Sequence of Exons and the Flanking Regions of Human Bilirubin–Udp–Glucuronosyltransferase Gene Complex and Identification of A Genetic Mutation in A Patient With Crigler–Najjar Syndrome, Type I

Abstract

Crigler-Najjar syndrome, type I is a heterogeneous disorder that may result from mutations of various regions of the bilirubin-UDP-glucuronosyltransferase gene complex that encodes two bilirubin-UDP-glucuronosyltransferase isoforms and a phenol-UDP-glucuronosyltransferase isoform in the human liver. The two bilirubin-UDP-glucuronosyltransferase messenger RNAs and the phenol-UDP-glucuronosyltransferase messenger RNA have identical 3' regions derived from four consecutive exons. The 5' region of each messenger RNA is unique and is derived from distinct single exons. By screening a human genomic library with probes corresponding to various regions of the messenger RNAs, we have isolated five cosmid clones containing overlapping segments of this large gene complex that spans at least 84 kb of the human genome. To facilitate the amplification of each exon by polymerase chain reaction and their adjacent splice junctions, we have delineated the intron-exon boundaries of the four common region exons and the two single exons that encode the unique regions of the two bilirubin-UDP-glucuronosyltransferase isoforms and have described sequences of the regions flanking each exon. All exons encoding the two bilirubin-UDP-glucuronosyltransferase isoforms and their splice junctions were amplified from the DNA of two control subjects and a Crigler-Najjar syndrome, type I patient. The DNA from the Crigler-Najjar syndrome, type I patient revealed a point mutation in exon 3 (a common region exon) resulting in a stop codon. RNA blot showed that the two bilirubin-UDP-glucuronosyltransferase messenger RNAs in the liver of the Crigler-Najjar syndrome, type I patient were of normal length but were reduced in concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of two single base substitutions in the UGT1 gene locus which abolish bilirubin uridine diphosphate glucuronosyltransferase activity in vitro.

“…This appears to be supported by the data so far available concerning sequence alterations in UGTI associated with CN-I. These alterations include a 13-base frameshift deletion in exon 2 (12), and point mutations in exons 2 (13) and 3 (14). For all ofthe mutations, especially in cases where the suspected mutation is a potentially silent mutation, both biochemical and genetic criteria are required to associate a given mutation in UGTI with the inactivation of bilirubin UDPGT and the onset of CN-I disease.…”

Three Japanese patients with Crigler-Najjar syndrome type I carry an identical nonsense mutation in the gene for UDP-glucuronosyltransferase

“…On the basis of the structure of the gene for human bilirubin UGT, the genetic backgrounds of patients with CN-I have been elucidated. While almost all reported patients with the disease have homozygous nonsense or deletion mutations in the coding region of the gene (Brierley and Burchell, 1993), a few cases with homozygous missense mutations were found recently (Bosma et al, 1992b;Erps et al, 1994). By screening, we found four patients who suffered from CN-I in Japan.…”

Analysis of the UDP-glucuronosyltransferase gene in Portuguese patients with a clinical diagnosis of Gilbert and Crigler–Najjar syndromes

“…The first mutation in this gene was described in 1992. It was a nonsense mutation found in homozygosity in a patient with Crigler -Najjar syndrome [6]. Only in 1995 were mutations in this gene found to be correlated with Gilbert syndrome [7].…”