A mutation in bilirubin uridine 5'-diphosphate-glucuronosyltransferase isoform 1 causing Crigler-Najjar syndrome type II.
BACKGROUND
Inherited unconjugated hyperbilirubinemia in Crigler-Najjar type II (CN II) is caused by a strong reduction of bilirubin uridine 5'-diphosphate-glucuronosyltransferase (B-UGT) activity. Both B-UGT isoenzymes (B-UGT1 and B-UGT2) identified in humans are derived from a single gene by alternative splicing. To clarify the genetic background of CN II and the role of both B-UGT forms in the physiological clearance of bilirubin, we have studied a large kindred with two CN II patients.


METHODS
From genomic DNA all B-UGT encoding exons were amplified by polymerase chain reaction and sequenced to identify mutations causing CN II.


RESULTS
The CN II patients were found to be homozygous for a nucleotide shift in the unique region of B-UGT1, changing a arginine into a tryptophan, and also for a nucleotide shift in the unique region of B-UGT2, changing a leucine into a valine. Analysis of other family members and of 50 control subjects showed that the mutation in B-UGT1 causes CN II, whereas the mutation in B-UGT2 is a polymorphism.


CONCLUSIONS
CN II syndrome appears to be caused by a homozygous mutation in B-UGT1. This indicates that B-UGT1 is the physiological important bilirubin glucuronidating isoform.
Bosma
P J
PJ
Department of Hepatogastroenterology, Academisch Medisch Centrum, Amsterdam, The Netherlands.
Goldhoorn
B
B
Oude Elferink
R P
RP
Sinaasappel
M
M
Oostra
B A
BA
Jansen
P L
PL
D000328:Adult; D003414:Crigler-Najjar Syndrome / Q000201:enzymology / Q000235:genetics*; D005260:Female; D014453:Glucuronosyltransferase / Q000235:genetics*; D006801:Humans; D007527:Isoenzymes / Q000235:genetics*; D008297:Male; D009154:Mutation; D010375:Pedigree
D007527:Isoenzymes; C019787:bilirubin glucuronoside glucuronosyltransferase; D014453:Glucuronosyltransferase