We performed a genome-wide association study (GWAS) of IgA nephropathy (IgAN), the most common form of glomerulonephritis, with discovery and follow-up in 20,612 individuals of European and East Asian ancestry. We identified six novel genome-wide significant associations, four in ITGAM-ITGAX, VAV3 and CARD9 and two new independent signals at HLA-DQB1 and DEFA. We replicated the nine previously reported signals, including known SNPs in the HLA-DQB1 and DEFA loci. The cumulative burden of risk alleles is strongly associated with age at disease onset. Most loci are either directly associated with risk of inflammatory bowel disease (IBD) or maintenance of the intestinal epithelial barrier and response to mucosal pathogens. The geo-spatial distribution of risk alleles is highly suggestive of multi-locus adaptation and the genetic risk correlates strongly with variation in local pathogens, particularly helminth diversity, suggesting a possible role for host-intestinal pathogen interactions in shaping the genetic landscape of IgAN.

Reduced glomerular filtration rate defines chronic kidney disease and is associated with cardiovascular and all-cause mortality. We conducted a meta-analysis of genome-wide association studies for estimated glomerular filtration rate (eGFR), combining data across 133,413 individuals with replication in up to 42,166 individuals. We identify 24 new and confirm 29 previously identified loci. Of these 53 loci, nineteen associate with eGFR among individuals with diabetes. Using bioinformatics, we show that identified genes at eGFR loci are enriched for expression in kidney tissues and in pathways relevant for kidney development and transmembrane transporter activity, kidney structure, and regulation of glucose metabolism. Chromatin state mapping and DNase I hypersensitivity analyses across adult tissues demonstrate preferential mapping of associated variants to regulatory regions in kidney but not extra-renal tissues. These findings suggest that genetic determinants of eGFR are mediated largely through direct effects within the kidney and highlight important cell types and biologic pathways.

Limited data are available on the independent associations of estimated glomerular filtration rate (eGFR) and albuminuria with mortality and end stage renal disease (ESRD) among individuals with chronic kidney disease (CKD). We conducted a collaborative meta-analysis of 21,688 participants selected for CKD from 13 cohorts. After adjustment for potential confounders and albuminuria, a 15 mL/min/1.73 m2 lower eGFR below 45 mL/min/1.73 m2 was significantly associated with mortality (pooled hazard ratio [HR] 1.47 [95% CI: 1.22–1.79]), and ESRD (pooled HR 6.24 [95% CI: 4.84–8.05]). There was significant heterogeneity between studies for both HR estimates. After adjustment for risk factors and eGFR, an eight-fold higher albumin:creatinine ratio (ACR) or protein:creatinine ratio (PCR) was significantly associated with mortality (pooled HR 1.40 [95% CI: 1.27–1.55]), without evidence of significant heterogeneity. An eight-fold higher ACR or PCR was also strongly associated with ESRD (pooled HR 3.04 [95% CI: 2.27–4.08]), with significant heterogeneity between HR estimates. Lower eGFR and more severe albuminuria independently predict mortality and ESRD among individuals selected for CKD. The associations are stronger for ESRD than for mortality. The observed associations are consistent with CKD classification based on eGFR stages, and suggest that albuminuria provides additional prognostic information among individuals with CKD.

IgA nephropathy (IgAN), major cause of kidney failure worldwide, is common in Asians, moderately prevalent in Europeans, and rare in Africans. It is not known if these differences represent variation in genes, environment, or ascertainment. In a recent GWAS, we localized five IgAN susceptibility loci on Chr.6p21 (HLA-DQB1/DRB1, PSMB9/TAP1, and DPA1/DPB2 loci), Chr.1q32 (CFHR3/R1 locus), and Chr.22q12 (HORMAD2 locus). These IgAN loci are associated with risk of other immune-mediated disorders such as type I diabetes, multiple sclerosis, or inflammatory bowel disease. We tested association of these loci in eight new independent cohorts of Asian, European, and African-American ancestry (N = 4,789), followed by meta-analysis with risk-score modeling in 12 cohorts (N = 10,755) and geospatial analysis in 85 world populations. Four susceptibility loci robustly replicated and all five loci were genome-wide significant in the combined cohort (P = 5×10−32–3×10−10), with heterogeneity detected only at the PSMB9/TAP1 locus (I2 = 0.60). Conditional analyses identified two new independent risk alleles within the HLA-DQB1/DRB1 locus, defining multiple risk and protective haplotypes within this interval. We also detected a significant genetic interaction, whereby the odds ratio for the HORMAD2 protective allele was reversed in homozygotes for a CFHR3/R1 deletion (P = 2.5×10−4). A seven–SNP genetic risk score, which explained 4.7% of overall IgAN risk, increased sharply with Eastward and Northward distance from Africa (r = 0.30, P = 3×10−128). This model paralleled the known East–West gradient in disease risk. Moreover, the prediction of a South–North axis was confirmed by registry data showing that the prevalence of IgAN–attributable kidney failure is increased in Northern Europe, similar to multiple sclerosis and type I diabetes. Variation at IgAN susceptibility loci correlates with differences in disease prevalence among world populations. These findings inform genetic, biological, and epidemiological investigations of IgAN and permit cross-comparison with other complex traits that share genetic risk loci and geographic patterns with IgAN.

Despite a large sample and a long follow-up, we found no increased risk of cognitive decline or dementia associated with low eGFR level. However, faster eGFR decline was associated with global cognitive decline and incident dementia with vascular component, suggesting that this association may be mediated by vascular mechanisms.

Chronic kidney disease, even at moderate stages, is characterized by a high incidence of cardiovascular events. Subclinical damage to large arteries, such as increased arterial stiffness and outward remodeling, is a classical hallmark of patients with chronic kidney disease. Whether large artery stiffness and remodeling influence the occurrence of cardiovascular events and the mortality of patients with chronic kidney disease (stages 2–5) is still debated. This prospective study included 439 patients with chronic kidney disease (mean age, 59.8±14.5 years) with a mean measured glomerular filtration rate of 37 mL/min per 1.73 m 2 . Baseline aortic stiffness was estimated through carotid-femoral pulse wave velocity measurements; carotid stiffness, diameter, and intima-media thickness were measured with a high-resolution echotracking system. For the overall group of patients, the 5-year estimated survival and cumulative incidence of cardiovascular events were 87% and 16%, respectively. In regression analyses adjusted on classical cardiovascular and renal risk factors, aortic stiffness remained significantly associated with all-cause mortality (for 1 SD, Cox model–derived relative risk [95% CI], 1.48 [1.09–2.02]) and with fatal and nonfatal cardiovascular events (for 1 SD, Fine and Gray competing risks model–derived relative risk [95% CI], 1.35 [1.05–1.75]). Net reclassification improvement index was significant (29.0% [2.3–42.0%]). Carotid internal diameter was also independently associated with all-cause mortality. This study shows that increased aortic stiffness and carotid internal diameter are independent predictors of mortality in patients with stages 2 to 5 chronic kidney disease and that aortic stiffness improves the prediction of the risk.

Background: There is strong biologic plausibility to support change in albuminuria as a surrogate endpoint for progression of chronic kidney disease (CKD), but empirical evidence to supports its validity in epidemiologic studies is lacking. Methods: We analyzed 28 cohorts including 693,816 individuals (80% with diabetes) and 7,461 end-stage kidney disease (ESKD) events, defined as initiation of kidney replacement therapy. Percent change in albuminuria was quantified during a baseline period of 1, 2 and 3 years using linear regression. Associations with subsequent ESKD were quantified using Cox regression in Coresh et al.

Elevated concentrations of albumin in the urine, albuminuria, are a hallmark of diabetic kidney disease and are associated with an increased risk for end-stage renal disease and cardiovascular events. To gain insight into the pathophysiological mechanisms underlying albuminuria, we conducted meta-analyses of genome-wide association studies and independent replication in up to 5,825 individuals of European ancestry with diabetes and up to 46,061 without diabetes, followed by functional studies. Known associations of variants in CUBN, encoding cubilin, with the urinary albumin-to-creatinine ratio (UACR) were confirmed in the overall sample (P = 2.4 × 10−10). Gene-by-diabetes interactions were detected and confirmed for variants in HS6ST1 and near RAB38/CTSC. Single nucleotide polymorphisms at these loci demonstrated a genetic effect on UACR in individuals with but not without diabetes. The change in the average UACR per minor allele was 21% for HS6ST1 (P = 6.3 × 10–7) and 13% for RAB38/CTSC (P = 5.8 × 10−7). Experiments using streptozotocin-induced diabetic Rab38 knockout and control rats showed higher urinary albumin concentrations and reduced amounts of megalin and cubilin at the proximal tubule cell surface in Rab38 knockout versus control rats. Relative expression of RAB38 was higher in tubuli of patients with diabetic kidney disease compared with control subjects. The loci identified here confirm known pathways and highlight novel pathways influencing albuminuria.