Wybrich R Cnossen

Polycystic liver disease: an overview of pathogenesis, clinical manifestations and management

Polycystic liver disease (PLD) is the result of embryonic ductal plate malformation of the intrahepatic biliary tree. The phenotype consists of numerous cysts spread throughout the liver parenchyma. Cystic bile duct malformations originating from the peripheral biliary tree are called Von Meyenburg complexes (VMC). In these patients embryonic remnants develop into small hepatic cysts and usually remain silent during life. Symptomatic PLD occurs mainly in the context of isolated polycystic liver disease (PCLD) and autosomal dominant polycystic kidney disease (ADPKD). In advanced stages, PCLD and ADPKD patients have massively enlarged livers which cause a spectrum of clinical features and complications. Major complaints include abdominal pain, abdominal distension and atypical symptoms because of voluminous cysts resulting in compression of adjacent tissue or failure of the affected organ. Renal failure due to polycystic kidneys and non-renal extra-hepatic features are common in ADPKD in contrast to VMC and PCLD. In general, liver function remains prolonged preserved in PLD. Ultrasonography is the first instrument to assess liver phenotype. Indeed, PCLD and ADPKD diagnostic criteria rely on detection of hepatorenal cystogenesis, and secondly a positive family history compatible with an autosomal dominant inheritance pattern. Ambiguous imaging or screening may be assisted by genetic counseling and molecular diagnostics. Screening mutations of the genes causing PCLD (PRKCSH and SEC63) or ADPKD (PKD1 and PKD2) confirm the clinical diagnosis. Genetic studies showed that accumulation of somatic hits in cyst epithelium determine the rate-limiting step for cyst formation. Management of adult PLD is based on liver phenotype, severity of clinical features and quality of life. Conservative treatment is recommended for the majority of PLD patients. The primary aim is to halt cyst growth to allow abdominal decompression and ameliorate symptoms. Invasive procedures are required in a selective patient group with advanced PCLD, ADPKD or liver failure. Pharmacological therapy by somatostatin analogues lead to beneficial outcome of PLD in terms of symptom relief and liver volume reduction.

Whole-exome sequencing reveals LRP5 mutations and canonical Wnt signaling associated with hepatic cystogenesis

Significance Polycystic liver disease (PCLD) is an autosomal dominantly inherited disorder characterized by multiple fluid-filled hepatic cysts that may cause an extremely enlarged liver. PCLD is genetically heterogeneous, and mutations in PRKCSH and SEC63 are present in ∼25% of PCLD patients. This research identifies four unique LRP5 mutations in four independent families that were all located at highly conserved protein domains. Functional activity analyses suggest that mutant LRP5 reduces wingless (Wnt) signal activation. This study suggests that imbalanced Wnt signaling is related to hepatic cyst formation. Polycystic livers are seen in the rare inherited disorder isolated polycystic liver disease (PCLD) and are recognized as the most common extrarenal manifestation in autosomal dominant polycystic kidney disease. Hepatic cystogenesis is characterized by progressive proliferation of cholangiocytes, ultimately causing hepatomegaly. Genetically, polycystic liver disease is a heterogeneous disorder with incomplete penetrance and caused by mutations in PRKCSH, SEC63, PKD1, or PKD2. Genome-wide SNP typing and Sanger sequencing revealed no pathogenic variants in hitherto genes in an extended PCLD family. We performed whole-exome sequencing of DNA samples from two members. A heterozygous variant c.3562C > T located at a highly conserved amino acid position (p.R1188W) in the low density lipoprotein receptor-related protein 5 (LRP5) gene segregated with the disease (logarithm of odds score, 4.62) but was not observed in more than 1,000 unaffected individuals. Screening of LRP5 in a PCLD cohort identified three additional mutations in three unrelated families with polycystic livers (p.V454M, p.R1529S, and p.D1551N), again all undetected in controls. All variants were predicted to be damaging with profound structural effects on LRP5 protein domains. Liver cyst tissue and normal hepatic tissue samples from patients and controls showed abundant LRP5 expression by immunohistochemistry. Functional activity analyses indicated that mutant LRP5 led to reduced wingless signal activation. In conclusion, we demonstrate that germ-line LRP5 missense mutations are associated with hepatic cystogenesis. The findings presented in this study link the pathophysiology of PCLD to deregulation of the canonical wingless signaling pathway.

Safely ruling out inflammatory bowel disease in children and teenagers without referral for endoscopy

Background Up to 70% of children and teenagers referred to a paediatric gastroenterology centre with suspected inflammatory bowel disease (IBD) do not have the disease. Objective To evaluate whether faecal calprotectin as an ‘add-on test’ improves the specificity of the clinical case definition for suspected IBD in a general paediatric practice. Design A prospective diagnostic accuracy study. Setting Six outpatient clinics for general paediatrics and one tertiary care hospital in the Netherlands. Patients 117 children and teenagers with a clinical suspicion of IBD. Diagnostic tests Faecal calprotectin was measured (index test) in all patients. Patients with a high index of suspicion on the basis of the paediatricians global assessment, physical examination and blood results were referred for endoscopy (reference standard). Children and teenagers who were not selected for endoscopy initially were followed for half a year for the appearance of possible additional symptoms (delayed type reference standard). Primary outcome The proportion of referred patients with confirmed IBD. Results The mean age of patients was 14 years (range 6–18). A total of 42 (36%) had confirmed IBD. The paediatricians, who were blinded to the faecal calprotectin result, referred 68 children and teenagers for endoscopy. If they had referred only those patients with a positive faecal calprotectin result (>50 μg/g), 54 patients would have undergone endoscopy. Limitation The study relied on clinical follow-up to detect missed IBD. Conclusions A diagnostic strategy in general paediatric practice of using a simple clinical case definition for suspected IBD in combination with a positive faecal calprotectin result increases the specificity to detect IBD and reduces the need for referral to a paediatric gastroenterology centre with a very low risk of missing cases.

LRP5 variants may contribute to ADPKD

Mutations in Polycystic Kidney Disease proteins (PKD1 or PKD2) are causative for autosomal dominant polycystic kidney disease (ADPKD). However, a small subset of ADPKD probands do not harbor a mutation in any of the known genes. Low density lipoprotein Receptor-related Protein 5 (LRP5) was recently associated with hepatic cystogenesis in isolated polycystic liver disease (PCLD). Here, we demonstrate that this gene may also have a role in unlinked and sporadic ADPKD patients. In a cohort of 79 unrelated patients with adult-onset ADPKD, we identified a total of four different LRP5 variants that were predicted to be pathogenic by in silico tools. One ADPKD patient has a positive family history for ADPKD and variant LRP5 c.1680G>T; p.(Trp560Cys) segregated with the disease. Although also two PKD1 variants probably affecting protein function were identified, luciferase activity assays presented for three LRP5 variants significant decreased signal activation of canonical Wnt signaling. This study contributes to the genetic spectrum of ADPKD. Introduction of the canonical Wnt signaling pathway provides new avenues for the study of the pathophysiology.

Somatic loss of polycystic disease genes contributes to the formation of isolated and polycystic liver cysts

We read with interest the paper by Urribarri et al 1 which describes that metalloprotease hyperactivity plays an important role in cyst expansion and that metalloprotease inhibition reduces cyst proliferation. As such, these results help to identify potential drug targets.2 We hypothesise that the expansion and maintenance of the cyst is preceded by mutational events that trigger cytogenesis, and we used genetic analysis to provide additional insight into this process. The majority of polycystic diseases are autosomal dominant disorders where every patient cell possesses one germ line mutation (first hit).3 As somatic second-hit mutations play an important role in liver and renal cyst formation,4–6 it was hypothesised that patients with polycystic disease have a DNA repair defect and accumulate somatic mutations.7 This was supported by a comparative genomic hybridisation study where renal cysts harboured multiple chromosomal aberrations, similar to cancers.8 ,9 In addition, patients without a germ line mutation can still develop …

Somatic Hits in Polycystic Liver Diseases

Polycystic Liver Disease (PLD) encompasses a number of disorders with the development of multiple cysts distributed throughout the liver either focally or equally. Hepatic cysts are fluid-filled cavities lined by benign epithelium. PLD is the major phenotype of isolated Polycystic Liver Disease (PCLD) and Autosomal Dominant Polycystic Kidney Disease (ADPKD). The molecular principles in carcinogenesis indicate that there is an accumulation of multiple (somatic) mutations. This concept assumes that presence of a germline mutation (‘first hit’) in an inherited disorder requires a ‘second hit’ at the somatic level for cyst development to occur. The second hit is the rate-limiting step and results in somatic inactivation of the normal allele. Studies have identified secondary, somatic hits in human liver cyst tissues in PCLD and ADPKD. Inactivation of both copies in PLD is demonstrated through somatic mutations or loss of heterozygosity (LOH). The frequency of somatic mutations varies between genes and genomic disorders. Genetic studies detected LOH in 9% and somatic mutations in 8-29% in ADPKD derived hepatic cysts. In PCLD, almost ~80% of hepatic cysts from PRKCSH carriers had completely lost the PRKCSH gene. There is important clinical heterogeneity among PLD patients. Differences in phenotypical expression may be explained by age, gender and environment, but also modifier genes or inactivating somatic events may play key roles. This review will give an overview of the data gained from genetic studies in liver cyst tissues from PCLD and ADPKD patients in relation to the clinical manifestations.

Severe Polycystic Liver Disease Is Not Caused by Large Deletions of the PRKCSH Gene

Isolated polycystic liver disease (ADPLD) is an autosomal dominant Mendelian disorder. Heterozygous PRKCSH (where PRKCSH is protein kinase C substrate 80K‐H (80 kDa protein, heavy chain; MIM*177060) mutations are the most frequent cause. Routine molecular testing using Sanger sequencing identifies pathogenic variants in the PRKCSH (15%) and SEC63 (where SEC63 is Saccharomyces cerevisiae homolog 63 (MIM*608648); 6%) genes, but about approximately 80% of patients meeting the clinical ADPLD criteria carry no PRKCSH or SEC63 mutation. Cyst tissue often shows somatic deletions with loss of heterozygosity that was recently recognized as a general mechanism in ADPLD. We hypothesized that germline deletions in the PRKCSH gene may be responsible for hepatic cystogenesis in a significant number of mutation‐negative ADPLD patients.

Chromosomal abnormalities in hepatic cysts point to novel polycystic liver disease genes.

Autosomal dominant polycystic liver disease (ADPLD) is caused by variants in PRKCSH, SEC63, and LRP5, whereas autosomal dominant polycystic kidney disease is caused by variants in PKD1 and PKD2. Liver cyst development in these disorders is explained by somatic loss-of-heterozygosity (LOH) of the wild-type allele in the developing cyst. We hypothesize that we can use this mechanism to identify novel disease genes that reside in LOH regions. In this study, we aim to map abnormal genomic regions using high-density SNP microarrays to find novel PLD genes. We collected 46 cysts from 23 patients with polycystic or sporadic hepatic cysts, and analyzed DNA from those cysts using high-resolution microarray (n=24) or Sanger sequencing (n=22). We here focused on regions of homozygosity on the autosomes (>3.0 Mb) and large CNVs (>1.0 Mb). We found frequent LOH in PRKCSH (22/29) and PKD1/PKD2 (2/3) cysts of patients with known heterozygous germline variants in the respective genes. In the total cohort, 12/23 patients harbored abnormalities outside of familiar areas. In individual ADPLD cases, we identified germline events: a 2q13 complex rearrangement resulting in BUB1 haploinsufficiency, a 47XXX karyotype, chromosome 9q copy-number loss, and LOH on chromosome 3p. The latter region was overlapping with an LOH region identified in two other cysts. Unique germline and somatic abnormalities occur frequently in and outside of known genes underlying cysts. Each liver cyst has a unique genetic makeup. LOH driver gene BUB1 may imply germline causes of genetic instability in PLD.

A novel twist in polycystic liver disease

Liver cysts are a frequent finding on radiological imaging. Prevalence rates depend on the technique, but with CT or MRI, simple hepatic cysts are seen in approximately one-fifth of the population.1 Usually no more than one or two small (<3 cm) cysts are present. These cysts are innocuous and do not require immediate clinical attention. The situation is different when there are multiple and/or large liver cysts such as in polycystic liver disease (PLD). Though PLD is infrequent, patients are seen in every gastroenterology practice. Many patients give a positive family history of PLD. The majority of PLD patients will also have multiple renal cysts and suffer from autosomal dominant polycystic kidney disease (ADPKD). This is a progressive disorder that leads to end-stage renal disease. By contrast, some PLD patients do not have that renal phenotype and they are affected by isolated autosomal dominant polycystic liver disease (PCLD). While the genetic background of ADPKD and PCLD is dissimilar, there is great analogy in their phenotypical behaviour. PLD is characterised by an age-dependent increase of number and size of the liver cysts.1 Within this context, the physiological function of the liver is usually unaffected, but because of the unrelenting growth, significant hepatomegaly develops over time. This is associated with onset of symptoms, such as abdominal pain, early satiety, and dyspnoea which causes a compromised quality of life.2 Thus far, the primary endpoint of treatment …