A homozygous mutation in a Chinese man with Crigler-Najjar syndrome type II and a family genetic analysis

Spectrum of UGT1A1 Variations in Chinese Patients with Crigler-Najjar Syndrome Type II

Crigler–Najjar Syndrome type II (CNS-II) is an autosomal recessive hereditary condition of unconjugated hyperbilirubinemia without hemolysis, with bilirubin levels ranging from 102.6 μmol/L to 342 μmol/L. CNS-II is caused by a deficiency of UDP-glucuronyl transferase (UGT), which is encoded by the UDP-glucuronyl transferase 1A1 gene (UGT1A1). In East Asian populations, the compound homozygous UGT1A1 G71R and Y486D variants are frequently observed in cases with bilirubin levels exceeding 200 μmol/L. In this study, we investigated the spectrum of UGT1A1 variations in Chinese CNS-II patients. We sequenced the enhancer, promoter, and coding regions of UGT1A1 in 11 unrelated Chinese CNS-II patients and 80 healthy controls. Nine of these patients carried variations that are here reported for the first time in CNS-II patients, although they have been previously reported for other types of hereditary unconjugated hyperbilirubinemia. These individual variations have less influence on UGT activity than do the compound homozygous variation (combination of homozygous G71R variant and Y486D variant). Therefore, we propose that the spectrum of UGT1A1 variations in CNS-II differs according to the bilirubin levels.

Crigler-Najjar syndrome type II in a Chinese boy resulting from three mutations in the bilirubin uridine 5'-diphosphate-glucuronosyltransferase (UGT1A1) gene and a family genetic analysis

Background

The UGT1A1 gene encodes a responsible enzyme, UDP-glucuronosyltransferase1A1 (UGT1A1), for bilirubin metabolism. Many mutations have already been identified in patients with inherited disorders with unconjugated hyperbilirubinemia, such as Crigler-Najjar syndromes and Gilbert’s syndrome.

Case presentation

In this report, we presented a boy with intermittent unconjugated hyperbilirubinemia, whose genetic analysis showed a new compound heterozygote determined by three mutations, c.211G > A (p.G71R), c.508_510delTTC (p.F170-) and c.1456 T > G (p.Y486D) in the hotspot regions of the UGT1A1 gene (exons 1 and 5) in Asian populations, presenting a genotype compatible with clinical picture of CNS-II. The family genetic analysis confirmed the origin of these mutations.

Conclusion

UGT1A1 gene analysis should be performed in all cases with unexplained unconjugated hyperbilirubinemia. The description of patients with peculiar genotypes especially including family analysis could help explain the relationship between the genotype and phenotype,it is helpful for clinicians to predict the outcome of the patients.