Previously, to understand human-specific neonatal jaundice, and to overcome species difference of the glucuronidation activities between humans and mice, we established humanized UGT1 (hUGT1) mice in which the original Ugt1 locus was disrupted and replaced with the human UGT1 locus [15,16]. Here, UGT1A8 is linked to neonatal jaundice.