Abstract: Objective Through analyzing the clinical, liver pathology and family uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) gene mutation characteristics of a patient with hereditary hyperbilirubinemia, in order to understand the genetic characteristics and diagnostic methods of Crigler-Najjar Syndrome type Ⅱ.Methods The medical history, liver biochemistry, imaging examination results, liver pathological data of a patient with Crigler-Najjar Syndrome type Ⅱ were collected, we also analyzed the UGT1A1 gene sequencing results of this patient and his parents.Results The increase of bilirubin in patients with Crigler-Najjar Syndrome type Ⅱ was usually greater than 5 times the upper limit of normal value, which was a significant increase in indirect bilirubin (IBIL). ALT and AST of the patient were normal, inflammation and necrosis of hepatocytes were seldom in hepatic pathology from the patient. The patient was a homozygous mutation in UGT1A1 gene Exon 5 c.1456T>G (p.Tyr486Asp), and heterozygotes of the mutation were found in his parents. The treatment of Phenobarbital was effective.Conclusion Missense mutation of Tyr486Asp in Exon 5 of UGT1A1 gene is the pathogenic factor of this patient with Crigler-Najjar Syndrome type Ⅱ and his family, which is autosomal recessive inheritance, with significantly increased IBIL. There is no inflammatory injury in the liver, and phenobarbital induction is effective.

Key words: Crigler-Najjar Syndrome Ⅱ, UGT1A1, Hepatic pathology