Exclusion of autosomal dominant polycystic kidney disease type II (ADPKD2) from 160 cM of chromosome 1

Cilia-enriched oxysterol 7β,27-DHC is required for polycystin ion channel activation

Polycystin-1 (PC-1) and PC-2 form a heteromeric ion channel complex that is abundantly expressed in primary cilia of renal epithelial cells. This complex functions as a non-selective cation channel, and mutations within the polycystin complex cause autosomal dominant polycystic kidney disease (ADPKD). The spatial and temporal regulation of the polycystin complex within the ciliary membrane remains poorly understood. Using both whole-cell and ciliary patch-clamp recordings, we identify a cilia-enriched oxysterol, 7β,27-dihydroxycholesterol (DHC), that serves as a necessary activator of the polycystin complex. We further identify an oxysterol-binding pocket within PC-2 and showed that mutations within this binding pocket disrupt 7β,27-DHC-dependent polycystin activation. Pharmacologic and genetic inhibition of oxysterol synthesis reduces channel activity in primary cilia. In summary, our findings reveal a regulator of the polycystin complex. This oxysterol-binding pocket in PC-2 may provide a specific target for potential ADPKD therapeutics.

Selective ablation of symptomatic dominant renal cysts using 99% ethanol in adult polycystic kidney disease

OBJECTIVES

To evaluate the clinical efficacy and outcome of 99% ethanol as a sclerosing agent for managing chronic flank pain due to dominant cysts in selected patients with adult polycystic kidney disease. Traditionally, such patients have been treated with analgesics and surgical/laparoscopic deroofing. Cyst aspiration sclerotherapy is a minimally invasive therapeutic option for such patients, and limited published data exist on this subject. This formed the basis for the present study.

METHODS

A pilot study was undertaken during a 1-year period to evaluate the clinical efficacy of ultrasound-guided cyst aspiration-ethanol injection sclerotherapy in 15 preselected patients with diagnosed adult polycystic kidney disease. All punctures were performed with strict aseptic precautions and local anesthesia on an outpatient basis. The patients were evaluated with serial scans, pain scores, and serum creatinine values.

RESULTS

A total of 48 dominant cysts were successfully treated in all 15 patients with regard to cyst aspiration and shrinkage. At the end of 1 year, the pain and dominant cysts had completely disappeared in 13 patients and had recurred in 2; repeat cyst aspiration and sclerotherapy was done in 3 patients. Nephrocutaneous fistula and urinary tract infection occurred in 1 patient each. The decrease in the pain score and the rise in the serum creatinine level were statistically significant at P <0.05 and P <0.001, respectively.

CONCLUSIONS

Alcohol cyst sclerotherapy is a minimally invasive, safe, and effective alternative to conventional surgical/laparoscopic deroofing for managing chronic flank pain due to adult polycystic kidney disease in selected patients. It should be considered as a safe and viable therapeutic option in patients in whom the primary symptom is chronic flank pain due to one or more dominant cysts.

Autosomal dominant polycystic kidney disease: localization of the second gene to chromosome 4q13-q23

At least two loci are known to exist for autosomal dominant polycystic kidney disease (ADPKD). One was localized to 16p, but the second less common locus has remained unlinked. Over 100 microsatellite markers, distributed across all chromosomes, have been typed on informative family members from the large Sicilian kindred in which the genetic heterogeneity was first discovered. Both the affected and the unaffected status of every family member used in the study were confirmed by renal ultrasonography. This search has resulted in the successful localization of a second ADPKD gene to chromosome 4q. It was found to be flanked by the markers D4S231 and D4S414, defining a segment that spans about 9 cM. The new locus has been designated PKD4. This second localization will allow researchers to target another ADPKD gene for isolation in an effort to understand the pathogenesis of this common disorder. Furthermore, when flanking markers for the second ADPKD gene are used in conjunction with flanking markers for PKD1, the accuracy of the diagnosis of the subtype of ADPKD present in any particular family will be enhanced. This will improve the accuracy of linkage-based presymptomatic diagnoses by reducing the error due to genetic heterogeneity.

Polycystic renal disease

Renal cystic disease is a relatively common disorder whose development and progression currently appear to be due to an interaction between an abnormal basement membrane matrix, a potentially immature, hyperproliferative epithelium, and an abnormal epithelial secretory apparatus. RCC risk in cystic kidneys is the most controversial sequela of PKD. Currently, RCC risk in ESRD patients appears to be close to that present in the general population and only coincidentally associated with renal cysts. Screening of all ESRD patients for RCC and prophylactic native nephrectomy in dialysis and transplant patients does not seem to be indicated.

Prenatal diagnosis of autosomal dominant polycystic kidney disease using flanking DNA markers and the polymerase chain reaction

A prenatal diagnosis was carried out on a 9-week-old fetus at risk for autosomal dominant polycystic kidney disease (ADPKD). Ten members of the family were previously typed using five DNA markers linked to the PKD1 locus on chromosome 16, and one marker linked to the putative PKD2 locus on chromosome 2. The polymerase chain reaction (PCR) was used to amplify the D16S125 locus. Pairwise and multipoint lod scores indicated that the family was most likely segregating a PKD1 mutation. The fetus inherited the disease haplotype from the affected parent. Diagnostic accuracy was greater than 99 per cent, taking into account the possibility of genetic heterogeneity.