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.
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.
Sappal
Baljit S
BS
Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Ghosh
Siddhartha S
SS
Shneider
Benjamin
B
Kadakol
Ajit
A
Chowdhury
Jayanta Roy
JR
Chowdhury
Namita Roy
NR
D003414:Crigler-Najjar Syndrome / Q000175:diagnosis / Q000235:genetics*; D014453:Glucuronosyltransferase / Q000172:deficiency / Q000235:genetics*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007438:Introns / Q000235:genetics; D009154:Mutation; D022821:RNA Splice Sites / Q000235:genetics; D017384:Sequence Deletion / Q000235:genetics; D000099148:UGT1A1 Enzyme
D014453:Glucuronosyltransferase; D022821:RNA Splice Sites; D000099148:UGT1A1 Enzyme