Nephropathy In African Americans Research Articles

540-P: Time Is an Independent Risk Factor for Diabetic Nephropathy in African Americans (AA) Compared with Caucasians

Background: AA have a higher prevalence of diabetic nephropathy (DN) than Caucasians. However, the prevalence of DN between AA and Caucasians as a function of time is less well understood. Methods: We retrospectively reviewed the medical charts of 1211 adults who consecutively presented to our diabetes clinic from 2001-10. We collected data from their initial clinic visit. We defined DN as microalbuminuria >300 mg/g or GFR <60 mL/min/1.73m2. Primary objectives were to estimate the prevalence of DN among AA and Caucasians, estimate DN prevalence as a function of time since diabetes diagnosis, and determine risk factors associated with DN. Findings: The prevalence of DN among AA and Caucasians was 32% and 19.6%, respectively. The prevalence of DN increased as a function of time for both AA and Caucasians, but was significantly higher among AA >10 years after diabetes diagnosis (Figure). In multivariable logistic regression, having hypertension (OR = 3.0, 95% CI 2.03 - 4.49), diabetes for >10 years (2.64, 1.91 - 3.68), A1c >8% (1.40, 1.01 - 1.96), and being AA (1.88, 1.32 - 2.66) were independently associated with DN. Diabetes subtype, BMI, and gender were not associated with DN. Interpretation: Differences in DN prevalence between AA and Caucasians appear ∼10 after diabetes diagnosis, independent of A1c and hypertension control. AA may benefit from early prevention and aggressive risk factors control. Disclosure A. De Ferrari: None. F. Ovalle: Speaker's Bureau; Self; Janssen Pharmaceuticals, Inc., Novo Nordisk A/S.

JC Viruria Is Associated With Reduced Risk of Diabetic Kidney Disease

African Americans who shed JC polyomavirus (JCV) in their urine have reduced rates of nondiabetic chronic kidney disease (CKD). We assessed the associations between urinary JCV and urine BK polyomavirus (BKV) with CKD in African Americans with diabetes mellitus. African Americans with diabetic kidney disease (DKD) and controls lacking nephropathy from the Family Investigation of Nephropathy and Diabetes Consortium (FIND) and African American-Diabetes Heart Study (AA-DHS) had urine tested for JCV and BKV using quantitative PCR. Of the 335 individuals tested, 148 had DKD and 187 were controls. JCV viruria was detected more often in the controls than in the patients with DKD (FIND: 46.6% vs 32.2%; OR, 0.52; 95% CI, 0.29 to 0.93; P = 0.03; AA-DHS: 30.4% vs 26.2%; OR, 0.63; 95% CI, 0.27 to 1.48; P = 0.29). A joint analysis adjusted for age, sex, and study revealed that JC viruria was inversely associated with DKD (OR, 0.56; 95% CI, 0.35 to 0.91; P = 0.02). Statistically significant relationships between BKV and DKD were not observed. The results from the present study extend the inverse association between urine JCV and nondiabetic nephropathy in African Americans to DKD. These results imply that common pathways likely involving the innate immune system mediate coincident chronic kidney injury and restriction of JCV replication. Future studies are needed to explore causative pathways and characterize whether the absence of JC viruria can serve as a biomarker for DKD in the African American population.

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.

JC polyoma viruria associates with protection from chronic kidney disease independently from apolipoprotein L1 genotype in African Americans.

Viral infections can trigger chronic kidney disease (CKD) and the urine virome may inform risk. The Natural History of APOL1-Associated Nephropathy Study (NHAANS) reported that urine JC polyomavirus (JCPyV) associated with a lower risk of APOL1-associated nephropathy in African Americans. Herein, association was assessed between urine JCPyV with CKD in African Americans independent from the APOL1 genotype. Quantitative polymerase chain reaction was performed for urinary detection of JCPyV and BK polyoma virus (BKPyV) in 200 newly recruited nondiabetic African Americans. A combined analysis was performed in these individuals plus 300 NHAANS participants. In the 200 new participants, urine JCPyV was present in 8.8% of CKD cases and 45.8% of nonnephropathy controls (P = 3.0 × 10-8). In those with APOL1 renal-risk genotypes, JCPyV was detected in 5.1% of cases and 40.0% of controls (P = 0.0002). In those lacking APOL1 renal-risk genotypes, JCPyV was detected in 12.2% of cases and 48.8% of controls (P = 8.5 × 10-5). BKPyV was detected in 1.3% of cases and 0.8% of controls (P = 0.77). In a combined analysis with 300 NHAANS participants (n = 500), individuals with urine JCPyV had a 63% lower risk of CKD compared with those without urine JCPyV (odds ratio 0.37; P = 4.6 × 10-6). RNA fluorescence in situ hybridization confirmed the presence of JCPyV genomic DNA and JCPyV messenger RNA (mRNA) in nondiseased kidney. Inverse relationships exist between JCPyV viruria and non-diabetic CKD. Future studies should determine whether renal inflammation associated with CKD is less permissive for JCPyV reactivation/replication or whether JCPyV is a marker of reduced host immune responsiveness that diminishes immune pathologic contributions to CKD.

Markers of endothelial dysfunction and inflammation predict progression of diabetic nephropathy in African Americans with type 1 diabetes

African Americans with early onset type 1 diabetes mellitus are at a high risk for severe diabetic nephropathy and end-stage renal disease. In order to determine whether baseline plasma levels of inflammatory markers predict incidence of overt proteinuria or renal failure in African Americans with type 1 diabetes mellitus we reexamined data of 356 participants in our observational follow-up study of 725 New Jersey African-Americans with Type 1 diabetes. At baseline and 6-year follow-up, a detailed structured clinical interview was conducted to document medical history including kidney dialysis or transplant, other diabetic complications, and renal-specific mortality. Plasma levels of 28 inflammatory biomarkers were measured using a multiplex bead analysis system. After adjusting for baseline age, glycohemoglobin and other confounders, the baseline plasma levels of intercellular adhesion molecule-1(s-ICAM-1) in the upper two quartiles were respectively associated with a 3 to 5-fold increases in the risk of progression from none or microalbuminuria to overt proteinuria. Baseline plasma levels of the chemokine eotaxin in the upper quartile were significantly associated with a 7-fold increase in risk of incident renal failure. These associations were independent of traditional risk factors for progression of diabetic nephropathy. Thus, in type 1 diabetic African Americans, s-ICAM-1 predicted progression to overt proteinuria and eotaxin predicted progression to renal failure.

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.

Coding variants in nephrin (NPHS1) and susceptibility to nephropathy in African Americans.

Presumed genetic risk for diabetic and nondiabetic end stage renal disease is strong in African Americans. Exome sequencing data from African Americans with type 2 diabetic end stage renal disease and nondiabetic, non-nephropathy controls in the T2D-GENES study (Discovery, n=529 patients and n=535 controls) were evaluated, focusing on missense variants in NPHS1. Associated variants were then evaluated in independent type 2 diabetic end stage renal disease (Replication, n=1305 patients and n=760 controls), nondiabetic end stage renal disease (n=1705), and type 2 diabetes-only, non-nephropathy samples (n=503). All participants were recruited from dialysis facilities and internal medicine clinics across the southeastern United States from 1991 to present. Additional NPHS1 missense variants were identified from exome sequencing resources, genotyped, and sequence kernel association testing was then performed. Initial analysis identified rs35238405 (T233A; minor allele frequency=0.0096) as associated with type 2 diabetic end stage renal disease (adjustment for admixture P=0.042; adjustment for admixture+APOL1 P=0.080; odds ratio, 2.89 and 2.36, respectively); with replication in independent type 2 diabetic end stage renal disease samples (P=0.018; odds ratio, 4.30) and nondiabetic end stage renal disease samples (P=0.016; odds ratio, 4.48). In a combined analysis (all patients with end stage renal disease versus all controls), T233A was associated with all-cause end stage renal disease (P=0.0038; odds ratio, 2.82; n=3270 patients and n=1187 controls). A P-value of <0.001 was obtained after adjustment for admixture and APOL1 in sequence kernel association testing. Two additional variants (H800R and Y1174H) were nominally associated with protection from end stage renal disease (P=0.036; odds ratio, 0.44; P=0.0084; odds ratio, 0.040, respectively) in the locus-wide single-variant association tests. Coding variants in NPHS1 are associated with both risk for and protection from common forms of nephropathy in African Americans.

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.

Resurgence of membranous nephropathy in African Americans in inner city Chicago.

BackgroundIt is well established that the incidence of focal segmental glomerular sclerosis (FSGS) increased from 1970–1990 to become the leading primary glomerular disease in patients of African descent.MethodsTo determine whether this trend has continued in the past years in Chicago, adult, native kidney biopsies from January 2001 to December 2011 at our hospital were reviewed and collected relevant clinical information in patients with a primary glomerular disease including FSGS, membranous nephropathy (MN), minimal change disease (MCD), membranoproliferative glomerulonephritis (MPGN), and IgA nephropathy (IgAN).ResultsIn the 204 patients analyzed, MN was the most prevalent (32.7%), followed by FSGS (29.7%), IgAN (15.8%), MCD (14.4%), and MPGN (4.5%). Patients with MN had the highest proteinuria (7.9 gms/d) and were significantly older, more edematous, hypoalbuminemic, and hypercholesterolemic than those with FSGS. In both African Americans and Hispanics, MN was the most prevalent primary glomerular lesion at 39.2% and 34% respectively.ConclusionsComparable in size to prior cohorts of African Americans and Hispanics, our report demonstrates a reversal in the incidence of FSGS and MN in both ethnic groups where MN is now more prevalent. To our knowledge, this is the first demonstration of a reverse in the upward trend of the prevalence of FSGS in African Americans.

The new era of APOL1-associated glomerulosclerosis

The association between apolipoprotein L1 gene (APOL1)variants and non-diabetic chronic kidney disease (CKD)has dramatically altered the landscape in nephrology [1,2]. The pathogenesis of glomerulosclerosis is now betterunderstood, providing the possibility of novel treatmentsand hope for millions with, and at risk of, CKD worldwide[3, 4]. The article by Tzur et al. [5] in the current issue ofNephrology Dialysis Transplantation provides importantnew information in this fast moving field. To put this paperin perspective, it is appropriate to review how APOL1has revolutionized our understanding of non-diabeticglomerulosclerosis.Relative to European Americans (EAs), nephrologistshave observed ‘different renal responses’ to systemic hyper-tension and Type 2 diabetes mellitus in African Americans(AAs) [6]. This vague phenomenon was widely applied toexplain the higher incidence rates of common forms ofend-stage renal disease (ESRD) in AAs compared to EAs.The hypothesis that mild–moderate essential hypertensionwas the proximate cause of ‘hypertensive kidney disease’or arteriolar nephrosclerosis in non-diabetic AAs with low-level proteinuria was deeply ingrained in the literature,despite strong evidence to the contrary [3, 7, 8]. Higher ratesof non-diabetic nephropathy in AAs, relative to EAs, werealso ascribed to differences in socioeconomic status andenvironment between population groups.Three important developments led to identification ofAPOL1 and variants in the adjacent non-muscle myosinheavy chain 9 gene (MYH9), as initiating factors for mostcases of ‘hypertension-attributed’ nephropathy in those withAfrican ancestry, as well as a spectrum of related kidneydiseases in AAs, Hispanic Americans (HAs), Europeansand EAs. The first development was recognition of markedfamilial aggregation of kidney disease. In AA families, clus-tering of disparate forms of ESRD was often present. Thisobservation suggested the presence of an overarching kidneyfailure susceptibility gene inherited independently from sys-temic disorders, such as hypertension, HIV infection, diabe-tes and systemic lupus erythematosus [9–13]. The seconddevelopment was a series of molecular genetic advances,particularly admixture mapping (also called mapping by ad-mixture linkage disequilibrium; MALD) [14]. MALD is apowerful genome-wide method useful to detect associatedgenes in admixed populations, where ancestral populationshave markedly different disease frequencies. AAs are anadmixed population with ~80% African and 20% Europeanancestry, while kidney disease is far more common inAfricans than Europeans. MALD detected linkage betweengenetic markers on Chromosome 22q containing the MYH9and APOL1 genes with focal segmental glomerulosclerosis(FSGS) and HIV-associated collapsing glomerulopathy inAAs [15, 16]. The third development was broad geneticscreening for MYH9 and APOL1 polymorphisms, whosevariants were strongly associated with the clearly definedFSGS phenotype, in large numbers of AAs and HAs withcommon complex forms of ESRD [1, 2, 17]. These sequen-tial developments led to the realization that FSGS,HIV-associated nephropathy, arteriolar nephrosclerosis andhypertension-attributed ESRD were members of a single dis-ease spectrum [18]. This spectrum has expanded to includesickle cell nephropathy [19] and C1q-associated collapsingglomerulopathy [20].It is now apparent that many patients with African an-cestry and ESRD attributed to diabetes or lupus had beenmisdiagnosed, they actually have APOL1-associated FSGS(with coexisting diabetes or lupus) [21, 22]. APOL1 geno-typing has been used to ‘genetically dissect’ cases withdiabetes and ESRD, enriching for those with diabeticnephropathy by removing those with two APOL1 risk var-iants likely with FSGS. This allowed for detection of dia-betic nephropathy genes [23, 24]. Variation in APOL1 isstrongly associated with the kidney disease that has histor-ically been labeled ‘hypertensive’ or arteriolar nephroscle-rosis, as in the African American Study of Kidney Diseaseand Hypertension (AASK) [25]. The strongest APOL1 as-sociation was present in AASK participants with higherbaseline proteinuria and progressive nephropathy [26].Aggressive hypertension control and universal use ofangiotensin-converting enzyme inhibitors failed to reliablyhalt nephropathy progression in AASK, strongly supportingnephropathy initiation from mechanisms other than hyper-tension. It appears that AASK patients predominantly hadfocal global glomerulosclerosis (FGGS) with interstitial and

Sickle cell trait is not independently associated with susceptibility to end-stage renal disease in African Americans

Conflicting reports exist as to whether sickle cell trait is a risk factor for the progression of nephropathy. In order to determine whether African Americans with sickle cell trait are at increased risk for kidney disease, we assessed the genetic association between sickle cell trait and end-stage renal disease (ESRD). Hemoglobin S, non-muscle myosin heavy chain 9 (MYH9), and apolipoprotein L1 (APOL1) risk variants were genotyped in 3258 unrelated African Americans: 1085 with non-diabetic ESRD, 996 with type 2 diabetes-associated ESRD, and 1177 controls. Since APOL1 is strongly associated with ESRD in African Americans, interactions between APOL1 and MYH9 risk variants and hemoglobin S were assessed using case-only and case-control centered two-way logistic regression interaction analyses. The sickle cell trait genotype frequencies were 8.7% in non-diabetic ESRD, 7.1% in type 2 diabetes-ESRD, and 7.2% in controls. There was no age-, gender-, and admixture-adjusted significance for sickle cell trait association with non-diabetic ESRD (odds ratio 1.16); type 2 diabetes-ESRD (odds ratio 1.01); or all-cause ESRD (combined non-diabetic and type 2 diabetic-ESRD patients compared to the controls; odds ratio 1.05) in dominant models. In addition, no evidence of APOL1 or MYH9 interactions with sickle cell trait was detected. Hence, sickle cell trait is not associated with diabetic or non-diabetic ESRD in a large sample of African Americans.

Genetic Association and Gene-Gene Interaction Analyses in African American Dialysis Patients With Nondiabetic Nephropathy

African Americans have increased susceptibility to nondiabetic nephropathy relative to European Americans. Follow-up of a pooled genome-wide association study (GWAS) in African American dialysis patients with nondiabetic nephropathy; novel gene-gene interaction analyses. Wake Forest sample: 962 African American nondiabetic nephropathy cases, 931 non-nephropathy controls. Replication sample: 668 Family Investigation of Nephropathy and Diabetes (FIND) African American nondiabetic nephropathy cases, 804 non-nephropathy controls. Individual genotyping of top 1,420 pooled GWAS-associated single-nucleotide polymorphisms (SNPs) and 54 SNPs in 6 nephropathy susceptibility genes. APOL1 genetic association and additional candidate susceptibility loci interacting with or independently from APOL1. The strongest GWAS associations included 2 noncoding APOL1 SNPs, rs2239785 (OR, 0.33; dominant; P = 5.9 × 10(-24)) and rs136148 (OR, 0.54; additive; P = 1.1 × 10(-7)) with replication in FIND (P = 5.0 × 10(-21) and 1.9 × 10(-05), respectively). rs2239785 remained associated significantly after controlling for the APOL1 G1 and G2 coding variants. Additional top hits included a CFH SNP (OR from meta-analysis in the 3,367 African American cases and controls, 0.81; additive; P = 6.8 × 10(-4)). The 1,420 SNPs were tested for interaction with APOL1 G1 and G2 variants. Several interactive SNPs were detected; the most significant was rs16854341 in the podocin gene (NPHS2; P = 0.0001). Nonpooled GWASs have not been performed in African American patients with nondiabetic nephropathy. This follow-up of a pooled GWAS provides additional and independent evidence that APOL1 variants contribute to nondiabetic nephropathy in African Americans and identified additional associated and interactive nondiabetic nephropathy susceptibility genes.

Target Organ Damage in African American Hypertension: Role of APOL1

Apolipoprotein L1 (APOL1) gene association studies and results of the African American Study of Kidney Disease and Hypertension are disproving the longstanding concept that mild to moderate essential hypertension contributes substantially to end-stage renal disease susceptibility in African Americans. APOL1 coding variants underlie a spectrum of kidney diseases, including that attributed to hypertension (labeled arteriolar or hypertensive nephrosclerosis), focal segmental glomerulosclerosis, and HIV-associated nephropathy. APOL1 nephropathy risk variants persist because of protection afforded from the parasite that causes African sleeping sickness. This breakthrough will lead to novel treatments for hypertensive African Americans with low-level proteinuria, for whom effective therapies are lacking. Furthermore, APOL1 nephropathy risk variants contribute to racially variable allograft survival rates after kidney transplantation and assist in detecting nondiabetic forms of nephropathy in African Americans with diabetes. Discovery of APOL1-associated nephropathy was a major success of the genetics revolution, demonstrating that secondary hypertension is typically present in nondiabetic African Americans with nephropathy.

Apolipoprotein L1 nephropathy risk variants associate with HDL subfraction concentration in African Americans

Coding variants in the apolipoprotein L1 gene (APOL1) are strongly associated with non-diabetic nephropathy in African Americans. ApoL1 proteins associate with high-density lipoprotein (HDL) particles in the circulation. Plasma HDL particle subclass concentrations were compared in 73 African Americans based on APOL1 genotypes to detect differences potentially contributing to renal disease. HDL subclass concentrations were measured using nuclear magnetic resonance spectroscopy in African American first-degree relatives of patients with non-diabetic end-stage renal disease. Participants had estimated glomerular filtration rates (GFRs) > 80 mL/min and lacked albuminuria. Additive effects of the number of APOL1 risk variants on natural logarithm-transformed HDL subclass concentrations were computed. Participants were 58.9% female with mean ± SD age 47.2 ± 13.3 years and GFR 92.4 ± 18.8 mL/min. The numbers with 2, 1 and 0 APOL1 nephropathy risk variants, respectively, were 36, 17 and 20. Mean ± SD medium-sized HDL concentrations were significantly lower for each additional APOL1 risk variant (2 versus 1 versus 0 risk variants: 9.0 ± 5.6 versus 10.1 ± 5.5 versus 13.1 ± 8.2 μmol/L, respectively; P = 0.0222 unadjusted; P = 0.0162 triglyceride- and ancestry adjusted). Lower medium-sized HDL subclass concentrations are present in African Americans based on increasing numbers of APOL1 nephropathy risk variants. Potential mechanistic roles of altered medium HDL concentrations on APOL1-associated renal microvascular diseases should be evaluated.

The APOL1 Gene and Allograft Survival after Kidney Transplantation

Coding variants in the apolipoprotein L1 gene (APOL1) are strongly associated with nephropathy in African Americans (AAs). The effect of transplanting kidneys from AA donors with two APOL1 nephropathy risk variants is unknown. APOL1 risk variants were genotyped in 106 AA deceased organ donors and graft survival assessed in 136 resultant kidney transplants. Cox-proportional hazard models tested for association between time to graft failure and donor APOL1 genotypes. The mean follow-up was 26.4 ± 21.8 months. Twenty-two of 136 transplanted kidneys (16%) were from donors with two APOL1 nephropathy risk variants. Twenty-five grafts failed; eight (32%) had two APOL1 risk variants. A multivariate model accounting for donor APOL1 genotype, overall African ancestry, expanded criteria donation, recipient age and gender, HLA mismatch, CIT and PRA revealed that graft survival was significantly shorter in donor kidneys with two APOL1 risk variants (hazard ratio [HR] 3.84; p = 0.008) and higher HLA mismatch (HR 1.52; p = 0.03), but not for overall African ancestry excluding APOL1. Kidneys from AA deceased donors harboring two APOL1 risk variants failed more rapidly after renal transplantation than those with zero or one risk variants. If replicated, APOL1 genotyping could improve the donor selection process and maximize long-term renal allograft survival.

A genome-wide association study for diabetic nephropathy genes in African Americans

A genome-wide association study was performed using the Affymetrix 6.0 chip to identify genes associated with diabetic nephropathy in African Americans. Association analysis was performed adjusting for admixture in 965 type 2 diabetic African American patients with end-stage renal disease (ESRD) and in 1029 African Americans without type 2 diabetes or kidney disease as controls. The top 724 single nucleotide polymorphisms (SNPs) with evidence of association to diabetic nephropathy were then genotyped in a replication sample of an additional 709 type 2 diabetes-ESRD patients and 690 controls. SNPs with evidence of association in both the original and replication studies were tested in additional African American cohorts consisting of 1246 patients with type 2 diabetes without kidney disease and 1216 with non-diabetic ESRD to differentiate candidate loci for type 2 diabetes-ESRD, type 2 diabetes, and/or all-cause ESRD. Twenty-five SNPs were significantly associated with type 2 diabetes-ESRD in the genome-wide association and initial replication. Although genome-wide significance with type 2 diabetes was not found for any of these 25 SNPs, several genes, including RPS12, LIMK2, and SFI1 are strong candidates for diabetic nephropathy. A combined analysis of all 2890 patients with ESRD showed significant association SNPs in LIMK2 and SFI1 suggesting that they also contribute to all-cause ESRD. Thus, our results suggest that multiple loci underlie susceptibility to kidney disease in African Americans with type 2 diabetes and some may also contribute to all-cause ESRD.

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

Mapping by admixture linkage disequilibrium (LD) detected strong association between nonmuscle myosin heavy chain 9 gene (MYH9) variants on chromosome 22 and nondiabetic nephropathy in African Americans. MYH9-related variants were posited to be the probable, but not necessarily the definitive, causal variants as a result of impressive statistical evidence of association, renal expression, and a role in autosomal dominant MYH9 disorders characterized by progressive glomerulosclerosis (Epstein and Fechtner syndromes). Dense mapping within MYH9 revealed striking LD patterns and racial variation in risk allele frequencies, suggesting population genetic factors such as selection may be operative in this region. Genovese and colleagues examined large chromosomal regions adjacent to MYH9 using genome-wide association methods and non-HapMap single nucleotide polymorphisms identified in Yoruba from the 1000 Genomes project. Statistically stronger associations were detected between two independent sequence variants in the Apolipoprotein L1 gene (APOL1) and nondiabetic nephropathy in African Americans, with odds ratios of 10.5 in idiopathic FSGS and 7.3 in hypertension-attributed ESRD. These kidney disease risk variants likely rose to high frequency in Africa because they confer resistance to trypanosomal infection and protect from African sleeping sickness. Risk variants in MYH9 and APOL1 are in strong LD, and the genetic risk that was previously attributed to MYH9 may reside, in part or in whole, in APOL1, although more complex models of risk cannot be excluded. This association likely explains racial disparities in nondiabetic nephropathy as a result of the high prevalence of risk alleles in individuals of African ancestry.

Variants in Intron 13 of the ELMO1 Gene are Associated with Diabetic Nephropathy in African Americans

Variants in the engulfment and cell motility 1 (ELMO1) gene are associated with nephropathy due to type 2 diabetes mellitus (T2DM) in a Japanese cohort. We comprehensively evaluated this gene in African American (AA) T2DM patients with end-stage renal disease (ESRD). Three hundred and nine HapMap tagging SNPs and 9 reportedly associated SNPs were genotyped in 577 AA T2DM-ESRD patients and 596 AA non-diabetic controls, plus 43 non-diabetic European American controls and 45 Yoruba Nigerian samples for admixture adjustment. Replication analyses were conducted in 558 AA with T2DM-ESRD and 564 controls without diabetes. Extension analyses included 328 AA with T2DM lacking nephropathy and 326 with non-diabetic ESRD. The original and replication analyses confirmed association with four SNPs in intron 13 (permutation p-values for combined analyses = 0.001-0.003), one in intron 1 (P = 0.004) and one in intron 5 (P = 0.002) with T2DM-associated ESRD. In a subsequent combined analysis of all 1,135 T2DM-ESRD cases and 1,160 controls, an additional 7 intron 13 SNPs produced evidence of association (P = 3.5 x 10(-5)- P = 0.05). No associations were seen with these SNPs in those with T2DM lacking nephropathy or with ESRD due to non-diabetic causes. Variants in intron 13 of the ELMO1 gene appear to confer risk for diabetic nephropathy in AA.

Functional ENTPD1 polymorphisms in African Americans with diabetes and end-stage renal disease.

OBJECTIVEThe vascular ectonucleotidase ENTPD1 protects against renal injury and modulates glucose homeostasis in mouse models. We sought to determine whether human variation in ENTPD1 influences predisposition to diabetes or diabetic nephropathy.RESEARCH DESIGN AND METHODSWe analyzed ENTPD1 single nucleotide polymorphisms (SNPs) in 363 African American control subjects, 380 subjects with type 2 diabetes and end-stage renal disease (DM-ESRD), and 326 subjects with ESRD unrelated to diabetes (non–DM-ESRD). Using human cell lines, we correlated disease-associated ENTPD1 haplotypes with ENTPD1 gene expression. Finally, we studied consequences of ENTPD1 deletion in a mouse model of type 2 diabetes (db/db).RESULTSA common ENTPD1 two-SNP haplotype was associated with increased risk for DM-ESRD (P = 0.0027), and an uncommon four-SNP haplotype was associated with protection against DM-ESRD (P = 0.004). These haplotypes correlated with ENTPD1 gene expression levels in human cell lines in vitro. Subjects with high ENTPD1-expressing haplotypes were enriched in the DM-ESRD group. By crossing ENTPD1-null mice with db mice, we show that ENTPD1 deletion has prominent effects on metabolic syndrome traits. Specifically, deletion of ENTPD1 lowered glucose levels in control (db/−) mice with one functional leptin receptor and dramatically lowered weights in db/db mice with no functional leptin receptors. Similar effects were seen in aged ENTPD1-null mice with normal leptin receptors.CONCLUSIONSENTPD1 polymorphisms appear to influence susceptibility to type 2 diabetes and/or diabetic nephropathy in African Americans. Studies in human cell lines and in vivo mouse data support a potential role for ENTPD1 genetic variation in susceptibility to type 2 diabetes.

Association of Adiponectin Gene Polymorphisms With Type 2 Diabetes in an African American Population Enriched for Nephropathy

OBJECTIVE—Polymorphisms in the adiponectin gene (ADIPOQ) have been associated with type 2 diabetes and diabetic nephropathy in type 1 diabetes, in mostly European-derived populations.RESEARCH DESIGN AND METHODS—A comprehensive association analysis of 24 single-nucleotide polymorphisms (SNPs) in the adiponectin gene was performed for type 2 diabetes and diabetic nephropathy in African Americans.RESULTS—The minor allele (A) in a single SNP in intron 1 (rs182052) was associated with diabetic nephropathy (P = 0.0015, odds ratio [OR] 1.37, CI 1.13–1.67, dominant model) in an African American sample of 851 case subjects with diabetic nephropathy and 871 nondiabetic control subjects in analyses incorporating adjustment for varying levels of racial admixture. This association remained significant after adjustment of the data for BMI, age, and sex (P = 0.0013–0.0004). We further tested this SNP for association with longstanding type 2 diabetes without nephropathy (n = 317), and evidence of association was also significant (P = 0.0054, OR 1.46, CI 1.12–1.91, dominant model) when compared with the same set of 871 nondiabetic control subjects. Combining the type 2 diabetes and diabetic nephropathy samples into a single group of case subjects (n = 1,168) resulted in the most significant evidence of association (P = 0.0003, OR 1.40, CI 1.17–1.67, dominant model). Association tests between age at onset of type 2 diabetes and the rs182052 genotypes also revealed significant association between the presence of the minor allele (A/A or A/G) and earlier onset of type 2 diabetes.CONCLUSIONS—The SNP rs182052 in intron 1 of the adiponectin gene is associated with type 2 diabetes in African Americans.