Mutations in multiple PKD genes may explain early and severe polycystic kidney disease

How Does ADPKD Severity Differ Between Family Members?

Thousands of pathogenic variants in more than 100 genes can cause kidney cysts with substantial variability in phenotype and risk of subsequent kidney failure. Despite an established genotype-phenotype correlation in cystic kidney diseases, incomplete penetrance and variable disease expressivity are present as is the case in all monogenic diseases. In family members with autosomal dominant polycystic kidney disease (ADPKD), the same causal variant is responsible in all affected family members; however, there can still be striking discordance in phenotype severity. This narrative review explores contributors to within-family discordance in ADPKD severity. Cases of biallelic and digenic inheritance, where 2 rare pathogenic variants in cystogenic genes are coexistent in one family, account for a small proportion of within-family discordance. Genetic background, including cis and trans factors and the polygenic propensity for comorbid disease, also plays a role but has not yet been exhaustively quantified. Environmental exposures, including diet; smoking; alcohol, salt, and protein intake, and comorbid diseases, including obesity, diabetes, hypertension, kidney stones, dyslipidemia, and additional coexistent kidney diseases all contribute to ADPKD phenotypic variability among family members. Given that many of the factors contributing to phenotype variability are preventable, modifiable, or treatable, health care providers and patients need to be aware of these factors and address them in the treatment of ADPKD.

Epidemiology and outcomes of pediatric autosomal recessive polycystic kidney disease in the Middle East and North Africa

The incidence of rare diseases is expected to be comparatively higher in the Middle East and North Africa (MENA) region than in other parts of the world, attributed to the high prevalence of consanguinity. Most MENA countries share social and economic statuses, cultural relativism, religious beliefs, and healthcare policies. Polycystic kidney diseases (PKDs) are the most common genetic causes of kidney failure, accounting for nearly 8.0% of dialysis cases. The development of PKDs is linked to variants in several genes, including PKD1, PKD2, PKHD1, DZIP1L, and CYS1. Autosomal recessive PKD (ARPKD) is the less common yet aggressive form of PKD. ARPKD has an estimated incidence between 1:10,000 and 1:40,000. Most patients with ARPKD require kidney replacement therapy earlier than patients with autosomal dominant polycystic kidney disease (ADPKD), often in their early years of life. This review gathered data from published research studies and reviews of ARPKD, highlighting the epidemiology, phenotypic presentation, investigations, genetic analysis, outcomes, and management. Although limited data are available, the published literature suggests that the incidence of ARPKD may be higher in the MENA region due to consanguineous marriages. Patients with ARPKD from the MENA region usually present at a later disease stage and have a relatively short time to progress to kidney failure. Limited data are available regarding the management practice in the region, which warrants further investigations.

Primary cilia and actin regulatory pathways in renal ciliopathies

Ciliopathies are a group of rare genetic disorders caused by defects to the structure or function of the primary cilium. They often affect multiple organs, leading to brain malformations, congenital heart defects, and anomalies of the retina or skeletal system. Kidney abnormalities are among the most frequent ciliopathic phenotypes manifesting as smaller, dysplastic, and cystic kidneys that are often accompanied by renal fibrosis. Many renal ciliopathies cause chronic kidney disease and often progress to end-stage renal disease, necessitating replacing therapies. There are more than 35 known ciliopathies; each is a rare hereditary condition, yet collectively they account for a significant proportion of chronic kidney disease worldwide. The primary cilium is a tiny microtubule-based organelle at the apex of almost all vertebrate cells. It serves as a "cellular antenna" surveying environment outside the cell and transducing this information inside the cell to trigger multiple signaling responses crucial for tissue morphogenesis and homeostasis. Hundreds of proteins and unique cellular mechanisms are involved in cilia formation. Recent evidence suggests that actin remodeling and regulation at the base of the primary cilium strongly impacts ciliogenesis. In this review, we provide an overview of the structure and function of the primary cilium, focusing on the role of actin cytoskeleton and its regulators in ciliogenesis. We then describe the key clinical, genetic, and molecular aspects of renal ciliopathies. We highlight what is known about actin regulation in the pathogenesis of these diseases with the aim to consider these recent molecular findings as potential therapeutic targets for renal ciliopathies.

Relevance of next generation sequencing (NGS) data re-analysis in the diagnosis of monogenic diseases leading to organ failure

BACKGROUND

In 2018, our center started a program to offer genetic diagnosis to patients with kidney and liver monogenic rare conditions, potentially eligible for organ transplantation. We exploited a clinical exome sequencing approach, followed by analyses of in silico gene panels tailored to clinical suspicions, obtaining detection rates in line with what reported in literature. However, a percentage of patients remains without a definitive genetic diagnosis. This work aims to evaluate the utility of NGS data re-analysis for those patients with an inconclusive or negative genetic test at the time of first analysis considering that (i) the advance of alignment and variant calling processes progressively improve the detection rate, limiting false positives and false negatives; (ii) gene panels are periodically updated and (iii) variant annotation may change over time.

METHODS

114 patients, recruited between 2018 and 2020, with an inconclusive or negative NGS report at the time of first analysis, were included in the study. Re-alignment and variant calling of previously generated sequencing raw data were performed using the GenomSys Variant Analyzer software.

RESULTS

21 previously not reported potentially causative variants were identified in 20 patients. In most cases (n = 19), causal variants were retrieved out of the re-classification from likely benign to variants of unknown significance (VUS). In one case, the variant was included because of inclusion in the analysis of a newly disease-associated gene, not present in the original gene panel, and in another one due to the improved data alignment process. Whenever possible, variants were validated with Sanger sequencing and family segregation studies. As of now, 16 out of 20 patients have been analyzed and variants confirmed in 8 patients. Specifically, in two pediatric patients, causative variants were de novo mutations while in the others, the variant was present also in other affected relatives. In the remaining patients, variants were present also in non-affected parents, raising questions on their re-classification.

CONCLUSIONS

Overall, these data indicate that periodic and systematic re-analysis of negative or inconclusive NGS data reports can lead to new variant identification or reclassification in a small but significant proportion of cases, with benefits for patients' management.

Assessing the Risk of Progression to Kidney Failure in Patients With Autosomal Dominant Polycystic Kidney Disease

While autosomal dominant polycystic kidney disease (ADPKD) is a dichotomous diagnosis, substantial variability in disease severity exists. Identification of inherited risk through family history, genetic testing, and environmental risk factors through clinical assessment are important components of risk assessment for optimal management of patients with ADPKD. Genetic testing is especially helpful in cases with diagnostic uncertainty, particularly in cases with no apparent family history, in young cases (age less than 25 years) where a definitive diagnosis is sought, or in atypical presentations with early, severe, or discordant findings. Currently, risk assessment in ADPKD may be performed with the use of age-adjusted estimated glomerular filtration rate thresholds, evidence of rapid estimated glomerular filtration rate decline on serial measurements, age- and height-adjusted total kidney volume by Mayo Clinic Imaging Classification, or evidence of early hypertension and urological complications combined with PKD1 or PKD2 mutation class; however, caveats exist with each of these approaches. Fine-tuning of risk stratification with advanced imaging features and biomarkers is the subject of research but is not yet ready for general clinical practice. While conservative treatment strategies will be advised for all patients, those with the greatest rate of disease progression will have the most benefit from aggressive disease-modifying therapy. In this narrative review, we will summarize the evidence behind the clinical assessment and risk stratification of patients with ADPKD.

Co-Inheritance of Pathogenic Variants in PKD1 and PKD2 Genes Determined by Parental Segregation and De Novo Origin: A Case Report

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary renal disease, and it is typically caused by PKD1 and PKD2 heterozygous variants. Nonetheless, the extensive phenotypic variability observed among affected individuals, even within the same family, suggests a more complex pattern of inheritance. We describe an ADPKD family in which the proband presented with an earlier and more severe renal phenotype (clinical diagnosis at the age of 14 and end-stage renal disease aged 24), compared to the other affected family members. Next-generation sequencing (NGS)-based analysis of polycystic kidney disease (PKD)-associated genes in the proband revealed the presence of a pathogenic PKD2 variant and a likely pathogenic variant in PKD1, according to the American College of Medical Genetics and Genomics (ACMG) criteria. The PKD2 nonsense p.Arg872Ter variant was segregated from the proband's father, with a mild phenotype. A similar mild disease presentation was found in the proband's aunts and uncle (the father's siblings). The frameshift p.Asp3832ProfsTer128 novel variant within PKD1 carried by the proband in addition to the pathogenic PKD2 variant was not found in either parent. This report highlights that the co-inheritance of two or more PKD genes or alleles may explain the extensive phenotypic variability among affected family members, thus emphasizing the importance of NGS-based techniques in the definition of the prognostic course.

A Role for Genetic Modifiers in Tubulointerstitial Kidney Diseases

With the increased availability of genomic sequencing technologies, the molecular bases for kidney diseases such as nephronophthisis and mitochondrially inherited and autosomal-dominant tubulointerstitial kidney diseases (ADTKD) has become increasingly apparent. These tubulointerstitial kidney diseases (TKD) are monogenic diseases of the tubulointerstitium and result in interstitial fibrosis and tubular atrophy (IF/TA). However, monogenic inheritance alone does not adequately explain the highly variable onset of kidney failure and extra-renal manifestations. Phenotypes vary considerably between individuals harbouring the same pathogenic variant in the same putative monogenic gene, even within families sharing common environmental factors. While the extreme end of the disease spectrum may have dramatic syndromic manifestations typically diagnosed in childhood, many patients present a more subtle phenotype with little to differentiate them from many other common forms of non-proteinuric chronic kidney disease (CKD). This review summarises the expanding repertoire of genes underpinning TKD and their known phenotypic manifestations. Furthermore, we collate the growing evidence for a role of modifier genes and discuss the extent to which these data bridge the historical gap between apparently rare monogenic TKD and polygenic non-proteinuric CKD (excluding polycystic kidney disease).

Experimental Models of Polycystic Kidney Disease: Applications and Therapeutic Testing

Polycystic kidney diseases (PKDs) are genetic disorders characterized by the formation and expansion of numerous fluid-filled renal cysts, damaging normal parenchyma and often leading to kidney failure. Although PKDs comprise a broad range of different diseases, with substantial genetic and phenotypic heterogeneity, an association with primary cilia represents a common theme. Great strides have been made in the identification of causative genes, furthering our understanding of the genetic complexity and disease mechanisms, but only one therapy so far has shown success in clinical trials and advanced to US Food and Drug Administration approval. A key step in understanding disease pathogenesis and testing potential therapeutics is developing orthologous experimental models that accurately recapitulate the human phenotype. This has been particularly important for PKDs because cellular models have been of limited value; however, the advent of organoid usage has expanded capabilities in this area but does not negate the need for whole-organism models where renal function can be assessed. Animal model generation is further complicated in the most common disease type, autosomal dominant PKD, by homozygous lethality and a very limited cystic phenotype in heterozygotes while for autosomal recessive PKD, mouse models have a delayed and modest kidney disease, in contrast to humans. However, for autosomal dominant PKD, the use of conditional/inducible and dosage models have resulted in some of the best disease models in nephrology. These have been used to help understand pathogenesis, to facilitate genetic interaction studies, and to perform preclinical testing. Whereas for autosomal recessive PKD, using alternative species and digenic models has partially overcome these deficiencies. Here, we review the experimental models that are currently available and most valuable for therapeutic testing in PKD, their applications, success in preclinical trials, advantages and limitations, and where further improvements are needed.

Modifiers of Autosomal Dominant Polycystic Kidney Disease Severity: The Role of PKD1 Hypomorphic Alleles

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic cause of kidney failure in adult life. Rarely, ADPKD can be diagnosed in utero or in infancy, and the genetic mechanism underlying such severe presentation has been shown to be related to reduced gene dosage. Biallelic PKD1 variants are often identified in early onset ADPKD, with one main pathogenic variant and a modifier hypomorphic variant showing an in trans configuration. We describe two unrelated individuals with early onset cystic kidney disease and unaffected parents, where a combination of next-generation sequencing of cystic genes including PKHD1, HNF1B and PKD1 allowed the identification of biallelic PKD1 variants. Furthermore, we review the medical literature in order to report likely PKD1 hypomorphic variants reported to date and estimate a minimal allele frequency of 1/130 for this category of variants taken as a group. This figure could help to orient genetic counseling, although the interpretation and the real clinical impact of rare PKD1 missense variants, especially if previously unreported, remain challenging.

Calcium signaling in polycystic kidney disease- cell death and survival

Polycystic kidney disease is typified by cysts in the kidney and extra-renal manifestations including hypertension and heart failure. The main genetic underpinning this disease are loss-of function mutations to the two polycystin proteins, polycystin 1 and polycystin 2. Molecularly, the disease is characterized by changes in multiple signaling pathways including down regulation of calcium signaling, which, in part, is contributed by the calcium permeant properties of polycystin 2. These signaling pathways enable the cystic cells to survive and avoid cell death. This review focuses on the studies that have emerged in the past 5 years describing how the structural insights gained from PC-1 and PC-2 inform the calcium dependent molecular pathways of autophagy and the unfolded protein response that are regulated by the polycystin proteins and how it leads to cell survival and/or cell death.

Complement-Mediated Thrombotic Microangiopathy with 10 Years of Stable Renal Function After a Year-Long Treatment with Eculizumab with Coincidental Polycystic Kidney Disease

BACKGROUND Complement-mediated thrombotic microangiopathy (cTMA), is a genetic disease that results when an unchecked alternative complement pathway is triggered by an external factor, resulting in endothelial cell injury with microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure, though other organ systems may be involved. CASE REPORT A 5-year-old girl presented with non-bloody diarrhea, hemolysis, renal failure, and thrombocytopenia. She was negative for Shiga toxin. She was diagnosed with cTMA, and this diagnosis was confirmed later by a mutation in the complement factor H (CFH) gene. The patient was started on eculizumab 8 weeks after onset of symptoms. A month later, she was able to stop hemodialysis. Eculizumab was given for a year, and then, because of clinical remission, was stopped. At the time of stopping hemodialysis, serum creatinine was 2.07 mg/dL; at the end of eculizumab therapy, it was 1.23 mg/dL. Now, 10 years later, it is 1.10 mg/dL. Glomerular filtration rate by Schwartz equation was 52 mL/min/1.73 m² after eculizumab and 60 mL/min/1.73 m² currently. The cTMA lab parameters normalized after 2 doses of eculizumab and have remained normal for 10 years. Two years ago, on routine ultrasound, renal cysts were noted. Recent genetic testing re-confirmed the CFH mutation and additionally showed a polycystic kidney disease (PKD1) mutation. Notably, there is no family history of either. Currently, the patient has mild proteinuria. CONCLUSIONS Instead of lifelong eculizumab treatment, we successfully managed the patient's condition with a year of eculizumab and intensive followup on sixty occasions over a decade. This approach can work if there are no relapses. Genetic tests revealed mutations for cTMA and autosomal dominant polycystic kidney disease (ADPKD)/PKD1 in the same patient. These have not been reported before, to the best of our knowledge.

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.

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.

Novel PKD2 Missense Mutation p.Ile424Ser in an Individual with Multiple Hepatic Cysts: A Case Report

We report a novel missense mutation, p.Ile424Ser, in the PKD2 gene of an autosomal dominant polycystic kidney disease (ADPKD) patient with multiple liver cysts. A 57-year-old woman presented to our university hospital with abdominal fullness, decreasing appetite, and dyspnea for three months. A percutaneous drainage of hepatic cysts was performed with no significant symptomatic relief. A computed tomography (CT) scan revealed a hepatic cyst in the lateral portion of the liver with appreciable compression of the stomach. Prior to this admission, the patient had undergone three drainage procedures with serial CT-based follow-up of the cysts over the past 37 years. With a presumptive diagnosis of extrarenal manifestation of ADPKD, we performed both a hepatic cystectomy and a hepatectomy. Because the patient reported a family history of hepatic cysts, we conducted a postoperative genetic analysis. A novel missense mutation, p.Ile424Ser, was detected in the PKD2 gene. Mutations in either the PKD1 or PKD2 genes account for most cases of ADPKD. To the extent of our knowledge, this point mutation has not been reported in the general population. Our in-silico analysis suggests a hereditary likely pathogenic mutation.

Multidisciplinary approaches for elucidating genetics and molecular pathogenesis of urinary tract malformations

Advances in clinical diagnostics and molecular tools have improved our understanding of the genetically heterogeneous causes underlying congenital anomalies of kidney and urinary tract (CAKUT). However, despite a sharp incline of CAKUT reports in the literature within the past 2 decades, there remains a plateau in the genetic diagnostic yield that is disproportionate to the accelerated ability to generate robust genome-wide data. Explanations for this observation include (i) diverse inheritance patterns with incomplete penetrance and variable expressivity, (ii) rarity of single-gene drivers such that large sample sizes are required to meet the burden of proof, and (iii) multigene interactions that might produce either intra- (e.g., copy number variants) or inter- (e.g., effects in trans) locus effects. These challenges present an opportunity for the community to implement innovative genetic and molecular avenues to explain the missing heritability and to better elucidate the mechanisms that underscore CAKUT. Here, we review recent multidisciplinary approaches at the intersection of genetics, genomics, in vivo modeling, and in vitro systems toward refining a blueprint for overcoming the diagnostic hurdles that are pervasive in urinary tract malformation cohorts. These approaches will not only benefit clinical management by reducing age at molecular diagnosis and prompting early evaluation for comorbid features but will also serve as a springboard for therapeutic development.

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.

Monoallelic IFT140 pathogenic variants are an important cause of the autosomal dominant polycystic kidney-spectrum phenotype

Autosomal dominant polycystic kidney disease (ADPKD), characterized by progressive cyst formation/expansion, results in enlarged kidneys and often end stage kidney disease. ADPKD is genetically heterogeneous; PKD1 and PKD2 are the common loci (∼78% and ∼15% of families) and GANAB, DNAJB11, and ALG9 are minor genes. PKD is a ciliary-associated disease, a ciliopathy, and many syndromic ciliopathies have a PKD phenotype. In a multi-cohort/-site collaboration, we screened ADPKD-diagnosed families that were naive to genetic testing (n = 834) or for whom no PKD1 and PKD2 pathogenic variants had been identified (n = 381) with a PKD targeted next-generation sequencing panel (tNGS; n = 1,186) or whole-exome sequencing (WES; n = 29). We identified monoallelic IFT140 loss-of-function (LoF) variants in 12 multiplex families and 26 singletons (1.9% of naive families). IFT140 is a core component of the intraflagellar transport-complex A, responsible for retrograde ciliary trafficking and ciliary entry of membrane proteins; bi-allelic IFT140 variants cause the syndromic ciliopathy, short-rib thoracic dysplasia (SRTD9). The distinctive monoallelic phenotype is mild PKD with large cysts, limited kidney insufficiency, and few liver cysts. Analyses of the cystic kidney disease probands of Genomics England 100K showed that 2.1% had IFT140 LoF variants. Analysis of the UK Biobank cystic kidney disease group showed probands with IFT140 LoF variants as the third most common group, after PKD1 and PKD2. The proximity of IFT140 to PKD1 (∼0.5 Mb) in 16p13.3 can cause diagnostic confusion, and PKD1 variants could modify the IFT140 phenotype. Importantly, our studies link a ciliary structural protein to the ADPKD spectrum.

A practical approach to the genomics of kidney disorders

Rapid technological advances in genomic testing continue to increase our understanding of the genetic basis of a wide range of kidney disorders. Establishing a molecular diagnosis benefits the individual by bringing an end to what is often a protracted diagnostic odyssey, facilitates accurate reproductive counselling for families and, in the future, is likely to lead to the delivery of more targeted management and surveillance regimens. The selection of the most appropriate testing modality requires an understanding both of the technologies available and of the genetic architecture and heterogeneity of kidney disease. Whilst we are witnessing a far greater diagnostic yield with broader genetic testing, such approaches invariably generate variants of uncertain significance and secondary incidental findings, which are not only difficult to interpret but present ethical challenges with reporting and feeding back to patients and their families. Here, we review the spectrum of nephrogenetic disorders, consider the optimal approach to genetic testing, explore the clinical utility of obtaining a molecular diagnosis, reflect on the challenges of variant interpretation and look to the future of this dynamic field.

The wind of change in the management of autosomal dominant polycystic kidney disease in childhood

Significant progress has been made in understanding the genetic basis of autosomal dominant polycystic kidney disease (ADPKD), quantifying disease manifestations in children, exploring very-early onset ADPKD as well as pharmacological delay of disease progression in adults. At least 20% of children with ADPKD have relevant, yet mainly asymptomatic disease manifestations such as hypertension or proteinuria (in line with findings in adults with ADPKD, where hypertension and cardiovascular damage precede decline in kidney function). We propose an algorithm for work-up and management based on current recommendations that integrates the need to screen regularly for hypertension and proteinuria in offspring of affected parents with different options regarding diagnostic testing, which need to be discussed with the family with regard to ethical and practical aspects. Indications and scope of genetic testing are discussed. Pharmacological management includes renin-angiotensin system blockade as first-line therapy for hypertension and proteinuria. The vasopressin receptor antagonist tolvaptan is licensed for delaying disease progression in adults with ADPKD who are likely to experience kidney failure. A clinical trial in children is currently ongoing; however, valid prediction models to identify children likely to suffer kidney failure are lacking. Non-pharmacological interventions in this population also deserve further study.

Translational research approaches to study pediatric polycystic kidney disease

Polycystic kidney diseases (PKD) are severe forms of genetic kidney disorders. The two main types of PKD are autosomal recessive and autosomal dominant PKD (ARPKD, ADPKD). While ARPKD typically is a disorder of early childhood, patients with ADPKD often remain pauci-symptomatic until adulthood even though formation of cysts in the kidney already begins in children. There is clinical and genetic overlap between both entities with very variable clinical courses. Subgroups of very early onset ADPKD may for example clinically resemble ARPKD. The basis of the clinical variability in both forms of PKD is not well understood and there are also limited prediction markers for disease progression for daily clinical life or surrogate endpoints for clinical trials in ARPKD or early ADPKD.

As targeted therapeutic approaches to slow disease progression in PKD are emerging, it is becoming more important to reliably identify patients at risk for rapid progression as they might benefit from early therapy. Over the past years regional, national and international data collections to jointly analyze the clinical courses of PKD patients have been set up. The clinical observations are complemented by genetic studies and biorepositories as well as basic science approaches to elucidate the underlying molecular mechanisms in the PKD field. These approaches may serve as a basis for the development of novel therapeutic interventions in specific subgroups of patients. In this article we summarize some of the recent developments in the field with a focus on kidney involvement in PKD during childhood and adolescence and findings obtained in pediatric cohorts.

Elamipretide treatment during pregnancy ameliorates the progression of polycystic kidney disease in maternal and neonatal mice with PKD1 mutations

Pregnancy is proposed to aggravate cyst progression in autosomal dominant polycystic kidney disease (ADPKD) but Tolvaptan, the only FDA-approved drug for adult ADPKD, is not recommended for pregnant ADPKD patients because of potential fetal harm. Since pregnancy itself may increase the risk for ADPKD progression, we investigated the safety and efficacy of Elamipretide, a mitochondrial-protective tetrapeptide. Elamipretide was found to ameliorate the progression of kidney disease in pregnant Pkd1^RC/RC mice, in parallel with attenuation of ERK1/2 phosphorylation and improvement of mitochondrial supercomplex formation. Furthermore, Elamipretide was found to pass through the placenta and breast milk and ameliorate aggressive infantile polycystic kidney disease without any observed teratogenic or harmful effect. Elamipretide has an excellent safety profile and is currently tested in multiple phase II and phase III clinical trials. These preclinical studies support a potential clinical trial of Elamipretide for the treatment of ADPKD, particularly for patients that cannot take Tolvaptan.

Next-Generation Sequencing-Based Genetic Diagnostic Strategies of Inherited Kidney Diseases

BACKGROUND

At least 10% of adults and most of the children who receive renal replacement therapy have inherited kidney diseases. These disorders substantially decrease their life quality and have a large effect on the health-care system. Multisystem complications, with typical challenges for rare disorders, including variable phenotypes and fragmented clinical and biological data, make genetic diagnosis of inherited kidney disorders difficult. In current clinical practice, genetic diagnosis is important for clinical management, estimating disease development, and applying personal treatment for patients.

SUMMARY

Inherited kidney diseases comprise hundreds of different disorders. Here, we have summarized various monogenic kidney disorders. These disorders are caused by mutations in genes coding for a wide range of proteins including receptors, channels/transporters, enzymes, transcription factors, and structural components that might also have a role in extrarenal organs (bone, eyes, brain, skin, ear, etc.). With the development of next-generation sequencing technologies, genetic testing and analysis become more accessible, promoting our understanding of the pathophysiologic mechanisms of inherited kidney diseases. However, challenges exist in interpreting the significance of genetic variants and translating them to guide clinical managements. Alport syndrome is chosen as an example to introduce the practical application of genetic testing and diagnosis on inherited kidney diseases, considering its clinical features, genetic backgrounds, and genetic testing for making a genetic diagnosis.

KEY MESSAGES

Recent advances in genomics have highlighted the complexity of Mendelian disorders, which is due to allelic heterogeneity (distinct mutations in the same gene produce distinct phenotypes), locus heterogeneity (mutations in distinct genes result in similar phenotypes), reduced penetrance, variable expressivity, modifier genes, and/or environmental factors. Implementation of precision medicine in clinical nephrology can improve the clinical diagnostic rate and treatment efficiency of kidney diseases, which requires a good understanding of genetics for nephrologists.

Predictors of progression in autosomal dominant and autosomal recessive polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD) are characterized by bilateral cystic kidney disease leading to progressive kidney function decline. These diseases also have distinct liver manifestations. The range of clinical presentation and severity of both ADPKD and ARPKD is much wider than was once recognized. Pediatric and adult nephrologists are likely to care for individuals with both diseases in their lifetimes. This article will review genetic, clinical, and imaging predictors of kidney and liver disease progression in ADPKD and ARPKD and will briefly summarize pharmacologic therapies to prevent progression.

Neonatal polycystic kidney disease: a novel variant

Polycystic kidney disease (PKD) is a condition typified by multiple renal cysts and renal enlargement. Classification is usually determined by mode of inheritance-autosomal dominant PKD (ADPKD) or autosomal recessive PKD (ARPKD). ARPKD frequently presents in fetal life, but here we report a rare case of a family with two siblings diagnosed with ADPKD manifesting in utero with novel genetic findings. During the first pregnancy, enlarged cystic kidneys were noted at the gestational age (GA) of 18 weeks, which became progressively larger and anyhdramnios ensued by GA of 25 weeks. The couple opted to terminate the pregnancy. The second pregnancy similarly presented with bilateral enlarged cystic kidneys, but amniotic fluid remained normal throughout and she delivered at GA of 36 weeks. Genetic testing revealed the fetus to be heterozygous in AD PKD1, which is known to cause ADPKD and heterozygous for a hypomorphic allele for ADPKD of uncertain significance. The fetus was also found to be heterozygous in the AR PKHD1 gene with a variant not previously described in the literature. Where fetal features consistent with ARPKD are identified in the setting of familial ADPKD, this fetal manifestation of ADPKD, resulting from combined variants in the PKD1 gene, should be considered.

Molecular Pathophysiology of Autosomal Recessive Polycystic Kidney Disease

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

Insights into Autosomal Dominant Polycystic Kidney Disease from Genetic Studies

Autosomal dominant polycystic kidney disease is the most common monogenic cause of ESKD. Genetic studies from patients and animal models have informed disease pathobiology and strongly support a "threshold model" in which cyst formation is triggered by reduced functional polycystin dosage below a critical threshold within individual tubular epithelial cells due to (1) germline and somatic PKD1 and/or PKD2 mutations, (2) mutations of genes (e.g., SEC63, SEC61B, GANAB, PRKCSH, DNAJB11, ALG8, and ALG9) in the endoplasmic reticulum protein biosynthetic pathway, or (3) somatic mosaicism. Genetic testing has the potential to provide diagnostic and prognostic information in cystic kidney disease. However, mutation screening of PKD1 is challenging due to its large size and complexity, making it both costly and labor intensive. Moreover, conventional Sanger sequencing-based genetic testing is currently limited in elucidating the causes of atypical polycystic kidney disease, such as within-family disease discordance, atypical kidney imaging patterns, and discordant disease severity between total kidney volume and rate of eGFR decline. In addition, environmental factors, genetic modifiers, and somatic mosaicism also contribute to disease variability, further limiting prognostication by mutation class in individual patients. Recent innovations in next-generation sequencing are poised to transform and extend molecular diagnostics at reasonable costs. By comprehensive screening of multiple cystic disease and modifier genes, targeted gene panel, whole-exome, or whole-genome sequencing is expected to improve both diagnostic and prognostic accuracy to advance personalized medicine in autosomal dominant polycystic kidney disease.

Molecular genetics of renal ciliopathies

Renal ciliopathies are a heterogenous group of inherited disorders leading to an array of phenotypes that include cystic kidney disease and renal interstitial fibrosis leading to progressive chronic kidney disease and end-stage kidney disease. The renal tubules are lined with epithelial cells that possess primary cilia that project into the lumen and act as sensory and signalling organelles. Mutations in genes encoding ciliary proteins involved in the structure and function of primary cilia cause ciliopathy syndromes and affect many organ systems including the kidney. Recognised disease phenotypes associated with primary ciliopathies that have a strong renal component include autosomal dominant and recessive polycystic kidney disease and their various mimics, including atypical polycystic kidney disease and nephronophthisis. The molecular investigation of inherited renal ciliopathies often allows a precise diagnosis to be reached where renal histology and other investigations have been unhelpful and can help in determining kidney prognosis. With increasing molecular insights, it is now apparent that renal ciliopathies form a continuum of clinical phenotypes with disease entities that have been classically described as dominant or recessive at both extremes of the spectrum. Gene-dosage effects, hypomorphic alleles, modifier genes and digenic inheritance further contribute to the genetic complexity of these disorders. This review will focus on recent molecular genetic advances in the renal ciliopathy field with a focus on cystic kidney disease phenotypes and the genotypes that lead to them. We discuss recent novel insights into underlying disease mechanisms of renal ciliopathies that might be amenable to therapeutic intervention.

Biallelic inheritance of hypomorphic PKD1 variants is highly prevalent in very early onset polycystic kidney disease

PURPOSE

To investigate the prevalence of biallelic PKD1 and PKD2 variants underlying very early onset (VEO) polycystic kidney disease (PKD) in a large international pediatric cohort referred for clinical indications over a 10-year period (2010-2020).

METHODS

All samples were tested by Sanger sequencing and multiplex ligation-dependent probe amplification (MLPA) of PKD1 and PKD2 genes and/or a next-generation sequencing panel of 15 additional cystic genes including PKHD1 and HNF1B. Two patients underwent exome or genome sequencing.

RESULTS

Likely causative PKD1 or PKD2 variants were detected in 30 infants with PKD-VEO, 16 of whom presented in utero. Twenty-one of 30 (70%) had two variants with biallelic in trans inheritance confirmed in 16/21, 1 infant had biallelic PKD2 variants, and 2 infants had digenic PKD1/PKD2 variants. There was no known family history of ADPKD in 13 families (43%) and a de novo pathogenic variant was confirmed in 6 families (23%).

CONCLUSION

We report a high prevalence of hypomorphic PKD1 variants and likely biallelic disease in infants presenting with PKD-VEO with major implications for reproductive counseling. The diagnostic interpretation and reporting of these variants however remains challenging using current American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) and Association of Clinical Genetic Science (ACGS) variant classification guidelines in PKD-VEO and other diseases affected by similar variants with incomplete penetrance.

Patients with Protein-Truncating PKD1 Mutations and Mild ADPKD

BACKGROUND AND OBJECTIVES

Progression of autosomal dominant polycystic kidney disease (ADPKD) is highly variable. On average, protein-truncating PKD1 mutations are associated with the most severe kidney disease among all mutation classes. Here, we report that patients with protein-truncating PKD1 mutations may also have mild kidney disease, a finding not previously well recognized.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

From the extended Toronto Genetic Epidemiologic Study of Polycystic Kidney Disease, 487 patients had PKD1 and PKD2 sequencing and typical ADPKD imaging patterns by magnetic resonance imaging or computed tomography. Mayo Clinic Imaging Classification on the basis of age- and height-adjusted total kidney volume was used to assess their cystic disease severity; classes 1A or 1B were used as a proxy to define mild disease. Multivariable linear regression was performed to test the effects of age, sex, and mutation classes on log-transformed height-adjusted total kidney volume and eGFR.

RESULTS

Among 174 study patients with typical imaging patterns and protein-truncating PKD1 mutations, 32 (18%) were found to have mild disease on the basis of imaging results (i.e., Mayo Clinic Imaging class 1A-1B), with their mutations spanning the entire gene. By multivariable analyses of age, sex, and mutation class, they displayed mild disease similar to patients with PKD2 mutations and Mayo Clinic Imaging class 1A-1B. Most of these mildly affected patients with protein-truncating PKD1 mutations reported a positive family history of ADPKD in preceding generations and displayed significant intrafamilial disease variability.

CONCLUSIONS

Despite having the most severe mutation class, 18% of patients with protein-truncating PKD1 mutations had mild disease on the basis of clinical and imaging assessment.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2021_02_18_CJN11100720_final.mp3.

Polyvisceral polycystic disease: a case study and review

Polycystic kidney disease (PKD) occurs in one per 20,000 births. Presence of cysts in other organs like adrenal, liver and bladder is even rarer. On reviewing the literature, there is evidence of PKD occurring in conjunction with polycystic liver disease but cysts in multiple viscera are, so far, not reported. A fetal autopsy of a 36-week fetus showed the presence of multiple cysts in the kidney, liver, adrenal and bladder. Further histopathology reports confirmed the diagnosis of polycystic kidney disease. The history of a previous intrauterine death, of another child at 28-week gestation, suggests the presence of familial type. Serial prenatal ultrasonogram did not detect the abnormalities, emphasizing the important role of fetal autopsy in a case with an incomplete obstetric history. The diagnosis of a fetal abnormality aids to counselling the parents to be aware of possible recurrences in new pregnancies.

Polycystic liver disease genes: Practical considerations for genetic testing

The development of a polycystic liver is a characteristic of the monogenic disorders: autosomal dominant polycystic kidney disease (ADPKD), autosomal recessive polycystic kidney disease (ARPKD), and autosomal dominant polycystic liver disease (ADPLD). Respectively two and one genes mainly cause ADPKD and ARPKD. In contrast, ADPLD is caused by at least six different genes which combined do not even explain the disease development in over half of the ADPLD population. Genetic testing is mainly performed to confirm the likelihood of developing PKD and if renal therapy is essential. However, pure ADPLD patients are frequently not genetically screened as knowledge about the genotype-phenotype correlation is currently limited. This paper will clarify the essence of genetic testing in ADPLD patients.

Clinical utility of genetic testing in early-onset kidney disease: seven genes are the main players

BACKGROUND

Inherited kidney diseases are one of the leading causes of chronic kidney disease (CKD) that manifests before the age of 30 years. Precise clinical diagnosis of early-onset CKD is complicated due to the high phenotypic overlap, but genetic testing is a powerful diagnostic tool. We aimed to develop a genetic testing strategy to maximize the diagnostic yield for patients presenting with early-onset CKD and to determine the prevalence of the main causative genes.

METHODS

We performed genetic testing of 460 patients with early-onset CKD of suspected monogenic cause using next-generation sequencing of a custom-designed kidney disease gene panel in addition to targeted screening for c.428dupC MUC1.

RESULTS

We achieved a global diagnostic yield of 65% (300/460), which varied depending on the clinical diagnostic group: 77% in cystic kidney diseases, 76% in tubulopathies, 67% in autosomal dominant tubulointerstitial kidney disease, 61% in glomerulopathies, and 38% in congenital anomalies of the kidney and urinary tract. Among the 300 genetically diagnosed patients, the clinical diagnosis was confirmed in 77%, a specific diagnosis within a clinical diagnostic group was identified in 15%, and 7% of cases were reclassified. Of the 64 causative genes identified in our cohort, seven (COL4A3, COL4A4, COL4A5, HNF1B, PKD1, PKD2, and PKHD1) accounted for 66% (198/300) of the genetically diagnosed patients.

CONCLUSIONS

Two-thirds of patients with early-onset CKD in this cohort had a genetic cause. Just seven genes were responsible for the majority of diagnoses. Establishing a genetic diagnosis is crucial to define the precise etiology of CKD, which allows accurate genetic counseling and improved patient management.

Renal cystic diseases during the perinatal and neonatal period

Renal cystic diseases are a clinically and genetically diverse group of renal diseases that can manifest in utero, infancy, or throughout childhood and adulthood. These diseases may be unilateral or bilateral with a single cyst or multiple cysts, or with increased echogenicity of the renal cortex without macroscopic cysts. Certain cystic renal diseases are life-threatening, with many developing chronic kidney and hepatic disease if not recognized early enough. Therefore, due to the prevalence and life-altering complications of this specific group of diseases in vulnerable populations, it is crucial for clinicians and healthcare providers to have an overall understanding of cystic diseases and how to pre-emptively detect and manage these conditions. In this review, we discuss in detail the epidemiology, genetics and pathophysiology, diagnosis, presentation, and management of numerous genetic and sporadic renal cystic diseases, such as polycystic kidney disease, multicystic dysplastic kidney, and calyceal diverticula, with an emphasis on prenatal care and pregnancy counseling.

Early clinical management of autosomal recessive polycystic kidney disease

Autosomal recessive polycystic kidney disease (ARPKD) is a rare but highly relevant disorder in pediatric nephrology. This genetic disease is mainly caused by variants in the PKHD1 gene and is characterized by fibrocystic hepatorenal phenotypes with major clinical variability. ARPKD frequently presents perinatally, and the management of perinatal and early disease symptoms may be challenging. This review discusses aspects of early manifestations in ARPKD and its clincial management with a special focus on kidney disease.

Roles of telomeres and telomerase in age‑related renal diseases (Review)

Age‑related renal diseases, which account for various progressive renal disorders associated with cellular and organismal senescence, are becoming a substantial public health burden. However, their aetiologies are complicated and their pathogeneses remain poorly understood. Telomeres and telomerase are known to be essential for maintaining the integrity and stability of eukaryotic genomes and serve crucial roles in numerous related signalling pathways that activate renal functions, such as repair and regeneration. Previous studies have reported that telomere dysfunction served a role in various types of age‑related kidney disease through various different molecular pathways. The present review aimed to summarise the current knowledge of the association between telomeres and ageing‑related kidney diseases and explored the contribution of dysfunctional telomeres to these diseases. The findings may help to provide novel strategies for treating patients with renal disease.

Imaging Identification of Rapidly Progressing Autosomal Dominant Polycystic Kidney Disease: Simple Eligibility Criterion for Tolvaptan

BACKGROUND

Tolvaptan was approved for the treatment of autosomal dominant polycystic kidney disease (ADPKD). However, the official indication of "rapidly progressive disease" is described differently in the clinical guidelines. We aim to define "rapidly progressive disease" by risk of ESRD, which is evaluated using estimated height-adjusted total kidney volume (HtTKV) growth rate.

METHODS

The risk of ESRD was retrospectively analyzed in 617 initially non-ESRD adults with ADPKD and observed with standard of care between 2007 and 2018. The estimated annual growth rate of the HtTKV, termed as eHTKV-α (%/year), is derived from the following equation: [HtTKV at age t] = K(1 + eHTKV-α/100)t, where K = 150 mL/m is used in Mayo Imaging Classification and K = 130 mL/m is proposed for individually stable eHTKV-α value from baseline. The accuracy of eHTKV-α to predict ESRD for censored ages was analyzed using time-dependent receiver-operating characteristic curves (ROC). The cutoff point of initially measured eHTKV-α to predict ESRD was assessed using Kaplan-Meier and Cox's proportional hazards models. Performance characteristics of the cutoff point for censored ages were calculated using time-dependent ROC and validated by the bootstrap method.

RESULTS

The area under the time-dependent ROC of eHTKV-α to predict ESRD at age 65 was 0.89 ± 0.04 (K = 130). The mean renal survival was less than 70 years at eHTKV-α ≥4.0%/year (K = 130). Mean renal survival was approximately 12 years shorter, and hazard ratio of ESRD was more than 5-time higher at this cutoff point than at lower point. Time-dependent sensitivity for age 65 and cutoff point of 4.0%/year (K = 130) was 93.4 ± 0.3%. Between cutoff points ≥4.0%/year (K = 130) and ≥3.5%/year (K = 150), there was no significant difference in performance characteristics and accuracy to predict ESRD.

CONCLUSION

eHTKV-α well predicts ESRD. Initially, measured eHTKV-α ≥4.0%/year (K = 130) defines high-risk ESRD. Without additional conditions, a single eHTKV-α cutoff point identifies subjects that are most likely to benefit from tolvaptan.

Rare genetic causes of complex kidney and urological diseases

Although often considered a single-entity, chronic kidney disease (CKD) comprises many pathophysiologically distinct disorders that result in persistently abnormal kidney structure and/or function, and encompass both monogenic and polygenic aetiologies. Rare inherited forms of CKD frequently span diverse phenotypes, reflecting genetic phenomena including pleiotropy, incomplete penetrance and variable expressivity. Use of chromosomal microarray and massively parallel sequencing technologies has revealed that genomic disorders and monogenic aetiologies contribute meaningfully to seemingly complex forms of CKD across different clinically defined subgroups and are characterized by high genetic and phenotypic heterogeneity. Investigations of prevalent genomic disorders in CKD have integrated genetic, bioinformatic and functional studies to pinpoint the genetic drivers underlying their renal and extra-renal manifestations, revealing both monogenic and polygenic mechanisms. Similarly, massively parallel sequencing-based analyses have identified gene- and allele-level variation that contribute to the clinically diverse phenotypes observed for many monogenic forms of nephropathy. Genome-wide sequencing studies suggest that dual genetic diagnoses are found in at least 5% of patients in whom a genetic cause of disease is identified, highlighting the fact that complex phenotypes can also arise from multilocus variation. A multifaceted approach that incorporates genetic and phenotypic data from large, diverse cohorts will help to elucidate the complex relationships between genotype and phenotype for different forms of CKD, supporting personalized medicine for individuals with kidney disease.

Bi-allelic pathogenic variations in DNAJB11 cause Ivemark II syndrome, a renal-hepatic-pancreatic dysplasia

DNAJB11 (DnaJ Heat Shock Protein Family (Hsp40) Member B11) heterozygous loss of function variations have been reported in autosomal dominant cystic kidney disease with extensive fibrosis, associated with maturation and trafficking defect involving both the autosomal dominant polycystic kidney disease protein polycystin-1 and the autosomal dominant tubulointerstitial kidney disease protein uromodulin. Here we show that biallelic pathogenic variations in DNAJB11 lead to a severe fetal disease including enlarged cystic kidneys, dilation and proliferation of pancreatic duct cells, and liver ductal plate malformation, an association known as Ivemark II syndrome. Cysts of the kidney were developed exclusively from uromodulin negative tubular segments. In addition, tubular cells from the affected kidneys had elongated primary cilia, a finding previously reported in ciliopathies. Thus, our data show that the recessive disease associated with DNAJB11 variations is a ciliopathy rather than a disease of the autosomal dominant tubulointerstitial kidney disease spectrum, and prompt screening of DNAJB11 in fetal hyperechogenic/cystic kidneys.

The carboxy-terminus of the human ARPKD protein fibrocystin can control STAT3 signalling by regulating SRC-activation

Autosomal recessive polycystic kidney disease (ARPKD) is mainly caused by variants in the PKHD1 gene, encoding fibrocystin (FC), a large transmembrane protein of incompletely understood cellular function. Here, we show that a C‐terminal fragment of human FC can suppress a signalling module of the kinase SRC and signal transducer and activator of transcription 3 (STAT3). Consistently, we identified truncating genetic variants specifically affecting the cytoplasmic tail in ARPKD patients, found SRC and the cytoplasmic tail of fibrocystin in a joint dynamic protein complex and observed increased activation of both SRC and STAT3 in cyst‐lining renal epithelial cells of ARPKD patients.

Preimplantation Genetic Testing for Monogenic Kidney Disease

BACKGROUND AND OBJECTIVES

A genetic cause can be identified for an increasing number of pediatric and adult-onset kidney diseases. Preimplantation genetic testing (formerly known as preimplantation genetic diagnostics) is a reproductive technology that helps prospective parents to prevent passing on (a) disease-causing mutation(s) to their offspring. Here, we provide a clinical overview of 25 years of preimplantation genetic testing for monogenic kidney disease in The Netherlands.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This is a retrospective cohort study of couples counseled on preimplantation genetic testing for monogenic kidney disease in the national preimplantation genetic testing expert center (Maastricht University Medical Center+) from January 1995 to June 2019. Statistical analysis was performed through chi-squared tests.

RESULTS

In total, 98 couples were counseled regarding preimplantation genetic testing, of whom 53% opted for preimplantation genetic testing. The most frequent indications for referral were autosomal dominant polycystic kidney disease (38%), Alport syndrome (26%), and autosomal recessive polycystic kidney disease (9%). Of couples with at least one preimplantation genetic testing cycle with oocyte retrieval, 65% experienced one or more live births of an unaffected child. Of couples counseled, 38% declined preimplantation genetic testing for various personal and technical reasons.

CONCLUSIONS

Referrals, including for adult-onset disease, have increased steadily over the past decade. Though some couples decline preimplantation genetic testing, in the couples who proceed with at least one preimplantation genetic testing cycle, almost two thirds experienced at least one live birth rate.

Metabolic Changes in Polycystic Kidney Disease as a Potential Target for Systemic Treatment

Autosomal recessive and autosomal dominant polycystic kidney disease (ARPKD, ADPKD) are systemic disorders with pronounced hepatorenal phenotypes. While the main underlying genetic causes of both ARPKD and ADPKD have been well-known for years, the exact molecular mechanisms resulting in the observed clinical phenotypes in the different organs, remain incompletely understood. Recent research has identified cellular metabolic changes in PKD. These findings are of major relevance as there may be an immediate translation into clinical trials and potentially clinical practice. Here, we review important results in the field regarding metabolic changes in PKD and their modulation as a potential target of systemic treatment.

Novel PKD1 Mutations in Patients with Autosomal Dominant Polycystic Kidney Disease

OBJECTIVE

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic kidney disease. Identifying mutated causative genes can provide diagnostic and prognostic information. In this study, we describe the clinical application of a next generation sequencing (NGS)-based, targeted multi-gene panel test for the genetic diagnosis of patients with ADPKD.

METHODS

We applied genetic analysis on 26 unrelated known or suspected patients with ADPKD. A total of 10 genes related to cystic change of kidney were targeted. Detected variants were classified according to standard guidelines.

RESULTS

We identified 19 variants (detection rate: 73.1%), including PKD1 (n = 18) and PKD2 (n = 1). Of the 18 PKD1 variants, 8 were novel.

CONCLUSION

Multigene panel test can be a comprehensive tool in a clinical setting for genetic diagnosis of ADPKD. It allows us to identify clinically significant novel variants and confirm the diagnosis, and these objectives are difficult to achieve using conventional diagnostic tools.

Diverse Receptor Tyrosine Kinase Phosphorylation in Urine-Derived Tubular Epithelial Cells from Autosomal Dominant Polycystic Kidney Disease Patients

BACKGROUNDS

The clinical features of autosomal dominant polycystic kidney disease (ADPKD) differ among patients even if they have the same gene mutation in PKD1 or PKD2. This suggests that there is diversity in the expression of other modifier genes or in the underlying molecular mechanisms of ADPKD, but these are not well understood.

METHODS

We primarily cultured solute carrier family 12 member 3 (SLC12A3)-positive urine-derived distal tubular epithelial cells from 6 ADPKD patients and 4 healthy volunteers and established immortalized cell lines. The diversity in receptor tyrosine kinase (RTK) phosphorylation by phospho-RTK array in immortalized tubular epithelial cells was analyzed.

RESULTS

We noted diversity in the activation of several molecules, including Met, a receptor of hepatocyte growth factor (HGF). Administration of golvatinib, a selective Met inhibitor, or transfection of small interfering RNA for Met suppressed cell proliferation and downstream signaling only in the cell lines in which hyperphosphorylation of Met was observed. In three-dimensional culture of Madin-Darby canine kidney (MDCK) cells as a cyst formation model of ADPKD, HGF activated Met, resulting in an increased total cyst number and total cyst volume. Administration of golvatinib inhibited these phenotypes in MDCK cells.

CONCLUSION

Analysis of urine-derived tubular epithelial cells demonstrated diverse RTK phosphorylation in ADPKD, and Met phosphorylation was noted in some patients. Considering the difference in the effects of golvatinib on immortalized tubular epithelial cells among patients, this analysis may aid in selecting suitable drugs for individual ADPKD patients.

[Kidney Cysts and Cystic Nephropathies in Children - A Consensus Guideline by 10 German Medical Societies]

This consensus-based guideline was developed by all relevant German pediatric medical societies. Ultrasound is the standard imaging modality for pre- and postnatal kidney cysts and should also exclude extrarenal manifestations in the abdomen and internal genital organs. MRI has selected indications. Suspicion of a cystic kidney disease should prompt consultation of a pediatric nephrologist. Prenatal management must be tailored to very different degrees of disease severity. After renal oligohydramnios, we recommend delivery in a perinatal center. Neonates should not be denied renal replacement therapy solely because of their age. Children with unilateral multicystic dysplastic kidney do not require routine further imaging or nephrectomy, but long-term nephrology follow-up (as do children with uni- or bilateral kidney hypo-/dysplasia with cysts). ARPKD (autosomal recessive polycystic kidney disease), nephronophthisis, Bardet-Biedl syndrome and HNF1B mutations cause relevant extrarenal disease and genetic testing is advisable. Children with tuberous sclerosis complex, tumor predisposition (e. g. von Hippel Lindau syndrome) or high risk of acquired kidney cysts should have regular ultrasounds. Even asymptomatic children of parents with ADPKD (autosomal dominant PKD) should be monitored for hypertension and proteinuria. Presymptomatic diagnostic ultrasound or genetic examination for ADPKD in minors should only be done after thorough counselling. Simple cysts are very rare in children and ADPKD in a parent should be excluded. Complex renal cysts require further investigation.