Extrarenal manifestations of ADPKD

Safety and efficacy of tolvaptan in real‑world Japanese patients with autosomal dominant polycystic kidney disease: final results of SLOW‑PKD surveillance

BACKGROUND

Tolvaptan, a vasopressin type 2 receptor antagonist, has been used to treat autosomal dominant polycystic kidney disease in Japan since 2014.

METHODS

This long-term, real-world, post-marketing surveillance (PMS) was conducted in Japan from March 2014 to March 2022. Safety was assessed based on adverse drug reactions (ADRs). For efficacy, changes in the slope of total kidney volume (TKV) and estimated glomerular filtration rate (eGFR) were assessed before and during the administration of tolvaptan.

RESULTS

A total of 1676 patients were enrolled, with mean TKV (n = 1000) of 2149 ± 1339 mL and eGFR (n = 1641) of 44.4 ± 21.7 mL/min/1.73 m2. Frequent ADRs were hepatic function abnormal (9.6%), hyperuricaemia (8.3%), and thirst (8.1%). Most of the increased alanine aminotransferase exceeding 3 times the upper limit of the reference level occurred from 3  to  14 months after the start of treatment, but about 20% was observed after 15 months. There was no increase in ADRs over 36 months, suggesting that no other safety concerns need to be monitored during administration over 3-7 years. The mean slope of the estimated TKV increase before and during tolvaptan treatment was 6.58 and 3.71%/year, respectively (P = 0.0020). The mean slope of eGFR decline was - 3.63 and - 3.26 mL/min/1.73 m2/year, respectively (P = 0.2728).

CONCLUSION

There were no major problems with the safety of tolvaptan treatment, and efficacy in limiting TKV increase in this PMS was comparable to the previous, pivotal randomized control trials. Trial registration ClinicalTrials.gov; NCT02847624.

Generation of heterozygous PKD1 mutant pigs exhibiting early-onset renal cyst formation

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease, manifesting as the progressive development of fluid-filled renal cysts. In approximately half of all patients with ADPKD, end-stage renal disease results in decreased renal function. In this study, we used CRISPR-Cas9 and somatic cell cloning to produce pigs with the unique mutation c.152_153insG (PKD1insG/+). Pathological analysis of founder cloned animals and progeny revealed that PKD1insG/+ pigs developed many pathological conditions similar to those of patients with heterozygous mutations in PKD1. Pathological similarities included the formation of macroscopic renal cysts at the neonatal stage, number and cystogenic dynamics of the renal cysts formed, interstitial fibrosis of the renal tissue, and presence of a premature asymptomatic stage. Our findings demonstrate that PKD1insG/+ pigs recapitulate the characteristic symptoms of ADPKD.

Safety and efficacy of Tolvaptan in real-world patients with autosomal dominant polycystic kidney disease- interim results of SLOW-PKD surveillance

BACKGROUND

Tolvaptan is a vasopressin type 2 receptor antagonist and has been used to treat autosomal dominant polycystic kidney disease (ADPKD) since 2014. There has been limited real-world data on the safety and efficacy of tolvaptan.

METHODS

This post-marketing surveillance was conducted to evaluate the long-term safety and the efficacy of tolvaptan in Japanese patients with ADPKD in real-world clinical settings. The baseline characteristics of 1630 patients treated with tolvaptan are reported. Safety analysis comprises evaluation of adverse drug reactions (ADRs). The efficacy evaluation includes percent change in total kidney volume (TKV) and change in estimated glomerular filtration rate (eGFR) before and after tolvaptan treatment.

RESULTS

Mean age was 49.7 ± 11.2 years and 843 (51.7%) patients were male. Baseline TKV was 2158 ± 1346 mL and eGFR was 44.4 ± 21.7 mL/min/1.73 m². The majority of CKD patients were stage G3b (27.0%) and G4 (30.1%). Frequently reported ADRs were hepatic function abnormal (8.3%), thirst (8.2%), and hyperuricaemia (6.9%). The frequency of ALT elevation (> 30 and > 90 IU/L) was slightly high (32.9 and 8.3%) to previous studies. After tolvaptan treatment, the annual rate of percentage change in TKV reduced from 11.68%/year to 2.73%/year (P < 0.0001). Similar results were also obtained for the effect on change in eGFR from - 3.31 to - 2.28 mL/min/1.73 m²/year after initiation of tolvaptan treatment (P = 0.0403).

CONCLUSION

There were no major problems with safety of tolvaptan treatment and comparable efficacy for TKV and eGFR was observed in relation to the previous pivotal two randomized control trials in this post-marketing surveillance.

Colonic diverticular disease in autosomal dominant polycystic kidney disease: is there really an association? A nationwide analysis

PURPOSE

Colonic diverticulosis, diverticulitis, and diverticular bleeding are reportedly more common in patients with autosomal dominant polycystic kidney disease (ADPKD). Other studies have questioned this association. The objectives of our study are to clarify this association using a larger patient population and to identify risk factors in general to develop diverticular disease.

METHODS

The Nationwide Inpatient Sample weighted discharges from 2003 to 2011 were used to assess for the prevalence of diverticular disease in the population with ADPKD compared with the general population without ADPKD. A multivariable direct logistic regression model was constructed to determine independent predictors of diverticular disease in the general population.

RESULTS

The prevalence of diverticulosis, diverticulitis, and diverticular bleeding were considerably increased in patients with ADPKD compared with the general population without ADPKD. The prevalence of colonic surgery was less in ADPKD patients with diverticulitis. In patients with kidney transplant, the prevalence of diverticulitis was increased in the ADPKD group, but colonic surgery was not significantly different between both groups. The prevalence of diverticular bleeding was slightly elevated in patients with ADPKD, but colonic surgery was significantly increased in patients with ADPKD. NSAID use, hypertension, constipation, and ADPKD had increased odds ratios for diverticular disease during multivariate analysis.

CONCLUSION

There is an increased prevalence of colonic diverticular disease in the population with ADPKD.

Klotho/FGF23 and Wnt Signaling as Important Players in the Comorbidities Associated with Chronic Kidney Disease

Fibroblast Growth Factor 23 (FGF23) and Klotho play an essential role in the regulation of mineral metabolism, and both are altered as a consequence of renal failure. FGF23 increases to augment phosphaturia, which prevents phosphate accumulation at the early stages of chronic kidney disease (CKD). This effect of FGF23 requires the presence of Klotho in the renal tubules. However, Klotho expression is reduced as soon as renal function is starting to fail to generate a state of FGF23 resistance. Changes in these proteins directly affect to other mineral metabolism parameters; they may affect renal function and can produce damage in other organs such as bone, heart, or vessels. Some of the mechanisms responsible for the changes in FGF23 and Klotho levels are related to modifications in the Wnt signaling. This review examines the link between FGF23/Klotho and Wnt/β-catenin in different organs: kidney, heart, and bone. Activation of the canonical Wnt signaling produces changes in FGF23 and Klotho and vice versa; therefore, this pathway emerges as a potential therapeutic target that may help to prevent CKD-associated complications.

A Case Report of a Ventral Hernia Containing a Liver Cyst in a Patient with Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most commonly inherited renal disorder and the fourth most common cause of end-stage renal disease. ADPKD is a systemic disease with multiple extrarenal manifestations, including cystic involvement of other organs, such as the liver and pancreas, and connective tissue abnormalities. The prevalence of hernias is higher in patients with ADPKD. It has been hypothesized that these hernias are the result of abnormal extracellular matrix production and/or increased intra-abdominal pressure from the cyst burden. We present a case of a 56-year-old female with polycystic kidney disease who was admitted for an incarcerated ventral hernia. The patient presented with obstructive symptoms concerning for bowel impingement. The patient underwent operative management, and during the procedure, an incarcerated liver cyst was identified in the hernia sac. This was successfully reduced, and the hernia was repaired with mesh.

Bile Acids as Potential Biomarkers to Assess Liver Impairment in Polycystic Kidney Disease

Polycystic kidney disease is characterized by the progressive development of kidney cysts and declining renal function with frequent development of cysts in other organs including the liver. The polycystic kidney (PCK) rat is a rodent model of polycystic liver disease that has been used to study hepatorenal disease progression and evaluate pharmacotherapeutic interventions. Biomarkers that describe the cyst progression, liver impairment, and/or hepatic cyst burden could provide clinical utility for this disease. In the present study, hepatic cyst volume was measured by magnetic resonance imaging in PCK rats at 12, 16, and 20 weeks. After 20 weeks, Sprague Dawley (n = 4) and PCK (n = 4) rats were sacrificed and 42 bile acids were analyzed in the liver, bile, serum, and urine by liquid chromatography coupled to tandem mass spectrometry. Bile acid profiling revealed significant increases in total bile acids (molar sum of all measured bile acids) in the liver (13-fold), serum (6-fold), and urine (3-fold) in PCK rats, including those speciated bile acids usually associated with hepatotoxicity. Total serum bile acids correlated with markers of liver impairment (liver weight, total liver bile acids, total hepatotoxic liver bile acids, and cyst volume [ r > 0.75; P < 0.05]). Based on these data, serum bile acids may be useful biomarkers of liver impairment in polycystic hepatorenal disease.

Expression of Na+/H+ exchanger regulatory factor 1 in autosomal-dominant polycystic kidney disease

OBJECTIVE

To explore the role of Na(+)/H(+) exchanger regulatory factor 1 (NHERF1) in autosomal-dominant polycystic kidney disease (ADPKD).

METHODS

NHERF1 and β-catenin protein were detected by immunohistochemistry and Western blotting of kidney tissue samples from patients with ADPKD and controls (normal kidney tissue [>5 cm from the foci] collected from patients undergoing unilateral nephrectomy for kidney cancer). NHERF1 and β-catenin protein and mRNA were quantified by Western blot and real-time fluorescent quantitative polymerase chain reaction, respectively, in kidney tissue samples from Han:SPRD (+/+) and (cy/+) rats. The effects of human recombinant NHERF1 on proliferation and cell cycle of ADPKD cyst-lining epithelial cells (WT9-12) were evaluated by MTT assay and flow cytometry, respectively.

RESULTS

Levels of NHERF1 protein and mRNA were significantly lower, and β-catenin levels significantly higher, in patients with ADPKD and Han:SPRD (cy/+) rats, compared with control subjects and (+/+) rats, respectively. Exogenous recombinant NHERF1 significantly inhibited proliferation of WT9-12 cells and increased the proportion of cells in G(0)/G(1) phase.

CONCLUSIONS

ADPKD is associated with a decrease in NHERF1 protein and mRNA levels. Supplementing exogenous NHERF1 inhibited the proliferation of WT9-12 cells.

Multiple cardiovascular manifestations in a patient with autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a systemic disorder associated with various extrarenal complications. The major cardiovascular complications of ADPKD include valvulopathies and vascular ectasia. A 64-year-old man who was diagnosed with ADPKD seven years previously was admitted to our hospital for heart failure. Pelvic computed tomography revealed multiple variable-sized cysts in both kidneys. Transthoracic echocardiography showed enlargement of the left ventricle and left atrium. Severe mitral regurgitation and moderate aortic regurgitation with annuloaortic ectasia were observed. The left main coronary artery was dilated. The patient had various cardiovascular features associated with ADPKD.

Current management of noninfectious hepatic cystic lesions: A review of the literature

Nonparasitic hepatic cysts consist of a heterogeneous group of disorders, which differ in etiology, prevalence, and manifestations. With improving diagnostic techniques, hepatic cysts are becoming more common. Recent advancements in minimally invasive technology created a new Era in the management of hepatic cystic disease. Herein, the most current recommendations for management of noninfectious hepatic cysts are described, thereby discussing differential diagnosis, new therapeutic modalities and outcomes.

Evaluation of hepatic cystic lesions

Hepatic cysts are increasingly found as a mere coincidence on abdominal imaging techniques, such as ultrasonography (USG), computed tomography (CT) and magnetic resonance imaging (MRI). These cysts often present a diagnostic challenge. Therefore, we performed a review of the recent literature and developed an evidence-based diagnostic algorithm to guide clinicians in characterising these lesions. Simple cysts are the most common cystic liver disease, and diagnosis is based on typical USG characteristics. Serodiagnostic tests and microbubble contrast-enhanced ultrasound (CEUS) are invaluable in differentiating complicated cysts, echinococcosis and cystadenoma/cystadenocarcinoma when USG, CT and MRI show ambiguous findings. Therefore, serodiagnostic tests and CEUS reduce the need for invasive procedures. Polycystic liver disease (PLD) is arbitrarily defined as the presence of > 20 liver cysts and can present as two distinct genetic disorders: autosomal dominant polycystic kidney disease (ADPKD) and autosomal dominant polycystic liver disease (PCLD). Although genetic testing for ADPKD and PCLD is possible, it is rarely performed because it does not affect the therapeutic management of PLD. USG screening of the liver and both kidneys combined with extensive family history taking are the cornerstone of diagnostic decision making in PLD. In conclusion, an amalgamation of these recent advances results in a diagnostic algorithm that facilitates evidence-based clinical decision making.

The mechanosensory role of primary cilia in vascular hypertension

Local regulation of vascular tone plays an important role in cardiovascular control of blood pressure. Aside from chemical or hormonal regulations, this local homeostasis is highly regulated by fluid-shear stress. It was previously unclear how vascular endothelial cells were able to sense fluid-shear stress. The cellular functions of mechanosensory cilia within vascular system have emerged recently. In particular, hypertension is insidious and remains a continuous problem that evolves during the course of polycystic kidney disease (PKD). The basic and clinical perspectives on primary cilia are discussed with regard to the pathogenesis of hypertension in PKD.

Jejunal Diverticulitis: A Rare Case of Severe Peritonitis

A 25-year-old African American female with no prior medical/surgical history presented with abdominal pain and fever. A computed tomography scan of the abdomen and pelvis showed jejunal wall thickening with an air-fluid-filled mass in the adjacent mesentery. At laparotomy, a segmental jejunal resection with the abscess cavity followed by primary anastomosis was performed. Pathological evaluation of the specimen revealed a large mesenteric abscess contiguous with a perforated solitary jejunal diverticulum. We provide a discussion of jejunal diverticulitis as an unusual cause of peritonitis.

Extrarenal manifestations of autosomal dominant polycystic kidney disease

Although asymptomatic in most patients, extrarenal manifestations of ADPKD may become more clinically relevant with the increasing life expectancy of affected patients. They mainly encompass cysts in other organs than the kidney (liver: 94%, seminal vesicle: 40%, pancreas: 9%, arachnoid membrane: 8%, and spinal meningeal, 2%) and connective tissue abnormalities (mitral valve prolapse: 25%, intracranial aneurysms: 8%, and abdominal hernia: 10%). Their recognition may spare the patient from other, useless investigations (eg, when an arachnoid cyst is incidentally found) or lead to the implementation of prophylactic or therapeutic measures (eg, screening, sometimes followed by the treatment of an asymptomatic intracranial aneurysm in at-risk patients, or, in the presence of a severe polycystic liver disease, avoidance from estrogens and treatment aimed to slow cyst growth).

Thrombosis in inferior vena cava due to enlarged renal cysts in autosomal dominant polycystic kidney disease

We report a rare case of thrombosis in the inferior vena cava (IVC) due to enlarged cysts in autosomal dominant polycystic kidney disease. A 71-year-old woman visited our hospital with a complaint of rapid left lower extremity swelling. Computed tomography (CT) revealed massive thrombosis from the IVC to the bilateral common iliac vein. The extrinsic mechanical stress of renal cysts to the IVC seemed to have induced thrombosis in the vein that resulted in the cause of severe edema in the left lower extremity. Her renal cysts were percutaneously punctured for the relief of compression and she received injection of 99.5% ethanol for prevention against reaccumulation of cyst fluid after IVC filter had been positioned. The edema of her left lower extremity improved temporarily, however, follow-up CT two months after cyst puncture showed reaccumulation of the fluid. Therefore, excision of the responsible cyst wall by open surgery was carried out.

CD2-associated protein is widely expressed and differentially regulated during embryonic development

CD2-associated protein (CD2AP) is an adapter protein that is involved in various signaling and vesicular trafficking processes and also functions as a linker between plasma membrane proteins and the actin cytoskeleton. The protein is known to have important functions in T cells and glomerular podocytes, but it is also expressed by many other adult-type tissues and cells. Here we analyzed the expression of the protein during early embryonic development and organogenesis of the mouse. The results showed differential tissue-specific regulation of CD2AP in developing and maturing organs. In oocytes and pre-implantation embryos, CD2AP was located diffusely in the cytoplasm, whereas in late blastocysts it was concentrated to the intercellular contacts. During organogenesis, CD2AP was distinctly upregulated upon, e.g., the pretubular aggregation of metanephric mesenchyme cells and the appearance of the osteoblastic rim around cartilages during endochondral ossification. High CD2AP expression was also observed during epithelial-like conversion of some highly specialized secretory cell types such as the odontoblasts, the cells of the choroid plexus and the decidualized cells of the endometrial stroma. In other instances, such as the development of the proximal tubuli of the kidney and the flat alveolar epithelium of the lung, the protein was downregulated upon differentiation and maturation of the cells. Finally, certain cells, e.g., glomerular podocytes, those forming the collecting ducts of the kidney, and the urothelium of the kidney pelvis, expressed CD2AP throughout their differentiation and maturation. Multiple molecules and complex pathways regulate embryogenesis, and scaffolding proteins apparently have pivotal roles in targeting and finetuning, e.g., growth factor- or hormone-induced processes. The cell-type specific spatio-temporal regulation of CD2AP during development suggests that this adapter protein is a key regulatory partner in many signaling pathways and cellular processes governing differentiation and morphogenesis.

Zebrafish mutations affecting cilia motility share similar cystic phenotypes and suggest a mechanism of cyst formation that differs from pkd2 morphants

Zebrafish are an attractive model for studying the earliest cellular defects occurring during renal cyst formation because its kidney (the pronephros) is simple and genes that cause cystic kidney diseases (CKD) in humans, cause pronephric dilations in zebrafish. By comparing phenotypes in three different mutants, locke, swt and kurly, we find that dilations occur prior to 48 hpf in the medial tubules, a location similar to where cysts form in some mammalian diseases. We demonstrate that the first observable phenotypes associated with dilation include cilia motility and luminal remodeling defects. Importantly, we show that some phenotypes common to human CKD, such as an increased number of cells, are secondary consequences of dilation. Despite having differences in cilia motility, locke, swt and kurly share similar cystic phenotypes, suggesting that they function in a common pathway. To begin to understand the molecular mechanisms involved in cyst formation, we have cloned the swt mutation and find that it encodes a novel leucine rich repeat containing protein (LRRC50), which is thought to function in correct dynein assembly in cilia. Finally, we show that knock-down of polycystic kidney disease 2 (pkd2) specifically causes glomerular cysts and does not affect cilia motility, suggesting multiple mechanisms exist for cyst formation.

Cardiovascular characterization of Pkd2+/LacZ mice, an animal model for the autosomal dominant polycystic kidney disease type 2 (ADPKD2)

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in PKD1 or PKD2. Patients with ADPKD have an increased incidence of cardiac valve abnormalities and left ventricular hypertrophy. Systematic analyses of cardiovascular involvement have so far been performed only on genetically unclassified patients or on ADPKD1 patients, but not on genetically defined ADPKD2 patients. Even existing Pkd1 or Pkd2 mouse models were not thoroughly analyzed in this respect. Therefore, the aim of this project was the noninvasive functional cardiovascular characterization of a mouse model for ADPKD2.

METHODS

Pkd2(+/LacZ) mice and wildtype controls were classified into 8 groups with respect to gender, age and genotype. In addition, two subgroups of female mice were analyzed for cardiac function before and during advanced pregnancy. Doppler-echocardiographic as well as histological studies were performed.

RESULTS

Doppler-echocardiography did not reveal significant cardiovascular changes. Heart rate and left ventricular (LV) length, LV mass, LV enddiastolic and LV endsystolic diameters did not differ significantly among the various groups when comparing wildtype and knockout mice. There were no significant differences except for a tendency towards higher maximal early and late flow velocities over the mitral valve in old wildtype mice.

CONCLUSIONS

Non-invasive phenotyping using ultrasound did not reveal significant cardiovascular difference between adult Pkd2(+/LacZ) and WT mice. Due to the lack of an obvious renal phenotype in heterozygous mice, it is likely that in conventional ADPKD knock out mouse models severe cardiac problems appear too late to be identified during the reduced lifespan of the animals.

Renal and extrarenal manifestations of autosomal dominant polycystic kidney disease

The objective of the present study was to determine the frequency of the most common clinical features in patients with autosomal dominant polycystic kidney disease in a sample of the Brazilian population. The medical records of 92 patients with autosomal dominant polycystic kidney disease attended during the period from 1985 to 2003 were reviewed. The following data were recorded: age at diagnosis, gender, associated clinical manifestations, occurrence of stroke, age at loss of renal function (beginning of dialysis), and presence of a family history. The involvement of abdominal viscera was investigated by ultrasonography. Intracranial alterations were prospectively investigated by magnetic resonance angiography in 42 asymptomatic patients, and complemented with digital subtraction arteriography when indicated. Mean age at diagnosis was 35.1 +/- 14.9 years, and mean serum creatinine at referral was 2.4 +/- 2.8 mg/dL. The most frequent clinical manifestations during the disease were arterial hypertension (63.3%), lumbar pain (55.4%), an abdominal mass (47.8%), and urinary infection (35.8%). Loss of renal function occurred in 27 patients (mean age: 45.4 +/- 9.5 years). The liver was the second organ most frequently affected (39.1%). Stroke occurred in 7.6% of the patients. Asymptomatic intracranial aneurysm was detected in 3 patients and arachnoid cysts in 3 other patients. In conclusion, the most common clinical features were lumbar pain, arterial hypertension, abdominal mass, and urinary infection, and the most serious complications were chronic renal failure and stroke. Both intracranial aneurysms and arachnoid cysts occurred in asymptomatic patients at a frequency of 7.14%.

Polycystic liver and kidney diseases

There have been remarkable advances in research on polycystic liver and kidney diseases recently, covering cloning of new genes, refining disease classifications, and advances in understanding more about the molecular pathology of these diseases. Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary disease affecting kidneys. It affects 1/400 to 1/1000 live births and accounts for 5% of the end stage renal disease in the United States and Europe, and is caused by gene defects in the PKD1 or PKD2 genes. Compared to ADPKD, polycystic liver disease (PCLD) is a milder disease and does not lower life expectancy. Both diseases are usually adult-onset diseases. Defects in genes, which code the hepatocystin and SEC63 proteins, have just recently been found to cause PCLD. It now seems that ADPKD is caused by malfunction of the primary cilia, a cell organ sensing fluid movement, and that PCLD is a sequel from defects in protein processing. Autosomal recessive polycystic kidney disease (ARPKD) belongs to a group of congenital hepatorenal fibrocystic syndromes. All ARPKD patients have a gene defect in a gene called PKHD1, the protein product of which localizes to primary cilia. We summarize the present clinical and molecular knowledge of these diseases in this review.

Clinical Laboratory Evaluation of Male Subfertility

Male subfertility is a common problem with a complex etiology, requiring a complete andrological work-up for proper diagnosis. The male reproductive tract is controlled by a well-balanced hormonal system, in which hypothalamic (GnRH), pituitary (LH, FSH) and testicular hormones (androgens, inhibin B) participate. Any disturbance of this hormonal system may therefore lead to testicular dysfunction and interfere with the spermatogenesis process. In addition, also other components along the ductal system, such as epididymis, prostate and seminal vesicles, that improve sperm fertility by contributing their secretions to the semen, might function inadequately and thus fail to enhance the fertilizing capacity of the sperm cells. External factors (heat, chemicals, life style) and anatomical abnormalities (varicocele) were shown to have a negative influence on male fertility. In a number of patients genetic defects can be identified as the cause of their infertility. Laboratory tests are available to assess hormone concentrations, semen composition, accessory gland function and sperm cell function. Conventional semen analysis includes the determination of sperm concentration, semen volume, sperm motility (qualitative and quantitative), sperm morphology, sperm cell vitality, pH, leucocytes and antibodies. The usefulness of the determination of these parameters as predictor of fertility appears to be rather limited, however. Therefore, alternative tests, some based on more functional aspects (sperm penetration, capacitation, acrosome reaction), have been developed. Furthermore, there is an increasing attention for the assessment of DNA integrity, for instance by the flowcytometer-based Sperm Chromation Structure Assay (SCSA), as an additional or alternative parameter of sperm quality. It is likely and desirable that further assays with better predictive value are being developed in the near future.

Lowering of Pkd1 expression is sufficient to cause polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a major cause of renal failure and is characterized by the formation of many fluid-filled cysts in the kidneys. It is a systemic disorder that is caused by mutations in PKD1 or PKD2. Homozygous inactivation of these genes at the cellular level, by a 'two-hit' mechanism, has been implicated in cyst formation but does not seem to be the sole mechanism for cystogenesis. We have generated a novel mouse model with a hypomorphic Pkd1 allele, Pkd1(nl), harbouring an intronic neomycin-selectable marker. This selection cassette causes aberrant splicing of intron 1, yielding only 13-20% normally spliced Pkd1 transcripts in the majority of homozygous Pkd1(nl) mice. Homozygous Pkd1(nl) mice are viable, showing bilaterally enlarged polycystic kidneys. This is in contrast to homozygous knock-out mice, which are embryonic lethal, and heterozygous knock-out mice that show only a very mild cystic phenotype. In addition, homozygous Pkd1(nl) mice showed dilatations of pancreatic and liver bile ducts, and the mice had cardiovascular abnormalities, pathogenic features similar to the human ADPKD phenotype. Removal of the neomycin selection-cassette restored the phenotype of wild-type mice. These results show that a reduced dosage of Pkd1 is sufficient to initiate cystogenesis and vascular defects and indicate that low Pkd1 gene expression levels can overcome the embryonic lethality seen in Pkd1 knock-out mice. We propose that in patients reduced PKD1 expression of the normal allele below a critical level, due to genetic, environmental or stochastic factors, may lead to cyst formation in the kidneys and other clinical features of ADPKD.

Clinical and histological presentation of 3 siblings with mutations in the NPHP4 gene

Nephronophthisis (NPH) is an autosomal recessive kidney disease characterized by tubular basement membrane disruption, interstitial infiltration, and tubular cysts. NPH leads to end-stage renal failure in the first 2 decades of life. Four genes responsible for different types of NPH have been identified: NPHP1, NPHP2, NPHP3, and NPHP4. The NPHP1 gene encodes nephrocystin; NPHP2, inversin; NPHP3, nephrocystin-3; and NPHP4, nephrocystin-4. We report 3 siblings from a consanguineous family with NPH who were previously described as carrying a homozygous mutation in the NPHP4 gene. Renal imaging showed cysts in the children. The histological picture of NPHP4 showed the same characteristic features as those known for NPHP1 and NPHP3. Progression to end-stage renal disease occurred between the ages of 17 and 22 years. None of the renal transplants showed recurrence of the disease. Retinitis pigmentosa was absent in all affected family members.

Progression of kidney disease varies between families with defects in the polycystic kidney disease type 1 gene in eastern Finland

OBJECTIVE

To characterize, for the first time, the phenotype and clinical course of autosomal dominant polycystic kidney disease (ADPKD) in Finnish patients.

MATERIAL AND METHODS

All patients underwent an abdominal sonographic examination and most of those with ADPKD underwent magnetic resonance angiography of the head. Haplotype analysis was used to classify 20 ADPKD families into those with defects in either the polycystic kidney disease type 1 (PKD1) or polycystic kidney disease type 2 (PKD2) genes. Evaluation of the rate of progression of kidney disease in patients with ADPKD was based on creatinine values.

RESULTS

Haplotype analysis showed that 16 families had defects in the PKD1 gene and one had defects in the PKD2 gene. Three families were excluded because of uninformative haplotypes. The final study population consisted of 79 unaffected family members, 109 patients with defects in the PKD1 gene and 10 with defects in the PKD2 gene. Higher prevalences of hepatic cysts (3% in healthy relatives, 60% in PKD1 patients and 90% in PKD2 patients; p < 0.001), subarachnoid hemorrhage or cerebral aneurysms (1%, 12% and 0%, respectively; p < 0.001), proteinuria (1%, 23% and 0%, respectively; p < 0.001) and hematuria (5%, 30% and 0%, respectively; p < 0.001) were found in PKD1 patients compared to the healthy relatives. PKD1 patients had a faster progression of kidney disease than PKD2 patients (p < 0.001). The progression of kidney disease varied substantially among the PKD1 families.

CONCLUSION

The relative proportions of PKD1 and PKD2 patients and the phenotype of ADPKD were similar in our Finnish patients compared to previous studies in other populations. However, the progression of kidney disease differed substantially among PKD1 families, indicating a heterogeneic genetic background of PKD1 in Finnish patients.

Drosophila Pkd2 Is Haploid-insufficient for Mediating Optimal Smooth Muscle Contractility

Humans heterozygous for PKD1 or PKD2 develop autosomal dominant polycystic kidney disease, a common genetic disorder characterized by renal cyst formation and extrarenal complications such as hypertension and vascular aneurysms. Cyst formation requires the somatic inactivation of the wild type allele. However, it is unknown whether this recessive mechanism applies to life-threatening vascular aneurysms, which could involve weakening of the endothelial lining or surrounding vascular smooth muscle cells (SMCs). Drosophila Pkd2 at 33E3 (Pkd2) encodes a PKD2 family of Ca(2+)-activated Ca(2+)-permeable cation channels. We show here that loss-of-function Pkd2 mutations severely reduced the contractility of the visceral SMCs, which was restored by expressing wild type Pkd2 cDNA via a muscle-specific Gal4 driver. The effect of Pkd2 mutations alone on the skeletal muscle was minimal but was exacerbated by ryanodine-induced perturbation of intracellular Ca(2+) stores. Consistent with this, Pkd2 interacted strongly with a ryanodine receptor mutation, causing a synergistic reduction of larval body wall contraction rate that is normally regulated through Ca(2+) oscillation during excitation-contraction coupling in the skeletal muscle. These results suggest that PKD2 cooperates with the ryanodine receptor to promote optimal muscle contractility through intracellular Ca(2+) homeostasis. Further genetic analysis indicated that Pkd2 is strongly haploinsufficient for normal SMC contractility. Since Ca(2+) homeostasis is a conserved mechanism for optimal muscle performance, our results raise the possibility that inactivation of just one PKD2 copy is sufficient to compromise vascular SMC contractility and function in PKD2 heterozygous patients, thus explaining their increased susceptibility to hypertension and vascular aneurysms.

Murine models of polycystic kidney disease: molecular and therapeutic insights

Numerous murine (mouse and rat) models of polycystic kidney disease (PKD) have been described in which the mutant phenotype results from a spontaneous mutation or engineering via chemical mutagenesis, transgenic technologies, or gene-specific targeting in mouse orthologs of human PKD genes. These murine phenotypes closely resemble human PKD, with common abnormalities observed in tubular epithelia, the interstitial compartment, and the extracellular matrix of cystic kidneys. In both human and murine PKD, genetic background appears to modulate the renal cystic phenotype. In murine models, these putative modifying effects have been dissected into discrete factors called quantitative trait loci and genetically mapped. Several lines of experimental evidence support the hypothesis that PKD genes and their modifiers may define pathways involved in cystogenesis and PKD progression. Among the various pathway abnormalities described in murine PKD, recent provocative data indicate that structural and/or functional defects in the primary apical cilia of tubular epithelia may play a key role in PKD pathogenesis. This review describes the most widely studied murine models; highlights the data regarding specific gene defects and genetic modifiers; summarizes the data from these models that have advanced our understanding of PKD pathogenesis; and examines the effect of various therapeutic interventions in murine PKD.

Screening for intracranial aneurysms in autosomal dominant polycystic kidney disease. Review Article

Screening patients with autosomal dominant polycystic kidney disease (ADPKD) for asymptomatic intracranial aneurysms has been proposed as a method of reducing the morbidity and mortality associated with aneurysm rupture. However, recent studies have shown lower spontaneous rupture rates of small aneurysms and higher risks of significant complications with interventions than previously reported. Risk-benefit analysis has not demonstrated any benefit of screening ADPKD patients without a history of subarachnoid haemorrhage (SAH) for intracranial aneurysms, and has suggested that screening might cause harm.

The polycystic kidney disease proteins, polycystin-1, polycystin-2, polaris, and cystin, are co-localized in renal cilia

Recent evidence has suggested an association between structural and/or functional defects in the primary apical cilium of vertebrate epithelia and polycystic kidney disease (PKD). In Caenorhabditis elegans, the protein orthologues of the PKD-related proteins, polycystin-1 (LOV-1), polycystin-2 (PKD2), and polaris (OSM-5), co-localize in the cilia of male-specific sensory neurons, and defects in these proteins cause abnormalities of cilia structure and/or function. This study sought to determine whether the mammalian polycystins are expressed in primary cilia of renal epithelia and whether these proteins co-localize with polaris and cystin, the newly described, cilia-associated protein that is disrupted in the cpk mouse. To begin to address this issue, the expression of the protein products encoded by the PKD1, PKD2, Tg737, and cpk genes were examined in mouse cortical collecting duct (mCCD) cells using an immunofluorescence-based approach with a series of previously well-characterized antibodies. The mCCD cells were grown on cell culture inserts to optimize cell polarization and cilia formation. The data demonstrate co-localization in cilia of polycystin-1 and polycystin-2, which are the principal proteins involved in autosomal dominant polycystic kidney disease, with polaris and cystin, which are proteins that are disrupted in the Tg737(orpk)and cpk mouse models of autosomal recessive polycystic kidney disease, respectively. These data add to a growing body of evidence that suggests that primary cilium plays a key role in normal physiologic functions of renal epithelia and that defects in ciliary function contribute to the pathogenesis of PKD.

Mitral valve prolapse and mitral regurgitation are common in patients with polycystic kidney disease type 1

Patients with autosomal dominant polycystic kidney disease (ADPKD) have an increased occurrence of cardiac valve abnormalities. However, the prevalence of cardiac abnormalities in patients with a uniform genotype of ADPKD has not been previously reported. We performed M-mode and color Doppler echocardiography on 109 patients from 16 families with polycystic kidney disease type 1 (PKD1). Findings were compared with those of 73 unaffected family members and 73 healthy controls. Mitral valve prolapse was found in 26% of patients with PKD1, 14% of unaffected relatives, and 10% of control subjects. The prevalence of hemodynamically significant mitral regurgitation (grade 2 or 3) was 13%, 4%, and 3%, respectively. Prevalences of grade 2 or 3 aortic regurgitation (8%, 4%, and 3%, respectively) and tricuspid regurgitation (4%, 6%, and 7%, respectively) were not significantly different among the three groups. Left ventricular hypertrophy (LVH) was found in 19% of subjects with PKD1, 6% of unaffected relatives, and 4% of control subjects. Systolic blood pressure and severity of renal insufficiency were related to mitral regurgitation and LVH in subjects with PKD1. The prevalence of cardiac valve abnormalities did not differ between unaffected relatives and control subjects. Mitral valve prolapse is a characteristic finding in patients with PKD1. Conversely, mitral regurgitation and LVH are likely to be secondary to elevated blood pressure in these patients.

[Contribution of genetics to knowledge and management of hereditary kidney diseases progressing to renal failure]

Genes of most of the hereditary renal diseases progressing to renal insufficiency are now identified. In the first part of this paper we describe their multi-faceted genetics. Genetic heterogeneity has been demonstrated in many of these diseases, such as Alport's syndrome and nephronophtisis. In some of them an allelic heterogeneity is present as in the X-linked form of Alport's syndrome (more than 300 different mutations have been described along the COL4A5 gene). Besides these classical mendelian diseases, mendelian subentities have been isolated within common diseases such as cortico-resistant nephrosis. Many diseases also demonstrate a variability of their phenotype resulting from allelic and/or genetic heterogeneity, or from modifier genes. In the second part of the paper we discuss the consequences of this explosion of knowledge with respect to epidemiology, genetic diagnosis, prenatal diagnosis and treatment.

Molecular genetics and pathogenesis of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a common and systemic disease characterized by formation of focal cysts. Of the three potential causes of cysts, downstream obstruction, compositional changes in extracellular matrix, and proliferation of partially dedifferentiated cells, evidence strongly supports the latter as the primary abnormality. In the vast majority of cases, the disease is caused by mutations in PKD1 or PKD2, and appears to be recessive at the cellular level. Somatic second hits in the normal allele of cells containing the germ line mutation initiate or accelerate formation of cysts. The intrinsically high frequency of somatic second hits in epithelia appears to be sufficient to explain the frequent occurrence of somatic second hits in the disease-causing genes. PKD1 and PKD2 encode a putative adhesive/ion channel regulatory protein and an ion channel, respectively. The two proteins interact directly in vitro. Their cellular and subcellular localization suggest that they may also function independently in a common signaling pathway that may involve the membrane skeleton and that links cell-cell and cell-matrix adhesion to the development of cell polarity.

De novo renal artery aneurysm presenting 6 years after transplantation: a complication of recurrent arterial stenosis?

Pseudoaneurysms represent a well-recognized vascular complication of renal transplantation, but true aneurysms involving the donor renal artery have not been described. We report a patient who had a de novo aneurysm of the donor renal artery 6 years after receiving a cadaveric renal transplant from a child. The aneurysm was repaired successfully, and allograft function was preserved. Histologic evidence confirmed that the lesion was a true aneurysm. Given the potential for graft loss associated with complications of unrepaired aneurysms, we believe that the presence of a true aneurysm in a donor renal artery represents an indication for repair.

Autosomal dominant polycystic kidney disease-type 2. Ultrasound, genetic and clinical correlations

BACKGROUND

Ultrasound, genetic and clinical correlations are available for ADPKD-1, but lacking for ADPKD-2. The present study was carried out to address: (i) the age-related diagnostic usefulness of ultrasound compared with genetic linkage studies; (ii) the age-related incidence and prevalence of relevant symptoms and complications; and (iii) the age and causes of death in patients with ADPKD-2.

METHODS

Two hundred and eleven alive subjects, from three ADPKD-2 families at 50% risk, were evaluated by physical examination, consultation of hospital records, biochemical parameters, ultrasound and with genetic linkage and DNA mutation analyses. Nineteen deceased and affected family members were also included in the study.

RESULTS

Of the 211 alive members, DNA linkage studies and direct mutation analyses showed that 106 were affected and 105 were not. Ultrasound indicated 94 affected, 108 not affected and nine equivocal results in nine children under the age of 15. For all ages, the false-positive diagnostic rate for ultrasound was 7.5% and the false-negative rate was 12.9%. The difference between ultrasound and DNA findings was most evident in children aged 5-14 years where the ultrasound was correct in only 50% and wrong or inconclusive in the remaining 50%. The mean age of the 106 alive, ADPKD-2 genetically affected patients was 37.9 years (range: 6-66 years). Among them, 23.5% had experienced episodes of renal pain, 22.6% were treated for hypertension, 22.6% had experienced at least one urinary tract infection, 19.8% had nephrolithiasis, 11.3% had at least one episode of haematuria, 9.4% had asymptomatic liver cysts, 7.5% had developed chronic renal failure and 0.9% had reached end-stage renal failure. Of the 19 deceased members, nine died before reaching end-stage renal failure at a mean age of 58.7 years (range: 40-68 years), mainly due to vascular complications, while the remaining 10 died on haemodialysis at a mean age of 71.4 years (range: 66-82 years).

CONCLUSIONS

DNA analysis is the gold standard for the diagnosis of ADPKD-2, especially in young people. Ultrasound diagnosis is highly dependent on age. Under the age of 14, ultrasound is not recommended as a routine diagnostic procedure, but ultrasound becomes 100% reliable in excluding ADPKD-2 in family members at 50% risk, over the age of 30. ADPKD-2 represents a mild variant of polycystic kidney disease with a low prevalence of symptoms and a late onset of end-stage renal failure.

Cellular localization and tissue distribution of polycystin-1

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the formation of fluid-filled cysts in both kidneys, in addition to a variety of extra-renal manifestations. The PKD1 gene product, polycystin-1, encodes a novel protein with a putative role in cell-cell/cell-matrix interactions. The present study we focused on the (sub)cellular localization of polycystin-1 in cultured cells, and on its tissue distribution in various organs. In Madin Darby canine kidney (MDCK) cells, several polyclonal antibodies showed intense staining at the sites of interaction between adjacent cells, which remained after Triton extraction. Weak cytoplasmic staining was observed. No signal was detected at the free borders of cell aggregates, supporting a role for polycystin-1 in cell-cell interactions. At the tissue level, polycystin-1 expression was observed in specific cell types in tissues with known manifestations of the disease, but also in tissues of organs which have not been reported to be affected in ADPKD. Expression was frequently seen in epithelia, but also in endocrine cells (pancreatic islets, parathyroid-producing cells, clusters in the adenohypophysis, clusters in the adrenal gland, and Leydig cells in the testis). In addition, expression was observed in myocardium and more weakly in myocytes of cardiac valves, of the cerebral arteries, and of skeletal muscles.