High-density Association Mapping and Interaction Analysis of PLA2R1 and HLA Regions with Idiopathic Membranous Nephropathy in Japanese

Membranous nephropathy: pathogenesis and treatments

Membranous nephropathy (MN), an autoimmune disease, can manifest at any age and is among the most common causes of nephrotic syndrome in adults. In 80% of cases, the specific etiology of MN remains unknown, while the remaining cases are linked to drug use or underlying conditions like systemic lupus erythematosus, hepatitis B virus, or malignancy. Although about one-third of patients may achieve spontaneous complete or partial remission with conservative management, another third face an elevated risk of disease progression, potentially leading to end-stage renal disease within 10 years. The identification of phospholipase A2 receptor as the primary target antigen in MN has brought about a significant shift in disease management and monitoring. This review explores recent advancements in the pathophysiology of MN, encompassing pathogenesis, clinical presentations, diagnostic criteria, treatment options, and prognosis, with a focus on emerging developments in pathogenesis and therapeutic strategies aimed at halting disease progression. By synthesizing the latest research findings and clinical insights, this review seeks to contribute to the ongoing efforts to enhance our understanding and management of this challenging autoimmune disorder.

Association of 10 Polymorphisms in PLA2R1 and HLA DQA1 Genes with Primary Membranous Nephropathy Risk: A Meta-Analysis and a Meta-Regression

Background

Although, several studies have assessed the association of the phospholipase A2 receptor (PLA2R) and HLA-DQA1 SNPs with primary membranous nephropathy (PMN), results were inconsistent and between-studies heterogeneity needs to be investigated.

Objectives

The aim of this review was to summarize existing data on the contribution of 10 SNPs in the PLA2R and HLA-DQA1 genes to PMN susceptibility and to investigate the between-studies heterogeneity by subgroup analyses and meta-regressions.

Design

This study was performed according to the PRISMA guidelines for systematic reviews and meta-analyses.

Data sources and methods

An electronic literature search for eligible studies among all papers published prior to January 10, 2024, was conducted through PubMed, EMBASE, Web of science and Scopus databases. Meta-analyses together with subgroup analyses and meta-regressions were performed for the 10 following SNPs: rs4664308, rs3749117, rs3749119, rs35771982, rs3828323, rs16844715, rs1511223, rs6757188, rs2715918, and rs2187668.

Results

Combined analyses revealed a significant increase in PMN risk conferred by the following alleles: rs4664308*A, rs3749117*T, rs3749119*C, rs35771982*G, rs3828323*C, rs16844715*C, rs1511223*A, rs2715918*A, and rs2187668*A, all P-values < .001. Moreover, the PLA2R-rs4664308/HLA-DQA1-rs2187668 interaction was significantly associated with an increased PMN risk, P < .001. However, there was a substantial between-studies heterogeneity for some SNPs. Subgroup analyses by ethnicity for the 9 PLA2R SNPs did not show any cross-ethnic disparity. Inversely, the risk conferred by the HLA-DQA1 rs2187668*A allele was significantly higher in Caucasians (OR [95% CI] = 3.929 [3.251-4.748]) than in Asians (OR [95% CI] = 2.537 [1.94-3.318], P = .007. Besides, meta-regressions revealed for the majority of investigated SNPs significant correlations of the effect size with albumin, 24-hours proteinuria, serum creatinine, and eGFR levels. Hence, the influence on PMN risk conferred by the PLA2R and HLA-DQA1 SNPs was rather noted in patients with a severe disease.

Conclusion

This meta-analysis showed that 9 out of the 10 investigated SNPs in PLA2R and HLA-DQA1 genes were associated with increased PMN risk. Heterogeneity could be due to disparate patient groups in terms of disease presentation for almost all SNPs, and ethnicity for the HLA-DQA1 rs2187668 SNP.

Registration

This review has been registered on PROSPERO: CRD42024506729. Available from: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42024506729.

Association between PLA2R gene polymorphism and idiopathic membranous nephropathy in Heilongjiang Chinese

Background

The aim of this study was to investigate the correlation between the phospholipase A2 receptor (PLA2R) gene polymorphism and idiopathic membranous nephropathy (IMN) in Heilongjiang Chinese.

Methods

Thirty-five patients with IMN confirmed by renal biopsy attending the Heilongjiang Hospital of Traditional Chinese Medicine between June 2021 and December of 2021 were selected as the IMN group, and a group of 25 healthy participants from the Physical Examination Center of Heilongjiang Hospital of Traditional Chinese Medicine were enrolled as healthy controls. Polymerase chain reaction (PCR) was used to identify and genotype 8 single-nucleotide polymorphism (SNP) loci (rs16844715, rs2715918, rs2715928, rs35771982, rs3749119, rs3828323, rs4665143, and rs6757188) of PLA2R and to analyze the PLA2R gene polymorphisms that correlated with IMN. SPSS 26.0 statistical software was used for data analysis, and the chi-squared (χ²) goodness-of-fit test was used to determine whether each SNP genotype and allele in the PLA2R gene complied with the Hardy-Weinberg equilibrium. The qualitative data were analyzed via χ² or Fisher exact probability method. Logistic regression was used to analyze risk factors, and the odds ratios (ORs) values and 95% confidence intervals (CIs) were calculated. α=0.05 was taken as the test level, and P<0.05 was considered statistically significant.

Results

Statistically significant differences were found in the genotype and allele frequencies of rs35771982 and rs3749119 between the IMN and control groups (P<0.05). Logistic regression analysis showed that the genotypes rs35771982 GG and rs3749119 CC were associated with IMN susceptibility. Statistically significant differences in uric acid level were found between the rs35771982 GG and CG + CC genotypes (P<0.05), while statistically significant differences in serum albumin were detected between rs3749119 CC and the CT + TT genotypes (P<0.05). Multivariate logistic regression analysis showed that gender, age, and triglyceride levels affected the occurrence of IMN (P<0.05).

Conclusions

The PLA2R gene polymorphisms rs35771982 and rs3749119 in Heilongjiang Chinese may be related to IMN susceptibility and correlated with clinical indicators of IMN. Gender, age, and triglyceride levels may influence the occurrence of IMN.

Comparative efficacy of three regimens (cyclosporine, tacrolimus, and cyclophosphamide) combined with steroids for the treatment of idiopathic membranous nephropathy

INTRODUCTION AND OBJECTIVES

To investigate the efficacy of combined immunosuppressive regimens of cyclosporine (CsA), tacrolimus (TAC), or cyclophosphamide (CTX) combined with steroids in the treatment of idiopathic membranous nephropathy (IMN).

MATERIALS AND METHODS

A total of 150 biopsy-proven IMN patients were divided into three groups: CTX, TAC, and CsA groups (50 cases each). Patients received a selected regimen for 48 weeks. The efficacy (remission rate, 24h urinary protein, and serum albumin and creatinine) and safety (adverse events) profiles of administered regimens were evaluated at 12, 24 and 48 weeks.

RESULTS

At 12 weeks, the response rates for CsA, TAC, and CTX groups were 14%, 50%, and 22%, respectively. This increased to 74%, 84%, and 82%, respectively at 48 weeks. During follow-up, 24h urinary protein significantly reduced from baseline in all regimens (P<0.05), while serum albumin increased in TAC and CTX groups after 12 weeks (P<0.05), and CsA group at 48 weeks (P<0.05). No significant changes in serum creatinine levels were noted in all three regimens (P>0.05). Safety was comparable in all groups, with lower respiratory tract infection being the most frequent adverse event.

CONCLUSIONS

The combined regimens (i.e., TAC, CsA, and CTX) are effective in the treatment of patients with IMN at 48 weeks, while TAC and CTX might be more beneficial in terms of shortened time to remission and increased complete response rate.

Revisiting immunological and clinical aspects of membranous nephropathy

Idiopathic or primary membranous nephropathy (IMN) is one of the most frequent causes of nephrotic syndrome in adults and the elderly. It is characterized by a thickening of the wall of the glomerular capillaries due to the presence of immune complex deposits. 85% of membranous nephropathy cases are classified as primary or idiopathic (IMN). The rest are of secondary origin (SMN), caused by autoimmune conditions or malignant tumors as lung cancer, colon and melanomas. It is an organ-specific autoimmune disease in which the complement system plays an important role with the formation of the membrane attack complex (MAC; C5b-9), which produces an alteration of the podocyte structure. The antigen responsible for 70-80% of IMN is a podocyte protein called M-type phospholipase A2 receptor (PLA2R). More recently, another podocyte antigen has been identified, the "Thrombospondin type-1 domain-containing 7A" (THSD7A), which is responsible for 10% of the cases of negative IMN for anti- PLA2R.

Association between HLA alleles and sub-phenotype of childhood steroid-sensitive nephrotic syndrome

BACKGROUND

Few studies have addressed the effects of human leukocyte antigen (HLA) alleles on different clinical sub-phenotypes in childhood steroid-sensitive nephrotic syndrome (SSNS), including SSNS without recurrence (SSNSWR) and steroid-dependent nephrotic syndrome/frequently relapse nephrotic syndrome (SDNS/FRNS). In this study, we investigated the relationship between HLA system and children with SSNSWR and SDNS/FRNS and clarified the value of HLA allele detection for precise typing of childhood SSNS.

METHODS

A total of 241 Chinese Han individuals with SSNS were genotyped using GenCap-WES Capture Kit, and four-digit resolution HLA alleles were imputed from available Genome Wide Association data. The distribution and carrying frequency of HLA alleles in SSNSWR and SDNS/FRNS were investigated. Additionally, logistic regression and mediating effects were used to examine the relationship between risk factors for disease process and HLA system.

RESULTS

Compared with SSNSWR, significantly decreased serum levels of complement 3 (C3) and complement 4 (C4) at onset were detected in SDNS/FRNS (C3, P < 0.001; C4, P = 0.018). The average time to remission after sufficient initial steroid treatment in SDNS/FRNS was significantly longer than that in SSNSWR (P = 0.0001). Low level of C4 was further identified as an independent risk factor for SDNS/FRNS (P = 0.008, odds ratio = 0.174, 95% confidence interval 0.048-0.630). The HLA-A*11:01 allele was independently associated with SSNSWR and SDNS/FRNS (P = 0.0012 and P = 0.0006, respectively). No significant HLA alleles were detected between SSNSWR and SDNS/FRNS. In addition, a mediating effect among HLA-I alleles (HLA-B*15:11, HLA-B*44:03 and HLA-C*07:06), C4 level and SDNS/FRNS was identified.

CONCLUSIONS

HLA-I alleles provide novel genetic markers for SSNSWR and SDNS/FRNS. HLA-I antigens may be involved in steroid dependent or frequent relapse in children with SSNS as mediators of immunoregulation.

Glomerular Kidney Diseases in the Single-Cell Era

Recent advances in single-cell technology have enabled investigation of genomic profiles and molecular crosstalk among individual cells obtained from tissues and biofluids at unprecedented resolution. Glomerular diseases, either primary or secondary to systemic diseases, often manifest elements of inflammation and of innate and adaptive immune responses. Application of single-cell methods have revealed cellular signatures of inflammation, cellular injury, and fibrosis. From these signatures, potential therapeutic targets can be inferred and in theory, this approach might facilitate identification of precision therapeutics for these diseases. Single-cell analyses of urine samples and skin lesions from patients with lupus nephritis and of urine samples from patients with diabetic nephropathy and focal segmental glomerulosclerosis have presented potential novel approaches for the diagnosis and monitoring of disease activity. These single-cell approaches, in contrast to kidney biopsy, are non-invasive and could be repeated multiple times as needed.

Associations between m-type phospholipase A2 receptor,human leukocyte antigen gene polymorphisms and idiopathic membranous nephropathy

Primary membranous nephropathy, also known as idiopathic membranous nephropathy, is an autoimmune disease. As an autoimmune disease, genetic factors are essential in the pathogenesis of IMN. People pay more and more attention to genetics and bioinformatics. With the continuous improvement and development of high-throughput gene sequencing and genotyping technology, it has been confirmed that many genes and their single nucleotide polymorphisms are strongly correlated with IMN disease susceptibility. However, there are few studies on HLA-DQA1 and PLA2R gene polymorphisms and IMN susceptibility in China. The purpose of this study was to investigate whether PLA2R rs2715928 and rs16844715 are related to IMN, the correlation between five SNP loci of PLA2R and HLA-DQA1 and IMN, and the effect of gene-gene interaction among different genotypes of each locus on disease. In this study, 86 patients with IMN confirmed by renal biopsy in the first hospital of Harbin Medical University and 90 healthy controls were selected. All subjects were excluded from secondary membranous nephropathy, pregnant or breastfeeding women, severe primary disease of vital organs, severe infection, major surgery, and severe trauma. Seven selected SNP loci were genotyped using the IMLDR multiple SNP typing kit. Chi-square test and logistic regression were used to analyze the correlation between each SNP and IMN. The general clinical data and laboratory indicators of each subject were recorded, and the relationship between different genotypes and clinical manifestations was analyzed. Among the 7 SNP loci included in the study, except HLA-DQA1 rs2187668, the other 6 loci all met Hardy-Weiberg equilibrium test (P > 0.05). The allele distribution of PLA2R rs2715928 and rs16844715 was significantly different between the IMN group and the healthy control group, and it was closely related to IMN (P < 0.05). There was no statistical difference in the distribution of alleles of rs2715918 between the IMN group and the control group (P* > 0.05), and there was also statistical difference in the distribution of alleles of rs35771982, rs3749117, and rs4664308 between the IMN group and the healthy control group (P < 0.05).The C allele of rs16844715 (OR = 2.03, 95%CI: 1.29–3.19, P* = 0.0140) and the A allele of rs2715928 (OR = 3.18, 95%CI: 1.94–5.24, P* = 3.54E-5), G allele of rs35771982 (OR = 4.07, 95%CI: 2.34–7.08, P* = 4.96E-6), T allele of rs3749117 (OR = 4.07, 95%CI: 2.34–7.08, P* = 4.96E-6), the A allele of rs4664308 (OR = 2.63, 95%CI: 1.54–4.49, P* = 0.0028) was the risk gene of IMN.Through the establishment of different genetic models, we found that,in the additive model, the three SNPs of PLA2R rs2715928 (OR = 5.40, 95%CI: 1.77–16.50, P* = 0.0217) and rs35771982 (OR = 15.15, 95%CI: 2.92–78.48, P* = 0.0084), rs3749117 (OR = 15.15, 95%CI: 2.92–78.48, P* = 0.0084) had a strong correlation with IMN. In the stealth model,homozygous gene risk type of the five SNPs,PLA2R rs16844715 (OR = 2.52, 95%CI: 1.38–4.61, P* = 0.0189) and rs2715928 (OR = 4.30, 95%CI: 2.31–8.03, P* = 3.14E-5), rs35771982 (OR = 4.85, 95%CI: 5.53–9.31, P* = 1.42E-5), rs3749117 (OR = 4.85, 95%CI: 5.53–9.31, P* = 1.42E-5) and rs4664308 (OR = 3.16, 95%CI: 1.67–5.97, P* = 0.0028) had a strong correlation with IMN. The distribution of GT haplotypes and CC haplotypes of rs35771982 and rs3749117 and CA haplotypes and TG haplotypes of rs16844715 and rs4664308 were significantly different between IMN group and control group (P < 0.05). When GMDR software was used to establish a model to analyze the interaction between various SNP sites, it was found that the combination of GG genotype at rs35771982 and AA genotype at rs2715928 was the highest risk of disease. The risk genotypes of rs16844715, rs2715928 and rs4664308 had no effect on the clinical manifestations of IMN (P > 0.05). PLA2R rs2715928 and rs16844715 are associated with susceptibility to IMN. The C allele of rs16844715, the A allele of rs2715928, the G allele of rs35771982, the T allele of rs3749117, and the A allele of rs4664308 are the dangerous genes of IMN. The combination of GG genotype at rs35771982 and AA genotype at rs2715928 poses the greatest risk of disease. Haplotype may affect susceptibility to IMN. The risk genotype had no effect on the clinical manifestations of IMN.

Autoimmune-mediated renal disease and hypertension

Hypertension is a major risk factor for cardiovascular disease, chronic kidney disease (CKD), and mortality. Troublingly, hypertension is highly prevalent in patients with autoimmune renal disease and hastens renal functional decline. Although progress has been made over the past two decades in understanding the inflammatory contributions to essential hypertension more broadly, the mechanisms active in autoimmune-mediated renal diseases remain grossly understudied. This Review provides an overview of the pathogenesis of each of the major autoimmune diseases affecting the kidney that are associated with hypertension, and describes the current state of knowledge regarding hypertension in these diseases and their management. Specifically, discussion focuses on Systemic Lupus Erythematosus (SLE) and Lupus Nephritis (LN), Immunoglobulin A (IgA) Nephropathy, Idiopathic Membranous Nephropathy (IMN), Anti-Neutrophil Cytoplasmic Antibody (ANCA)-associated glomerulonephritis, and Thrombotic Thrombocytopenic Purpura (TTP). A summary of disease-specific animal models found to exhibit hypertension is also included to highlight opportunities for much needed further investigation of underlying mechanisms and novel therapeutic approaches.

HLA Alleles and Prognosis of PLA2R-Related Membranous Nephropathy

BACKGROUND AND OBJECTIVES

Associations between HLA alleles and susceptibility to M-type phospholipase A2 receptor (PLA2R)-related membranous nephropathy have been well defined previously in Chinese patients. However, the relationships between HLA alleles and kidney outcome remain unclear.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Five HLA genes (DRB1, DQA1, DQB1, DRB3, and DRB5) were genotyped in a prospective cohort of 392 patients with PLA2R-related membranous nephropathy. The associations between HLA alleles and kidney outcomes were studied.

RESULTS

A total of 79 HLA alleles were identified in this study. Four HLA alleles, DRB1*13:01 (n=12; hazard ratio, 3.7; 95% confidence interval, 1.8 to 7.8; P<0.001), DQB1*06:03 (n=12; hazard ratio, 3.7; 95% confidence interval, 1.8 to 7.8; P<0.001), DRB1*04:05 (n=12; hazard ratio, 3.8; 95% confidence interval, 1.5 to 9.5; P=0.004), and DQB1*03:02 (n=21; hazard ratio, 3.1; 95% confidence interval, 1.4 to 6.7; P=0.005), were associated with a ≥40% eGFR decline during follow-up. DRB1*13:01 and DQB1*06:03 were tightly linked with each other. Forty-four of the 392 patients (11%) carried at least one of the four identified risk HLA alleles in this study. Compared with patients who were negative for all risk HLA alleles, those carrying at least one risk HLA allele had a significant risk of a ≥40% eGFR decline during follow-up (hazard ratio, 3.9; 95% confidence interval, 2.3 to 6.7; P<0.001). After adjusting for age, sex, proteinuria, albumin, eGFR, and anti-PLA2R antibody levels, multivariable Cox analysis showed that patients carrying any of the four risk HLA alleles remained associated with a higher risk of a ≥40% decline in eGFR (hazard ratio, 4.1; 95% confidence interval, 2.3 to 7.1; P<0.001).

CONCLUSIONS

Carrying any of the HLA alleles, DRB1*13:01/DQB1*06:03, DRB1*04:05, and DQB1*03:02, was independently associated with poor prognosis in Chinese patients with PLA2R-related membranous nephropathy.

PLA2R1 and HLA-DQA1 gene variations in idiopathic membranous nephropathy in South China

INTRODUCTION

Associations of variations in PLA2R1 and HLA-DQA1 genes with susceptibility to idiopathic membranous nephropathy (IMN) have been well documented. Association with spontaneous remission, however, is poorly defined in the Chinese Han population.

METHODS

A Chinese cohort of 117 IMN patients and 138 healthy controls were recruited between July 2009 and November 2019. Case-control studies for single-nucleotide polymorphisms (SNPs) within HLA-DQA1 (rs2187668) and PLA2R1 (rs35771982, rs4664308, rs3749117, rs3749119) genes were performed. The contributions of these polymorphisms to predict susceptibility, titre of autoantibodies against the M-type phospholipase A2 receptor (anti-PLA2R1), glomerular PLA2R1 expression, and spontaneous remission were analysed.

RESULTS

We found that variations in PLA2R1 (SNPs rs35771982, rs4664308, rs3749117) were strongly associated with IMN susceptibility, while SNP (rs2187668) within HLA-DQA1 did not increase the risk of IMN. All SNPs in PLA2R1 and HLA-DQA1 were not statistically associated with anti-PLA2R1 titre, glomerular PLA2R1 expression and spontaneous remission after Bonferroni correction (P>0.0167). Clinical and pathological parameters such as lower levels of serum albumin, higher levels of anti-PLA2R1 and glomerular PLA2R1 expression were independent risk factors for non-spontaneous remission.

CONCLUSION

This study confirms that variations in PLA2R1 (SNPs rs35771982, rs4664308, rs3749117) are risk factors for IMN. We found excellent association of serum albumin level, anti-PLA2R1 titre and glomerular PLA2R1 positivity with non-spontaneous remission in IMN.

Th17-Immune Response in Patients With Membranous Nephropathy Is Associated With Thrombosis and Relapses

Membranous nephropathy (MN) is a rare autoimmune kidney disease. Most autoimmune diseases are associated with a pro-inflammatory Th17-immune response, but little is known about immune dysregulation in MN. In China, MN was associated with exposure to fine air particulate matter (PM_2.5) that could act as a danger signal and redirect immune response toward the Th2 or Th17 pathway. We aimed to analyze the cytokine profile of MN patients and to study the possible environmental factors involved in this immune reorientation, as well as the consequences on the prognosis of the disease. In this prospective study, 59 MN patients filled a comprehensive lifestyle questionnaire. Peripheral blood cells from MN patients were stimulated in vitro to measure the cytokines produced in supernatant. Cytokine profiles of MN patients were compared to 28 healthy donors and analyzed regarding individual PM_2.5 exposure. Compared to healthy donors, MN patients had higher serum levels of Th17 and Th2 cytokines IL-17A (62 pg/ml [IQR, 16–160] versus 31 [IQR, 13–51], P=0.035), IL-6 (66767 pg/ml [IQR, 36860–120978] versus 27979 [IQR, 18672–51499], P=0.001), and IL-4 (12 pg/ml [IQR, 0–33] versus 0 pg/ml [IQR, 0–0], P=0.0003), respectively, as well as a deficiency of Th1 and regulatory T cell cytokines IFN-γ (5320 pg/ml [IQR, 501–14325] versus 18037 [IQR, 4889–31329], P=0.0005) and IL-10 (778 pg/ml [IQR, 340–1247] versus 1102 [IQR, 737–1652], P=0.04), respectively. MN patients with high IL-17A levels lived in areas highly exposed to PM_2.5: 51 μg/m³ versus 31 μg/m³ for patients with low IL-17A levels (P=0.002) while the World Health Organization recommends an exposition below 10 μg/m³. MN patients with Th17-mediated inflammation had more venous thromboembolic events (P=0.03) and relapsed more often (P=0.0006). Rituximab treatment induced Th1 and regulatory T cell cytokines but did not impact Th17 cytokines. MN patients with Th17-mediated inflammation which appears to be related to an urban environment have worse prognosis. Alternative strategies targeting dysregulated cytokine balance could be considered for these patients at high risk of relapse.

Advances in Pathogenesis of Idiopathic Membranous Nephropathy

BACKGROUND

Membranous nephropathy (MN), a major cause of nephrotic syndrome, has attracted people's attention in recent years for its growing prevalence. It is the second or third leading cause of ESRD in patients with primary glomerulonephritis and is the leading glomerulopathy that recurs after kidney transplantation.

SUMMARY

MN can be classified as idiopathic membranous nephropathy (IMN) and secondary MN. The discovery of the M-type phospholipase A2 receptor (PLA2R) and thrombospondin type-1 domain-containing 7A (THSD7A) provides the new diagnostic methods and treatment strategies for IMN on the molecular level. The study on single nucleotide polymorphism of IMN genes, such as the single M-type phospholipase A2 receptor 1 (PLA2R1) gene and human leukocyte antigen (HLA) gene, explains the pathogenesis of the disease from the perspective of genetics and conforms to the trend of the era of precision medicine.

KEY MESSAGES

This review focuses on advances in the pathogenesis of IMN, including molecular and genetic pathogenesis, as well as discussing the diagnostic and treatment guiding value brought by these new discoveries.

Single-nucleotide polymorphism rs4664308 in PLA2R1 gene is associated with the risk of idiopathic membranous nephropathy: a meta-analysis

Although many studies investigated the associations between single-nucleotide polymorphisms (SNPs) in the M-type phospholipase A2 receptor-1 (PLA2R1) gene and susceptibility to idiopathic membranous nephropathy (IMN), some showed inconsistent results. Here, we conducted a meta-analysis examining the associations between PLA2R1 SNPs and IMN susceptibility after systematic searches in the PubMed and Web of Science databases. Our meta-analysis for rs4664308 A>G including 2,542 IMN patients and 4,396 controls in seven studies showed a significant association between the G allele and a lower risk of IMN, as determined using an allelic model (odds ratio, 0.45; 95% confidence interval [0.41–0.50]), an additive model (for GG vs. AA: 0.26; [0.21–0.33]; for AG vs. AA: 0.40; [0.36–0.45]), a dominant model (0.37; [0.34–0.42]) and a recessive model (0.38; [0.31–0.48]). Our meta-analysis also suggested associations between rs3828323, rs35771982, rs3749117 and rs3749119 and IMN susceptibility although high heterogeneities and/or publication biases were observed. We did not study in our meta-analysis, but other studies indicated that high-risk genotype combinations of rs2187668 in the human leucocyte antigen-DQ a-chain 1 gene and rs4664308 in the PLA2R1 gene had even stronger associations and could affect the formation of anti-PLA2R1 antibodies, suggesting these SNPs could be novel therapeutic targets.

Identical twins with idiopathic membranous nephropathy

The pathogenesis of idiopathic membranous nephropathy is associated with autoantibodies, most often against the phospholipase A2 receptor (PLA2R) and with genetic factors, especially those involving human leukocyte antigen (HLA) genes. Idiopathic membranous nephropathy is not a typical inherited Mendelian disorder. Reports of idiopathic membranous nephropathy in twins are rare. Herein, we report on two twin sisters diagnosed with PLA2R-associated idiopathic membranous nephropathy. We identified the HLA-DRB1*0301, HLA-DRB1*1501, and HLA-DQB1*0602 alleles in the twin sisters, which were reported as independent risk alleles for idiopathic membranous nephropathy in the Asian population. This case report provides novel evidence for the role of predisposing HLA alleles in the pathogenesis of idiopathic membranous nephropathy.

Single-Nucleotide Polymorphisms (SNPs) Both Associated with Hypertension and Contributing to Accelerated-Senescence Traits in OXYS Rats

Aging is a major risk factor of numerous human diseases. Adverse genetic variants may contribute to multiple manifestations of aging and increase the number of comorbid conditions. There is evidence of links between hypertension and age-related diseases, although the genetic relationships are insufficiently studied. Here, we investigated the contribution of hypertension to the development of accelerated-senescence syndrome in OXYS rats. We compared transcriptome sequences of the prefrontal cortex, hippocampus, and retina of OXYS rats with the genotypes of 45 rat strains and substrains (which include models with hypertension) to find single-nucleotide polymorphisms (SNPs) both associated with hypertension and possibly contributing to the development of age-related diseases. A total of 725 polymorphisms were common between OXYS rats and one or more hypertensive rat strains/substrains being analyzed. Multidimensional scaling detected significant similarities between OXYS and ISIAH rat genotypes and significant differences between these strains and the other hypertensive rat strains/substrains. Nonetheless, similar sets of SNPs produce a different phenotype in OXYS and ISIAH rats depending on hypertension severity. We identified 13 SNPs causing nonsynonymous amino-acid substitutions having a deleterious effect on the structure or function of the corresponding proteins and four SNPs leading to functionally significant structural rearrangements of transcripts in OXYS rats. Among them, SNPs in genes Ephx1, Pla2r1, and Ccdc28b were identified as candidates responsible for the concomitant manifestation of hypertension and signs of accelerated aging in OXYS rats.

Molecular Pathogenesis of Membranous Nephropathy

Membranous nephropathy is a noninflammatory autoimmune disease of the kidney glomerulus, characterized by the formation of immune deposits, complement-mediated proteinuria, and risk of renal failure. Considerable advances in understanding the molecular pathogenesis have occurred with the identification of several antigens [neutral endopeptidase, phospholipase A2 receptor (PLA₂R), thrombospondin domain-containing 7A (THSD7A)] in cases arising from the neonatal period to adulthood and the characterization of antibody-binding domains (that is, epitopes). Immunization against PLA2R occurs in 70% to 80% of adult cases. The development of highly specific and sensitive assays of circulating antibodies has induced a paradigm shift in diagnosis and treatment monitoring. In addition, several interacting loci in HLA-DQ, HLA-DR, and PLA2R1, as well as classical human leukocyte antigen (HLA)-D alleles have been identified as being risk factors, depending on a patient's ethnicity. Additionally, mechanisms of antibody pathogenicity and pathways of complement activation are now better understood. Further research is mandatory for designing new therapeutic strategies, including the identifying triggering events, the molecular bases of remission and progression, and the T cell epitopes involved.

Clinicopathological characteristics of thrombospondin type 1 domain-containing 7A-associated membranous nephropathy

Thrombospondin type 1 domain-containing 7A (THSD7A) is a recently identified target antigen of idiopathic membranous nephropathy (iMN). The clinicopathological characteristics of THSD7A-associated MN are poorly characterised due to low prevalence among MN patients. Among 469 consecutive cases of pathologically confirmed MN diagnosed at four centres in Japan, 14 cases were confirmed positive for THSD7A by immunohistochemistry (3.0%). The prevalence of THSD7A-associated MN tended to be higher in northern Japan. Most cases demonstrated nephrotic-range proteinuria (12/14 cases, 86%). In two patients, cancer was detected at the time of renal biopsy (small-cell carcinoma of the lung and prostatic adenocarcinoma with neuroendocrine differentiation). Both tumours were negative for THSD7A. Four patients had concurrent or previous incidence of allergic diseases, including one patient with Kimura’s disease. Pathological analysis of kidney biopsy tissue revealed slight mesangial cell proliferation in three cases and spike formation in one case. Immunofluorescence studies demonstrated that IgG subclass was mainly IgG4-dominant/codominant (12/13, 92% cases), while the case with prostatic cancer had an IgG2-dominant distribution. The immunostaining profile for components of the lectin complement pathways was not significant in three cases including two patients with malignancy. One case was dual positive for THSD7A and PLA2R. Of 10 cases with known clinical follow-up data, 6 demonstrated reduced serum creatinine and 8 presented reduced proteinuria. In summary, although the major IgG phenotype was usually IgG4-dominant/codominant, clinical background was otherwise heterogeneous. Further investigation of regional differences in THSD7A-associated MN prevalence may reveal genetic and environmental risk factor and associated pathogenic mechanisms.

Identification of a two-SNP PLA2R1 Haplotype and HLA-DRB1 Alleles as Primary Risk Associations in Idiopathic Membranous Nephropathy

The associations of single nucleotide polymorphisms (SNPs) in PLA2R1 and HLA-DQA1, as well as HLA-DRB1*15:01-DQB1*06:02 haplotype with idiopathic membranous nephropathy (IMN) is well known. However, the primary associations of these loci still need to be determined. We used Japanese-specific SNP genotyping array and imputation using 2,048 sequenced Japanese samples to fine-map PLA2R1 region in 98 patients and 413 controls. The most significant SNPs were replicated in a separate sample set of 130 patients and 288 controls. A two-SNP haplotype of intronic and missense SNPs showed the strongest association. The intronic SNP is strongly associated with PLA2R1 expression in the Genotype-Tissue Expression (GTEx) database, and the missense SNP is predicted to alter peptide binding with HLA-DRB1*15:01 by the Immune Epitope Database (IEDB). In HLA region, we performed relative predispositional effect (RPE) tests and identified additional risk alleles in both HLA-DRB1 and HLA-DQB1. We collapsed the risk alleles in each of HLA-DRB1 and HLA-DQB1 into single risk alleles. Reciprocal conditioning of these collapsed risk alleles showed more residual significance for HLA-DRB1 collapsed risk than HLA-DQB1 collapsed risk. These results indicate that changes in the expression levels of structurally different PLA2R protein confer risk for IMN in the presence of risk HLA-DRB1 alleles.

Genetics of membranous nephropathy

An HLA-DR3 association with membranous nephropathy (MN) was described in 1979 and additional evidence for a genetic component to MN was suggested in 1984 in reports of familial MN. In 2009, a pathogenic autoantibody was identified against the phospholipase A2 receptor 1 (PLA2R1). Here we discuss the genetic studies that have proven the association of human leucocyte antigen class II and PLA2R1 variants and disease in MN. The common variants in PLA2R1 form a haplotype that is associated with disease incidence. The combination of the variants in both genes significantly increases the risk of disease by 78.5-fold. There are important genetic ethnic differences in MN. Disease outcome is difficult to predict and attempts to correlate the genetic association to outcome have so far not been helpful in a reproducible manner. The role of genetic variants may not only extend beyond the risk of disease development, but can also help us understand the underlying molecular biology of the PLA2R1 and its resultant pathogenicity. The genetic variants identified thus far have an association with disease and could therefore become useful biomarkers to stratify disease risk, as well as possibly identifying novel drug targets in the near future.

Strong Association of the HLA-DR/DQ Locus with Childhood Steroid-Sensitive Nephrotic Syndrome in the Japanese Population

Background Nephrotic syndrome is the most common cause of chronic glomerular disease in children. Most of these patients develop steroid-sensitive nephrotic syndrome (SSNS), but the loci conferring susceptibility to childhood SSNS are mainly unknown.Methods We conducted a genome-wide association study (GWAS) in the Japanese population; 224 patients with childhood SSNS and 419 adult healthy controls were genotyped using the Affymetrix Japonica Array in the discovery stage. Imputation for six HLA genes (HLA-A, -C, -B, -DRB1, -DQB1, and -DPB1) was conducted on the basis of Japanese-specific references. We performed genotyping for HLA-DRB1/-DQB1 using a sequence-specific oligonucleotide-probing method on a Luminex platform. Whole-genome imputation was conducted using a phased reference panel of 2049 healthy Japanese individuals. Replication was performed in an independent Japanese sample set including 216 patients and 719 healthy controls. We genotyped candidate single-nucleotide polymorphisms using the DigiTag2 assay.Results The most significant association was detected in the HLA-DR/DQ region and replicated (rs4642516 [minor allele G], combined P_allelic=7.84×10^-23; odds ratio [OR], 0.33; 95% confidence interval [95% CI], 0.26 to 0.41; rs3134996 [minor allele A], combined P_allelic=1.72×10^-25; OR, 0.29; 95% CI, 0.23 to 0.37). HLA-DRB1*08:02 (Pc=1.82×10^-9; OR, 2.62; 95% CI, 1.94 to 3.54) and HLA-DQB1*06:04 (Pc=2.09×10^-12; OR, 0.10; 95% CI, 0.05 to 0.21) were considered primary HLA alleles associated with childhood SSNS. HLA-DRB1*08:02-DQB1*03:02 (Pc=7.01×10^-11; OR, 3.60; 95% CI, 2.46 to 5.29) was identified as the most significant genetic susceptibility factor.Conclusions The most significant association with childhood SSNS was detected in the HLA-DR/DQ region. Further HLA allele/haplotype analyses should enhance our understanding of molecular mechanisms underlying SSNS.

The Genetic and Environmental Factors of Primary Membranous Nephropathy: An Overview from China

Background

Primary membranous nephropathy (pMN) is the most common cause of nephrotic syndrome in adults. The discovery of the 2 autoantigens, M-type phospholipase A2 receptor (PLA2R) and thrombospondin type-1 domain-containing 7A (THSD7A), has defined pMN as an autoimmune disease. A remarkable increase in the frequency of pMN in primary glomerular disease was witnessed in China. The genetic and environmental contributors to disease susceptibility have been investigated in these patients.

Summary

We reviewed recent publications in genetic and environmental studies of pMN, focusing mainly on those undertaken in China. Following a genome-wide association study, the gene-gene interaction between the 2 most significant risk factors, PLA2R1 and DQA1, was validated in Chinese patients with MN. Fine mapping on human leukocyte antigen (HLA) locus found that DRB1*1501 and DRB1*0301 were risk alleles. Three amino acid residues on positions 13 and 71 of HLA-DRβ1 chain may confer the susceptibility to pMN by presenting T-cell epitopes on PLA2R. Another study found that DRB3*0202 was the most likely culprit allele for the signal at DRB1*0301. One environmental risk factor for pMN has been identified as the long-term exposure to high levels of PM_2.5 in Chinese patients with MN. Each 10 μg/m³ increase in PM_2.5 concentration was associated with 14% higher odds for pMN in the regions with PM_2.5 above 70 μg/m³.

Key Message

A gene-environment interaction is suspected as an underlying mechanism for the increasing trend of pMN in China.

Recent Progress in Deciphering the Etiopathogenesis of Primary Membranous Nephropathy

Primary membranous nephropathy (MN) is the leading cause of nephrotic syndrome in adults. Discovery of several antibodies has contributed to an increased understanding of MN. Antibodies against the M-type phospholipase A2 receptor (PLA2R) are present in 50-100% with primary MN and are associated with a lower frequency of spontaneous remission. High levels are linked with a higher probability of treatment resistance, higher proteinuria, and impaired renal function, as well as a more rapid decline of kidney function during follow-up. Immunologic remission precedes reduction of proteinuria by months. Pretransplant evaluation of PLA2R antibodies is warranted to predict recurrence of disease following renal transplantation. Several risk alleles related to the PLA2R1 gene and within the HLA loci have been identified, whereas epitope spreading of PLA2R may predict treatment response. More recently, thrombospondin type 1 domain-containing 7A (THSD7A) antibodies have been discovered in primary MN. Several other rare antigens have been described, including antibodies against neutral endopeptidase as a cause of antenatal MN and circulating cationic bovine serum albumin as an antigen with implications in childhood MN. This review focuses on the progress with a special focus on diagnostic accuracy, predictive value, and treatment implications of the established and proposed antigens.

PLA2R and THSD7A: Disparate Paths to the Same Disease?

The phospholipase A2 receptor (PLA2R) and thrombospondin type-1 domain-containing 7A (THSD7A) are the two major autoantigens in primary membranous nephropathy (MN), and define two molecular subclasses of this disease. Both proteins are large transmembrane glycoproteins expressed by the podocyte, and both induce IgG4-predominant humoral immune responses that produce circulating autoantibodies that can be used clinically for diagnostic and monitoring purposes. The biologic roles of these proteins remain speculative, although several features of THSD7A suggest a role in adhesion. PLA2R-associated MN was initially found to associate with risk alleles within HLA-DQA1, but subsequent studies have shifted the focus to the HLA-DRB locus. Three distinct humoral epitope-containing regions have been defined within the extracellular portion of PLA2R, and it appears that the number of targeted epitopes may determine disease severity. Although similar information is not yet available for THSD7A-associated MN, this form of MN may have a unique association with malignancy. Finally, it appears likely that other autoantigens in primary MN exist. Although protocols similar to those that identified PLA2R and THSD7A may be successful in the identification of novel antigenic targets in MN, newer techniques such as laser-capture mass spectrometry or protein arrays may be helpful as well.