Autosomal dominant polycystic kidney disease - clinical and genetic aspects

Intestinal fistula accompanied by recurrent peritonitis associated with peritoneal dialysis: a case report

Background

Intestinal perforation from peritoneal dialysis is rare, but the resulting complications are serious. Some patients do not necessarily have symptoms, and it can be difficult to differentiate their condition from PD-related (peritoneal dialysis-related) peritonitis, which may lead to misdiagnosis. Here we report a peritoneal dialysis patient with intestinal fistula associated with recurrent peritonitis.

Case presentation

A 44-year-old man had been treated for more than 6 years with peritoneal dialysis for chronic kidney disease stage-V. Abdominal computed tomography and electronic colonoscopy revealed an appendiceal fossa with adjacent fistula. The peritoneal dialysis catheter was removed, and the patient recovered with no recurrence of complications.

Conclusion

We report a case of a rare complication of peritoneal dialysis. The intestinal fistula in this patient was mainly caused by recurrent peritonitis and removal of the catheter could control the peritonitis.

Proteinuria in children with autosomal dominant polycystic kidney disease

BACKGROUND

Proteinuria is a common complication in adults with autosomal dominant polycystic kidney disease (ADPKD) and serves as a risk factor for progression. However, proteinuria has rarely been examined in children with ADPKD and the type of proteinuria has not yet been investigated. The aim of the study was to assess the prevalence and to analyse the types of proteinuria in children with ADPKD.

METHODS

Children with ADPKD followed-up in our tertiary centres during the years 2012-2013 were investigated in a cross-sectional study. Morning urine was tested for total protein (PROT), albumin (ALB) and alpha-1-microglobulin (AMG). Renal function was assessed from serum creatinine as estimated glomerular filtration rate.

RESULTS

Thirty-seven children of median age 11.2 (2.0-18.0) years were investigated. Median (range) PROT, ALB and AMG (in mg/mmol creatinine) were 15.1 (6.2-64.8), 2.54 (0.54-37.25) and 3.22 (0.04-10.16), respectively. Pathological total proteinuria (>22) was found in 30% of children, albuminuria (>2.2) in 49% of children and alpha-1-microglobulinuria (>0.55) in 65% of children. No correlation was found between PROT, ALB or AMG and office blood pressure, kidney size or estimated glomerular filtration rate.

CONCLUSIONS

Proteinuria in children with ADPKD is a frequent finding, the most common type is tubular proteinuria. It should be measured in all ADPKD children.

Evaluation of zebrafish kidney function using a fluorescent clearance assay

The zebrafish embryo offers a tractable model to study organogenesis and model human genetic disease. Despite its relative simplicity, the zebrafish kidney develops and functions in almost the same way as humans. A major difference in the construction of the human kidney is the presence of millions of nephrons compared to the zebrafish that has only two. However, simplifying such a complex system into basic functional units has aided our understanding of how the kidney develops and operates. In zebrafish, the midline located glomerulus is responsible for the initial blood filtration into two pronephric tubules that diverge to run bilaterally down the embryonic axis before fusing to each other at the cloaca. The pronephric tubules are heavily populated by motile cilia that facilitate the movement of filtrate along the segmented tubule, allowing the exchange of various solutes before finally exiting via the cloaca. Many genes responsible for CKD, including those related to ciliogenesis, have been studied in zebrafish. However, a major draw back has been the difficulty in evaluating zebrafish kidney function after genetic manipulation. Traditional assays to measure kidney dysfunction in humans have proved non translational to zebrafish, mainly due to their aquatic environment and small size. For example, it is not physically possible to extract blood from embryonic staged fish for analysis of urea and creatinine content, as they are too small. In addition, zebrafish do not produce enough urine for testing on a simple proteinuria 'dipstick', which is often performed during initial patient examinations. We describe a fluorescent assay that utilizes the optical transparency of the zebrafish to quantitatively monitor the clearance of a fluorescent dye, over time, from the vasculature and out through the kidney, to give a read out of renal function.

The polymorphism of the ACE gene affects left ventricular hypertrophy and causes disturbances in left ventricular systolic/diastolic function in patients with autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most frequently occurring autosomal diseases inherited in the dominant manner. Due to this, lesions in the cardiovascular system of ADPKD patients have caught the attention of clinical investigators worldwide. The aim of the study was to analyse cardiovascular complications in ADPKD patients with a focus on left ventricular hypertrophy (LVH) and selected components of its systolic/diastolic function based on echocardiography. The study was conducted on 55 patients with ADPKD (24 males, 31 females), subdivided into three groups according to the stage of chronic kidney disease (CKD). The patient group with ADPKD and ESRD (group C) manifested an increased incidence of the D allele as compared to group A and group B (χ² = 4.217, P = 0.04). In all ADPKD patients with the DD genotype, left ventricular mass (LVM), posterior wall thickness (PWT), and interventricular septal thickness (IVS) were significantly higher compared to patients possessing the II and ID genotypes (P < 0.02, P < 0.003, and P < 0.009, resp.). The DD genotype exists more frequently in ADPKD patients with ESRD and is associated with a higher occurrence of LVH and disturbances in systolic-diastolic function when compared to ADPKD ESRD patients with the II and ID genotypes.

Racial and ethnic disparities in end-stage kidney failure-survival paradoxes in African-Americans

The risk of death is nearly 45% lower in African-Americans than Caucasians undergoing chronic hemodialysis. In light of the higher mortality rate in African-Americans in the general US population, this paradox requires explanation and further investigation. Factors that may contribute to this survival advantage include a younger age at which African-Americans arrive at end-stage renal disease (ESRD) and the slightly higher body mass index. On the other hand, factors, such as lower residual renal function, lower mean hemoglobin and hematocrit, increased prevalence of hypertension, a higher prevalence of catheter use for initial dialysis, and generally lower dose of dialysis should put African-Americans on dialysis at a higher risk of death. This survival advantage seems to be completely annulled with a successful renal transplant. Finally, it should be noted that ESRD carries with it a very high mortality rate in all racial and ethnic groups. A successful renal transplant improves but does not restore the expected remaining life times. Therefore, aggressive approach is required in investigating the factors that confer such high mortality risk on ESRD patients.

Annexin A5 interacts with polycystin-1 and interferes with the polycystin-1 stimulated recruitment of E-cadherin into adherens junctions

Polycystin-1 is the gene product of PKD1, the first gene identified to be causative for the condition of autosomal dominant polycystic kidney disease (ADPKD). Mutations in PKD1 are responsible for the majority of ADPKD cases worldwide. Polycystin-1 is a protein of the transient receptor potential channels superfamily, with 11 transmembrane spans and an extracellular N-terminal region of approximately 3109 amino acid residues, harboring multiple putative ligand binding domains. We demonstrate here that annexin A5 (ANXA5), a Ca(2+) and phospholipid binding protein, interacts with the N-terminal leucine-rich repeats of polycystin-1, in vitro and in a cell culture model. This interaction is direct and specific and involves a conserved sequence of the ANXA5 N-terminal domain. Using Madin-Darby canine kidney cells expressing polycystin-1 in an inducible manner we also show that polycystin-1 colocalizes with E-cadherin at cell-cell contacts and accelerates the recruitment of intracellular E-cadherin to reforming junctions. This polycystin-1 stimulated recruitment is significantly delayed by extracellular annexin A5.

Expression and functions of annexins in the kidney

This review article summarizes current knowledge about the locations and possible functions of annexin family members in the kidney. Beginning with an introduction on common structural and biochemical features as well as general functional characteristics of annexins, the paper focuses on individual members with documented and/or proposed physiological relevance for renal development, structure, and functions. Three main aspects of annexin function in kidney epithelia emerge from the available experimental data. First, annexins are required for membrane organization and membrane transport events required for the establishment/maintenance of epithelial polarity. Second, there is accumulating evidence of an association of annexins with ion channels, as membrane-guiding auxiliary proteins or modulators of channel activity. Last but not least, some annexins seem to work as extracellular autocrine modulators of receptor function under different physiological conditions.

Fish mesonephric model of polycystic kidney disease in medaka (Oryzias latipes) pc mutant

BACKGROUND

Polycystic kidney disease (PKD) is a common hereditary disease. A number of murine and zebrafish mutants have been generated and used for the study of PKD as metanephric and pronephric models, respectively. Here, we report a medaka (Oryzias latipes) mutant that develops numerous cysts in the kidney in adulthood fish in an autosomal-recessive manner as a mesonephric model of PKD.

METHODS

The phenotypes of the medaka pc mutant were described in terms of morphologic, histologic, and ultrastructural features. The pc see-through stock was produced by crossing a pc mutant and a fish from the see-through stock and used for observing the kidney through the transparent body wall of a live fish.

RESULTS

The mutant developed bilateral massive enlargement of the kidney in adulthood. They sexually matured normally within 2 months of age and died within 6 months of age. The affected kidney was occupied by numerous, fluid-filled cysts, which were lined by attenuated squamous epithelial cells. Developmentally, cystic formation began in the pronephros in 10-day-old fry and in the mesonephros in 20-day-old fry at the microscopic level. The pc see-through stock was useful in observing disease progression in live fish.

CONCLUSION

The kidney disorder that develops in the medaka pc mutant is a mesonephric counterpart of PKD, particularly an autosomal-dominant PKD, based on its morphologic, histologic, and ultrastructural features, and slow progression.

Patients with autosomal dominant polycystic kidney disease hyperfiltrate early in their disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) ranks among the most common genetic disorders. The development of end-stage renal failure usually is after the fourth decade of life. Angiotensin-converting enzyme (ACE) inhibitors often are used as agents to slow the progression of renal failure, although their effectiveness and starting point in ADPKD remain unclear.

METHODS

We measured technetium 99m diethylenetriamine pentaacetic acid glomerular filtration rate (GFR) and serum cystatin C (Cys-C) levels in 18 children with ADPKD and 41 control patients. Data are given as mean +/- SD. Mean age was 9.8 +/- 5.9 years, mean height was 137.5 +/- 34.3 cm, and mean weight was 39.2 +/- 22.8 kg in the ADPKD group, not significantly different from controls, with an average age of 10.4 +/- 4.9 years, height of 138.0 +/- 26.1 cm, and weight of 38.0 +/- 16.8 kg.

RESULTS

Mean serum creatinine levels did not differ between the ADPKD (0.6 +/- 0.2 mg/dL [51.1 +/- 20.4 micromol/L]) and control groups (0.7 +/- 0.2 mg/dL [59.8 +/- 15.3 micromol/L]; P = 0.19). Mean GFR was 142 +/- 33.2 mL/min/1.73 m2 in the ADPKD group, significantly greater than that in controls (110 +/- 12 mL/min/1.73 m2; P < 0.0001). Mean Cys-C level for the ADPKD group was 0.71 +/- 0.11 mg/L, significantly lower than that of controls (0.81 +/- 0.12 mg/L; P = 0.0011). No patient with ADPKD had hypertension, and only 1 patient had minimal microalbuminuria. Although renal length on ultrasound was significantly increased, there was no correlation between renal length and GFR or number of cysts.

CONCLUSION

Therefore, the high GFR measurements represent early hyperfiltration in children and adolescents with ADPKD, which may give a rationale to start ACE inhibitor therapy.