Type of PKD1 mutation influences renal outcome in ADPKD

A Low-Cost Sequencing Platform for Rapid Genotyping in ADPKD and its Impact on Clinical Care

Introduction

Autosomal-dominant polycystic kidney disease (ADPKD) is the most common genetic cause of kidney failure. Because of the heterogeneity in disease progression in ADPKD, parameters predicting future outcome are important. The disease-causing genetic variant is one of these parameters.

Methods

A multiplex polymerase chain reaction (PCR)-based panel (MPP) was established for analysis of 6 polycystic kidney disease (PKD) genes (PKD1, PKD2, HNF1B, GANAB, DZIP1L, and PKHD1) in 441 patients with ADPKD. Selected patients were additionally sequenced using Sanger sequencing or a custom enrichment-based gene panel. Results were combined with clinical characteristics to assess the impact of genetic data on clinical decision-making. Variants of unclear significance (VUS) were considered diagnostic based on a classic ADPKD clinical phenotype.

Results

Using the MPP, disease-causing variants were detected in 65.3% of patients. Sanger sequencing and the custom gene panel in 32 patients who were MPP-negative revealed 20 variants missed by MPP, (estimated overall false negative rate 24.6%, false-positive rate 9.4%). Combining clinical and genetic data revealed that knowledge of the genotype could have impacted the treatment decision in 8.2% of patients with a molecular genetic diagnosis. Sequencing only the PKD1 pseudogene homologous region in MPP-negative patients resulted in an acceptable false-negative rate of 3.28%.

Conclusion

The MPP yields rapid genotype information at lower costs and allows for simple extension of the panel for new disease genes. Additional sequencing of the PKD1 pseudogene homologous region is required in negative cases. Access to genotype information even in settings with limited resources is important to allow for optimal patient counseling in ADPKD.

Cystic Diseases of the Kidneys: From Bench to Bedside

Exploration into the causes of hereditary renal cystic diseases demonstrates a deep-rooted connection with the proteomic components of the cellular organelle cilia. Cilia are essential to the signaling cascades, and their dysfunction has been tied to a range of renal cystic diseases initiating with studies on the oak ridge polycystic kidney (ORPK) mouse model. Here, we delve into renal cystic pathologies that have been tied with ciliary proteosome and highlight the genetics associated with each. The pathologies are grouped based on the mode of inheritance, where inherited causes that result in cystic kidney disease phenotypes include autosomal dominant and autosomal recessive polycystic kidney disease, nephronophthisis (Bardet-Biedl syndrome and Joubert Syndrome), and autosomal dominant tubulointerstitial kidney disease. Alternatively, phakomatoses-, also known as neurocutaneous syndromes, associated cystic kidney diseases include tuberous sclerosis (TS) and Von Hippel-Lindau (VHL) disease. Additionally, we group the pathologies by the mode of inheritance to discuss variations in recommendations for genetic testing for biological relatives of a diagnosed individual.

The genetic landscape of autosomal dominant polycystic kidney disease in Kuwait

Background

Autosomal dominant polycystic kidney disease (ADPKD) is the most common renal monogenic disease, characterized by bilateral accumulation of renal fluid-filled cysts leading to progressive renal volume enlargement and gradual impairment of kidney function, often resulting in end-stage renal disease. Kuwait could provide valuable genetic insights about ADPKD, including intrafamilial phenotypic variation, given its large household size. This study aims to provide a comprehensive description of the pathogenic variants linked to ADPKD in the Kuwaiti population using multiple genetic analysis modalities and to describe and analyse the ADPKD phenotypic spectrum in terms of kidney function, kidney volume and renal survival.

Methods

A total of 126 ADPKD patients from 11 multiplex families and 25 singletons were recruited into the study. A combination of targeted next-generation sequencing (tNGS), long-range polymerase chain reaction, Sanger sequencing and multiplex ligation-dependent probe amplification were utilized for genetic diagnosis. Clinical evaluation was conducted through renal function testing and ultrasonographic kidney volume analysis.

Results

We identified 29 ADPKD pathogenic mutations from 36 families achieving an overall molecular genetic diagnostic rate of 112/126 (88.9%), including 29/36 (80.6%) in families. A total of 28/36 (77.8%) families had pathogenic mutations in PKD1, of which 17/28 (60.7%) were truncating, and 1/36 (2.8%) had a pathogenic variant in the IFT140 gene. A total of 20/29 (69%) of the identified ADPKD mutations were novel and described for the first time, including a TSC2-PKD1 contiguous syndrome. Clinical analysis indicated that genetically unresolved ADPKD cases had no apparent association between kidney volume and age.

Conclusion

We describe for the first time the genetic landscape of ADPKD in Kuwait. The observed genetic heterogeneity underlining ADPKD along with the wide phenotypic spectrum reveal the level of complexity in disease pathophysiology. ADPKD genetic testing could improve the care of patients through improved disease prognostication, guided treatment and genetic counselling. However, to fulfil the potential of genetic testing, it is important to overcome the hurdle of genetically unresolved ADPKD cases.

The Clinical and Mutational Spectrum of 69 Turkish Children with Autosomal Recessive or Autosomal Dominant Polycystic Kidney Disease: A Multicenter Retrospective Cohort Study

INTRODUCTION

Autosomal recessive polycystic kidney disease (ARPKD) is associated with pathogenic variants in the PKHD1 gene. Autosomal dominant polycystic kidney disease (ADPKD) is mainly associated with pathogenic variants in PKD1 or PKD2. The present study aimed to identify the clinical and genetic features of Turkish pediatric ARPKD and ADPKD patients.

METHODS

This multicenter, retrospective cohort study included 21 genetically confirmed ARPKD and 48 genetically confirmed ADPKD patients from 7 pediatric nephrology centers. Demographic features, clinical, and laboratory findings at presentation and during 12-month intervals were recorded.

RESULTS

The median age of the ARPKD patients at diagnosis was lower than the median age of ADPKD patients (10.5 months [range: 0-15 years] vs. 5.2 years [range: 0.1-16 years], respectively, [p = 0.014]). At the time of diagnosis, the median eGFR in the ARPKD patients was lower compared to that of ADPKD patients (81.6 [IQR: 28.7-110.5] mL/min/1.73 m2 and 118 [IQR: 91.2-139.8] mL/min/1.73 m2, respectively, [p = 0.0001]). In total, 11 (52.4%) ARPKD patients had malnutrition; 7 (33.3%) patients had growth retardation at presentation; and 4 (19%) patients had both malnutrition and growth retardation. At diagnosis, 8 (16.7%) of the ADPKD patients had malnutrition, and 5 (10.4%) patients had growth retardation. The malnutrition, growth retardation, and hypertension rates at diagnosis were higher in the ARPKD patients than the ADPKD patients (p = 0.002, p = 0.02, and p = 0.0001, respectively). ARPKD patients with malnutrition and growth retardation had worse renal survival compared to the patients without (p = 0.03 and p = 0.01). Similarly, ADPKD patients with malnutrition had worse renal survival compared to the patients without (p = 0.002). ARPKD patients with truncating variants had poorer 3- and 6-year renal outcome than those carrying non-truncating variants (p = 0.017).

CONCLUSION

Based on renal survival analysis, type of genetic variant, growth retardation, and/or malnutrition at presentation were observed to be factors associated with progression to chronic kidney disease (CKD). Differentiation of ARPKD and ADPKD, and identification of the predictors of the development of CKD are vital for optimal management of patients with ARPKD or ADPKD.

Preclinical evaluation of tolvaptan and salsalate combination therapy in a Pkd1-mouse model

Background: Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic disorder and an important cause of end stage renal disease (ESRD). Tolvaptan (a V2R antagonist) is the first disease modifier drug for treatment of ADPKD, but also causes severe polyuria. AMPK activators have been shown to attenuate cystic kidney disease. Methods: In this study, we tested the efficacy of the combined administration of salsalate (a direct AMPK activator) and tolvaptan using clinically relevant doses in an adult-onset conditional Pkd1 knock-out (KO) mouse model. Results: Compared to untreated Pkd1 mutant mice, the therapeutic effects of salsalate were similar to that of tolvaptan. The combined treatment tended to be more effective than individual drugs used alone, and was associated with improved kidney survival (p < 0.0001) and reduced kidney weight to body weight ratio (p < 0.0001), cystic index (p < 0.001) and blood urea levels (p < 0.001) compared to untreated animals, although the difference between combination and single treatments was not statistically significant. Gene expression profiling and protein expression and phosphorylation analyses support the mild beneficial effects of co-treatment, and showed that tolvaptan and salsalate cooperatively attenuated kidney injury, cell proliferation, cell cycle progression, inflammation and fibrosis, and improving mitochondrial health, and cellular antioxidant response. Conclusion: These data suggest that salsalate-tolvaptan combination, if confirmed in clinical testing, might represent a promising therapeutic strategy in the treatment of ADPKD.

Review of the Use of Animal Models of Human Polycystic Kidney Disease for the Evaluation of Experimental Therapeutic Modalities

Autosomal dominant polycystic kidney disease, autosomal recessive polycystic kidney disease, and nephronophthisis are hereditary disorders with the occurrence of numerous cysts in both kidneys, often causing chronic and end-stage renal failure. Animal models have played an important role in recent advances in research not only on disease onset and progressive mechanisms but also on the development of therapeutic interventions. For a long time, spontaneous animal models have been used as the primary focus for human diseases; however, after the identification of the nucleotide sequence of the responsible genes, PKD1, PKD2, PKHD1, and NPHPs, various types of genetically modified models were developed by genetic and reproductive engineering techniques and played the leading role in the research field. In this review, we present murine models of hereditary renal cystic diseases, discussing their potential benefits in the development of therapeutic strategies.

XBP1 Activation Reduces Severity of Polycystic Kidney Disease due to a Nontruncating Polycystin-1 Mutation in Mice

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in Pkd1 and Pkd2. They encode the polytopic integral membrane proteins polycystin-1 (PC1) and polycystin-2 (PC2), respectively, which are expressed on primary cilia. Formation of kidney cysts in ADPKD starts when a somatic second hit mechanism inactivates the wild-type Pkd allele. Approximately one quarter of families with ADPDK due to Pkd1 have germline nonsynonymous amino acid substitution (missense) mutations. A subset of these mutations is hypomorphic, retaining some residual PC1 function. Previous studies have shown that the highly conserved Ire1 α -XBP1 pathway of the unfolded protein response can modulate levels of functional PC1 in the presence of mutations in genes required for post-translational maturation of integral membrane proteins. We examine how activity of the endoplasmic reticulum chaperone-inducing transcription factor XBP1 affects ADPKD in a murine model with missense Pkd1 .

METHODS

We engineered a Pkd1 REJ domain missense murine model, Pkd1 R2216W , on the basis of the orthologous human hypomorphic allele Pkd1 R2220W , and examined the effects of transgenic activation of XBP1 on ADPKD progression.

RESULTS

Expression of active XBP1 in cultured cells bearing PC1 R2216W mutations increased levels and ciliary trafficking of PC1 R2216W . Mice homozygous for Pkd1 R2216W or heterozygous for Pkd1 R2216Win trans with a conditional Pkd1 fl allele exhibit severe ADPKD following inactivation in neonates or adults. Transgenic expression of spliced XBP1 in tubule segments destined to form cysts reduced cell proliferation and improved Pkd progression, according to structural and functional parameters.

CONCLUSIONS

Modulating ER chaperone function through XBP1 activity improved Pkd in a murine model of PC1, suggesting therapeutic targeting of hypomorphic mutations.

The natural history of autosomal dominant polycystic kidney disease. A strategy for grouping families and mutations

Autosomal dominant polycystic kidney disease (ADPKD) is a main cause of end-stage renal disease. Today, knowledge of its genetic basis has made it possible to develop strategies that prevent the transmission of the disease.

OBJECTIVES

The objective of the study was to analyze the natural history of ADPKD in the province of Córdoba and to design a database that allows grouping families with different mutations.

PATIENTS AND METHODS

All patients (n = 678) diagnosed with ADPKD followed by the Córdoba nephrology service are included. Various clinical variables (age and sex), genetic variables (mutation in PKD1, PKD2) and the need for renal replacement therapy (RRT) were retrospectively analyzed.

RESULTS

The prevalence was 61 cases per 100,000 inhabitants. Median renal survival was significantly worse in PKD1 (57.5 years) than in PKD2 (70 years) (log-rank p = 0.000). We have genetically identified 43.8% of the population, detecting PKD1 mutations in 61.2% and PKD2 mutations in 37.4% of cases, respectively. The most frequent mutation, in PKD2 (c.2159del), appeared in 68 patients belonging to 10 different families. The one with the worst renal prognosis was a truncating mutation in PKD1 (c.9893 G > A). These patients required RRT at a median age of 38.7 years.

CONCLUSIONS

Renal survival of ADPKD in the province of Córdoba is similar to that described in the literature. We detected PKD2 mutations in 37.4% of cases. This strategy allows us to know the genetic basis of a large proportion of our population while saving resources. This is essential to be able to offer primary prevention of ADPKD through preimplantation genetic diagnosis.

Health Disparities in Kidney Failure Among Patients With Autosomal Dominant Polycystic Kidney Disease: A Cross-Sectional Study

Rationale & Objective

Understanding potential differences in patterns of kidney failure among patients with autosomal dominant polycystic kidney disease (ADPKD) may provide insights into improving disease management. We sought to characterize patients with ADPKD and kidney failure across different race/ethnicities.

Study Design

Cross-sectional study.

Setting & Participants

Kaiser Permanente Southern California members diagnosed with ADPKD between January1, 2002, and December 31, 2018.

Exposure

ADPKD.

Outcome

Kidney failure, dialysis, or receipt of kidney transplant.

Analytical Approach

Differences in characteristics by race/ethnicity were assessed using analysis of variance F test and χ² test. To compare the range and distribution of the average age at onset of kidney failure by race/ethnicity and sex, we used box plots and confidence intervals. Multivariable logistic regression was used to estimate OR for kidney transplant.

Results

Among 3,677 ADPKD patients, 1,027 (27.3%) had kidney failure. The kidney failure cohort was comprised of Black (n=138; 30.7%), White (n=496; 30.6%), Hispanic (n=306; 24.7%), and Asian (n=87; 23.6%) patients. Hispanic patients had the youngest mean age of kidney failure onset (50 years) compared to Black (56 years) and White (57 years) patients. Black (44.2%; OR, 0.72) and Hispanic (49.7%; OR, 0.65) patients had lower rates of kidney transplantation compared to White (53.8%) patients. Preemptive kidney transplantations occurred in 15.0% of patients.

Limitations

Retrospective study design and possible misclassification of ADPKD cases. Kidney function calculations were based on equations incorporating race, potentially overestimating kidney function in African Americans. The study was conducted within a single, integrated health care system in 1 geographic region and may not be generalizable to all ADPKD patients.

Conclusions

Among a large diverse ADPKD population, we observed racial/ethnic differences in rates of kidney failure, age of kidney failure onset, and rates of kidney transplantation. Our real-world ADPKD cohort provides insight into racial/ethnic variation in clinical features of disease and potential disparities in care, which may affect ADPKD outcomes.

Identification of Serum Metabolites for Predicting Chronic Kidney Disease Progression according to Chronic Kidney Disease Cause

Early detection and proper management of chronic kidney disease (CKD) can delay progression to end-stage kidney disease. We applied metabolomics to discover novel biomarkers to predict the risk of deterioration in patients with different causes of CKD. We enrolled non-dialytic diabetic nephropathy (DMN, n = 124), hypertensive nephropathy (HTN, n = 118), and polycystic kidney disease (PKD, n = 124) patients from the KNOW-CKD cohort. Within each disease subgroup, subjects were categorized as progressors (P) or non-progressors (NP) based on the median eGFR slope. P and NP pairs were randomly selected after matching for age, sex, and baseline eGFR. Targeted metabolomics was performed to quantify 188 metabolites in the baseline serum samples. We selected ten progression-related biomarkers for DMN and nine biomarkers each for HTN and PKD. Clinical parameters showed good ability to predict DMN (AUC 0.734); however, this tendency was not evident for HTN (AUC 0.659) or PKD (AUC 0.560). Models constructed with selected metabolites and clinical parameters had better ability to predict CKD progression than clinical parameters only. When selected metabolites were used in combination with clinical indicators, random forest prediction models for CKD progression were constructed with AUCs of 0.826, 0.872, and 0.834 for DMN, HTN, and PKD, respectively. Select novel metabolites identified in this study can help identify high-risk CKD patients who may benefit from more aggressive medical treatment.

Identification and Characterization of Novel Mutations in Chronic Kidney Disease (CKD) and Autosomal Dominant Polycystic Kidney Disease (ADPKD) in Saudi Subjects by Whole-Exome Sequencing

Background: Autosomal dominant polycystic kidney disease (ADPKD) is a condition usually caused by a single gene mutation and manifested by both renal and extrarenal features, eventually leading to end-stage renal disease (ESRD) by the median age of 60 years worldwide. Approximately 89% of ADPKD patients had either PKD1 or PKD2 gene mutations. The majority (85%) of the mutations are in the PKD1 gene, especially in the context of family history. Objectives: This study investigated the genetic basis and the undiscovered genes that are involved in ADPKD development among the Saudi population. Materials and Methods: In this study, 11 patients with chronic kidney disease were enrolled. The diagnosis of ADPKD was based on history and diagnostic images: CT images include enlargement of renal outlines, renal echogenicity, and presence of multiple renal cysts with dilated collecting ducts, loss of corticomedullary differentiation, and changes in GFR and serum creatinine levels. Next-generation whole-exome sequencing was conducted using the Ion Torrent PGM platform. Results: Of the 11 Saudi patients diagnosed with chronic kidney disease (CKD) and ADPKD, the most common heterozygote nonsynonymous variant in the PKD1 gene was exon15: (c.4264G > A). Two missense mutations were identified with a PKD1 (c.1758A > C and c.9774T > G), and one patient had a PKD2 mutation (c.1445T > G). Three detected variants were novel, identified at PKD1 (c.1758A > C), PKD2L2 (c.1364A > T), and TSC2 (deletion of a’a at the 3’UTR, R1680C) genes. Other variants in PKD1L1 (c.3813_381 4delinsTG) and PKD1L2 (c.404C > T) were also detected. The median age of end-stage renal disease for ADPK patients in Saudi Arabia was 30 years. Conclusion: This study reported a common variant in the PKD1 gene in Saudi patients with typical ADPKD. We also reported (to our knowledge) for the first time two novel missense variants in PKD1 and PKD2L2 genes and one indel mutation at the 3’UTR of the TSC2 gene. This study establishes that the reported mutations in the affected genes resulted in ADPKD development in the Saudi population by a median age of 30. Nevertheless, future protein−protein interaction studies to investigate the influence of these mutations on PKD1 and PKD2 functions are required. Furthermore, large-scale population-based studies to verify these findings are recommended.

Cystic Kidney Diseases That Require a Differential Diagnosis from Autosomal Dominant Polycystic Kidney Disease (ADPKD)

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary cystic kidney disease, with patients often having a positive family history that is characterized by a similar phenotype. However, in atypical cases, particularly those in which family history is unclear, a differential diagnosis between ADPKD and other cystic kidney diseases is important. When diagnosing ADPKD, cystic kidney diseases that can easily be excluded using clinical information include: multiple simple renal cysts, acquired cystic kidney disease (ACKD), multilocular renal cyst/multilocular cystic nephroma/polycystic nephroma, multicystic kidney/multicystic dysplastic kidney (MCDK), and unilateral renal cystic disease (URCD). However, there are other cystic kidney diseases that usually require genetic testing, or another means of supplementing clinical information to enable a differential diagnosis of ADPKD. These include autosomal recessive polycystic kidney disease (ARPKD), autosomal dominant tubulointerstitial kidney disease (ADTKD), nephronophthisis (NPH), oral-facial-digital (OFD) syndrome type 1, and neoplastic cystic kidney disease, such as tuberous sclerosis (TSC) and Von Hippel-Lindau (VHL) syndrome. To help physicians evaluate cystic kidney diseases, this article provides a review of cystic kidney diseases for which a differential diagnosis is required for ADPKD.

Identification of osteopontin as a urinary biomarker for autosomal dominant polycystic kidney disease progression

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD), one of the most common human monogenic diseases, is characterized by the presence of numerous fluid-filled renal cysts and is a leading cause of end-stage renal disease (ESRD). Urinary biomarkers may be useful for predicting the variable course of ADPKD progression from cyst growth to ESRD.

METHODS

To identify candidate urinary biomarkers of ADPKD progression, we used CRISPR/Cas9 genome editing to generate porcine fibroblasts with mono- and biallelic ADPKD gene knockout (PKD2+/- and PKD2-/-, respectively). We then performed RNA-sequencing analysis on these cells.

RESULTS

Levels of osteopontin (OPN), which is expressed by renal epithelial tubular cells and excreted into urine, were reduced in PKD2-/- cells but not in PKD2+/- cells. OPN levels were also reduced in the renal cyst cells of ADPKD patients. Next, we investigated whether OPN excretion was decreased in patients with ADPKD via enzyme-linked immunosorbent assay. OPN levels excreted into renal cyst cell culture media and urine from ADPKD patients were decreased. To investigate whether OPN can predict the rate of ADPKD progression, we compared urinary excretion of OPN in ADPKD patients with slow progression and those with rapid progression. Those with rapid progression had an estimated glomerular filtration rate of >60 mL/min/1.73 m2 . Urinary OPN excretion levels were lower in rapid progressors than in slow progressors.

CONCLUSION

These findings suggest that OPN is a useful urinary biomarker for predicting ADPKD progression.

Impact of kidney function and kidney volume on intracranial aneurysms in patients with autosomal dominant polycystic kidney disease

Presently, only personal or family history of intracranial aneurysm/subarachnoid hemorrhage (IA/SAH) has been established as a risk factor for IA in autosomal dominant polycystic kidney disease (ADPKD). This study aimed to verify the association between kidney function/volume and IAs in patients with ADPKD. This study included 519 patients with ADPKD. At baseline IA screening, the median age and estimated glomerular filtration rate were 44 years and 54.5 mL/min/1.73 m², respectively. Family IA/SAH history was confirmed in 18.1% of the patients, and 54.3% of the patients had hypertension. The IA point prevalence was 12.5%. During clinical follow up of 3104 patient-years, de novo IA was detected in 29 patients (0.93% patient-years). The IA period prevalence was 18.1% (median age, 60 years). Multivariable logistic regression demonstrated that total kidney volume (TKV) ≥ 1000 mL (odds ratio [OR] = 2.81), height-adjusted TKV ≥ 500 mL (OR = 2.81), Mayo imaging classification Class 1D-1E (OR = 2.52), and chronic kidney disease stages 3-5 (OR = 2.31) were significantly associated with IA formation. IAs in patients with ADPKD may be associated not only with general risk factors for IAs but also with declining kidney function and increased KV. Kidney disease progression may contribute to effective IA screening and treatment planning in patients with ADPKD.

A single-center analysis of genotype–phenotype characteristics of Chinese patients with autosomal dominant polycystic kidney disease by targeted exome sequencing

Background: Autosomal dominant polycystic kidney disease (ADPKD) is mainly caused by PKD1 and PKD2 mutations. However, only a few studies have investigated the genotype and phenotype characteristics of Asian patients with ADPKD. This study aimed to investigate the relationship between the natural course of ADPKD genotype and phenotype.

Methods: Genetic studies of PKD1/2 genes of Chinese patients with ADPKD in a single center were performed using targeted exome sequencing and next-generation sequencing on peripheral blood DNA.

Results: Among the 140 patients analyzed, 80.00% (n = 112) harbored PKD1 mutations, 11.43% (n = 16) harbored PKD2 mutations, and 8.57% (n = 12) harbored neither PKD1 nor PKD2 mutations. The average age at dialysis was 52.60 ± 11.36, 60.67 ± 5.64, and 52.11 ± 14.63 years, respectively. The renal survival rate of ADPKD patients with PKD1 mutations (77/112) was significantly lower than that of those with PKD2 mutations (9/16), leading to an earlier onset of end-stage renal disease (ESRD). Renal prognosis was poor for those with nonsense mutations, and they required earlier renal replacement therapy.

Conclusions: The genotype and phenotype characteristics of ADPKD patients potentially vary across ethnic groups. Our findings supplement the genetic profiles of Chinese ADPKD patients, could serve as a guide for therapy monitoring and prognosis assessment of ADPKD, and may improve the clinical diagnosis.

Genetics, pathobiology and therapeutic opportunities of polycystic liver disease

Polycystic liver diseases (PLDs) are inherited genetic disorders characterized by progressive development of intrahepatic, fluid-filled biliary cysts (more than ten), which constitute the main cause of morbidity and markedly affect the quality of life. Liver cysts arise in patients with autosomal dominant PLD (ADPLD) or in co-occurrence with renal cysts in patients with autosomal dominant or autosomal recessive polycystic kidney disease (ADPKD and ARPKD, respectively). Hepatic cystogenesis is a heterogeneous process, with several risk factors increasing the odds of developing larger cysts. Depending on the causative gene, PLDs can arise exclusively in the liver or in parallel with renal cysts. Current therapeutic strategies, mainly based on surgical procedures and/or chronic administration of somatostatin analogues, show modest benefits, with liver transplantation as the only potentially curative option. Increasing research has shed light on the genetic landscape of PLDs and consequent cholangiocyte abnormalities, which can pave the way for discovering new targets for therapy and the design of novel potential treatments for patients. Herein, we provide a critical and comprehensive overview of the latest advances in the field of PLDs, mainly focusing on genetics, pathobiology, risk factors and next-generation therapeutic strategies, highlighting future directions in basic, translational and clinical research.

Shared pathobiology identifies AMPK as a therapeutic target for obesity and autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common Mendelian kidney disease, affecting approximately one in 1,000 births and accounting for 5% of end-stage kidney disease in developed countries. The pathophysiology of ADPKD is strongly linked to metabolic dysregulation, which may be secondary to defective polycystin function. Overweight and obesity are highly prevalent in patients with ADPKD and constitute an independent risk factor for progression. Recent studies have highlighted reduced AMP-activated protein kinase (AMPK) activity, increased mammalian target of rapamycin (mTOR) signaling, and mitochondrial dysfunction as shared pathobiology between ADPKD and overweight/obesity. Notably, mTOR and AMPK are two diametrically opposed sensors of energy metabolism that regulate cell growth and proliferation. However, treatment with the current generation of mTOR inhibitors is poorly tolerated due to their toxicity, making clinical translation difficult. By contrast, multiple preclinical and clinical studies have shown that pharmacological activation of AMPK provides a promising approach to treat ADPKD. In this narrative review, we summarize the pleiotropic functions of AMPK as a regulator of cellular proliferation, macromolecule metabolism, and mitochondrial biogenesis, and discuss the potential for pharmacological activation of AMPK to treat ADPKD and obesity-related kidney disease.

PKD1 and PKD2 mRNA cis-inhibition drives polycystic kidney disease progression

Autosomal dominant polycystic kidney disease (ADPKD), among the most common human genetic conditions and a frequent etiology of kidney failure, is primarily caused by heterozygous PKD1 mutations. Kidney cyst formation occurs when PKD1 dosage falls below a critical threshold. However, no framework exists to harness the remaining allele or reverse PKD1 decline. Here, we show that mRNAs produced by the noninactivated PKD1 allele are repressed via their 3'-UTR miR-17 binding element. Eliminating this motif (Pkd1∆17) improves mRNA stability, raises Polycystin-1 levels, and alleviates cyst growth in cellular, ex vivo, and mouse PKD models. Remarkably, Pkd2 is also inhibited via its 3'-UTR miR-17 motif, and Pkd2∆17-induced Polycystin-2 derepression retards cyst growth in Pkd1-mutant models. Moreover, acutely blocking Pkd1/2 cis-inhibition, including after cyst onset, attenuates murine PKD. Finally, modeling PKD1∆17 or PKD2∆17 alleles in patient-derived primary ADPKD cultures leads to smaller cysts, reduced proliferation, lower pCreb1 expression, and improved mitochondrial membrane potential. Thus, evading 3'-UTR cis-interference and enhancing PKD1/2 mRNA translation is a potentially mutation-agnostic ADPKD-arresting approach.

Management of autosomal dominant polycystic kidney disease in the era of disease-modifying treatment options

Autosomal dominant polycystic kidney disease (ADPKD) is the reported etiology in 10% of end-stage kidney disease (ESKD) patients and has an estimated prevalence of 12.5 million cases worldwide across all ethnicities. There have been major advancements over the last two decades in understanding the pathogenesis and development of disease-modifying treatment options for ADPKD, culminating in regulatory approval of tolvaptan for ADPKD patients at risk of rapid progression to kidney failure. This review highlights the genetic mutations associated with ADPKD, defines patients at risk of rapid progression to ESKD, and focuses on the management of ADPKD in the era of disease-modifying agents.

Consensus document on autosomal dominant polycystic kindey disease from the Spanish Working Group on Inherited Kindey Diseases. Review 2020

Autosomal dominant polycystic kidney disease (ADPKD) is the most frequent cause of genetic renal disease and accounts for 6-10% of patients on kidney replacement therapy (KRT). Very few prospective, randomized trials or clinical studies address the diagnosis and management of this relatively frequent disorder. No clinical guidelines are available to date. This is a revised consensus statement from the previous 2014 version, presenting the recommendations of the Spanish Working Group on Inherited Kidney Diseases, which were agreed to following a literature search and discussions. Levels of evidence mostly are C and D according to the Centre for Evidence-Based Medicine (University of Oxford). The recommendations relate to, among other topics, the use of imaging and genetic diagnosis, management of hypertension, pain, cyst infections and bleeding, extra-renal involvement including polycystic liver disease and cranial aneurysms, management of chronic kidney disease (CKD) and KRT and management of children with ADPKD. Recommendations on specific ADPKD therapies are provided as well as the recommendation to assess rapid progression.

Health Disparities in Autosomal Dominant Polycystic Kidney Disease (ADPKD) in the United States

BACKGROUND AND OBJECTIVES

Autosomal dominant polycystic kidney disease (ADPKD) occurs at conception and is often diagnosed decades prior to kidney failure. Nephrology care and transplantation access should be independent of race and ethnicity. However, institutional racism and barriers to health care may affect patient outcomes in ADPKD. We sought to ascertain the effect of health disparities on outcomes in ADPKD by examining age at onset of kidney failure and access to preemptive transplantation and transplantation after dialysis initiation.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Retrospective cohort analyses of adults with ADPKD in the United States Renal Data System from January 2000 to June 2018 were merged to US Census income data and evaluated by self-reported race and ethnicity. Age at kidney failure was analyzed in a linear model, and transplant rates before and after dialysis initiation were analyzed in logistic and proportional hazards models in Black and Hispanic patients with ADPKD compared with White patients with ADPKD.

RESULTS

A total of 41,485 patients with ADPKD were followed for a median of 25 (interquartile range, 5-54) months. Mean age was 56±12 years; 46% were women, 13% were Black, and 10% were Hispanic. Mean ages at kidney failure were 55±13, 53±12, and 57±12 years for Black patients, Hispanic patients, and White patients, respectively. Odds ratios for preemptive transplant were 0.33 (95% confidence interval, 0.29 to 0.38) for Black patients and 0.50 (95% confidence interval, 0.44 to 0.56) for Hispanic patients compared with White patients. Transplant after dialysis initiation was 0.61 (95% confidence interval, 0.58 to 0.64) for Black patients and 0.78 (95% confidence interval, 0.74 to 0.83) for Hispanic patients.

CONCLUSIONS

Black and Hispanic patients with ADPKD reach kidney failure earlier and are less likely to receive a kidney transplant preemptively and after initiating dialysis compared with White patients with ADPKD.

PKD2 founder mutation is the most common mutation of polycystic kidney disease in Taiwan

Autosomal Dominant polycystic kidney disease (ADPKD) is the most common inherited adult kidney disease. Although ADPKD is primarily caused by PKD1 and PKD2, the identification of several novel causative genes in recent years has revealed more complex genetic heterogeneity than previously thought. To study the disease-causing mutations of ADPKD, a total of 920 families were collected and their diagnoses were established via clinical and image studies by Taiwan PKD Consortium investigators. Amplicon-based library preparation with next-generation sequencing, variant calling, and bioinformatic analysis was used to identify disease-causing mutations in the cohort. Microsatellite analysis along with genotyping and haplotype analysis was performed in the PKD2 p.Arg803* family members. The age of mutation was calculated to estimate the time at which the mutation occurred or the founder arrived in Taiwan. Disease-causing mutations were identified in 634 families (68.9%) by detection of 364 PKD1, 239 PKD2, 18 PKHD1, 7 GANAB, and 6 ALG8 pathogenic variants. 162 families (17.6%) had likely causative but non-diagnostic variants of unknown significance (VUS). A single PKD2 p.Arg803* mutation was found in 17.8% (164/920) of the cohort in Taiwan. Microsatellite and array analysis showed that 80% of the PKD2 p.Arg803* families shared the same haplotype in a 250 kb region, indicating those families may originate from a common ancestor 300 years ago. Our findings provide a mutation landscape as well as evidence that a founder effect exists and has contributed to a major percentage of the ADPKD population in Taiwan.

Flank pain has a significant adverse impact on quality of life in ADPKD: the CYSTic-QoL study

Background

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disorder and a major cause of kidney failure worldwide. However, its impact on quality-of-life has not been systematically explored.

Methods

The CYSTic-QoL study was an observational study designed to study quality-of-life in adult European ADPKD patients with an estimated glomerular filtration rate (eGFR) ≥30 mL/min/1.73 m². A total of 465 patients were recruited from six expert European centres with baseline data recorded, including health-related quality-of-life (HRQoL), incorporating a Kidney Disease QoL short form questionnaire (KDQoL-SF, version 1.3), magnetic resonance imaging (MRI) for total kidney volume (TKV) measurements and DNA for genotyping. The cohort was stratified by baseline eGFR, TKV or genotype and correlated with HRQoL scores. Bivariate and multivariate analyses were applied to examine the relationship between HRQoL and variables of interest. KDQoL-SF scores were calculated using an online tool provided by the RAND organization. For 36-item short form values, mean centre scores were normalized to their native populations.

Results

The mean age of participants was 43 years and 55% were female, with a mean eGFR of 77 mL/min/1.73 m² and height-adjusted TKV (ht-TKV) of 849 mL/min; 66% had PKD1 pathogenic variants. ADPKD patients uniformly reported decreased general health and less energy, with the majority also experiencing poorer physical, mental or emotional health and limitations in social functioning. A total of 32.5% of participants experienced flank pain, which was significantly and negatively correlated with the majority of KDQoL-SF subscales by multivariate analysis. Higher ht-TKV and lower eGFR were negatively associated with decreased energy and poorer physical health, respectively, although not with flank pain.

Conclusion

ADPKD patients suffer from significantly decreased QoL in multiple domains, exacerbated particularly by chronic pain.

The causes and consequences of paediatric kidney disease on adult nephrology care

Adult nephrologists often look after patients who have been diagnosed with kidney disease in childhood. This does present unique challenges to the adult nephrologist, who may be unfamiliar with the underlying cause of kidney disease as well as the complications of chronic kidney disease (CKD) that may have accumulated during childhood. This review discusses common causes of childhood CKD, in particular congenital anomalies of the kidney and urinary tract (CAKUT), autosomal dominant tubulointerstitial kidney disease (ADTKD), polycystic kidney disease, hereditary stone disease, nephrotic syndrome and atypical haemolytic uraemic syndrome. The long-term consequences of childhood CKD, such as the cardiovascular consequences, cognition and education as well as bone health, nutrition and growth are also discussed.

Establishment and Characterization of MUi027-A: A Novel Patient-Derived Cell Line of Polycystic Kidney Disease with PKD1 Mutation

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most prevalent genetic diseases affecting the kidneys. A genetically specific mutation model is required to comprehend its pathophysiology and to develop a drug treatment. In this study, we successfully developed human induced pluripotent stem cells (hiPSCs) named MUi027-A from skin fibroblasts of a patient diagnosed with ADPKD and carrying the PKD1 frameshift mutation (c.7946_7947delCT). MUi027-A cells showed the same genetic fingerprints as the parental cells, including the presence of the PKD1 mutation. MUi027-A hiPSCs displayed embryonic stem cell-like characteristics with the capability of differentiating into the three germ layers. Upon directed differentiation, MUi027-A hiPSCs could be differentiated into tubular organoids with the expression of renal cell markers. Furthermore, we compared the efficiency of cyst formation in two human iPSC lines with different PKD1 mutations. When cyst formation was induced by either forskolin or blebbistatin, MUi027-A hiPSC-derived kidney organoids displayed higher frequencies of cyst formation when compared to organoids generated from an iPSC cell line with non-truncating PKD1 mutation genotype (c.5878C > T), suggesting the presence of physiological differences in the mechanism of cyst formation between different PKD1 mutants. Overall, we generated and characterized a novel human iPSC line with a specific PKD mutation and demonstrated its potential as a disease model to study the pathophysiology of genetic determinants in the development of ADPKD disease.

Polycystic Kidney/Liver Disease

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder that leads to chronic kidney disease and end-stage kidney disease (ESKD). Polycystic liver disease (PCLD) is the most common extrarenal manifestation of ADPKD. Though isolated PCLD and PCLD due to ADPKD are genetically distinct, they follow a similar clinical course of hepatomegaly from multiple cysts with preserved liver function. Tolvaptan use in ADPKD can slow down the deterioration of renal function and growth of cysts. Somatostatin analogs can slow the growth of polycystic livers but the effect is short-lived. The only curative therapy for PCLD is liver transplantation. Renal transplantation can significantly improve survival in patients with ESKD due to ADPKD.

Autosomal dominant polycystic kidney disease (ADPKD) in Tunisia: From molecular genetics to the development of prognostic tools

A high prevalence of genetic kidney disease in Tunisia has been detected, and their study provides very important clinical and genetic information. Autosomal dominant polycystic kidney disease (ADPKD) is one of the main causes of morbidity and mortality associated with the kidneys in Tunisia. We present here clinical and genetic characteristics of a cohort of Tunisian patients with ADPKD. Nineteen Tunisian patients with ADPKD, among 4 familial cases and 11 sporadic cases, and 50 Healthy individuals were included in this cohort. Genetic studies of PKD1/2 were carried on using Sanger sequencing and MLPA. In our study, the mean age at diagnosis was 47 ± 18 years. In addition, 84.21% of cases present a family history of ADPKD. Overall, 57.89% of the affected individuals had HTA and 26.31% patients had hematuria. 15.78 % of the patient has extra-renal cysts i.e. one patient with splenic cysts and two patients had liver cysts. 57.89 % of patients were diagnosed with various extra-renal clinical presentations i.e. myopia, hernia, deafness, intracranial aneurysm, respiratory distress, hyperthyroidism, urinary tract infection and lower back pains. The PKD1 genotype showed earlier onset of ESRD compared to PKD2 genotype (43 vs. 55 years old). Six mutations have been detected in PKD1 gene. Among them, three were novels e.g. c.688 T>G, p.C230G and c.690C>G, p.C230W among exon 5 and c.8522A>G, p.N2841S among exon 23. In addition, thirteen single nucleotides polymorphisms have been reported in PKD1 gene. Among them, eleven previously reported in heterozygous state and two novel single nucleotides polymorphisms in heterozygous and homozygous state and predicted to be probable polymorphisms by computational tools: c.496C>T, p.L166= among the exon 4, and c.10165G>C and p.E3389Gln among the exon 31. Only three single nucleotides polymorphisms previously reported in ADPKD database have been identified in PKD2 gene. The description and analysis of our cohort can help in rapid and reliable diagnosis for early management of patients in Tunisia. Indeed, predictive genetic testing can facilitate donor evaluation and increase living related kidney transplantation.

Emerging Role of Clinical Genetics in CKD

Chronic kidney disease (CKD) afflicts 15% of adults in the United States, of whom 25% have a family history. Genetic testing is supportive in identifying and possibly confirming diagnoses of CKD, thereby guiding care. Advances in the clinical genetic evaluation include next-generation sequencing with targeted gene panels, whole exome sequencing, and whole genome sequencing. These platforms provide DNA sequence reads with excellent coverage throughout the genome and have identified novel genetic causes of CKD. New pathologic genetic variants identified in previously unrecognized biological pathways have elucidated disease mechanisms underlying CKD etiologies, potentially establishing prognosis and guiding treatment selection. Molecular diagnoses using genetic sequencing can detect rare, potentially treatable mutations, avoid misdiagnoses, guide selection of optimal therapy, and decrease the risk of unnecessary and potentially harmful interventions. Genetic testing has been widely adopted in pediatric nephrology; however, it is less frequently used to date in adult nephrology. Extension of clinical genetic approaches to adult patients may achieve similar benefits in diagnostic refinement and treatment selection. This review aimed to identify clinical CKD phenotypes that may benefit the most from genetic testing, outline the commonly available platforms, and provide examples of successful deployment of these approaches in CKD.

Metformin Therapy in Autosomal Dominant Polycystic Kidney Disease: A Feasibility Study

RATIONALE & OBJECTIVE

Autosomal dominant polycystic kidney disease (ADPKD) is a common inherited disorder that leads to kidney failure and has few treatment options. Metformin is well tolerated and safe in other patient populations. The primary objective of this clinical trial was to determine the safety and tolerability of metformin in patients with ADPKD and without diabetes mellitus.

STUDY DESIGN

Prospective randomized controlled double-blind clinical trial.

SETTING & PARTICIPANTS

51 adults aged 30-60 years with ADPKD, without diabetes, and an estimated glomerular filtration rate (eGFR) 50-80 mL/min/1.73 m2.

EXPOSURE

Metformin (maximum dose 2,000 mg/d) or placebo for 12 months.

OUTCOME

Coprimary end points were the percentage of participants in each group prescribed at the end of the 12-month period: (1) the full randomized dose or (2) at least 50% of the randomized dose. Secondary and exploratory outcomes were the effect of metformin compared with placebo on (1) the percentage change in total kidney volume (TKV) referenced to height (htTKV in mL/m) and (2) the change in eGFR over a 12-month period.

RESULTS

The participants' mean age was 48 ± 8 (SD) years, and eGFR was 70 ± 14 mL/min/1.73 m2. The metformin group had no cases of lactic acidosis, and there was 1 episode of mild hypoglycemia in each group. Participants in the metformin group reported more adverse symptoms, mostly related to the gastrointestinal tract. Eleven of 22 metformin-treated participants (50%) completed the treatment phase on the full dose compared with 23 of 23 in the placebo group (100%). In the metformin group, 82% of participants tolerated at least 50% of the dose, compared with 100% in the placebo group. In exploratory analyses, changes in htTKV or eGFR were not significantly different between the groups.

LIMITATIONS

Short study duration.

CONCLUSIONS

We found that 50% or more of the maximal metformin dose was safe and well tolerated over 12 months in patients with ADPKD. Safety of other preparations of metformin as well as its efficacy should be tested in future clinical trials.

FUNDING

Government and philanthropic grants (NIDDK and the Zell Foundation).

TRIAL REGISTRATION

Registered at ClinicalTrials.gov with study number NCT02903511.

[Genetic screening is essential in polycystic kidney disease: It is never too late!]

In France, numerous patients suffered from chronic kidney disease on polycystic kidney disorder. If PKD1 and PKD2 inactivating mutations are the most prevalent, several other genetic polycystic kidney diseases are responsible for similar kidney features and may be associated with severe extrarenal phenotypes. Genetic analysis in front of a polycystic disorder is not systematic, but is essential to assess the genetic diagnosis, discuss the intensity of treatment (vaptan) and precise the prognostic and the transmission of the phenotype. We detailed the case of a patient with end stage renal disease due to a polycystic kidney disease. Genetic analysis at 70 year of age revealed an oral-facial-digital syndrome type 1. The diagnosis had an important impact in the familial history and to attach the extrarenal phenotype to the syndrome. Our case illustrates that, in front of a polycystic kidney disease (even in aged patients with end stage renal disease) genetic screening is essential, for the propositus and their family and to take care of the extrarenal manifestations.

Factors that lead to dialysis as the preferred treatment modality for patients with chronic kidney disease

PURPOSE OF REVIEW

To describe forces that lead to dialysis as the preferred treatment modality for patients with chronic kidney disease.

RECENT FINDINGS

Although chronic dialysis is life-saving and the only option available for many individuals, treatment of the underlying causes of kidney disease and transplantation may be preferable options for many patients. Factors that favor dialysis instead of treatment of underlying kidney disease or transplantation include lack of proper diagnosis, lack of proper treatment of underlying kidney disease, poor compliance, lack of consideration for transplantation, early initiation of dialysis therapy, and financial incentives. New developments that may reverse this trend include genetic panels that improve diagnosis of kidney disease, new methods of transplantation, and legislation that will encourage kidney transplantation.

SUMMARY

By recognizing factors that favor dialysis over other therapies, nephrologists may be better able to provide care to their patients and prevent dialysis, researchers may be able to focus on research that will prevent the need for dialysis, and professional societies may work to prevent unneeded dialysis.

Metabolic reprogramming in a slowly developing orthologous model of polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease and affects 1 in 1,000 individuals. There is accumulating evidence suggesting that there are shared cellular mechanisms responsible for cystogenesis in human and murine PKD and that reprogramming of metabolism is a key disease feature. In this study, we used a targeted metabolomics approach in an orthologous mouse model of PKD (Pkd1RC/RC) to investigate the metabolic modifications a cystic kidney undergoes during disease progression. Using the Kyoto Encyclopedia of Genes and Genomes pathway database, we identified several biologically relevant metabolic pathways that were altered early in this disease (in 3-mo-old Pkd1RC/RC mice), the most highly represented being arginine biosynthesis and metabolism and tryptophan and phenylalanine metabolism. During the next 6 mo of disease progression, multiple uremic solutes accumulated in the kidney of cystic mice, including several established markers of oxidative stress and endothelial dysfunction (allantoin, asymmetric dimethylarginine, homocysteine, malondialdehyde, methionine sulfoxide, and S-adenosylhomocysteine). Levels of kynurenines and polyamines were also augmented in kidneys of Pkd1RC/RC versus wild-type mice, as were the levels of bacteria-produced indoles, whose increase within PKD kidneys suggests microbial dysbiosis. In summary, we confirmed previously published and identified novel metabolic markers and pathways of PKD progression that may prove helpful for diagnosis and monitoring of cystic kidney disease in patients. Furthermore, they provide targets for novel therapeutic approaches that deserve further study and hint toward currently understudied pathomechanisms.NEW & NOTEWORTHY This report delineates the evolution of metabolic changes occurring during autosomal dominant polycystic kidney disease (ADPKD) progression. Using an orthologous model, we performed kidney metabolomics and confirmed dysregulation of metabolic pathways previously found altered in nonorthologous or rapidly-progressive PKD models. Importantly, we identified novel alterations, including augmentation of kynurenines, polyamines, and indoles, suggesting increased inflammation and microbial dysbiosis that provide insights into PKD pathomechanisms and may prove helpful for diagnosing, monitoring, and treating ADPKD.

Rapidly Progressing to ESRD in an Individual with Coexisting ADPKD and Masked Klinefelter and Gitelman Syndromes

Autosomal dominant polycystic kidney disease (ADPKD) is the most common monogenetic hereditary renal disease, promoting end-stage renal disease (ESRD). Klinefelter syndrome (KS) is a consequence of an extra copy of the X chromosome in males. Main symptoms in KS include hypogonadism, tall stature, azoospermia, and a risk of cardiovascular diseases, among others. Gitelman syndrome (GS) is an autosomal recessive disorder caused by SLC12A3 variants, and is associated with hypokalemia, hypomagnesemia, hypocalciuria, normal or low blood pressure, and salt loss. The three disorders have distinct and well-delineated clinical, biochemical, and genetic findings. We here report a male patient with ADPKD who developed early chronic renal failure leading to ESRD, presenting with an intracranial aneurysm and infertility. NGS identified two de novo PKD1 variants, one known (likely pathogenic), and a previously unreported variant of uncertain significance, together with two SLC12A3 pathogenic variants. In addition, cytogenetic analysis showed a 47, XXY karyotype. We investigated the putative impact of this rare association by analyzing possible clinical, biochemical, and/or genetic interactions and by comparing the evolution of renal size and function in the proband with three age-matched ADPKD (by variants in PKD1) cohorts. We hypothesize that the coexistence of these three genetic disorders may act as modifiers with possible synergistic actions that could lead, in our patient, to a rapid ADPKD progression.

Diagnosis and Risk Factors for Intracranial Aneurysms in Autosomal Polycystic Kidney Disease: A cross-sectional study from the Genkyst Cohort

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is associated with an increased risk for developing intracranial aneurysms (IAs). We aimed to evaluate the frequency of diagnosis of IAs in the cross-sectional, population-based, Genkyst cohort, to describe ADPKD-associated IAs and to analyze the risk factors associated with the occurrence of IAs in ADPKD patients.

METHODS

Cross-sectional study performed in 26 nephrology centers from the Western part of France. All patients underwent genetic testing for PKD1/PKD2 and other cystogenes.

RESULTS

Among the 2449 Genkyst participants, 114 (4.65%) had a previous diagnosis of ruptured or unruptured IAs at inclusion, and ∼47% of them had a positive familial history for IAs. Most aneurysms were small and saccular and located in the anterior circulation; 26.3% of the patients had multiple IAs. The cumulative probabilities of a previous diagnosis of IAs were 3.9, 6.2 and 8.1% at 50, 60 and 70 y, respectively. While this risk appeared to be similar in male and female individuals <50 y, after that age, the risk continued to increase more markedly in female patients, reaching 10.8% vs 5.4% at 70 y. The diagnosis rate of IAs was more than twofold higher in PKD1 compared to PKD2 with no influence of PKD1 mutation type or location. In multivariate analysis, female sex, hypertension <35 y, smoking and PKD1 genotype were associated with an increased risk for diagnosis of IAs.

CONCLUSIONS

This study presents epidemiological data reflecting real-life clinical practice. The increased risk for IAs in postmenopausal women suggests a possible protective role of estrogen.

Pooled Data Analysis of the Long-Term Treatment Effects of Tolvaptan in ADPKD

Introduction

Methods

Results

Conclusion

The utility of a genetic kidney disease clinic employing a broad range of genomic testing platforms: experience of the Irish Kidney Gene Project

BACKGROUND AND AIMS

Genetic testing presents a unique opportunity for diagnosis and management of genetic kidney diseases (GKD). Here, we describe the clinical utility and valuable impact of a specialized GKD clinic, which uses a variety of genomic sequencing strategies.

METHODS

In this prospective cohort study, we undertook genetic testing in adults with suspected GKD according to prespecified criteria. Over 7 years, patients were referred from tertiary centres across Ireland to an academic medical centre as part of the Irish Kidney Gene Project.

RESULTS

Among 677 patients, the mean age was of 37.2 ± 13 years, and 73.9% of the patients had family history of chronic kidney disease (CKD). We achieved a molecular diagnostic rate of 50.9%. Four genes accounted for more than 70% of identified pathogenic variants: PKD1 and PKD2 (n = 186, 53.4%), MUC1 (8.9%), and COL4A5 (8.3%). In 162 patients with a genetic diagnosis, excluding PKD1/PKD2, the a priori diagnosis was confirmed in 58% and in 13% the diagnosis was reclassified. A genetic diagnosis was established in 22 (29.7%) patients with CKD of uncertain aetiology. Based on genetic testing, a diagnostic kidney biopsy was unnecessary in 13 (8%) patients. Presence of family history of CKD and the underlying a priori diagnosis were independent predictors (P < 0.001) of a positive genetic diagnosis.

CONCLUSIONS

A dedicated GKD clinic is a valuable resource, and its implementation of various genomic strategies has resulted in a direct, demonstrable clinical and therapeutic benefits to affected patients.

Increased Body Fat and Organic Acid Anions Production Are Associated with Larger Kidney Size in ADPKD

Background and Objectives: A high body mass index (BMI) is associated with the progression of autosomal dominant polycystic kidney disease (ADPKD). However, body fat (BF), which is another adiposity marker, has not yet been studied. Excessive weight may promote elevation in the endogenous synthesis of organic acid (OA) anions. Accordingly, we aimed to investigate the possible association of the aforementioned markers with kidney volume and renal function in patients with ADPKD. Materials and Methods: We conducted a retrospective cohort study of adult ADPKD outpatients involving clinical, serum, and urinary laboratorial data and body composition assessments retrieved from their medical records. BF was estimated by skinfold thickness (mm) on the non-dominant arm and was considered as normal or high for each sex. Total kidney volume (TKV) and height-adjusted volume (htTKV) were measured by magnetic resonance imaging. The annual estimated glomerular filtration rate (eGFR) slope was analyzed during a median follow-up time of 6 (5.0-7.0) years to calculate rapid progression (decline in renal function ≥2.5 mL/min/year over 5 years). Results: A total of 104 patients were included (41.9 ± 11.9 years old, 38.5% men), with 62.5% of the patients classified as high BF. The High BF group presented higher levels of OA, glycosylated hemoglobin (HbA1c), C-reactive protein (CRP), 24 h urinary sodium (UNa), and htTKV, and lower eGFR than those with a normal BF. In the multivariate linear regression, the associated variables with TKV were high BF, OA and BMI (std. β 0.47, p < 0.05; std. β 0.36, p = 0.001; std. β 0.25, p = 0.01, respectively). In the binary logistic regression, when adjusted for potential confounders, UNa was the only parameter associated with an increased risk of eGFR decline ≥2.5 mL/min/year (OR 1.02, 95% CI 1.01-1.03, p = 0.02). Conclusions: Increased body fat and endogenous production of organic acid anions are associated with larger kidney size in ADPKD but not with a decline in renal function.

Practical Issues in the Management of Polycystic Kidney Disease: Blood Pressure and Water Balance

Autosomal dominant polycystic kidney disease is the most common hereditary renal disease affecting more than 13 million people worldwide. Renal function deteriorates as the cysts in both kidneys increase in number and size, which eventually results in end-stage kidney failure. Until recently, conservative management for chronic kidney disease such as blood pressure control, low sodium diet, adequate water intake, and weight control were known for the only treatment of polycystic kidney disease. However, the introduction of disease-modifying drug has led to the new paradigm shift in the management of polycystic kidney disease. Tolvaptan, the vasopressin V2 receptor antagonist, has been introduced to the patients with large kidneys since it can inhibit cyclic adenosine monophosphate, attenuates cyst growth, and delays renal failure. This article reviews the two important practical issues in the management of polycystic kidney disease: blood pressure and water balance. Firstly, the article will review the pathogenesis of high blood pressure in polycystic kidney disease and will demonstrate the current up-to-date management plan for blood pressure control. Secondly, this article will explain the mechanism of Tolvaptan on the treatment of polycystic kidney disease and its possible adverse effect on water and sodium balance.

Germline Mutations for Kidney Volume in ADPKD

Introduction

Valid prediction models or predictors of disease progression in children and young patients with autosomal dominant polycystic kidney disease (ADPKD) are lacking. Although total kidney volume (TKV) and Mayo imaging classification are generally used to predict disease progression in patients with ADPKD, it remains unclear whether germline mutation types are associated with these factors. We therefore investigated the association between mutation type and TKV and Mayo imaging classification among patients with ADPKD.

Methods

A total of 129 patients with ADPKD who underwent genetic analyses were enrolled in the study. The associations between the severity of PKD (TKV ≥ 1000 ml and Mayo classes 1C–1E) and the PKD1 mutation types (nonsense mutation, frameshift or splicing mutation, and substitution) were evaluated.

Results

Among the mutation types, only PKD1 splicing/frameshift mutation had significant associations with TKV ≥ 1000 ml in sex-adjusted and multivariable logistic analyses. Similarly, only the PKD1 splicing/frameshift mutation was significantly associated with Mayo 1C–1E in sex-adjusted and multivariable logistic analyses. PKD1 nonsense mutation, PKD1 substitution, or PKD1 mutation position had no significant association with TKV ≥ 1000 ml or Mayo 1C–1E.

Conclusion

Kidney cyst severity differs according to the mutation types in PKD1. Patients with PKD1 splicing mutations or PKD1 frameshift mutations are associated with TKV ≥ 1000 ml or Mayo 1C–1E. Detailed assessment of mutation types may be useful for predicting renal prognosis in patients with ADPKD and may especially contribute to the care of a high-risk group of children with ADPKD.

Renal plasticity revealed through reversal of polycystic kidney disease in mice

Initiation of cyst formation in autosomal dominant polycystic kidney disease (ADPKD) occurs when kidney tubule cells are rendered null for either PKD1 or PKD2 by somatic 'second hit' mutations. Subsequent cyst progression remodels the organ through changes in tubule cell shape, proliferation and secretion. The kidney develops inflammation and fibrosis. We constructed a mouse model in which adult inactivation of either Pkd gene can be followed by reactivation of the gene at a later time. Using this model, we show that re-expression of Pkd genes in cystic kidneys results in rapid reversal of ADPKD. Cyst cell proliferation is reduced, autophagy is activated and cystic tubules with expanded lumina lined by squamoid cells revert to normal lumina lined by cuboidal cells. Increases in inflammation, extracellular matrix deposition and myofibroblast activation are reversed, and the kidneys become smaller. We conclude that phenotypic features of ADPKD are reversible and that the kidney has an unexpected capacity for plasticity controlled at least in part by ADPKD gene function.

Metformin induces lactate accumulation and accelerates renal cyst progression in Pkd1-deficient mice

Metabolic reprogramming is a potential treatment strategy for autosomal dominant polycystic kidney disease (ADPKD). Metformin has been shown to inhibit the early stages of cyst formation in animal models. However, metformin can lead to lactic acidosis in diabetic patients with advanced chronic kidney disease, and its efficacy in ADPKD is still not fully understood. Here, we investigated the effect of metformin in an established hypomorphic mouse model of PKD that presents stable and heritable knockdown of Pkd1. The Pkd1 miRNA transgenic mice of both genders were randomized to receive metformin or saline injections. Metformin was administrated through daily intraperitoneal injection from postnatal day 35 for 4 weeks. Unexpectedly, metformin treatment at a concentration of 150 mg/kg increased disease severity, including kidney-to-body weight ratio, cystic index and plasma BUN levels, and was associated with increased renal tubular cell proliferation and plasma lactate levels. Functional enrichment analysis for cDNA microarrays from kidney samples revealed significant enrichment of several pro-proliferative pathways including β-catenin, hypoxia-inducible factor-1α, protein kinase Cα and Notch signaling pathways in the metformin-treated mutant mice. The plasma metformin concentrations were still within the recommended therapeutic range for type 2 diabetic patients. Short-term metformin treatment in a second Pkd1 hypomorphic model (Pkd1RC/RC) was however neutral. These results demonstrate that metformin may exacerbate late-stage cyst growth associated with the activation of lactate-related signaling pathways in Pkd1 deficiency. Our findings indicate that using metformin in the later stage of ADPKD might accelerate disease progression and call for the cautious use of metformin in these patients.

Mainstreaming Genetic Testing for Adult Patients With Autosomal Dominant Polycystic Kidney Disease

PURPOSE

Genetic testing results are currently obtained approximately 1 year after referral to a medical genetics team for autosomal dominant polycystic kidney disease (ADPKD). We evaluated a mainstream genetic testing (MGT) pathway whereby the nephrology team provided pre-test counseling and selection of patients with suspected ADPKD for genetic testing prior to direct patient interaction by a medical geneticist.

SOURCES OF INFORMATION

A multidisciplinary team of nephrologists, genetic counselors, and medical geneticists developed an MGT pathway for ADPKD using current testing criteria for adult patient with suspected ADPKD and literature from MGT in oncology.

METHODS

An MGT pathway was assessed using a prospective cohort and compared to a retrospective cohort of 56 patients with ADPKD who received genetic testing using the standard, traditional pathway prior to implementing the MGT for ADPKD. The mainstream pathway was evaluated using time to diagnosis, diagnostic yield, and a patient survey to assess patient perceptions of the MGT pathway.

KEY FINDINGS

We assessed 26 patients with ADPKD using the MGT and 18 underwent genetic testing with return of results. Of them, 52 patients had data available for analysis in the traditional control cohort. The time for return of results using our MGT pathway was significantly shorter with a median time to results of 6 months compared to 12 months for the traditional pathway. We identified causative variants in 61% of patients, variants of uncertain significance in 28%, and 10% had negative testing which is in line with expectations from the literature. The patient surveys showed high satisfaction rates with the MGT pathway.

LIMITATIONS

This report is an evaluation of a new genetic testing pathway restricted to a single, publicly funded health care center. The MGT pathway involved a prospective collection of a limited number of patients with ADPKD with comparison to a retrospective cohort of patients with ADPKD evaluated by standard testing.

IMPLICATIONS

A MGT pathway using clearly defined criteria and commercially available gene panels for ADPKD can be successfully implemented in a publicly funded health care system to reduce the time required to obtain genetic results.

Molecular Basis, Diagnostic Challenges and Therapeutic Approaches of Bartter and Gitelman Syndromes: A Primer for Clinicians

Gitelman and Bartter syndromes are rare inherited diseases that belong to the category of renal tubulopathies. The genes associated with these pathologies encode electrolyte transport proteins located in the nephron, particularly in the Distal Convoluted Tubule and Ascending Loop of Henle. Therefore, both syndromes are characterized by alterations in the secretion and reabsorption processes that occur in these regions. Patients suffer from deficiencies in the concentration of electrolytes in the blood and urine, which leads to different systemic consequences related to these salt-wasting processes. The main clinical features of both syndromes are hypokalemia, hypochloremia, metabolic alkalosis, hyperreninemia and hyperaldosteronism. Despite having a different molecular etiology, Gitelman and Bartter syndromes share a relevant number of clinical symptoms, and they have similar therapeutic approaches. The main basis of their treatment consists of electrolytes supplements accompanied by dietary changes. Specifically for Bartter syndrome, the use of non-steroidal anti-inflammatory drugs is also strongly supported. This review aims to address the latest diagnostic challenges and therapeutic approaches, as well as relevant recent research on the biology of the proteins involved in disease. Finally, we highlight several objectives to continue advancing in the characterization of both etiologies.

Systematic Review of Genotype-Phenotype Correlations in Frasier Syndrome

Introduction

Frasier syndrome (FS) is a rare inherited kidney disease caused by intron 9 splicing variants of WT1. For wild-type WT1, 2 active splice donor sites in intron 9 cause a mixture of 2 essential transcripts (with or without lysine-threonine-serine [+/KTS or −KTS]), and imbalance of the +KTS/−KTS ratio results in the development of FS. To date, 6 causative intron 9 variants have been identified; however, detailed transcript analysis has not yet been conducted and the genotype-phenotype correlation also remains to be elucidated.

Methods

We conducted an in vitro minigene splicing assay for 6 reported causative variants and in vivo RNA sequencing to determine the +KTS/−KTS ratio using patients’ samples. We also performed a systematic review of reported FS cases with a description of the renal phenotype.

Results

The in vitro assay revealed that although all mutant alleles produced −KTS transcripts only, the wild-type allele produced both +KTS and −KTS transcripts at a 1:1 ratio. In vivo RNA sequencing showed that patients’ samples with all heterozygous variants produced similar ratios of +KTS to −KTS (1:3.2−1:3.5) and wild-type kidney showed almost a 1:1 ratio (1:0.85). A systematic review of 126 cases clarified that the median age of developing ESKD was 16 years in all FS patients, and there were no statistically significant differences between the genotypes or sex chromosome karyotypes in terms of the renal survival period.

Conclusion

Our study suggested no differences in splicing pattern or renal survival period among reported intron 9 variants causative of FS.

Tolvaptan in Pediatric Autosomal Dominant Polycystic Kidney Disease: From Here to Where?

Background

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disorder, accounting for approximately 5% of all ESRD cases worldwide. As a vasopressin receptor 2 antagonist, tolvaptan is the FDA-approved therapeutic agent for ADPKD, which is only made available to a limited number of adult patients; however, its efficacy in pediatric patients has not been reported widely.

Summary

Tolvaptan was shown to delay ADPKD progression in the Tolvaptan Efficacy and Safety in Management of Autosomal Dominant Polycystic Kidney Disease and Its Outcomes (TEMPO) 3:4 study, Replicating Evidence of Preserved Renal Function: an Investigation of Tolvaptan Safety and Efficacy in ADPKD (REPRISE) trial, and other clinical studies. In addition to its effects on aquaretic adverse events and alanine aminotransferase elevation, the effect of tolvaptan on ADPKD is clear, sustained, and cumulative. While ADPKD is a progressive disease, the early intervention has been shown to be important and beneficial in hypotheses as well as in trials. The use of tolvaptan in pediatric ADPKD involves the following challenges: patient assessment, quality of life assessment, cost-effectiveness, safety, and tolerability. The ongoing, phase 3b, 2-part study (ClinicalTrials.gov identifier: NCT02964273) on the evaluation of tolvaptan in pediatric ADPKD (patients aged 12-17 years) may help obtain some insights.

Key Messages

This review focuses on the rationality of tolvaptan use in pediatric patients with ADPKD, the associated challenges, and the suggested therapeutic approaches.

A Presumed Synonymous Mutation of PKD2 Caused Autosomal Dominant Polycystic Kidney Disease in a Chinese Family

OBJECTIVE

Autosomal dominant polycystic kidney disease (ADPKD) is mainly caused by the pathogenic mutation of PKD1 or PKD2 gene and usually affects bilateral kidneys. Synonymous mutations are generally assumed to be neutral as they do not alter amino acids. Herein, we described an extremely rare ADPKD child caused by a heterozygous synonymous mutation of PKD2 gene accompanied by massive proteinuria and congenital solitary kidney.

METHODS

Clinical characteristics of the patients were summarized. Whole-exome sequencing was performed to screen the disease-causing gene mutation, and reverse transcription polymerase chain reaction (RT-PCR) and Sanger sequencing were applied to analyze the impact of the identified mutation on gene transcription and splicing.

RESULTS

Polycystic changes were found in the solitary kidney of a girl initially presented with nephrotic-range proteinuria. Thereafter her mother and 2 other family members were diagnosed to be ADPKD. Whole-exome sequencing of the proband identified a heterozygous synonymous mutation (c.1716G>A, p.Lys572=) located in the splicing site of exon 7 in PKD2 gene, which was co-segregated with the PKD phenotype in the family. RT-PCR and direct sequencing of amplified products revealed that this heterozygous synonymous mutation led to exon7 skipping in PKD2 gene.

CONCLUSION

We reported an extremely rare child case of ADPKD2 in combination with solitary kidney and nephrotic-range proteinuria, and firstly confirmed the pathogenicity of a heterozygous synonymous mutation (c.1716G>A) in PKD2 gene. The results indicate that synonymous mutations should not be excluded from disease-causing if they are located in splicing site of an exon.