Identification of novel mutations in Chinese Hans with autosomal dominant polycystic kidney disease

Single-Base Substitution Causing Dual-Exon Skipping Event in PKD2 Gene: Unusual Molecular Finding from Exome Sequencing in a Patient with Autosomal Dominant Polycystic Kidney Disease

Background: Pathogenic variants in the Polycystic Kidney Disease 2 (PKD2) gene are associated with Autosomal Dominant Polycystic Kidney Disease (ADPKD) in approximately 30% of cases. In recent years, the high-throughput sequencing techniques have significantly increased the number of variants identified in affected patients. Here, we described the peculiar effect of a PKD2 splicing variant, the c.1717-2A>G, identified in an Italian male patient with ADPKD. This variant led to the unusual and rare skipping of two consecutive exons, causing a large in-frame deletion. Methods: The genetic evaluation of the patient was performed using the Next-Generation Sequencing (NGS) assay Clinical Exome Solution® (SOPHiA Genetics). Bioinformatics analysis was performed using the SOPHiA DDM platform (SOPHiA Genetics). Prediction of pathogenicity was carried out by integrating several in silico tools. RNA evaluation was performed to test the effect of the variant on the PKD2 splicing using a Reverse-Transcription PCR coupled with cDNA sequencing. Results: NGS revealed the presence of the PKD2 c.1717-2A>G variant that lies in the canonical splice site of intron 7. This rare variant was predicted to have a significant impact on the splicing, proved by the RNA-based analysis. We identified the presence of a transcript characterised by the simultaneous skipping of exons 8 and 9, with a retained reading frame and the merging of exons 7-10. Conclusions: We described for the first time a dual-exon skip event related to the presence of a single-base substitution in the PKD2 gene in an ADPKD-affected patient. We assumed that the molecular basis of such a rare mechanism lies in the specific order of intron removal. The finding represents novel evidence of an alternative and unusual splicing mechanism in the PKD2 gene, adding insights to the pathogenesis of the ADPKD.

Disease causing property analyzation of variants in 12 Chinese families with polycystic kidney disease

Background

Polycystic kidney disease (PKD) is an inherited disease that is life‐threatening. Multiple cysts are present in the bilateral kidneys of PKD patients. The progressively enlarged cysts cause structural damage and loss of kidney function.

Methods

This study examined and analyzed 12 families with polycystic kidney disease. Whole exome sequencing (WES) or whole genome sequencing (WGS) of the probands was performed to detect the pathogenic genes. The candidate gene segments for lineal consanguinity in the family were amplified by the nest PCR followed by Sanger sequencing. The variants were assessed by pathogenic and conservational property prediction analysis and interpreted according to the American College of Medical Genetics and Genomics.

Results

Nine of the 12 pedigrees were identified the disease causing variants. Among them, four novel variants in PKD1, c.6930delG:p.C2311Vfs*3, c.1216T>C:p.C406R, c.8548T>C:p.S2850P, and c.3865G>A:p.V1289M (NM_001009944.2) were detected. After assessment, the four novel variants were considered to be pathogenic variants and cause autosomal dominant polycystic kidney disease in family. The detected variants were interpreted.

Conclusion

The four novel variants in PKD1, c.6930delG:p.C2311Vfs*3, c.1216T>C:p.C406R, c.8548T>C:p.S2850P, and c.3865G>A:p.V1289M (NM_001009944.2) are pathogenic variants and cause autosomal dominant polycystic kidney disease in family.

Novel PKD1 Mutations in Patients with Autosomal Dominant Polycystic Kidney Disease

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Co-segregation of candidate polymorphism rs201204878 of the PKD1 gene in a large Iranian family with autosomal dominant polycystic disease

Autosomal dominant polycystic kidney disease (ADPKD) is the fourth most common cause of end-stage renal disease, occurring at a frequency of 1 in 400 to 1 in 800 individuals among different populations. The disease affects all ethnic groups worldwide, and there is a requirement for population-based studies to be conducted in order to improve diagnosis, genetic counseling and treatment. A large Iranian family with ADPKD was recruited for the current study. Clinical evaluation was performed to diagnose and assess disease progression in 11 members of this family, including 7 affected members and 4 unaffected members. PKD1 and PKD2 genes were genotyped in subjects by next-generation sequencing (NGS). Mutational analysis of PKD1 and PKD2 genes in this family revealed three intronic variations and three synonymous exonic variants in the PKD2 gene, and two non-synonymous exonic variants and eight intronic variants in PKD1, resulting in a total of 16 heterozygous variations among these two genes. Among the 16 variations, all except three intronic variants in the PKD1 gene have already reported in the Iranian population. The three novel mutations were predicted to be deleterious polymorphisms using in silico methods. Among the reported intronic variations, rs201204878 was identified as a splice region variant, leading to truncation of the polycystin-1 protein. In conclusion, genotyping of PKD1 and PKD2 in this family with ADPKD revealed no mutational hot spots. However, genetic screening identified three novel variants in the Iranian population. The data generated in the present study will contribute to improving the diagnosis, genetic counseling and treatment of patients with ADPKD.

Examining the Role of Polymorphisms in Exon 25 of the PKD1 Gene in the Pathogenesis of Autosomal Dominant Polycystic Kidney Disease in ranian Patients

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a highly prevalent life-threatening monogenic disorder with high morbidity and mortality. Roughly 1:400-1000 individuals are affected with this disease worldwide. The development of ADPKD is largely attributed to mutations in the polycystic kidney disease (PKD)1 and PKD2 genes. However, the pathogenicity of the different polymorphisms in PDK1 in the development of ADPKD remains unclear. The aim of this study was to further elucidate the role of the polymorphisms in exon 25 of the PDK1 gene in relation to the pathogenesis of ADPKD in Iranian patients.

METHODS

The genomic DNA of 36 Iranian patients with ADPKD was isolated using the standard salting out method. The PCR products were directly sequenced and analyzed.

RESULTS

The frequencies of CAG>GAG, ATG>GTG, GTC>GTA, and GTG>ATG polymorphisms in exon 25 of the PKD1 gene were 34 (94.44%), 33 (91.67%), 26 (72.22%), and 5 (13.89%), respectively. The most frequent polymorphism associated with ADPKD was the homozygous CAG→GAG which causes an amino acid change of Q[Gln] to E[Glu] at codon 3005.

CONCLUSION

Our data suggests that there is potentially a common polymorphism of PDK1 among the Iranian population with ADPKD. This may aid in the diagnosis and genetic screening of at-risk patients for ADPKD.

Molecular genetic analysis of polycystic kidney disease 1 and polycystic kidney disease 2 mutations in pedigrees with autosomal dominant polycystic kidney disease

BACKGROUND

Dysfunction of polycystin-1 or polycystin-2, the proteins encoded by polycystic kidney disease 1 (PKD1) and PKD2, respectively, are the cause of autosomal dominant PKD (ADPKD). This genetically heterogeneous monogenic disorder is the most common inherited kidney disease. The disease manifests are progressive cyst growth, renal enlargement, and renal failure, due to abnormal proliferation of kidney tubular epithelium.

MATERIALS AND METHODS

In this study, mutation analysis of PKD1 and PKD2 genes in nine Iranian families was performed using next-generation sequencing. All patients met the diagnostic criteria of ADPKD.

RESULTS

Mutations were found in all 9 families in PKD1 gene, comprising 2 novel and 7 previously reported mutations. No mutation in PKD2 was identified.

CONCLUSION

Finding more mutations and expanding the spectrum of PKD1 and PKD2 mutations can increase the diagnostic value of molecular testing in the screening of ADPKD patients.

Identifying gene mutations of Chinese patients with polycystic kidney disease through targeted next-generation sequencing technology

BACKGROUND

Polycystic kidney disease (PKD) is the most common hereditary kidney disease. The main mutational genes causing autosomal dominant polycystic kidney disease (ADPKD) are PKD1 and PKD2 as well as some rare pathogenic genes. Unilateral PKD is rare in clinics, and its association with gene mutations is unclear.

METHODS

Targeted next-generation sequencing (NGS) was performed to detect the renal ciliopathy-associated genes (targeted NGS panel including 63 genes) in PKD patients.

RESULTS

Forty-eight PKD1 and PKD2 mutation sites were detected in 44 bilateral PKD patients, of which 48 were PKD1 mutation sites (87.5%) and six were PKD2 mutation sites (12.5%). All of which exhibited typical ADPKD. Furthermore, we detected HNF1B heterozygous mutations in three families. Although these three patients showed HNF1B heterozygous mutations, their clinical characteristics differed and showed phenotypic heterogeneity.

CONCLUSIONS

Targeted NGS panel was helpful in detecting typical ADPKD patients and even in non-typical PKD patients. Macromutation in HNF1B may lead to bilateral PKD. The 16 novel PKD gene mutation sites and two novel PKD2 gene mutation sites discovered in this study have some significance in genetic counseling for ADPKD patients, and increase the number of studied families and expand the mutation database of ADPKD.

PKD1 Duplicated regions limit clinical Utility of Whole Exome Sequencing for Genetic Diagnosis of Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited monogenic renal disease characterised by the accumulation of clusters of fluid-filled cysts in the kidneys and is caused by mutations in PKD1 or PKD2 genes. ADPKD genetic diagnosis is complicated by PKD1 pseudogenes located proximal to the original gene with a high degree of homology. The next generation sequencing (NGS) technology including whole exome sequencing (WES) and whole genome sequencing (WGS), is becoming more affordable and its use in the detection of ADPKD mutations for diagnostic and research purposes more widespread. However, how well does NGS technology compare with the Gold standard (Sanger sequencing) in the detection of ADPKD mutations? Is a question that remains to be answered. We have evaluated the efficacy of WES, WGS and targeted enrichment methodologies in detecting ADPKD mutations in the PKD1 and PKD2 genes in patients who were clinically evaluated by ultrasonography and renal function tests. Our results showed that WES detected PKD1 mutations in ADPKD patients with 50% sensitivity, as the reading depth and sequencing quality were low in the duplicated regions of PKD1 (exons 1–32) compared with those of WGS and target enrichment arrays. Our investigation highlights major limitations of WES in ADPKD genetic diagnosis. Enhancing reading depth, quality and sensitivity of WES in the PKD1 duplicated regions (exons 1–32) is crucial for its potential diagnostic or research applications.

Identification of PKD1 and PKD2 gene variants in a cohort of 125 Asian Indian patients of ADPKD

Autosomal Dominant Polycystic Kidney Disease (ADPKD) accounts for 2.6% of the patients with chronic kidney disease in India. ADPKD is caused by pathogenic variants in either PKD1 or PKD2 gene. There is no comprehensive genetic data from Indian subcontinent. We aimed to identify the pathogenic variants in the heterogeneous Indian population. PKD1 and PKD2 variants were identified by direct gene sequencing and/or multiplex ligation-dependent probe amplification (MLPA) in 125 unrelated patients of ADPKD. The pathogenic potential of the variants was evaluated computationally and were classified according to ACMG guidelines. Overall 300 variants were observed in PKD1 and PKD2 genes, of which 141 (47%) have been reported previously as benign. The remaining 159 variants were categorized into different classes based on their pathogenicity. Pathogenic variants were observed in 105 (84%) of 125 patients, of which 99 (94.3%) were linked to PKD1 gene and 6 (6.1%) to PKD2 gene. Of 159 variants, 97 were novel variants, of which 43 (44.33%) were pathogenic, and 10 (10.31%) were of uncertain significance. Our data demonstrate the diverse genotypic makeup of single gene disorders in India as compared to the West. These data would be valuable in counseling and further identification of probable donors among the relatives of patients with ADPKD.

Identification of a pathogenic mutation in a Chinese pedigree with polycystic kidney disease

Polycystic kidney disease (PKD) is a life-threatening inherited disease with a morbidity of 1:500–1,000 worldwide. Numerous progressively enlarging cysts are observed in the bilateral kidneys of patients with PKD, inducing structural damage and loss of kidney function. The present study analyzed one family with PKD. Whole exome sequencing of the proband was performed to detect the pathogenic gene present in the family. Candidate gene segments for lineal consanguinity in the family were amplified by nest polymerase chain reaction, followed by Sanger sequencing. One novel duplication variant (NM_001009944.2:c.9359dupA:p.Y3120_E3121delinsX) and one missense mutation (c.G9022A:p.V3008M) were detected in PKD1. Additionally, the pathogenic substitutions in PKD1 published from the dataset were analyzed. Following analysis and confirmation, the duplication variant NM_001009944.2:c.9359dupA:p.Y3120_E3121delinsX in PKD1, within the polycystin-1, lipoxygenase, α-toxin domain, was considered to be the pathogenic factor in the examined family with autosomal dominant PKD. Additionally, based on the analysis of 4,805 pathogenic substitutions in PKD1 within various regions, the presence of the missense mutation in the N-terminal domain of polycystin-1 may present high pathogenicity in ADPKD.

Identification of novel mutations and risk assessment of Han Chinese patients with autosomal dominant polycystic kidney disease

AIM

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary renal disease in humans and is caused by mutations in the PKD1 or PKD2 gene. ADPKD is heterogeneous with regard to locus and allele heterogeneity and phenotypic variability.

METHODS

Using targeted capture associated with next generation sequencing (NGS), we performed a mutational analysis of Han Chinese patients with ADPKD from 62 unrelated families. Multivariate Cox proportional hazard modelling of their different clinical characteristics and mutation classes was performed.

RESULTS

The detection rate for a PKD1 and PKD2 mutation in the Chinese ADPKD patients was 95.2% (59/62). We identified pathogenic mutations in 64.4% (38/59) of patients, including 32PKD1 mutations (15 nonsense mutations, 15 frameshift mutation, one splice mutation, and one large deletion) and six PKD2 mutations (three nonsense mutations and three frameshift mutations). Of the pathogenic variants we identified, 50% (19/38) were novel variants and 50% (19/38) were known variants. Patients with PKD2 mutations had milder and indistinguishable phenotypes. Significant phenotypic differences were observed among the various types of PKD1 mutations.

CONCLUSION

Our results show that targeted capture associated with next-generation sequencing is an effective strategy for genetically testing ADPKD patients. This mutation analysis of ADPKD in Han Chinese extends our understanding of the genetic diversity of different ethnic groups, enriches the mutation database, and contributes to the genetic counselling of ADPKD patients.

Novel Mutations in the PKD1 and PKD2 Genes of Chinese Patients with Autosomal Dominant Polycystic Kidney Disease

BACKGROUND/AIMS

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disorder with mutations in PKD1 or PKD2. This study aimed to identify novel PKD1 and PKD2 mutations in Chinese patients with ADPKD.

METHODS

Mutational analyses of both PKD genes were performed in 120 Chinese families with inherited ADPKD using long-range PCR and targeted next-generation sequencing approaches. Sanger sequencing was performed to check the positive mutations, while multiplex ligation-dependent probe amplification was adopted to examine those without mutations for the presence of large deletions.

RESULTS

A total of 93 mutations in PKD1 and PKD2 were identified in 98 Chinese families with ADPKD inheritance and the detection rate was 81.7% (98/120). The mutation rates of PKD1 and PKD2 were 91.4% (85/93) and 8.6% (85/93), respectively. Among the 93 mutations, 59.1% (55/93) were reported for the first time. A total of 65 mutations (26 nonsense, 33 frameshift, 2 large deletion, and 4 typical splicing mutations) were identified as definite pathogenic mutations. The remaining 28 mutations (21 missense, 3 in-frame deletion, and 4 atypical splicing mutations) were determined as probable pathogenic mutations. In addition, 9 de novo mutations were found by pedigree analysis. Correlation analysis between genotype and phenotype revealed that patients with PKD1 mutations or truncating mutations exhibited the most severe clinical outcome.

CONCLUSION

The newly identified sites for known mutations will facilitate the early diagnosis and prediction of prognosis in patients with ADPKD, and provide fundamental genetic information for clinical intervention to prevent the inheritance of this disease in affected families.

Generation of special autosomal dominant polycystic kidney disease iPSCs with the capability of functional kidney-like cell differentiation

BACKGROUND

Human induced pluripotent stem cells (iPSCs) have been verified as a powerful cell model for the study of pathogenesis in hereditary disease. Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations of PKD or non-PKD genes. The pathogenesis of ADPKD remains unexplored because of the lack of a true human cell model.

METHODS

Six ADPKD patients and four healthy individuals were recruited as donors of somatic cells from a Chinese ADPKD family without mutations of the PKD genes but carrying SAMSN1 gene deletion. The ADPKD-iPSCs were generated from somatic cells and were induced into kidney-like cells (KLCs) by a novel three-step method involving cytokines and renal epithelium growth medium. Furthermore, we analyzed functional properties of these KLCs by water transportation and albumin absorption assays.

RESULTS

We successfully generated iPSCs from ADPKD patients and differentiated them into KLCs that showed morphological and functional characteristics of human kidney cells. Further, we also found that ADPKD-iPSC-KLCs had a significantly higher rate of apoptosis and a significantly lower capacity for water transportation and albumin absorption compared to healthy sibling-derived differentiated KLCs. Furthermore, knockdown of SAMSN1 in control iPSCs may attenuate differentiation and/or function of KLCs.

CONCLUSIONS

These data show that we have created the first iPSCs established from ADPKD patients without mutations in the PKD genes, and suggest that the deletion mutation of SAMSN1 might be involved in the differentiation and/or function of KLCs. ADPKD-iPSC-KLCs can be used as a versatile model system for the study of kidney disease.

Pathogenicity analysis of novel variations in Chinese Han patients with polycystic kidney disease

OBJECTIVE

Locus and allellic heterogeneity in polycystic kidney disease (PKD) is a great challenge in precision diagnosis. We aim to establish comprehensive methods to distinguish the pathogenic mutations from the variations in PKD1, PKD2 and PKHD1 genes in a limited time and lay the foundation for precisely prenatal diagnosis, preimplantation genetic diagnosis and presymptom diagnosis of PKD.

METHODS

Nested PCR combined with direct DNA sequencing were used to screen variations in PKD1, PKD2 and PKHD1 genes. The pathogenicity of de novel variations was assessed by the comprehensive methods including clinic data and literature review, databases query, analysis of co-segregation of the variants with the disease, variant frequency screening in the population, evolution conservation comparison, protein structure analysis and splice sites predictions.

RESULTS

17 novel mutations from 15 Chinese Han families were clarified including 10 mutations in PKD1 gene and 7 mutations in PKHD1 gene. The novel mutations were classified as 4 definite pathogenic, 2 highly likely pathogenic, 4 likely pathogenic, 7 indeterminate by the comprehensive analysis. The results were verified the truth by the follow-up visits.

CONCLUSIONS

The comprehensive methods may be useful in distinguishing the pathogenic mutations from the variations in PKD1, PKD2 and PKHD1 genes for prenatal diagnosis and presymptom diagnosis of PKD. Our results also enriched PKD genes mutation spectrum and evolved possible genotype-phenotype correlations of Chinese Han population.

Rare co-occurrence of osteogenesis imperfecta type I and autosomal dominant polycystic kidney disease

BACKGROUND

There are several clinical reports about the co-occurrence of autosomal dominant polycystic kidney disease (ADPKD) and connective tissue disorders. A simultaneous occurrence of osteogenesis imperfecta (OI) type I and ADPKD has not been observed so far.

METHODS

This report presents the first patient with OI type I and ADPKD.

RESULTS

Mutational analysis of PKD1 and COL1A1 in the index patient revealed a heterozygous mutation in each of the two genes. Mutational analysis of the parents indicated the mother as a carrier of the PKD1 mutation and the father as a carrier of the COL1A1 mutation. The simultaneous occurrence of both disorders has an estimated frequency of 3.5:100 000 000.

CONCLUSION

In singular cases, ADPKD can occur in combination with other rare disorders, e.g. connective tissue disorders.

System analysis of gene mutations and clinical phenotype in Chinese patients with autosomal-dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disorder mainly caused by mutation in PKD1/PKD2. However, ethnic differences in mutations, the association between mutation genotype/clinical phenotype, and the clinical applicable value of mutation detection are poorly understood. We made systematically analysis of Chinese ADPKD patients based on a next-generation sequencing platform. Among 148 ADPKD patients enrolled, 108 mutations were detected in 127 patients (85.8%). Compared with mutations in Caucasian published previously, the PKD2 mutation detection rate was lower, and patients carrying the PKD2 mutation invariably carried the PKD1 mutation. The definite pathogenic mutation detection rate was lower, whereas the multiple mutations detection rate was higher in Chinese patients. Then, we correlated PKD1/PKD2 mutation data and clinical data: patients with mutation exhibited a more severe phenotype; patients with >1 mutations exhibited a more severe phenotype; patients with pathogenic mutations exhibited a more severe phenotype. Thus, the PKD1/PKD2 mutation status differed by ethnicity, and the PKD1/PKD2 genotype may affect the clinical phenotype of ADPKD. Furthermore, it makes sense to detect PKD1/PKD2 mutation status for early diagnosis and prognosis, perhaps as early as the embryo/zygote stage, to facilitate early clinical intervention and family planning.

The Clinical Manifestation and Management of Autosomal Dominant Polycystic Kidney Disease in China

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most common monogenic hereditary kidney disease characterized by progressive enlargement of renal cysts. The incidence is 1-2‰ worldwide. Mutations in two genes (PKD1 and PKD2) cause ADPKD. Currently, there is no pharmaceutical treatment available for ADPKD patients in China. Summary: This review focused on advances in clinical manifestation, gene diagnosis, risk factors, and management of ADPKD in China. There is an age-dependent increase in total kidney volume (TKV) and decrease in renal function in Chinese ADPKD patients. ADPKD is more severe in males than in females. Great progress has been made in molecular diagnosis in the last two decades. Nephrologists found many novel PKD mutations in Chinese ADPKD patients early through polymerase chain reaction, and then through liquid chromatography in 2000s, and recently through next-generation sequencing. Major predictive factors for ADPKD progression are age, PKD genotype, sex, estimated glomerular filtration rate (eGFR), and TKV. With respect to the management of ADPKD, inhibitors targeting mTOR and cAMP are the focus of clinical trials. Triptolide has been used to treat ADPKD patients in clinical trials in China. Triptolide significantly protected eGFR of ADPKD patients compared with placebo.

KEY MESSAGES

ADPKD affects about 1.5 million people in China. An additional PKD gene besides PKD1 and PKD2 was not found in the Chinese. The prevalence of intracranial aneurysm in Chinese ADPKD patients was 12.4%. The predictive factors for eGFR decrease in Chinese ADPKD patients are TKV, proteinuria, history of hypertension, and age. The treatment strategies in clinical trials for ADPKD patients in China are similar to those in the West except for triptolide.

FACTS FROM EAST AND WEST

(1) ADPKD is diagnosed globally by ultrasound detection of kidney enlargement and presence of cysts. Recent analyses of variants of the PKD1 and PKD2 genes by next-generation sequencing in Chinese and Western ADPKD patients might lead to the development of reliable genetic tests. (2) Besides lifestyle changes (low-salt diet, sufficient fluid intake, and no smoking), blood pressure control is the primary nonspecific treatment recommended by Kidney Disease - Improving Global Outcomes (KDIGO) for ADPKD patients. How low the blood pressure target should be and what the means of achieving it are remain open questions depending on the severity of chronic kidney disease and the age of the patients. In a recent Chinese study, diagnostic needle aspiration and laparoscopic unroofing surgery successfully improved infection, pain, and hypertension. Peritoneal dialysis was found to be a feasible treatment for most Chinese ADPKD patients with end-stage renal disease. In most Western centers, patients without contraindication are selected for peritoneal dialysis. Kidney transplantation with concurrent bilateral nephrectomy was successful in relieving hypertension and infection in Chinese ADPKD patients. In Western countries, sequential surgical intervention with kidney transplantation after nephrectomy, or the other way round, is preferred in order to reduce risks. (3) The vasopressin 2 receptor antagonist tolvaptan was approved in Europe, Canada, Japan, and Korea to slow down progression of kidney disease in ADPKD patients. Tolvaptan is not yet approved in the USA or in China. mTOR pathway-targeting drugs are currently under evaluation: mTOR inhibitors could slow down the increase in total kidney volume in a cohort of Western and Japanese ADPKD patients. Western studies as well as an ongoing study in China failed to show benefit from rapamycin. A study performed in Italy indicates protective effects of the somatostatin analog octreotide in ADPKD patients. Western and Chinese studies revealed a potential beneficial effect of triptolide, the active substance of the traditional Chinese medicine Tripterygium wilfordii (Lei Gong Teng) to prevent worsening in ADPKD patients.

Identification of MMP1 as a novel risk factor for intracranial aneurysms in ADPKD using iPSC models

Cardiovascular complications are the leading cause of death in autosomal dominant polycystic kidney disease (ADPKD), and intracranial aneurysm (ICA) causing subarachnoid hemorrhage is among the most serious complications. The diagnostic and therapeutic strategies for ICAs in ADPKD have not been fully established. We here generated induced pluripotent stem cells (iPSCs) from seven ADPKD patients, including four with ICAs. The vascular cells differentiated from ADPKD-iPSCs showed altered Ca(2+) entry and gene expression profiles compared with those of iPSCs from non-ADPKD subjects. We found that the expression level of a metalloenzyme gene, matrix metalloproteinase (MMP) 1, was specifically elevated in iPSC-derived endothelia from ADPKD patients with ICAs. Furthermore, we confirmed the correlation between the serum MMP1 levels and the development of ICAs in 354 ADPKD patients, indicating that high serum MMP1 levels may be a novel risk factor. These results suggest that cellular disease models with ADPKD-specific iPSCs can be used to study the disease mechanisms and to identify novel disease-related molecules or risk factors.

Identification of novel PKD1 and PKD2 mutations in a Chinese population with autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most frequently inherited renal diseases caused by mutations in PKD1 and PKD2. We performed mutational analyses of PKD genes in 49 unrelated patients using direct PCR-sequencing and multiplex ligation-dependent probe amplification (MLPA) for PKD1 and PKD2. RT-PCR analysis was also performed in a family with a novel PKD2 splicing mutation. Disease-causing mutations were identified in 44 (89.8%) of the patients: 42 (95.5%) of the patients showed mutations in PKD1, and 2 (4.5%) showed mutations in PKD2. Ten nonsense, 17 frameshift, 4 splicing and one in-frame mutation were found in 32 of the patients. Large rearrangements were found in 3 patients, and missense mutations were found in 9 patients. Approximately 61.4% (27/44) of the mutations are first reported with a known mutation rate of 38.6%. RNA analysis of a novel PKD2 mutation (c.595_595 + 14delGGTAAGAGCGCGCGA) suggested monoallelic expression of the wild-type allele. Furthermore, patients with PKD1-truncating mutations reached end-stage renal disease (ESRD) earlier than patients with non-truncating mutations (47 ± 3.522 years vs. 59 ± 11.687 years, P = 0.016). The mutation screening of PKD genes in Chinese ADPKD patients will enrich our mutation database and significantly contribute to improve genetic counselling for ADPKD patients.

Analysis of gene mutations in PKD1/PKD2 by multiplex ligation-dependent probe amplification: some new findings

Autosomal dominant polycystic kidney disease (ADPKD) is a serious genetic disorder that can lead to chronic renal disease. Protein dysfunction caused by mutations in the genes polycystic kidney disease 1 (PKD1) and polycystic kidney disease 2 (PKD2) is an important factor in the pathogenesis of ADPKD. In the present study, 30 Chinese patients with confirmed diagnosis of ADPKD, based on ultrasound or computerized tomography (CT) findings were selected, and the exon copy numbers of PKD1 and PKD2 were determined using multiplex ligation-dependent probe amplification (MLPA). MLPA identified exon deletion in 1 case, suspected exon deletion in 4 cases, and suspected duplications in 3 cases. One case of suspected exon deletion was confirmed using quantitative real-time polymerase chain reaction (q-PCR) and sequencing (PKD2 exon 8). A missense mutation was observed in 1 case of exon deletion using q-PCR and sequencing (PKD1 exon 40, c.11333 C>A). The cases of suspected duplications were verified by q-PCR, and the copy number of exon 6 of PKD1 in 1 case of suspected duplication was 3.8 times greater than that in normal controls. Our findings provide new insights into ADPKD screening and mark a possibly meaningful step toward improved diagnosis and treatment of patients with ADPKD.

Comprehensive PKD1 and PKD2 Mutation Analysis in Prenatal Autosomal Dominant Polycystic Kidney Disease

Prenatal forms of autosomal dominant polycystic kidney disease (ADPKD) are rare but can be recurrent in some families, suggesting a common genetic modifying background. Few patients have been reported carrying, in addition to the familial mutation, variation(s) in polycystic kidney disease 1 (PKD1) or HNF1 homeobox B (HNF1B), inherited from the unaffected parent, or biallelic polycystic kidney and hepatic disease 1 (PKHD1) mutations. To assess the frequency of additional variations in PKD1, PKD2, HNF1B, and PKHD1 associated with the familial PKD mutation in early ADPKD, these four genes were screened in 42 patients with early ADPKD in 41 families. Two patients were associated with de novo PKD1 mutations. Forty patients occurred in 39 families with known ADPKD and were associated with PKD1 mutation in 36 families and with PKD2 mutation in two families (no mutation identified in one family). Additional PKD variation(s) (inherited from the unaffected parent when tested) were identified in 15 of 42 patients (37.2%), whereas these variations were observed in 25 of 174 (14.4%, P=0.001) patients with adult ADPKD. No HNF1B variations or PKHD1 biallelic mutations were identified. These results suggest that, at least in some patients, the severity of the cystic disease is inversely correlated with the level of polycystin 1 function.

Exon sequencing of PKD1 gene in an Iranian patient with autosomal-dominant polycystic kidney disease

Introduction: Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common genetic kidney disorders with the incidence of 1 in 1,000 births. ADPKD is genetically heterogeneous with two genes identified: PKD1 (16p13.3, 46 exons) and PKD2 (4q21, 15 exons). Eighty five percent of the patients with ADPKD have at least one mutation in the PKD1 gene. Genetic studies have demonstrated an important allelic variability among patients, but very few data are known about the genetic variation among Iranian populations. Methods: In this study, exon direct sequencing of PKD1 was performed in a seven-year old boy with ADPKD and in his parents. The patient’s father was ADPKD who was affected without any kidney dysfunction, and the patient’s mother was congenitally missing one kidney. Results: Molecular genetic testing found a mutation in all three members of this family. It was a missense mutation GTG>ATG at position 3057 in exon 25 of PKD1. On the other hand, two novel missense mutations were reported just in the 7-year-old boy: ACA>GCA found in exon 15 at codon 2241 and CAC>AAC found in exon 38 at codon 3710. For checking the pathogenicity of these mutations, exons 15, 25, and 38 of 50 unrelated normal cases were sequenced. Conclusion: our findings suggested that GTG>ATG is a polymorphism with high frequency (60%) as well as ACA>GCA and CAC>AAC are polymorphisms with frequencies of 14% and 22%, respectively in the population of Southwest Iran.

Identification of novel PKD1 and PKD2 mutations in Korean patients with autosomal dominant polycystic kidney disease

Background

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disorder. It is caused by mutations in the PKD1 and PKD2 genes, and manifests as progressive cyst growth and renal enlargement, resulting in renal failure. Although there have been a few studies on the frequency and spectrum of mutations in PKD1 and PKD2 in Korean patients with ADPKD, only exons 36–46, excluding the duplicated region, were analyzed, which makes it difficult to determine accurate mutation frequencies and mutation spectra.

Methods

We performed sequence analysis of 20 consecutive unrelated ADPKD patients using long-range polymerase chain reaction (PCR) to avoid pseudogene amplification, followed by exon-specific PCR and sequencing of the all exons of these two genes. Multiplex ligation-dependent probe amplification was performed in patients in whom pathogenic mutations in PKD1 or PKD2 were not identified by LR-PCR and direct sequencing to detect large genomic rearrangements.

Results

All patients met the diagnostic criteria of ADPKD, and pathogenic mutations were found in 18 patients (90.0%), comprising 15 mutations in PKD1 and three in PKD2. Among 10 novel mutations, eight mutations were found in the PKD1 gene while two mutations were found in the PKD2 gene. Eight of 14 PKD1 mutations (57.1%) were located in the duplicated region.

Conclusions

This study expands the spectra of mutations in the PKD1 and PKD2 genes and shows that the mutation frequencies of these genes in Korean ADPKD patients are similar to those reported in other ethnicities. Sequence analysis, including analysis of the duplicated region, is essential for molecular diagnosis of ADPKD.

Modification of PCR conditions and design of exon-specific primers for the efficient molecular diagnosis of PKD1 mutations

BACKGROUND/AIMS

Autosomal-dominant polycystic kidney disease (ADPKD) is a heterogeneous genetic disorder caused by mutations in the PKD1 and PKD2 genes. Currently, long-range PCR followed by nested PCR and sequencing (LRNS) is the gold standard approach for PKD1 testing. However, LRNS is complicated by the high structural and sequence complexity of PKD1, which makes the procedure for amplification and analysis of PKD1 difficult.

METHODS

Here in, we modified the PCR conditions and designed primers for efficient and specific amplification of both the long-range and individual exons of PKD1.

RESULTS

Using the modified system, seven long-range fragments were specifically amplified using two distinct sets of conditions, and all individual exon PCR assays were easily performed using a touch-down PCR method. Seven pathogenic or likely pathogenic variants, including two novel truncated frameshift indels and two novel likely pathogenic missense mutations, were identified in eight unrelated patients with or without histories of ADPKD disease (one variant was observed in two unrelated patients). Using combined bioinformatics tools, two indeterminate missense variants were identified in two sporadic patients.

CONCLUSION

Four novel PKD1 variants were identified in this study. We demonstrated that the modified LRNS method achieves high sensitivity and specificity for detecting pathogenic variants of ADPKD.

A new PKD1 mutation discovered in a Chinese family with autosomal polycystic kidney disease

BACKGROUND/AIMS

Autosomal-dominant polycystic kidney disease (ADPKD), a heterogeneous genetic disorder characterized by massive kidney enlargement and progressive chronic kidney disease, is due to abnormal proliferation of renal tubular epithelium. ADPKD is known to be caused by mutations in PKD1 and PKD2 genes.

METHODS

In the present study, the mutation analysis of PKD genes was performed in a new Chinese family with ADPKD using Long-Range (LR) PCR sequencing and targeted next-generation sequencing (targeted DNA-HiSeq).

RESULTS

A unique 28 bp deletion (c.12605_12632del28) in exon 46 of the PKD1 gene was identified in two affected family members by LR PCR method, but not in any unaffected relatives or unrelated controls. Higher accuracy and less missing detection presented in LR PCR method compared with targeted DNA-HiSeq. This mutation c.12605_12632del28 (p.Arg4202ProextX146) resulted in a delayed termination of amino acid code, and was highly speculated pathogenic in this ADPKD family. Moreover, this newly identified frame-shift change was compared to the PKD gene database, but no similar mutation was yet reported.

CONCLUSION

A novel frame-shift mutation, c. 12605_12632del28, in the PKD1 gene was found in a Chinese ADPKD family. All evidence available suggested that it might be the mutation responsible for the disease in that family.

Novel mutations of PKD genes in the Czech population with autosomal dominant polycystic kidney disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary renal disorder caused by mutation in either one of two genes, PKD1 and PKD2. High structural and sequence complexity of PKD genes makes the mutational diagnostics of ADPKD challenging. The present study is the first detailed analysis of both PKD genes in a cohort of Czech patients with ADPKD using High Resolution Melting analysis (HRM) and Multiplex Ligation-dependent Probe Amplification (MLPA).

METHODS

The mutational analysis of PKD genes was performed in a set of 56 unrelated patients. For mutational screening of the PKD1 gene, the long-range PCR (LR-PCR) strategy followed by nested PCR was used. Resulting PCR fragments were analyzed by HRM; the positive cases were reanalyzed and confirmed by direct sequencing. Negative samples were further examined for sequence changes in the PKD2 gene by the method of HRM and for large rearrangements of both PKD1 and PKD2 genes by MLPA.

RESULTS

Screening of the PKD1 gene revealed 36 different likely pathogenic germline sequence changes in 37 unrelated families/individuals. Twenty-five of these sequence changes were described for the first time. Moreover, a novel large deletion was found within the PKD1 gene in one patient. Via the mutational analysis of the PKD2 gene, two additional likely pathogenic mutations were detected.

CONCLUSIONS

Probable pathogenic mutation was detected in 71% of screened patients. Determination of PKD mutations and their type and localization within corresponding genes could help to assess clinical prognosis of ADPKD patients and has major benefit for prenatal and/or presymptomatic or preimplantational diagnostics in affected families as well.

Two novel mutations affecting the same splice site of PKD1 correlate with different phenotypes in ADPKD

Genetic heterogeneity is the main factor for significant variation in the course of autosomal dominant polycystic kidney disease (ADPKD). PKD1 patients have more severe renal outcomes compared with PKD2 patients. Co-inheritance of a mutation in both genes is associated with more severe phenotypes than that found with either mutation alone. However, the genotype-phenotype relationship is far from clear in ADPKD. Here, we observed two novel mutations, PKD1:c.12444G > A and PKD1:c.12444 + 1G > A, which alter the same splice donor site of intron 45, correlate with different renal outcomes. To explain the phenomenon, we analyzed the genic and allelic background of the patients, as well as the genetic modifiers, DKK3 and HNF-1β as suggested. Only PKD1 variants were found, which highlights the allelic influence of PKD1 gene to be the last candidate factor. Segregation analysis, online mutation prediction, and recurrence mutation searching were applied to sort the variants. However, none of variants was found to be damaging or associated with the disease except PKD1:c.12444G > A and PKD1:c.12444 + 1G > A. Cloning and sequencing of the mutated cDNA sequences had shown unexpected different splicing effects caused by the mutations. PKD1:c.12444 + 1G > A definitely destroyed the native splice site and created a novel donor site with truncating effect on PC1. In contrast, PKD1:c.12444G > A mainly weakened the site and decreased the expression of normal PC1. Since PC1 negatively regulates cell proliferation in the process of cyst formation and enlargement, our observation may explain this new genotype-phenotype correlation and help to improve genetic counseling and diagnosis of the disease.

Identification of novel mutations of PKD1 gene in Chinese patients with autosomal dominant polycystic kidney disease by targeted next-generation sequencing

BACKGROUND

Mutations of PKD1 and PKD2 accounted for the most cases of autosomal dominant polycystic kidney disease (ADPKD). The presence of the large transcript, numerous exons and complex reiterated regions within the gene has significantly complicated the analysis of PKD1 with routine PCR-based approaches.

METHODS

We developed a strategy to analyze both the PKD1/PKD2 genes simultaneously using targeted next-generation sequencing (NGS). All coding exons plus the flanking sequences of PKD1 and PKD2 genes from probands were captured, individually barcoded and followed by HiSeq2000 sequencing. The candidate variants were validated by using classic Sanger sequencing. PKD1-specific primers were designed to amplify the replicated areas of PKD1 gene.

RESULTS

Five novel variations and one known mutation in PKD1 gene were detected in five familial and one sporadic Chinese ADPKD patients. Through pedigree and bioinformatic analysis, five of them were identified as pathogenic mutations (p.G1319R, p.Y3781*, p.W4122*, p.Val700Glyfs*14, and p.Leu3656Trpfs*28) and one was as polymorphism (p.T2420I).

CONCLUSIONS

Our result showed that targeted capture and NGS technology were effective for the gene testing of ADPKD disorder. Mutation study of PKD1 and PKD2 genes in Chinese patients may contribute to better understanding of the genetic diversity between different ethnic groups and enrich the mutation database in Asian population.

Novel PKD1 and PKD2 mutations in Taiwanese patients with autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a heterogeneous disease caused by mutations in PKD1 and PKD2. The genotype-phenotype correlations are not completely understood. We performed direct PCR-sequencing plus multiplex ligation-dependent probe amplification for PKD1 and PKD2 in 46 unrelated patients. Disease-causing mutations were identified in 30 (65%) patients: 23 (77%) patients have mutations in PKD1 and 7 (23%) have mutations in PKD2. Nonsense, splicing or frame-shifting mutations were found in 18 patients, exon duplication in 1 and missense mutations in 11 patients. Two likely PKD1 hypomorphic alleles (p.Arg2477His and p.Arg3439Trp) segregated with mild disease in a family. A total of 34 mutations were identified and 17 (50%) of which are novel. The median age at onset of dialysis was significantly earlier in patients with PKD1 mutations (52 years) than in patients with PKD2 mutations (65.5 years) and those with an undetermined genotype (67 years) by survival analysis (log-rank test, P=0.014). Patients carrying PKD1-truncating mutations have a trend toward earlier initiation of dialysis compared with carriers of non-truncating mutations (52 years vs 57 years, P=0.061). A family history of dialysis before 55 years was more common in PKD1 patients than in others (P<0.05). In conclusion, this study identified novel mutations in PKD1 and PKD2 and demonstrated the presence of PKD1 hypomorphic alleles in Taiwanese patients. Patients carrying PKD1 mutations, especially those with truncating mutations, could have a more rapidly progressive disease than others. These results might have implications for diagnosis and risk stratification in patients with ADPKD.

Autosomal dominant polycystic kidney disease: comprehensive mutation analysis of PKD1 and PKD2 in 700 unrelated patients

Autosomal dominant polycystic kidney disease (ADPKD), the most common inherited kidney disorder, is caused by mutations in PKD1 or PKD2. The molecular diagnosis of ADPKD is complicated by extensive allelic heterogeneity and particularly by the presence of six highly homologous sequences of PKD1 exons 1-33. Here, we screened PKD1 and PKD2 for both conventional mutations and gross genomic rearrangements in up to 700 unrelated ADPKD patients--the largest patient cohort to date--by means of direct sequencing, followed by quantitative fluorescent multiplex polymerase chain reaction or array-comparative genomic hybridization. This resulted in the identification of the largest number of new pathogenic mutations (n = 351) in a single publication, expanded the spectrum of known ADPKD pathogenic mutations by 41.8% for PKD1 and by 23.8% for PKD2, and provided new insights into several issues, such as the population-dependent distribution of recurrent mutations compared with founder mutations and the relative paucity of pathogenic missense mutations in the PKD2 gene. Our study, together with others, highlights the importance of developing novel approaches for both mutation detection and functional validation of nondefinite pathogenic mutations to increase the diagnostic value of molecular testing for ADPKD.