Three novel mutations of the PKD1 gene in Korean patients with autosomal dominant polycystic kidney disease

The genetic spectrum of polycystic kidney disease in children

OBJECTIVE

Autosomal dominant polycystic kidney disease is an inherited kidney disorder with mutations in polycystin-1 or polycystin-2. Autosomal recessive polycystic kidney disease is a severe form of polycystic kidney disease that is characterized by enlarged kidneys and congenital hepatic fibrosis. Mutations at PKHD1 are responsible for all typical forms of autosomal recessive polycystic kidney disease.

METHODS

We evaluated the children diagnosed with polycystic kidney disease between October 2020 and May 2022. The diagnosis was established by family history, ultrasound findings, and/or genetic analysis. The demographic, clinical, and laboratory findings were evaluated retrospectively.

RESULTS

There were 28 children (male/female: 11:17) evaluated in this study. Genetic analysis was performed in all patients (polycystin-1 variants in 13, polycystin-2 variants in 7, and no variants in 8 patients). A total of 18 variants in polycystin-1 and polycystin-2 were identified and 9 (50%) of them were not reported before. A total of eight novel variants were identified as definite pathogenic or likely pathogenic mutations. There was no variant detected in the PKDH1 gene.

CONCLUSION

Our results highlighted molecular features of Turkish children with polycystic kidney disease and demonstrated novel variations that can be utilized in clinical diagnosis and prognosis.

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.

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.

High Resolution Melt analysis for mutation screening in PKD1 and PKD2

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary kidney disorder. It is characterized by focal development and progressive enlargement of renal cysts leading to end-stage renal disease. PKD1 and PKD2 have been implicated in ADPKD pathogenesis but genetic features and the size of PKD1 make genetic diagnosis tedious.

METHODS

We aim to prove that high resolution melt analysis (HRM), a recent technique in molecular biology, can facilitate molecular diagnosis of ADPKD. We screened for mutations in PKD1 and PKD2 with HRM in 37 unrelated patients with ADPKD.

RESULTS

We identified 440 sequence variants in the 37 patients. One hundred and thirty eight were different. We found 28 pathogenic mutations (25 in PKD1 and 3 in PKD2 ) within 28 different patients, which is a diagnosis rate of 75% consistent with literature mean direct sequencing diagnosis rate. We describe 52 new sequence variants in PKD1 and two in PKD2.

CONCLUSION

HRM analysis is a sensitive and specific method for molecular diagnosis of ADPKD. HRM analysis is also costless and time sparing. Thus, this method is efficient and might be used for mutation pre-screening in ADPKD genes.

Candesartan Reduces Urinary Fatty Acid-Binding Protein Excretion in Patients with Autosomal Dominant Polycystic Kidney Disease

BACKGROUND

Free fatty acids (FFAs) bound to albumin are overloaded in renal proximal tubules and exacerbate tubulointerstitial damage. Liver-type fatty acid-binding protein (L-FABP) is an intracellular carrier protein of FFAs that is expressed in renal proximal tubules in humans. Urinary L-FABP reflects the clinical prognosis of chronic glomerulonephritis. The aim of the present study was to determine whether urinary L-FABP excretion is altered in patients with autosomal dominant polycystic kidney disease (ADPKD) and whether candesartan cilexetil, an angiotensin II receptor antagonist, affects these levels.

METHODS

Subjects comprised 20 normotensive ADPKD patients (8 men and 12 women, mean age 42.6 years) and 20 age-matched healthy volunteers (8 men and 12 women, mean age 44.0 years). The 20 ADPKD patients participated in a randomized double-blind placebo-controlled study of candesartan cilexetil for 6 months. Urinary L-FABP levels were measured by a newly established ELISA method.

RESULTS

Urinary L-FABP levels were significantly higher in ADPKD patients (154.5 +/- 110.6 microg/g Cr) than in healthy subjects (5.5 +/- 3.8 microg/g Cr) (P < 0.001). Candesartan cilexetil reduced urinary L-FABP levels from 168.5 +/- 104.5 microg/g Cr to 98.5 +/- 68.5 microg/g Cr after 3 months (P < 0.01) and to 44.6 +/- 30.8 microg/g Cr after 6 months (P < 0.001). Placebo had no effect on L-FABP levels (before, 140.5 +/- 100.5 microg/g Cr; at 3 months, 148.5 +/- 108.5 microg/g Cr; at 6 months, 150.5 +/- 110.8 microg/g Cr). During the 6 months, serum creatinine, blood urea nitrogen, 24-hour creatinine clearance and blood pressure showed little change in either group.

CONCLUSIONS

Increased urinary L-FABP levels may be associated with the development of ADPKD, and candesartan cilexetil has a beneficial effect on reducing these levels.

Novel and de novo PKD1 mutations identified by multiple restriction fragment-single strand conformation polymorphism (MRF-SSCP)

Background

We have previously developed a long RT-PCR method for selective amplification of full-length PKD1 transcripts (13.6 kb) and a long-range PCR for amplification in the reiterated region (18 kb) covering exons 14 and 34 of the PKD1 gene. These have provided us with an opportunity to study PKD1 mutations especially in its reiterated region which is difficult to examine. In this report, we have further developed the method of multiple restriction fragment-single strand conformation polymorphism (MRF-SSCP) for analysis of PKD1 mutations in the patients with autosomal dominant polycystic kidney disease (ADPKD). Novel and de novo PKD1 mutations are identified and reported.

Methods

Full-length PKD1 cDNA isolated from the patients with ADPKD was fractionated into nine overlapping segments by nested-PCR. Each segment was digested with sets of combined restriction endonucleases before the SSCP analysis. The fragments with aberrant migration were mapped, isolated, and sequenced. The presence of mutation was confirmed by the long-range genomic DNA amplification in the PKD1 region, sequencing, direct mutation detection, and segregation analysis in the affected family.

Results

Five PKD1 mutations identified are two frameshift mutations caused by two di-nucleotide (c. 5225_5226delAG and c.9451_9452delAT) deletions, a nonsense (Q1828X, c.5693C>T) mutation, a splicing defect attributable to 31 nucleotide deletion (g.33184_33214del31), and an in-frame deletion (L3287del, c.10070_10072delCTC). All mutations occurred within the reiterated region of the gene involving exons 15, 26, 15, 19 and 29, respectively. Three mutations (one frameshift, splicing defect, and in-frame deletion) are novel and two (one frameshift and nonsense) known. In addition, two mutations (nonsense and splicing defect) are possibly de novo.

Conclusion

The MRF-SSCP method has been developed to analyze PCR products generated by the long RT-PCR and nested-PCR technique for screening PKD1 mutations in the full-length cDNA. Five mutations identified were all in the reiterated region of this gene, three of which were novel. The presence of de novo PKD1 mutations indicates that this gene is prone to mutations.