An efficient linkage analysis strategy for autosomal dominant polycystic kidney disease

Hints to the diagnosis of uromodulin kidney disease

Background

Uromodulin kidney disease (UKD) is an inherited kidney disease caused by a uromodulin (UMOD) gene mutation. The UMOD gene encodes the Tamm–Horsfall protein (THP), which is the most abundant protein in healthy human urine. Because of its rarity, the incidence of UKD has not been fully elucidated. The purpose of the present study is to clarify the frequency of UKD among patients who underwent renal biopsy.

Methods

Immunostaining for THP was performed for patients <50 years of age with renal insufficiency and hyperuricemia without overt urinalysis abnormality from renal biopsy databases. Serum and urinary THP concentrations were evaluated in available individuals.

Results

Fifteen patients were selected for immunostaining from a total of 3787 patients. In three independent patients, abnormal THP accumulation in renal tubular cells was observed. A novel missense A247P UMOD mutation was detected in two of the three patients, including one having a typical family history of familial juvenile hyperuricemic nephropathy. Serum and urinary THP concentrations of all available patients with UMOD A247P mutation were significantly lower than those of controls.

Conclusions

In the present study, UKD was detected in <1 in 1000 subjects who underwent renal biopsies. However, in subjects meeting all of the above criteria, abnormal THP accumulation was detected in 20% (3/15), suggesting that renal biopsy with immunostaining for THP is a good tool for diagnosing UKD. Also, low serum THP concentration detected in the present subjects might be a good diagnostic marker or important in understanding the pathogenesis of UKD.

Sudden death of a young male with previously undiagnosed autosomal dominant polycystic kidney disease (ADPKD)

Autosomal dominant polycystic kidney disease (ADPKD) is one of the best known genetic diseases. However, in only very rare cases does it present as an abnormal death followed by clarification of its genetic background. We experienced a case in which ADPKD first became evident from the results of forensic autopsy, on the basis of which all potentially affected family members were offered genetic and other medical examinations. In this way, forensic medicine was able not only to determine the cause of death but to contribute to preventive medicine as well.

A pathogenic C terminus-truncated polycystin-2 mutant enhances receptor-activated Ca2+ entry via association with TRPC3 and TRPC7

Mutations in PKD2 gene result in autosomal dominant polycystic kidney disease (ADPKD). PKD2 encodes polycystin-2 (TRPP2), which is a homologue of transient receptor potential (TRP) cation channel proteins. Here we identify a novel PKD2 mutation that generates a C-terminal tail-truncated TRPP2 mutant 697fsX with a frameshift resulting in an aberrant 17-amino acid addition after glutamic acid residue 697 from a family showing mild ADPKD symptoms. When recombinantly expressed in HEK293 cells, wild-type (WT) TRPP2 localized at the endoplasmic reticulum (ER) membrane significantly enhanced Ca(2+) release from the ER upon muscarinic acetylcholine receptor (mAChR) stimulation. In contrast, 697fsX, which showed a predominant plasma membrane localization characteristic of TRPP2 mutants with C terminus deletion, prominently increased mAChR-activated Ca(2+) influx in cells expressing TRPC3 or TRPC7. Coimmunoprecipitation, pulldown assay, and cross-linking experiments revealed a physical association between 697fsX and TRPC3 or TRPC7. 697fsX but not WT TRPP2 elicited a depolarizing shift of reversal potentials and an enhancement of single-channel conductance indicative of altered ion-permeating pore properties of mAChR-activated currents. Importantly, in kidney epithelial LLC-PK1 cells the recombinant 679fsX construct was codistributed with native TRPC3 proteins at the apical membrane area, but the WT construct was distributed in the basolateral membrane and adjacent intracellular areas. Our results suggest that heteromeric cation channels comprised of the TRPP2 mutant and the TRPC3 or TRPC7 protein induce enhanced receptor-activated Ca(2+) influx that may lead to dysregulated cell growth in ADPKD.

DNA microsatellite analysis in families with autosomal dominant polycystic kidney disease (ADPKD): the first Polish study

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common inherited renal disorders with genetic heterogeneity. Mutations of two known genes are responsible for this disease: PKD1 at 16p13.3 and PKD2 at 4q21-23. A majority of cases (85%) are caused by mutations in PKD1. Because direct mutation screening remains complex, we describe here the application of an efficient approach to studies based on highly informative dinucleotide and tetranucleotide repeats flanking genes PKD1 and PKD2.

METHODS

For this study a series of microsatellites closely linked to locus PKD1 (D16S291, D16S663, D16S665, D16S283, D16S407, D16S475) and to locus PKD2 (D4S1563, D4S2929, D4S414, D4S1534, D4S423) were selected. Short (81-242 bp) DNA fragments containing the tandem repeats were amplified by polymerase chain reaction (PCR). The number of repeat units of microsatelite markers was determined by fluorescent capillary electrophoresis.

RESULTS

DNA microsatellite analysis was performed in 25 Polish ADPKD families and established the type of disease (21 families PKD1-type, 1 family PKD2-type).

CONCLUSIONS

While a disease-causing mutation in the PKD1 and PKD2 genes cannot be identified, DNA microsatellite analysis provided an early diagnosis and may be considered in ADPKD families.