BACKGROUND & AIMS The bile salt export pump (BSEP, ABCB11), multidrug resistance protein 3 (MDR3, ABCB4) and the ATPase familial intrahepatic cholestasis 1 (FIC1, ATP8B1) mediate bile formation. This study aimed to determine the contribution of mutations and common variants in the FIC1, BSEP and MDR3 genes to cholestatic disorders of differing disease onset and severity. METHODS Coding exons with flanking intron regions of ATP8B1, ABCB11, and ABCB4 were sequenced in cholestatic patients with assumed genetic cause. The effects of new variants were evaluated by bioinformatic tools and 3D protein modeling. RESULTS In 427 patients with suspected inherited cholestasis, 149 patients carried at least one disease-causing mutation in FIC1, BSEP or MDR3, respectively. Overall, 154 different mutations were identified, of which 25 were novel. All 13 novel missense mutations were disease-causing according to bioinformatics analyses and homology modeling. Eighty-two percent of patients with at least one disease-causing mutation in either of the three genes were children. One or more common polymorphism(s) were found in FIC1 in 35.3%, BSEP in 64.3% and MDR3 in 72.6% of patients without disease-causing mutations in the respective gene. Minor allele frequencies of common polymorphisms in BSEP and MDR3 varied in our cohort compared to the general population, as described by gnomAD. However, differences in ethnic background may contribute to this effect. CONCLUSIONS In a large cohort of patients, 154 different variants were detected in FIC1, BSEP, and MDR3, 25 of which were novel. In our cohort, frequencies for risk alleles of BSEP (p.V444A) and MDR3 (p.I237I) polymorphisms were significantly overrepresented in patients without disease-causing mutation in the respective gene, indicating that these common variants can contribute to a cholestatic phenotype. LAY SUMMARY FIC1, BSEP, and MDR3 represent hepatobiliary transport proteins essential for bile formation. Genetic variants in these transporters underlie a broad spectrum of cholestatic liver diseases. To confirm a genetic contribution to the patients' phenotypes, gene sequencing of these three major cholestasis-related genes was performed in 427 patients and revealed 154 different variants of which 25 have not been previously reported in a database. In patients without a disease-causing mutation, common genetic variants were detected in a high number of cases, indicating that these common variants may contribute to cholestasis development.

中文翻译：

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大量胆汁淤积患者中 FIC1、BSEP 和 MDR3 的测序揭示了大量不同的遗传变异

背景与目的 胆盐输出泵（BSEP、ABCB11）、多药耐药蛋白 3（MDR3、ABCB4）和 ATPase 家族性肝内胆汁淤积 1（FIC1、ATP8B1）介导胆汁形成。本研究旨在确定 FIC1、BSEP 和 MDR3 基因中的突变和常见变异对不同疾病发作和严重程度的胆汁淤积症的贡献。方法 在具有假定遗传原因的胆汁淤积患者中对具有 ATP8B1、ABCB11 和 ABCB4 的侧翼内含子区域的编码外显子进行测序。新变体的影响通过生物信息学工具和 3D 蛋白质建模进行评估。结果 在 427 名疑似遗传性胆汁淤积患者中，149 名患者分别携带至少一种 FIC1、BSEP 或 MDR3 致病突变。总的来说，鉴定了 154 种不同的突变，其中 25 种是新的。根据生物信息学分析和同源性建模，所有 13 个新的错义突变都是致病的。在这三个基因中的任何一个中至少有一个致病突变的患者中，有 82% 是儿童。在 35.3% 的 FIC1、64.3% 的 BSEP 和 72.6% 的 MDR3 中发现了一种或多种常见的多态性，在相应基因中没有致病突变。如 gnomAD 所述，与一般人群相比，BSEP 和 MDR3 中常见多态性的次要等位基因频率在我们的队列中有所不同。然而，种族背景的差异可能会导致这种影响。结论 在一大群患者中，在 FIC1、BSEP 和 MDR3 中检测到 154 种不同的变异，其中 25 种是新的。在我们的队列中，BSEP (p.V444A) 和 MDR3 (p. I237I) 多态性在相应基因中没有致病突变的患者中显着过度表达，表明这些常见变异可能导致胆汁淤积表型。概述 FIC1、BSEP 和 MDR3 代表胆汁形成所必需的肝胆转运蛋白。这些转运蛋白中的遗传变异是广泛的胆汁淤积性肝病的基础。为了证实对患者表型的遗传贡献，对 427 名患者进行了这三个主要胆汁淤积相关基因的基因测序，发现了 154 种不同的变异，其中 25 种以前未在数据库中报告过。在没有致病突变的患者中，在大量病例中检测到常见的遗传变异，表明这些常见变异可能导致胆汁淤积的发展。