Kidney Disease In African Americans Research Articles

APOL1-mediated monovalent cation transport contributes to APOL1-mediated podocytopathy in kidney disease.

Two coding variants of apolipoprotein L1 (APOL1), called G1 and G2, explain much of the excess risk of kidney disease in African Americans. While various cytotoxic phenotypes have been reported in experimental models, the proximal mechanism by which G1 and G2 cause kidney disease is poorly understood. Here, we leveraged 3 experimental models and a recently reported small molecule blocker of APOL1 protein, VX-147, to identify the upstream mechanism of G1-induced cytotoxicity. In HEK293 cells, we demonstrated that G1-mediated Na+ import/K+ efflux triggered activation of GPCR/IP3-mediated calcium release from the ER, impaired mitochondrial ATP production, and impaired translation, which were all reversed by VX-147. In human urine-derived podocyte-like epithelial cells (HUPECs), we demonstrated that G1 caused cytotoxicity that was again reversible by VX-147. Finally, in podocytes isolated from APOL1 G1 transgenic mice, we showed that IFN-γ-mediated induction of G1 caused K+ efflux, activation of GPCR/IP3 signaling, and inhibition of translation, podocyte injury, and proteinuria, all reversed by VX-147. Together, these results establish APOL1-mediated Na+/K+ transport as the proximal driver of APOL1-mediated kidney disease.

Abstract MP19: An eGFR Polygenic Score Predicts Chronic Kidney Disease in African Americans

Chronic kidney disease (CKD) is a risk factor for cardiovascular disease and early death. Genetic factors contribute to CKD, and recently, polygenic scores (PGS) have been developed to quantify risk for complex diseases, such as CKD. However, African ancestry populations are underrepresented in both CKD genetic studies and PGS development overall; moreover, European-ancestry derived PGSs demonstrate diminished predictive performance in African ancestry populations. This study aimed to develop a PGS for CKD using genotype and phenotype data from African American (AA) participants of observational cohort studies. We obtained score weights from a meta-analysis of genome-wide association studies (GWAS) for estimated glomerular filtration rate (eGFR) in the Million Veteran Program (MVP) and Reasons for Geographical and Racial Differences in Stroke (REGARDS) Study (total n~66,000). We then optimized the PGS in a cohort of AAs from the Hypertension Genetic Epidemiology Network (HyperGEN) Study (n~1,900) using the PRS-CS software and evaluated the predictive performance of the PGS at multiple global shrinkage parameters. We further adjusted the PGS for APOL1 risk status. In HyperGEN, the eGFR-based PGS was significantly associated with the odds of prevalent CKD—defined as baseline eGFR <60 mL/min/1.73m 2 — in logistic regression models adjusted for age, sex, and population structure. Further, accounting for APOL1 risk status—a putative variant for CKD unique to those of sub-Saharan African descent—improved the score’s accuracy, with the APOL1 -adjusted PGS explaining 1.9% (1.1% without APOL1 ) of the variance in CKD and an area under the curve (AUC) of 58.9% [95% CI: 53.0%-64.9%] (without APOL1 , 58.2% [95% CI: 52.3%-64.1%]). Sensitivity analyses and validation in external cohorts, as well as comparisons to previously published PGS, are ongoing. In this study, we developed a PGS that was significantly associated with CKD with improved predictive accuracy in AAs over previously published PGS.

Modeling the Progression of Hypertensive Kidney Disease in African Americans

Chronic kidney disease (CKD) is associated with the progressive functional loss of nephrons and hypertension (HTN). Several clinical studies demonstrate calcium channel blocker (CCB) therapy mitigates the decline in renal function in humans with essential HTN, but there are few long‐term clinical studies that determine the impact of CCBs in patients with hypertensive CKD. African Americans (AA) have a faster progression to end stage renal disease as compared to the white population which may be partially explained by factors such as salt‐sensitive blood pressure (BP) and greater prevalence of uncontrolled HTN. Observational studies demonstrate BP to be a strong independent risk factor for CKD progression, yet intense BP lowering in AA does not diminish the renal function decline any more than standard therapy. The African American Study of Kidney Disease and Hypertension (AASK) trial suggests AA with proteinuric CKD may have detrimental responses to CCB as compared to an angiotensin converting enzyme (ACE) inhibitor. Therefore, using a large physiological model, we set out to replicate the AASK trial findings and predict the roles of the renin‐angiotensin system, salt intake, and intensive antihypertensive therapy in a virtual population during CCB therapy. Our current mathematical model, HumMod, is a large physiological simulator that is comprised of key systems that play an integral role in BP control such as neural, endocrine, circulatory, and renal systems. All of the parameters (n=335) that control these systems were randomly varied and resulted in over 3,000 unique models that we define as a virtual population. We calibrated this virtual population to patient level data from the AASK trial (BP and glomerular filtration rate [GFR] before and after 3 years of amlodipine). After matching the virtual population to individual level data, the virtual population (n=140) was associated with statistically similar BP and GFR before and after CCB therapy (Figure) as well as similar increases in glomerular damage. Baseline factors such as elevated single nephron GFR and increased tubuloglomerular feedback were correlated with greater declines in renal function and increased glomerulosclerosis after 3 years of CCB. Interestingly, when looking at the models with severe CKD (<35 mL/min), glomerulosclerosis and angiotensin II significantly increased with CCB despite significant falls in mean BP (‐7 ± 7 mmHg). Adding an ACE inhibitor decreased angiotensin II levels and abrogated the increase in glomerulosclerosis while further decreasing BP (‐12 ± 9 mmHg). Decreasing salt intake in addition to the CCB+ACE inhibitor therapy further benefited systemic and glomerular pressures but significantly decreased overall GFR independent of any glomerular damage. Finally, all antihypertensive therapies were associated with significant decreases in left ventricular mass. These data suggest the current clinical markers of renal function such as eGFR may not fully reflect the actual progression of CKD, especially with intensive antihypertensive treatment. Our simulation also supports that angiotensin system inhibitors are renoprotective and cardioprotective when combined with CCB therapy in African American CKD patients.

A Lifestyle Intervention to Delay Early Chronic Kidney Disease in African Americans With Diabetic Kidney Disease: Pre-Post Pilot Study.

BackgroundBehavioral factors, such as lifestyle, have been shown to explain approximately 24% of the excess risk of chronic kidney disease (CKD) among African Americans. However, there are limited intervention studies culturally tailored to African Americans with type 2 diabetes mellitus and CKD.ObjectiveThe main objective of this study was to examine the feasibility and preliminary efficacy of a culturally tailored lifestyle intervention among African Americans with type 2 diabetes mellitus and CKD.MethodsA pre-post design was used to test the feasibility of a lifestyle intervention in 30 African American adults recruited from the Medical University of South Carolina between January 2017 and February 2017. A research nurse delivered the manualized study intervention weekly for 6 weeks. Clinical outcomes (hemoglobin A1c, blood pressure, and estimated glomerular filtration rate [eGFR]) were measured at baseline and postintervention. Disease knowledge, self-care, and behavior outcomes were also measured using validated structured questionnaires at baseline and postintervention. Descriptive statistics and effect sizes were calculated to determine clinically important changes from baseline.ResultsSignificant pre-post mean differences and decreases were observed for hemoglobin A1c (mean 0.75%, 95% CI 0.16-1.34; P=.01), total cholesterol (mean 16.38 mg/dL, 95% CI 5.82-26.94; P=.004), low-density lipoprotein (mean 13.73 mg/dL, 95% CI 3.91-23.54; P=.008), and eGFR (mean 6.73 mL/min/1.73m2, 95% CI 0.97-12.48; P=.02). Significant pre-post mean differences and increases were observed for CKD self-efficacy (mean −11.15, 95% CI −21.55 to −0.75; P=.03), CKD knowledge (mean −2.62, 95% CI −3.98 to −1.25; P<.001), exercise behavior (mean −1.21, 95% CI −1.96 to −0.46; P=.003), and blood sugar testing (mean −2.15, 95% CI −3.47 to −0.83; P=.003).ConclusionsThis study provides preliminary data for a large-scale appropriately powered randomized controlled trial to examine a culturally tailored lifestyle intervention in African Americans with type 2 diabetes mellitus and CKD in order to improve clinical, knowledge, self-care, and behavior outcomes in this population.

APOL1 G3 Variant Is Associated with Cardiovascular Mortality and Sudden Cardiac Death in Patients Receiving Maintenance Hemodialysis of European Ancestry

Introduction: The G1 and G2 variants in the APOL1 gene convey high risk for the progression of chronic kidney disease in African Americans. The G3 variant in APOL1 is more common in patients of European ancestry (EA); outcomes associated with this variant have not been explored previously in EA patients receiving dialysis. Methods: DNA was collected from approximately half of the patients enrolled in the Evaluation of Cinacalcet HCl Therapy to Lower Cardiovascular Events (EVOLVE) trial and genotyped for the G3 variants. We utilized an additive genetic model to test associations of G3 with the EVOLVE adjudicated endpoints of all-cause mortality, cardiovascular mortality, sudden cardiac death (SCD), and heart failure. EA and African ancestry samples were analyzed separately. Validation was done in the Vanderbilt BioVU using ICD codes for cardiovascular events that parallel the adjudicated endpoints in EVOLVE. Results: In EVOLVE, G3 in EA patients was associated with the adjudicated endpoints of cardiovascular mortality and SCD. In a validation cohort from the Vanderbilt BioVU, cardiovascular events and cardiovascular mortality defined by ICD codes showed similar associations in EA participants who had been on dialysis for 2 to <5 years. Discussion/Conclusions: G3 in APOL1 variant was associated with cardiovascular events and cardiovascular mortality in the EA patients receiving dialysis. This suggests that variations in the APOL1 gene that differ in populations of different ancestry may contribute to cardiovascular disease.

APOL1 genotyping in kidney transplantation: to do or not to do, that is the question? (pro)

Dogma, a principle laid down by authorities as incontrovertibly true, is difficult to change once proven incorrect. Considering chronic kidney disease (CKD) in African Americans, the dogma that nearly 40% have mild-moderate hypertension as the cause of nephropathy, low-level proteinuria excludes glomerular disease, and focal segmental glomerulosclerosis is a nonspecific pathology was suddenly struck down with discovery of association between the apolipoprotein L1 gene (APOL1) and nondiabetic CKD. 1 Freedman B.I. Cohen A.H. Hypertension-attributed nephropathy: what's in a name?. Nat Rev Nephrol. 2016; 12: 27-36 Crossref PubMed Scopus (51) Google Scholar ,2 Skorecki K.L. Wasser W.G. Hypertension-misattributed kidney disease in African Americans. Kidney Int. 2013; 83: 6-9 Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar APOL1 G1 and G2 kidney-risk variants (KRVs) display the strongest genetic association in complex disease; G0 is nonrisk. KRVs are found virtually only in populations with recent African ancestry and provide protection from African sleeping sickness. 3 Genovese G. Friedman D.J. Ross M.D. et al. Association of trypanolytic ApoL1 variants with kidney disease in African Americans. Science. 2010; 329: 841-845 Crossref PubMed Scopus (1388) Google Scholar Possessing 2 KRVs, autosomal recessive inheritance (G1G1/G2G2/G1G2, 1 KRV from each parent) defines high-risk genotypes with markedly increased risk for CKD. Approximately 13% of African Americans possess 2 KRVs, and 87% have APOL1 low-risk genotypes (∼39% G0G1/G0G2; ∼48% G0G0). 3 Genovese G. Friedman D.J. Ross M.D. et al. Association of trypanolytic ApoL1 variants with kidney disease in African Americans. Science. 2010; 329: 841-845 Crossref PubMed Scopus (1388) Google Scholar APOL1 genotyping in kidney transplantation: a look into the futureKidney InternationalVol. 100Issue 1PreviewChronic kidney disease (CKD) and end-stage kidney disease disproportionately affect individuals with African ancestry.1 African Americans have a lower rate of referral for kidney transplantation and lower graft survival than other ethnic groups.2 The risk of end-stage kidney disease is higher in Black living donors compared with White counterparts.3 Variants in the apolipoprotein L1 (APOL1) gene (G1: S342G and I384M; and G2: del N388 and Y389) explain most of this disparate risk for nondiabetic kidney disease, with the magnitude of risk varying depending on the clinical phenotype. Full-Text PDF

APOL1 genotyping in kidney transplantation: to do or not to do, that is the question? (contra)

Discussions regarding genetic testing for variants in apolipoprotein L1 (APOL1), a gene located on chromosome 22 whose risk variants are strongly associated with end-stage kidney disease (ESKD), in the context of kidney transplantation must address donors (deceased and living) and recipients. In addition, these discussions must occur in the context of known genetic epidemiology regarding APOL1. Specifically, APOL1 risk variants are only found among individuals of African descent, as these variants are derived from exposure to African sleeping sickness that is largely confined to countries along the west coast of Africa. 1 Genovese G. Friedman D.J. Ross M.D. et al. Association of trypanolytic ApoL1 variants with kidney disease in African Americans. Science. 2010; 329: 841-845 Crossref PubMed Scopus (1388) Google Scholar In other words, not every individual who self identifies as Black or African American will even be at risk for carrying these genetic variants, and in fact, 87% of African Americans do not actually carry 2 APOL1 renal risk variants. 2 Foster M.C. Coresh J. Fornage M. et al. APOL1 variants associate with increased risk of CKD among African Americans. J Am Soc Nephrol. 2013; 24: 1484-1491 Crossref PubMed Scopus (180) Google Scholar More important, among the 13% of African Americans who do carry 2 APOL1 renal risk variants, the presence of these variants alone is insufficient to cause ESKD. 2 Foster M.C. Coresh J. Fornage M. et al. APOL1 variants associate with increased risk of CKD among African Americans. J Am Soc Nephrol. 2013; 24: 1484-1491 Crossref PubMed Scopus (180) Google Scholar We question the rationale for routine testing of all African American donors and recipients. Those in favor would likely remind us of the Hippocratic Oath—first do no harm—and that it is our duty to assign and avoid such risk. Paternalistic strategies such as this, although good intentioned, often overlook the broader context of how such dogmas may eliminate patient autonomy in decision making and even exacerbate existing disparities. In the following paragraphs, we will lay the foundation for the case against routine APOL1 testing in kidney transplantation with the hope of encouraging a more balanced approach to the care of donors and recipients alike. APOL1 genotyping in kidney transplantation: a look into the futureKidney InternationalVol. 100Issue 1PreviewChronic kidney disease (CKD) and end-stage kidney disease disproportionately affect individuals with African ancestry.1 African Americans have a lower rate of referral for kidney transplantation and lower graft survival than other ethnic groups.2 The risk of end-stage kidney disease is higher in Black living donors compared with White counterparts.3 Variants in the apolipoprotein L1 (APOL1) gene (G1: S342G and I384M; and G2: del N388 and Y389) explain most of this disparate risk for nondiabetic kidney disease, with the magnitude of risk varying depending on the clinical phenotype. Full-Text PDF

Apolipoprotein L1 and mechanisms of kidney disease susceptibility.

Allelic variants in the gene for apolipoprotein L1 (APOL1), found only in individuals of African ancestry, explain a majority of the excess risk of kidney disease in African Americans. However, a clear understanding how the disease-associated APOL1 variants cause kidney injury and the identity of environmental stressors that trigger the injury process have not been determined. Basic mechanistic studies of APOL1 biochemistry and cell biology, bolstered by new antibody reagents and inducible pluripotent stem cell-derived cell systems, have focused on the cytotoxic effect of the risk variants when APOL1 gene expression is induced. Since the APOL1 variants evolved to alter a key protein-protein interaction with the trypanosome serum resistance-associated protein, additional studies have begun to address differences in APOL1 interactions with other proteins expressed in podocytes, including new observations that APOL1 variants may alter podocyte cytoskeleton dynamics. A unified mechanism of pathogenesis for the various APOL1 nephropathies still remains unclear and controversial. As ongoing studies have consistently implicated the pathogenic gain-of-function effects of the variant proteins, novel therapeutic development inhibiting the synthesis or function of APOL1 proteins is moving toward clinical trials.

Apolipoprotein L1 (APOL1) risk variant toxicity depends on the haplotype background

The Apolipoprotein L1 (APOL1) risk variants G1 and G2 are associated with high rates of kidney disease in African Americans in genetic studies. However, our understanding of APOL1 biology has lagged far behind. Here we report that engineering G1 and G2 mutations on unnatural haplotype backgrounds instead of on the specific G1 and G2 haplotype backgrounds that occur in nature profoundly alters APOL1-mediated cytotoxicity in experimental systems. Thus, in addition to helping resolve some important controversies in the APOL1 field, our demonstration of the critical influence of haplotype background may apply more generally to the study of other genetic variants that cause or predispose to human disease.

APOL1 high-risk genotypes and renal transplantation.

The discovery of apolipoprotein L1 (APOL1) gene variants and its association with kidney disease in African-Americans represent a significant breakthrough in understanding the genetic basis of ancestry-based differences in a public health problem. The role these variants play in renal transplantation is still incompletely understood. This article reviews the epidemiologic data and current reports of APOL1 variant pathogenesis in transplantation. We examine existing data on outcomes in APOL1 high-risk kidneys, high-risk APOL1 recipients, live donors with high-risk mutations and non-renal transplantation of high-risk APOL1 organs. We discuss the rapidly evolving role and potential pros and cons of APOL1 genotyping of donors and recipients in transplantation. Finally, we highlight the ongoing nationwide National Institutes of Health-sponsored "APOL1 Long-term Kidney Transplantation Outcomes (APOLLO)" study, which will quantify outcomes and "second hits" in pertinent to APOL1 high-risk variants in renal transplantation.

Genome-wide association study identifies novel loci for type 2 diabetes-attributed end-stage kidney disease in African Americans

BackgroundEnd-stage kidney disease (ESKD) is a significant public health concern disproportionately affecting African Americans (AAs). Type 2 diabetes (T2D) is the leading cause of ESKD in the USA, and efforts to uncover genetic susceptibility to diabetic kidney disease (DKD) have had limited success. A prior genome-wide association study (GWAS) in AAs with T2D-ESKD was expanded with additional AA cases and controls and genotypes imputed to the higher density 1000 Genomes reference panel. The discovery analysis included 3432 T2D-ESKD cases and 6977 non-diabetic non-nephropathy controls (N = 10,409), followed by a discrimination analysis in 2756 T2D non-nephropathy controls to exclude T2D-associated variants.ResultsSix independent variants located in or near RND3/RBM43, SLITRK3, ENPP7, GNG7, and APOL1 achieved genome-wide significant association (P < 5 × 10−8) with T2D-ESKD. Following extension analyses in 1910 non-diabetic ESKD cases and 908 non-diabetic non-nephropathy controls, a meta-analysis of 5342 AA all-cause ESKD cases and 6977 AA non-diabetic non-nephropathy controls revealed an additional novel all-cause ESKD locus at EFNB2 (rs77113398; P = 9.84 × 10–9; OR = 1.94). Exclusion of APOL1 renal-risk genotype carriers identified two additional genome-wide significant T2D-ESKD-associated loci at GRAMD3 and MGAT4C. A second variant at GNG7 (rs373971520; P = 2.17 × 10–8, OR = 1.46) remained associated with all-cause ESKD in the APOL1-negative analysis.ConclusionsFindings provide further evidence for genetic factors associated with advanced kidney disease in AAs with T2D.

APOL1 risk allele RNA contributes to renal toxicity by activating protein kinase R

APOL1 risk alleles associate with chronic kidney disease in African Americans, but the mechanisms remain to be fully understood. We show that APOL1 risk alleles activate protein kinase R (PKR) in cultured cells and transgenic mice. This effect is preserved when a premature stop codon is introduced to APOL1 risk alleles, suggesting that APOL1 RNA but not protein is required for the effect. Podocyte expression of APOL1 risk allele RNA, but not protein, in transgenic mice induces glomerular injury and proteinuria. Structural analysis of the APOL1 RNA shows that the risk variants possess secondary structure serving as a scaffold for tandem PKR binding and activation. These findings provide a mechanism by which APOL1 variants damage podocytes and suggest novel therapeutic strategies.

African Americans, Kidney Disease, and Drug Development: A Regulatory Perspective

Given the burden of kidney disease in African Americans, the discovery of safe and effective medical products to slow the progression of kidney disease and reduce the risk for kidney failure would have a tremendous impact on this population. Differences in response to treatment have been observed in African Americans, highlighting the importance of studying medical products in African Americans. Although historically the African American community has not been well represented in clinical trials, efforts are underway to address this issue. Recent advances in understanding the genetic contributions to disease progression in African Americans, including the discovery of risk variants in the apolipoprotein L1 gene (APOL1), raise the possibility of using genetic information to better tailor treatments for African Americans. One could envision developing therapies that target these variants or possibly using them to help enrich trial populations with patients more likely to experience disease progression.

A Putative Role of Apolipoprotein L1 Polymorphism in Renal Parenchymal Scarring Following Febrile Urinary Tract Infection in Nigerian Under-Five Children: Proposal for a Case-Control Association Study.

BackgroundAlthough urinary tract infection (UTI) resolves with prompt treatment in a majority of children, some children, especially those aged less than 5 years, also develop renal parenchymal scarring (RPS). RPS causes high blood pressure that may lead to severe chronic kidney disease and end-stage renal disease (ESRD). Although the risk of UTI is higher in white children than in black children, it is unknown whether RPS is more common in white children than in black children as data are scarce in this regard. A common genetic predisposition to kidney disease in African Americans and the sub-Saharan African blacks is the possession of apolipoprotein L1 (APOL1). APOL1 risk variants regulate the production of APOL1. APOL1 circulates in the blood, and it is also found in the kidney tissue. While circulating, APOL1 kills the trypanosome parasites; an increased APOL1 in kidney tissues, under the right environmental conditions, can also result in the death of kidney tissue (vascular endothelium, the podocytes, proximal tubules, and arterial cells), which, ultimately, is replaced by fibrous tissue. APOL1 may influence the development of RPS, as evidence affirms that its expression is increased in kidney tissue following UTI caused by bacteria. Thus, UTI may be a putative environmental risk factor responsible for APOL1-induced kidney injury.ObjectiveThe aim of this proposal was to outline a study that seeks to determine if the possession of two copies of either G1 or G2 APOL1 variant increases the risk of having RPS, 6 months following a febrile UTI among Nigerian under-five children.MethodsThis case-control association study seeks to determine whether the risk of RPS from febrile UTI is conditional on having 2 APOL1 risk alleles (either G1 or G2). Cases will be children with a confirmed RPS following a febrile UTI. Controls will be age-, gender-, and ethnic-matched children with a febrile UTI but without RPS. Children with vesicoureteral reflux and other congenital anomalies of the urinary tract are to be excluded. Association between predictor variables (ethnicity, APOL1 G1 or G2, and others) and RPS will be tested at bivariate logistic regression analyses. Predictors that attained significance at a P value of ˂.05 will be considered for multiple logistic regressions. Likelihood-based tests will be used for hypothesis testing. Estimation will be done for the effect size for each of the APOL1 haplotypes using a generalized linear model.ResultsThe study is expected to last for 3 years.ConclusionsThe study is contingent on having a platform for undergoing a research-based PhD program in any willing university in Europe or elsewhere. The findings of this study will be used to improve the care of African children who may develop RPS following febrile UTI.Registered Report IdentifierRR1-10.2196/9514

Genome-wide association studies suggest that APOL1-environment interactions more likely trigger kidney disease in African Americans with nondiabetic nephropathy than strong APOL1–second gene interactions

African Americans carrying two apolipoprotein L1 gene (APOL1) renal risk variants have a high risk for nephropathy. However, only a minority develops end-stage renal disease (ESRD). Hence, modifying factors likely contribute to initiation of kidney disease such as endogenous (HIV infection) or exogenous (interferon treatment) environmental modifiers. In this report, genome-wide association studies and a meta-analysis were performed to identify novel loci for nondiabetic ESRD in African Americans and to detect genetic modifiers in APOL1-associated nephropathy. Two African American cohorts were analyzed, 1749 nondiabetic ESRD cases and 1136 controls from Wake Forest and 901 lupus nephritis (LN)-ESRD cases and 520 controls with systemic lupus erythematosus but lacking nephropathy from the LN-ESRDConsortium. Association analyses adjusting for APOL1 G1/G2renal-risk variants were completed and stratified by APOL1 risk genotype status. Individual genome-wide association studies and meta-analysis results of all 2650 ESRD cases and 1656 controls did not detect significant genome-wide associations with ESRD beyond APOL1. Similarly, no single nucleotide polymorphism showed significant genome-wide evidence of an interaction with APOL1 risk variants. Thus, although variants with small individual effects cannot be ruled out and are likely to exist, our results suggest that APOL1-environment interactions may be of greater clinical importance in triggering nephropathy in African Americans than APOL1 interactions with other single nucleotide polymorphisms.

Advances in molecular diagnosis and therapeutics in nephrotic syndrome and focal and segmental glomerulosclerosis.

The widespread adoption of next-generation sequencing by research and clinical laboratories has begun to uncover the previously unknown genetic basis of many diseases. In nephrology, one of the best examples of this is seen in focal and segmental glomerulosclerosis (FSGS) and nephrotic syndrome. We review advances made in 2017 as a result of human and molecular genetic studies as it relates to FSGS and nephrotic syndrome. There are more than 50 monogenic genes described in steroid-resistant nephrotic syndrome and FSGS, with seven reported in 2017. In individuals presenting with FSGS or nephrotic syndrome before or at the age of 18 years, the commonest genes in which a mutation is found continues to be limited to only a few including NPHS1 and NPHS2 based on multiple studies. For FSGS or nephrotic syndrome that presents after 18 years, mutations in COl4A3/4/5, traditionally associated with Alport syndrome, are increasingly being reported. Despite the extensive genetic heterogeneity in FSGS, there is evidence that some of these genes converge onto common pathways. There are also reports of in-vivo models exploring apolipoprotein 1 biology, variants in which account for part of the increased risk of nondiabetic kidney disease in African-Americans. Finally, genetic testing has several clinical uses including clarification of diagnosis and treatment; identification of suitable young biologic relatives for kidney donation; and preimplantation genetic diagnosis. CRISPR gene editing is currently an experimental tool only, but the recent reports of excising mutations in embryos could be a therapeutic option for individuals with any monogenic disorder in the future. Sequencing efforts are bringing novel variants into investigation and directing the efforts to understand how these lead to disease phenotypes. Expanding our understanding of the genetic basis of health and disease processes is the necessary first step to elaborate the repertoire of therapeutic agents available for patients with FSGS and nephrotic syndrome.

Association of Apolipoprotein L-1 polymorphisms with blood pressure in three multi-ethnic African studies

# Background Genetic variants in the Apolipoprotein L1 (APOL1) gene greatly increase risk for chronic kidney disease in African Americans. We hypothesized that the APOL1 renal risk alleles would be associated with higher blood pressure in Africans. # Methods We used data from three multi-ethnic, population-based studies from Kenya, Ghana, and Nigeria to examine the association between ethnic group prevalence of APOL1 risk variants and blood pressure. Using available genotype data, we were able to link ethnic group status to APOL1 risk variant frequency in 10 423 persons. # Results Age, sex, body mass index, and frequency of the APOL1 high-risk genotype (two risk alleles) were associated with mean systolic blood pressure (SBP). In the adjusted model, a 1% higher prevalence of the APOL1 risk genotype was associated with 0.18 mmHg (95% confidence interval CI 0.05-0.32) higher systolic blood pressure (SBP). # Conclusions Mean SBP was 5 mmHg higher in African ethnic groups where nearly a third of persons carry two high risk APOL1 alleles, compared with ethnic groups where homozygosity is rare. Since uncontrolled blood pressure predisposes to high risks for death and substantial disability prior to development of end-stage kidney disease, studies exploring the link between the APOL1 risk alleles and blood pressure are crucial to understanding the full implications of APOL1 genetic variation in Africa.

Abstract MP07: Soluble Urokinase-type Plasminogen Activator Receptor is associated with progression of hypertension-attributed chronic kidney disease in African Americans

Introduction: Soluble urokinase-type plasminogen activator receptor (suPAR), a circulating signaling protein and marker of immune activation, has been linked to incident and progressive chronic kidney disease (CKD) in select patient populations, often with few African Americans. Hypothesis: We assessed the hypothesis that higher circulating levels of suPAR are associated with risk for progression of hypertension-attributed CKD in African Americans. Methods: We quantified baseline plasma levels of suPAR in participants of the African-American Study of Kidney Disease and Hypertension (AASK), a clinical trial of African Americans with hypertension-attributed CKD, and regular assessment of measured glomerular filtration rate (mGFR), and proteinuria. We used Cox proportional hazards regression to assess the associations of suPAR with CKD progression (defined as doubling of serum creatinine or end-stage renal disease [ESRD]), ESRD, worsening proteinuria (pre-ESRD doubling of 24-hour urine protein to creatinine ratio [UPCR] to ≥220 mg/g), and all-cause death. Results: Among 955 AASK participants, the median baseline suPAR was 4462 pg/mL (25 th to 75 th percentile: 3425-5923 pg/mL), mean mGFR was 46 mL/min per 1.73 m 2 , and median 24-hour UPCR was 79.6 mg/g. After controlling for baseline demographics, AASK trial arm, mGFR, proteinuria, APOL1 risk status, and clinical risk factors, there was a 1.42-times higher risk for CKD progression per two-fold higher baseline suPAR (HR 1.42, 95% CI: 1.17-1.71, p &lt;0.001). Higher suPAR was also independently associated with ESRD (HR 1.59, 95% CI: 1.26-2.00, p &lt;0.001) and death (HR 1.40, 95% CI: 1.12-1.75, p =0.003). Only in patients with two APOL1 risk alleles was suPAR associated with worsening proteinuria (HR 1.77, 95% CI 1.11-2.82, p =0.016; p interaction =0.008). Conclusion: Our study provides evidence of associations between higher suPAR levels and risk for various adverse outcomes in African Americans with hypertension-attributed CKD, independent of proteinuria and GFR.

An Exome-wide Association Study for Type 2 Diabetes–Attributed End-Stage Kidney Disease in African Americans

IntroductionCompared with European Americans, African Americans (AAs) are at higher risk for developing end-stage kidney disease (ESKD). Genome-wide association studies (GWAS) have identified >70 genetic variants associated with kidney function and chronic kidney disease (CKD) in patients with and without diabetes. However, these variants explain a small proportion of disease liability. This study examined the contribution of coding genetic variants for risk of type 2 diabetes (T2D)-attributed ESKD and advanced CKD in AAs.MethodsExome sequencing was performed in 456 AA T2D-ESKD cases, and 936 AA nondiabetic, non-nephropathy control individuals at the discovery stage. A mixed logistic regression model was used for association analysis. Nominal associations (P < 0.05) were replicated in an additional 2020 T2D-ESKD cases and 1121 nondiabetic, non-nephropathy control individuals. A meta-analysis combining 4533 discovery and replication samples was performed. Putative T2D-ESKD associations were tested in additional 1910 nondiabetic ESKD and 219 T2D-ESKD cases, as well as 912 AA nondiabetic non-nephropathy control individuals.ResultsA total of 11 suggestive T2D-ESKD associations (P < 1 x 10−4) from 8 loci (PLEKHN1, NADK, RAD51AP2, RREB1, PEX6, GRM8, PRX, APOL1) were apparent in the meta-analysis. Exclusion of APOL1 renal-risk genotype carriers identified 3 additional suggestive loci (OTUD7B, IFITM3, DLGAP5). Rs41302867 in RREB1 displayed consistent association with T2D-ESKD and nondiabetic ESKD (odds ratio: 0.47; P = 1.2 x 10−6 in 4605 all-cause ESKD and 2969 nondiabetic non-nephropathy control individuals).ConclusionOur findings suggest that coding genetic variants are implicated in predisposition to T2D-ESKD in AAs.

Chronic kidney disease in African Americans: Puzzle pieces are falling into place.

Recent decades have seen great advances in the understanding of chronic kidney disease, spurred by standardizing disease definitions and large-scale patient surveillance. African Americans are disproportionately affected by the disease, and recently discovered genetic variants in APOL1 that protect against sleeping sickness in Africa provide an important explanation for the increased burden. Studies are now under way to determine if genetic testing of African American transplant donors and recipients is advisable.