Discrimination between Crigler-Najjar type I and II by expression of mutant bilirubin uridine diphosphate-glucuronosyltransferase

J Clin Invest. 1994 Dec;94(6):2385-91. doi: 10.1172/JCI117604.


Crigler-Najjar (CN) disease is classified into two subtypes, type I and II. The molecular basis for the difference between these types is not well understood. Several mutations in the bilirubin UDP-glucuronosyl-transferase (B-UGT) gene of six CN type I and two CN type II patients were identified. Recombinant cDNAs containing these mutations were expressed in COS cells. B-UGT activity was measured using HPLC and the amount of expressed protein was quantitated using a sandwich ELISA. This enabled us to determine the specific activities of the expressed enzymes. All type I patients examined had mutations in the B-UGT1 gene that lead to completely inactive enzymes. The mutations in the B-UGT1 gene of patients with CN type II only partially inactivated the enzyme. At saturating concentrations of bilirubin (75 microM) CN type II patient A had 4.4 +/- 2% residual activity and CN type II patient B had 38 +/- 2% residual activity. Kinetic constants for the glucuronidation of bilirubin were determined. The affinities for bilirubin of B-UGT1 expressed in COS cells and B-UGT from human liver microsomes were similar with Km of 5.1 +/- 0.9 microM and 7.9 +/- 5.3 microM, respectively. B-UGT1 from patient B had a tenfold decreased affinity for bilirubin, Km = 56 +/- 23 microM. At physiological concentrations of bilirubin both type II patients will have a strongly reduced conjugation capacity, whereas type I patients have no B-UGT activity. We conclude that CN type I is caused by a complete absence of functional B-UGT and that in CN type II B-UGT activity is reduced.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Animals
  • Bilirubin / analogs & derivatives
  • Bilirubin / biosynthesis
  • Cells, Cultured
  • Child
  • Child, Preschool
  • Crigler-Najjar Syndrome / classification*
  • Crigler-Najjar Syndrome / enzymology
  • Crigler-Najjar Syndrome / genetics*
  • Enzyme-Linked Immunosorbent Assay
  • Female
  • Glucuronosyltransferase / biosynthesis
  • Glucuronosyltransferase / genetics*
  • Glucuronosyltransferase / immunology
  • Humans
  • Infant
  • Male
  • Microsomes, Liver / enzymology
  • Mutagenesis, Site-Directed
  • Mutation*
  • Recombinant Proteins / biosynthesis
  • Recombinant Proteins / immunology
  • Transfection


  • Recombinant Proteins
  • bilirubin glucuronoside glucuronosyltransferase
  • bilirubin glucuronate
  • Glucuronosyltransferase
  • Bilirubin