Crigler-Najjar Syndrome Type 2 (CNS2) is a rare autosomal recessive disorder characterized by unconjugated hyperbilirubinemia due to partial deficiency of the enzyme uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1). We present a case of a 13-month-old male admitted to Kanti Children's Hospital with persistent jaundice since birth. Diagnostic evaluation accompanied by gene sequencing confirmed CNS2 and the patient was effectively managed with orally administered phenobarbitone. CNS2 can be distinguished from other potential causes of unconjugated hyperbilirubinemia based on bilirubin concentration and the affected patient's response to phenobarbitone. Genetic counselling is essential for the recognition and prevention of severe hyperbilirubinemia which, in the absence of timely medical intervention, may lead to neurotoxicity. Keywords: Case report; crigler-Najjar syndrome; genetic counseling; phenobarbitone; unconjugated hyperbilirubinemia.

Crigler-Najjar Syndrome Type 2 (CNS2) is a rare autosomal recessive disorder characterized by unconjugated hyperbilirubinemia due to partial deficiency of the enzyme uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1). We present a case of a 13-month-old male admitted to Kanti Children's Hospital with persistent jaundice since birth. Diagnostic evaluation accompanied by gene sequencing confirmed CNS2 and the patient was effectively managed with orally administered phenobarbitone. CNS2 can be distinguished from other potential causes of unconjugated hyperbilirubinemia based on bilirubin concentration and the affected patient's response to phenobarbitone. Genetic counselling is essential for the recognition and prevention of severe hyperbilirubinemia which, in the absence of timely medical intervention, may lead to neurotoxicity. Keywords: Case report; crigler-Najjar syndrome; genetic counseling; phenobarbitone; unconjugated hyperbilirubinemia.

Crigler-Najjar syndrome (CNS) and Gilbert syndrome (GS; OMIM: 143500) are rare autosomal recessive diseases that cause unconjugated hyperbilirubinemia due to decreased UGT1A1 enzyme activity. Crigler-Najjar syndrome type 2 (CNS2; OMIM: 606785) increases the risk of gallbladder stone formation and cholecystitis, while GS seldom causes health issues. We found a 28-year-old male patient with recurring right upper abdomen pain who experienced persistent jaundice from birth. CNS2 with gallbladder stones and cholecystitis was diagnosed after genetic testing revealed rare double homozygous mutations A(TA)7TAA (rs3064744) and P229Q (rs35350960) in the UGT1A1 gene. After pedigree investigation, we found that the patient's parents with modestly increased bilirubin had compound heterozygous mutations A(TA)7TAA and P229Q, which were GS. Bioinformatics analysis showed that A(TA)7TAA is in the TATA-box region of the gene UGT1A1 promoter, affecting gene transcriptional initiation, whereas P229Q modifies protein three-dimensional structure and may be harmful. In this pedigree, double homozygous mutations have a more severe phenotype than compound heterozygous mutations. Inherited causes of hyperbilirubinemia should be suspected after ruling out biliary obstruction, and early bilirubin reduction (< 103 µmol/L (6 mg/dL)) may reduce the risk of complications like cholecystitis in CNS2 patients, though further studies with longer follow-up are needed to confirm this observation.

Objective: To explore the relevancy between the uridine diphosphate-glucuronylgly-cosyltransferase 1A1 (UGT1A1) gene mutation and the phenotype of indirect hyperbilirubinemia in children. Methods: Sixteen cases with indirect hyperbilirubinemia who visited the Department of Gastroenterology, Children's Hospital of Nanjing Medical University from July 2013 to November 2019 were retrospectively analyzed and were divided into Gilbert syndrome (GS), Crigler-Najjar syndrome type II (CNS-II), and indirect hyperbilirubinemia groups unexplained by UGT1A1 gene mutations. The differences in gene mutation site information and general clinical data were compared. The association between gene mutation spectrum and bilirubin level was explored by t-test analysis. Results: Ten of the sixteen cases with indirect hyperbilirubinemia had GS, three had CNS-II, and three had indirect hyperbilirubinemia unexplained by UGT1A1 gene mutations. A total of six mutation types were detected, of which c.211G > A accounted for 37.5% (6/16), c.1456T > G accounted for 62.5% (10/16), and TATA accounted for 37.5% (6/16), respectively. Compared with the GS group, the CNS group had early disease onset incidence, high serum total bilirubin (t = 5.539, P < 0.05), and indirect bilirubin (t = 5.312, P < 0.05). However, there was no significant difference in direct bilirubin levels (t = 1.223, P > 0.05) and age of onset (t = 0.3611, P > 0.05) between the two groups. There was no significant correlation between the number of UGT1A1 gene mutations and serum bilirubin levels. Children with c.1456T > G homozygous mutations had the highest serum bilirubin levels. Conclusion: The common pathogenic variants of the UGT1A1 gene sequence are c.1456T > G, c.211G > A, and TATA, indicating that these site mutations are related to the occurrence of indirect hyperbilirubinemia and have important guiding significance for the etiological analysis of indirect hyperbilirubinemia in children. 目的： 探讨尿苷二磷酸-葡萄糖醛酸转移酶1A1（UGT1A1）基因突变与儿童高间接胆红素血症表型的相关性。 方法： 回顾性分析2013年7月至2019年11月于南京医科大学附属儿童医院消化科就诊的16例高间接胆红素血症患儿，分为Gilbert综合征(GS)、Crigler-Najjar综合征II型(CNS-II)及UGT1A1基因突变无法解释的高间接胆红素血症组，比较其一般临床资料、基因突变位点信息的差别，并通过t检验分析探讨基因突变谱与胆红素水平的关系。 结果： 16例高间接胆红素血症的患者中，10例为GS，3例为CNS-II, 3例为UGT1A1基因突变无法解释的高间接胆红素血症。共检测到6个变异类型，其中c.211G > A占37.5%(6/16)，c.1456T > G占62.5%(10/16), TATA占37.5% (6/16)；与GS相比，CNS发病较早，且血清总胆红素（t = 5.539，P < 0.05）及间接胆红素水解（t = 5.312，P <0.05）均较高，但两组直接胆红素水平(t = 1.223，P > 0.05)和发病年龄(t = 0.361，P > 0.05)差异无统计学意义。UGT1A1基因变异的数量与血清胆红素水平之间无相关性，c.1456T > G纯合突变儿童的血清胆红素水平最高。 结论： 儿童UGT1A1基因常见致病变异依次为c.1456T > G、c.211G > A、TATA，说明这些位点突变与儿童高间接胆红素血症的发生相关，对于儿童高间接胆红素血症病因分析，具有重要指导意义。.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency and variants of the UDP-glucuronosyltransferase 1A1 (UGT1A1) gene are the most common genetic causes of neonatal unconjugated hyperbilirubinemia (NUH). In this review, we searched PubMed for articles on the genetic causes of NUH published before December 31, 2022, and analyzed the data. On the basis of the results, we reached eight conclusions: (1) 37 mutations of the G6PD gene are associated with NUH; (2) the clinical manifestation of G6PD deficiency depends not only on ethnicity but also on the molecular mechanisms underlying the deficiency (and thus its severity); (3) of mutations in the UGT1A1 gene, homozygous c.-53A(TA)6TAA > A(TA)7TAA is the main cause of NUH in Caucasians and Africans, whereas homozygous c.211G > A is the main genetic cause of NUH in East Asians; (4) in Indonesian neonates, homozygous c.-3279T > G is the most common cause of NUH development, and neither c.-53 A(TA)6TAA > A(TA)7TAA nor c.211G > A causes it; (5) in breast-fed East Asian neonates, the TA7 repeat variant of the UGT1A1 gene protects against the development of NUH; (6) G6PD deficiency combined with homozygous c.211G > A variation of the UGT1A1 gene increases the risk of severe NUH; (7) in Pakistani and Caucasian patients with Crigler-Najjar syndrome type 2 (CN-2), point mutations of the UGT1A1 gene are widely distributed and frequently occur with variation at nucleotide -53, whereas in Asian patients with CN-2, compound homozygous variations in the coding region are frequently observed; and (8) records of G6PD deficiency and UGT1A1 variation status for a neonate offer useful pharmacogenomic information that can aid long-term care. These results indicate that timely diagnosis of NUH through molecular tests is crucial and that early initiation of treatment for the neonates and educational programs for their parents improves outcomes. Crigler-Najjar syndrome is a rare autosomal recessive disorder causing hyperbilirubinemia in newborns. Bilirubin metabolism involves the uptake of bilirubin from circulation, intracellular storage, conjugation with glucuronic acid, and excretion into bile. Abnormalities in any of these processes lead to hyperbilirubinemia. Crigler-Najjar syndrome is characterized by the absence or decreased activity of UDP-glucuronosyltransferase (UGT), an enzyme required for glucuronidation of unconjugated bilirubin in the liver. This deficiency is a significant cause of congenital nonhemolytic jaundice. The syndrome is classified into 2 types based on the level of UGT activity: Type 1: Characterized by severe symptoms due to minimal or a complete absence of enzyme activity, individuals with Crigler-Najjar syndrome type 1 (CN1) experience life-threatening and severe jaundice, requiring regular phototherapy for treatment. Patients with this form of the disease are at very high risk of developing neurological complications, including permanent damage such as kernicterus. The only cure for CN1 syndrome is a liver transplant. Type 2: This form of Crigler-Najjar syndrome is characterized by milder symptoms resulting from reduced enzyme activity. Individuals with Crigler-Najjar syndrome type 2 (CN2) experience intermittent jaundice triggered by stress and typically manage the condition through conservative measures. Permanent neurological damage is rare in CN2, and the need for a liver transplant is infrequent.