PKD2-Related Autosomal Dominant Polycystic Kidney Disease: Prevalence, Clinical Presentation, Mutation Spectrum, and Prognosis

Data driven approach to characterize rapid decline in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic kidney disease with high phenotypic variability. Furthering insights into patients' ADPKD progression could lead to earlier detection, management, and alter the course to end stage kidney disease (ESKD). We sought to identify patients with rapid decline (RD) in kidney function and to determine clinical factors associated with RD using a data-driven approach. A retrospective cohort study was performed among patients with incident ADPKD (1/1/2002-12/31/2018). Latent class mixed models were used to identify RD patients using differences in eGFR trajectories over time. Predictors of RD were selected based on agreements among feature selection methods, including logistic, regularized, and random forest modeling. The final model was built on the selected predictors and clinically relevant covariates. Among 1,744 patients with incident ADPKD, 125 (7%) were identified as RD. Feature selection included 42 clinical measurements for adaptation with multiple imputations; mean (SD) eGFR was 85.2 (47.3) and 72.9 (34.4) in the RD and non-RD groups, respectively. Multiple imputed datasets identified variables as important features to distinguish RD and non-RD groups with the final prediction model determined as a balance between area under the curve (AUC) and clinical relevance which included 6 predictors: age, sex, hypertension, cerebrovascular disease, hemoglobin, and proteinuria. Results showed 72%-sensitivity, 70%-specificity, 70%-accuracy, and 0.77-AUC in identifying RD. 5-year ESKD rates were 38% and 7% among RD and non-RD groups, respectively. Using real-world routine clinical data among patients with incident ADPKD, we observed that six variables highly predicted RD in kidney function.

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.

PKD1 Truncating Mutations Accelerate eGFR Decline in Autosomal Dominant Polycystic Kidney Disease Patients

INTRODUCTION

Autosomal dominant polycystic kidney disease (ADPKD) is a monogenic disease characterized by the accumulation of fluid-filled cysts in the kidneys, leading to renal volume enlargement and progressive kidney function impairment. Disease severity, though, may vary due to allelic and genetic heterogeneity. This study aimed to determine genotype-phenotype correlations between PKD1 truncating and non-truncating mutations and kidney function decline in ADPKD patients.

METHODS

We established a single-center retrospective cohort study in Kuwait where we followed every patient with a confirmed PKD1-ADPKD diagnosis clinically and genetically. Renal function tests were performed annually. We fitted generalized additive mixed effects models with random intercepts for each individual to analyze repeated measures of kidney function across mutation type. We then calculated survival time to kidney failure in a cox proportional hazards model. Models were adjusted for sex, age at visit, and birth year.

RESULTS

The study included 22 truncating and 20 non-truncating (42 total) patients followed for an average of 6.6 years (range: 1-12 years). Those with PKD1 truncating mutations had a more rapid rate of eGFR decline (-4.7 mL/min/1.73 m2 per year; 95% CI: -5.0, -4.4) compared to patients with PKD1 non-truncating mutations (-3.5 mL/min/1.73 m2 per year; 95% CI: -4.0, -3.1) (p for interaction <0.001). Kaplan-Meier survival analysis of time to kidney failure showed that patients with PKD1 truncating mutations had a shorter renal survival time (median 51 years) compared to those with non-truncating mutations (median 56 years) (P for log-rank = 0.008).

CONCLUSION

In longitudinal and survival analyses, patients with PKD1 truncating mutations showed a faster decline in kidney function compared to patients PKD1 non-truncating mutations. Early identification of patients with PKD1 truncating mutations can, at best, inform early clinical interventions or, at least, help suggest aggressive monitoring.

Polygenic risk alters the penetrance of monogenic kidney disease

Chronic kidney disease (CKD) is determined by an interplay of monogenic, polygenic, and environmental risks. Autosomal dominant polycystic kidney disease (ADPKD) and COL4A-associated nephropathy (COL4A-AN) represent the most common forms of monogenic kidney diseases. These disorders have incomplete penetrance and variable expressivity, and we hypothesize that polygenic factors explain some of this variability. By combining SNP array, exome/genome sequence, and electronic health record data from the UK Biobank and All-of-Us cohorts, we demonstrate that the genome-wide polygenic score (GPS) significantly predicts CKD among ADPKD monogenic variant carriers. Compared to the middle tertile of the GPS for noncarriers, ADPKD variant carriers in the top tertile have a 54-fold increased risk of CKD, while ADPKD variant carriers in the bottom tertile have only a 3-fold increased risk of CKD. Similarly, the GPS significantly predicts CKD in COL4A-AN carriers. The carriers in the top tertile of the GPS have a 2.5-fold higher risk of CKD, while the risk for carriers in the bottom tertile is not different from the average population risk. These results suggest that accounting for polygenic risk improves risk stratification in monogenic kidney disease.

Diagnosing Fabry nephropathy: the challenge of multiple kidney disease

Fabry disease (FD) is an X-linked inherited lysosomal disorder due to a deficiency of the enzyme alpha-galactosidase A (α-gla) due to mutations in the GLA gene. These mutations result in plasma and lysosome accumulation of glycosphingolipids, leading to progressive organ damage and reduced life expectancy. Due to the availability of specific disease-modifying treatments, proper and timely diagnosis and therapy are essential to prevent irreversible complications. However, diagnosis of FD is often delayed because of the wide clinical heterogeneity of the disease and multiple organ involvement developing in variable temporal sequences. This observation is also valid for renal involvement, which may manifest with non-specific signs, such as proteinuria and chronic kidney disease, which are also common in many other nephropathies. Moreover, an additional confounding factor is the possibility of the coexistence of FD with other kidney disorders. Thus, suspecting and diagnosing FD nephropathy in patients with signs of kidney disease may be challenging for the clinical nephrologist. Herein, also through the presentation of a unique case of co-occurrence of autosomal dominant polycystic kidney disease and FD, we review the available literature on cases of coexistence of FD and other renal diseases and discuss the implications of these conditions. Moreover, we highlight the clinical, laboratory, and histological elements that may suggest clinical suspicion and address a proper diagnosis of Fabry nephropathy.

Autosomal Dominant Polycystic Kidney Disease: Is There a Role for Autophagy?

Autosomal-Dominant Polycystic Kidney Disease (ADPKD) is a monogenic disorder initiated by mutations in either PKD1 or PKD2 genes, responsible for encoding polycystin 1 and polycystin 2, respectively. These proteins are primarily located within the primary cilia. The disease follows an inexorable progression, leading most patients to severe renal failure around the age of 50, and extra-renal complications are frequent. A cure for ADPKD remains elusive, but some measures can be employed to manage symptoms and slow cyst growth. Tolvaptan, a vasopressin V2 receptor antagonist, is the only drug that has been proven to attenuate ADPKD progression. Recently, autophagy, a cellular recycling system that facilitates the breakdown and reuse of aged or damaged cellular components, has emerged as a potential contributor to the pathogenesis of ADPKD. However, the precise role of autophagy in ADPKD remains a subject of investigation, displaying a potentially twofold impact. On the one hand, impaired autophagy may promote cyst formation by inducing apoptosis, while on the other hand, excessive autophagy may lead to fibrosis through epithelial to mesenchymal transition. Promising results of autophagy inducers have been observed in preclinical studies. Clinical trials are warranted to thoroughly assess the long-term safety and efficacy of a combination of autophagy inducers with metabolic and/or aquaferetic drugs. This research aims to shed light on the complex involvement of autophagy in ADPKD, explore the regulation of autophagy in disease progression, and highlight the potential of combination therapies as a promising avenue for future investigations.

Genetic Counseling in Kidney Disease: A Perspective

As genetic testing is increasingly integrated into nephrology practice there is a growing need for partnership with genetic experts. Genetic counselors are ideally suited to fill this role. The value of genetic counseling is born out of the clinical value of genetic test results against the backdrop of the complexity of genetic testing. Genetic counselors who specialize in nephrology are trained to understand and explain the potential effects of genes on kidney disease, which can enable patients to make informed decisions about proceeding with genetic testing, navigating variants of uncertain significance, educating on extrarenal features of hereditary kidney disease, facilitating cascade testing, providing post-test education about testing results, and assisting with family planning. Genetic counselors can partner with the nephrologist and provide the knowledge needed to maximize the use of genetic testing for patients for nephrology consultation. Genetic counseling is more than an element or extension of genetic testing; it is a dynamic, shared conversation between the patient and the genetic counselor where concerns, sentiments, information, and education are exchanged, and value-based decision making is facilitated.

Molecular Diagnosis and Identification of Novel Pathogenic Variants in a Large Cohort of Italian Patients Affected by Polycystic Kidney Diseases

Polycystic Kidney Diseases (PKDs) consist of a genetically and phenotypically heterogeneous group of inherited disorders characterized by numerous renal cysts. PKDs include autosomal dominant ADPKD, autosomal recessive ARPKD and atypical forms. Here, we analyzed 255 Italian patients using an NGS panel of 63 genes, plus Sanger sequencing of exon 1 of the PKD1 gene and MPLA (PKD1, PKD2 and PKHD1) analysis. Overall, 167 patients bore pathogenic/likely pathogenic variants in dominant genes, and 5 patients in recessive genes. Four patients were carriers of one pathogenic/likely pathogenic recessive variant. A total of 24 patients had a VUS variant in dominant genes, 8 patients in recessive genes and 15 patients were carriers of one VUS variant in recessive genes. Finally, in 32 patients we could not reveal any variant. Regarding the global diagnostic status, 69% of total patients bore pathogenic/likely pathogenic variants, 18.4% VUS variants and in 12.6% of patients we could not find any. PKD1 and PKD2 resulted to be the most mutated genes; additional genes were UMOD and GANAB. Among recessive genes, PKHD1 was the most mutated gene. An analysis of eGFR values showed that patients with truncating variants had a more severe phenotype. In conclusion, our study confirmed the high degree of genetic complexity at the basis of PKDs and highlighted the crucial role of molecular characterization in patients with suspicious clinical diagnosis. An accurate and early molecular diagnosis is essential to adopt the appropriate therapeutic protocol and represents a predictive factor for family members.

Mutation Analysis of PKD1 and PKD2 Genes in a Large Italian Cohort Reveals Novel Pathogenic Variants Including a Novel Complex Rearrangement

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited disease of the kidney. It occurs in adulthood but is also rarely diagnosed in early childhood. The majority of the disease-causing variants observed in ADPKD patients are in two genes: PKD1 and PKD2.

METHODS

237 patients from 198 families with a clinical diagnosis of ADPKD were screened for PKD1 and PKD2 genetic variants using Sanger sequencing and multiple ligation-dependent probe amplification analysis.

RESULTS

Disease-causing (diagnostic) variants were identified in 173 families (211 patients), 156 on PKD1 and 17 on PKD2. Variants of unknown significance were detected in 6 additional families, while no mutations were found in the remaining 19 families. Among the diagnostic variants detected, 51 were novel. In ten families, seven large rearrangements were found and the molecular breakpoints of 3 rearrangements were identified. Renal survival was significantly worse for PKD1-mutated patients, particularly those carrying truncating mutations. In patients with PKD1 truncating (PKD1-T) mutations, disease onset was significantly earlier than in patients with PKD1 non-truncating variants or PKD2-mutated patients.

CONCLUSIONS

Comprehensive genetic testing confirms its utility in diagnosing patients with ADPKD and contributes to explaining the clinical heterogeneity observed in this disease. Moreover, the genotype-phenotype correlation can allow for a more accurate disease prognosis.

Polygenic risk affects the penetrance of monogenic kidney disease

Background

Chronic kidney disease (CKD) is a genetically complex disease determined by an interplay of monogenic, polygenic, and environmental risks. Most forms of monogenic kidney diseases have incomplete penetrance and variable expressivity. It is presently unknown if some of the variability in penetrance can be attributed to polygenic factors.

Methods

Using the UK Biobank (N=469,835 participants) and the All of Us (N=98,622 participants) datasets, we examined two most common forms of monogenic kidney disorders, autosomal dominant polycystic kidney disease (ADPKD) caused by deleterious variants in the PKD1 or PKD2 genes, and COL4A-associated nephropathy (COL4A-AN caused by deleterious variants in COL4A3, COL4A4, or COL4A5 genes). We used the eMERGE-III electronic CKD phenotype to define cases (estimated glomerular filtration rate (eGFR) <60 mL/min/1.73m2 or kidney failure) and controls (eGFR >90 mL/min/1.73m2 in the absence of kidney disease diagnoses). The effects of the genome-wide polygenic score (GPS) for CKD were tested in monogenic variant carriers and non-carriers using logistic regression controlling for age, sex, diabetes, and genetic ancestry.

Results

As expected, the carriers of known pathogenic and rare predicted loss-of-function variants in PKD1 or PKD2 had a high risk of CKD (ORmeta=17.1, 95% CI: 11.1-26.4, P=1.8E-37). The GPS was comparably predictive of CKD in both ADPKD variant carriers (ORmeta=2.28 per SD, 95%CI: 1.55-3.37, P=2.6E-05) and non-carriers (ORmeta=1.72 per SD, 95% CI=1.69-1.76, P< E-300) independent of age, sex, diabetes, and genetic ancestry. Compared to the middle tertile of the GPS distribution for non-carriers, ADPKD variant carriers in the top tertile had a 54-fold increased risk of CKD, while ADPKD variant carriers in the bottom tertile had only a 3-fold increased risk of CKD. Similarly, the GPS was predictive of CKD in both COL4-AN variant carriers (ORmeta=1.78, 95% CI=1.22-2.58, P=2.38E-03) and non-carriers (ORmeta=1.70, 95%CI: 1.68-1.73 P

Conclusions

Variable penetrance of kidney disease in ADPKD and COL4-AN is partially explained by differences in polygenic risk profiles. Accounting for polygenic factors has the potential to improve risk stratification in monogenic kidney disease and may have implications for genetic counseling.

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Key Words

• APOL1
• GWAS
• chronic kidney disease (CKD)
• polygenic risk score (PRS)

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MESH Headings Collapse

Grants

• OT2 OD026556 NIH HHS
• U2C OD023196 NIH HHS
• OT2 OD026551 NIH HHS
• U24 OD023121 NIH HHS
• OT2 OD026552 NIH HHS
• OT2 OD026549 NIH HHS
• OT2 OD025337 NIH HHS
• OT2 OD025277 NIH HHS
• OT2 OD026555 NIH HHS
• OT2 OD026550 NIH HHS
• OT2 OD026553 NIH HHS
• OT2 OD023205 NIH HHS
• U01 HG008680 NHGRI NIH HHS
• OT2 OD025276 NIH HHS
• OT2 OD026557 NIH HHS
• U24 OD023163 NIH HHS
• OT2 OD023206 NIH HHS
• R01 LM013061 NLM NIH HHS
• U24 OD023176 NIH HHS
• OT2 OD026548 NIH HHS
• OT2 OD025315 NIH HHS
• K25 DK128563 NIDDK NIH HHS
• OT2 OD026554 NIH HHS
• UL1 TR001873 NCATS NIH HHS

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Affiliation(s)

Atlas Khan Division of Nephrology, Dept of Medicine, Vagelos College of Physicians & Surgeons, Columbia University, New York, NY
Ning Shang Division of Nephrology, Dept of Medicine, Vagelos College of Physicians & Surgeons, Columbia University, New York, NY
Jordan G. Nestor Division of Nephrology, Dept of Medicine, Vagelos College of Physicians & Surgeons, Columbia University, New York, NY
Chunhua Weng Department of Biomedical Informatics, Vagelos College of Physicians & Surgeons, Columbia University, New York, NY, USA
George Hripcsak Department of Biomedical Informatics, Vagelos College of Physicians & Surgeons, Columbia University, New York, NY, USA
Peter C. Harris Division of Nephrology and Hypertension, Mayo Clinic, Rochester, Minnesota 55905, USA
Ali G. Gharavi Division of Nephrology, Dept of Medicine, Vagelos College of Physicians & Surgeons, Columbia University, New York, NY
Krzysztof Kiryluk Division of Nephrology, Dept of Medicine, Vagelos College of Physicians & Surgeons, Columbia University, New York, NY

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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.

Combing Genome-Wide Association Studies and Single-Cell Analysis to Elucidate the Mechanisms of Kidney Disease: Proceedings of the Henry Shavelle Professorship

Background

Kidney diseases pose a significant global health burden; there is an urgent need to deepen our understanding of their underlying mechanisms.

Summary

This review focuses on new innovative approaches that merge genome-wide association studies (GWAS) and single-cell omics (including transcriptomics) in kidney disease research. We begin by detailing how GWAS has identified numerous genetic risk factors, offering valuable insight into disease susceptibility. Then, we explore the application of scRNA-seq, highlighting its ability to unravel how genetic variants influence cellular phenotypes. Through a synthesis of recent studies, we illuminate the synergy between these two powerful methodologies, demonstrating their potential in elucidating the complex etiology of kidney diseases. Moreover, we discuss how this integrative approach could pave the way for precise diagnostics and personalized treatments.

Key Message

This review underscores the transformative potential of combining GWAS and scRNA-seq in the journey toward a deeper understanding of kidney diseases.

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.

Targeted Next Generation Sequencing Revealed Novel Variants in the PKD1 and PKD2 Genes of Iranian Patients with Autosomal Dominant Polycystic Kidney Disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD), one of the common inherited disorders in humans, is characterized by the development and enlargement of renal cysts, often leading to end-stage renal disease (ESRD). In this study, Iranian ADPKD families were subjected to high-throughput DNA sequencing to find potential causative variants facilitating the way toward risk assessment and targeted therapy.

METHODS

Our protocol was based on the targeted next generation sequencing (NGS) panel previously developed in our center comprising 12 genes involved in PKD. This panel has been applied to investigate the genetic causes of 32 patients with a clinical suspicion of ADPKD.

RESULTS

We identified a total of 31 variants for 32 individuals, two of which were each detected in two individuals. Twenty-seven out of 31 detected variants were interpreted as pathogenic/likely pathogenic and the remaining 4 of uncertain significance with a molecular diagnostic success rate of 87.5%. Among these variants, 25 PKD1/2 pathogenic/likely pathogenic variants were detected in 32 index patients (78.1%), and variants of uncertain significance in four individuals (12.5% in PKD1/2). The majority of variants was identified in PKD1 (74.2%). Autosomal recessive PKD was identified in one patient, indicating the similarities between recessive and dominant PKD. In concordance with earlier studies, this biallelic PKD1 variant, p.Arg3277Cys, leads to rapidly progressive and severe disease with very early-onset ADPKD.

CONCLUSION

Our findings suggest that targeted gene panel sequencing is expected to be the method of choice to improve diagnostic and prognostic accuracy in PKD patients with heterogeneity in genetic background.

Crosstalk between lysine methyltransferase Smyd2 and TGF-β-Smad3 signaling promotes renal fibrosis in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited genetic disorder, which is caused by mutations of PKD1 or PKD2 gene and is characterized by renal fluid-filled cyst formation and interstitial fibrosis. PKD1 gene mutation results in the upregulation of SET and MYND domain-containing lysine methyltransferase 2 (SMYD2) in Pkd1 mutant mouse and ADPKD patient kidneys. However, the role and mechanism of Smyd2 in the regulation of renal fibrosis in ADPKD remains elusive. In this study, we show that: 1) the expression of Smyd2 can be regulated by TGF-β-Smad3 in normal rat kidney 49F (NRK-49F) cells and mouse fibroblast NIH3T3 cells; 2) knockdown of Smyd2 and inhibition of Smyd2 with its specific inhibitor, AZ505, decreases TGF-β-induced expression of α-smooth muscle actin (α-SMA), fibronectin, collagens 1 and 3 and plasminogen activator inhibitor-1( PAI1) in NRK-49F cells; 3) Smyd2 regulates the transcription of fibrotic marker genes through binding on the promoters of those genes or through methylating histone H3 to indirectly regulate the expression of those genes; and 4) knockout and inhibition of Smyd2 significantly decreases renal fibrosis in Pkd1 knockout mice, supporting that targeting Smyd2 can not only delay cyst growth but also attenuate renal fibrosis in ADPKD. This study identifies a crosstalk between TGF-β signaling and Smyd2 in the regulation of fibrotic gene transcription and the activation of fibroblasts in cystic kidneys, suggesting that targeting Smyd2 with AZ505 is a potential therapeutic strategy for ADPKD treatment.

Polycystin-2 (TRPP2): Ion channel properties and regulation

Polycystin-2 (TRPP2, PKD2, PC2) is the product of the PKD2 gene, whose mutations cause Autosomal Dominant Polycystic Kidney Disease (ADPKD). PC2 belongs to the superfamily of TRP (Transient Receptor Potential) proteins that generally function as Ca²⁺-permeable nonselective cation channels implicated in Ca²⁺ signaling. PC2 localizes to various cell domains with distinct functions that likely depend on interactions with specific channel partners. Functions include receptor-operated, nonselective cation channel activity in the plasma membrane, intracellular Ca²⁺ release channel activity in the endoplasmic reticulum (ER), and mechanosensitive channel activity in the primary cilium of renal epithelial cells. Here we summarize our current understanding of the properties of PC2 and how other transmembrane and cytosolic proteins modulate this activity, providing functional diversity and selective regulatory mechanisms to its role in the control of cellular Ca²⁺ homeostasis.

The dynamic effect of genetic variation on the in vivo ER stress transcriptional response in different tissues

The genetic regulation of gene expression varies greatly across tissue-type and individuals and can be strongly influenced by the environment. Many variants, under healthy control conditions, may be silent or even have the opposite effect under diseased stress conditions. This study uses an in vivo mouse model to investigate how the effect of genetic variation changes with cellular stress across different tissues. Endoplasmic reticulum stress occurs when misfolded proteins accumulate in the endoplasmic reticulum. This triggers the unfolded protein response, a large transcriptional response which attempts to restore homeostasis. This transcriptional response, despite being a conserved, basic cellular process, is highly variable across different genetic backgrounds, making it an ideal system to study the dynamic effects of genetic variation. In this study, we sought to better understand how genetic variation alters expression across tissues, in the presence and absence of endoplasmic reticulum stress. The use of different mouse strains and their F1s allow us to also identify context-specific cis- and trans- regulatory variation underlying variable transcriptional responses. We found hundreds of genes that respond to endoplasmic reticulum stress in a tissue- and/or genotype-dependent manner. The majority of the regulatory effects we identified were acting in cis-, which in turn, contribute to the variable endoplasmic reticulum stress- and tissue-specific transcriptional response. This study demonstrates the need for incorporating environmental stressors across multiple different tissues in future studies to better elucidate the effect of any particular genetic factor in basic biological pathways, like the endoplasmic reticulum stress response.

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.

Profiling renal sodium transporters in mice with nephron Ift88 disruption: Association with sex, cysts, and blood pressure

Loss of nephron primary cilia due to disruption of the Ift88 gene results in sex‐ and age‐specific phenotypes involving renal cystogenesis, blood pressure (BP) and urinary Na⁺ excretion. Previous studies demonstrated that male mice undergoing induction of nephron‐specific Ift88 gene disruption at 2 months of age developed reduced BP and increased salt‐induced natriuresis when pre‐cystic (2 months post‐induction) and became hypertensive associated with frankly cystic kidneys by 9 months post‐induction; in contrast, female Ift88 KO mice manifested no unique phenotype 2 months post‐induction and had mildly reduced BP 9 months post‐induction. The current study utilized these Ift88 KO mice to investigate associated changes in renal Na⁺ transporter and channel protein expression. At 2 months post‐induction, pre‐cystic male Ift88 KO mice had reduced high salt diet associated total NKCC2 levels while female mice had no alterations in Na⁺ transporters or channels. At 9 months post‐induction, cystic male Ift88 KO mice had increased total and phosphorylated NHE3 levels together with reduced NKCC2, phosphorylated and/or total NCC, and ENaC‐α expression on normal and high salt diets. In contrast, female Ift88 KO mice at 9 months post‐induction had no changes in Na⁺ transporters or channels beyond an increase in phosphorylated‐NCC during high salt intake. Thus, reduced BP in pre‐cystic, and elevated BP in renal cystic, male Ift88 KO mice are associated with unique sex‐dependent changes in nephron Na⁺ transporter/channel expression.

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.

Multiomic identification of factors associated with progression to cystic kidney disease in mice with nephron Ift88 disruption

Ift88 gene mutations cause primary cilia loss and polycystic kidney disease (PKD) in mice. Nephron intraflagellar transport protein 88 (Ift88) knockout (KO) at 2 mo postnatal does not affect renal histology at 4 mo postnatal and causes PKD only in males by 11 mo postnatal. To identify factors associated with PKD development, kidneys from 4-mo-old male and female control and Ift88 KO mice underwent transcriptomic, proteomic, Western blot, metabolomic, and lipidomic analyses. mRNAs involved in extracellular matrix (ECM) synthesis and degradation were selectively upregulated in male KO mice. Proteomic analysis was insufficiently sensitive to detect most ECM components, while Western blot analysis paradoxically revealed reduced fibronectin and collagen type I in male KO mice. Only male KO mice had upregulated mRNAs encoding fibrinogen subunits and receptors for vascular endothelial growth factor and platelet-derived growth factor; period 2, period 3, and nuclear receptor subfamily 1 group D member 1 clock mRNAs were selectively decreased in male KO mice. Proteomic, metabolomic, and lipidomic analyses detected a relative (vs. the same-sex control) decrease in factors involved in fatty acid β-oxidation in female KO mice, while increased or unchanged levels in male KO mice, including medium-chain acyl-CoA dehydrogenase, 3-hydroxybutyrate, and acylcarnitine. Three putative mRNA biomarkers of cystogenesis in male Ift88 KO mice (similar control levels between sexes and uniquely altered by KO in males) were identified, including high levels (fibrinogen α-chain and stromal cell-derived factor 2-like 1) and low levels (BTG3-associated nuclear protein) in male KO mice. These findings suggest that relative alterations in renal ECM metabolism, fatty acid β-oxidation, and other pathways precede cystogenesis in Ift88 KO mice. In addition, potential novel biomarkers of cystogenesis in Ift88 KO mice have been identified.NEW & NOTEWORTHY Male, but not female, mice with nephron intraflagellar transport protein 88 (Ift88) gene knockout (KO) develop polycystic kidneys by ∼1 yr postnatal. We performed multiomic analysis of precystic male and female Ift88 KO and control kidneys. Precystic male Ift88 KO mice exhibited differential alterations (vs. females) in mRNA, proteins, metabolites, and/or lipids associated with renal extracellular matrix metabolism, fatty acid β-oxidation, circadian rhythm, and other pathways. These findings suggest targets for evaluation in the pathogenesis of Ift88 KO polycystic kidneys.

Ion Channels of Cilia: Paramecium as a Model

Holotrichous ciliates, like Paramecium, swim through their aqueous environment by beating their many cilia. They can alter swimming speed and direction, which seems to have mesmerized early microscopists of the 1600's. We know from extensive and elegant physiological studies and generation of mutants that these cells can be considered little swimming neurons because their ciliary beating is under bioelectric control of ion channels in the cilia. This chapter will focus on the ionic control of swimming behavior by ciliary ion channels, primarily in the holotrichous ciliate Paramecium. Voltage gated and calcium activated channels for calcium, magnesium, sodium, and potassium are regulated in a closely orchestrated manner that allows cilia to bend and propel the cell forward or backward. Sensory input that generates receptor potentials feeds into the control of this channel activity and allows the cell to turn or speed up. This in turn helps the cell to avoid predators or toxic conditions. While the focus is on P. tetraurelia and P. caudatum, the principles of ciliary ion channel activity and control are easily extendable to other ciliates and protists. The high conservation of channel and ion pump structures also extends the lessons from Paramecium to higher organisms.

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.

Using Paramecium as a Model for Ciliopathies

Paramecium has served as a model organism for the studies of many aspects of genetics and cell biology: non-Mendelian inheritance, genome duplication, genome rearrangements, and exocytosis, to name a few. However, the large number and patterning of cilia that cover its surface have inspired extraordinary ultrastructural work. Its swimming patterns inspired exquisite electrophysiological studies that led to a description of the bioelectric control of ciliary motion. A genetic dissection of swimming behavior moved the field toward the genes and gene products underlying ciliary function. With the advent of molecular technologies, it became clear that there was not only great conservation of ciliary structure but also of the genes coding for ciliary structure and function. It is this conservation and the legacy of past research that allow us to use Paramecium as a model for cilia and ciliary diseases called ciliopathies. However, there would be no compelling reason to study Paramecium as this model if there were no new insights into cilia and ciliopathies to be gained. In this review, we present studies that we believe will do this. For example, while the literature continues to state that immotile cilia are sensory and motile cilia are not, we will provide evidence that Paramecium cilia are clearly sensory. Other examples show that while a Paramecium protein is highly conserved it takes a different interacting partner or conducts a different ion than expected. Perhaps these exceptions will provoke new ideas about mammalian systems.

Sex-Dependent Effects of Nephron Ift88 Disruption on BP, Renal Function, and Cystogenesis

BACKGROUND

Primary cilia regulation of renal function and BP in health and disease is incompletely understood. This study investigated the effect of nephron ciliary loss on renal physiology, BP, and ensuing cystogenesis.

METHODS

Mice underwent doxycycline (DOX)-inducible nephron-specific knockout (KO) of the Ift88 gene at 2 months of age using a Cre-LoxP strategy. BP, kidney function, and renal pathology were studied 2 and 9 months after DOX (Ift88 KO) or vehicle (control).

RESULTS

At 2 months post-DOX, male, but not female, Ift88 KO, compared with sex-matched control, mice had reduced BP, enhanced salt-induced natriuresis, increased urinary nitrite and nitrate (NOx) excretion, and increased kidney NOS3 levels, which localized to the outer medulla; the reductions in BP in male mice were prevented by L-NAME. At 9 months post-DOX, male, but not female, Ift88 KO mice had polycystic kidneys, elevated BP, and reduced urinary NOx excretion. No differences were observed in plasma renin concentration, plasma aldosterone, urine vasopressin, or urine PGE₂ between Ift88 KO and control mice at 2 or 9 months post-DOX.

CONCLUSIONS

Nephron cilia disruption in male, but not female, mice (1) reduces BP prior to cyst formation, (2) increases NOx production that may account for the lower BP prior to cyst formation, and (3) induces polycystic kidneys that are associated with hypertension and reduced renal NO production.

PKD2 gene variants in Chinese patients with autosomal dominant polycystic kidney disease

PKD2 gene variants account for 4.5% to 20% of patients with autosomal dominant polycystic kidney disease (ADPKD). Little is known about the clinical characteristics of PKD2 variants in Chinese patients with ADPKD. Herein, we performed a comprehensive search for variants of PKD2 gene in 44 Chinese ADPKD pedigrees and a total of 37 variants were identified. Of these 37 variants, 18 were nonsense variants, 10 frameshift variants, 4 missense variants, and 5 splice site variants. 11/37 variants were detected for the first time. The median age at diagnosis was 30.5 years, and positive family history was detected in 77.27% patients, liver cysts in 68.18%, hypertension in 45.45%, nephrolithiasis in 31.82%, macro-hematuria in 22.73%, and proteinuria in 13.63%. The level of estimated glomerular filtration rate in 8/39 patients were blow 60 ml/min/1.73m² . 11/17 patients were classified as rapid progression by Mayo Clinic classification. The end stage renal disease (ESRD) events were reported in 9/22 pedigrees, and the presence of nephrolithiasis and macro-hematuria were significantly associated with ESRD in the pedigrees with PKD2 variants. The identified variants and clinical features will facilitate the early diagnosis and prognosis prediction in Chinese ADPKD patients with PKD2 variants.

The genetic landscape of polycystic kidney disease in Ireland

Polycystic kidney diseases (PKDs) comprise the most common Mendelian forms of renal disease. It is characterised by the development of fluid-filled renal cysts, causing progressive loss of kidney function, culminating in the need for renal replacement therapy or kidney transplant. Ireland represents a valuable region for the genetic study of PKD, as family sizes are traditionally large and the population relatively homogenous. Studying a cohort of 169 patients, we describe the genetic landscape of PKD in Ireland for the first time, compare the clinical features of patients with and without a molecular diagnosis and correlate disease severity with autosomal dominant pathogenic variant type. Using a combination of molecular genetic tools, including targeted next-generation sequencing, we report diagnostic rates of 71-83% in Irish PKD patients, depending on which variant classification guidelines are used (ACMG or Mayo clinic respectively). We have catalogued a spectrum of Irish autosomal dominant PKD pathogenic variants including 36 novel variants. We illustrate how apparently unrelated individuals carrying the same autosomal dominant pathogenic variant are highly likely to have inherited that variant from a common ancestor. We highlight issues surrounding the implementation of the ACMG guidelines for variant pathogenicity interpretation in PKD, which have important implications for clinical genetics.

Assessing Risk of Rapid Progression in Autosomal Dominant Polycystic Kidney Disease and Special Considerations for Disease-Modifying Therapy

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited cause of kidney failure, accounting for 5%-10% of cases. Predicting which patients with ADPKD will progress rapidly to kidney failure is critical to assess the risk-benefit ratio of any intervention and to consider early initiation of long-term kidney protective measures that will maximize the cumulative benefit of slowing disease progression. Surrogate prognostic biomarkers are required to predict future decline in kidney function. Clinical, genetic, environmental, epigenetic, and radiologic factors have been studied as predictors of progression to kidney failure in ADPKD. A complex interaction of these prognostic factors determines the number of kidney cysts and their growth rates, which affect total kidney volume (TKV). Age-adjusted TKV, represented by the Mayo imaging classification, estimates each patient's unique rate of kidney growth and provides the most individualized approach available clinically so far. Tolvaptan has been approved to slow disease progression in patients at risk of rapidly progressive disease. Several other disease-modifying treatments are being studied in clinical trials. Selection criteria for patients at risk of rapid progression vary widely among countries and are based on a combination of age, baseline glomerular filtration rate (GFR), GFR slope, baseline TKV, and TKV rate of growth. This review details the approach in assessing the risk of disease progression in ADPKD and identifying patients who would benefit from long-term therapy with disease-modifying agents.

A no-nonsense approach to hereditary kidney disease

The advent of a new class of aminoglycosides with increased translational readthrough of nonsense mutations and reduced toxicity offers a new therapeutic strategy for a subset of patients with hereditary kidney disease. The renal uptake and retention of aminoglycosides at a high intracellular concentration makes the kidney an ideal target for this approach. In this review, we explore the potential of aminoglycoside readthrough therapy in a number of hereditary kidney diseases and discuss the therapeutic window of opportunity for subclasses of each disease, when caused by nonsense mutations.

'A sword of Damocles': patient and caregiver beliefs, attitudes and perspectives on presymptomatic testing for autosomal dominant polycystic kidney disease: a focus group study

BACKGROUND AND OBJECTIVES

Presymptomatic testing is available for early diagnosis of hereditary autosomal dominant polycystic kidney disease (ADPKD). However, the complex ethical and psychosocial implications can make decision-making challenging and require an understanding of patients' values, goals and priorities. This study aims to describe patient and caregiver beliefs and expectations regarding presymptomatic testing for ADPKD.

DESIGN, SETTING AND PARTICIPANTS

154 participants (120 patients and 34 caregivers) aged 18 years and over from eight centres in Australia, France and Korea participated in 17 focus groups. Transcripts were analysed thematically.

RESULTS

We identified five themes: avoiding financial disadvantage (insecurity in the inability to obtain life insurance, limited work opportunities, financial burden); futility in uncertainty (erratic and diverse manifestations of disease limiting utility, taking preventive actions in vain, daunted by perplexity of results, unaware of risk of inheriting ADPKD); lacking autonomy and support in decisions (overwhelmed by ambiguous information, medicalising family planning, family pressures); seizing control of well-being (gaining confidence in early detection, allowing preparation for the future, reassurance in family resilience); and anticipating impact on quality of life (reassured by lack of symptoms, judging value of life with ADPKD).

CONCLUSIONS

For patients with ADPKD, presymptomatic testing provides an opportunity to take ownership of their health through family planning and preventive measures. However, these decisions can be wrought with tensions and uncertainty about prognostic implications, and the psychosocial and financial burden of testing. Healthcare professionals should focus on genetic counselling, mental health and providing education to patients' families to support informed decision-making. Policymakers should consider the cost burden and risk of discrimination when informing government policies. Finally, patients are recommended to focus on self-care from an early age.

Co-occurrence of neurofibromatosis type 1 and optic nerve gliomas with autosomal dominant polycystic kidney disease type 2

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) and neurofibromatosis type 1 (NF1) are both autosomal dominant disorders with a high rate of novel mutations. However, the two disorders have distinct and well-delineated genetic, biochemical, and clinical findings. Only a few cases of coexistence of ADPKD and NF1 in a single individual have been reported, but the possible implications of this association are unknown.

METHODS

We report an ADPKD male belonging to a family of several affected members in three generations associated with NF1 and optic pathway gliomas. The clinical diagnosis of ADPKD and NF1 was performed by several image techniques.

RESULTS

Linkage analysis of ADPKD family was consistent to the PKD2 locus by a nonsense mutation, yielding a truncated polycystin-2 by means of next-generation sequencing. The diagnosis of NF1 was confirmed by mutational analysis of this gene showing a 4-bp deletion, resulting in a truncated neurofibromin, as well. The impact of this association was investigated by analyzing putative genetic interactions and by comparing the evolution of renal size and function in the proband with his older brother with ADPKD without NF1 and with ADPKD cohorts.

CONCLUSION

Despite the presence of both conditions there was not additive effect of NF1 and PKD2 in terms of the severity of tumor development and/or ADPKD progression.

Initial experience from a renal genetics clinic demonstrates a distinct role in patient management

Purpose

A Renal Genetics Clinic (RGC) was established to optimize diagnostic testing, facilitate genetic counseling, and direct clinical management.

Methods

Retrospective review of patients seen over a two-year period in the RGC.

Results

One hundred eleven patients (mean age: 39.9 years) were referred to the RGC: 65 for genetic evaluation, 19 for management of a known genetic disease, and 18 healthy living kidney donors (LKDs) and their 9 related transplant candidates for screening. Forty-three patients underwent genetic testing with a diagnosis in 60% of patients including 9 with Alport syndrome, 7 with autosomal dominant polycystic kidney disease (ADPKD), 2 with genetic focal segmental glomerulosclerosis (FSGS), 2 with PAX2-mediated CAKUT, and 1 each with autosomal recessive polycystic kidney disease (ARPKD), Dent, Frasier, Gordon, Gitelman, and Zellweger syndromes. Four of 18 LKDs were referred only for APOL1 screening. For the remaining 14 LKDs, their transplant candidates were first tested to establish a genetic diagnosis. Five LKDs tested negative for the familial genetic variant, four were positive for their familial variant. In five transplant candidates, a genetic variant could not be identified.

Conclusion

An RGC that includes genetic counseling enhances care of renal patients by improving diagnosis, directing management, affording presymptomatic family focused genetic counseling, and assisting patients and LKDs to make informed decisions.

Polycystin 2 is increased in disease to protect against stress-induced cell death

Polycystin 2 (PC2 or TRPP1, formerly TRPP2) is a calcium-permeant Transient Receptor Potential (TRP) cation channel expressed primarily on the endoplasmic reticulum (ER) membrane and primary cilia of all cell and tissue types. Despite its ubiquitous expression throughout the body, studies of PC2 have focused primarily on its role in the kidney, as mutations in PC2 lead to the development of autosomal dominant polycystic kidney disease (ADPKD), a debilitating condition for which there is no cure. However, the endogenous role that PC2 plays in the regulation of general cellular homeostasis remains unclear. In this study, we measure how PC2 expression changes in different pathological states, determine that its abundance is increased under conditions of cellular stress in multiple tissues including human disease, and conclude that PC2-deficient cells have increased susceptibility to cell death induced by stress. Our results offer new insight into the normal function of PC2 as a ubiquitous stress-sensitive protein whose expression is up-regulated in response to cell stress to protect against pathological cell death in multiple diseases.

Prediction of Renal Prognosis in Patients with Autosomal Dominant Polycystic Kidney Disease Using PKD1/PKD2 Mutations

Autosomal dominant polycystic kidney disease (ADPKD) patients with PKD1 mutations, particularly those with truncating mutations, show poor prognosis. However, the differences in disease progression with different mutation types are unclear. Here, a comparative study was conducted on the renal prognosis of patients with ADPKD who were categorized based on genotype (PKD1 versus PKD2 mutation), mutation type (truncating mutation: nonsense, frameshift, splicing mutation, and large deletion; non-truncating mutation: substitution and in-frame deletion), and mutation position. A total of 123 patients visiting our hospital were enrolled. Renal prognosis was poor for those with PKD1 splicing, PKD1 frameshift, and PKD2 splicing mutations. Despite the truncating mutation, the renal prognosis was relatively favorable for patients with nonsense mutations. Three out of five patients with PKD2 mutation required renal replacement therapy before 58 years of age. In conclusion, we showed that renal prognosis differs according to mutation types in both PKD1 and PKD2, and that it was favorable for those with nonsense mutations among patients with PKD1 truncating mutations. It was also confirmed that renal prognosis was not always favorable in patients with PKD2 mutations. A detailed assessment of mutation types may be useful for predicting the renal prognosis of patients with ADPKD.

Stone Prevalence in Autosomal Dominant Polycystic Kidney Disease: A Systematic Review and Meta-Analysis

Background:

It is uncertain how often patients with autosomal dominant polycystic kidney disease (ADPKD) develop kidney stones.

Objective:

To review English-language studies reporting the incidence and prevalence of stones and stone interventions in adults with ADPKD.

Design:

Systematic review and meta-analysis.

Setting:

Any country of origin.

Patients:

Adult patients with ADPKD.

Measurements:

Incidence or prevalence of kidney stones and stone interventions.

Methods:

We reviewed 1812 citations from bibliographic databases, abstracted data from 49 eligible studies, and assessed methodological quality in duplicate. In some studies, the proportion of adults with ADPKD with the outcome were compared to adults without ADPKD; for these studies, prevalence risk ratios were calculated and pooled using a random effects model.

Results:

We identified 49 articles that met our review criteria. The methodological quality of many studies was limited (scores ranging from 2 to 14 out of 22, with a higher score indicating higher quality). No study clearly reported stone incidence, and in the cross-sectional studies, the definition of stones was often unclear. The prevalence of stones ranged from 3% to 59%, and a prevalence of stone interventions ranged from 1% to 8%; the average patient age at the time of assessment ranged from 26 to 61 years across the studies. Two studies reported a nonstatistically significant higher stone prevalence in patients with ADPKD compared to unaffected family members. Compared to unaffected family members, patients with ADPKD had a higher prevalence of kidney stones (6 cross-sectional studies; unadjusted prevalence ratio: 1.8; 95% confidence interval: 1.3 to 2.6; P = .0007; test for heterogeneity: I² = 0%, P = .8).

Limitations:

Studies were limited to articles published in English.

Conclusions:

The prevalence of kidney stones and stone interventions in adults with ADPKD remains uncertain. Future studies of higher methodological quality are needed to better characterize the incidence and prevalence of kidney stones in patients with ADPKD.

Trial registration:

We did not register the protocol for this systematic review.

Autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary kidney disease and one of the most common causes of end-stage kidney disease. Multiple clinical manifestations, such as enlarged kidneys filled with growing cysts, hypertension, and multiple extrarenal complications, including liver cysts, intracranial aneurysms, and cardiac valvular disease, show that ADPKD is a systemic disorder. New information derived from clinical research using molecular genetics and advanced imaging techniques has provided enhanced tools for assessing the diagnosis and prognosis for individual patients and their families. Phase 3 randomised, placebo-controlled clinical trials have clarified aspects of disease management and a disease-modifying therapeutic drug is now available for patients with high risk of rapid disease progression. These developments provide a strong basis on which to make clear recommendations about the management of affected patients and families. Implementation of these advances has the potential to delay kidney failure, reduce the symptom burden, lessen the risk of cardiovascular complications, and prolong life.

Analysis of Nationwide Data to Determine the Incidence and Diagnosed Prevalence of Autosomal Dominant Polycystic Kidney Disease in the USA: 2013-2015

BACKGROUND

This study addresses an important gap, as it is the first US nationwide, epidemiologic study of ADPKD incidence and prevalence.

SUMMARY

This 3-year, observational study utilized data from Truven Health MarketScan® administrative claims, as well as cross-sectional data from the National Ambulatory Medical Care Survey (NAMCS). We estimated the annual incidence and diagnosed prevalence using population-based data on over 170 million de-identified patients to provide the most current epidemiologic estimates available. The ADPKD-diagnosed prevalence was 4.3 per 10,000 in the NAMCS, which closely corresponded with age-adjusted rates from patients with either commercial insurance or employer-sponsored Medicare supplemental insurance. The annual incidence was 0.62 per 10,000. Both nationwide data sets indicate that approximately 140,000 patients are currently diagnosed in the USA. We also found significant differences by gender and age. Females are nearly twice as likely as males to be diagnosed in early adulthood, while the incidence in males was highest in those aged 65 years or older. ADPKD appears more likely to be diagnosed in men after disease progression or the development of chronic kidney disease.

KEY MESSAGES

Our results revealed striking age and gender differences in the incidence of ADPKD. Young women are diagnosed with ADPKD at nearly twice the rate of young men, perhaps due to the use of ultrasound in women during child-bearing years. This points to a need for increased recognition of ADPKD, with an emphasis on younger men in particular. ADPKD has been inaccurately perceived as a common condition based on misinterpretation of early epidemiologic data (1957) confirmed by our data and recent European data. ADPKD affects approximately 140,000 patients in the USA and meets the criterion for a rare disease. Our results indicate a need for further study of gender and ADPKD diagnosis, progression, management, and outcomes.

A novel frameshift PKD1 mutation in a Chinese patient with autosomal dominant polycystic kidney disease and azoospermia: A case report

Autosomal dominant polycystic kidney disease (ADPKD) is primarily caused by mutations in polycystin 1, transient receptor potential channel interacting (PKD1) and PKD2, and characterized by numerous cysts in various organs, primarily the kidneys and liver. The present case report is on a 33-year-old Chinese male patient who suffered from abdominal pain and hypertension, and presented with long-term infertility. Laboratory tests indicated that the patient had a normal renal function, while abdominal computed tomography demonstrated that the patient had enlarged kidneys with a volume of 1,127.21 cm³. In a semen analysis, no sperm was detected, while a subsequent testicular biopsy analysis demonstrated numerous mature sperms with progressive motility which suggests that the cysts of the epididymis and the dilated seminal vesicles may have obstructed the ejaculation of semen. Genetic testing identified that a novel missense mutation (c.9053delT) that was responsible for the disease. ADPKD has various disease severities, which depend on whether there is a PKD1 or PKD2 mutation and whether the mutation impairs the function of the polycystin protein. Therefore, genetic testing is important for the clinical diagnosis and prognosis of ADPKD patients, as well as prenatal diagnosis.

Population data improves variant interpretation in autosomal dominant polycystic kidney disease

PURPOSE

Autosomal dominant polycystic kidney disease (ADPKD) is a common adult-onset monogenic disorder, with prevalence of 1/1000. Population databases including ExAC have improved pathogenic variant prioritization in many diseases. Due to pseudogene homology of PKD1, the predominant ADPKD disease gene, and the variable disease severity and age of onset, we aimed to investigate the utility of ExAC for variant assessment in ADPKD.

METHODS

We assessed coverage and variant quality in the ExAC cohort and combined allele frequency and age data from the ExAC database (n = 60,706) with curated variants from 2000 ADPKD pedigrees (ADPKD Mutation Database).

RESULTS

Seventy-six percent of PKD1 and PKD2 were sequenced adequately for variant discovery and variant quality was high in ExAC. In ExAC, we identified 25 truncating and 393 previously reported disease-causing variants in PKD1 and PKD2, 6.9-fold higher than expected. Fifty-four different variants, previously classified as disease-causing, were observed in ≥5 participants in ExAC.

CONCLUSION

Our study demonstrates that many previously implicated disease-causing variants are too common, challenging their pathogenicity, or penetrance. The presence of protein-truncating variants in older participants in ExAC demonstrates the complexity of variant classification and highlights need for further study of prevalence and penetrance of this common monogenic disease.

Bilineal inheritance of pathogenic PKD1 and PKD2 variants in a Czech family with autosomal dominant polycystic kidney disease - a case report

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary renal disorder, leading to end stage renal failure and kidney transplantation in its most serious form. The severity of the disease's manifestation depends on the genetic determination of ADPKD. The huge variability of different phenotypes (even within a single family) is not only modulated by the two main ADPKD genes (PKD1 and PKD2) but also by modifier genes and the whole genetic background.

CASE PRESENTATION

This is a report of an ADPKD family with co-inheritance of PKD1 and PKD2 pathogenic variants. The proband, with an extremely serious manifestation of ADPKD (the man was diagnosed in early childhood, and with end stage renal disease aged 23), underwent genetic analysis of PKD1 and PKD2, which revealed the presence of pathogenic mutations in both of these genes. The missense PKD2 mutation p.Arg420Gly came from the proband's father, with a mild ADPKD phenotype. The same mutation of the PKD2 gene and similar mild disease presentation were found in the proband's aunt (father's sister) and her son. The nonsense mutation p.Gln2196* within the PKD1 gene was probably inherited from the proband's mother, who died at the age of 45. It was only discovered post mortem, that the real cause of her death was kidney failure as a consequence of untreated ADPKD. Unfortunately, neither the DNA of the proband's mother nor the DNA of any other family members from this side of the pedigree were available for further examination. The proband underwent successful cadaveric kidney transplantation at the age of 24, and this replacement therapy lasted for the next 15 years.

CONCLUSIONS

Here, we present a first case of bilineal ADPKD inheritance in the Czech Republic. This report highlights the significant role of modifier genes in genetic determination of ADPKD, especially in connection with seriously deteriorated disease phenotypes. In our case, the modifying role is probably mediated by the PKD2 gene.

Estimation of minimal disease prevalence from population genomic data: Application to primary familial brain calcification

Primary Familial Brain Calcification (PFBC) is a rare calcifying disorder of the brain with autosomal dominant inheritance, of unknown prevalence. Four causal genes have been identified so far: SLC20A2, PDGFB, PDGFRB, and XPR1, with pathogenic, probably pathogenic or missense variants of unknown significance found in 27.7% probands in the French PFBC series. Estimating PFBC prevalence from a clinical input is arduous due to a large diversity of symptoms and ages of onset and to incomplete clinical penetrance. Abnormal calcifications on CT scan can be used as a reliable diagnostic biomarker whatever the clinical status, but differential diagnoses should be ruled out including the challenging exclusion of common basal ganglia calcifications. Our primary aim was to estimate the minimal prevalence of PFBC due to a variant in one of the known genes. We extracted variants from the four known genes present in the gnomAD database gathering genomic data from 138,632 individuals. We interpreted all variants based on their predicted effect, their frequency, and previous studies on PFBC patients. Using the most conservative estimate, the minimal prevalence of PFBC related to a variant in one of the four known genes was 4.5 p. 10,000 (95%CI [3.4-5.5] p. 10,000). We then used variant detection rates in patients to extrapolate an overall minimal prevalence of PFBC to 2.1 p. 1,000 (95%CI [1.9-2.4] p. 1,000). The population-based genomic analysis indicates that PFBC is not an exceptionally rare disorder, still underestimated and underdiagnosed.

Genetic Complexity of Autosomal Dominant Polycystic Kidney and Liver Diseases

Data indicate significant phenotypic and genotypic overlap, plus a common pathogenesis, between two groups of inherited disorders, autosomal dominant polycystic kidney diseases (ADPKD), a significant cause of ESRD, and autosomal dominant polycystic liver diseases (ADPLD), which result in significant PLD with minimal PKD. Eight genes have been associated with ADPKD (PKD1 and PKD2), ADPLD (PRKCSH, SEC63, LRP5, ALG8, and SEC61B), or both (GANAB). Although genetics is only infrequently used for diagnosing these diseases and prognosing the associated outcomes, its value is beginning to be appreciated, and the genomics revolution promises more reliable and less expensive molecular diagnostic tools for these diseases. We therefore propose categorization of patients with a phenotypic and genotypic descriptor that will clarify etiology, provide prognostic information, and better describe atypical cases. In genetically defined cases, the designation would include the disease and gene names, with allelic (truncating/nontruncating) information included for PKD1 Recent data have shown that biallelic disease including at least one weak ADPKD allele is a significant cause of symptomatic, very early onset ADPKD. Including a genic (and allelic) descriptor with the disease name will provide outcome clues, guide treatment, and aid prevalence estimates.

The Genetic and Cellular Basis of Autosomal Dominant Polycystic Kidney Disease-A Primer for Clinicians

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common genetic disorders worldwide. In recent decades, the field has undergone a revolution, starting with the identification of causal ADPKD genes, including PKD1, PKD2, and the recently identified GANAB. In addition, advances defining the genetic mechanisms, protein localization and function, and the identification of numerous pathways involved in the disease process, have contributed to a better understanding of this illness. Together, this has led to a better prognosis, diagnosis, and treatment in clinical practice. In this mini review, we summarize and discuss new insights about the molecular mechanisms underlying ADPKD, including its genetics, protein function, and cellular pathways.