The hereditary hyperbilirubinemias include (1) those resulting in predominantly unconjugated hyperbilirubinemia: Gilbert or Arias syndrome, Crigler-Najjar syndrome type I, and Crigler-Najjar syndrome type II; and (2) those resulting in predominantly conjugated hyperbilirubinemia: Dubin-Johnson syndrome, Rotor syndrome, and several forms of intrahepatic cholestasis. Detailed studies show that patients with Gilbert syndrome have reduced activity of bilirubin glucuronosyltransferase. Genetic Heterogeneity of Hyperbilirubinemia See also Crigler-Najjar syndrome type I (HBLRCN1), Crigler-Najjar syndrome type II (HBLRCN2), and transient familial neonatal hyperbilirubinemia (HBLRTFN), all caused by mutation in the UGT1A1 gene on chromosome 2q37; Dubin-Johnson syndrome (DJS, HBLRDJ), caused by mutation in the ABCC2 gene on chromosome 10q24; and Rotor syndrome (HBLRR), caused by digenic mutation in the SLCO1B1 and SLCOB3 genes, both on chromosome 12p [From OMIM].