Volume Progression in Autosomal Dominant Polycystic Kidney Disease: The Major Factor Determining Clinical Outcomes

Evaluation of urine biomarkers of kidney injury in polycystic kidney disease

Progressive disruption of renal tubular integrity in the setting of increased cellular proliferation and apoptosis is a feature of ADPKD. Here we evaluated the effect of these processes on the expression of NGAL and IL-18, markers of tubular injury, in rodent models and in the cyst fluid and urine of patients with ADPKD. Two mouse models where Pkd2 was inactivated which resulted in early or adult onset cysts, were used to evaluate NGAL levels. Further, the Han:SPRD rat model of polycystic disease was used to study IL-18 levels. In four annual serial urine samples from 107 patients with ADPKD in the Consortium for Radiologic Imaging for the Study of Polycystic Kidney Disease (CRISP) study, NGAL and IL-18 excretion rates were determined in conjunction with measures of total kidney volume and estimated GFR (eGFR) by the MDRD equation. Kidneys from affected mice and rats showed prominent expression of NGAL and IL-18/IL-18R, respectively, in epithelial cells lining kidney cysts. In human ADPKD cyst fluid, both NGAL and IL-18 were elevated. In CRISP patients, the mean percentage increase in total kidney volume was 5.4 /year and the mean decline in eGFR 2.4 mL/min/year. The trend of increased mean urine NGAL and IL-18 over three years was statistically significant; however, there was no association of tertiles of IL-18 or quartiles of NGAL and the change in total kidney volume or eGFR over this period. Thus, urinary NGAL and IL-18 excretion are mildly and stably elevated in ADPKD, but do not correlate with changes in total kidney volume or kidney function. This may be due, in part, to the lack of communication between individual cysts and the urinary collecting system in this disorder.

Analysis of baseline parameters in the HALT polycystic kidney disease trials

HALT PKD consists of two ongoing randomized trials with the largest cohort of systematically studied patients with autosomal dominant polycystic kidney disease to date. Study A will compare combined treatment with an angiotensin-converting inhibitor and receptor blocker to inhibitor alone and standard compared with low blood pressure targets in 558 early-stage disease patients with an eGFR over 60 ml/min per 1.73 m(2). Study B will compare inhibitor-blocker treatment to the inhibitor alone in 486 late-stage patients with eGFR 25-60 ml/min per 1.73 m(2). We used correlation and multiple regression cross-sectional analyses to determine associations of baseline parameters with total kidney, liver, or liver cyst volumes measured by MRI in Study A and eGFR in both studies. Lower eGFR and higher natural log-transformed urine albumin excretion were independently associated with a larger natural log-transformed total kidney volume adjusted for height (ln(HtTKV)). Higher body surface area was independently associated with a higher ln(HtTKV) and lower eGFR. Men had larger height-adjusted total kidney volume and smaller liver cyst volumes than women. A weak correlation was found between the ln(HtTKV) and natural log-transformed total liver volume adjusted for height or natural log liver cyst volume in women only. Women had higher urine aldosterone excretion and lower plasma potassium. Thus, our analysis (1) confirms a strong association between renal volume and functional parameters, (2) shows that gender and other factors differentially affect the development of polycystic disease in the kidney and liver, and (3) suggests an association between anthropomorphic measures reflecting prenatal and/or postnatal growth and disease severity.

[Slow the pace of renal failure in autosomal dominant polycystic kidney disease: hopes and disappointments]

Autosomal dominant polycystic kidney disease is the most frequent renal genetic disease. Its main complication is renal failure. Despite a better understanding of the mechanisms leading to cyst development and growth, no specific treatment is available. Inhibition of mTOR pathway was a great hope, unfortunately, two clinical trials failed to show a clinical benefit. Numerous new drugs are in clinical trials or in the pipe-line. We could hope, in the 5 years to the emergence of an efficient treatment to slow the pace of renal failure in ADPKD.

Tolvaptan in autosomal dominant polycystic kidney disease: three years' experience

BACKGROUND AND OBJECTIVES

Autosomal dominant polycystic kidney disease (ADPKD), a frequent cause of end-stage renal disease, has no cure. V2-specific vasopressin receptor antagonists delay disease progression in animal models.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

This is a prospectively designed analysis of annual total kidney volume (TKV) and thrice annual estimated GFR (eGFR) measurements, from two 3-year studies of tolvaptan in 63 ADPKD subjects randomly matched 1:2 to historical controls by gender, hypertension, age, and baseline TKV or eGFR. Prespecified end points were group differences in log-TKV (primary) and eGFR (secondary) slopes for month 36 completers, using linear mixed model (LMM) analysis. Sensitivity analyses of primary and secondary end points included LMM using all subject data and mixed model repeated measures (MMRM) of change from baseline at each year. Pearson correlation tested the association between log-TKV and eGFR changes.

RESULTS

Fifty-one subjects (81%) completed 3 years of tolvaptan therapy; all experienced adverse events (AEs), with AEs accounting for six of 12 withdrawals. Baseline TKV (controls 1422, tolvaptan 1635 ml) and eGFR (both 62 ml/min per 1.73 m(2)) were similar. Control TKV increased 5.8% versus 1.7%/yr for tolvaptan (P < 0.001, estimated ratio of geometric mean 0.96 [95% confidence interval 0.95 to 0.97]). Corresponding annualized eGFR declined: -2.1 versus -0.71 ml/min per 1.73 m(2)/yr (P = 0.01, LMM group difference 1.1 ml/min per 1.73 m(2)/yr [95% confidence interval 0.24 to 1.9]). Sensitivity analyses including withdrawn subjects were similar, whereas MMRM analyses were significant at each year for TKV and nonsignificant for eGFR. Increasing TKV correlated with decreasing eGFR (r = -0.21, P < 0.01).

CONCLUSION

ADPKD cyst growth progresses more slowly with tolvaptan than in historical controls, but AEs are common.

Glomerular hyperfiltration and renal progression in children with autosomal dominant polycystic kidney disease

BACKGROUND AND OBJECTIVES

The purpose of this study was to determine whether glomerular hyperfiltration (GH) occurring early in autosomal dominant polycystic kidney disease (ADPKD) is indicative of more rapid disease progression in children.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

One hundred eighty children with ADPKD (ages 4 to 18 years) with normal renal function were examined by renal ultrasound. Renal volume was calculated using a standard formula for a modified ellipsoid. Creatinine clearance was calculated from serum creatinine and 24-hour urine creatinine. GH was defined as creatinine clearance ≥140 ml/min per 1.73 m(2).

RESULTS

Thirty-two children had GH (mean age 11.4 ± 3.6 years) and 148 had normal renal function (mean age 10.8 ± 3.9 years). Patients with GH at baseline demonstrated an increased rate of total renal volume growth (β: rate of change = +19.3 ± 10.8 cm(3)/year) over 5 years compared with those without GH at baseline (β = -4.3 ± 7.7 cm(3)/year), P = 0.008. Those with GH at baseline experienced a faster decline in creatinine clearance in subsequent years (β = -5.0 ± 0.8 ml/min per 1.73 m(2) per year) compared with those without GH at baseline (β = +1.0 ± 0.4 ml/min per 1.73 m(2) per year), P < 0.0001.

CONCLUSIONS

This study revealed that occurrence of GH in ADPKD children is associated with a significantly faster decline in renal function and higher rate of kidney enlargement over time. GH combined with the increased renal volume may therefore be used as an early marker for a more severe progression of ADPKD in children.

Why kidneys fail in autosomal dominant polycystic kidney disease

The weight of evidence gathered from studies in humans with hereditary polycystic kidney disease (PKD)1 and PKD2 disorders, as well as from experimental animal models, indicates that cysts are primarily responsible for the decline in glomerular filtration rate that occurs fairly late in the course of the disease. The processes underlying this decline include anatomic disruption of glomerular filtration and urinary concentration mechanisms on a massive scale, coupled with compression and obstruction by cysts of adjacent nephrons in the cortex, medulla and papilla. Cysts prevent the drainage of urine from upstream tributaries, which leads to tubule atrophy and loss of functioning kidney parenchyma by mechanisms similar to those found in ureteral obstruction. Cyst-derived chemokines, cytokines and growth factors result in a progression to fibrosis that is comparable with the development of other progressive end-stage renal diseases. Treatment of renal cystic disorders early enough to prevent or reduce cyst formation or slow cyst growth, before the secondary changes become widespread, is a reasonable strategy to prolong the useful function of kidneys in patients with autosomal dominant polycystic kidney disease.

Potent, metabolically stable benzopyrimido-pyrrolo-oxazine-dione (BPO) CFTR inhibitors for polycystic kidney disease

We previously reported the discovery of pyrimido-pyrrolo-quinoxalinedione (PPQ) inhibitors of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel and showed their efficacy in an organ culture model of polycystic kidney disease (PKD) (J. Med. Chem. 2009, 52, 6447-6455). Here, we report related benzopyrimido-pyrrolo-oxazinedione (BPO) CFTR inhibitors. To establish structure-activity relationships and select lead compound(s) with improved potency, metabolic stability, and aqueous solubility compared to the most potent prior compound 8 (PPQ-102, IC(50) ∼ 90 nM), we synthesized 16 PPQ analogues and 11 BPO analogues. The analogues were efficiently synthesized in 5-6 steps and 11-61% overall yield. Modification of 8 by bromine substitution at the 5-position of the furan ring, replacement of the secondary amine with an ether bridge, and carboxylation, gave 6-(5-bromofuran-2-yl)-7,9-dimethyl-8,10-dioxo-11-phenyl-7,8,9,10-tetrahydro-6H-benzo[b]pyrimido [4',5':3,4]pyrrolo [1,2-d][1,4]oxazine-2-carboxylic acid 42 (BPO-27), which fully inhibited CFTR with IC(50) ∼ 8 nM and, compared to 8, had >10-fold greater metabolic stability and much greater polarity/aqueous solubility. In an embryonic kidney culture model of PKD, 42 prevented cyst growth with IC(50) ∼ 100 nM. Benzopyrimido-pyrrolo-oxazinediones such as 42 are potential development candidates for antisecretory therapy of PKD.

Intermediate volume on computed tomography imaging defines a fibrotic compartment that predicts glomerular filtration rate decline in autosomal dominant polycystic kidney disease patients

Total kidney and cyst volumes have been used to quantify disease progression in autosomal dominant polycystic kidney disease (ADPKD), but a causal relationship with progression to renal failure has not been demonstrated. Advanced image processing recently allowed to quantify extracystic tissue, and to identify an additional tissue component named "intermediate," appearing hypoenhanced on contrast-enhanced computed tomography (CT). The aim of this study is to provide a histological characterization of intermediate volume, investigate its relation with renal function, and provide preliminary evidence of its role in long-term prediction of functional loss. Three ADPKD patients underwent contrast-enhanced CT scans before nephrectomy. Histological samples of intermediate volume were drawn from the excised kidneys, and stained with hematoxylin and eosin and with saturated picrosirius solution for histological analysis. Intermediate volume showed major structural changes, characterized by tubular dilation and atrophy, microcysts, inflammatory cell infiltrate, vascular sclerosis, and extended peritubular interstitial fibrosis. A significant correlation (r = -0.69, P < 0.001) between relative intermediate volume and baseline renal function was found in 21 ADPKD patients. Long-term prediction of renal functional loss was investigated in an independent cohort of 13 ADPKD patients, followed for 3 to 8 years. Intermediate volume, but not total kidney or cyst volume, significantly correlated with glomerular filtration rate decline (r = -0.79, P < 0.005). These findings suggest that intermediate volume may represent a suitable surrogate marker of ADPKD progression and a novel therapeutic target.

The relationship between renal volume and renal function in autosomal dominant polycystic kidney disease

BACKGROUND

In patients with autosomal dominant polycystic kidney disease (ADPKD), renal cysts grow exponentially. Since remaining renal parenchyma has a capacity to compensate for the loss of glomerular filtration, the glomerular filtration rate (GFR) may be sustained until the disease progresses. The purpose of this study was to determine if renal volumetric indices and clinical parameters are associated with renal function in Japanese patients with ADPKD.

METHODS

In 73 ADPKD patients (28 men, 45 women), the associations of mean systolic blood pressure, mean diastolic blood pressure, estimated GFR (eGFR), the amount of proteinuria and albuminuria, body mass index (BMI), brachial-ankle pulse wave velocity (baPWV), ankle-brachial index, and total kidney volume (TKV) were retrospectively analyzed.

RESULTS

Multivariate linear regression analysis showed that eGFR was significantly and independently inversely correlated with patients' age and BMI. The median change in eGFR per year (ΔeGFR/y) was -2.8 ml/min/1.73 m(2)/year. Multiple linear regression analysis showed that ΔeGFR/y was significantly and independently inversely correlated with the change in TKV per year (ΔTKV/y). Multiple linear regression analysis showed that ΔTKV/y was significantly related to initial TKV and the change in albuminuria per year.

CONCLUSIONS

This study demonstrated a significant relationship between the change in renal function and the change in renal volume in Japanese ADPKD patients without renal insufficiency. It is possible that the volume measurements can be used as useful markers for disease progression in Japanese ADPKD patients.

Phosphorylation, protein kinases and ADPKD

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disease characterized by renal cyst formation and caused by mutations in the PKD1 and PKD2 genes, which encode polycystin-1(PC-1) and -2 (PC-2) proteins, respectively. PC-1 is a large plasma membrane receptor involved in the regulation of several biological functions and signaling pathways including the Wnt cascade, AP-1, PI3kinase/Akt, GSK3β, STAT6, Calcineurin/NFAT and the ERK and mTOR cascades. PC-2 is a calcium channel of the TRP family. The two proteins form a functional complex and prevent cyst formation, but the precise mechanism(s) involved remains unknown. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Detection of autosomal dominant polycystic kidney disease by NMR spectroscopic fingerprinting of urine

Autosomal dominant polycystic kidney disease (ADPKD) is a frequent cause of kidney failure; however, urinary biomarkers for the disease are lacking. In a step towards identifying such markers, we used multidimensional-multinuclear nuclear magnetic resonance (NMR) spectroscopy with support vector machine-based classification and analyzed urine specimens of 54 patients with ADPKD and slightly reduced estimated glomerular filtration rates. Within this cohort, 35 received medication for arterial hypertension and 19 did not. The results were compared with NMR profiles of 46 healthy volunteers, 10 ADPKD patients on hemodialysis with residual renal function, 16 kidney transplant patients, and 52 type 2 diabetic patients with chronic kidney disease. Based on the average of 51 out of 701 NMR features, we could reliably discriminate ADPKD patients with moderately advanced disease from ADPKD patients with end-stage renal disease, patients with chronic kidney disease of other etiologies, and healthy probands with an accuracy of >80%. Of the 35 patients with ADPKD receiving medication for hypertension, most showed increased excretion of proteins and also methanol. In contrast, elevated urinary methanol was not found in any of the control and other patient groups. Thus, we found that NMR fingerprinting of urine differentiates ADPKD from several other kidney diseases and individuals with normal kidney function. The diagnostic and prognostic potential of these profiles requires further evaluation.

Cilium, centrosome and cell cycle regulation in polycystic kidney disease

Polycystic kidney disease is the defining condition of a group of common life-threatening genetic disorders characterized by the bilateral formation and progressive expansion of renal cysts that lead to end stage kidney disease. Although a large body of information has been acquired in the past years about the cellular functions that characterize the cystic cells, the mechanisms triggering the cystogenic conversion are just starting to emerge. Recent findings link defects in ciliary functions, planar cell polarity pathway, and centrosome integrity in early cystic development. Many of the signals dysregulated during cystogenesis may converge on the centrosome for its central function as a structural support for cilia formation and a coordinator of protein trafficking, polarity, and cell division. Here, we will discuss the contribution of proliferation, cilium and planar cell polarity to the cystic signal and will analyze in particular the possible role that the basal bodies/centrosome may play in the cystogenetic mechanisms. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Rationale and design of the TEMPO (Tolvaptan Efficacy and Safety in Management of Autosomal Dominant Polycystic Kidney Disease and its Outcomes) 3-4 Study

BACKGROUND

Current management of autosomal dominant polycystic kidney disease (ADPKD) is focused on treating disease complications, not on slowing cyst development or preventing progression to kidney failure. Tolvaptan, a selective vasopressin V2 (vasopressin 2) receptor antagonist, has been proved to inhibit kidney cyst growth and preserve kidney function in multiple animal models of polycystic kidney disease. The TEMPO (Tolvaptan Efficacy and Safety in Management of Autosomal Dominant Polycystic Kidney Disease and Its Outcomes) 3-4 Study will examine the long-term effectiveness and safety of tolvaptan in patients with ADPKD. We report baseline characteristics and revised power calculations for the trial.

STUDY DESIGN

A prospective, 3-year, multicenter, double-blind, placebo-controlled trial of tolvaptan, a selective V2 receptor antagonist. Primary outcome is total kidney volume percentage of change from baseline for tolvaptan relative to placebo. Secondary outcome parameters include time to ADPKD-associated complications (kidney function decrease, blood pressure control, renal pain, and albuminuria) and safety end points.

SETTING & PARTICIPANTS

This trial includes patients with ADPKD with relatively preserved kidney function (baseline estimated creatinine clearance ≥60 mL/min), aged 50 years or younger, and with total kidney volume measured using magnetic resonance imaging ≥750 mL.

INTERVENTION

Administration of placebo or tolvaptan, dose titrated to tolerance.

OUTCOMES

Number of subjects enrolled and baseline characteristics.

MEASUREMENTS

Total kidney volume, kidney function, albuminuria, kidney pain, and vital signs.

RESULTS

1,445 patients with ADPKD were enrolled between March 2007 and January 2009. Preliminary baseline median total kidney volume was 1.46 L, and estimated creatinine clearance was 105 ± 34 mL/min. A prespecified blinded sample-size recalculation at two-thirds enrollment confirmed the likely power of the study to detect 20% differences from placebo in the primary and key secondary end points at P < 0.05.

LIMITATIONS

This is a preselected ADPKD population chosen for its risk of progression to kidney failure and may not represent the general ADPKD population. If study results are positive with regard to the primary end point, positive effects on other secondary clinical outcomes will be required to assess overall benefit.

CONCLUSIONS

This randomized trial is the largest clinical study of a proposed ADPKD intervention to date. It targets patients with ADPKD with early disease who are projected to have rapid cyst growth and accelerated outcomes. Blockade of vasopressin V2 receptor is hypothesized to inhibit cyst growth, thereby delaying additional adverse clinical outcomes.

Fluid transport and cystogenesis in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most frequent inherited nephropathy. The development and enlargement of cysts in ADPKD requires tubular cell proliferation, abnormalities in the extracellular matrix and transepithelial fluid secretion. Multiple studies have suggested that fluid secretion across ADPKD cyst-lining cells is driven by the transepithelial secretion of chloride, mediated by the apical CFTR channel and specific basolateral transporters. The whole secretory process is stimulated by increased levels of cAMP in the cells, probably reflecting modifications in the intracellular calcium homeostasis and abnormal stimulation of the vasopressin V2 receptor. This review will focus on the pathophysiology of fluid secretion in ADPKD cysts, starting with classic, morphological and physiological studies that were followed by investigations of the molecular mechanisms involved and therapeutic trials targeting these pathways in cellular and animal models and ADPKD patients. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Advantages and controversies in the era of intrarenal volumetry

BACKGROUND/AIMS

Ultrasound is the preferred imaging modality in nephrology. In many kidney diseases, however, more accurate methods are needed to distinguish between relevant intrarenal structures. MRI could be a solution, although the use of MRI contrast has caused severe complications in some cases, and invasive kidney biopsies may follow, even though such small specimens traditionally provide inaccurate quantitative data. We evaluated the usefulness of MRI volumetry and quantitative kidney biopsies to assess glomerular number and volume as well as cortical volume.

METHODS

We specifically highlight an experimental study in which different MRI scans were performed in healthy pigs as well as pigs with unilateral ureteral obstruction to assess intrarenal volume. Single-kidney glomerular filtration rate (GFR) was measured using ureteral cannulation and (51)Cr-EDTA. Kidney biopsies were taken and evaluated employing stereological techniques to measure number and volume of glomeruli. Pigs were sacrificed and kidneys were removed for stereological analysis. Non-contrast-based MRI intrarenal volumes were - without significant difference to intrarenal volumes - obtained using contrast-enhanced MRI and ex vivo techniques.

RESULTS

Kidney biopsies gave valid estimates regarding quantitative parameters, such as mean number and volume of glomeruli in the cortex. Different structural parameters correlated with kidney GFR with high, although varying, correlation coefficients.

CONCLUSION

Non-contrast MRI is suitable for estimating intrarenal volumes in healthy and diseased kidneys. We advocate further research in diagnostic modalities combining MRI and biopsies. Major challenges are the cortical architecture and heterogeneous distribution of glomeruli within the kidney.

Polycystic kidney disease: pathogenesis and potential therapies

Autosomal dominant polycystic kidney disease (ADPKD) is a prevalent, inherited condition for which there is currently no effective specific clinical therapy. The disease is characterized by the progressive development of fluid-filled cysts derived from renal tubular epithelial cells which gradually compress the parenchyma and compromise renal function. Current interests in the field focus on understanding and exploiting signaling mechanisms underlying disease pathogenesis as well as delineating the role of the primary cilium in cystogenesis. This review highlights the pathogenetic pathways underlying renal cyst formation as well as novel therapeutic targets for the treatment of PKD. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Association of urinary biomarkers with disease severity in patients with autosomal dominant polycystic kidney disease: a cross-sectional analysis

BACKGROUND

Disease monitoring of autosomal dominant polycystic kidney disease (ADPKD) will become more important with potential upcoming therapeutic interventions. Because serum creatinine level is considered of limited use and measurement of effective renal blood flow (ERBF) and total renal volume are time consuming and expensive, there is a need for other biomarkers. We aimed to investigate which urinary markers have increased levels in patients with ADPKD; whether these urinary markers are associated with measured glomerular filtration rate (mGFR), ERBF, and total renal volume; and whether these associations are independent of albuminuria (urine albumin excretion [UAE]).

STUDY DESIGN

Diagnostic test study.

SETTING & PARTICIPANTS

102 patients with ADPKD (Ravine criteria) and 102 age- and sex-matched healthy controls.

INDEX TEST

24-hour urinary excretion of glomerular (immunoglobulin G), proximal tubular (kidney injury molecule 1 [KIM-1], N-acetyl-β-d-glucosaminidase, neutrophil gelatinase-associated lipocalin [NGAL], and β(2)-microglobulin), and distal tubular (heart-type fatty acid binding protein [H-FABP]) damage markers and inflammatory markers (monocyte chemotactic protein 1 [MCP-1] and macrophage migration inhibitory factor).

REFERENCE TEST

Disease severity assessed using measures of kidney function (mGFR and ERBF, measured using clearance of iothalamate labeled with iodine 125 and hippuran labeled with iodine 131 during continuous infusion, respectively) and structure (total renal volume, measured using magnetic resonance imaging).

OTHER MEASUREMENTS

24-hour UAE.

RESULTS

In 102 patients with ADPKD (aged 40 ± 11 years; 58% men), levels of all measured urinary biomarkers were increased compared with healthy controls. Excretion of immunoglobulin G and albumin relatively were most increased. ERBF and mGFR values were associated with urinary excretion of β(2)-microglobulin, NGAL, and H-FABP independent of UAE, whereas total renal volume was associated with KIM-1, NGAL, and MCP-1 independent of UAE.

LIMITATIONS

Cross-sectional, single center.

CONCLUSIONS

Levels of markers for multiple parts of the nephron are increased in patients with ADPKD. In addition to measurement of UAE, measurement of urinary β(2)-microglobulin, KIM-1, H-FABP, MCP-1, and especially NGAL could be of value for determination of disease severity in patients with ADPKD.

Similar renal outcomes in children with ADPKD diagnosed by screening or presenting with symptoms

Autosomal dominant polycystic kidney disease (ADPKD) in children is sometimes considered to be a benign condition, with morbidity manifesting in adulthood. Therefore, diagnostic screening of children at risk is controversial. The aim of our study was to to compare the manifestations of ADPKD in children diagnosed by postnatal ultrasound (US) screening versus those presenting with symptoms. This was a retrospective chart review of children with ADPKD assessed in a single centre between 1987 and 2007. Age and reason for diagnosis were noted, and children were separated into two groups: (1) those diagnosed on the basis of family-based screening; (2) those presenting with a symptom. The two groups were compared for renal size, number of cysts, estimated glomerular filtration rate (eGFR), the presence of hypertension and microalbuminuria. In the 47 children with ADPKD (21 females) from 33 families who satisfied the enrollment criteria, mean (standard deviation) age at referral and last follow-up was 7.2 (4.4) and 12.9 (5.1) years, respectively, and the mean follow-up duration was 5.7 (3.6) years. Diagnosis was based on postnatal US screening in 31 children, whereas 16 were diagnosed after presenting with symptoms. The proportions of children with nephromegaly, hypertension, microalbuminuria and decreased eGFR, respectively, were similar in both groups. Based on these results, we conclude that renal-related morbidities, including hypertension and microalbuminia, do occur in children with ADPKD and at a similar frequency in those diagnosed after presenting with symptoms and those diagnosed upon postnatal screening. We suggest that at-risk children should have regular checks to detect hypertension. Moreover, affected children may benefit from novel therapies to minimise cystic disease progression.

Copeptin, a surrogate marker of vasopressin, is associated with disease severity in autosomal dominant polycystic kidney disease

BACKGROUND AND OBJECTIVES

Experimental studies suggest a detrimental role for vasopressin in the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD). However, it is unknown whether endogenous vasopressin concentration is associated with disease severity in patients with ADPKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Plasma copeptin concentration (a marker of endogenous vasopressin levels) was measured in 102 ADPKD patients (diagnosis based on Ravine criteria) by an immunoassay. Plasma and urinary osmolarity were also measured. To assess disease severity, GFR and effective renal blood flow were measured by continuous infusion of 125I-iothalamate and 131I-hippuran, total renal volume by magnetic resonance imaging, and 24-hour urinary albumin excretion by nephelometry.

RESULTS

In these ADPKD patients, copeptin was associated with the various markers of disease severity in ADPKD (positively with total renal volume [R=0.47] and albuminuria [R=0.39] and negatively with GFR [R=-0.58] and effective renal blood flow [R=-0.52], all P<0.001). These associations were independent of age, gender, and use of diuretics. Copeptin was furthermore associated with plasma osmolarity (P<0.001) but not with 24-hour urinary volume, 24-hour urinary osmolarity or fractional urea excretion (P=0.7, 0.9, and 0.3, respectively).

CONCLUSIONS

On cross-sectional analysis, copeptin is associated with disease severity in ADPKD patients, supporting the results of experimental studies that suggest that vasopressin antagonists have a renoprotective effect in ADPKD and offering a good prospect for clinical studies with these agents.

Water prescription in autosomal dominant polycystic kidney disease: a pilot study

BACKGROUND AND OBJECTIVES

In animal models of polycystic kidney disease, the ingestion of large amounts of water promotes diuresis by suppressing plasma levels of arginine vasopressin (AVP) and renal levels of cAMP, slowing cyst progression. Whether simple water ingestion is a potential therapeutic strategy for individuals with autosomal dominant polycystic kidney disease (ADPKD) is unknown. In this study, a simple method to quantify the amount of water to achieve a specific mean urine osmolality target in patients with ADPKD was developed and tested.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In eight ADPKD patients eating typical diets, osmolality and volume were measured in 24-hour urine collections. The amount of additional ingested water required daily to achieve a mean urine osmolality of 285 ± 45 mosm/kg was determined. Participants were instructed to distribute the prescribed water over waking hours for each of 5 days. Blood chemistries, 24-hour urine collections, BP, and weight were measured before and after the period of supplemental water intake.

RESULTS

Five patients achieved the 285 mosm/kg urine target without difficulty. Mean urine osmolality decreased and mean urine volume increased; serum sodium, weight, and BP were unchanged. Daily osmolar excretion remained constant, indicating a stable ad lib dietary intake of solutes and protein over the 2-week study period.

CONCLUSIONS

The amount of additional water needed to achieve a urine osmolality target can be approximated from the urine osmolar excretion in ADPKD patients eating typical diets, providing a quantitative method to prescribe supplemental water for such individuals.

Early renal abnormalities in autosomal dominant polycystic kidney disease

BACKGROUND AND OBJECTIVES

Potential therapeutic interventions are being developed for autosomal dominant polycystic kidney disease (ADPKD). A pivotal question will be when to initiate such treatment, and monitoring disease progression will thus become more important. Therefore, the prevalence of renal abnormalities in ADPKD at different ages was evaluated.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Included were 103 prevalent ADPKD patients (Ravine criteria). Measured were mean arterial pressure (MAP), total renal volume (TRV), GFR, effective renal plasma flow (ERPF), renal vascular resistance (RVR), and filtration fraction (FF). Twenty-four-hour urine was collected. ADPKD patients were compared with age- and gender-matched healthy controls.

RESULTS

Patients and controls were subdivided into quartiles of age (median ages 28, 37, 42, and 52 years). Patients in the first quartile of age had almost the same GFR when compared with controls, but already a markedly decreased ERPF and an increased FF (GFR 117 +/- 32 versus 129 +/- 17 ml/min, ERPF 374 +/- 119 versus 527 +/- 83 ml/min, FF 32% +/- 4% versus 25% +/- 2%, and RVR 12 (10 to 16) versus 8 (7 to 8) dynes/cm(2), respectively). Young adult ADPKD patients also had higher 24-hour urinary volumes, lower 24-hour urinary osmolarity, and higher urinary albumin excretion (UAE) than healthy controls, although TRV in these young adult patients was modestly enlarged (median 1.0 L).

CONCLUSIONS

Already at young adult age, ADPKD patients have marked renal abnormalities, including a decreased ERPF and increased FF and UAE, despite modestly enlarged TRV and near-normal GFR. ERPF, FF, and UAE may thus be better markers for disease severity than GFR.

The HALT polycystic kidney disease trials: design and implementation

BACKGROUND AND OBJECTIVES

Two HALT PKD trials will investigate interventions that potentially slow kidney disease progression in hypertensive autosomal dominant polycystic kidney disease (ADPKD) patients. Studies were designed in early and later stages of ADPKD to assess the impact of intensive blockade of the renin-angiotensin-aldosterone system and level of BP control on progressive renal disease. Design, settings, participants, and measurements: PKD-HALT trials are multicenter, randomized, double-blind, placebo-controlled trials studying 1018 hypertensive ADPKD patients enrolled over 3 yr with 4 to 8 yr of follow-up. In study A, 548 participants, estimated GFR (eGFR) of >60 ml/min per 1.73 m(2) were randomized to one of four arms in a 2-by-2 design: combination angiotensin converting enzyme inhibitor (ACEi) and angiotensin receptor blocker (ARB) therapy versus ACEi monotherapy at two levels of BP control. In study B, 470 participants, eGFR of 25 to 60 ml/min per 1.73 m2 compared ACEi/ARB therapy versus ACEi monotherapy, with BP control of 120 to 130/70 to 80 mmHg. Primary outcomes of studies A and B are MR-based percent change kidney volume and a composite endpoint of time to 50% reduction of baseline estimated eGFR, ESRD, or death, respectively.

RESULTS

This report describes design issues related to (1) novel endpoints such as kidney volume, (2) home versus office BP measures, and (3) the impact of RAAS inhibition on kidney and patient outcomes, safety, and quality of life.

CONCLUSIONS

HALT PKD will evaluate potential benefits of rigorous BP control and inhibition of the renin-angiotensin-aldosterone system on kidney disease progression in ADPKD.

Novel targets for the treatment of autosomal dominant polycystic kidney disease

IMPORTANCE OF THE FIELD

Autosomal dominant (AD) polycystic kidney disease (PKD) is the most common life-threatening hereditary disorder. There is currently no therapy that slows or prevents cyst formation and kidney enlargement in humans. An increasing number of animal studies have advanced our understanding of molecular and cellular targets of PKD.

AREAS COVERED IN THE REVIEW

The purpose of this review is to summarize the molecular and cellular targets involved in cystogenesis and to update on the promising therapies that are being developed and tested based on knowledge of these molecular and cellular targets.

WHAT THE READER WILL GAIN

Insight into the pathogenesis of PKD and how a better understanding of the pathogenesis of PKD has led to the development of potential therapies to inhibit cyst formation and/or growth and improve kidney function.

TAKE HOME MESSAGE

The results of animal studies in PKD have led to the development of clinical trials testing potential new therapies to reduce cyst formation and/or growth. A vasopressin V2 receptor antagonist, mTOR inhibitors, blockade of the renin-angiotensin system and statins that reduce cyst formation and improve renal function in animal models of PKD are being tested in interventional studies in humans.

Hypertension in autosomal dominant polycystic kidney disease

Hypertension is common and occurs in a majority of autosomal dominant polycystic kidney disease (ADPKD) patients before the loss of kidney function. Hypertension relates to progressive kidney enlargement and is a significant independent risk factor for progression to ESRD. The pathogenesis of hypertension in ADPKD is complex and dependent on many factors that influence each other. Pkd1 and Pkd2 expression levels are highest in the major vessels and are present in the cilia of endothelial cells and in vascular smooth muscle cells. Decreased or absent polycystin 1 or 2 expression is associated with abnormal vascular structure and function. Pkd1/Pkd2 deficiency results in reduced nitric oxide (NO) levels, altered endothelial response to shear stress with attenuation in vascular relaxation. Ten percent to 20% of ADPKD children show hypertension and the majority of adults are hypertensive before any loss of kidney function. Cardiac abnormalities such as left ventricular hypertrophy and carotid intimal wall thickening are present before the development of hypertension in ADPKD. The activation of the renin-angiotensin-aldosterone system occurs in ADPKD because of decreased NO production as well as bilateral cyst expansion and intrarenal ischemia. With increasing cyst size, further activation of the RAAS occurs, blood pressure increases, and a vicious cycle ensues with enhanced cyst growth and hypertension ultimately leading to ESRD. The inhibition of the angiotensin aldosterone system is possible with angiotensin converting enzyme inhibitors and angiotensin receptor blockers. However, interventional studies have not yet shown benefit in slowing progression to renal failure in ADPKD. Currently, large multicenter studies are being performed to determine the beneficial effects of RAAS inhibition both early and late in ADPKD.

Liver and kidney disease in ciliopathies

Hepatorenal fibrocystic diseases (HRFCDs) are among the most common inherited human disorders. The discovery that proteins defective in the autosomal dominant and recessive polycystic kidney diseases (ADPKD and ARPKD) localize to the primary cilia and the recognition of the role these organelles play in the pathogenesis of HRFCDs led to the term "ciliopathies." While ADPKD and ARPKD are the most common ciliopathies associated with both liver and kidney disease, variable degrees of renal and/or hepatic involvement occur in many other ciliopathies, including Joubert, Bardet-Biedl, Meckel-Gruber, and oral-facial-digital syndromes. The ductal plate malformation (DPM), a developmental abnormality of the portobiliary system, is the basis of the liver disease in ciliopathies that manifest congenital hepatic fibrosis (CHF), Caroli syndrome (CS), and polycystic liver disease (PLD). Hepatocellular function remains relatively preserved in ciliopathy-associated liver diseases. The major morbidity associated with CHF is portal hypertension (PH), often leading to esophageal varices and hypersplenism. In addition, CD predisposes to recurrent cholangitis. PLD is not typically associated with PH, but may result in complications due to mass effects. The kidney pathology in ciliopathies ranges from non-functional cystic dysplastic kidneys to an isolated urinary concentration defect; the disorders contributing to this pathology, in addition to ADPKD and ARPKD, include nephronophithisis (NPHP), glomerulocystic kidney disease and medullary sponge kidneys. Decreased urinary concentration ability, resulting in polyuria and polydypsia, is the first and most common renal symptom in ciliopathies. While the majority of ADPKD, ARPKD, and NPHP patients require renal transplantation, the frequency and rate of progression to renal failure varies considerably in other ciliopathies. This review focuses on the kidney and liver disease found in the different ciliopathies.

Cystic kidney diseases and planar cell polarity signaling

Renal cystic diseases are a major clinical concern as they are the most common genetic cause of end-stage renal disease. While many of the genes causing cystic disease have been identified in recent years, knowing the molecular nature of the mutations has not clarified the mechanisms underlying cyst formation. Recent research in model organisms has suggested that cyst formation may be because of defective planar cell polarity (PCP) and/or ciliary defects. In this review, we first outline the clinical features of renal cystic diseases and then discuss current research linking our understanding of cystic kidney disease to PCP and cilia.

Quality of life in autosomal dominant polycystic kidney disease patients not yet on dialysis

BACKGROUND AND OBJECTIVES

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited progressive disorder associated with significant pain and discomfort affecting quality of life. This study determined the impact of pain medication use and other clinical, biochemical and genetic characteristics on the physical and mental well being of predialysis ADPKD patients using the Short Form 36 (SF-36) questionnaire.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The authors prospectively evaluated ADPKD patients in the Cohort Study, funded by the Polycystic Kidney Disease Foundation. Data on clinical, biochemical, and radiologic variables were collected in patients who were given the Short Form-36 questionnaire. Variables independently associated with the Physical Component Summary (PCS) and the Mental Component Summary (MCS) scores were identified.

RESULTS

One hundred fifty-two patients had a mean PCS and MCS of 46.9 +/- 11.3 and 51.0 +/- 9.0, similar to the general population and better than the ESRD population. Eleven (7%) reported pain medication intake within 1 mo of evaluation and demonstrated lower PCS than those not taking pain medications. Patients with GFR >or= 80 ml/min/1.73 m(2) had greater PCS than those with GFR < 80 ml/min/1.73 m(2). Age, BMI, pulse pressure, pain medication use, and education level independently associate with PCS and account for 32% of the variability of the measurement. Pulse pressure correlated with MCS.

CONCLUSIONS

Predialysis ADPKD patients assess their quality of life similar to the general population. Age, BMI, pulse pressure, pain medication intake, and education level link to their physical well-being.

Increases in kidney volume in autosomal dominant polycystic kidney disease can be detected within 6 months

Kidney volume growth is considered the best surrogate marker predicting the decline of renal function in autosomal dominant polycystic kidney disease. To assess the therapeutic benefit of new drugs more rapidly, changes in kidney volume need to be determined over a short time interval. Here we measured renal volume changes by manual segmentation volumetry applied to magnetic resonance imaging scans obtained with an optimized T1-weighted acquisition protocol without gadolinium-based contrast agents. One hundred young patients with autosomal dominant polycystic kidney disease and preserved renal function had a significant increase in total kidney volume by 2.71+/-4.82% in 6 months. Volume measurements were highly reproducible and accurate, as indicated by correlation coefficients of 1.000 for intra-observer and 0.996 for inter-observer agreement, with acceptable within-subject standard deviations. The change in renal volume correlated with baseline total kidney volume in all age subgroups. Total kidney volume positively correlated with male gender, hypertension, albuminuria and a history of macrohematuria but negatively with creatinine clearance. Albuminuria was associated with accelerated volume progression. Our study shows that increases in kidney volume can be reliably measured over a 6 month period in early autosomal dominant polycystic kidney disease using unenhanced magnetic resonance imaging sequences.

Strategies to inhibit cyst formation in ADPKD

The many hundreds of cysts that grow and expand and ultimately overwhelm and destroy polycystic kidneys arise from the slow but unrelenting proliferation of tubular epithelial cells, eventually giving rise to very large, thin-walled, fluid-filled structures. The growth of these cystic bodies requires two processes: Cell proliferation and fluid secretion. Cyst epithelial cells seem to have a unique phenotype that could offer opportunities for therapeutic intervention. Current evidence has demonstrated that cAMP drives both abnormal cell proliferation, by stimulating the Ras/mitogen-activated protein kinase (MAPK) pathway, and cyst-filling fluid secretion, by activating the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel. Both of these cAMP-mediated processes should be considered in the design of strategies targeted to slow cyst growth and enlargement in autosomal dominant polycystic kidney disease.

Chloride channels as drug targets

Chloride channels represent a relatively under-explored target class for drug discovery as elucidation of their identity and physiological roles has lagged behind that of many other drug targets. Chloride channels are involved in a wide range of biological functions, including epithelial fluid secretion, cell-volume regulation, neuroexcitation, smooth-muscle contraction and acidification of intracellular organelles. Mutations in several chloride channels cause human diseases, including cystic fibrosis, macular degeneration, myotonia, kidney stones, renal salt wasting and hyperekplexia. Chloride-channel modulators have potential applications in the treatment of some of these disorders, as well as in secretory diarrhoeas, polycystic kidney disease, osteoporosis and hypertension. Modulators of GABA(A) (gamma-aminobutyric acid A) receptor chloride channels are in clinical use and several small-molecule chloride-channel modulators are in preclinical development and clinical trials. Here, we discuss the broad opportunities that remain in chloride-channel-based drug discovery.

Determinants of renal volume in autosomal-dominant polycystic kidney disease

The Consortium of Radiologic Imaging Studies of Polycystic Kidney Disease (CRISP) recently showed that renal enlargement in autosomal-dominant polycystic kidney disease mimicked exponential growth. We determined the effects of cyst initiation rate, total number, and growth rate on the time-dependent change of total cyst volume (TCV). Mathematical models with equations integrating cyst surface area, volume, and an invariant growth rate constant were used to compute the time-dependent change in volume of solitary and multiple cysts. Multiple expanding cysts increased TCV in an exponential-like pattern even when individual cysts formed at different rates or exhibited different but constant growth rates. TCV depended on the rate of cyst initiation and on the total number of cysts; however, the compounding effect of exponential-like growth was the most powerful determinant of long-term cyst expansion. Extrapolation of TCV data plots for individual subjects back to an age of 18 predicted TCV values within an established range. We conclude that cysts started early in life were the main contributor to eventual TCV while their growth rate primarily determined renal size; although the rate of formation and the ultimate number of cysts also contributed. The good fit between the exponential models and the extrapolated CRISP data indicates that the TCV growth rate is a defining trait for individual patients and may be used as a prognostic marker.

Autosomal Dominant Polycystic Kidney Disease: Time for a Change?

Diagnosis and treatment of autosomal dominant polycystic kidney disease (ADPKD) is rapidly changing. Cellular pathways that involve the polycystins are being mapped and involve the primary cilium, intracellular calcium and cAMP regulation, and the mammalian target of rapamycin (mTOR) pathway. With the use of new imaging approaches, earlier diagnosis of hepatic cystic disease is possible, and measurement of kidney and cystic growth as well as kidney blood flow is possible over relatively short periods. PKD gene type, gender, proteinuria, and the presence of hypertension relate to the rate of kidney growth in ADPKD. On the basis of risk factors for progression to ESRD and the pathogenic roles that intracellular cAMP and mTOR play in cystogenesis, novel therapies are now being tested, including maximal inhibition of the renin-angiotensin system, inhibition of renal intracellular cAMP using vasopressin V2 receptor antagonists, and somatostatin analogues, as well as inhibitors of mTOR. This review addresses the current understanding of the pathogenesis and the natural history of ADPKD; accuracy and reliability of diagnostic approaches in utero, childhood, and adulthood; the value of reliable magnetic resonance imaging to measure disease progression early in the course of ADPKD; and novel therapeutic approaches that are being evaluated in ADPKD.

Identification of a forskolin-like molecule in human renal cysts

Renal cyst enlargement is increased by adenosine cAMP, which is produced within mural epithelial cells. In a search for modulators of cAMP synthesis cyst fluids from 18 patients with autosomal dominant or recessive polycystic kidney disease (PKD) were analyzed, and in 15 of them, a stable lipophilic molecule that increased cAMP levels, stimulated transepithelial chloride and fluid secretion, and promoted the proliferation of human cyst epithelial cells was characterized. With the use of HPLC-mass spectrometry, a bioactive lipid with the same mass spectral fingerprint, the same chromatographic retention time, and the same biologic properties as forskolin, a widely known, potent adenylyl cyclase agonist, has been isolated and identified within the cyst fluid. Forskolin is synthesized by the plant Coleus forskohlii, but its appearance or compounds like it have not been reported in animals. The origin of forskolin in patients with PKD was not revealed by this study. Synthesis by mural cyst epithelial cells or an exogenous source are the most likely possibilities. Forskolin is sold for weight management and as a cardiovascular tonic in health stores and through the Worldwide Web. It is concluded that forskolin may have a role in promoting the enlargement of cysts in autosomal dominant PKD and recommended that patients avoid oral and parenteral preparations that contain this compound.

Magnetic resonance measurements of renal blood flow and disease progression in autosomal dominant polycystic kidney disease

Whether changes in renal blood flow (RBF) are associated with and possibly contribute to cystic disease progression in autosomal dominant polycystic kidney disease (ADPKD) has not been ascertained. The Consortium for Radiologic Imaging Studies of Polycystic Kidney Disease (CRISP) was created to develop imaging techniques and analyses to evaluate progression. A total of 131 participants with early ADPKD had measurements of RBF and total kidney (TKV) and cyst (TCV) volumes by magnetic resonance and of GFR by iothalamate clearance at baseline and 1, 2, and 3 yr. The effects of age, gender, body mass index, hypertension status, mean arterial pressure (MAP), TKV, TCV, RBF, renal vascular resistance (RVR), GFR, serum uric acid, HDL and LDL cholesterol, 24-h urine volume, sodium (UNaE) and albumin (UAE) excretions, and estimated protein intake were examined at baseline on TKV, TCV, and GFR slopes. TKV and TCV increased, RBF decreased, and GFR remained stable. TKV, TCV, RVR, serum uric acid, UAE, UNaE, age, body mass index, MAP, and estimated protein intake were positively and RBF and GFR negatively correlated with TKV and TCV slopes. TKV, RBF, UNaE, and UAE were independent predictors of TKV and TCV slopes (structural disease progression). TKV, TCV, RVR, and MAP were negatively and RBF positively correlated with GFR slopes. Regression to the mean confounded the analysis of GFR slopes. TKV and RBF were independent predictors of GFR decline (functional disease progression). In ADPKD, RBF reduction (1) parallels TKV increase, (2) precedes GFR decline, and (3) predicts structural and functional disease progression.

Cyst number but not the rate of cystic growth is associated with the mutated gene in autosomal dominant polycystic kidney disease

Data from serial renal magnetic resonance imaging of the Consortium of Radiologic Imaging Study of PKD (CRISP) autosomal dominant polycystic kidney disease (PKD) population showed that cystic expansion occurs at a consistent rate per individual, although it is heterogeneous in the population, and that larger kidneys are associated with more rapid disease progression. The significance of gene type to disease progression is analyzed in this study of the CRISP cohort. Gene type was determined in 183 families (219 cases); 156 (85.2%) had PKD1, and 27 (14.8%) had PKD2. PKD1 kidneys were significantly larger, but the rate of cystic growth (PKD1 5.68%/yr; PKD2 4.82%/yr) was not different (P = 0.24). Cyst number increased with age, and more cysts were detected in PKD1 kidneys (P < 0.0001). PKD1 is more severe because more cysts develop earlier, not because they grow faster, implicating the disease gene in cyst initiation but not expansion. These insights will inform the development of targeted therapies in autosomal dominant PKD.

Computed tomography evaluation of autosomal dominant polycystic kidney disease progression: a progress report

At the moment, there are no effective therapies to prevent or slow the progression of autosomal dominant polycystic kidney disease (ADPKD). Radiologic evaluations are used to monitor volume of renal cysts and parenchyma during disease evolution. Volumetric quantifications based on computed tomography were used to investigate the relation between structural and functional changes in patients with advanced-stage ADPKD. By use of image-processing techniques, volume of kidneys, renal cysts, fully enhanced parenchyma, and faintly contrast-enhanced parenchyma, referred to as intermediate, was estimated. GFR measurements and computed tomography evaluations were repeated 6 mo later. No statistically significant correlations were found between volumes of cysts and parenchyma and intermediate volume and GFR. However, the ratio of intermediate over parenchymal volume strongly correlated with GFR (r = -0.81, P < 0.001). In addition, there were significant correlations between percentage changes in intermediate volume (absolute or relative to parenchyma) and GFR changes during the observation period (r = -0.70 and r = -0.75, P < 0.01). These data support the hypothesis of a significant relation between radiologic appearance of renal structure and functional changes and suggest new ways that renal dysfunction in ADPKD may be predicted. Further work is necessary to determine the nature of faintly contrast-enhanced parenchyma and its role in renal functional loss.

Volume progression in polycystic kidney disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by progressive enlargement of cyst-filled kidneys.

METHODS

In a three-year study, we measured the rates of change in total kidney volume, total cyst volume, and iothalamate clearance in patients with ADPKD. Of a total of 241 patients, in 232 patients without azotemia who were 15 to 46 years old at baseline we used magnetic-resonance imaging to correlate the total kidney volume and total cyst volume with iothalamate clearance. Statistical methods included analysis of variance, Pearson correlation, and multivariate regression analysis.

RESULTS

Total kidney volume and total cyst volume increased exponentially, a result consistent with an expansion process dependent on growth. The mean (+/-SD) total kidney volume was 1060+/-642 ml at baseline and increased by a mean of 204+/-246 ml (5.27+/-3.92 percent per year, P<0.001) over a three-year period among 214 patients. Total cyst volume increased by 218+/-263 ml (P<0.001) during the same period among 210 patients. The baseline total kidney volume predicted the subsequent rate of increase in volume, independently of age. A baseline total kidney volume above 1500 ml in 51 patients was associated with a declining glomerular filtration rate (by 4.33+/-8.07 ml per minute per year, P<0.001). Total kidney volume increased more in 135 patients with PKD1 mutations (by 245+/-268 ml) than in 28 patients with PKD2 mutations (by 136+/-100 ml, P=0.03).

CONCLUSIONS

Kidney enlargement resulting from the expansion of cysts in patients with ADPKD is continuous and quantifiable and is associated with the decline of renal function. Higher rates of kidney enlargement are associated with a more rapid decrease in renal function.