UGT1A1 and Decreased total neutrophil count: Some of these isoforms have been shown to have clinical significance for SN-38 glucuronidation and irinotecan-related toxicity; in particular, the low-activity UGT1A1 isoform, UGT1A1*28, is strongly associated with irinotecan-induced neutropenia [3,4], especially in Western populations.