These mice have a targeted mutation in the Ugt1 gene, complete absence of glucuronidation activity, severe hyperbilirubinemia from birth, severe cerebellar abnormalities, and death by kernicterus before P16 [(Bortolussi et al, 2012, 2014a) and Fig EV3A–C]. Here, UGT1A1 is linked to Hyperbilirubinemia.