Progressive Loss of Renal Function Is an Age-Dependent Heritable Trait in Type 1 Autosomal Dominant Polycystic Kidney Disease

A new atypical splice mutation in PKD2 leading to autosomal dominant polycystic kidney disease in a Chinese family

INTRODUCTION

Autosomal dominant polycystic kidney disease (ADPKD) is a very common hereditary renal disorder. Mutations in PKD1 and PKD2 , identified as disease-causing genes, account for 85% and 15% of the ADPKD cases, respectively.

METHODS

In this study, the mutation analysis of polycystic kidney disease (PKD) genes was performed in a Chinese family with suspected ADPKD using targeted clinical exome sequencing (CES). The candidate pathogenic variants were further tested by using Sanger sequencing and validated for co-segregation. In addition, reverse transcription-polymerase chain reaction (RT-PCR) was performed to test for abnormal splicing and assess its potential pathogenicity.

RESULTS

A novel atypical splicing mutation that belongs to unclassified variants (UCVs), IVS6+5G>C, was identified in three family members by CES and was shown to co-segregate only with the affected individuals. The RT-PCR revealed the abnormal splicing of exon 6, which thus caused truncating mutation. These findings suggested that the atypical splice site alteration, IVS6+5G>C, in the PKD2 gene was the potential pathogenic mutation leading to ADPKD in this Chinese family.

CONCLUSION

The data available in this study provided strong evidence that IVS6+5G>C is the potential pathogenic mutation for ADPKD. In addition, our findings emphasised the significance of functional analysis of UCVs and genotype-phenotype correlation in ADPKD.

Diet and Physical Activity in Adult Dominant Polycystic Kidney Disease: A Review of the Literature

Autosomal polycystic kidney disease is the most common inherited kidney disease determining 5% of all end-stage kidney disease. The only therapy approved for this condition is Tolvaptan, which, with its aquaretic effect, has a strong effect on patients' daily life. Recently, the literature has been enriched with new works that analyze possible non-pharmacological therapeutic strategies to slow cysts' enlargement and chronic kidney disease progression. Among them, dietary schemes reducing carbohydrate intake and inducing ketoses have been demonstrated to have efficacy in several pre-clinical and clinical studies. A ketogenic diet, calorie restriction, intermittent fasting, and time-restricted feeding can reduce aerobic glycolysis and inhibit the mTOR pathway, producing a reduction in cyst cell proliferation, a reduction in kidney volume, and helping to preserve kidney function. ADPKD's burden of disease has an impact on patients' quality of life, and the possibility to play sports or carry out physical exercise can help people in everyday life. The multisystemic character of the disease, especially cardiovascular involvement, needs to be carefully evaluated to establish the quality and quantity of physical activity that patients can safely carry out.

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

Rationale & Objective

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

Study Design

Cross-sectional study.

Setting & Participants

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

Exposure

ADPKD.

Outcome

Kidney failure, dialysis, or receipt of kidney transplant.

Analytical Approach

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

Results

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

Limitations

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

Conclusions

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

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.

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.

Global microRNA profiling in human urinary exosomes reveals novel disease biomarkers and cellular pathways for autosomal dominant polycystic kidney disease

MicroRNAs (miRNAs) play an important role in regulating gene expression in health and disease but their role in modifying disease expression in Autosomal Dominant Polycystic Kidney Disease (ADPKD) remains uncertain. Here, we profiled human urinary exosome miRNA by global small RNA-sequencing in an initial discovery cohort of seven patients with ADPKD with early disease (eGFR over 60ml/min/1.73m²), nine with late disease (eGFR under 60ml/min/1.73m²), and compared their differential expression with six age and sex matched healthy controls. Two kidney-enriched candidate miRNA families were identified (miR-192/miR-194-2 and miR-30) and selected for confirmatory testing in a 60 patient validation cohort by quantitative polymerase chain reaction. We confirmed that miR-192-5p, miR-194-5p, miR-30a-5p, miR-30d-5p and miR-30e-5p were significantly downregulated in patient urine exosomes, in murine Pkd1 cystic kidneys and in human PKD1 cystic kidney tissue. All five miRNAs showed significant correlations with baseline eGFR and ultrasound-determined mean kidney length and improved the diagnostic performance (area under the curve) of mean kidney length for the rate of disease progression. Finally, inverse correlations of these two miRNA families with increased expression in their predicted target genes in patient PKD1 cystic tissue identified dysregulated pathways and transcriptional networks including novel interactions between miR-194-5p and two potentially relevant candidate genes, PIK3R1 and ANO1. Thus, our results identify a subset of urinary exosomal miRNAs that could serve as novel biomarkers of disease progression and suggest new therapeutic targets in ADPKD.

Identification of housekeeping genes for microRNA expression analysis in kidney tissues of Pkd1 deficient mouse models

Polycystic kidney disease is a complex clinical entity which comprises a group of genetic diseases that leads to renal cyst development. We evaluated the most suitable housekeeping genes for microRNA expression by RT-qPCR analyses of kidney tissues in Pkd1-deficient mouse models from a panel of five candidates genes (miR-20a, miR-25, miR-26a, miR-191 and U6) and 3 target genes (miR-17, miR-21 and let-7a) using samples from kidneys of cystic mice (Pkd1^flox/flox:Nestin^cre, CY), non-cystic controls (Pkd1^flox/flox, NC), Pkd1-haploinsufficient (Pkd1^+/−, HT), wild-type controls (Pkd1^+/+, WT), severely cystic mice (Pkd1^V/V, SC), wild-type controls (CO). The stability of the candidate genes was investigated using NormFinder, GeNorm, BestKeeper, DataAssist, and RefFinder software packages and the comparative ΔCt method. The analyses identified miR-26a as the most stable housekeeping gene for all kidney samples, miR-20a for CY and NC, miR-20a and miR-26a for HT and WT, and miR-25 and miR-26a for SC and CO. Expression of miR-21 was upregulated in SC compared to CO and trends of miR-21 upregulation and let-7a downregulation in CY and HT compared to its control kidneys, when normalized by different combinations of miR-20a, miR-25 and miR-26a. Our findings established miR-20a, miR-25, and miR-26a as the best housekeeping genes for miRNA expression analyses by RT-qPCR in kidney tissues of Pkd1-deficient mouse models.

Growth Pattern of Kidney Cyst Number and Volume in Autosomal Dominant Polycystic Kidney Disease

BACKGROUND AND OBJECTIVES

To evaluate the growth pattern of kidney cyst number and cyst volume in association with kidney size, demographics, and genotypes in autosomal dominant polycystic kidney disease.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Kidney cyst number and cyst volume were measured from serial magnetic resonance images, giving a maximum follow-up of 14.23 years, from 241 patients with autosomal dominant polycystic kidney disease (15-46 years old at baseline). The growth pattern was analyzed, in association with sex, age, height-adjusted total kidney volume, and genotype, using linear mixed models of repeated measurements and tests of interactions with age (as a time-dependent covariate) to assess rates of change over time. Models were also fit using Irazabal class. Genotypic groups were characterized as either (1) PKD1 truncating, PKD1 nontruncating, and PKD2 plus patients with no mutation detected; or (2) in combination with PKD1 mutation strength groups.

RESULTS

Imaging and genetic data were collected (at least one visit) for 236 participants. The mean height-adjusted total cyst number increased exponentially over time from a baseline value of 762 to 1715 at the last clinic visit, while the mean height-adjusted total cyst volume increased exponentially from 305 to 770 ml. Height-adjusted total kidney volume, height-adjusted total cyst number, and height-adjusted total cyst volume were all highly correlated over time. Female participants and participants with larger height-adjusted total kidney volume at baseline showed smaller rates of change in the log of height-adjusted total cyst number and cyst volume. PKD1 was associated with significant increases in both cyst number and volume at a given age, but genotype did not significantly affect the rate of growth.

CONCLUSIONS

Both height-adjusted total cyst number and height-adjusted total cyst volume increased exponentially and more than doubled over 14.23 years of follow-up. Compared with PKD2 plus no mutation detected, PKD1 was associated with a greater cyst number and volume at a given age, but no significant difference in the rate of growth.

Intrafamilial Variability of ADPKD

Introduction

Discordance in kidney disease severity between affected relatives is a recognized feature of autosomal dominant polycystic kidney disease (ADPKD). Here, we report a systematic study of a large cohort of families to define the prevalence and clinical features of intrafamilial discordance in ADPKD.

Methods

The extended Toronto Genetic Epidemiology Study of Polycystic Kidney Disease (eTGESP) cohort includes 1390 patients from 612 unrelated families with ADPKD ascertained in a regional polycystic kidney disease center. All probands underwent comprehensive PKD1 and PKD2 mutation screening. Total kidney volume by magnetic resonance imaging (MRI) was available in 500 study patients.

Results

Based on (i) rate of estimated glomerular filtration rate (eGFR) decline, (ii) age at onset of end-stage renal disease (ESRD), and (iii) Mayo Clinic Imaging Classification (MCIC), 20% of patients were classified as having mild disease, and 33% as having severe disease. Intrafamilial ADPKD discordance with at least 1 mild and 1 severe case was observed in 43 of 371 (12%) families, at a similar frequency regardless of the responsible gene (PKD1/PKD2/no mutation detected) or mutation type (protein-truncating versus nontruncating). Intrafamilial discordance was more common in larger families and was present in 30% of families with more than 5 affected members. The heritability of age at onset of ESRD was similar between different mutation types.

Conclusion

Extreme kidney disease discordance is present in at least 12% of families with ADPKD, regardless of the underlying mutated gene or mutation class. Delineating genetic and environmental modifiers underlying the observed intrafamilial ADPKD variability will provide novel insights into the mechanisms of progression in ADPKD.

Safe Nanocomposite-Mediated Efficient Delivery of MicroRNA Plasmids for Autosomal Dominant Polycystic Kidney Disease (ADPKD) Therapy

There is currently no cure for gene mutation-caused autosomal dominant polycystic kidney disease (ADPKD). Over half of patients with ADPKD eventually develop kidney failure, requiring dialysis or kidney transplantation. Current treatment modalities for ADPKD focus on reducing morbidity and mortality from renal and extrarenal complications of the disease. MicroRNA has been shown to be useful in treating ADPKD. This study combines anti-miRNA plasmids and iron oxide/alginate nanoparticles for conjugation with antikidney antibodies. These nanocomposites can specifically target renal tubular cells, providing a potential treatment for ADPKD. Magnetic resonance imaging and in vivo imaging system results show effective targeting of renal cells. Anti-miRNA plasmids released from the nanocomposites inhibit cell proliferation and cyst formation in the PKD cellular and animal models. The results suggest the novel combination of the anti-miRNA plasmids and nanomaterials provides potential clinical implications for ADPKD treatment.

Polycystic kidney disease

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

Prevalence Estimates of Polycystic Kidney and Liver Disease by Population Sequencing

BACKGROUND

Estimating the prevalence of autosomal dominant polycystic kidney disease (ADPKD) is challenging because of age-dependent penetrance and incomplete clinical ascertainment. Early studies estimated the lifetime risk of ADPKD to be about one per 1000 in the general population, whereas recent epidemiologic studies report a point prevalence of three to five cases per 10,000 in the general population.

METHODS

To measure the frequency of high-confidence mutations presumed to be causative in ADPKD and autosomal dominant polycystic liver disease (ADPLD) and estimate lifetime ADPKD prevalence, we used two large, population sequencing databases, gnomAD (15,496 whole-genome sequences; 123,136 exome sequences) and BRAVO (62,784 whole-genome sequences). We used stringent criteria for defining rare variants in genes involved in ADPKD (PKD1, PKD2), ADPLD (PRKCSH, SEC63, GANAB, ALG8, SEC61B, LRP5), and potential cystic disease modifiers; evaluated variants for quality and annotation; compared variants with data from an ADPKD mutation database; and used bioinformatic tools to predict pathogenicity.

RESULTS

Identification of high-confidence pathogenic mutations in whole-genome sequencing provided a lower boundary for lifetime ADPKD prevalence of 9.3 cases per 10,000 sequenced. Estimates from whole-genome and exome data were similar. Truncating mutations in ADPLD genes and genes of potential relevance as cyst modifiers were found in 20.2 cases and 103.9 cases per 10,000 sequenced, respectively.

CONCLUSIONS

Population whole-genome sequencing suggests a higher than expected prevalence of ADPKD-associated mutations. Loss-of-function mutations in ADPLD genes are also more common than expected, suggesting the possibility of unrecognized cases and incomplete penetrance. Substantial rare variation exists in genes with potential for phenotype modification in ADPKD.

Refining Genotype-Phenotype Correlation in Autosomal Dominant Polycystic Kidney Disease

Renal disease variability in autosomal dominant polycystic kidney disease (ADPKD) is strongly influenced by the gene locus (PKD1 versus PKD2). Recent studies identified nontruncating PKD1 mutations in approximately 30% of patients who underwent comprehensive mutation screening, but the clinical significance of these mutations is not well defined. We examined the genotype-renal function correlation in a prospective cohort of 220 unrelated ADPKD families ascertained through probands with serum creatinine ≤1.4 mg/dl at recruitment. We screened these families for PKD1 and PKD2 mutations and reviewed the clinical outcomes of the probands and affected family members. Height-adjusted total kidney volume (htTKV) was obtained in 161 affected subjects. Multivariate Cox proportional hazard modeling for renal and patient survival was performed in 707 affected probands and family members. Overall, we identified pathogenic mutations in 84.5% of our families, in which the prevalence of PKD1 truncating, PKD1 in-frame insertion/deletion, PKD1 nontruncating, and PKD2 mutations was 38.3%, 4.3%, 27.1%, and 30.3%, respectively. Compared with patients with PKD1 truncating mutations, patients with PKD1 in-frame insertion/deletion, PKD1 nontruncating, or PKD2 mutations have smaller htTKV and reduced risks (hazard ratio [95% confidence interval]) of ESRD (0.35 [0.14 to 0.91], 0.10 [0.05 to 0.18], and 0.03 [0.01 to 0.05], respectively) and death (0.31 [0.11 to 0.87], 0.20 [0.11 to 0.38], and 0.18 [0.11 to 0.31], respectively). Refined genotype-renal disease correlation coupled with targeted next generation sequencing of PKD1 and PKD2 may provide useful clinical prognostication for ADPKD.

High-resolution genetic localization of a modifying locus affecting disease severity in the juvenile cystic kidneys (jck) mouse model of polycystic kidney disease

We have previously demonstrated that a locus on proximal Chr 4 modifies disease severity in the juvenile cystic kidney (jck) mouse, a model of polycystic kidney disease (PKD) that carries a mutation of the Nek8 serine-threonine kinase. In this study, we used QTL analysis of independently constructed B6.D2 congenic lines to confirm this and showed that this locus has a highly significant effect. We constructed sub-congenic lines to more specifically localize the modifier and have determined it resides in a 3.2 Mb interval containing 28 genes. These include Invs and Anks6, which are both excellent candidates for the modifier as mutations in these genes result in PKD and both genes are known to genetically and physically interact with Nek8. However, examination of strain-specific DNA sequence and kidney expression did not reveal clear differences that might implicate either gene as a modifier of PKD severity. The fact that our high-resolution analysis did not yield an unambiguous result highlights the challenge of establishing the causality of strain-specific variants as genetic modifiers, and suggests that alternative strategies be considered.

Endothelin and tubulointerstitial renal disease

All components of the endothelin (ET) system are present in renal tubular cells. In this review, we summarize current knowledge about ET and the most common tubular diseases: acute kidney injury (AKI) and polycystic kidney disease. AKI originally was called acute tubular necrosis, pointing to the most prominent morphologic findings. Similarly, cysts in polycystic kidney disease, and especially in autosomal-dominant polycystic kidney disease, are of tubular origin. Preclinical studies have indicated that the ET system and particularly ETA receptors are involved in the pathogenesis of ischemia-reperfusion injury, although these findings have not been translated to clinical studies. The ET system also has been implicated in radiocontrast-dye-induced AKI, however, ET-receptor blockade in a large human study was not successful. The ET system is activated in sepsis models of AKI; the effectiveness of ET blocking agents in preclinical studies is variable depending on the model and the ET-receptor antagonist used. Numerous studies have shown that the ET system plays an important role in the complex pathophysiology associated with cyst formation and disease progression in polycystic kidney disease. However, results from selective targeting of ET-receptor subtypes in animal models of polycystic kidney disease have proved disappointing and do not support clinical trials. These studies have shown that a critical balance between ETA and ETB receptor action is necessary to maintain structure and function in the cystic kidney. In summary, ETs have been implicated in the pathogenesis of several renal tubulointerstitial diseases, however, experimental animal findings have not yet led to use of ET blockers in human beings.

Genetics and pathogenesis of autosomal dominant polycystic kidney disease: 20 years on

Autosomal dominant polycystic kidney disease (ADPKD), the most common inherited kidney disorder, is characterized by the progressive development and expansion of bilateral fluid-filled cysts derived from the renal tubule epithelial cells. Although typically leading to end-stage renal disease in late middle age, ADPKD represents a continuum, from neonates with hugely enlarged cystic kidneys to cases with adequate kidney function into old age. Since the identification of the first causative gene (i.e., PKD1, encoding polycystin 1) 20 years ago, genetic studies have uncovered a large part of the key factors that underlie the phenotype variability. Here, we provide a comprehensive review of these significant advances as well as those related to disease pathogenesis models, including mutation analysis of PKD1 and PKD2 (encoding polycystin 2), current mutation detection rate, allelic heterogeneity, genotype and phenotype relationships (in terms of three different inheritance patterns: classical autosomal dominant inheritance, complex inheritance, and somatic and germline mosaicism), modifier genes, the role of second somatic mutation hit in renal cystogenesis, and findings from mouse models of polycystic kidney disease. Based upon a combined consideration of the current knowledge, we attempted to propose a unifying framework for explaining the phenotype variability in ADPKD.

Autosomal dominant polycystic kidney disease: the changing face of clinical management

Autosomal dominant polycystic kidney disease is the most common inherited kidney disease and accounts for 7-10% of all patients on renal replacement therapy worldwide. Although first reported 500 years ago, this disorder is still regarded as untreatable and its pathogenesis is poorly understood despite much study. During the past 40 years, however, remarkable advances have transformed our understanding of how the disease develops and have led to rapid changes in diagnosis, prognosis, and treatment, especially during the past decade. This Review will summarise the key findings, highlight recent developments, and look ahead to the changes in clinical practice that will likely arise from the adoption of a new management framework for this major kidney disease.

Imaging-based diagnosis of autosomal dominant polycystic kidney disease

The clinical use of conventional ultrasonography (US) in autosomal dominant polycystic kidney disease (ADPKD) is currently limited by reduced diagnostic sensitivity, especially in at-risk subjects younger than 30 years of age. In this single-center prospective study, we compared the diagnostic performance of MRI with that of high-resolution (HR) US in 126 subjects ages 16-40 years born with a 50% risk of ADPKD who underwent both these renal imaging studies and comprehensive PKD1 and PKD2 mutation screening. Concurrently, 45 healthy control subjects without a family history of ADPKD completed the same imaging protocol. We analyzed 110 at-risk subjects whose disease status was unequivocally defined by molecular testing and 45 unaffected healthy control subjects. Using a total of >10 cysts as a test criterion in subjects younger than 30 years of age, we found that MRI provided both a sensitivity and specificity of 100%. Comparison of our results from HR US with those from a previous study of conventional US using the test criterion of a total of three or more cysts found a higher diagnostic sensitivity (approximately 97% versus approximately 82%) with a slightly decreased specificity (approximately 98% versus 100%) in this study. Similar results were obtained in test subjects between the ages of 30 and 40 years old. These results suggest that MRI is highly sensitive and specific for diagnosis of ADPKD. HR US has the potential to rival the diagnostic performance of MRI but is both center- and operator-dependent.

Renal transplantation in autosomal dominant polycystic kidney disease

In patients with autosomal dominant polycystic kidney disease (ADPKD) evaluated for kidney transplantation, issues related to native nephrectomy, cystic liver involvement, screening for intracranial aneurysms and living-related kidney donation deserve special consideration. Prophylactic native nephrectomy is restricted to patients with a history of cyst infection or recurrent haemorrhage or to those in whom space must be made to implant the graft. Patients with liver involvement require pretransplant imaging. Selection of patients for pretransplant screening of intracranial aneurysms should follow the general recommendations for patients with ADPKD. In living related-donor candidates aged <30 years and at-risk of ADPKD, molecular genetic testing should be carried out when ultrasonography and MRI findings are normal or equivocal. After kidney transplantation, patient and graft survival rates are excellent and the volume of native kidneys decreases. However, liver cysts continue to grow and treatment with a somatostatin analogue should be considered in patients with massive cyst involvement. Cerebrovascular events have a marginal effect on post-transplant morbidity and mortality. An increased risk of new-onset diabetes mellitus and nonmelanoma skin cancers has been reported, but several studies have challenged these findings. Finally, no data currently support the preferential use of mammalian target of rapamycin inhibitors as immunosuppressive agents in transplant recipients with ADPKD.

Experimental therapies and ongoing clinical trials to slow down progression of ADPKD

The improvement of imaging techniques over the years has contributed to the understanding of the natural history of autosomal dominant polycystic kidney disease, and facilitated the observation of its structural progression. Advances in molecular biology and genetics have made possible a greater understanding of the genetics, molecular, and cellular pathophysiologic mechanisms responsible for its development and have laid the foundation for the development of potential new therapies. Therapies targeting genetic mechanisms in ADPKD have inherent limitations. As a result, most experimental therapies at the present time are aimed at delaying the growth of the cysts and associated interstitial inflammation and fibrosis by targeting tubular epithelial cell proliferation and fluid secretion by the cystic epithelium. Several interventions affecting many of the signaling pathways disrupted in ADPKD have been effective in animal models and some are currently being tested in clinical trials.

[Kidney and smoking: literature review and focus]

Smoking remains a major public health problem. It is associated with a considerable number of deaths in the world's population. Smoking is just like high blood pressure, an independent predictor of progression to any primary renal disease and renal transplant patients. It seems that smoking cessation slows the progression of kidney disease in smokers. The literature data are sometimes contradictory about it because of some methodological weaknesses. However, experimental models highlight the harmful effects of tobacco by hemodynamic and non-hemodynamic factors. The conclusion is that a major effort should be further produced by the nephrology community to motivate our patients to stop smoking.

Clinical utility of PKD2 mutation testing in a polycystic kidney disease cohort attending a specialist nephrology out-patient clinic

Background

ADPKD affects approximately 1:1000 of the worldwide population. It is caused by mutations in two genes, PKD1 and PKD2. Although allelic variation has some influence on disease severity, genic effects are strong, with PKD2 mutations predicting later onset of ESRF by up to 20 years. We therefore screened a cohort of ADPKD patients attending a nephrology out-patient clinic for PKD2 mutations, to identify factors that can be used to offer targeted gene testing and to provide patients with improved prognostic information.

Methods

142 consecutive individuals presenting to a hospital nephrology out-patient service with a diagnosis of ADPKD and CKD stage 4 or less were screened for mutations in PKD2, following clinical evaluation and provision of a detailed family history (FH).

Results

PKD2 mutations were identified in one fifth of cases. 12% of non-PKD2 patients progressed to ESRF during this study whilst none with a PKD2 mutation did (median 38.5 months of follow-up, range 16–88 months, p < 0.03). A significant difference was found in age at ESRF of affected family members (non-PKD2 vs. PKD2, 54 yrs vs. 65 yrs; p < 0.0001). No PKD2 mutations were identified in patients with a FH of ESRF occurring before age 50 yrs, whereas a PKD2 mutation was predicted by a positive FH without ESRF.

Conclusions

PKD2 testing has a clinically significant detection rate in the pre-ESRF population. It did not accurately distinguish those individuals with milder renal disease defined by stage of CKD but did identify a group less likely to progress to ESRF. When used with detailed FH, it offers useful prognostic information for individuals and their families. It can therefore be offered to all but those whose relatives have developed ESRF before age 50.

Loss of GM3 synthase gene, but not sphingosine kinase 1, is protective against murine nephronophthisis-related polycystic kidney disease

Genetic forms of polycystic kidney diseases (PKDs), including nephronophthisis, are characterized by formation of fluid-filled cysts in the kidneys and progression to end-stage renal disease. No therapies are currently available to treat cystic diseases, making it imperative to dissect molecular mechanisms in search of therapeutic targets. Accumulating evidence suggests a pathogenic role for glucosylceramide (GlcCer) in multiple forms of PKD. It is not known, however, whether other structural glycosphingolipids (GSLs) or bioactive signaling sphingolipids (SLs) modulate cystogenesis. Therefore, we set out to address the role of a specific GSL (ganglioside GM3) and signaling SL (sphingosine-1-phosphate, S1P) in PKD progression, using the jck mouse model of nephronopthisis. To define the role of GM3 accumulation in cystogenesis, we crossed jck mice with mice carrying a targeted mutation in the GM3 synthase (St3gal5) gene. GM3-deficient jck mice displayed milder PKD, revealing a pivotal role for ganglioside GM3. Mechanistic changes in regulation of the cell-cycle machinery and Akt-mTOR signaling were consistent with reduced cystogenesis. Dramatic overexpression of sphingosine kinase 1 (Sphk1) mRNA in jck kidneys suggested a pathogenic role for S1P. Surprisingly, genetic loss of Sphk1 exacerbated cystogenesis and was associated with increased levels of GlcCer and GM3. On the other hand, increasing S1P accumulation through pharmacologic inhibition of S1P lyase had no effect on the progression of cystogenesis or kidney GSL levels. Together, these data suggest that genes involved in the SL metabolism may be modifiers of cystogenesis, and suggest GM3 synthase as a new anti-cystic therapeutic target.

Low birth weight is associated with earlier onset of end-stage renal disease in Danish patients with autosomal dominant polycystic kidney disease

Low-birth-weight individuals have a higher risk of hypertension and end-stage renal disease (ESRD). Here we investigated whether low birth weight was associated with earlier onset of ESRD in patients with autosomal dominant polycystic kidney disease (ADPKD). In collaboration with all Danish departments of nephrology, 307 of 357 patients with ADPKD and ESRD born and living in Denmark were recruited. We were able to analyze complete data of 284 patients obtained from both hospital medical files and midwife protocols in the Danish State Archives. Multivariable linear regression adjusted for birth weight, adult height, mean arterial pressure, gender, birth decade, and type of antihypertensive treatment showed that for every kilogram increase in birth weight, the age at onset of ESRD significantly increased by 1.7 years. Male gender and increased mean arterial pressure were both associated with earlier onset of ESRD. Patients treated with renin-angiotensin system blockade or calcium channel blockers during follow-up had significantly later onset of ESRD by 4.3 years and 2.1 years, respectively. Treatment with beta-blockade or a diuretic was not associated with the age at onset of ESRD. Thus, low birth weight may contribute to considerable phenotypic variability in the progression of renal disease between individuals with ADPKD.

A missense mutation in PKD1 attenuates the severity of renal disease

Mutations of PKD1 and PKD2 account for most cases of autosomal dominant polycystic kidney disease (ADPKD). Compared with PKD2, patients with PKD1 typically have more severe renal disease. Here, we report a follow-up study of a unique multigeneration family with bilineal ADPKD (NFL10) in which a PKD1 disease haplotype and a PKD2 (L736X) mutation co-segregated with 18 and 14 affected individuals, respectively. In our updated genotype-phenotype analysis of the family, we found that PKD1-affected individuals had uniformly mild renal disease similar to the PKD2-affected individuals. By sequencing all the exons and splice junctions of PKD1, we identified two missense mutations (Y528C and R1942H) from a PKD1-affected individual. Although both variants were predicted to be damaging to the mutant protein, only Y528C co-segregated with all of the PKD1-affected individuals in NFL10. Studies in MDCK cells stably expressing wild-type and mutant forms of PKD found that cell lines expressing the Y528C variant formed cysts in culture and displayed increased rates of growth and apoptosis. Thus, Y528C functions as a hypomorphic PKD1 allele. These findings have important implications for pathogenic mechanisms and molecular diagnostics of ADPKD.

Cystogenic potential of CD133+ progenitor cells of human polycystic kidneys

In autosomal dominant polycystic kidney disease, cysts arise focally and disrupt normal renal tissue leading to renal failure. In the present study, we show that cyst-lining cells express the stem cell marker CD133. CD133+ progenitor cells isolated from polycystic kidney, carrying mutations of PKD genes, showed a dedifferentiated phenotype similar to CD133+ progenitor cells from normal kidney. However, these cells were more proliferative and presented a defective epithelial differentiation phenotype with respect to normal renal CD133+ cells as they were not able to express all tubular epithelial cell markers when cultured in epithelial differentiation medium. Polycystic CD133+ cells, in contrast to normal renal CD133+ cells, formed cysts in vitro in a three-dimensional culture system and in vivo when injected subcutaneously within Matrigel in SCID mice. Rapamycin treatment reduced in vitro proliferation of polycystic CD133+ cells and decreased cystogenesis both in vitro and in vivo. The in vitro epithelial differentiation was only partially improved by rapamycin. These results indicate that polycystic CD133+ cells retain a dedifferentiated phenotype and the ability to generate cysts.

Diagnosis of autosomal-dominant polycystic kidney disease: an integrated approach

Autosomal-dominant polycystic kidney disease (ADPKD) is the most common Mendelian disorder of the kidney and accounts for approximately 5% of end-stage renal disease in developed countries. It is characterized by focal and sporadic development of renal cysts that increase in number and size with age. Mutations of 2 genes (ie, PKD1 and PKD2) account for most of the cases. Although the clinical manifestations of both gene types overlap completely, PKD1 is associated with more severe disease than PKD2, with bigger kidneys and earlier onset of end-stage renal disease. In general, the diagnosis of ADPKD is commonly made by renal ultrasonography. Age-dependent ultrasound criteria have been established for both diagnosis and disease exclusion in subjects at risk of PKD1. However, the utility of these criteria in the clinic setting is unclear because their performance characteristics have not been defined for the milder PKD2 and the gene type for most test subjects is unknown. Recently, highly predictive ultrasound diagnostic criteria have been derived for at-risk subjects of unknown gene type. In addition, molecular genetic testing is now available for the diagnosis of ADPKD, especially in subjects with equivocal imaging results, with a negative or indeterminate family history, or in younger at-risk individuals with a negative ultrasound study being evaluated as potential living-related kidney donor. Here, we review the clinical utilities and limitations of these imaging- and molecular-based diagnostic tests, and outline our approach for the evaluation of individuals suspected to have ADPKD.

Genetic variation of DKK3 may modify renal disease severity in ADPKD

Significant variation in the course of autosomal dominant polycystic kidney disease ( ADPKD) within families suggests the presence of effect modifiers. Recent studies of the variation within families harboring PKD1 mutations indicate that genetic background may account for 32 to 42% of the variance in estimated GFR (eGFR) before ESRD and 43 to 78% of the variance in age at ESRD onset, but the genetic modifiers are unknown. Here, we conducted a high-throughput single-nucleotide polymorphism (SNP) genotyping association study of 173 biological candidate genes in 794 white patients from 227 families with PKD1. We analyzed two primary outcomes: (1) eGFR and (2) time to ESRD (renal survival). For both outcomes, we used multidimensional scaling to correct for population structure and generalized estimating equations to account for the relatedness among individuals within the same family. We found suggestive associations between each of 12 SNPs and at least one of the renal outcomes. We genotyped these SNPs in a second set of 472 white patients from 229 families with PKD1 and performed a joint analysis on both cohorts. Three SNPs continued to show suggestive/significant association with eGFR at the Dickkopf 3 (DKK3) gene locus; no SNPs significantly associated with renal survival. DKK3 antagonizes Wnt/beta-catenin signaling, which may modulate renal cyst growth. Pending replication, our study suggests that genetic variation of DKK3 may modify severity of ADPKD resulting from PKD1 mutations.

Heritability of measures of kidney disease among Zuni Indians: the Zuni Kidney Project

BACKGROUND

The long-term goal of the GKDZI (Genetics of Kidney Disease in Zuni Indians) Study is to identify genes, environmental factors, and genetic-environmental interactions that modulate susceptibility to renal disease and intermediate phenotypes.

STUDY DESIGN

A community-based participatory research approach was used to recruit family members of individuals with kidney disease.

SETTING & PARTICIPANTS

The study was conducted in the Zuni Indians, a small endogamous tribe located in rural New Mexico. We recruited members of extended families, ascertained through a proband with kidney disease and at least 1 sibling with kidney disease. 821 participants were recruited, comprising 7,702 relative pairs. PREDICTOR OUTCOMES & MEASUREMENTS: Urine albumin-creatinine ratio (UACR) and hematuria were determined in 3 urine samples and expressed as a true ratio. Glomerular filtration rate (GFR) was estimated using the Modification of Diet in Renal Disease (MDRD) Study equation modified for American Indians. Probands were considered to have kidney disease if UACR was >or=0.2 in 2 or more of 3 spot urine samples or estimated GFR was decreased according to the CRIC (Chronic Renal Insufficiency Cohort) Study criteria.

RESULTS

Kidney disease was identified in 192 participants (23.4%). There were significant heritabilities for estimated GFR, UACR, serum creatinine, serum urea nitrogen, and uric acid and a variety of phenotypes related to obesity, diabetes, and cardiovascular disease. There were significant genetic correlations of some kidney-related phenotypes with these other phenotypes.

LIMITATIONS

Limitations include absence of renal biopsy, possible misclassification bias, lack of direct GFR measurements, and failure to include all possible environmental interactions.

CONCLUSIONS

Many phenotypes related to kidney disease showed significant heritabilities in Zuni Indians, and there were significant genetic correlations with phenotypes related to obesity, diabetes, and cardiovascular disease. The study design serves as a paradigm for the conduct of research in relatively isolated, endogamous, underserved populations.

Glomerulocystic kidney: one hundred-year perspective

CONTEXT

Glomerular cysts, defined as Bowman space dilatation greater than 2 to 3 times normal size, are found in disorders of diverse etiology and with a spectrum of clinical manifestations. The term glomerulocystic kidney (GCK) refers to a kidney with greater than 5% cystic glomeruli. Although usually a disease of the young, GCK also occurs in adults.

OBJECTIVE

To assess the recent molecular genetics of GCK, review our files, revisit the literature, and perform in silico experiments.

DATA SOURCES

We retrieved 20 cases from our files and identified more than 230 cases published in the literature under several designations.

CONCLUSIONS

Although GCK is at least in part a variant of autosomal dominant or recessive polycystic kidney disease (PKD), linkage analysis has excluded PKD-associated gene mutations in many cases of GCK. A subtype of familial GCK, presenting with cystic kidneys, hyperuricemia, and isosthenuria is due to uromodullin mutations. In addition, the familial hypoplastic variant of GCK that is associated with diabetes is caused by mutations in TCF2, the gene encoding hepatocyte nuclear factor-1beta. The term GCK disease (GCKD) should be reserved for the latter molecularly recognized/inherited subtypes of GCK (not to include PKD). Review of our cases, the literature, and our in silico analysis of the overlapping genetic entities integrates established molecular-genetic functions into a proposed model of glomerulocystogenesis; a classification scheme emerged that (1) emphasizes the clinical significance of glomerular cysts, (2) provides a pertinent differential diagnosis, and (3) suggests screening for probable mutations.

Cystic diseases of the kidney: molecular biology and genetics

CONTEXT

Cystic diseases of the kidney are a very heterogeneous group of renal inherited conditions, with more than 33 genes involved and encompassing X-linked, autosomal dominant, and autosomal recessive inheritance. Although mostly monogenic with mendelian inheritance, there are clearly examples of oligogenic inheritance, such as 3 mutations in 2 genes, while the existence of genetic modifiers is perhaps the norm, based on the extent of variable expressivity and the broad spectrum of symptoms.

OBJECTIVES

To present in the form of a mini review the major known cystic diseases of the kidney for which genes have been mapped or cloned and characterized, with some information on their cellular and molecular biology and genetics, and to pay special attention to commenting on the issues of molecular diagnostics, in view of the genetic and allelic heterogeneity. Data Sources.-We used major reviews that make excellent detailed presentation of the various diseases, as well as original publications.

CONCLUSIONS

There is already extensive genetic heterogeneity in the group of cystic diseases of the kidney; however, there are still many more genes awaiting to be discovered that are implicated or mutated in these diseases. In addition, the synergism and interaction among this repertoire of gene products is largely unknown, while a common unifying aspect is the expression of nearly all of them at the primary cilium or the basal body. A major interplay of functions is anticipated, while mutations in all converge in the unifying phenotype of cyst formation.

Molecular diagnostics for autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a common nephropathy caused by mutations in either PKD1 or PKD2. Mutations in PKD1 account for approximately 85% of cases and cause more severe disease than mutations in PKD2. Diagnosis of ADPKD before the onset of symptoms is usually performed using renal imaging by either ultrasonography, CT or MRI. In general, these modalities are reliable for the diagnosis of ADPKD in older individuals. However, molecular testing can be valuable when a definite diagnosis is required in young individuals, in individuals with a negative family history of ADPKD, and to facilitate preimplantation genetic diagnosis. Although linkage-based diagnostic approaches are feasible in large families, direct mutation screening is generally more applicable. As ADPKD displays a high level of allelic heterogeneity, complete screening of both genes is required. Consequently, such screening approaches are expensive. Screening of individuals with ADPKD detects mutations in up to 91% of cases. However, only approximately 65% of patients have definite mutations with approximately 26% having nondefinite changes that require further evaluation. Collation of known variants in the ADPKD mutation database and systematic scoring of nondefinite variants is increasing the diagnostic value of molecular screening. Genic information can be of prognostic value and recent investigation of hypomorphic PKD1 alleles suggests that allelic information may also be valuable in some atypical cases. In the future, when effective therapies are developed for ADPKD, molecular testing may become increasingly widespread. Rapid developments in DNA sequencing may also revolutionize testing.

Determinants of renal disease variability in ADPKD

In common with other Mendelian diseases, the presentation and progression of autosomal dominant polycystic kidney disease (ADPKD) vary widely in the population. The typical course is of adult-onset disease with ESRD in the 6th decade. However, a small proportion has adequate renal function into the 9th decade, whereas others present with enlarged kidneys as neonates. ADPKD is genetically heterogeneous, and the disease gene is a major determinant of severity; PKD1 on average is associated with ESRD 20 years earlier than PKD2. The majority of PKD1 and PKD2 mutations are likely fully inactivating although recent studies indicate that some alleles retain partial activity (hypomorphic alleles). Homozygotes for such alleles are viable and in combination with an inactivating allele can result in early-onset disease. Hypomorphic alleles and mosaicism may also account for some cases with unusually mild disease. The degree of phenotypic variation detected in families indicates that genetic background influences disease severity. Genome-wide association studies are planned to map common variants associated with severity. Although ADPKD is a simple genetic disease, fully understanding the phenotypic variability requires consideration of influences at the genic, allelic, and genetic background level, and so, ultimately, it is complex.

Pkd2 dosage influences cellular repair responses following ischemia-reperfusion injury

Autosomal dominant polycystic kidney disease (ADPKD) results from mutations in either PKD1 or PKD2 and accounts for 10% of all patients on renal replacement therapy. The kidney disease phenotype is primarily characterized by cyst formation, but there are also prominent interstitial changes (inflammation, apoptosis, proliferation, and fibrosis). Using a model of unilateral ischemia-reperfusion injury, we tested the hypothesis that Pkd2 heterozygous kidneys are more sensitive to injury and that this could lead to interstitial inflammation and fibrosis. Baseline tubular proliferation in heterozygous kidneys was twofold higher than in wild-type kidneys. The magnitude and duration of tubular and interstitial proliferative responses was consistently greater in injured heterozygous compared with wild-type kidneys at all time points. Conversely, tubular p21 expression in heterozygotes was lower at baseline and following injury at all time points. Significantly more neutrophils and macrophages were detected in injured Pkd2 heterozygous kidneys at 2 days, correlating with increased expression of the cytokines interleukin (IL)-1beta and keratinocyte-derived chemokine and resulting in interstitial fibrosis at 28 days. We conclude that Pkd2 dosage influences both susceptibility and nature of the repair responses following injury. Polycystin-2 is therefore likely to play multiple roles in regulating tubular cell viability, repair, and remodeling in the mature kidney.

Fostering translation of genetics research: an NIDDK perspective

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the NIH, supports a large and varied portfolio of genetic research grants and contracts. As a funding agency, the NIDDK aims to support research that can be translated into discoveries that help to reduce the burden of genetic diseases. Except for the major advances in diagnostics for Mendelian diseases and a few disease-specific therapies, there has only been modest clinical benefit from the investment in human genetics research. For genetically complex, multifactorial diseases, including many of the common diseases in the USA, the risk genes are harder to find than for Mendelian diseases, and translation seems even further off. How can NIDDK make its investment in human genetics research pay off? This report describes the challenges in human genetics research and NIDDK's fivefold funding strategy to support science that will eventually lead to meaningful translation.

The diversity of PKD1 alleles: implications for disease pathogenesis and genetic counseling

Rossetti et al. identify non- and incompletely penetrant alleles of PKD1. Although such alleles are well recognized in other human mendelian disorders, they have not been associated with autosomal dominant polycystic kidney disease (ADPKD). These alleles produce atypical, mild, or severe disease depending on whether they are inherited in the heterozygous or homozygous state or in trans with another mutation, providing an intriguing potential mechanism for the considerable phenotypic variability seen in families with ADPKD.

Family history of renal disease severity predicts the mutated gene in ADPKD

Mutations of PKD1 and PKD2 account for 85 and 15% of cases of autosomal dominant polycystic kidney disease (ADPKD), respectively. Clinically, PKD1 is more severe than PKD2, with a median age at ESRD of 53.4 versus 72.7 yr. In this study, we explored whether a family history of renal disease severity predicts the mutated gene in ADPKD. We examined the renal function (estimated GFR and age at ESRD) of 484 affected members from 90 families who had ADPKD and whose underlying genotype was known. We found that the presence of at least one affected family member who developed ESRD at age < or =55 was highly predictive of a PKD1 mutation (positive predictive value 100%; sensitivity 72%). In contrast, the presence of at least one affected family member who continued to have sufficient renal function or developed ESRD at age >70 was highly predictive of a PKD2 mutation (positive predictive value 100%; sensitivity 74%). These data suggest that close attention to the family history of renal disease severity in ADPKD may provide a simple means of predicting the mutated gene, which has prognostic implications.

Systems biology of autosomal dominant polycystic kidney disease (ADPKD): computational identification of gene expression pathways and integrated regulatory networks

To elucidate the molecular pathways that modulate renal cyst growth in ADPKD, we performed global gene profiling on cysts of different size (<1 ml, n = 5; 10-20 ml, n = 5; >50 ml, n = 3) and minimally cystic tissue (MCT, n = 5) from five PKD1 human polycystic kidneys using Affymetrix HG-U133 Plus 2.0 arrays. We used gene set enrichment analysis to identify overrepresented signaling pathways and key transcription factors (TFs) between cysts and MCT. We found down-regulation of kidney epithelial restricted genes (e.g. nephron segment-specific markers and cilia-associated cystic genes such as HNF1B, PKHD1, IFT88 and CYS1) in the renal cysts. On the other hand, PKD1 cysts displayed a rich profile of gene sets associated with renal development, mitogen-mediated proliferation, cell cycle progression, epithelial-mesenchymal transition, hypoxia, aging and immune/inflammatory responses. Notably, our data suggest that up-regulation of Wnt/beta-catenin, pleiotropic growth factor/receptor tyrosine kinase (e.g. IGF/IGF1R, FGF/FGFR, EGF/EGFR, VEGF/VEGFR), G-protein-coupled receptor (e.g. PTGER2) signaling was associated with renal cystic growth. By integrating these pathways with a number of dysregulated networks of TFs (e.g. SRF, MYC, E2F1, CREB1, LEF1, TCF7, HNF1B/ HNF1A and HNF4A), our data suggest that epithelial dedifferentiation accompanied by aberrant activation and cross-talk of specific signaling pathways may be required for PKD1 cyst growth and disease progression. Pharmacological modulation of some of these signaling pathways may provide a potential therapeutic strategy for ADPKD.

Incompletely penetrant PKD1 alleles suggest a role for gene dosage in cyst initiation in polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) caused by mutations in PKD1 is significantly more severe than PKD2. Typically, ADPKD presents in adulthood but is rarely diagnosed in utero with enlarged, echogenic kidneys. Somatic mutations are thought crucial for cyst development, but gene dosage is also important since animal models with hypomorphic alleles develop cysts, but are viable as homozygotes. We screened for mutations in PKD1 and PKD2 in two consanguineous families and found PKD1 missense variants predicted to be pathogenic. In one family, two siblings homozygous for R3277C developed end stage renal disease at ages 75 and 62 years, while six heterozygotes had few cysts. In the other family, the father and two children with moderate to severe disease were homozygous for N3188S. In both families homozygous disease was associated with small cysts of relatively uniform size while marked cyst heterogeneity is typical of ADPKD. In another family, one patient diagnosed in childhood was found to be a compound heterozygote for the PKD1 variants R3105W and R2765C. All three families had evidence of developmental defects of the collecting system. Three additional ADPKD families with in utero onset had a truncating mutation in trans with either R3277C or R2765C. These cases suggest the presence of incompletely penetrant PKD1 alleles. The alleles alone may result in mild cystic disease; two such alleles cause typical to severe disease; and, in combination with an inactivating allele, are associated with early onset disease. Our study indicates that the dosage of functional PKD1 protein may be critical for cyst initiation.

Presence of de novo mutations in autosomal dominant polycystic kidney disease patients without family history

BACKGROUND

At the University of Colorado Health Sciences Center, on detailed questioning, approximately 10% of patients with autosomal dominant polycystic kidney disease (ADPKD) gave no family history of ADPKD. There are several explanations for this observation, including occurrence of a de novo pathogenic sequence variant or extreme phenotypic variability. To confirm de novo sequence variants, we have undertaken clinical and genetic screening of affected offspring and their parents.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

24 patients with a well-documented ADPKD phenotype and no family history of polycystic kidney disease (PKD) and both parents of each patient.

OUTCOME

Presence or absence of PKD1 or PKD2 pathogenic sequence variants in parents of affected offspring.

MEASUREMENTS

Abdominal ultrasound of affected offspring and their parents for ADPKD diagnosis. Parentage testing by genotyping. Complete screening of PKD1 and PKD2 genes by using genomic DNA from affected offspring; analysis of genomic DNA from both parents to confirm the absence or presence of all DNA variants found.

RESULTS

A positive diagnosis of ADPKD by means of ultrasound or genetic screening was made in 1 parent of 4 patients (17%). No PKD1 or PKD2 pathogenic sequence variants were identified in 10 patients (42%), whereas possible pathological DNA variants were identified in 4 patients (17%) and 1 of their respective parents. Parentage was confirmed in the remaining 6 patients (25%), and de novo sequence variants were documented.

LIMITATIONS

Size of patient group. No direct examination of RNA.

CONCLUSION

Causes other than de novo pathogenic sequence variants may explain the negative family history of ADPKD in certain families.

Characterization of large rearrangements in autosomal dominant polycystic kidney disease and the PKD1/TSC2 contiguous gene syndrome

Large DNA rearrangements account for about 8% of disease mutations and are more common in duplicated genomic regions, where they are difficult to detect. Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in either PKD1 or PKD2. PKD1 is located in an intrachromosomally duplicated region. A tuberous sclerosis gene, TSC2, lies immediately adjacent to PKD1 and large deletions can result in the PKD1/TSC2 contiguous gene deletion syndrome. To rapidly identify large rearrangements, a multiplex ligation-dependent probe amplification assay was developed employing base-pair differences between PKD1 and the six pseudogenes to generate PKD1-specific probes. All changes in a set of 25 previously defined deletions in PKD1, PKD2 and PKD1/TSC2 were detected by this assay and we also found 14 new mutations at these loci. About 4% of the ADPKD patients in the CRISP study were found to have gross rearrangements, and these accounted for about a third of base-pair mutation negative families. Sensitivity of the assay showed that about 40% of PKD1/TSC contiguous gene deletion syndrome families contained mosaic cases. Characterization of a family found to be mosaic for a PKD1 deletion is discussed here to illustrate family risk and donor selection considerations. Our assay improves detection levels and the reliability of molecular testing of patients with ADPKD.

TCF7L2 variants associate with CKD progression and renal function in population-based cohorts

Genetic variants may increase susceptibility to both diabetes and kidney disease. Whether known diabetes-associated variants in the transcription factor 7-like 2 (TCF7L2) gene are associated with chronic kidney disease (CKD) progression and markers of kidney function is unknown. Participants of the Atherosclerosis Risk in Communities Study (ARIC; n = 11,061 self-identified white and n = 4014 black), Framingham Heart Offspring Cohort (FHS; n = 2468), and Heredity and Phenotype Intervention Heart Study (HAPI; n = 861) were genotyped at five (ARIC) and two (FHS) common TCF7L2 variants. The diabetes-conferring risk alleles at rs7903146 and rs7901695 were significantly associated with CKD progression among ARIC participants overall and among those without baseline diabetes. The overall adjusted hazard ratios per rs7903146 T allele were 1.17 (95% confidence interval [CI] 1.04 to 1.32) for white individuals and 1.20 (95% CI 1.03 to 1.41) for black individuals. Similarly, the overall hazard ratios per rs7901695 C allele were 1.19 (95% CI 1.06 to 1.34) for white individuals and 1.27 (95% CI 1.09 to 1.48) for black individuals. The FHS cohort supported these results: The rs7903146 T allele was significantly associated with lower estimated GFR (P = 0.01) and higher cystatin C (P = 0.004) in adjusted analyses overall and among those without diabetes. In the HAPI cohort, the rs7901695 C allele was significantly associated with lower estimated GFR in adjusted analyses (P = 0.049), as were several variants upstream and downstream of TCF7L2 (P < 0.003). No identified variant in the ARIC or FHS cohorts was associated with albuminuria. In conclusion, several population-based samples suggest that variants in the TCF7L2 gene are associated with reduced kidney function or CKD progression, overall and specifically among participants without diabetes.

Diagnosis of autosomal dominant polycystic kidney disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary kidney disease and accounts for 5 - 10% of end stage renal disease. Mutations of two genes, PKD1 and PKD2, account for ∼ 85 and ∼ 15% of cases, respectively.

OBJECTIVE

This paper reviews the clinical features of ADPKD, highlights the current roles for image- and molecular-based diagnostics, and the potential for new innovations to improve the clinical diagnostics for ADPKD.

METHODS

This paper reviews the literature on the clinical features, differential diagnosis, and image- and molecular-based diagnostics for ADPKD.

RESULTS/CONCLUSION

At present, presymptomatic diagnosis of ADPKD in subjects born with 50% risk is typically performed by renal ultrasonography. Renal MRI, with improved sensitivity for detecting smaller cysts, is a promising modality. There is also a clear role for molecular diagnostics, especially in patients with equivocal imaging results, in those with a negative family history and in younger at-risk subjects with a negative ultrasound study being evaluated as a living-related kidney donor. Also, several classes of promising disease-modifying drugs are being tested in clinical trials and, if proved effective, some of them will be used in early disease. Therefore, it is likely that there will be an increased demand for accurate and early diagnosis of ADPKD in the not so distant future.

Socioeconomic status and the incidence of ESRD

BACKGROUND

Persons of low socioeconomic status (SES) may be at increased risk of end-stage renal disease (ESRD). This study examines the association between SES and incidence of ESRD caused by all primary renal diseases and caused by 3 diseases that differ in the availability of effective treatment: diabetes mellitus, lupus nephritis, and autosomal dominant polycystic kidney disease (ADPKD).

STUDY DESIGN

Retrospective cohort study.

SETTING & PARTICIPANTS

Adults with incident ESRD in the United States from January 1, 1996, to June 30, 2004 (N = 747,556).

PREDICTOR

SES, based on characteristics of the patient's ZIP code of residence.

OUTCOMES

Incidence of ESRD.

RESULTS

In all sex-race groups, the incidence of ESRD caused by all primary renal diseases was greatest in those in the lowest SES score quartile and decreased progressively with higher SES. For example, for white women, the incidence of ESRD was 388.9 per million in the lowest quartile of SES and 200.8 per million in the highest quartile of SES (relative risk, 1.92; 95% confidence interval, 1.89 to 1.95). However, this association differed among patients with primary renal diseases. There were strong associations between SES and ESRD caused by diabetes mellitus, weaker associations for ESRD caused by lupus nephritis, and generally no associations for ESRD caused by ADPKD. For example, for white women, relative risks of ESRD in the lowest compared with the highest SES quartile were 2.84 for ESRD caused by diabetes mellitus, 1.63 for ESRD caused by lupus nephritis, and 1.27 for ESRD caused by ADPKD.

LIMITATIONS

Use of an area-based measure of SES.

CONCLUSIONS

The strength of the association between SES and ESRD differs among patients with diabetes mellitus, lupus nephritis, and ADPKD, suggesting that socioeconomic factors act differently in the progression of chronic kidney disease in these conditions.

Variation in age at ESRD in autosomal dominant polycystic kidney disease

BACKGROUND

Heterogeneity manifest as more severe disease in successive generations has been attributed to genetic anticipation in patients with autosomal dominant polycystic kidney disease (ADPKD). We evaluated variation in age at end-stage renal disease (ESRD) in ADPKD families for evidence of anticipation.

STUDY DESIGN

Retrospective.

SETTING & PARTICIPANTS

413 families with ADPKD seen at our single center between 1985 and 2004 (including 95 families with documented polycystic disease type 1 [PKD1] and 213 ADPKD families with parents born before 1930).

PREDICTOR

Generational status.

OUTCOME

Age at ESRD onset.

MEASUREMENTS

Time to ESRD was evaluated by using survival analysis, Cox regression, and descriptive statistics. Unstable trinucleotide repeat expansion was evaluated by means of genotyping in 6 PKD1 families.

RESULTS

We analyzed 413 ADPKD families (1,391 parent-offspring pairs) with known age at ESRD or last known age without ESRD (informative pairs). There was no difference in age at ESRD between parents and offspring by means of Cox regression after adjusting for correlations among family members and sex (hazard ratio, 1.019; 95% confidence interval, 0.919 to 1.13; P = 0.7). Similar analysis of PKD1 informative pairs and those with parents born before 1930 showed no differences in age at ESRD. Male ADPKD patients were 42% more likely to reach ESRD (P < 0.001), and male patients with documented PKD1 were 41% more likely to reach ESRD (P = 0.01) than female patients.

LIMITATIONS

Hypertension treatment unknown.

CONCLUSIONS

We found no evidence for anticipation of ESRD in patients with ADPKD; thus, the observed variation in age at ESRD may result from other genetic, sex, or environmental causes.

Autosomal dominant polycystic kidney disease: recent advances in pathogenesis and treatment

Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disorder affecting 1 in 1,000 people in the general population and accounts for up to 10% of all patients on renal replacement therapy. Numerous fluid-filled epithelial cysts arise from different nephron segments as spherical dilatations or small out-pouchings, enlarge progressively and eventually become disconnected from the rest of the renal tubule. The development of cysts is accompanied by destruction of the renal parenchyma, interstitial fibrosis, cellular infiltration and loss of functional nephrons. ADPKD is not only a kidney disease but also a systemic disorder associated with intracranial arterial aneurysms, cardiac valvular defects, colonic diverticulosis and cyst formation in other organs such as the liver, spleen and pancreas. The identification of PKD1 and PKD2 together with the drive to elucidate the functions of their encoded proteins, polycystin-1 (PC1) and polycystin-2 (PC2), has led to an explosion of clinical and scientific interest in this common disorder. The aim of this review is to highlight recent advances in our understanding of ADPKD pathogenesis which are leading to exciting new treatment strategies.

Molecular diagnostics in autosomal dominant polycystic kidney disease: utility and limitations

BACKGROUND AND OBJECTIVES

Gene-based mutation screening is now available and has the potential to provide diagnostic confirmation or exclusion of autosomal dominant polycystic kidney disease. This study illustrates its utility and limitations in the clinical setting.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Using a molecular diagnostic service, genomic DNA of one affected individual from each study family was screened for pathologic PKD1 and PKD2 mutations. Bidirectional sequencing was performed to identify sequence variants in all exons and splice junctions of both genes and to confirm the specific mutations in other family members. In two multiplex families, microsatellite markers were genotyped at both PDK1 and PKD2 loci, and pair-wise and multipoint linkage analysis was performed.

RESULTS

Three of five probands studied were referred for assessment of renal cystic disease without a family history of autosomal dominant polycystic kidney disease, and two others were younger at-risk members of families with autosomal dominant polycystic kidney disease being evaluated as living-related kidney donors. Gene-based mutation screening identified pathogenic mutations that provided confirmation or exclusion of disease in three probands, but in the other two, only unclassified variants were identified. In one proband in which mutation screening was indeterminate, DNA linkage studies provided strong evidence for disease exclusion.

CONCLUSIONS

Gene-based mutation screening or DNA linkage analysis should be considered in individuals in whom the diagnosis of autosomal dominant polycystic kidney disease is uncertain because of a lack of family history or equivocal imaging results and in younger at-risk individuals who are being evaluated as living-related kidney donors.

Smoking: a risk factor for progression of chronic kidney disease and for cardiovascular morbidity and mortality in renal patients--absence of evidence or evidence of absence?

Although it is beyond any doubt that smoking is the number one preventable cause of death in most countries, smoking as an independent progression factor in renal disease has been questioned against the background of evidence-based criteria. This is because information from large, randomized, prospective studies that investigate the effects of smoking on renal function in healthy individuals as well as in patients with primary or secondary renal disease are lacking. Since 2003, a substantial number of clinical and experimental data concerning the adverse renal effects of smoking have been published, including large, prospective, population-based, observational studies. These more recent data together with evidence from experimental studies clearly indicate that smoking is a relevant risk factor, conferring a substantial increase in risk for renal function deterioration. This review summarizes the present knowledge about the renal risks of smoking as well as the increased cardiovascular risk caused by smoking in patients with chronic kidney disease. The conclusion is that smoking is an important renal risk factor, and nephrologists have to invest more efforts to motivate patients to stop smoking.

Autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease is the most prevalent, potentially lethal, monogenic disorder. It is associated with large interfamilial and intrafamilial variability, which can be explained to a large extent by its genetic heterogeneity and modifier genes. An increased understanding of the disorder's underlying genetic, molecular, and cellular mechanisms and a better appreciation of its progression and systemic manifestations have laid out the foundation for the development of clinical trials and potentially effective treatments.