Racial variation in autosomal dominant polycystic kidney disease

Health Disparities in Kidney Failure Among Patients With Autosomal Dominant Polycystic Kidney Disease: A Cross-Sectional Study

Rationale & Objective

Understanding potential differences in patterns of kidney failure among patients with autosomal dominant polycystic kidney disease (ADPKD) may provide insights into improving disease management. We sought to characterize patients with ADPKD and kidney failure across different race/ethnicities.

Study Design

Cross-sectional study.

Setting & Participants

Kaiser Permanente Southern California members diagnosed with ADPKD between January1, 2002, and December 31, 2018.

Exposure

ADPKD.

Outcome

Kidney failure, dialysis, or receipt of kidney transplant.

Analytical Approach

Differences in characteristics by race/ethnicity were assessed using analysis of variance F test and χ² test. To compare the range and distribution of the average age at onset of kidney failure by race/ethnicity and sex, we used box plots and confidence intervals. Multivariable logistic regression was used to estimate OR for kidney transplant.

Results

Among 3,677 ADPKD patients, 1,027 (27.3%) had kidney failure. The kidney failure cohort was comprised of Black (n=138; 30.7%), White (n=496; 30.6%), Hispanic (n=306; 24.7%), and Asian (n=87; 23.6%) patients. Hispanic patients had the youngest mean age of kidney failure onset (50 years) compared to Black (56 years) and White (57 years) patients. Black (44.2%; OR, 0.72) and Hispanic (49.7%; OR, 0.65) patients had lower rates of kidney transplantation compared to White (53.8%) patients. Preemptive kidney transplantations occurred in 15.0% of patients.

Limitations

Retrospective study design and possible misclassification of ADPKD cases. Kidney function calculations were based on equations incorporating race, potentially overestimating kidney function in African Americans. The study was conducted within a single, integrated health care system in 1 geographic region and may not be generalizable to all ADPKD patients.

Conclusions

Among a large diverse ADPKD population, we observed racial/ethnic differences in rates of kidney failure, age of kidney failure onset, and rates of kidney transplantation. Our real-world ADPKD cohort provides insight into racial/ethnic variation in clinical features of disease and potential disparities in care, which may affect ADPKD outcomes.

Health Disparities in Autosomal Dominant Polycystic Kidney Disease (ADPKD) in the United States

BACKGROUND AND OBJECTIVES

Autosomal dominant polycystic kidney disease (ADPKD) occurs at conception and is often diagnosed decades prior to kidney failure. Nephrology care and transplantation access should be independent of race and ethnicity. However, institutional racism and barriers to health care may affect patient outcomes in ADPKD. We sought to ascertain the effect of health disparities on outcomes in ADPKD by examining age at onset of kidney failure and access to preemptive transplantation and transplantation after dialysis initiation.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Retrospective cohort analyses of adults with ADPKD in the United States Renal Data System from January 2000 to June 2018 were merged to US Census income data and evaluated by self-reported race and ethnicity. Age at kidney failure was analyzed in a linear model, and transplant rates before and after dialysis initiation were analyzed in logistic and proportional hazards models in Black and Hispanic patients with ADPKD compared with White patients with ADPKD.

RESULTS

A total of 41,485 patients with ADPKD were followed for a median of 25 (interquartile range, 5-54) months. Mean age was 56±12 years; 46% were women, 13% were Black, and 10% were Hispanic. Mean ages at kidney failure were 55±13, 53±12, and 57±12 years for Black patients, Hispanic patients, and White patients, respectively. Odds ratios for preemptive transplant were 0.33 (95% confidence interval, 0.29 to 0.38) for Black patients and 0.50 (95% confidence interval, 0.44 to 0.56) for Hispanic patients compared with White patients. Transplant after dialysis initiation was 0.61 (95% confidence interval, 0.58 to 0.64) for Black patients and 0.78 (95% confidence interval, 0.74 to 0.83) for Hispanic patients.

CONCLUSIONS

Black and Hispanic patients with ADPKD reach kidney failure earlier and are less likely to receive a kidney transplant preemptively and after initiating dialysis compared with White patients with ADPKD.

Autosomal Dominant Polycystic Kidney Disease Prevalence among a Racially Diverse United States Population, 2002 through 2018

Among a large racially and ethnically diverse US population, the prevalence of diagnosed ADPKD between 2002 and 2018 was 42.6 per 100,000 persons.ADPKD prevalence (per 100,000) was higher in (non-Hispanic) White (63.2) and Black (73.0) patients compared with Hispanic (39.9) and Asian (48.9) patients.Given the variable penetrance of ADPKD, our findings suggest race may be a factor in the clinical presentation and diagnosis of ADPKD.

Possible role of the mitochondrial genome in the pathogenesis of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common monogenic renal disease in adults and is due to heterozygous germ line variants in either PKD1, PKD2 or rarely other genes. It is characterized by marked intra-familial disease variability suggesting that other genetic and/or environmental factors are involved in determining the lifetime course ADPKD. Recently, research indicates that polycystin-mediated mitochondrial dysfunction and metabolic re-programming contributes to the progression of ADPKD. Although biochemical abnormalities have gained the most interest, variants in the mitochondrial genome could be one of the mechanisms underlying the phenotypic variability in ADPKD. This narrative review aims to evaluate the role of the mitochondrial genome in the pathogenesis of APDKD.

African American polycystic kidney patients receive higher risk kidneys, but do not face increased risk for graft failure or post-transplant mortality

African Americans (AA) are disproportionately affected by end-stage renal disease (ESRD) and have worse outcomes following renal transplantation. Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic condition leading to ESRD necessitating transplant. We explored this population with respect to race by conducting a retrospective analysis of the UNOS database between 2005 and 2019. Our study included 10,842 (AA n = 1661; non-AA n = 9181) transplant recipients whose primary diagnosis was ADPKD. We further stratified the AA ADPKD population with respect to blood groups (AA blood type B n = 295 vs AA non-B blood type n = 1366), and also compared this cohort to AAs with a diagnosis of DM (n = 16,706) to identify unique trends in the ADPKD population. We analyzed recipient and donor characteristics, generated survival curves, and conducted multivariate analyses. African American ADPKD patients waited longer for transplants (924 days vs 747 days P < .001), and were more likely to be on dialysis (76% vs 62%; p < .001). This same group was also more likely to have AA donors (21% vs 9%; p < .001) and marginally higher KDPI kidneys (0.48 vs 0.45; p < .001). AA race was a risk factor for delayed graft function (DGF), increasing the chance of DGF by 45% (OR 1.45 95% CI 1.26-1.67; p < .001). AA race was not associated with graft failure (HR 1.10 95% CI 0.95-1.28; p = .21) or patient mortality (HR 0.84 95% CI 0.69-1.03; p = .09). Racial disparities exist in the ADPKD population. They should be continually studied and addressed to improve transplant equity.

RAPID-ADPKD (Retrospective epidemiological study of Asia-Pacific patients with rapId Disease progression of Autosomal Dominant Polycystic Kidney Disease): study protocol for a multinational, retrospective cohort study

INTRODUCTION

Patients with autosomal dominant polycystic kidney disease (ADPKD) reach end-stage renal disease in their fifth decade on average. For effective treatment and early intervention, identifying subgroups with rapid disease progression is important in ADPKD. However, there are no epidemiological data on the clinical manifestations and disease progression of patients with ADPKD from the Asia-Pacific region.

METHODS AND ANALYSIS

The RAPID-ADPKD (Retrospective epidemiological study of Asia-Pacific patients with rapId Disease progression of Autosomal Dominant Polycystic Kidney Disease) study is a multinational, retrospective, observational cohort study of patients with ADPKD in the Asia-Pacific region (Australia, China, Hong Kong, South Korea, Taipei and Turkey). This study was designed to identify the clinical characteristics of patients with ADPKD with rapid disease progression. Adult patients with ADPKD diagnosed according to the unified ultrasound criteria and with an estimated glomerular filtration rate (eGFR) ≥45 mL/min/1.73 m² at baseline will be included. The cohort will include patients with ≥2 records of eGFR and at least 24 months of follow-up data. Demographic information, clinical characteristics, comorbidities, medications, eGFR, radiological findings that allow calculation of height-adjusted total kidney volume, ADPKD-related complications and the Predicting Renal Outcomes in autosomal dominant Polycystic Kidney Disease (PRO-PKD) score will be collected. Rapid progression will be defined based on the European Renal Association - European Dialysis and Transplant Association (ERA-EDTA) guideline. All other patients without any of these criteria will be classified to be of slow progression. Clinical characteristics will be compared between patients with rapid progression and those with slow progression. The incidence of complications and the effects of race and water intake on renal progression will also be analysed. The planned sample size of the cohort is 1000 patients, and data from 600 patients have been collected as of 30 May 2019.

ETHICS AND DISSEMINATION

This study was approved or is in the process of approval by the institutional review boards at each participating centre. The results will be presented in conferences and published in a journal, presenting data on the clinical characteristics, risk factors for disease progression and patterns of complications of ADPKD in Asian populations.

Revisiting racial differences in ESRD due to ADPKD in the United States

Introduction

Autosomal dominant polycystic kidney disease (ADPKD) affects all races. Whether the progression of ADPKD varies by race remains unclear.

Methods

In this retrospective cohort study from 2004 to 2013 non-Hispanic blacks and non-Hispanic whites of all ages classified in the US Renal Data System (USRDS) with incident ESRD from ADPKD (n = 23,647), hypertension/large vessel disease (n = 296,352), or diabetes mellitus (n = 451,760) were stratified into five-year age categories ranging from < 40 to > 75 (e.g., < 40, 40–44, 45–49, …, 75+). The Cochran-Mantel-Haenszel test was used to determine the association of race and incidence of ESRD from ADPKD, diabetes, or hypertension. The difference in the proportions of ESRD in non-Hispanic black and non-Hispanic white patients at each age categorical bin was compared by two-sample proportion test. The age of ESRD onset between non-Hispanic black and non-Hispanic white patients at each year was compared using two-sample t-test with unequal variance.

Results

1.068% of non-Hispanic blacks and 2.778% of non-Hispanic whites had ESRD attributed to ADPKD. Non-Hispanic blacks were less likely than non-Hispanic whites to have ESRD attributed to ADPKD (odds ratio (OR) (95% CI) = 0.38 (0.36–0.39), p <  0.0001). Using US Census data as the denominator to adjust for population differences non-Hispanic blacks were still slightly under-represented (OR (95% CI) 0.94 (0.91–0.96), p = 0.004). However, non-Hispanic blacks with ADPKD had a younger age of ESRD (54.4 years ±13) than non-Hispanic whites (55.9 years ±12.8) (p <  0.0001). For those < 40 years old, more non-Hispanic blacks had incident ESRD from ADPKD than non-Hispanic whites (9.49% vs. 7.68%, difference (95% CI) = 1.81% (0.87–2.84%), p <  0.001) for the combined years examined.

Conclusions

As previously shown, we find the incidence of ESRD from ADPKD in non-Hispanic blacks is lower than in non-Hispanic whites. Among the younger ADPKD population (age < 40), however, more non-Hispanic blacks initiated dialysis than non-Hispanic whites. Non-Hispanic blacks with ADPKD initiated dialysis younger than non-Hispanic whites. A potential implication of these findings may be that black race should be considered an additional risk factor for progression in ADPKD.

A Large Database Analysis of Rates of Aneurysm Screening, Elective Treatment, and Subarachnoid Hemorrhage in Patients With Polycystic Kidney Disease

BACKGROUND

Professional societies provide conflicting guidelines on aneurysm screening in patients with polycystic kidney disease (PKD), and the rate of subarachnoid hemorrhage (SAH) is poorly understood.

OBJECTIVE

To evaluate screening, elective treatment, and the rate of SAH in patients with known PKD.

METHODS

We examined longitudinally linked claims data from a large private insurer, identifying screening, elective treatment, aneurysmal subarachnoid hemorrhage (aSAH) and secured aneurysmal SAH (saSAH) in 2004 to 2014 amongst patients with known PKD.

RESULTS

We identified 20 704 patients diagnosed with PKD. Among patients with an initial PKD diagnosis, 51/446 (15.9%) underwent angiographic screening within 2 yr. Forty aneurysms were treated electively in 48 868 yr at risk in PKD patients (82/100K patient yr, 95% confidence interval [CI] 60-112) vs 24 elective treatments in 349 861 yr at risk in age- and sex-matched controls (7/100K patient yr, 95% CI 5-10, P < .0001). Eleven admissions for aSAH were identified in PKD patients (23/100K patient yr, 95% CI 13-41) and 22 admissions for aSAH in controls (6/100K patient yr, 95% CI 4-10), giving an incidence rate ratio (IRR) of 3.6 (95% CI 1.7-7.4, P < .0001) and a comorbidity-adjusted IRR of 3.1 (95% CI 1.4-6.9). The incidence of saSAH was proportionally even higher in PKD patients than controls, 16 vs 2/100K patient years, IRR 9.5 (95% CI 3.3-27.5, P < .0001).

CONCLUSION

Screening in PKD is performed only selectively, though resulting rates of elective treatment were over 10× those of controls. Despite screening and treatment, the rate of SAH remains significantly elevated over that of controls.

Polycystin-1 regulates the stability and ubiquitination of transcription factor Jade-1

Autosomal-dominant polycystic kidney disease (ADPKD) and von Hippel-Lindau (VHL) disease lead to large kidney cysts that share pathogenetic features. The polycystin-1 (PC1) and pVHL proteins may therefore participate in the same key signaling pathways. Jade-1 is a pro-apoptotic and growth suppressive ubiquitin ligase for beta-catenin and transcriptional coactivator associated with histone acetyltransferase activity that is stabilized by pVHL in a manner that correlates with risk of VHL renal disease. Thus, a relationship between Jade-1 and PC1 was sought. Full-length PC1 bound, stabilized and colocalized with Jade-1 and inhibited Jade-1 ubiquitination. In contrast, the cytoplasmic tail or the naturally occurring C-terminal fragment of PC1 (PC1-CTF) promoted Jade-1 ubiquitination and degradation, suggesting a dominant-negative mechanism. ADPKD-associated PC1 mutants failed to regulate Jade-1, indicating a potential disease link. Jade-1 ubiquitination was mediated by Siah-1, an E3 ligase that binds PC1. By controlling Jade-1 abundance, PC1 and the PC1-CTF differentially regulate Jade-1-mediated transcriptional activity. A key target of PC1, the cyclin-dependent kinase inhibitor p21, is also up-regulated by Jade-1. Through Jade-1, PC1 and PC1 cleaved forms may exert fine control of beta-catenin and canonical Wnt signaling, a critical pathway in cystic renal disease. Thus, Jade-1 is a transcription factor and ubiquitin ligase whose activity is regulated by PC1 in a manner that is physiologic and may correlate with disease. Jade-1 may be an important therapeutic target in renal cystogenesis.

ADPKD: Prototype of Cardiorenal Syndrome Type 4

The cardiorenal syndrome type 4 (Chronic Renocardiac Syndrome) is characterized by a condition of primary chronic kidney disease (CKD) that leads to an impairment of the cardiac function, ventricular hypertrophy, diastolic dysfunction, and/or increased risk of adverse cardiovascular events. Clinically, it is very difficult to distinguish between CRS type 2 (Chronic Cardiorenal Syndrome) and CRS type 4 (Chronic Renocardiac Syndrome) because often it is not clear whether the primary cause of the syndrome depends on the heart or the kidney. Autosomal dominant polycystic kidney disease (ADPKD), a genetic disease that causes CKD, could be viewed as an ideal prototype of CRS type 4 because it is certain that the primary cause of cardiorenal syndrome is the kidney disease. In this paper, we will briefly review the epidemiology of ADPKD, conventional and novel biomarkers which may be useful in following the disease process, and prevention and treatment strategies.

Renal function and healthcare costs in patients with polycystic kidney disease

BACKGROUND AND OBJECTIVES

Characterizing relationships of kidney function to healthcare costs in polycystic kidney disease has applications for economic evaluations of standard and emerging therapies.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The administrative records (2003 to 2006) of a private health insurer were examined to identify polycystic kidney disease patients (n = 1913) from ICD9 diagnosis codes on billing claims. The first available diagnostic claim was assumed as an index date, and baseline estimated GFR (eGFR) was computed using closest serum creatinine value. The associations of eGFR with annualized charges were modeled by nonlinear and linear regression.

RESULTS

Medical, pharmacy, and total healthcare costs varied significantly by baseline kidney function, such that mean total annualized charges (unadjusted) were approximately 5-fold higher in patients with eGFR < 15 ml/min compared with those with eGFR >or= 90 ml/min. After adjustment for age and gender, total charges did not differ significantly among patients with eGFR > 30 ml/min, and but rose precipitously with eGFR < 30 ml/min. Each ml/min decline <30 ml/min predicted approximately $5435 higher adjusted annual charges. Results were similar after adjustment for baseline diabetes and cardiovascular disease as identified in claims, while significantly higher adjusted charges were detected with eGFR = 31 to 60 ml/min versus >or=90 ml/min in a subgroup free of diabetes and cardiovascular disease.

CONCLUSIONS

Healthcare charges are associated with advanced renal dysfunction in polycystic kidney disease patients. Strategies that prevent loss of renal function below 30 ml/min have the potential to generate substantial reductions in medical charges.

Role of Free Hemoglobin in 8-Iso Prostaglandin F2-Alpha Synthesis in Chronic Renal Failure and Its Impact on CD163-Hb Scavenger Receptor and on Coronary Artery Endothelium

Free hemoglobin (Hb) during autoxidation increases 8-iso-prostaglandin-F2-alpha (8-isoprostane) formation in vitro. Because 8-isoprostane and plasma Hb are elevated in chronic renal failure (CRF), we evaluated the role of Hb in this isoprostane synthesis in vivo. By monitoring correlations between Hb, haptoglobin (Hp), CD163-Hb-scavenger receptor, and 8-isoprostane that is known to induce CD163 shedding, we examined whether 8-isoprostane blocks Hb catabolism in CRF. Additionally, by studying the effect of 8-isoprostane on human coronary artery endothelium (HCAEC) in vitro and its impact on intercellular adhesion molecule-1 (ICAM-1) in vivo, we tested its role in promotion of cardiovascular events in CRF. Twenty-two never-dialyzed CRF patients and 18 control patients were screened for renal function, plasma and urine 8-isoprostane, and plasma Hb, Hp, thiobarbituric-acid-reactants (TBARS), C-reactive-protein (CRP), and soluble (s) ICAM-1 and sCD163. HCAEC exposed to 8-isoprostane were tested for ICAM-1 and apoptosis. In CRF, urine 8-isoprostane was significantly elevated and correlated with free-Hb and TBARS. The increased free-Hb, Hp, and sCD163 in CRF suggested 8-isoprostane-mediated suppression of Hb catabolism through CD163 receptor shedding. 8-Isoprostane enhanced ICAM-1 expression and apoptosis in HCAEC. CRF patients showed elevated sICAM-1. In conclusion, free-Hb, via 8-isoprostane, paradoxically blocks its own catabolism. Free-Hb and/or 8-isoprostane may intensify cardiovascular events in CRF.

Polycystic Kidney Disease

Polycystic kidney disease, an inherited systemic disorder, is characterized by the development of multiple cysts in the kidneys and other organs. Patients can present at any age, but more often come to clinical attention (unless there is a family history) after age 30. Patients who are diagnosed before age 30 have a worse renal survival. Although palpation of the abdomen occasionally provides a clue to the presence of polycystic kidney disease, radiographic procedures most often suggest the diagnosis. Mutations in the PKD1 or PKD2 genes give rise to cyst formation. Flank pain, hematuria, polyuria, nephrolithiasis, urinary tract infections, and hypertension may be part of the syndrome of polycystic kidney disease. It is the fourth most common cause of end-stage renal disease. Blood pressure treatment goals are less than 130/80 mm Hg. Treatment should include the use of angiotensin-converting enzyme inhibitors.

Polycystin-1L2 is a novel G-protein-binding protein

Mutations in genes encoding polycystin-1 (PC1) and polycystin-2 cause autosomal dominant polycystic kidney disease. The polycystin protein family is composed of Ca2+-permeable pore-forming subunits and receptor-like integral membrane proteins. Here we describe a novel member of the polycystin-1-like subfamily, polycystin-1L2 (PC1L2), encoded by PKD1L2, which has various alternative splicing forms with two translation initiation sites. PC1L2 short form starts in exon 12 of the long form. The longest open reading frame of PKD1L2 short form, determined from human testis cDNA, encodes a 1775-amino-acid protein and 32 exons, whereas the long form is predicted to encode a 2460-residue protein. Both forms have a small receptor for egg jelly domain, a G-protein-coupled receptor proteolytic site, an LH2/PLAT, and 11 putative transmembrane domains, as well as a number of rhodopsin-like G-protein-coupled receptor signatures. RT-PCR analysis shows that the short form, but not the long form, of human PKD1L2 is expressed in the developing and adult heart and kidney. Furthermore, by GST pull-down assay we observed that PC1L2 and polycystin-1L1 are able to bind to specific G-protein subunits. We also show that PC1 C-terminal cytosolic domain binds to Galpha12, Galphas, and Galphai1, while it weakly interacts with Galphai2. Our results indicate that both PC1-like molecules may act as G-protein-coupled receptors.

Does type 2 diabetes mellitus delay renal failure in autosomal dominant polycystic kidney disease?

Autosomal dominant polycystic kidney disease (ADPKD) is a common renal disease without an effective therapeutic intervention to delay renal failure. Within kindreds, renal dysfunction often develops at a similar age in affected individuals, although there are known modifying factors. Two kindreds with ADPKD have shown a striking pattern of delayed onset of renal insufficiency in those individuals also suffering from type 2 diabetes mellitus. Eight nondiabetic patients with ADPKD had onset of dialysis or renal death at ages 38-52 years, (mean +/- SEM 46 +/- 1.9, n = 7) as compared with four diabetics who started dialysis or are still off dialysis at the age of 61 +/- 2.8 years (p < 0.01). Two of the four diabetics still have reasonable renal function at age 61 and 66. The diabetes was diagnosed at age 32 +/- 2 years and was treated with oral hypoglycemics for 19 +/- 2 years before institution of insulin. Cardiovascular disease dominated the clinical picture in the diabetics. In conclusion, onset of renal failure in ADPKD was delayed for over 15 years in individuals who also suffered from type 2 diabetes mellitus, in two ADPKD kindreds. Possible mechanisms are discussed, including glibenclamide inhibition of the cystic fibrosis transmembrane conductance regulator. The striking delay associated with type 2 diabetes mellitus in ADPKD induced renal failure should be evaluated further.

Current advances in molecular genetics of autosomal-dominant polycystic kidney disease

Autosomal-dominant polycystic kidney disease results from at least two causal genes, PKD1 and PKD2. The identical clinical phenotype in human patients and targeted Pkd1 and Pkd2 mutant mouse models provides evidence that both gene products act in the same pathogenic pathway. The discovery of direct PKD1 and PKD2 interactions implies that both gene products, polycystin-1 and polycystin-2, play a functional role in the same molecular complex. The spectrum of germ-line mutations in both genes and the somatic mutations identified from individual PKD1 or PKD2 cysts indicate that loss of function of either PKD1 or PKD2 is the mechanism of cystogenesis in autosomal-dominant polycystic kidney disease. A novel mouse model, Pkd2WS25/-, has proved that loss of heterozygosity is the molecular mechanism of autosomal-dominant polycystic kidney disease. Recently, studies on the expression patterns of PKD1 and PKD2 in humans or mice indicate that polycystin 1 and polycystin 2 seem to have their own respective functional roles, even though most of the functions of these polycystins are parallel during human and mouse development. Pkd2-deficient mice have cardiac septum defects, but Pkd1 knockout mice do not have this phenotype. On the other hand, Pkd2 has a very low level of expression in the central nervous system when compared with Pkd1. In addition, the level of expression of Pkd1 is increased during mesenchymal condensation, whereas Pkd2 expression is unchanged. Preliminary data have shown that the PKD1/PKD2 compound trans-heterozygous has a more severe cystic phenotype in the kidney than that of an age-matched heterozygous type 1 or type 2 of autosomal-dominant polycystic kidney disease alone. This finding suggests that PKD1 may be a modifier of disease severity for PKD2, and vice versa. The characteristics of the contiguous PKD1/TSC2 syndrome phenotypes and the data from Krd mice imply that TSC2 and PAX2 may also serve as potential modifiers for the disease severity of autosomal-dominant polycystic kidney disease.