The apolipoprotein L1 (APOL1) gene and nondiabetic nephropathy in African Americans

Association of Race With Mortality and Cardiovascular Events in a Large Cohort of US Veterans

BACKGROUND

In the general population, blacks experience higher mortality than their white peers, attributed in part to their lower socioeconomic status, reduced access to care, and possibly intrinsic biological factors. Patients with kidney disease are a notable exception, among whom blacks experience lower mortality. It is unclear if similar differences affecting outcomes exist in patients with no kidney disease but with equal or similar access to health care.

METHODS AND RESULTS

We compared all-cause mortality, incident coronary heart disease, and incident ischemic stroke using multivariable-adjusted Cox models in a nationwide cohort of 547 441 black and 2 525 525 white patients with baseline estimated glomerular filtration rate ≥ 60 mL·min⁻¹·1.73 m⁻² receiving care from the US Veterans Health Administration. In parallel analyses, we compared outcomes in black versus white individuals in the National Health and Nutrition Examination Survey (NHANES) 1999 to 2004. After multivariable adjustments in veterans, black race was associated with 24% lower all-cause mortality (adjusted hazard ratio, 0.76; 95% confidence interval, 0.75-0.77; P<0.001) and 37% lower incidence of coronary heart disease (adjusted hazard ratio, 0.63; 95% confidence interval, 0.62-0.65; P<0.001) but a similar incidence of ischemic stroke (adjusted hazard ratio, 0.99; 95% confidence interval, 0.97-1.01; P=0.3). Black race was associated with a 42% higher adjusted mortality among individuals with estimated glomerular filtration rate ≥ 60 mL·min⁻¹·1.73 m⁻² in NHANES (adjusted hazard ratio, 1.42; 95% confidence interval, 1.09-1.87).

CONCLUSIONS

Black veterans with normal estimated glomerular filtration rate and equal access to healthcare have lower all-cause mortality and incidence of coronary heart disease and a similar incidence of ischemic stroke. These associations are in contrast to the higher mortality experienced by black individuals in the general US population.

Examination of Potential Modifiers of the Association of APOL1 Alleles with CKD Progression

BACKGROUND AND OBJECTIVES

Common apolipoprotein L1 (APOL1) variants are associated with increased risk of progressive CKD; however, not all individuals with high-risk APOL1 variants experience CKD progression. Identification of factors contributing to heterogeneity has important scientific and clinical implications.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Using multivariable Cox models, we analyzed data from 693 participants in the African American Study of Kidney Disease and Hypertension to identify factors that modify the association between APOL1 genotypes and CKD progression (doubling of serum creatinine or incident ESRD).

RESULTS

Participant mean age was 54 years old, median GFR was 49 ml/min per 1.73 m(2), and 23% had the APOL1 high-risk genotype (two copies of the high-risk allele). Over a mean follow-up of 7.8 years, 288 (42%) participants experienced CKD progression. As previously reported, the high-risk genotype was associated with higher risk of CKD progression compared with the low-risk genotype (hazard ratio [HR], 1.88; 95% confidence interval [95% CI], 1.46 to 2.41). Although we found some suggestion that obesity (HR, 1.48; 95% CI, 1.05 to 2.08 and HR, 2.44; 95% CI, 1.66 to 3.57 for body mass index ≥ 30 versus <30 kg/m(2); P interaction =0.04) and increased urinary excretion of urea nitrogen (HR, 1.43; 95% CI, 0.98 to 2.09 versus HR, 2.33; 95% CI, 1.65 to 3.30 for urine urea nitrogen ≥ 8 versus <8 g/d; P interaction =0.04) were associated with lower APOL1-associated risk for CKD progression, these findings were not robust in sensitivity analyses with alternative cut points. No other sociodemographic (e.g., education and income), clinical (e.g., systolic BP and smoking), or laboratory (e.g., net endogenous acid production, urinary sodium and potassium excretions, 25-hydroxy vitamin D, intact parathyroid hormone, or fibroblast growth factor 23) variables modified the association between APOL1 and CKD progression (P interaction >0.05 for each).

CONCLUSIONS

Sociodemographic factors and common risk factors for CKD progression do not seem to alter APOL1-related CKD progression. Additional investigation is needed to identify nontraditional factors that may affect the association between APOL1 and progressive CKD.

The peopling of the African continent and the diaspora into the new world

Africa is the birthplace of anatomically modern humans, and is the geographic origin of human migration across the globe within the last 100,000 years. The history of African populations has consisted of a number of demographic events that have influenced patterns of genetic and phenotypic variation across the continent. With the increasing amount of genomic data and corresponding developments in computational methods, researchers are able to explore long-standing evolutionary questions, expanding our understanding of human history within and outside of Africa. This review will summarize some of the recent findings regarding African demographic history, including the African Diaspora, and will briefly explore their implications for disease susceptibility in populations of African descent.

In vivo Modeling Implicates APOL1 in Nephropathy: Evidence for Dominant Negative Effects and Epistasis under Anemic Stress

African Americans have a disproportionate risk for developing nephropathy. This disparity has been attributed to coding variants (G1 and G2) in apolipoprotein L1 (APOL1); however, there is little functional evidence supporting the role of this protein in renal function. Here, we combined genetics and in vivo modeling to examine the role of apol1 in glomerular development and pronephric filtration and to test the pathogenic potential of APOL1 G1 and G2. Translational suppression or CRISPR/Cas9 genome editing of apol1 in zebrafish embryos results in podocyte loss and glomerular filtration defects. Complementation of apol1 morphants with wild-type human APOL1 mRNA rescues these defects. However, the APOL1 G1 risk allele does not ameliorate defects caused by apol1 suppression and the pathogenicity is conferred by the cis effect of both individual variants of the G1 risk haplotype (I384M/S342G). In vivo complementation studies of the G2 risk allele also indicate that the variant is deleterious to protein function. Moreover, APOL1 G2, but not G1, expression alone promotes developmental kidney defects, suggesting a possible dominant-negative effect of the altered protein. In sickle cell disease (SCD) patients, we reported previously a genetic interaction between APOL1 and MYH9. Testing this interaction in vivo by co-suppressing both transcripts yielded no additive effects. However, upon genetic or chemical induction of anemia, we observed a significantly exacerbated nephropathy phenotype. Furthermore, concordant with the genetic interaction observed in SCD patients, APOL1 G2 reduces myh9 expression in vivo, suggesting a possible interaction between the altered APOL1 and myh9. Our data indicate a critical role for APOL1 in renal function that is compromised by nephropathy-risk encoding variants. Moreover, our interaction studies indicate that the MYH9 locus is also relevant to the phenotype in a stressed microenvironment and suggest that consideration of the context-dependent functions of both proteins will be required to develop therapeutic paradigms.

African Americans have a disproportionate risk for developing chronic kidney disease compared to European Americans. Previous studies have identified a region on chromosome 22 containing two genes, MYH9 and APOL1, which likely accounts for nearly all of this difference. Previous reports provided strong statistical evidence implicating APOL1 as the major contributor to nephropathy risk in African Americans, driven by two coding variants, termed G1 and G2. However, other groups still report statistical evidence for MYH9 association in kidney disease, and animal models have demonstrated biological relevance for MYH9 function in the kidney. Here, we show that suppressing apol1 in zebrafish embryos results in perturbed kidney function. Importantly, using this in vivo assay, we show that the G1 variant appears to cause a loss of APOL1 function, while the G2 variant results in an altered protein that may be acting antagonistically in the presence of normal APOL1. We also report a genetic interaction between apol1 and myh9 under anemic stress, which is consistent with our previous findings in sickle cell disease (SCD) nephropathy patients. Finally, we provide functional evidence in vivo that the G2-altered APOL1 may be interacting with MYH9 to confer nephropathy risk.

APOL1 nephropathy risk variants are associated with altered high-density lipoprotein profiles in African Americans

BACKGROUND

Two independent coding variants in the apolipoprotein L1 gene (APOL1), G1 and G2, strongly associate with nephropathy in African Americans; associations with cardiovascular disease are more controversial. Although APOL1 binds plasma high-density lipoproteins (HDLs), data on APOL1 risk variant associations with HDL subfractions are sparse.

METHODS

Two APOL1 G1 single nucleotide polymorphisms and the G2 insertion/deletion polymorphism were genotyped in 2010 Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study participants with nuclear magnetic resonance spectroscopy-based lipoprotein subfraction measurements. Linear regression was used to model associations between numbers of APOL1 G1/G2 risk variants and HDL subfractions, adjusting for demographic, clinical and ancestral covariates.

RESULTS

Female sex and higher percentage of African ancestry were positively associated with the number of APOL1 G1/G2 risk alleles. In the unadjusted analysis, mean (standard error) small HDL concentrations (μmol/L) for participants with zero, one and two G1/G2 risk alleles were 19.0 (0.2), 19.7 (0.2) and 19.9 (0.4), respectively (P = 0.02). Adjustment for age, sex, diabetes and African ancestry did not change the results but strengthened the statistical significance (P = 0.004). No significant differences in large or medium HDL, very low-density lipoprotein or low-density lipoprotein particle concentrations were observed by APOL1 genotype.

CONCLUSIONS

Greater numbers of APOL1 G1/G2 risk alleles were associated with higher small HDL particle concentrations in African Americans. These results may suggest novel areas of investigation to uncover reasons for the association between APOL1 risk variants with adverse outcomes in African Americans.

Biogenesis and cytotoxicity of APOL1 renal risk variant proteins in hepatocytes and hepatoma cells

Two APOL1 gene variants, which likely evolved to protect individuals from African sleeping sickness, are strongly associated with nondiabetic kidney disease in individuals with recent African ancestry. Consistent with its role in trypanosome killing, the pro-death APOL1 protein is toxic to most cells, but its mechanism of cell death is poorly understood and little is known regarding its intracellular trafficking and secretion. Because the liver appears to be the main source of circulating APOL1, we examined its secretory behavior and mechanism of toxicity in hepatoma cells and primary human hepatocytes. APOL1 is poorly secreted in vitro, even in the presence of chemical chaper-ones; however, it is efficiently secreted in wild-type transgenic mice, suggesting that APOL1 secretion has specialized requirements that cultured cells fail to support. In hepatoma cells, inducible expression of APOL1 and its risk variants promoted cell death, with the G1 variant displaying the highest degree of toxicity. To explore the basis for APOL1-mediated cell toxicity, endoplasmic reticulum stress, pyroptosis, autophagy, and apoptosis were examined. Our results suggest that autophagy represents the predominant mechanism of APOL1-mediated cell death. Overall, these results increase our understanding of the basic biology and trafficking behavior of circulating APOL1 from the liver.

Podocyte endocytosis in the regulation of the glomerular filtration barrier

Severe defects in the glomerular filtration barrier result in nephrotic syndrome, which is characterized by massive proteinuria. The podocyte, a specialized epithelial cell with interdigitating foot processes separated by a slit diaphragm, plays a vital role in regulating the passage of proteins from the capillary lumen to Bowman's space. Recent findings suggest a critical role for endocytosis in podocyte biology as highlighted by genetic mouse models of disease and human genetic mutations that result in the loss of the integrity of the glomerular filtration barrier. In vitro podocyte studies have also unraveled a plethora of constituents that are differentially internalized to maintain homeostasis. These observations provide a framework and impetus for understanding the precise regulation of podocyte endocytic machinery in both health and disease.

Apolipoprotein L1 gene variants in deceased organ donors are associated with renal allograft failure

Apolipoprotein L1 gene (APOL1) nephropathy variants in African American deceased kidney donors were associated with shorter renal allograft survival in a prior single-center report. APOL1 G1 and G2 variants were genotyped in newly accrued DNA samples from African American deceased donors of kidneys recovered and/or transplanted in Alabama and North Carolina. APOL1 genotypes and allograft outcomes in subsequent transplants from 55 U.S. centers were linked, adjusting for age, sex and race/ethnicity of recipients, HLA match, cold ischemia time, panel reactive antibody levels, and donor type. For 221 transplantations from kidneys recovered in Alabama, there was a statistical trend toward shorter allograft survival in recipients of two-APOL1-nephropathy-variant kidneys (hazard ratio [HR] 2.71; p = 0.06). For all 675 kidneys transplanted from donors at both centers, APOL1 genotype (HR 2.26; p = 0.001) and African American recipient race/ethnicity (HR 1.60; p = 0.03) were associated with allograft failure. Kidneys from African American deceased donors with two APOL1 nephropathy variants reproducibly associate with higher risk for allograft failure after transplantation. These findings warrant consideration of rapidly genotyping deceased African American kidney donors for APOL1 risk variants at organ recovery and incorporation of results into allocation and informed-consent processes.

African origins and chronic kidney disease susceptibility in the human immunodeficiency virus era

Chronic kidney disease (CKD) is a major public health problem worldwide with the estimated incidence growing by approximately 6% annually. There are striking ethnic differences in the prevalence of CKD such that, in the United States, African Americans have the highest prevalence of CKD, four times the incidence of end stage renal disease when compared to Americans of European ancestry suggestive of genetic predisposition. Diabetes mellitus, hypertension and human immunodeficiency virus (HIV) infection are the major causes of CKD. HIV-associated nephropathy (HIVAN) is an irreversible form of CKD with considerable morbidity and mortality and is present predominantly in people of African ancestry. The APOL1 G1 and G2 alleles were more strongly associated with the risk for CKD than the previously examined MYH9 E1 risk haplotype in individuals of African ancestry. A strong association was reported in HIVAN, suggesting that 50% of African Americans with two APOL1 risk alleles, if untreated, would develop HIVAN. However these two variants are not enough to cause disease. The prevailing belief is that modifying factors or second hits (including genetic hits) underlie the pathogenesis of kidney disease. This work reviews the history of genetic susceptibility of CKD and outlines current theories regarding the role for APOL1 in CKD in the HIV era.

Human trypanolytic factor APOL1 forms pH-gated cation-selective channels in planar lipid bilayers: relevance to trypanosome lysis

Apolipoprotein L-1 (APOL1), the trypanolytic factor of human serum, can lyse several African trypanosome species including Trypanosoma brucei brucei, but not the human-infective pathogens T. brucei rhodesiense and T. brucei gambiense, which are resistant to lysis by human serum. Lysis follows the uptake of APOL1 into acidic endosomes and is apparently caused by colloid-osmotic swelling due to an increased ion permeability of the plasma membrane. Here we demonstrate that nanogram quantities of full-length recombinant APOL1 induce ideally cation-selective macroscopic conductances in planar lipid bilayers. The conductances were highly sensitive to pH: their induction required acidic pH (pH 5.3), but their magnitude could be increased 3,000-fold upon alkalinization of the milieu (pK(a) = 7.1). We show that this phenomenon can be attributed to the association of APOL1 with the bilayer at acidic pH, followed by the opening of APOL1-induced cation-selective channels upon pH neutralization. Furthermore, the conductance increase at neutral pH (but not membrane association at acidic pH) was prevented by the interaction of APOL1 with the serum resistance-associated protein, which is produced by T. brucei rhodesiense and prevents trypanosome lysis by APOL1. These data are consistent with a model of lysis that involves endocytic recycling of APOL1 and the formation of cation-selective channels, at neutral pH, in the parasite plasma membrane.

Stress and the kidney

The prevalence of CKD has increased considerably over the past 2 decades. The rising rates of CKD have been attributed to known comorbidities such as diabetes, hypertension, and obesity; however, recent research has begun to explore the degree to which social, economic, and psychological factors have implications for the prevalence and progression of CKD, especially among high-risk populations such as African Americans. It has been suggested that stress can have implications for CKD, but this area of research has been largely unexplored. One contributing factor associated with the paucity of research on CKD is that many of the social, psychological, and environmental stressors cannot be recreated or simulated in a laboratory setting. Social science has established that stress can have implications for health, and we believe that stress is an important determinant of the development and progression of CKD. We draw heavily from the social scientific and social epidemiologic literature to present an intersectional conceptual frame specifying how stress can have implications for kidney disease, its progression, and its complications through multiple stressors and pathways.

Hypertensive renal injury is associated with gene variation affecting immune signaling

BACKGROUND

The spontaneously hypertensive rat (SHR) strain exists in lines that contrast strongly in susceptibility to renal injury in hypertension. These inbred lines share common ancestry, and only 13% of their genomes arise from different ancestors.

METHODS AND RESULTS

We used next gen sequencing to detect natural allelic variation in 5 genes of the immunoreceptor signaling pathway (IgH, Dok3, Src, Syk, and JunD) that arise from different ancestors in the injury-prone SHR-A3 and the resistant SHR-B2 lines. We created an intercross between these lines, and in the F2 progeny, we observed that the inheritance of haplotype blocks containing the SHR-A3 alleles of these 5 genes correlated with increased albuminuria and histological measures of renal injury. To test whether accumulated genetic variation in this pathway may create a therapeutic target in hypertensive renal injury, rats of both lines were treated with the immunosuppressant mycophenolate mofetil (MMF). MMF reduced proteinuria (albumin to creatinine ratio) from 6.6 to 1.2 mg/mg (P<0.001) in SHR-A3. Glomerular injury scores were reduced in MMF-treated SHR-A3 from 1.6 to 1.4 (P<0.002). Tubulo-interstitial injury was reduced in MMF-treated SHR-A3 from 2.62 to 2.0 (P=0.001). MMF treatment also reduced renal fibrosis in SHR-A3 (3.9 versus 2.0; P<0.001).

CONCLUSIONS

Polygenic susceptibility to renal injury in hypertension arises in association with genetic variation in genes that participate in immune responses and is dramatically improved by reduction of immune system activity.

APOL1 kidney risk alleles: population genetics and disease associations

APOL1 kidney disease is a unique case in the field of the genetics of common disease: 2 variants (termed G1 and G2) with high population frequency have been repeatedly associated with nondiabetic CKDs, with very strong effect size (odds ratios 3-29) in populations of sub-Saharan African descent. This review provides an update on the spectrum of APOL1 kidney disease and on the worldwide distribution of these kidney risk variants. We also summarize the proper way to run a recessive analysis on joint and independent effects of APOL1 G1 and G2 kidney risk variants.

The impact of APOL1, CAV1, and ABCB1 gene variants on outcomes in kidney transplantation: donor and recipient effects

Dramatic improvements have been seen in short-term kidney allograft survival over recent decades with introduction of more potent immunosuppressant medications and regimens. Unfortunately, improvements in long-term graft survival have lagged behind. The genomics revolution is providing new insights regarding the potential impact of kidney donor genotypes on long-term graft survival. Variation in the donor apolipoprotein L1 (APOL1), caveolin 1 (CAV1), and multi-drug resistance 1 encoding P-glycoprotein genes (ABCB1) are all associated with graft survival after kidney transplantation. Although the precise mechanisms whereby these donor gene variants confer risk for graft loss have yet to be determined, these findings provide novel opportunities for modifying interactive environmental factors and optimizing kidney allocation with the ultimate goal of improving long-term graft survival rates.

Developments in renal pharmacogenomics and applications in chronic kidney disease

Chronic kidney disease (CKD) has shown an increasing prevalence in the last century. CKD encompasses a poor prognosis related to a remarkable number of comorbidities, and many patients suffer from this disease progression. Once the factors linked with CKD evolution are distinguished, it will be possible to provide and enhance a more intensive treatment to high-risk patients. In this review, we focus on the emerging markers that might be predictive or related to CKD progression physiopathology as well as those related to a different pattern of response to treatment, such as inhibitors of the renin–angiotensin system (including angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers; the vitamin D receptor agonist; salt sensitivity hypertension; and progressive kidney-disease markers with identified genetic polymorphisms). Candidate-gene association studies and genome-wide association studies have analyzed the genetic basis for common renal diseases, including CKD and related factors such as diabetes and hypertension. This review will, in brief, consider genotype-based pharmacotherapy, risk prediction, drug target recognition, and personalized treatments, and will mainly focus on findings in CKD patients. An improved understanding will smooth the progress of switching from classical clinical medicine to gene-based medicine.

Nonmuscle Myosin II Regulates the Morphogenesis of Metanephric Mesenchyme-Derived Immature Nephrons

The kidney develops from reciprocal interactions between the metanephric mesenchyme and ureteric bud. The mesenchyme transforms into epithelia and forms complicated nephron structures, whereas the ureteric bud extends its pre-existing epithelial ducts. Although the roles are well established for extracellular stimuli, such as Wnt and Notch, it is unclear how the intracellular cytoskeleton regulates these morphogenetic processes. Myh9 and Myh10 encode nonmuscle myosin II heavy chains, and Myh9 mutations in humans are implicated in congenital kidney diseases and focal segmental glomerulosclerosis in adults. Here, we analyzed the roles of Myh9 and Myh10 in the developing kidney. Ureteric bud-specific depletion of Myh9 resulted in no apparent phenotypes, whereas mesenchyme-specific Myh9 deletion caused proximal tubule dilations and renal failure. Mesenchyme-specific Myh9/Myh10 mutant mice died shortly after birth and showed a severe defect in nephron formation. The nascent mutant nephrons failed to form a continuous lumen, which likely resulted from impaired apical constriction of the elongating tubules. In addition, nephron progenitors lacking Myh9/Myh10 or the possible interactor Kif26b were less condensed at midgestation and reduced at birth. Taken together, nonmuscle myosin II regulates the morphogenesis of immature nephrons derived from the metanephric mesenchyme and the maintenance of nephron progenitors. Our data also suggest that Myh9 deletion in mice results in failure to maintain renal tubules but not in glomerulosclerosis.

Familial clustering of ESRD in the Norwegian population

BACKGROUND AND OBJECTIVES

Studies and clinical experience suggest that kidney disease clusters in families, but few population-based studies have been performed. This study investigates risks and causes of ESRD in Norwegians with and without a first-degree relative with ESRD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

On the basis of data from the Norwegian Population Registry, first-degree relatives for most Norwegians were identified. All Norwegians with ESRD (defined as chronic RRT) since 1980 have been registered in the Norwegian Renal Registry. All Norwegians born in Norway who were alive in 1980 and had at least one registered relative were included. For this study, data on ESRD were available through 2009, and individuals without ESRD were censored at December 31, 2009. Data were analyzed in a cohort design, with ESRD in a first-degree relative of the included person as the main explanatory variable. Risks of ESRD and different causes of ESRD were analyzed using Cox regression statistics.

RESULTS

In total, 5,119,134 individuals were included, of whom 8203 individuals developed ESRD during follow-up and 27,046 individuals had a first-degree relative with ESRD. Compared with individuals without a first-degree relative with ESRD, individuals with a first-degree relative with ESRD had a relative risk of ESRD of 7.2 (95% confidence interval, 6.5 to 8.1). Similar analyses showed that relative risk of ESRD caused by nonhereditary causes was 3.7 (95% confidence interval, 3.1 to 4.4), relative risk of ESRD caused by glomerular disease was 5.2 (95% confidence interval, 4.1 to 6.6), relative risk of ESRD caused by interstitial disease was 4.7 (95% confidence interval, 3.1 to 7.3), relative risk of ESRD caused by diabetic nephropathy was 2.6 (95% confidence interval, 1.6 to 4.1), and relative risk of ESRD caused by hypertensive nephrosclerosis was 2.6 (95% confidence interval, 1.6 to 4.1). Relative risk of nonhereditary parenchymal renal disease was 3.8 (95% confidence interval, 3.1 to 4.7).

CONCLUSIONS

As expected, ESRD clusters in families. Interestingly, ESRD without known hereditary cause also clusters in families.

Explaining the racial difference in AKI incidence

African Americans face higher risk of AKI than Caucasians. The extent to which this increased risk is because of differences in clinical, socioeconomic, or genetic risk factors is unknown. We evaluated 10,588 African-American and Caucasian participants in the Atherosclerosis Risk in Communities study, a community-based prospective cohort of middle-aged individuals. Participants were followed from baseline study visit (1996-1999) to first hospitalization for AKI (defined by billing code), ESRD, death, or December 31, 2010. African-American participants were slightly younger (61.7 versus 63.1 years, P<0.001), were more often women (64.5% versus 53.2%, P<0.001), and had higher baseline eGFR compared with Caucasians. Annual family income, education level, and prevalence of health insurance were lower among African Americans than Caucasians. The unadjusted incidence of hospitalized AKI was 7.4 cases per 1000 person-years among African Americans and 5.8 cases per 1000 person-years among Caucasians (P=0.002). The elevated risk of AKI among African Americans persisted after adjustment for demographics, cardiovascular risk factors, kidney markers, and time-varying number of hospitalizations (adjusted hazard ratio, 1.20; 95% confidence interval [95% CI], 1.01 to 1.43; P=0.04); however, accounting for differences in income and/or insurance by race attenuated the association (P>0.05). High-risk APOL1 variants did not associate with AKI among African Americans (demographic-adjusted hazard ratio, 1.07; 95% CI, 0.69 to 1.65; P=0.77). In summary, the higher risk of AKI among African Americans may be related to disparities in socioeconomic status.

Localization of APOL1 protein and mRNA in the human kidney: nondiseased tissue, primary cells, and immortalized cell lines

Although APOL1 gene variants are associated with nephropathy in African Americans, little is known about APOL1 protein synthesis, uptake, and localization in kidney cells. To address these questions, we examined APOL1 protein and mRNA localization in human kidney and human kidney-derived cell lines. Indirect immunofluorescence microscopy performed on nondiseased nephrectomy cryosections from persons with normal kidney function revealed that APOL1 protein was markedly enriched in podocytes (colocalized with synaptopodin and Wilms' tumor suppressor) and present in lower abundance in renal tubule cells. Fluorescence in situ hybridization detected APOL1 mRNA in glomeruli (podocytes and endothelial cells) and tubules, consistent with endogenous synthesis in these cell types. When these analyses were extended to renal-derived cell lines, quantitative RT-PCR did not detect APOL1 mRNA in human mesangial cells; however, abundant levels of APOL1 mRNA were observed in proximal tubule cells and glomerular endothelial cells, with lower expression in podocytes. Western blot analysis revealed corresponding levels of APOL1 protein in these cell lines. To explain the apparent discrepancy between the marked abundance of APOL1 protein in kidney podocytes observed in cryosections versus the lesser abundance in podocyte cell lines, we explored APOL1 cellular uptake. APOL1 protein was taken up readily by human podocytes in vitro but was not taken up efficiently by mesangial cells, glomerular endothelial cells, or proximal tubule cells. We hypothesize that the higher levels of APOL1 protein in human cryosectioned podocytes may reflect both endogenous protein synthesis and APOL1 uptake from the circulation or glomerular filtrate.

Racial disparities in kidney disease outcomes

Chronic kidney disease (CKD) is a national public health problem. Although the prevalence of early stages of CKD is similar across different racial/ethnic and socioeconomic groups, the prevalence of end-stage renal disease is greater for minorities than their non-Hispanic white peers. Paradoxically, once on dialysis, minorities experience survival rates that exceed their non-Hispanic white peers. Advancing our understanding of the unique interplay of biological, genetic, environmental, sociocultural, and health care system level factors may prompt reorientation of our approach to health promotion and disease prevention. The potential of this new approach is to create previously unimagined gains to improve patient outcomes and reduce health inequities for patients with CKD.

Race and the insulin resistance syndrome

Type 2 diabetes remains an important cause of morbidity and mortality. The metabolic syndrome affects 25% of the adult US population based on the Third Report of the Expert Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults from the National Cholesterol Education Program. Knowledge on the impact of obesity on metabolic health parameters has increased greatly over the past decade. This review discusses the limitations of the National Cholesterol Education Program metabolic syndrome definition and the racial disparities in the clinical presentation of the insulin resistance syndrome. We also examine the current literature with particular emphasis on albuminuria, nonalcoholic fatty liver disease, and intramyocellular lipid content. This review explores potential environmental and genetic reasons for differences in the manifestation of insulin resistance across racial/ethnic groups and highlights several promising areas for further study.

APOL1 and nephropathy progression in populations of African ancestry

Marked familial aggregation of chronic kidney disease suggests that inherited factors play a major role in nephropathy susceptibility. Molecular genetics analyses have identified a number of genes reproducibly associated with a broad range of renal phenotypes. Most associations show polygenic inheritance patterns with limited effect size. In contrast, genetic association between the apolipoprotein L1 (APOL1) gene and several severe nondiabetic forms of kidney disease in African Americans approach Mendelian inheritance patterns and account for a large proportion of glomerulosclerosis in populations of African ancestry. Emerging data support an important role for APOL1 in the progression of diverse etiologies of kidney disease, in concert with requisite environmental (gene*environment) and inherited (gene*gene) interactions. This article reviews the current status of APOL1-associated nephropathy and discusses research questions under active investigation in the search for a cure for these severe and often progressive kidney diseases.

Clinical perspectives on lupus genetics: advances and opportunities

In recent years, genome-wide association studies have led to an expansion in the identification of regions containing confirmed genetic risk variants within complex human diseases, such as systemic lupus erythematosus (SLE). Many of the strongest SLE genetic associations can be divided into groups based on their potential roles in different processes implicated in lupus pathogenesis, including ubiquitination, DNA degradation, innate immunity, cellular immunity, lymphocyte development, and antigen presentation. Recent advances have also shown several genetic associations with SLE subphenotypes and subcriteria. Many areas for further exploration remain to move lupus genetic studies toward clinically informative end points.

Gene-gene and gene-environment interactions in apolipoprotein L1 gene-associated nephropathy

Molecular genetics have revolutionized the understanding of susceptibility to the broad spectrum of kidney diseases with light microscopic appearance of FSGS, particularly in populations with recent African ancestry. These disorders include idiopathic FSGS, HIV-associated nephropathy, severe lupus nephritis, sickle cell nephropathy, and the primary kidney disorder focal global glomerulosclerosis, which had historically been ascribed to systemic hypertension. FSGS was once thought to include a multitude of unrelated disorders with similar histologic appearance. However, variation in the apolipoprotein L1 gene locus is now known to account for the vast majority of such cases in African Americans as well as nearly all the excess risk for FSGS and related forms of progressive nondiabetic nephropathy in populations with recent African ancestry, relative to European ancestry. Inheriting two coding apolipoprotein L1 gene nephropathy risk variants is necessary for susceptibility to CKD; however, these variants alone are insufficient to produce disease. This work reviews the evidence supporting second hits or modifying factors that affect risk for apolipoprotein L1 gene-associated nephropathy and produce the protean manifestations of this common and complex syndrome. Targeting modifiable second factors will lead to preventive therapies for slowing progression of nondiabetic nephropathy in many patients possessing two apolipoprotein L1 gene risk variants. This model of genetic risk coupled with modifiable second hits will serve as a paradigm applicable to patients with CKD of various etiologies as well as a host of other complex disorders.

Modulation of renin angiotensin system predominantly alters sclerotic phenotype of glomeruli in HIVAN

HIV-associated nephropathy (HIVAN) is a common complication of HIV-1 infection in patients with African ancestry in general and with APOL1 gene risk variants in particular. Although collapsing glomerulopathy is considered a hallmark of HIVAN, significant numbers of glomeruli in patients with HIVAN also display other variants of focal segmental glomerulosclerosis (FSGS). We propose that collapsed glomeruli as well as glomeruli with other variants of FSGS are manifestations of HIVAN and their prevalence depends on associated host factors. We explored the role of the renin-angiotensin system (RAS) in the manifestation of any specific glomerular phenotype in HIVAN. To evaluate the role of the RAS we have used a genetically engineered mouse model of HIVAN (Tg26) with two and four copies of angiotensinogen (Agt) gene (Tg26/Agt2 and Tg26/Agt4). In Tg26/Agt2, 1 out of 6 glomeruli exhibited sclerosed phenotype, whereas 1 out of 25 glomeruli displayed collapsed phenotype; on the other hand, in Tg26/Agt4, 1 out of 3 glomeruli exhibited sclerotic phenotype and only 1 out of 7 glomeruli showed collapsed phenotype. To inhibit the effect of RAS, Tg26/Agt2 were administered captopril, aliskiren, aliskiren plus captopril or aliskiren plus telmisartan by miniosmotic pumps for 4 weeks. In all experimental groups there was a significant reduction in percentage of sclerosed glomeruli and only minimal reduction in collapsed glomeruli compared to normal saline receiving Tg26/Agt2. These findings suggest that the manifestation of the sclerosed phenotype in HIVAN is predominantly dependent on activation of the RAS.

Analysis of coding variants identified from exome sequencing resources for association with diabetic and non-diabetic nephropathy in African Americans

Prior studies have identified common genetic variants influencing diabetic and non-diabetic nephropathy, diseases which disproportionately affect African Americans. Recently, exome sequencing techniques have facilitated identification of coding variants on a genome-wide basis in large samples. Exonic variants in known or suspected end-stage kidney disease (ESKD) or nephropathy genes can be tested for their ability to identify association either singly or in combination with known associated common variants. Coding variants in genes with prior evidence for association with ESKD or nephropathy were identified in the NHLBI-ESP GO database and genotyped in 5,045 African Americans (3,324 cases with type 2 diabetes associated nephropathy [T2D-ESKD] or non-T2D ESKD, and 1,721 controls) and 1,465 European Americans (568 T2D-ESKD cases and 897 controls). Logistic regression analyses were performed to assess association, with admixture and APOL1 risk status incorporated as covariates. Ten of 31 SNPs were associated in African Americans; four replicated in European Americans. In African Americans, SNPs in OR2L8, OR2AK2, C6orf167 (MMS22L), LIMK2, APOL3, APOL2, and APOL1 were nominally associated (P = 1.8 × 10(-4)-0.044). Haplotype analysis of common and coding variants increased evidence of association at the OR2L13 and APOL1 loci (P = 6.2 × 10(-5) and 4.6 × 10(-5), respectively). SNPs replicating in European Americans were in OR2AK2, LIMK2, and APOL2 (P = 0.0010-0.037). Meta-analyses highlighted four SNPs associated in T2D-ESKD and all-cause ESKD. Results from this study suggest a role for coding variants in the development of diabetic, non-diabetic, and/or all-cause ESKD in African Americans and/or European Americans.

Hypertension in the teenager

Over the last two decades, essential hypertension has become common in adolescents, yet remains under-diagnosed in absence of symptoms. Diagnosis is based on normative percentiles that factor in age, sex and height. Evaluation is more similar to adult essential hypertension than childhood secondary hypertension. Modifiable risk factors such as obesity, sodium consumption and low exercise should be addressed first. Many anti-hypertensive medications now have specific regulatory approval for children. Sports participation need not be limited in mild or well-controlled cases. Primary care physicians play an important role in reduction of cardiovascular mortality by early detection and referral when needed.

Accounting for linkage disequilibrium in association analysis of diverse populations

The National Human Genome Research Institute's catalog of published genome-wide association studies (GWAS) lists over 10,000 genetic variants collectively associated with over 800 human diseases or traits. Most of these GWAS have been conducted in European-ancestry populations. Findings gleaned from these studies have led to identification of disease-associated loci and biologic pathways involved in disease etiology. In multiple instances, these genomic findings have led to the development of novel medical therapies or evidence for prescribing a given drug as the appropriate treatment for a given individual beyond phenotypic appearances or socially defined constructs of race or ethnicity. Such findings have implications for populations throughout the globe and GWAS are increasingly being conducted in more diverse populations. A major challenge for investigators seeking to follow up genomic findings between diverse populations is discordant patterns of linkage disequilibrium (LD). We provide an overview of common measures of LD and opportunities for their use in novel methods designed to address challenges associated with following up GWAS conducted in European-ancestry populations in African-ancestry populations or, more generally, between populations with discordant LD patterns. We detail the strengths and weaknesses associated with different approaches. We also describe application of these strategies in follow-up studies of populations with concordant LD patterns (replication) or discordant LD patterns (transferability) as well as fine-mapping studies. We review application of these methods to a variety of traits and diseases.

Actin-associated Proteins in the Pathogenesis of Podocyte Injury

Podocytes have a complex cellular architecture with interdigitating processes maintained by a precise organization of actin filaments. The actin-based foot processes of podocytes and the interposed slit diaphragm form the final barrier to proteinuria. The function of podocytes is largely based on the maintenance of the normal foot process structure with actin cytoskeleton. Cytoskeletal dynamics play important roles during normal podocyte development, in maintenance of the healthy glomerular filtration barrier, and in the pathogenesis of glomerular diseases. In this review, we focused on recent findings on the mechanisms of organization and reorganization of these actin-related molecules in the pathogenesis of podocyte injury and potential therapeutics targeting the regulation of actin cytoskeleton in podocytopathies.

Addressing the global burden of chronic kidney disease through clinical and translational research

Worldwide, an estimated 200 million people have chronic kidney disease (CKD). In the United States, African Americans (AAs) have a four-fold excess risk of CKD compared to non-Hispanic white people and globally, people in the low-to-middle income countries of Asia and Sub-Saharan Africa have the highest rates of CKD. Annually, more than 500,000 individuals develop end-stage renal disease (or CKD stage 5) in Sub-Saharan Africa alone and the vast majority of these patients suffer premature mortality. The health care costs and economic burden of CKD are huge and not sustainable even in advanced Western countries. A recent discovery on the role of Apolipoprotein 1 (APOL1) G1 and G2 renal risk variants in AAs has a huge potential to unravel the etiology of CKD in both AA and other black populations. Under the National Institutes of Health (NIH)-sponsored Human Heredity and Health in Africa (H3Africa) initiative, a large prospective genetic study of CKD is being conducted in 8000 participants in four African countries (Ethiopia, Ghana, Kenya, and Nigeria; for a total population of 320 million). This and other basic research studies in the United States could potentially shed great insight into the genetics and biologic mechanisms involved in the excess predilection of Africans and AAs to CKD.

Improving productivity of modern-day drug discovery

The pharmaceutical industry is confronted by increasing costs of clinical development and diminishing productivity. The most challenging aspect of drug development has been the failure of therapeutics in expensive Phase II or III trials, and this is most commonly due to lack of efficacy. More can be done during the drug discovery phase to optimize efficacy-testing in animal models by expending resources to explore the congruence of the animal model with the human disease. Historically, relatively little attention has been paid to validation of these models, but access to molecular mRNA and genetic profiling offers a new lens through which the similarity of these disease models to human diseases can be examined and their utility for exploring therapeutic efficacy can be optimized. Exploring congruent experimental end points in clinical and preclinical experiments will also increase confidence of success in late phase clinical development. The expense of this investment is trivial compared to the costs of a failed clinical trial, more than justifying this endeavor.

Hypertension, glomerular hypertrophy and nephrosclerosis: the effect of race

Background

African Americans have more severe hypertensive nephrosclerosis than white Americans, possibly at similar levels of blood pressure. Glomerular volume is increased in African Americans relative to whites, but it is uncertain how this relates to nephrosclerosis and whether it contributes to or compensates for glomerulosclerosis.

Methods

Stereological disector/fractionator estimates of glomerular number (N_glom) and average glomerular volume (V_glom) were obtained on autopsy kidneys of 171 African Americans and 131 whites. Eighty-eight African Americans and 49 whites were identified as hypertensive. Nephrosclerosis was measured morphometrically as the percentage of glomerulosclerosis, proportion of cortical fibrosis and interlobular artery intimal thickness, and analyzed with V_glom by age, race, gender, body mass index (BMI) and blood pressure.

Results

African Americans were more frequently hypertensive (58.5%) than whites (35.8%) and when hypertensive had higher levels of blood pressure (P = 0.02). N_glom was significantly lower in hypertensive compared with non-hypertensive subjects among white women (P = 0.02) but not white males (P = 0.34) or African American females (P = 0.10) or males (P = 0.41). For each race and gender, glomerulosclerosis, cortical fibrosis and arterial intimal thickening were statistically correlated with age (P < 0.001) and hypertension (P < 0.001) and increased V_glom with hypertension (P < 0.001) and BMI (P < 0.001). In multivariate analysis, African American race was associated with increased V_glom (P = 0.01) and arterial intimal thickening (P < 0.01), while interactions between race and blood pressure indicated that the severity of nephrosclerosis including increased V_glom was linked most directly to hypertension without significant contributions from race. The hypertension-associated enlargement of V_glom was present with mild degrees of glomerulosclerosis and changed little as the severity of glomerulosclerosis increased.

Conclusions

Glomerular hypertrophy was identified as an integral feature of hypertensive nephropathy and appeared to precede rather than compensate for glomerulosclerosis. An effect of race on V_glom and arterial intimal thickening seemed to be related to the more frequent and more severe hypertension among African Americans.

APOL1 risk variants, race, and progression of chronic kidney disease

BACKGROUND

Among patients in the United States with chronic kidney disease, black patients are at increased risk for end-stage renal disease, as compared with white patients.

METHODS

In two studies, we examined the effects of variants in the gene encoding apolipoprotein L1 (APOL1) on the progression of chronic kidney disease. In the African American Study of Kidney Disease and Hypertension (AASK), we evaluated 693 black patients with chronic kidney disease attributed to hypertension. In the Chronic Renal Insufficiency Cohort (CRIC) study, we evaluated 2955 white patients and black patients with chronic kidney disease (46% of whom had diabetes) according to whether they had 2 copies of high-risk APOL1 variants (APOL1 high-risk group) or 0 or 1 copy (APOL1 low-risk group). In the AASK study, the primary outcome was a composite of end-stage renal disease or a doubling of the serum creatinine level. In the CRIC study, the primary outcomes were the slope in the estimated glomerular filtration rate (eGFR) and the composite of end-stage renal disease or a reduction of 50% in the eGFR from baseline.

RESULTS

In the AASK study, the primary outcome occurred in 58.1% of the patients in the APOL1 high-risk group and in 36.6% of those in the APOL1 low-risk group (hazard ratio in the high-risk group, 1.88; P<0.001). There was no interaction between APOL1 status and trial interventions or the presence of baseline proteinuria. In the CRIC study, black patients in the APOL1 high-risk group had a more rapid decline in the eGFR and a higher risk of the composite renal outcome than did white patients, among those with diabetes and those without diabetes (P<0.001 for all comparisons).

CONCLUSIONS

Renal risk variants in APOL1 were associated with the higher rates of end-stage renal disease and progression of chronic kidney disease that were observed in black patients as compared with white patients, regardless of diabetes status. (Funded by the National Institute of Diabetes and Digestive and Kidney Diseases and others.).

Population ancestry and genetic risk for diabetes and kidney, cardiovascular, and bone disease: modifiable environmental factors may produce the cures

Variable rates of disease observed between members of different continental population groups may be mediated by inherited factors, environmental exposures, or their combination. This article provides evidence in support of differential allele frequency distributions that underlie the higher rates of nondiabetic kidney disease in the focal segmental glomerulosclerosis spectrum of disease and lower rates of coronary artery calcified atherosclerotic plaque and osteoporosis in populations of African ancestry. With recognition that these and other common complex diseases are affected by biological factors comes the realization that targeted manipulation of environmental exposures and pharmacologic treatments will have different effects based on genotype. The present era of precision medicine will couple one's genetic makeup with specific therapies to reduce rates of disease based on the presence of disease-specific alleles.

Perceptions regarding genetic testing in populations at risk for nephropathy

BACKGROUND

Population ancestry-based differences exist in genetic risk for many kidney diseases. Substantial debate remains regarding returning genetic test results to participants. African-Americans (AAs) and European-Americans (EAs) at risk for end-stage kidney disease were queried for views on the value and use of genetic testing in research.

METHODS

A standardized survey regarding attitudes toward genetic testing was administered to 130 individuals (64 AA, 66 EA) with first-degree relatives on dialysis. Fisher's exact test was used to assess differences in participant attitudes between population groups.

RESULTS

Mean (SD) age of surveyed AAs and EAs was 45.5 (12.8) and 50.5 (14.4) years, respectively (p = 0.04), with similar familial relationships (p = 0.22). AAs and EAs wished to know their test results if risk could be: (1) reduced by diet or exercise (100 and 98%, p = 0.99); (2) reduced by medical treatment (100 and 98%, p = 0.99), or (3) if no treatments were available (90 and 82%, p = 0.21). If informed they lacked a disease susceptibility variant, 87% of AAs and 88% of EAs would be extremely or pretty likely to inform family members (p = 0.84). If informed they had a disease susceptibility variant, 92% of AAs and 89% of EAs would be extremely or pretty likely to inform their family (p = 0.43).

CONCLUSIONS

Attitudes toward obtaining and using genetic test results for disease in research contexts were similar in AAs and EAs at risk for end-stage kidney disease. A substantial majority would want information regardless of available treatments and would share the information with the family. These results have important implications for patient care, study design and the informed consent process.

Gene-gene interactions in APOL1-associated nephropathy

BACKGROUND

Two APOL1 nephropathy variants confer substantial risk for non-diabetic end-stage kidney disease (ESKD) in African Americans (AAs). Since not all genetically high-risk individuals develop ESKD, modifying factors likely contribute. Forty-two potentially interactive single nucleotide polymorphisms (SNPs) from a genome-wide association study in non-diabetic ESKD were tested for interaction with APOL1 to identify genes modifying risk for non-diabetic nephropathy.

METHODS

SNPs were examined in an expanded sample of 1367 AA non-diabetic ESKD cases and 1504 AA non-nephropathy controls, with validation in an independent family-based cohort containing 608 first-degree relatives of index cases with non-diabetic ESKD. Logistic regression and mixed models were fitted to test for interaction effects with APOL1 on ESKD, estimated kidney function and albuminuria.

RESULTS

Among ESKD samples, 14 of 42 SNPs demonstrated suggestive APOL1 interaction with P-values <0.05. After Bonferroni correction, significant interactions with APOL1 were seen with SNPs in podocin (rs16854341; NPHS2, P = 8.0 × 10(-4)), in SDCCAG8 (rs2802723; P = 5.0 × 10(-4)) and near BMP4 (rs8014363; P = 1.0 × 10(-3)); with trends for ENOX1 (rs9533534; P = 2.2 × 10(-3)) and near TRIB1 (rs4457349; P = 5.7 × 10(-3)). The minor allele in NPHS2 markedly changed the APOL1-ESKD association odds ratio (OR) from 7.03 to 1.76 (∼50% reduction in effect per copy of the minor allele), rs2802723 changed the OR from 5.1 to 10.5, and rs8014363 increased the OR from 4.8 to 9.5. NPHS2 (P = 0.05) and SDCCAG8 (P = 0.03) SNPs demonstrated APOL1 interaction with albuminuria in independent family-based samples.

CONCLUSIONS

Variants in NPHS2, SDCCAG8 and near BMP4 appear to interact with APOL1 to modulate the risk for non-diabetic ESKD in AAs.

Conceptual shifts needed to understand the dynamic interactions of genes, environment, epigenetics, social processes, and behavioral choices

Social and behavioral research in public health is often intimately tied to profound, but frequently neglected, biological influences from underlying genetic, environmental, and epigenetic events. The dynamic interplay between the life, social, and behavioral sciences often remains underappreciated and underutilized in addressing complex diseases and disorders and in developing effective remediation strategies. Using a case-study format, we present examples as to how the inclusion of genetic, environmental, and epigenetic data can augment social and behavioral health research by expanding the parameters of such studies, adding specificity to phenotypic assessments, and providing additional internal control in comparative studies. We highlight the important roles of gene-environment interactions and epigenetics as sources of phenotypic change and as a bridge between the life and social and behavioral sciences in the development of robust interdisciplinary analyses.

Background strain and the differential susceptibility of podocyte-specific deletion of Myh9 on murine models of experimental glomerulosclerosis and HIV nephropathy

We previously reported that podocyte-specific deletion of Myh9 (conventional myosin heavy chain 2A) in C57BL/6 mice does not cause spontaneous kidney disease but instead results in a predisposition to glomerulosclerosis in response to a second model of glomerular injury. In contrast, other investigators reported that podocyte-specific deletion of Myh9 (PodΔMyh9) resulted in spontaneous glomerulosclerosis in mice on a mixed background, suggesting that the glomerulosclerosis is dependent on background strain. In order to elucidate the cause of this strain dependent effect Podocin::Cre and Myh9(flox) alleles were backcrossed to mouse strain FVB/N, which is highly susceptible to glomerulosclerosis, with the aim of intercrossing susceptible FVB/N and resistant C57BL/6 mice in subsequent congenic analyses. However, after backcrossing mice to FVB/N and aging mice to 28 weeks, we found no evidence of glomerular disease in PodΔMyh9 mice vs control littermates (urine MAC ratio all p>0.05). We also tested C57BL/6 PodΔMyh9 mice for a predisposition to injury from models other than Adriamycin including HIV nephropathy (HIVAN), puromycin nephropathy, and sheep nephrotoxic serum. In the Tg26 model of HIVAN, we found that podocyte-specific deletion of Myh9 resulted in a modest hypersensitivity in adults compared to Tg26+ control littermates (urine MAC ratio, p<0.05 or less). In contrast, we found that PodΔMyh9 mice were not predisposed to injury in response to other injury models including puromycin nephropathy and sheep nephrotoxic serum. While the mechanism of injury in these models is not fully understood, we conclude that PodΔMyh9 results in a variable susceptibility to glomerulosclerosis in response to different models of glomerular injury. In addition, based on the lack of a spontaneous phenotype of glomerulosclerosis in both C57BL/6 and FVB/N mice, we propose that Myh9 is not absolutely required in adult podocytes.

Host APOL1 genotype is independently associated with proteinuria in HIV infection

Proteinuria is associated with adverse clinical outcomes in HIV infection. Here we evaluated whether APOL1 risk alleles, previously associated with advanced kidney disease, are independently associated with proteinuria in HIV infection in a cross-sectional study of HIV-infected women in the Women's Interagency HIV Study. We estimated the percent difference in urine protein excretion and odds of proteinuria (≥200 mg/g) associated with two versus one or no APOL1 risk allele using linear and logistic regression, respectively. Of 1285 women successfully genotyped, 379 carried one and 80 carried two risk alleles. Proteinuria was present in 124 women, 78 of whom had proteinuria confirmed on a second sample. In women without prior AIDS, two risk alleles were independently associated with a 69% higher urine protein excretion (95% confidence interval (CI): 36, 108) and five-fold higher odds of proteinuria (95% CI: 2.45, 10.37) as compared with one or no risk allele. No association was found in women with prior AIDS. Analyses in which women with impaired kidney function were excluded and proteinuria was confirmed by a second urine sample yielded similar estimates. Thus, APOL1 risk alleles are associated with significant proteinuria in HIV-infected persons without prior clinical AIDS, independent of clinical factors traditionally associated with proteinuria. Trials are needed to determine whether APOL1 genotyping identifies individuals who could benefit from earlier intervention to prevent overt renal disease.

Mycophenolate mofetil for primary focal segmental glomerulosclerosis: systematic review

BACKGROUND

Current treatments for primary focal segmental glomerulosclerosis (FSGS), including corticosteroids and cyclosporine, are not satisfactory for all patients and may induce significant side effects. Antidotal benefits of mycophenolate mofetil (MMF) as an add-on to these immunosuppressive therapies have been reported. This review aims to systematically summarize the efficacy and safety of MMF as a treatment for primary FSGS.

METHOD

Controlled and uncontrolled clinical trials evaluating the use of MMF in primary FSGS patients were identified from nine electronic databases and four clinical trial registries. Kidney failure was selected as the primary outcome.

RESULTS

Three randomized controlled trials (RCT) and 18 uncontrolled pre-post studies were included. Results from RCTs revealed that MMF is no more effective than cyclosporine or cyclophosphamide for promoting kidney function preservation when corticosteroid is used as baseline treatment. One underpowered RCT reported that MMF provides no extra benefit on top of prednisolone, but the result is unlikely to be reliable. Amongst the small, uncontrolled pre-post studies, three of them used MMF as monotherapy, two of which reported successful prevention of kidney failure in all patients. The remaining 15 uncontrolled studies used MMF as add-on therapy and 11 reported kidney failure as an outcome. Amongst them, eight reported no patients developed kidney failure. MMF was generally well tolerated with mild adverse effects, including abdominal discomfort, diarrhea and infections.

CONCLUSIONS

MMF tended to show beneficial effects in uncontrolled studies which recruited patients with resistance to routine treatments, but such favorable results have only been reported in small, uncontrolled trials. No RCT results suggested that MMF was a good alternative to cyclosporine or cyclophosphamide. The role of MMF as an add-on to current therapies, or as monotherapy, should further be evaluated.

JC polyoma virus interacts with APOL1 in African Americans with nondiabetic nephropathy

Individuals with HIV infection and two apolipoprotein L1 gene (APOL1) risk variants frequently develop nephropathy. Here we tested whether non-HIV viral infections influence nephropathy risk via interactions with APOL1 by assessing APOL1 genotypes and presence of urine JC and BK polyoma virus and plasma HHV6 and CMV by quantitative polymerase chain reaction. We analyzed 300 samples from unrelated and related first-degree relatives of African Americans with non-diabetic nephropathy using linear and non-linear mixed models to account for familial relationships. The four groups evaluated were APOL1 0/1 versus 2 risk alleles, with or without nephropathy. Urine JCV and BKV were detected in 90 and 29 patients while HHV6 and CMV were rare. Adjusting for family age at nephropathy, gender and ancestry, presence of JCV genomic DNA in urine and APOL1 risk alleles were significantly negatively associated with elevated serum cystatin C, albuminuria (albumin to creatinine ratio over 30 mg/g), and kidney disease defined as an eGFR under 60 ml/min per 1.73 m² and/or albuminuria in an additive (APOL1 plus JCV) model. BK viruria was not associated with kidney disease. Thus, African Americans at increased risk for APOL1-associated nephropathy (two APOL1 risk variants) with JC viruria had a lower prevalence of kidney disease, suggesting that JCV interaction with APOL1 genotype may influence kidney disease risk.

Genetic variation in APOL1 and MYH9 genes is associated with chronic kidney disease among Nigerians

PURPOSE

A region of chromosome 22 which includes APOL1 and MYH9 genes was recently identified as a risk locus for non-diabetic forms of kidney disease, including idiopathic and HIV-associated focal segmental glomerular sclerosis and kidney disease clinically attributed to hypertension among African Americans. The purposes of the current study were, therefore, to examine the frequency of these variants and to determine whether they are associated with chronic kidney disease (CKD) among native Africans.

METHODS

To investigate the possible evidence of association between variants in these genes and non-diabetic CKD among West Africans, we performed a case/control analysis in a sample of 166 Nigerians without history of European admixture. Our study included a total of 9 variants on APOL1 (n = 4) and MYH9 (n = 5) genes.

RESULTS

We observed significantly strong associations with previously reported APOL1 variants rs73885319 and rs60910145, and their two-allele "G1" haplotype (P < 0.005). We did not observe significant evidence of association between non-diabetic CKD and any of the MYH9 variants or haplotypes after accounting for multiple testing in our sample.

CONCLUSIONS

In conclusion, APOL1 risk variants are associated with non-diabetic forms of CKD among Nigerians of Yoruba ethnicity. Further information on APOL1/MYH9 variants may lead to screening programs, which could lead to earlier detection and interventions for non-diabetic kidney disease.

Hypertension and chronic kidney disease: controversies in pathogenesis and treatment

The relationship between hypertension and chronic kidney disease (CKD) has long been the subject of controversy. The pathogenetic mechanisms of nephropathy in non-diabetic individuals with hypertension, as well as optimal hypertension treatment targets in populations with nephropathy remain important clinical concerns. This manuscript reviews breakthroughs in molecular genetics that have clarified the complex relationship between hypertension and kidney disease, answering the question of which factor comes first. An overview of the potential roles that hyperuricemia plays in the pathogenesis of hypertension and CKD and current blood pressure treatment guidelines in populations with CKD are discussed. The ongoing National Institutes of Health-sponsored Systolic Blood Pressure Intervention Trial (SPRINT) is underway to help answer these important questions. Enrollment of 9250 hypertensive SPRINT participants will be completed in 2013; important results on ideal blood pressure control targets for reducing nephropathy progression, cardiovascular disease end-points, and preserving cognitive function are expected. As such, many of the controversial aspects of hypertension management will likely be clarified in the near future.

Salt sensitivity: a review with a focus on non-Hispanic blacks and Hispanics

The purpose of this review is to summarize the available information regarding salt sensitivity particularly as it relates to non-Hispanic blacks and Hispanics and to clarify possible etiologies, especially those that might shed light on potential treatment options. In non-Hispanic blacks, there is evidence that endothelial dysfunction, reduced potassium intake, decreased urinary kallikrein excretion, upregulation of sodium channel activity, dysfunction in atrial natriuretic peptide (ANP) production, and APOL1 gene nephropathy risk variants may cause or contribute to salt sensitivity. Supported treatment avenues include diets high in potassium and soybean protein, the components of which stimulate nitric oxide production. Racial heterogeneity complicates the study of salt sensitivity in Hispanic populations. Caribbean Hispanics, who have a higher proportion of African ancestry, may respond to commonly prescribed anti-hypertensive agents in a way that is characteristic of non-Hispanic black hypertensives. The low-renin hypertensive phenotype commonly seen in non-Hispanic blacks has been linked to salt sensitivity and may indicate an increased risk for salt sensitivity in a portion of the Hispanic population. In conclusion, increased morbidity and mortality associated with salt sensitivity mandates further studies evaluating the efficacy of tailored dietary and pharmacologic treatment in non-Hispanic blacks and determining the prevalence of low renin hypertension and salt sensitivity within the various subgroups of Hispanic Americans.