Hereditary Unconjugated Hyperbilirubinemia

Abstract

Congenital hereditary non-conjugate hyperbilirubinemias include Gilbert’s syndrome, Crigler-Najjar type 1 and Crigler-Najjar type 2 syndromes (or Arias’ disease). They are caused by a hereditary deficiency of the enzyme - bilirubinuridine-5’-diphosphate glucuronosyltransferase (UGT1A1), involved in the glucuronization of bilirubin. The enzyme deficiency is due to mutations in the UGT1A1 gene, which provides UGT1A1 activity. Complete or almost complete loss of (Crigler-Najjar syndrome type 1) or decreased UGT1A1 activity (Gilbert’s syndrome and Crigler-Najjar syndrome type 2) lead to impaired conversion of bilirubin in the liver with the accumulation of unconjugated bilirubin in the blood. Syndromes are distinguished by the level of bilirubin in blood plasma, the reaction to the introduction of phenobarbital, the presence or absence of bilirubin glucuronides in bile.