Autosomal recessive polycystic kidney disease in adulthood

Kidney concentrating capacity in children with autosomal recessive polycystic kidney disease is linked to glomerular filtration and hypertension

BACKGROUND

Impaired kidney concentration capacity is present in half of the patients with autosomal dominant polycystic kidney disease (ADPKD). The kidney concentrating capacity was further impaired within the animal model of autosomal recessive polycystic kidney disease (ARPKD). To date, only one small study has investigated it in children having ARPKD. Therefore, we aimed to study the kidney concentrating ability in a larger cohort of children with ARPKD.

METHODS

Eighteen children (median age 8.5 years, range 1.3-16.8) were retrospectively investigated. A standardized kidney concentrating capacity test was performed after the application of a nasal drop of desmopressin (urine osmolality > 900 mOsmol/kg). The glomerular filtration rate was estimated using the Schwartz formula (eGFR) and blood pressure (BP) was measured as office BP.

RESULTS

Kidney concentrating capacity was decreased (urine osmolality < 900 mOsmol/kg) in 100% of children with ARPKD. The median urine osmolality after desmopressin application was 389 (range 235-601) mOsmol/kg. Sixteen patients (89%) were defined as hypertensive based on their actual BP level or their use of antihypertensive drugs. The maximum amounts of urinary concentration correlated significantly with eGFR (r = 0.72, p < 0.0001) and hypertensive scores (r = 0.50, p < 0.05), but not with kidney size. Twelve patients (67%) were defined as having CKD stages 2-4. The median concentrating capacity was significantly lower in children within this group, when compared to children with CKD stage 1 possessing a normal eGFR (544 mOsmol/kg, range 413-600 mOsmol/kg vs. 327 mOsmol/kg, range 235-417 mOsmol/l, p < 0.001).

CONCLUSIONS

Impaired kidney concentrating capacity is present in most children with ARPKD and is associated with decreased eGFR and hypertension. A higher resolution version of the Graphical abstract is available as Supplementary information.

Genetic Kidney Diseases (GKDs) Modeling Using Genome Editing Technologies

Genetic kidney diseases (GKDs) are a group of rare diseases, affecting approximately about 60 to 80 per 100,000 individuals, for which there is currently no treatment that can cure them (in many cases). GKDs usually leads to early-onset chronic kidney disease, which results in patients having to undergo dialysis or kidney transplant. Here, we briefly describe genetic causes and phenotypic effects of six GKDs representative of different ranges of prevalence and renal involvement (ciliopathy, glomerulopathy, and tubulopathy). One of the shared characteristics of GKDs is that most of them are monogenic. This characteristic makes it possible to use site-specific nuclease systems to edit the genes that cause GKDs and generate in vitro and in vivo models that reflect the genetic abnormalities of GKDs. We describe and compare these site-specific nuclease systems (zinc finger nucleases (ZFNs), transcription activator-like effect nucleases (TALENs) and regularly clustered short palindromic repeat-associated protein (CRISPR-Cas9)) and review how these systems have allowed the generation of cellular and animal GKDs models and how they have contributed to shed light on many still unknown fields in GKDs. We also indicate the main obstacles limiting the application of these systems in a more efficient way. The information provided here will be useful to gain an accurate understanding of the technological advances in the field of genome editing for GKDs, as well as to serve as a guide for the selection of both the genome editing tool and the gene delivery method most suitable for the successful development of GKDs models.

Molecular Pathophysiology of Autosomal Recessive Polycystic Kidney Disease

Autosomal recessive polycystic kidney disease (ARPKD) is a rare disorder and one of the most severe forms of polycystic kidney disease, leading to end-stage renal disease (ESRD) in childhood. PKHD1 is the gene that is responsible for the vast majority of ARPKD. However, some cases have been related to a new gene that was recently identified (DZIP1L gene), as well as several ciliary genes that can mimic a ARPKD-like phenotypic spectrum. In addition, a number of molecular pathways involved in the ARPKD pathogenesis and progression were elucidated using cellular and animal models. However, the function of the ARPKD proteins and the molecular mechanism of the disease currently remain incompletely understood. Here, we review the clinics, treatment, genetics, and molecular basis of ARPKD, highlighting the most recent findings in the field.

Early nephrectomy in neonates with symptomatic autosomal recessive polycystic kidney disease

INTRODUCTION

Autosomal recessive polycystic kidney disease (ARPKD) is a rare cause of renal failure with a highly variable clinical course. Patients who are symptomatic early in life frequently require early nephrectomy and peritoneal dialysis. In these patients there are little data to guide clinicians on whether to select unilateral nephrectomy or bilateral nephrectomy at the initial operative intervention. We review our experience with this disease process.

METHODS

A retrospective review was performed of 11 patients at our institution with ARPKD symptomatic within the first month of life. Charts were reviewed for relevant clinical data, and patients were divided into groups based on undergoing either unilateral or bilateral nephrectomy at their initial intervention. The decision for unilateral versus bilateral nephrectomy was decided by the clinical team without any available guidelines.

RESULTS

Of the 11 patients reviewed, two patients died within the first two weeks from other complications. The remaining 9 all required nephrectomy, with 5 undergoing synchronous bilateral nephrectomy, and 4 undergoing initial unilateral nephrectomy. All four patients required removal of their contralateral kidney, a median of 25.5 days later. There was no difference in mortality, ventilator free days, or time to full feeds between the two groups, although the group undergoing initial unilateral nephrectomy had more TPN days than their counterparts (28 vs 17 days, p = 0.014).

CONCLUSIONS

In our cohort, there were few significant differences between the groups based on choice of initial unilateral or bilateral nephrectomy, and all children ultimately required removal of both kidneys. These data suggest that anesthetic exposures and other clinical outcomes might be optimized by initial bilateral nephrectomy.

LEVEL OF EVIDENCE

III.

Clinical and genetic characteristics of autosomal recessive polycystic kidney disease in Oman

BACKGROUND

There is a high prevalence of rare genetic disorders in the Middle East, and their study provides unique clinical and genetic insights. Autosomal recessive polycystic kidney disease (ARPKD) is one of the leading causes of kidney and liver-associated morbidity and mortality in Oman. We describe the clinical and genetic profile of cohort of ARPKD patients.

METHODS

We studied patients with a clinical diagnosis of ARPKD (n = 40) and their relatives (parents (n = 24) and unaffected siblings (n = 10)) from 32 apparently unrelated families, who were referred to the National Genetic Centre in Oman between January 2015 and December 2018. Genetic analysis of PKHD1 if not previously known was performed using targeted exon PCR of known disease alleles and Sanger sequencing.

RESULTS

A clinical diagnosis of ARPKD was made prenatally in 8 patients, 21 were diagnosed during infancy (0-1 year), 9 during early childhood (2-8 years) and 2 at later ages (9-13 years). Clinical phenotypes included polycystic kidneys, hypertension, hepatic fibrosis and splenomegaly. Twenty-four patients had documented chronic kidney disease (median age 3 years). Twenty-four out of the 32 families had a family history suggesting an autosomal recessive pattern of inherited kidney disease, and there was known consanguinity in 21 families (66%). A molecular genetic diagnosis with biallelic PKHD1 mutations was known in 18 patients and newly identified in 20 other patients, totalling 38 patients from 30 different families. Two unrelated patients remained genetically unsolved. The different PKHD1 missense pathogenic variants were: c.107C > T, p.(Thr36Met); c.406A > G, p.(Thr136Ala); c.4870C > T, p.(Arg1624Trp) and c.9370C > T, p.(His3124Tyr) located in exons 3, 6, 32 and 58, respectively. The c.406A > G, p.(Thr136Ala) missense mutation was detected homozygously in one family and heterozygously with a c.107C > T, p.(Thr36Met) allele in 5 other families. Overall, the most commonly detected pathogenic allele was c.107C > T; (Thr36Met), which was seen in 24 families.

CONCLUSIONS

Molecular genetic screening of PKHD1 in clinically suspected ARPKD cases produced a high diagnostic rate. The limited number of PKHD1 missense variants identified in ARPKD cases suggests these may be common founder alleles in the Omani population. Cost effective targeted PCR analysis of these specific alleles can be a useful diagnostic tool for future cases of suspected ARPKD in Oman.

Long-term Outcomes and Health Perceptions in Pediatric-onset Portal Hypertension Complicated by Varices

OBJECTIVES

Outcomes of pediatric-onset portal hypertension are poorly defined. We aimed to assess population-based long-term outcomes of pediatric-onset portal hypertension complicated by varices.

METHODS

All children with esophageal varices (n = 126) were identified from 14,144 single nationwide referral center endoscopy reports during 1987 to 2013, and followed up through national health care and death registers. A questionnaire was sent to survivors (n = 94) of whom 65 (69%) responded.

RESULTS

Nineteen underlying disorders included biliary atresia (35%), extrahepatic portal vein obstruction (35%), autosomal recessive polycystic kidney disease (7%), and other disorders (23%). During median follow-up of 15.2 (range 0.5-43.1) years patients underwent median 9 (1-74) upper gastrointestinal endoscopies. Esophageal varices were first observed at a median age of 4.0 (0.3-18.2) years, 112 (89%) patients underwent median 6 (1-56) sclerotherapy/banding sessions, and 61 (48%) experienced median 2 (range 1-20) variceal bleeding episodes. Forty-eight surgical shunt procedures were performed to 41 (36%) patients and 38% underwent liver transplantation. Portal hypertensive biliopathy was diagnosed in 4 patients. Hepatopulmonary syndrome necessitated liver transplantation in 2 patients, hepatic encephalopathy in 2, and hepatorenal syndrome in 1. No patient died of variceal bleeding. Patient-reported perception of health on a scale of 1 to 10 was 9 (range 4-10), and 86% reported no current symptoms attributable to esophageal varices.

CONCLUSIONS

Pediatric-onset portal hypertension is a heterogeneous disease with significant long-term morbidity, requiring multimodal approach with considerable resources and continuation of follow-up in adulthood. Although mortality to variceal bleeding was avoided, bleeding episodes recurred also in adulthood, while patient-reported health of long-term survivors was encouraging.

Early Hepatocellular Carcinoma Associated With Fibrocystic Liver Disease in a 10-Year-Old Child: A Case Report

BACKGROUND

Fibrocystic liver-kidney disease is caused by a group of rare and genetically diverse disorders that are associated with kidney cysts or dysplasia and ductal plate malformation in the liver. There have been several reports of liver neoplasias arising in hepatobiliary fibrocystic diseases. However, most were cholangiocarcinoma; cases involving hepatocellular carcinoma (HCC) are rare, and all the reported cases are related with adults.

CASE REPORT

A 10-year-old girl with a history of repeated gastrointestinal bleeding underwent banding and sclerotherapy multiple times and had a history of a Portosystemic shunt without any significant benefit. She was referred to us as a case of fibrocystic liver disease with decompensated liver disease for liver transplantation. The patient underwent living donor liver transplantation, and the explanted liver histopathology report is documented. The explant liver weighed 838 g and measured 21 × 13 × 8.5 cm with the attached gallbladder measuring 7 × 3 × 0.2 cm (in wall thickness). The external surface was covered with multiple white nodules ranging in size from 0.4 to 1 cm. Serial slicing revealed an ill-defined, yellow, soft lesion (4 × 2.5 × 2.5 cm) localized in the subcapsular area of the left lobe (segment 4). The rest of the cut surface was green and nodular (cirrhotic). Microscopy from largest nodule was consistent with early hepatocellular carcinoma.The rest of the liver was cirrhotic, and the morphology was consistent with fibrocystic disease of liver.

CONCLUSION

We report a rare case of HCC associated with fibrocystic liver disease. When diagnosing fibrocystic liver disease without known risk factors, the presence of HCC must be considered, and vice versa. To our knowledge, this is the first reported case of HCC associated with fibrocystic liver disease in a 10-year-old child.

Is polycystic kidney disease associated with malignancy in children?

Background

Polycystic kidney disease (PKD) is an inherited condition characterized by progressive development of end‐stage renal disease, hypertension, hepatic fibrosis, and cysts in the kidney, liver, pancreas, spleen, thyroid, and epididymis. While malignancies have been reported in association with PKD in adults, the incidence of malignancies in children with PKD is not currently known.

Methods

We report on five patients with a known history of PKD who developed a malignancy as children at the University of California, Los Angeles and the University of Colorado Anschutz Medical Campus. Patients were included from 2012 to 2017.

Results

We present five patients with a history of PKD diagnosed with a malignancy during childhood without any additional known mutations to suggest a genetic predisposition to develop cancer. This includes the first reported case of hepatocellular carcinoma in a patient with autosomal recessive polycystic kidney disease.

Conclusion

Our report illustrates the potential that PKD may be associated with an increased risk for developing cancer, even in children. Further research is necessary to better understand this relationship.

Clinical courses and complications of young adults with Autosomal Recessive Polycystic Kidney Disease (ARPKD)

Autosomal recessive polycystic kidney disease (ARPKD) is a severe pediatric hepatorenal disorder with pronounced phenotypic variability. A substantial number of patients with early diagnosis reaches adulthood and some patients are not diagnosed until adulthood. Yet, clinical knowledge about adult ARPKD patients is scarce. Here, we describe forty-nine patients with longitudinal follow-up into young adulthood that were identified in the international ARPKD cohort study ARegPKD. Forty-five patients were evaluated in a cross-sectional analysis at a mean age of 21.4 (±3.3) years describing hepatorenal findings. Renal function of native kidneys was within CKD stages 1 to 3 in more than 50% of the patients. Symptoms of hepatic involvement were frequently detected. Fourteen (31%) patients had undergone kidney transplantation and six patients (13%) had undergone liver transplantation or combined liver and kidney transplantation prior to the visit revealing a wide variability of clinical courses. Hepatorenal involvement and preceding complications in other organs were also evaluated in a time-to-event analysis. In summary, we characterize the broad clinical spectrum of young adult ARPKD patients. Importantly, many patients have a stable renal and hepatic situation in young adulthood. ARPKD should also be considered as a differential diagnosis in young adults with fibrocystic hepatorenal disease.

Polycystic kidney disease

Cystic kidneys are common causes of end-stage renal disease, both in children and in adults. Autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD) are cilia-related disorders and the two main forms of monogenic cystic kidney diseases. ADPKD is a common disease that mostly presents in adults, whereas ARPKD is a rarer and often more severe form of polycystic kidney disease (PKD) that usually presents perinatally or in early childhood. Cell biological and clinical research approaches have expanded our knowledge of the pathogenesis of ADPKD and ARPKD and revealed some mechanistic overlap between them. A reduced 'dosage' of PKD proteins is thought to disturb cell homeostasis and converging signalling pathways, such as Ca²⁺, cAMP, mechanistic target of rapamycin, WNT, vascular endothelial growth factor and Hippo signalling, and could explain the more severe clinical course in some patients with PKD. Genetic diagnosis might benefit families and improve the clinical management of patients, which might be enhanced even further with emerging therapeutic options. However, many important questions about the pathogenesis of PKD remain. In this Primer, we provide an overview of the current knowledge of PKD and its treatment.

Expanding the mutation spectrum in 130 probands with ARPKD: identification of 62 novel PKHD1 mutations by sanger sequencing and MLPA analysis

Autosomal recessive polycystic kidney disease (ARPKD) is a rare severe genetic disorder arising in the perinatal period, although a late-onset presentation of the disease has been described. Pulmonary hypoplasia is the major cause of morbidity and mortality in the newborn period. ARPKD is caused by mutations in the PKHD1 (polycystic kidney and hepatic disease 1) gene that is among the largest human genes. To achieve a molecular diagnosis of the disease, a large series of Italian affected subjects were recruited. Exhaustive mutation analysis of PKHD1 gene was carried out by Sanger sequencing and multiple ligation probe amplification (MLPA) technique in 110 individuals. A total of 173 mutations resulting in a detection rate of 78.6% were identified. Additional 20 unrelated patients, in whom it was not possible to analyze the whole coding sequence, have been included in this study. Taking into account the total number (n=130) of this cohort of patients, 107 different types of mutations have been detected in 193 mutated alleles. Out of 107 mutations, 62 were novel: 11 nonsense, 6 frameshift, 7 splice site mutations, 2 in-frame deletions and 2 multiexon deletion detected by MLPA. Thirty-four were missense variants. In conclusion, our report expands the spectrum of PKHD1 mutations and confirms the heterogeneity of this disorder. The population under study represents the largest Italian ARPKD cohort reported to date. The estimated costs and the time invested for molecular screening of genes with large size and allelic heterogeneity such as PKHD1 demand the use of next-generation sequencing (NGS) technologies for a faster and cheaper screening of the affected subjects.

Long-term pulmonary function in children with recessive polycystic kidney disease

BACKGROUND

Neonatal autosomal-recessive polycystic kidney disease (ARPKD) is associated with pulmonary hypoplasia and severe respiratory distress. There is no published information on long-term lung function in ARPKD survivors.

METHODS

Pulmonary function tests, including spirometry and diffusion capacity, were performed in a nationwide cohort of Finnish paediatric patients with ARPKD. The annual incidence of respiratory infections and the need for permanent asthma medication were also evaluated in this population.

RESULTS

Pulmonary function in 11 children surviving the neonatal period was good when measured after a median follow-up time of 10.4 years (range 5.4-16.1 years). None of the patients required oxygen supplementation, and only one patient had asthma. Patients who had received ventilator therapy during infancy had significantly lower maximal instantaneous forced expiratory flow (MEF%) (66%; 43-93% vs 105%; 63-110%; p=0.048) and forced expiratory volume/forced vital capacity (0.76; 0.7-0.81 vs 0.89; 0.77-0.91; p=0.03) than patients without a history of mechanical ventilation, suggesting tendency for airway obstruction in the former group of patients. The frequency of respiratory infections did not differ from Finnish paediatric population in general.

CONCLUSIONS

The results of pulmonary function tests were within reference values for most patients with ARPKD, which suggested good long-term lung prognosis. Lung function tests should be considered for patients with ARPKD with a history of mechanical ventilation during infancy.

Transplantation in autosomal recessive polycystic kidney disease: liver and/or kidney?

Autosomal recessive polycystic kidney disease (ARPKD) is characterized by enlarged kidneys with dilated collecting ducts and congenital hepatic fibrosis. There is a variable rate of progression of kidney and liver disease. Portal hypertension and Caroli's disease occur from liver involvement that contributes to morbidity and mortality. Approximately 40 % of patients have a severe disease phenotype leading to rapid onset of end-stage kidney disease (ESKD) and signs of portal hypertension and the rest may have predominant involvement of either the kidney or liver. It is important for the physician to establish the extent of organ involvement before deciding on the ultimate plan of management, especially when transplantation is required. Isolated renal transplantation can be considered when liver involvement is minimal. If hepatobiliary disease is prominent, and kidney function is preserved, management options are based on individual characteristics. In the presence of significant liver disease and ESKD, consideration should be given to combined liver kidney transplantation, which can be beneficial in eliminating the consequences of both kidney and liver disease. However, this is a complex surgical procedure that needs to be performed at experienced transplant centers. Improvement in surgical techniques has considerably improved short-term graft survival with the added advantage of the liver offering immunologic protection to the kidney allograft.

From the radiologic pathology archives: pediatric polycystic kidney disease and other ciliopathies: radiologic-pathologic correlation

Genetic defects of cilia cause a wide range of diseases, collectively known as ciliopathies. Primary, or nonmotile, cilia function as sensory organelles involved in the regulation of cell growth, differentiation, and homeostasis. Cilia are present in nearly every cell in the body and mutations of genes encoding ciliary proteins affect multiple organs, including the kidneys, liver, pancreas, retina, central nervous system (CNS), and skeletal system. Genetic mutations causing ciliary dysfunction result in a large number of heterogeneous phenotypes that can manifest with a variety of overlapping abnormalities in multiple organ systems. Renal manifestations of ciliopathies are the most common abnormalities and include collecting duct dilatation and cyst formation in autosomal recessive polycystic kidney disease (ARPKD), cyst formation anywhere in the nephron in autosomal dominant polycystic kidney disease (ADPKD), and tubulointerstitial fibrosis in nephronophthisis, as well as in several CNS and skeletal malformation syndromes. Hepatic disease is another common manifestation of ciliopathies, ranging from duct dilatation and cyst formation in ARPKD and ADPKD to periportal fibrosis in ARPKD and several malformation syndromes. The unifying molecular pathogenesis of this emerging class of disorders explains the overlap of abnormalities in disparate organ systems and links diseases of widely varied clinical features. It is important for radiologists to be able to recognize the multisystem manifestations of these syndromes, as imaging plays an important role in diagnosis and follow-up of affected patients.

Kidney and liver transplantation in children with fibrocystic liver-kidney disease: data from the US Scientific Registry of Transplant Recipients: 1990-2010

The natural history and survival of children with fibrocystic liver-kidney disease undergoing solid organ transplantation have infrequently been described. We report outcomes in a cohort of US children with fibrocystic liver-kidney disease receiving solid organ transplants over 20 yr. Retrospective cohort study of pediatric transplant recipients with diagnoses of fibrocystic liver-kidney disease from 1/1990 to 3/2010, using data from the SRTR. Subjects were categorized by the first transplanted organ: LT, KT, or SLK. Primary outcomes were death, re-transplant, transplant of the alternate organ, or initiation of dialysis. Seven hundred and sixteen subjects were transplanted in this period. Median age at first transplant was 9.7 yr. Of the LT, 14 (19%) required a second liver transplant at median of 0.2 yr, and five (7%) required kidney transplant or dialysis at a median of 9.0 yr. Of the KT, 188 (31%) required a second kidney transplant or dialysis at a median of 5.9 yr. Twenty-nine (5%) subsequently received liver transplant at a median of 6.0 yr. Among patients in this registry, far more children underwent kidney than liver transplants. The risk of subsequently needing transplantation of an alternate organ was low.

Clinical manifestations of autosomal recessive polycystic kidney disease (ARPKD): kidney-related and non-kidney-related phenotypes

Autosomal recessive polycystic kidney disease (ARPKD), although less frequent than the dominant form, is a common, inherited ciliopathy of childhood that is caused by mutations in the PKHD1-gene on chromosome 6. The characteristic dilatation of the renal collecting ducts starts in utero and can present at any stage from infancy to adulthood. Renal insufficiency may already begin in utero and may lead to early abortion or oligohydramnios and lung hypoplasia in the newborn. However, there are also affected children who have no evidence of renal dysfunction in utero and who are born with normal renal function. Up to 30 % of patients die in the perinatal period, and those surviving the neonatal period reach end stage renal disease (ESRD) in infancy, early childhood or adolescence. In contrast, some affected patients have been diagnosed as adults with renal function ranging from normal to moderate renal insufficiency to ESRD. The clinical spectrum of ARPKD is broader than previously recognized. While bilateral renal enlargement with microcystic dilatation is the predominant clinical feature, arterial hypertension, intrahepatic biliary dysgenesis remain important manifestations that affect approximately 45 % of infants. All patients with ARPKD develop clinical findings of congenital hepatic fibrosis (CHF); however, non-obstructive dilation of the intrahepatic bile ducts in the liver (Caroli's disease) is seen at the histological level in only a subset of patients. Cholangitis and variceal bleeding, sequelae of portal hypertension, are life-threatening complications that may occur more often in advanced cases of liver disease. In this review we focus on common and uncommon kidney-related and non-kidney-related phenotypes. Clinical management of ARPKD patients should include consideration of potential problems related to these manifestations.

Autosomal recessive polycystic kidney disease: a hepatorenal fibrocystic disorder with pleiotropic effects

Autosomal recessive polycystic kidney disease (ARPKD) is an important cause of chronic kidney disease in children. The care of ARPKD patients has traditionally been the realm of pediatric nephrologists; however, the disease has multisystem effects, and a comprehensive care strategy often requires a multidisciplinary team. Most notably, ARPKD patients have congenital hepatic fibrosis, which can lead to portal hypertension, requiring close follow-up by pediatric gastroenterologists. In severely affected infants, the diagnosis is often first suspected by obstetricians detecting enlarged, echogenic kidneys and oligohydramnios on prenatal ultrasounds. Neonatologists are central to the care of these infants, who may have respiratory compromise due to pulmonary hypoplasia and massively enlarged kidneys. Surgical considerations can include the possibility of nephrectomy to relieve mass effect, placement of dialysis access, and kidney and/or liver transplantation. Families of patients with ARPKD also face decisions regarding genetic testing of affected children, testing of asymptomatic siblings, or consideration of preimplantation genetic diagnosis for future pregnancies. They may therefore interface with genetic counselors, geneticists, and reproductive endocrinologists. Children with ARPKD may also be at risk for neurocognitive dysfunction and may require neuropsychological referral. The care of patients and families affected by ARPKD is therefore a multidisciplinary effort, and the general pediatrician can play a central role in this complex web of care. In this review, we outline the spectrum of clinical manifestations of ARPKD and review genetics of the disease, clinical and genetic diagnosis, perinatal management, management of organ-specific complications, and future directions for disease monitoring and potential therapies.

Risk of hepatobiliary cancer after solid organ transplant in the United States

BACKGROUND & AIMS

Studies of liver cancer risk in recipients of solid organ transplants generally have been small, yielding mixed results, and little is known about biliary tract cancers among transplant recipients.

METHODS

We identified incident hepatobiliary cancers among 201,549 US recipients of solid organs, from 1987 through 2008, by linking data from the US transplant registry with 15 cancer registries. We calculated standardized incidence ratios (SIRs), comparing risk relative to the general population. We also calculated incidence rate ratios (RRs), comparing risk for hepatocellular carcinoma (HCC) and total (intrahepatic and extrahepatic) cholangiocarcinoma among subgroups of recipients.

RESULTS

Of transplant recipients, 165 developed hepatobiliary cancers (SIR, 1.2; 95% confidence interval [CI], 1.0-1.4). HCC risk was increased among liver recipients (SIR, 1.5; 95% CI, 1.0-2.2), especially 5 or more years after transplant (SIR, 1.8; 95% CI, 1.0-3.0). Cholangiocarcinoma was increased among liver (SIR, 2.9; 95% CI, 1.6-4.8) and kidney recipients (SIR, 2.1; 95% CI, 1.3-3.1). HCC was associated with hepatitis B virus (RR, 3.2; 95% CI, 1.3-6.9), hepatitis C virus (RR, 10; 95% CI, 5.9-16.9), and non-insulin-dependent diabetes (RR, 2.5; 95% CI, 1.2-4.8). Cholangiocarcinoma was associated with azathioprine maintenance therapy (RR, 2.0; 95% CI, 1.1-3.7). Among liver recipients, primary sclerosing cholangitis was associated with an increased risk of cholangiocarcinoma, compared with the general population (SIR, 21; 95% CI, 8.2-42) and compared with liver recipients without primary sclerosing cholangitis (RR, 12.3; 95% CI, 4.1-36.4).

CONCLUSIONS

Risks for liver and biliary tract cancer are increased among organ transplant recipients. Risk factors for these cancers include medical conditions and potentially medications taken by recipients.

Liver disease in autosomal recessive polycystic kidney disease: clinical characteristics and management in relation to renal failure

OBJECTIVES

We correlated liver and kidney manifestations in a national cohort of patients with autosomal recessive polycystic kidney disease (ARPKD).

METHODS

A total of 27 consecutive patients with ARPKD were included. Hepatobiliary disorders were comparatively evaluated in 2 groups: children in group 1 (n = 10) displayed renal failure as infants and those in group 2 (n = 17) had normal kidney function through the first year of life.

RESULTS

Median follow-up time was 10.6 (range, 0.4-40) years. Portal hypertension was diagnosed in 13 patients (48%) at the median age 5.0 (1.5-27.9) years. Esophageal varices developed in 8 patients (30%) at age 8.0 (2.1-11.9) years; 4 patients (15%) had variceal bleeding, and hypersplenism/splenomegaly occurred in 52%, similarly in both groups. Biliary tract dilatation was detected at 2.8 years in group 1 and at 7.9 years in group 2, significantly more frequently in group 1 (60% vs 18%, P = 0.039), causing cholangitis in 2 (20%) versus none in group 2 (P = 0.055). A total of 10 patients (37%) underwent cadaveric liver transplantation (LT) at a median age of 6.6 (1.0-20.0) years. In 1 patient LT was performed because of hepatoblastoma. Nine of these were combined liver-kidney transplantations (CLKT). Patients in group 1 required LT earlier (4.1 years vs 18.2 years, P = 0.017) and more frequently (70% vs 18%, P = 0.01). Overall survival beyond neonatal period was 85%. Two patients died because of infectious complications after CLKT, and 1 patient because of recurrent hepatoblastoma.

CONCLUSIONS

Although correlation of renal and liver manifestations was variable, biliary dilatation was associated with early renal failure. CLKT may be a treatment for patients with ARPKD with marked hepatobiliary complications.

Cost-effective PKHD1 genetic testing for autosomal recessive polycystic kidney disease

BACKGROUND

Genetic diagnosis of autosomal recessive polycystic kidney disease (ARPKD) is challenging due to the length and allelic heterogeneity of the PKHD1 gene. Mutations appear to be clustered at specific exons, depending on the geographic origin of the patient. We aimed to identify the PKHD1 exons most likely mutated in Spanish ARPKD patients.

METHODS

Mutation analysis was performed in 50 ARPKD probands and nine ARPKD-suspicious patients by sequencing PKHD1 exons arranged by their reported mutation frequency. Haplotypes containing the most frequent mutations were analyzed. Other PKD genes (HNF1B, PKD1, PKD2) were sequenced in PKHD1-negative cases.

RESULTS

Thirty-six different mutations (concentrated in 24 PKHD1 exons) were detected, giving a mutation detection rate of 86%. The screening of five exons (58, 32, 34, 36, 37) yielded a 54% chance of detecting one mutation; the screening of nine additional exons (3, 9, 39, 61, 5, 22, 26, 41, 57) increased the chance to 76%. The c.9689delA mutation was present in 17 (34%) patients, all of whom shared the same haplotype. Two HNF1B mutations and one PKD1 variant were detected in negative cases.

CONCLUSIONS

Establishing a PKHD1 exon mutation profile in a specific population and starting the analysis with the most likely mutated exons might significantly enhance the efficacy of genetic testing in ARPKD. Analysis of other PKD genes might be considered, especially in suspicious cases.

An autopsy case of clinically un-diagnosed autosomal recessive polycystic kidney disease in 77-year-old male

Autosomal recessive polycystic kidney disease (ARPKD) is caused by genetic mutations of the gene encoding fibrocystin, and is characterized by the collecting duct cysts and congenital hepatic fibrosis. We report an autopsy-proven case of ARPKD in a 77-year-old male who presented with rapidly progressive renal and liver dysfunction. He had refused hemodialysis, and died 4 months later. At autopsy, both kidneys were enlarged with numerous small cysts throughout the cortex, which were revealed immunohistochemically to be the collecting ducts. Liver involvement was characterized by ductal plate malformation accompanied with portal fibrosis. The morphological appearances were compatible with ARPKD and the negative immunostaining for fibrocystin in the collecting ducts and bile ducts confirmed the diagnosis. ARPKD is known to occur in the neonatal period or in infancy with a high mortality rate. Although some patients who survive infancy are expected to live longer into young adulthood, most patients with ARPKD die of renal and hepatic failure in their childhood. The present case is extremely exceptional, in that no clinical symptoms suggestive of ARPKD were noticed until old age, and suggests that the disease spectrum of ARPKD is variable, and that a slowly progressive form of ARPKD may not be diagnosed until old age.

Characteristics of congenital hepatic fibrosis in a large cohort of patients with autosomal recessive polycystic kidney disease

BACKGROUND & AIMS

Autosomal recessive polycystic kidney disease (ARPKD), the most common ciliopathy of childhood, is characterized by congenital hepatic fibrosis and progressive cystic degeneration of kidneys. We aimed to describe congenital hepatic fibrosis in patients with ARPKD, confirmed by detection of mutations in PKHD1.

METHODS

Patients with ARPKD and congenital hepatic fibrosis were evaluated at the National Institutes of Health from 2003 to 2009. We analyzed clinical, molecular, and imaging data from 73 patients (age, 1-56 years; average, 12.7 ± 13.1 years) with kidney and liver involvement (based on clinical, imaging, or biopsy analyses) and mutations in PKHD1.

RESULTS

Initial symptoms were liver related in 26% of patients, and others presented with kidney disease. One patient underwent liver and kidney transplantation, and 10 others received kidney transplants. Four presented with cholangitis and one with variceal bleeding. Sixty-nine percent of patients had enlarged left lobes on magnetic resonance imaging, 92% had increased liver echogenicity on ultrasonography, and 65% had splenomegaly. Splenomegaly started early in life; 60% of children younger than 5 years had enlarged spleens. Spleen volume had an inverse correlation with platelet count and prothrombin time but not with serum albumin level. Platelet count was the best predictor of spleen volume (area under the curve of 0.88905), and spleen length corrected for patient's height correlated inversely with platelet count (R(2) = 0.42, P < .0001). Spleen volume did not correlate with renal function or type of PKHD1 mutation. Twenty-two of 31 patients who underwent endoscopy were found to have varices. Five had variceal bleeding, and 2 had portosystemic shunts. Forty-percent had Caroli syndrome, and 30% had an isolated dilated common bile duct.

CONCLUSIONS

Platelet count is the best predictor of the severity of portal hypertension, which has early onset but is underdiagnosed in patients with ARPKD. Seventy percent of patients with ARPKD have biliary abnormalities. Kidney and liver disease are independent, and variability in severity is not explainable by type of PKHD1 mutation; ClinicalTrials.gov number, NCT00068224.

Congenital hepatic fibrosis and autosomal recessive polycystic kidney disease

OBJECTIVES

The published natural history of congenital hepatic fibrosis (CHF) was examined to inform clinical decision making in autosomal recessive polycystic kidney disease (ARPKD).

METHODS

A systematic literature search of the data on CHF, ARPKD, Caroli disease, Caroli syndrome, and type V choledochal cyst was performed to extract data related to portal hypertension, infection, malignancy, mortality, and transplantation.

RESULTS

Information related to 1230 patients with CHF was extracted from 155 articles. Median and mean age at diagnosis were 2 and 11.2 years, respectively. Median and mean time followed after diagnosis were 5.0 and 7.5 years, respectively (range 0-38 years). Sequelae of portal hypertension (n = 409), cholangitis (n = 152), and malignancy (n = 21) were noted. The nature of the portal hypertension was similar to that in other pediatric conditions (164 with varices, 74 bleeding varices, 81 underwent portosystemic shunting). Documented cholangitis was fatal in 3 of 23 children who were infected after renal transplantation. Twenty-one patients developed hepatobiliary cancer, with the majority having cholangiocarcinoma (n = 19). Cholangiocarcinoma (CCA) was predominant in individuals older than 40 years with either Caroli syndrome or isolated CHF, not ARPKD (median and mean age at CCA diagnosis were 70.3 and 60.1 years, respectively; range 33-75 years). There was a relative paucity of data on combined liver-kidney transplantation.

CONCLUSIONS

Clinical decision making in ARPKD should reflect an understanding of the potential issues emanating from CHF. Accepted pediatric specific approaches to portal hypertension are warranted but must take into consideration the stage of renal insufficiency and potential plans for renal transplantation. Cholangitis is a major issue and necessitates anticipatory guidance and awareness. CCA, although a dreaded complication, does not appear to be a major issue during childhood. The indications for liver and combined liver-kidney transplantation are controversial and warrant further analysis.

Congenital hepatic fibrosis in autosomal recessive polycystic kidney disease

Autosomal recessive polycystic kidney disease (ARPKD) is a developmental disorder that mainly affects the kidneys and the biliary tract. Affected patients often have massively enlarged cystic kidneys as well as congenital hepatic fibrosis (CHF) characterized by dilated bile ducts and associated peribiliary fibrosis. This review will examine what is known about ARPKD-associated liver disease and will highlight areas of ongoing research into its pathogenesis and potential treatment.

The spectrum of polycystic kidney disease in children

Autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD) are important inherited kidney diseases with distinct clinical features and genetics. Although these diseases have classically been considered "adult" (ADPKD) or "infantile/pediatric" (ARPKD), it is now clear that both diseases can present in children and adults. ADPKD and ARPKD also share important pathophysiologic features, including cilia dysfunction. ADPKD is a systemic disease involving cysts in the kidneys and abdominal organs as well as abnormalities in the heart and vasculature. Although it typically presents in adults, ADPKD has been diagnosed in fetuses, infants, children, and adolescents. The majority of children diagnosed with ADPKD are asymptomatic. Those with symptoms typically present with hypertension or gross hematuria. Routine screening for renal cysts in asymptomatic children who have a parent with ADPKD is generally not recommended. ARPKD is a disorder confined to the kidneys (polycystic kidneys) and liver (a developmental biliary lesion called congenital hepatic fibrosis). Although most children with ARPKD present in infancy with large, echogenic kidneys, a subset present later in childhood and even adulthood, primarily with complications related to the liver disease. As more patients with ARPKD survive to adulthood, these liver complications are likely to become more prevalent.

[Cystic and hyperechogenic kidneys in children]

Thanks to prenatal ultrasound scan, cystic kidneys, as well as obstructive uropathies, are the most frequent renal anomalies identified during pregnancy. They should be recognized because of genetic and clinical implications. The most frequent are autosomal dominant and recessive polycystic kidney diseases, followed by renal developmental anomalies linked to TCF2 gene. Renal cysts are also observed in other hereditary diseases or multiple malformation syndromes (tuberosis sclerosis, Meckel-Grubber syndrome, Oro-facial digital type 1 syndrome...). The diagnosis is based on a sonographic and morphological analysis of renal abnormalities, on the search for family histories and extra-renal manifestations. A better classification of these patients allows tailor-made follow-up and care improvement.

Correlation of kidney function, volume and imaging findings, and PKHD1 mutations in 73 patients with autosomal recessive polycystic kidney disease

BACKGROUND AND OBJECTIVES

Renal function and imaging findings have not been comprehensively and prospectively characterized in a broad age range of patients with molecularly confirmed autosomal recessive polycystic kidney disease (ARPKD).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Ninety potential ARPKD patients were examined at the National Institutes of Health Clinical Center. Seventy-three fulfilled clinical diagnostic criteria, had at least one PKHD1 mutation, and were prospectively evaluated using magnetic resonance imaging (MRI), high-resolution ultrasonography (HR-USG), and measures of glomerular and tubular function.

RESULTS

Among 31 perinatally symptomatic patients, 25% required renal replacement therapy by age 11 years; among 42 patients who became symptomatic beyond 1 month (nonperinatal), 25% required kidney transplantation by age 32 years. Creatinine clearance (CrCl) for nonperinatal patients (103 +/- 54 ml/min/1.73 m(2)) was greater than for perinatal patients (62 +/- 33) (P = 0.002). Corticomedullary involvement on HR-USG was associated with a significantly worse mean CrCl (61 +/- 32) in comparison with medullary involvement only (131 +/- 46) (P < 0.0001). Among children with enlarged kidneys, volume correlated inversely with function, although with wide variability. Severity of PKHD1 mutations did not determine kidney size or function. In 35% of patients with medullary-only abnormalities, standard ultrasound was normal and the pathology was detectable with HR-USG.

CONCLUSIONS

In ARPKD, perinatal presentation and corticomedullary involvement are associated with faster progression of kidney disease. Mild ARPKD is best detected by HR-USG. Considerable variability occurs that is not explained by the type of PKHD1 mutation.

Liver and kidney disease in ciliopathies

Hepatorenal fibrocystic diseases (HRFCDs) are among the most common inherited human disorders. The discovery that proteins defective in the autosomal dominant and recessive polycystic kidney diseases (ADPKD and ARPKD) localize to the primary cilia and the recognition of the role these organelles play in the pathogenesis of HRFCDs led to the term "ciliopathies." While ADPKD and ARPKD are the most common ciliopathies associated with both liver and kidney disease, variable degrees of renal and/or hepatic involvement occur in many other ciliopathies, including Joubert, Bardet-Biedl, Meckel-Gruber, and oral-facial-digital syndromes. The ductal plate malformation (DPM), a developmental abnormality of the portobiliary system, is the basis of the liver disease in ciliopathies that manifest congenital hepatic fibrosis (CHF), Caroli syndrome (CS), and polycystic liver disease (PLD). Hepatocellular function remains relatively preserved in ciliopathy-associated liver diseases. The major morbidity associated with CHF is portal hypertension (PH), often leading to esophageal varices and hypersplenism. In addition, CD predisposes to recurrent cholangitis. PLD is not typically associated with PH, but may result in complications due to mass effects. The kidney pathology in ciliopathies ranges from non-functional cystic dysplastic kidneys to an isolated urinary concentration defect; the disorders contributing to this pathology, in addition to ADPKD and ARPKD, include nephronophithisis (NPHP), glomerulocystic kidney disease and medullary sponge kidneys. Decreased urinary concentration ability, resulting in polyuria and polydypsia, is the first and most common renal symptom in ciliopathies. While the majority of ADPKD, ARPKD, and NPHP patients require renal transplantation, the frequency and rate of progression to renal failure varies considerably in other ciliopathies. This review focuses on the kidney and liver disease found in the different ciliopathies.

Congenital cholestatic syndromes: what happens when children grow up?

Although advances in the management of children with congenital cholestasis have enabled many to survive into adulthood with their native livers, even the most common of these conditions remains rare in adult hepatology practice. Among four congenital cholestatic syndromes (biliary atresia, Alagille syndrome, Caroli disease and congenital hepatic fibrosis, and progressive familial intrahepatic cholestasis), the published data on outcomes of the syndromes into adulthood suggest that a spectrum of severity of liver disease can be expected, from cirrhosis (almost universal in adults with biliary atresia who have not required liver transplantation) to mild and subclinical (eg, in the previously undiagnosed affected parent of an infant with Alagille syndrome). Complications associated with portal hypertension and nutritional deficiencies are common, and other associated features of the cholestatic syndrome may require appropriate attention, such as congenital heart disease in Alagille syndrome. Indications for liver transplantation include synthetic failure, progressive encephalopathy, intractable pruritus, recurrent biliary sepsis and recurrent complications of portal hypertension. Improved understanding of biliary physiology will hopefully translate into improved therapy for children and adults with cholestasis.

Fibrocystin/polyductin modulates renal tubular formation by regulating polycystin-2 expression and function

Autosomal recessive polycystic kidney disease is caused by mutations in PKHD1, which encodes the membrane-associated receptor-like protein fibrocystin/polyductin (FPC). FPC associates with the primary cilia of epithelial cells and co-localizes with the Pkd2 gene product polycystin-2 (PC2), suggesting that these two proteins may function in a common molecular pathway. For investigation of this, a mouse model with a gene-targeted mutation in Pkhd1 that recapitulates phenotypic characteristics of human autosomal recessive polycystic kidney disease was produced. The absence of FPC is associated with aberrant ciliogenesis in the kidneys of Pkhd1-deficient mice. It was found that the COOH-terminus of FPC and the NH2-terminus of PC2 interact and that lack of FPC reduced PC2 expression but not vice versa, suggesting that PC2 may function immediately downstream of FPC in vivo. PC2-channel activities were dysregulated in cultured renal epithelial cells derived from Pkhd1 mutant mice, further supporting that both cystoproteins function in a common pathway. In addition, mice with mutations in both Pkhd1 and Pkd2 had a more severe renal cystic phenotype than mice with single mutations, suggesting that FPC acts as a genetic modifier for disease severity in autosomal dominant polycystic kidney disease that results from Pkd2 mutations. It is concluded that a functional and molecular interaction exists between FPC and PC2 in vivo.

Biliary and pancreatic dysgenesis in mice harboring a mutation in Pkhd1

Autosomal recessive polycystic kidney disease is a hereditary fibrocystic disease that involves the kidneys and the biliary tract. Mutations in the PKHD1 gene are responsible for typical forms of autosomal recessive polycystic kidney disease. We have generated a mouse model with targeted mutation of Pkhd1 by disrupting exon 4, resulting in a mutant transcript with deletion of 66 codons and expression at approximately 30% of wild-type levels. Pkhd1(del4/del4) mice develop intrahepatic bile duct proliferation with progressive cyst formation and associated periportal fibrosis. In addition, these mice exhibit extrahepatic manifestations, including pancreatic cysts, splenomegaly, and common bile duct dilation. The kidneys are unaffected both histologically and functionally. Fibrocystin is expressed in the apical membranes and cilia of bile ducts and distal nephron segments but is absent from the proximal tubule. This pattern is unchanged in orthologous models of autosomal dominant polycystic kidney disease due to mutation in Pkd1 or Pkd2. Mutant fibrocystin in Pkhd1(del4/del4) mice also retains this expression pattern. The hypomorphic Pkhd1(del4/del4) mouse model provides evidence that reduced functional levels of fibrocystin are sufficient for cystogenesis and fibrosis in the liver and pancreas, but not the kidney, and supports the hypothesis of species-dependent differences in susceptibility of tissues to Pkhd1 mutations.

PKHD1 gene silencing may cause cell abnormal proliferation through modulation of intracellular calcium in autosomal recessive polycystic kidney disease

Autosomal recessive polycystic kidney disease (ARPKD) is one of the important genetic disorders in pediatric practice. Mutation of the polycystic kidney and hepatic disease gene 1 (PKHD1) was identified as the cause of ARPKD. The gene encodes a 67-exon transcript for a large protein of 4074 amino acids termed fibrocystin, but its function remains unknown. The neoplastic-like in cystic epithelial proliferation and the epidermal growth factor/epidermal growth factor receptor (EGF/EGFR) axis overactivity are known as the most important characteristics of ARPKD. Since the misregulation of Ca(2+) signaling may lead to aberrant structure and function of the collecting ducts in kidney of rat with ARPKD, present study aimed to investigate the further mechanisms of abnormal proliferation of cystic cells by inhibition of PKHD1 expression. For this, a stable PKHD1-silenced HEK-293T cell line was established. Then cell proliferation rates, intracellular Ca(2+) concentration and extracellular signal-regulated kinase 1/2 (ERK1/2) activity were assessed after treatment with EGF, a calcium channel blocker and agonist, verapamil and Bay K8644. It was found that PKHD1-silenced HEK-293T cell lines were hyperproliferative to EGF stimulation. Also PKHD1-silencing lowered the intracellular Ca(2+) and caused EGF-induced ERK1/2 overactivation in the cells. An increase of intracellular Ca(2+) in PKHD1-silenced cells repressed the EGF-dependent ERK1/2 activation and the hyperproliferative response to EGF stimulation. Thus, inhibition of PKHD1 can cause EGF-induced excessive proliferation through decreasing intracellular Ca(2+) resulting in EGF-induced ERK1/2 activation. Our results suggest that the loss of fibrocystin may lead to abnormal proliferation in kidney epithelial cells and cyst formation in ARPKD by modulation of intracellular Ca(2+).

Polyductin undergoes notch-like processing and regulated release from primary cilia

Mutations at a single locus, PKHD1, are responsible for causing human autosomal recessive polycystic kidney disease (ARPKD). Recent studies suggest that the cystic disease might result from defects in planar cell polarity, but how the 4074 amino acid ciliary protein encoded by the longest open reading frame of this transcriptionally complex gene may regulate this process is unknown. Using novel in vitro expression systems, we show that the PKHD1 gene product polyductin/fibrocystin undergoes a complicated pattern of Notch-like proteolytic processing. Cleavage at a probable proprotein convertase site produces a large extracellular domain that is tethered to the C-terminal stalk by disulfide bridges. This fragment is then shed from the primary cilium by activation of a member of the ADAM metalloproteinase disintegrins family, resulting in concomitant release of an intra-cellular C-terminal fragment via a gamma-secretase-dependent process. The ectodomain of endogenous PD1 is similarly shed from the primary cilium upon activation of sheddases. This is the first known example of this process involving a protein of the primary cilium and suggests a novel mechanism whereby proteins that localize to this structure may function as bi-directional signaling molecules. Regulated release from the primary cilium into the lumen may be a mechanism to distribute signal to down-stream targets using flow.

Genotype-phenotype correlations in autosomal dominant and autosomal recessive polycystic kidney disease

The phenotypes that are associated with the common forms of polycystic kidney disease (PKD)--autosomal dominant (ADPKD) and autosomal recessive (ARPKD)--are highly variable in penetrance. This is in terms of severity of renal disease, which can range from neonatal death to adequate function into old age, characteristics of the liver disease, and other extrarenal manifestations in ADPKD. Influences of the germline mutation are at the genic and allelic levels, but intrafamilial variability indicates that genetic background and environmental factors are also key. In ADPKD, the gene involved, PKD1 or PKD2, is a major factor, with ESRD occurring 20 yr later in PKD2. Mutation position may also be significant, especially in terms of the likelihood of vascular events, with 5' mutations most detrimental. Variance component analysis in ADPKD populations indicates that genetic modifiers are important, but few such factors (beyond co-inheritance of a TSC2 mutation) have been identified. Hormonal influences, especially associated with more severe liver disease in female individuals, indicate a role for nongenetic factors. In ARPKD, the combination of mutations is critical to the phenotypic outcome. Patients with two truncating mutations have a lethal phenotype, whereas the presence of at least one missense change can be compatible with life, indicating that many missense changes are hypomorphic alleles that generate partially functional protein. Clues from animal models and other forms of PKD highlight potential modifiers. The information that is now available on both genes is of considerable prognostic value with the prospects from the ongoing genetic revolution that additional risk factors will be revealed.

Fibrocystin/polyductin, found in the same protein complex with polycystin-2, regulates calcium responses in kidney epithelia

Recent evidence suggests that fibrocystin/polyductin (FPC), polycystin-1 (PC1), and polycystin-2 (PC2) are all localized at the plasma membrane and the primary cilium, where PC1 and PC2 contribute to fluid flow sensation and may function in the same mechanotransduction pathways. To further define the exact subcellular localization of FPC, the protein product encoded by the PKHD1 gene responsible for autosomal recessive polycystic kidney disease (PKD) in humans, and whether FPC has direct and/or indirect cross talk with PC2, which, in turn, is pivotal for the pathogenesis of autosomal dominant PKD, we performed double immunostaining and coimmunoprecipitation as well as a microfluorimetry study of kidney tubular epithelial cells. FPC and PC2 are found to completely or partially colocalize at the plasma membrane and the primary cilium and can be reciprocally coimmunoprecipitated. Although incomplete removal of FPC by small interfering RNA and antibody 803 to intracellular epitopes of FPC did not abolish flow-induced intracellular calcium responses, antibody 804 to extracellular epitopes of FPC blocked cellular calcium responses to flow stimulation. These findings suggest that FPC and polycystins share, at least in part, a common mechanotransduction pathway.

[Polycystic kidney diseases: molecular genetics and counselling]

Autosomal dominant polycystic kidney disease (ADPKD) affects 1 newborn in 400 to 1000 making it the most common inherited form of genetic kidney disease and an important cause of medical morbidity and account for about 10% of end-stage renal disease. Autosomal recessive polycystic kidney disease (ARPKD) is a rare (1/20,000 to 1/40,000) inherited disease in children characterized by the association of dilation of collecting ducts and biliary dysgenesis. The clinical spectrum is variable but it represents an important cause of renal and liver-related morbidity and mortality in neonates and infancy. Symptoms of autosomal recessive PKD can begin before birth. ARPKD is genetically different from ADPKD. Parents who do not have the disease can have a child with the disease if both parents carry the abnormal gene and both pass the gene to their baby. Recently important advances in understanding the molecular basis of ADPKD (i.e. ADPKD1 and ADPKD2) and autosomal recessive PKD (i.e. PKHD1) have been done and are reported here. Genetic counselling is particularly advised in early onset disease families. It permits to determine the type of transmission, to describe the course and the major complications of the disease and to explain currents therapeutics possibilities.

Predominant extrahepatic biliary disease in autosomal recessive polycystic kidney disease: a new association

Autosomal recessive polycystic kidney disease (ARPKD) is characterized by dilation of ectatic renal collecting ducts, intrahepatic biliary dysgenesis, and portal fibrosis. Portal hypertension and recurrent bacterial cholangitis can dominate the clinical picture in long-term survivors. Predominant extrahepatic bile duct disease was revealed in four patients who underwent magnetic resonance cholangiopancreatography. All four patients had portal hypertension, although liver biochemistries did not suggest biliary disease. In two of the patients, cholangitis was clinically ascribed to the bile duct disease. Western blot analysis of plasma membranes from normal rat extrahepatic bile duct and kidney revealed the presence of polyductin as a single approximately 440 kDa protein. Although the exact function of polyductin in the extrahepatic duct is unknown, it may have a role in the development and control of lumenal size. Clinical management of patients with ARPKD should include consideration of potential problems related to extrahepatic bile duct disease.

The hepatic fibrocystic diseases

The hepatic fibrocystic diseases present with variable intrahepatic biliary abnormalities, which range from portal tract enlargement and fibrosis to cystic formations. They may present as autosomal recessive or dominant polycystic kidney diseases, with associated dilatation of the renal collecting system, or as incompletely characterized cystic diseases. Symptoms from the liver disease often result from complications of fibrosis or dilated ducts/cyst (sludge, lithiasis, infection). The treatment is supportive, with careful attention to associated renal disease. Liver transplantation is an option in selected patients.

Clinical and molecular characterization defines a broadened spectrum of autosomal recessive polycystic kidney disease (ARPKD)

The autosomal recessive form of polycystic kidney disease (ARPKD) is generally considered an infantile disorder with the typical presentation of greatly enlarged echogenic kidneys detected in utero or within the neonatal period, often resulting in neonatal demise. However, there is an increasing realization that survivors often thrive into adulthood with complications of the ductal plate malformation, manifesting as congenital hepatic fibrosis and Caroli disease, becoming prominent. Previous natural history studies have concentrated almost exclusively on the infantile presenting group. However, developments in understanding the genetic basis of ARPKD, through identification of the disease gene, PKHD1, have allowed exploration of the etiology in patients with ARPKD-like disease or congenital hepatic fibrosis presenting later in childhood or as adults. In the current study we retrospectively reviewed the clinical records, and where possible performed PKHD1 mutation screening, in patients diagnosed with ARPKD or congenital hepatic fibrosis at the Mayo Clinic, Rochester, MN, from 1961 to 2004. Of a total of 133 cases reviewed, 65 were considered to meet the diagnostic criteria with an average duration of follow-up of 8.6 +/- 6.4 years. Fifty-five cases had ARPKD and 10 had isolated congenital hepatic fibrosis with no or minimal renal involvement. The patients were analyzed as 3 groups categorized by the age at diagnosis; <1 years (n = 22), 1-20 years (n = 23), and >20 years (n = 20). The presenting feature in the neonates was typically associated with renal enlargement, but in the older groups, more often involved manifestations of liver disease, including hepatosplenomegaly, hypersplenism, variceal bleeding, and cholangitis. During follow-up, 22 patients had renal insufficiency and 8 developed end-stage renal disease (ESRD), most from the neonatal group. Liver disease was evident on follow-up in all diagnostic groups but particularly prevalent in those diagnosed later in life. A total of 12 patients died, 6 in the neonatal period, but 86% of patients were alive at 40 years of age. The likelihood of being alive without ESRD differed significantly between the diagnostic groups with 36%, 80%, and 88% survival in the 3 diagnostic groups, respectively, 20 years after the diagnosis. Considerable evidence of intrafamilial phenotype variability was observed. Mutation analysis was performed in 31 families and at least 1 mutation was detected in 25 (81%), with 76% of mutant alleles detected in those cases. Consistent with the relatively mild disease manifestations in this population, the majority of changes were missense (79%) and no case had 2 truncating changes. Mutations were detected in all diagnostic groups, indicating that congenital hepatic fibrosis with minimal kidney involvement can result from PKHD1 mutation. The finding of 6 cases with no detected mutations may represent missed mutations or possible evidence of genetic heterogeneity. The current study indicates a broadened spectrum for the ARPKD phenotype and that later presenting cases with predominant liver disease should be considered part of ARPKD.

New advances in evaluation and management of patients with polycystic liver disease

Adult polycystic liver disease (APLD) is an autosomal dominant condition most commonly associated with polycystic kidney disease. However, over the last decade it has come to be recognized that APLD is a genetically heterogeneous disorder involving derangements on at least three different chromosomes. Mutations involving chromosomes 16 and 4 accounting for autosomal dominant polycystic kidney disease (ADPKD) type 1 and type 2 have been well described as have their gene products, polycystin-1 and polycystin-2. These have since been joined by a more recently recognized mutation in the short arm of chromosome 19 thought to be responsible for a much rarer form of autosomal dominant polycystic liver disease without any associated renal involvement. Despite the sometimes impressive physical and radiologic findings, only a minority of patients will progress to advanced liver disease or develop complications as a result of massive hepatomegaly. In these patients, medical management alone has proved ineffectual. Therefore, in the symptomatic APLD patient, surgical therapy remains the mainstay of therapy and includes cyst aspiration and sclerosis, fenestration with and without hepatic resection and orthotopic liver transplantation. The surgical literature on treatment of APLD, to include outcome measurements and complication rates are summarized. Additionally, we review other potential organ involvement and resultant complications.

Congenital hepatic fibrosis: a very uncommon cause of pancytopenia in children

The disease presentation of autosomal recessive polycystic kidney disease (OMIM #263200, ARPKD) is highly variable and includes polycystic kidneys, pulmonary hypoplasia, and congenital hepatic fibrosis. The authors report an unusual case of ARPKD presenting with hepatosplenomegaly and cytopenia mimicking acute leukemia.