Primary shunt hyperbilirubinemia (PSHB) is a rare form of clinical jaundice characterized by increased serum levels of unconjugated bilirubin associated with ineffective erythropoiesis and a hyperplastic bone marrow. Peripheral red blood cell survival is normal (summary by Wang et al., 2006). Although primary shunt hyperbilirubinemia is clinically similar to Gilbert syndrome (143500), affected individuals do not have impaired activity of UDP-glucuronosyltransferase (UGT1A1; 191740). The term 'shunt' refers to a 'shortcut' in bilirubin production, from the bone marrow or from very young red blood cells as opposed to being derived from the hemoglobin of mature circulating erythrocytes (Israels et al., 1959). [from OMIM]