A novel intronic mutation results in the use of a cryptic splice acceptor site within the coding region of UGT1A1, causing Crigler-Najjar syndrome type 1

Baljit S. Sappal, Siddhartha S. Ghosh, Benjamin Shneider, Ajit Kadakol, Jayanta Roy Chowdhury, Namita Roy Chowdhury

Research output: Contribution to journalArticle

13 Scopus citations

Abstract

Crigler-Najjar syndrome type 1 (CN-1) is characterized by severe unconjugated hyperbilirubinemia due to an inherited deficiency of hepatic bilirubin uridinediphosphoglucuronate glucuronosyltransferase (UGT1A1), inherited as an autosomal recessive characteristic. CN-1 is potentially lethal because of the risk of bilirubin encephalopathy (kernicterus). Genetic lesions of the coding region of the UGT1A1 gene are known to cause CN-1. Here, we report a CN-1 patient who has a novel G > A mutation at the splice acceptor site in intron 4 (IVS4-1 G > A) on one allele, and a T > A substitution followed by a 13-nt deletion in exon 2 (877T > A 878-890del) of the other allele. As the UGT1A1 gene is expressed specifically in the liver, structural analysis of the expressed UGT1A1 mRNA requires liver biopsy. To use a noninvasive approach to determine the effect of the splice site mutation on splicing of the RNA transcript, we amplified the relevant region of the genomic DNA by long-range polymerase chain reaction (PCR). The amplicon was cloned in an expression plasmid and transfected into COS-7 cells. The expressed mRNA was amplified by reverse-transcription-primed PCR. Nucleotide sequence determination of the amplicon showed that the splice acceptor site mutation caused splicing of the 3′-end of exon 4 to a cryptic splice site within exon 5. This resulted in deletion of the first 7 nucleotides of exon 5, causing a frameshift and premature truncation of UGT1A1, with consequent inactivation of the enzyme.

Original languageEnglish (US)
Pages (from-to)134-142
Number of pages9
JournalMolecular Genetics and Metabolism
Volume75
Issue number2
DOIs
StatePublished - Jan 1 2002

Keywords

  • Bilirubin
  • Crigler-Najjar syndrome
  • Splicing abnormality
  • UDP-glucuronosyltransferase

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Biochemistry
  • Molecular Biology
  • Genetics
  • Endocrinology

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