Gilbert disease and type I and II Crigler-Najjar syndrome due to mutations in the same UGT1A1 gene locus

Background: Gilbert syndrome and the Crigler-Najjar syndromes Type I and II are disorders of bilirubin conjugation with consecutive indirect hyperbilirubinemia of different severity. Morbus Gilbert is a mild hyperbilirubinemia, which is only of significance in case of drug therapy or differential diagnosis. Crigler-Najjar syndrome II leads to a more serious kind of hyperbilirubinemia. In case of Crigler-Najjar syndrome I patients are suffering from a very severe hyperbilirubinemia, which often causes death during the first months of life. The molecular defects of these three syndromes have been characterized during the last decade. They are caused by mutations in the UGT1A1 gene locus. This locus codes for the enzyme bilirubin uridine 5'-diphosphate-(UDP-) glucuronosyltransferase (UGT1A1). In the case of Gilbert syndrome two bases are inserted into the promoter of the gene. In Crigler-Najjar syndrome type I and II mutations lead to the exchange of amino acids, changes of the reading frame or to stop codons.

Conclusions: All three forms of indirect hyperbilirubinemia are caused by mutations in the UGT1A1 gene locus, which codes for the enzyme UDP-glucuronosyltransferase.