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Two Different UGT1A1 Mutations causing Crigler–Najjar Syndrome types I and II in an Iranian Family

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Yoshihiro Maruo1, Mahdiyeh Behnam2, Shinichi Ikushiro3, Sayuri Nakahara1, Narges Nouri4, Mansour Salehi5

1) Department of Pediatrics, Shiga University of Medical Science, Otsu, Shiga, Japan
2) Medical Genetics Laboratory of Genome, Isfahan, Iran
3) Department of Biotechnology, Toyama Prefectural University, Imizu, Toyama, Japan
4) Labkhand Clinic;
5) Division of Genetics and Molecular Biology, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran

DOI: http://dx.doi.org/10.15403/jgld.2014.1121.244.ugt

ABSTRACT
Background: Crigler–Najjar syndrome type I (CN-1) and type II (CN-2) are rare hereditary unconjugated hyperbilirubinemia disorders. However, there have been no reports regarding the co-existence of CN-1 and CN-2 in one family. We experienced a case of an Iranian family that included members with either CN-1 or CN-2. Genetic analysis revealed a mutation in the bilirubin UDP-glucuronosyltransferase (UGT1A1) gene that resulted in residual enzymatic activity.
Case report: The female proband developed severe hyperbilirubinemia [total serum bilirubin concentration (TB) = 34.8 mg/dL] with bilirubin encephalopathy (kernicterus) and died after liver transplantation. Her family history included a cousin with kernicterus (TB = 30.0 mg/dL) diagnosed as CN-1. Her great grandfather (TB unknown) and uncle (TB = 23.0 mg/dL) developed jaundice, but without any treatment, they remained healthy as CN-2.

Results: The affected cousin was homozygous for a novel frameshift mutation (c.381insGG, p.C127WfsX23). The affected uncle was compound heterozygous for p.C127WfsX23 and p.V225G linked with A(TA)7TAA. p.V225G-UGT1A1 reduced glucuronidation activity to 60% of wild-type. Thus, linkage of A(TA)7TAA and p.V225G might reduce UGT1A1 activity to 18%–36 % of the wild-type.

Conclusion: Genetic and in vitro expression analyses are useful for accurate genetic counseling for a family with a history of both CN-1 and CN-2.

Key words: Crigler–Najjar syndrome – Gilbert syndrome – bilirubin UDP-glucuronosyltransferase – UGT1A1.

Abbreviations: CN-1: Crigler–Najjar syndrome type I; CN-2: Crigler–Najjar syndrome type II; GS: Gilbert syndrome; UGT1A1: bilirubin UDP-glucuronosyltransferase; WT: Wild type; TB: total serum bilirubin.