UGT1A1*6 and *28, missense variants leading to reduced enzyme activity (Beutler et al., 1998), showed clinical significance as pathogenic variants for a hyperbilirubinemia condition called Gilbert’s syndrome (Landrum et al., 2017), which is associated with irinotecan toxicity in Asians (Han et al., 2014; Atasilp et al., 2016). Here, UGT1A1 is linked to Gilbert syndrome.