Crigler-Najjar syndrome type I is characterized by unconjugated
hyperbilirubinemia resulting from an autosomal recessive inherited deficiency of hepatic
UDP-glucuronosyltransferase (UGT) 1A1 activity. The
enzyme is essential for glucuronidation and biliary excretion of
bilirubin, and its absence can be fatal. The Gunn rat is an excellent animal model of this disease, exhibiting a single
guanosine (G) base deletion within the UGT1A1 gene. The defect results in a frameshift and a
premature stop codon, absence of
enzyme activity, and
hyperbilirubinemia. Here, we show permanent correction of the UGT1A1 genetic defect in Gunn rat liver with site-specific replacement of the absent G residue at
nucleotide 1206 by using an
RNA/
DNA oligonucleotide designed to promote endogenous repair of genomic
DNA. The chimeric
oligonucleotide was either complexed with
polyethylenimine or encapsulated in anionic
liposomes, administered i.v., and targeted to the hepatocyte via the
asialoglycoprotein receptor. G insertion was determined by PCR amplification, colony lift hybridizations,
restriction endonuclease digestion, and
DNA sequencing, and confirmed by genomic Southern blot analysis. DNA repair was specific, efficient, stable throughout the 6-month observation period, and associated with reduction of serum
bilirubin levels. Our results indicate that correction of the UGT1A1 genetic lesion in the Gunn rat restores
enzyme expression and
bilirubin conjugating activity, with consequent improvement in the metabolic abnormality.