目的：总结CYP7B1基因变异引起的先天性胆汁酸合成障碍3型（BASD3）的临床特征和遗传特征。方法：这是一个案例系列研究。复旦大学附属儿童医院感染科及厦门医学院附属妇女儿童医院儿科2例CYP7B1基因变异所致先天性胆汁酸合成障碍3型临床资料及遗传学结果对2021年1月至2023年12月大学期间的情况进行回顾性收集和分析。以“先天性胆汁酸合成障碍3型”“氧化甾醇7-α-羟化酶”“氧化甾醇7α-羟化酶”组合关键词检索中国知网、万方数据和PubMed电子数据库截至2023年12月的文献缺乏”“BASD3”和“CYP7B1肝脏”中英文。总结CYP7B1基因变异引起的BASD3疾病的主要临床特征和遗传特征。结果：2例BASD3患者入院，男1例，女1例，年龄分别为3个月18天、2个月7天。两名患者均出现新生儿胆汁淤积和肝肿大。生化证据表明直接高胆红素血症伴有转氨酶水平升高，而γ-谷氨酰转移酶（GGT）和总胆汁酸水平正常或接近正常。患者1是CYP7B1基因变体c.525-526insCAAGTTGG(p.Asp176GInfs*15)和c.334C>T(p.Arg112Ter)的复合杂合子。口服鹅去氧胆酸 (CDCA) 后，1 号患者黄疸消退，肝功能检查恢复正常。患者 2 的 CYP7B1 基因中的变异 c.334C>T(p.Arg112Ter) 是纯合的。患者 2 已处于肝衰竭状态，并且对口服 CDCA 给药没有反应。 2号患者接受活体肝移植，腹部增强CT显示肝脏肿瘤可能起源于血管。文献综述显示，中文文献中未见BASD3病例报道，本研究中有2例患者，而9篇英文文献中报道了12例患者（男9例，女3例）。 12例均在婴儿期出现黄疸、肝脾肿大，伴有肝硬化、肝功能衰竭、肾脏肿大、低血糖，部分病例出现自发性出血，其中5例表现为多囊肾。 CYP7B1基因c.334C>T(p.Arg112Ter)纯合4例，复合杂合2例。 12例儿童中，6例接受CDCA治疗，6例未接受CDCA治疗。接受CDCA治疗的6例患者中，有4例患者的原生肝脏存活，而未接受CDCA治疗的6例患者中，无一例存活。结论：BASD3是一种罕见的遗传性胆汁淤积性疾病。结合胆红素和转氨酶水平显着升高，GGT 和总胆汁酸水平正常或接近正常，可以作为诊断线索。 c.334C>T 是 CYP7B1 基因最常见的致病性变异。及时给予CDCA可以挽救肝脏。

Objective: To summarize the clinical features and genetic characteristics of Congenital bile acid synthetic disorder type 3 (BASD3) disorder caused by CYP7B1 gene variation. Methods: This was a case series study. Clinical data and genetic results of 2 cases of congenital bile acid synthetic disorder type 3 caused by CYP7B1 gene variations in the Department of Infectious Diseases, Children's Hospital of Fudan University at Xiamen and Department of Pediatrics, Women and Children's Hospital, School of Medicine, Xiamen University from January 2021 to December 2023 were retrospectively collected and analyzed. Literature up to December 2023 was searched from electronic databases of China National Knowledge Infrastructure (CNKI), Wanfang Data and PubMed with the combined keywords of " Congenital bile acid synthetic disorder type 3""Oxysterol 7-alpha-hydroxylase""Oxysterol 7α-Hydroxylase Deficiency""BASD3" and "CYP7B1 liver" both in Chinese and English. The main clinical features and genetic characteristics of BASD3 disorder caused by CYP7B1 gene variations were summarized. Results: Two BASD3 patients, 1 male and 1 female, were admitted at the ages of 3 months and 18 days, and 2 months and 7 days, respectively. Both patients presented with neonatal cholestasis and hepatomegaly. Biochemical evidence indicated direct hyper-bilirubinemia with elevated aminotransferase levels, while gamma-glutamyltransferase (GGT) and total bile acid levels were normal or nearly normal. Patient 1 was a compound heterozygotes of the CYP7B1 gene variants c.525-526insCAAGTTGG(p.Asp176GInfs*15) and c.334C>T(p.Arg112Ter). Patient 1 jaundice resolved and liver function tests normalized after oral administration of chenodeoxycholic acid (CDCA). Patient 2 was homozygous for variant c.334C>T(p.Arg112Ter) in CYP7B1 gene. Patient 2 was in liver failure status already and not reactive to oral CDCA administration. Patient 2 received living-related liver transplantation for enhanced abdominal CT revealed a liver tumor likely vascular origin. Literature review revealed no cases of BASD3 reported in Chinese literature, including 2 patients in this study, while 12 patients (9 males and 3 females) were reported in 9 English literatures. All of the 12 manifested jaundice and hepatosplenomegaly in infancy, with cirrhosis, liver failure, kidney enlargement, hypoglycemia, and spontaneous bleeding in some cases, polycystic kidney disease was demonstrated in 5 cases of them. The c.334C>T (p.Arg112Ter) of the CYP7B1 gene was homozygous in 4 cases and compound heterozygous in 2 cases. Among the 12 children, 6 cases received CDCA treatment, while 6 cases not. Four survived with their native liver in the 6 cases who received CDCA therapy, while none in the 6 cases not received CDCA therapy. Conclusions: BASD3 is a rare hereditary cholestatic disorder. Markedly elevated levels of conjugated bilirubin and aminotransferases, with normal or nearly normal GGT and total bile acid levels can serve as diagnostic clue. c.334C>T is the most common pathogenic variant of the CYP7B1 gene. Timely administration of CDCA may save the liver.