Polycystic kidney and hepatic disease 1 gene mutations in von Meyenburg complexes: Case report

INTRODUCTION

Von Meyenburg complexes (VMCs), or biliary hamartomas, are a rare type of ductal plate malformation(DPM). Although generally benign, VMCs have been found to correlate with malignant diseases and progress towards adenocarcinomas[1]. Family cluster of VMCs has been observed clinically, indicating a genetic background of this disease. However, the gene mutation associated with this rare disorder has not been reported until now.

Mutations of the polycystic kidney and hepatic disease 1 (PKDH1) gene are confirmed to incur autosomal recessive polycystic kidney disease (ARPKD), a severe type of DPMs. Epigenetic changes in the liver and bile ducts vary from different exon mutation regions of PKHD1. Herein, we reported the PKHD1 gene sequences in two families of VMCs.

CASE REPORT

Two probands with histology-proved VMCs were included in this study. None of the family members/offspring in pedigree died or had clinical full-blown ARPKD.

为了保持网格的正确连接，应该重新生成网格或利用额外的连线重新组织这些具有共同边界的局部网格，但是这样造成大量的网格变动或者引入形态不佳的网格单元。例如，为使得图2（a）中的网格协调化，三角形单元1-2-5被分成3个子单元1-2-3，1-3-4和1-4-5。钝角三角形1-2-3不利于所形成矩阵的条件数和解的收敛性。图2（b）显示了在局部网格加密的情况下子区域中出现不协调网格的情形。图2（c）显示了单元类型不同的网格需要合并分析的情形。由于悬浮点的位置是随机的，往往不是等距分布，不能采用高阶单元或者Serendipity族单元处理。

Pedigree 1 (VMC1): Proband A was a 62-year-old woman with no medical history, who was referred due to abnormal echographic presentation of the liver(Figure 1A, Ⅰ: 2). Laboratory examinations showed 36 U/L alanine aminotransferase (ALT), 32 U/L aspartate aminotransferase (AST), 13.2 µmol/L total bilirubin,2.22 ng/mL α-fetoprotein (AFP), positive hepatitis B surface antigen (HBsAg) and e antigen (HBeAg), and 3.13 × 106 copies/mL HBV DNA, and hepatitis C virus and human immunodeficiency virus antibodies were both negative. Magnetic resonance imaging (MRI) displayed a typical feature of VMCs (Figure 1B); however,no renal cysts were found. She denied a history of alcohol consumption or drug administration. Liver biopsy confirmed the diagnosis of VMCs and chronic hepatitis B. The woman was given entecavir for successive 6 mo,and a 1-year follow-up by MRI displayed carcinoma in the right lobe of liver (Figure 1C). The subsequent intraoperative pathology revealed a moderately differentiated hepatocellular carcinoma (HCC) and the existence of VMCs (Figure 1D). The woman reported that one of her siblings was also diagnosed with HCC and VMCs 2 years ago and died of HCC. Subsequently,her five family members received MRI scans, and VMCs were identified in two members, without renal kidney cysts seen.

提升风电场MMC-HVDC系统LVRT能力的协调控制策略//朱蒙,李卫星,晁璞璞,徐殿国,李语童//(19):77

Pedigree 2 (VMC2): Proband B was a previously healthy 57-year-old woman (Figure 1F, Ⅲ: 2), and abdominal ultrasonography displayed intrahepatic diffuse lesions (Figure 1G and H) with no kidney cysts.Laboratory tests showed 34 U/L ALT, 32U/L AST, 10.8µmol/L total bilirubin, 3.8 ng/mL AFP, 1310.95 IU/mL HBsAg, 0.02 s/co HBeAb, 11.57 s/co HBeAb, and ＜500 copies/mL HBV-DNA viral load. She was finally diagnosed with VMCs, congenital hepatic fibrosis (CHF),and HBeAg-negative chronic hepatitis B after MRI and histopathological examinations. Liver ultrasonography was performed in three members of her family, and her husband, also her cousin (Figure 1F, Ⅲ: 1), reported an abnormal echographic presentation (Figure 1H).

Abdominal ultrasonography displayed intrahepatic diffuse lesions and magnetic resonance imaging (MRI) showed cystic lesions that shared no connection with the intra- and extra-hepatic bile duct system and were of normal size for von Meyenburg complexes (VMCs). A carcinoma in the right lobe of the liver was also found in proband A. No kidney cyst was seen in the imaging examinations of any family member.

Figure 1 Genetic, clinical, and molecular findings. A: Pedigree of the family cluster with five von Meyenburg complexes (VMCs) patients of two generations, with affected status indicated by black shading. The arrow indicates the proband; B: MRI findings display a typical feature of VMCs; C: A 1-year follow-up by MRI shows carcinoma in the right lobe of liver; D: Intraoperative pathology diagnoses a moderately differentiated HCC and VMCs; E: Electropherograms show a heterozygous deletion mutation at exon 32 in the PKHD1 gene (c.4280delG) in the proband (Ⅰ: 2); F: Pedigree of the family cluster with one von Meyenburg complexes (VMCs)patient of four generations, with affected status indicated by black shading. The arrow indicates the proband; G and H: B ultrasound findings of proband B; Ⅰ: B ultrasound findings of Ⅲ: 1; J: Electropherograms show a heterozygous deletion mutation at exon 28 in the PKHD1 gene (p.Arg1040Ter) in the proband B (Ⅲ: 2).HCC: Hepatocellular carcinoma; MRI: Magnetic resonance imaging

Outcomes

Venous blood samples were collected for amplifying exons 1-67 and the ambient intronic sequences of the PKDH1 gene, and genomic DNA from the proband A and Ⅱ: Two were sequenced for the entire coding region and splice sites of PKHD1. One heterozygous deletion mutation was detected at exon 32 in the PKHD1 gene (c.4280delG), leading to p.Gly1427ValfsX6 at protein level (Figure 1E). Further sequencing analysis of the entire family 1 revealed that other affected individuals (Ⅱ: 1, Ⅱ: 2) were also heterozygous for 4280delG, while unaffected siblings were wild type at the sequence position. Another mutation was located in exon 28 (p.Arg1040Ter) from proband B (Figure 1Ⅰ),while mutations of PKHD1 of the remaining members of family 2 were not detected.

Often found as small, symptomless and scattered cysts[7], VMCs are diagnosed accidentally upon their special radiologic appearance and sometimes in a manner of either not exact abdominal symptoms or the onset of liver sepsis[8]. A consecutive autopsy study indicates that the incidence in adults was about 5.6%and in children was 0.9%[9]. In another biopsy series,the incidence was only 0.6%[10]. Our previous study showed that the prevalence in patients subjected to diagnostic liver biopsy was 0.35%[11].

DISCUSSION

Ductal plate arises from single- or double-layered epithelial structures of hepatoblasts around the portal vein in the embryonic stage. Ductal plate undergoes remodeling (molding process from large bile ducts to microscopic bile ducts) and gives rise to the formation of bile ducts. DPM is defined as the developmental abnormalities considered to be resulted from the lack of ductal plate remodeling during bile duct morphogenesis.The congenital DPM diseases incorporate congenital hepatic fibrosis, autosomal dominant polycystic kidney disease (ADPKD), autosomal dominant polycystic liver disease (ADPLD), ARPKD, Caroli’s disease, Caroli’s syndrome, and VMCs[2]. ADPLD is a heritable disease characterized by the malformation of medium sizes ducts, which ultimately generate cysts full of fluid. This malformation is usually underdiagnosed and genetically distinct from polycystic liver disease associated with ADPKD but with similar pathogenesis, manifestations,and management[3]. Liver cysts are more frequently found in patients with ADPKD and adult-type polycystic liver disease, where the development of renal cysts precedes hepatic cysts[4]. Dissimilar to ADPLD, hepatic cysts in ADPKD are originated from peribiliary bile duct glands and dilated biliary microhamartomas[5]. By contrast, VMCs are caused from malformations of the small-sized intra-hepatic duct[4] and are considered a histopathological lesion that transforms into cysts[6].

本研究显示，单纯慢阻肺与ACO错失早期诊断时间都是3年，两者无明显差异。既往研究显示，ACO患者较单纯慢阻肺患者症状多且重，肺功能更差，急性加重及住院次数增加［19-22］。本研究提示，ACO病人与单纯慢阻肺相比，其错失早期诊断时间并未减少，这似与ACO病人具有更多的症状相矛盾。因为症状多就医机会增加，根据病史，医生判断慢阻肺可能性增加。实际上ACO病人可能因为症状反复，更易耐受，更不易引起病人足够重视，误认为是机体衰老的表现，其确切原因尚不清楚。

A 62-year-old woman and a 57-year-old woman were both previously healthy,who were referred due to abnormal echographic presentation of the liver.

In summary, our report provides four cases to the literature of VMCs associated with PKHD1 gene mutations. To be more persuasive, more clinicopathologic and molecular studies are needed to validate the findings and test the hypothesis from the present study.

ARTICLE HIGHLIGHTS

Case characteristics

Mutations of the PKHD1 gene have been demonstrated to cause ARPKD, a type of DPM[12]. PKHD1 gene contains 76 exons and more than 300 types of mutation. PKHD1 exon 2-deficient mice exhibit hepatic,pancreatic, and renal abnormalities, grossly cystic and fibrotic livers, and progressive bile duct dilatation as well as structural abnormalities and shortening of primary cilia in the bile ducts relative to the wild-type animals[13].Deletion of exon 40 on the PKHD1 gene resulted in bile duct abnormality in mice[14]. In addition, mutation of the PKHD1 gene by disrupting exon 4 down-regulated fibrocystin/polyductin (FPC) expression, resulting in intrahepatic bile duct proliferation with progressive cyst formation and associated periportal fibrosis in mice[15].Herein, we examined the genetic mutations of two VMCs pedigrees. Two mutations (c.4280delG and c.3118C＞T)of the PKHD1 gene located on exons 32 and 28 were detected, respectively, both of which led to early termination of synthesis. These heterozygous deletion mutations may result in a single-dose deficiency of the PKHD1 gene, which affects the development of bile ducts. The exon 28-32 of PKHD1 gene mainly encodes the IPT/TIG (Ig-like, plexins, transcription factors),IPT_PCSRP (plexins and cell surface receptors), and initial G8 (this domain is named G8 after its 8 conserved glycines) domains of the fibrocystin protein. These domains are involved in the regulation of cell growth,signal transduction, proliferation, and adhesion. Our previous study also showed that silencing of the PKHD1 gene promoted the proliferation, migration, and invasion of human intrahepatic cholangiocarcinoma HuCCT-1 cells via the PI3K/Akt signaling pathway, indicating that PKHD1 may contribute to the development and progression of intrahepatic cholangiocarcinoma[16]. It is therefore hypothesized that the protein component encoded by exon 28-32 of the PKHD1 gene may have a closer correlation with the development of bile duct than with renal tubules. The mutation in exon 28-32 may lead to the malformations of the ductal plate alone without kidney involvement.

Proband A and B were diagnosed with chronic hepatitis B and HBeAg-negative chronic hepatitis B, respectively, by laboratory examinations of positive hepatitis B surface antigen (HBsAg), negative anti-hepatitis C virus and anti-human immuno-deficiency virus tests, and normal liver function tests.

Differential diagnosis

Liver cirrhosis, metastases, microabscesses, and simple liver cysts.

Laboratory diagnosis

1.1 一般资料 选取2016年3月-2018年7月期间就诊我院诊断为肝内胆管细胞癌的患者，所以患者均不能进行手术治疗或术后复发转移。入组标准：⑴具有明确的可测量病灶；⑵2个月以上未行抗肿瘤治疗，包括放疗、化疗等；⑶KPS评分80分以上，估计生存期3个月以上；⑷肝肾功能基本正常，AST、ALT值低于正常值3倍以下，血清胆红素值低于正常值3倍以下。患者心肺功能良好，能口服药物，并签署知情同意书。

成都工贸职业技术学院电气工程及自动化系率先在系部层面建立创客空间，探索出“1+3+N”的大学生创新创业教育改革发展思路，即1个平台，创客空间创新创业平台；3个维度，创新工坊，创新创业课程体系，大学生创新创业大赛；N个项目，大学生创新创业项目。以创客空间平台为创新创业工作抓手，创新工坊为物理空间，大学生创新创业课程为教育内容，创新创业大赛为促进手段，形成二级学院(系部)部层面的创新创业生态链，孵化出若干具有专业特色的大学生创新创业项目，多个项目获得不同级别的荣誉。

Imaging diagnosis

The method of proteinase K and phenol were applied to extracted genomic DNA from venous blood of the members. Seventy-two primers were designed(Shanghai Genesky Biotechnology Co., Ltd.; Shanghai,China), adopting an online software (http://frodo.wi.mit.edu/cgi-bin/primer3/ primer3_www.cgi) to amplify exons 1-67 and the ambient introns of the PKDH1 gene(supplementary Table 1).

Pathological diagnosis

Pathological diagnosis confirmed the diagnoses of hepatocellular carcinoma VMCs and chronic hepatitis B in proband A and of congenital hepatic fibrosis(CHF) and VMCs in proband B.

现有的研究证实影响研究生培养质量的一个重要因素便是导师的因素,研究生导师素质对研究生的发展有着不可忽视的作用,导师作为直接教导、引领研究生的角色,其工作开展的好坏,影响力发挥的范围及程度直接影响研究生个体发展以及研究生整体质量[13]。然而,并非导师的所有特质都会对研究生培养质量产生显著影响,研究显示,导师职称、年龄等就与研究生培养质量无显著的相关性,但与导师的指导方式、指导频率、指导内容以及指导关系确立之间存在显著相关[14]。由以上的研究结果可以看出,导师对于研究生的影响是基础的、根本的影响,导师的角色功能决定了研究生的知识储备、研究视野、科研洞察力和敏感性,基于此,本文提出以下假设。

Treatment

Proband A was given entecavir and complete surgical resection of the hepatocellular carcinoma lesion. Proband B did not receive any medication and was followed up regularly.

Related reports

In most of cases, VMCs are incidentally detected, focusing on the location of the disease (liver surface, extrahepatic), relative symptoms, mimicking metastatic disease or malignancy, and association with liver tumor.

Term explanation

PKHD1 gene is located on chromosome 6p12. It encodes a protein named fibrocystin/polyductin (FPC). FPC protein is involved in the maintenance of the normal tubular structure of intrahepatic bile duct epithelial cells. Mutation of PKHD1 may cause the structural and functional disorder of FPC, leading eventually to the development of renal and hepatic cysts. VMCs are benign neoplasms characterized by the disorderly arrangement of biliary epithelium,which form abnormal biliary ducts surrounded by ample fibrous stroma.

Experiences and lessons

The PKHD1 gene mutations were identified in two VMCs patients, providing new insights into the pathogenesis, diagnosis, and progression of the VMCs.

REFERENCES

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