We performed a genome-wide association study of IgA nephropathy (IgAN), a major cause of kidney failure worldwide. Discovery was in 1,194 cases and 902 controls of Chinese Han ancestry, with targeted follow-up in Chinese and European cohorts comprising 1,950 cases and 1,920 controls. We identified three independent loci in the major histocompatibility complex (MHC), a common deletion of CFHR1 and CFHR3 at Chr. 1q32 and a locus at Chr. 22q12 that each surpassed genome-wide significance (p-values for association between 1.59 × 10−26 and 4.84 × 10−9 and minor allele odds ratios of 0.63–0.80). These five loci explain 4–7% of the disease variance and up to a 10-fold variation in interindividual risk. Many of the IgAN–protective alleles impart increased risk of other autoimmune or infectious diseases, and IgAN risk allele frequencies closely parallel the variation in disease prevalence among Asian, European and African populations, suggesting complex selective pressures.

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.

Individuals who are at risk for autosomal dominant polycystic kidney disease are often screened by ultrasound using diagnostic criteria derived from individuals with mutations in PKD1. Families with mutations in PKD2 typically have less severe disease, suggesting a potential need for different diagnostic criteria. In this study, 577 and 371 at-risk individuals from 58 PKD1 and 39 PKD2 families, respectively, were assessed by renal ultrasound and molecular genotyping. Using sensitivity data derived from genetically affected individuals and specificity data derived from genetically unaffected individuals, various diagnostic criteria were compared. In addition, data sets were created to simulate the PKD1 and PKD2 case mix expected in practice to evaluate the performance of diagnostic criteria for families of unknown genotype. The diagnostic criteria currently in use performed suboptimally for individuals with mutations in PKD2 as a result of reduced test sensitivity. In families of unknown genotype, the presence of three or more (unilateral or bilateral) renal cysts is sufficient for establishing the diagnosis in individuals aged 15 to 39 y, two or more cysts in each kidney is sufficient for individuals aged 40 to 59 y, and four or more cysts in each kidney is required for individuals Ն60 yr. Conversely, fewer than two renal cysts in at-risk individuals aged Ն40 yr is sufficient to exclude the disease. These unified diagnostic criteria will be useful for testing individuals who are at risk for autosomal dominant polycystic kidney disease in the usual clinical setting in which molecular genotyping is seldom performed.

Recent years have brought notable progress in the field of IgA nephropathy. Here, we highlight important new directions and latest developments, including successful discovery of several genetic susceptibility loci, formulation of the multi-hit pathogenesis model that integrates findings from studies of galactose-deficient IgA1, anti-glycan response and immune complex-induced kidney injury, introduction of the Oxford pathology scoring system, and formalization of the Kidney Disease Improving Global Outcomes (KDIGO) consensus treatment guidelines. We focus on the latest genetic findings that confirm a strong contribution of inherited factors and explain some of the geo-ethnic disparities in disease susceptibility. Most IgA nephropathy susceptibility loci discovered to date encode genes involved in the maintenance of the intestinal epithelial barrier and response to mucosal pathogens. The concerted pattern of inter-population allelic differentiation across all Genome Wide Association Studies (GWAS) loci parallels the disease prevalence and correlates with variation in local pathogens, suggesting that multi-locus adaptation might have shaped the present-day landscape of IgA nephropathy. Importantly, the “Intestinal Immune Network for IgA Production” emerged as one of the new targets for potential therapeutic intervention. We place these findings in the context of the multi-hit pathogenesis model and existing knowledge of IgA immunobiology. Lastly, we provide our perspective on the existing treatment options, discuss areas of clinical uncertainty, and outline ongoing clinical trials and translational studies.

The Oxford Classification of IgA nephropathy (IgAN) includes the following four histologic components: mesangial (M) and endocapillary (E) hypercellularity, segmental sclerosis (S) and interstitial fibrosis/tubular atrophy (T). These combine to form the MEST score and are independently associated with renal outcome. Current prediction and risk stratification in IgAN requires clinical data over 2 years of follow-up. Using modern prediction tools, we examined whether combining MEST with cross-sectional clinical data at biopsy provides earlier risk prediction in IgAN than current best methods that use 2 years of follow-up data. We used a cohort of 901 adults with IgAN from the Oxford derivation and North American validation studies and the VALIGA study followed for a median of 5.6 years to analyze the primary outcome (50% decrease in eGFR or ESRD) using Cox regression models. Covariates of clinical data at biopsy (eGFR, proteinuria, MAP) with or without MEST, and then 2-year clinical data alone (2-year average of proteinuria/MAP, eGFR at biopsy) were considered. There was significant improvement in prediction by adding MEST to clinical data at biopsy. The combination predicted the outcome as well as the 2-year clinical data alone, with comparable calibration curves. This effect did not change in subgroups treated or not with RAS blockade or immunosuppression. Thus, combining the MEST score with cross-sectional clinical data at biopsy provides earlier risk prediction in IgAN than our current best methods.

BackgroundA cyclic corticosteroid-cyclophosphamide regimen is the first-line therapy for membranous nephropathy. Compared with this regimen, rituximab therapy might have a more favorable safety profile, but a head-to-head comparison is lacking.MethodsWe randomly assigned 74 adults with membranous nephropathy and proteinuria >3.5 g/d to rituximab (1 g) on days 1 and 15, or a 6-month cyclic regimen with corticosteroids alternated with cyclophosphamide every other month. The primary outcome was complete remission of proteinuria at 12 months. Other outcomes included determination of complete or partial remission at 24 months and occurrence of adverse events.ResultsAt 12 months, six of 37 patients (16%) randomized to rituximab and 12 of 37 patients (32%) randomized to the cyclic regimen experienced complete remission (odds ratio [OR], 0.4; 95% CI, 0.13 to 1.23); 23 of 37 (62%) receiving rituximab and 27 of 37 (73%) receiving the cyclic regimen had complete or partial remission (OR, 0.61; 95% CI, 0.23 to 1.63). At 24 months, the probabilities of complete and of complete or partial remission with rituximab were 0.42 (95% CI, 0.26 to 0.62) and 0.83 (95% CI, 0.65 to 0.95), respectively, and 0.43 (95% CI, 0.28 to 0.61) and 0.82 (95% CI, 0.68 to 0.93), respectively, with the cyclic regimen. Serious adverse events occurred in 19% of patients receiving rituximab and in 14% receiving the cyclic regimen.ConclusionsThis pilot trial found no signal of more benefit or less harm associated with rituximab versus a cyclic corticosteroid-cyclophosphamide regimen in the treatment of membranous nephropathy. A head-to-head, pragmatic comparison of the cyclic regimen versus rituximab may require a global noninferiority trial.Clinical Trial registry name and registration number:Rituximab versus Steroids and Cyclophosphamide in the Treatment of Idiopathic Membranous Nephropathy (RI-CYCLO), NCT03018535

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