: Interestingly, adults experience higher frequencies of diarrhea and neutropenia owing to irinotecan because of UGT1A1 gene polymorphisms.[4,5] In Japanese adults, the UGT1A1∗28 and UGT1A1∗6 gene polymorphisms are associated with irinotecan-induced diarrhea and neutropenia.[6,7] However, pediatric studies conducted in the United States did not determine an association between the UGT1A1∗28 gene polymorphism and adverse effects of irinotecan, such as diarrhea and neutropenia.[8,9]