Crigler-Najjar syndrome

Crigler-Najjar (CN) syndrome is a familial unconjugated hyperbilirubinemia. It is caused by deficiency of bilirubin-UDP-glucuronosyltransferase (UGT1A1) which is involved in the detoxification of bilirubin. There are two forms of CN. CN-1 is characterized by almost complete absence of UGT1A1 enzyme activity. Left untreated, CN-1 almost invariably results in death from bilirubin encephalopathy (kernicterus). CN-2 is characterized by intermediate levels of hyperbilirubinemia, due to a severe, but incomplete lack of UGT1A1 activity.