Neonatal hUGT1 mice develop severe hyperbilirubinemia due to a reduction in liver UGT1A1 gene expression.15 In hUGT1/Pxr−/− mice, liver UGT1A1 is induced when compared to expression in hUGT1 mice. This evidence concerns the gene UGT1A1 and Hyperbilirubinemia.