Novel insights in the genetics of steroid-sensitive nephrotic syndrome in childhood

A genomic association study revealing subphenotypes of childhood steroid-sensitive nephrotic syndrome in a larger genomic sequencing cohort

Dissecting the genetic components that contribute to the two main subphenotypes of steroid-sensitive nephrotic syndrome (SSNS) using genome-wide association studies (GWAS) strategy is important for understanding the disease. We conducted a multicenter cohort study (360 patients and 1835 controls) combined with a GWAS strategy to identify susceptibility variants associated with the following two subphenotypes of SSNS: steroid-sensitive nephrotic syndrome without relapse (SSNSWR, 181 patients) and steroid-dependent/frequent relapse nephrotic syndrome (SDNS/FRNS, 179 patients). The distribution of two single-nucleotide polymorphisms (SNPs) in ANKRD36 and ALPG was significant between SSNSWR and healthy controls, and that of two SNPs in GAD1 and HLA-DQA1 was significant between SDNS/FRNS and healthy controls. Interestingly, rs1047989 in HLA-DQA1 was a candidate locus for SDNS/FRNS but not for SSNSWR. No significant SNPs were observed between SSNSWR and SDNS/FRNS. Meanwhile, chromosome 2:171713702 in GAD1 was associated with a greater steroid dose (>0.75 mg/kg/d) upon relapse to first remission in patients with SDNS/FRNS (odds ratio = 3.14; 95% confidence interval, 0.97-9.87; P = 0.034). rs117014418 in APOL4 was significantly associated with a decrease in eGFR of greater than 20% compared with the baseline in SDNS/FRNS patients (P = 0.0001). Protein-protein intersection network construction suggested that HLA-DQA1 and HLA-DQB1 function together through GSDMA. Thus, SSNSWR belongs to non-HLA region-dependent nephropathy, and the HLA-DQA/DQB region is likely strongly associated with disease relapse, especially in SDNS/FRNS. The study provides a novel approach for the GWAS strategy of SSNS and contributes to our understanding of the pathological mechanisms of SSNSWR and SDNS/FRNS.

Childhood nephrotic syndrome

Idiopathic nephrotic syndrome is the most common glomerular disease in children. Corticosteroids are the cornerstone of its treatment, and steroid response is the main prognostic factor. Most children respond to a cycle of oral steroids, and are defined as having steroid-sensitive nephrotic syndrome. Among the children who do not respond, defined as having steroid-resistant nephrotic syndrome, most respond to second-line immunosuppression, mainly with calcineurin inhibitors, and children in whom a response is not observed are described as multidrug resistant. The pathophysiology of nephrotic syndrome remains elusive. In cases of immune-mediated origin, dysregulation of immune cells and production of circulating factors that damage the glomerular filtration barrier have been described. Conversely, up to a third of cases of steroid-resistant nephrotic syndrome have a monogenic origin. Multidrug resistant nephrotic syndrome often leads to kidney failure and can cause relapse after kidney transplant. Although steroid-sensitive nephrotic syndrome does not affect renal function, most children with steroid-sensitive nephrotic syndrome have a relapsing course that requires repeated steroid cycles with significant side-effects. To minimise morbidity, some patients require steroid-sparing immunosuppressive agents, including levamisole, mycophenolate mofetil, calcineurin inhibitors, anti-CD20 monoclonal antibodies, and cyclophosphamide. Close monitoring and preventive measures are warranted at onset and during relapse to prevent acute complications (eg, hypovolaemia, acute kidney injury, infections, and thrombosis), whereas long-term management requires minimising treatment-related side-effects. A subset of patients have active disease into adulthood.

Common Risk Variants in AHI1 Are Associated With Childhood Steroid Sensitive Nephrotic Syndrome

Introduction

Steroid-sensitive nephrotic syndrome (SSNS) is the most common form of kidney disease in children worldwide. Genome-wide association studies (GWAS) have demonstrated the association of SSNS with genetic variation at HLA-DQ/DR and have identified several non-HLA loci that aid in further understanding of disease pathophysiology. We sought to identify additional genetic loci associated with SSNS in children of Sri Lankan and European ancestry.

Methods

We conducted a GWAS in a cohort of Sri Lankan individuals comprising 420 pediatric patients with SSNS and 2339 genetic ancestry matched controls obtained from the UK Biobank. We then performed a transethnic meta-analysis with a previously reported European cohort of 422 pediatric patients and 5642 controls.

Results

Our GWAS confirmed the previously reported association of SSNS with HLA-DR/DQ (rs9271602, P = 1.12 × 10-27, odds ratio [OR] = 2.75). Transethnic meta-analysis replicated these findings and identified a novel association at AHI1 (rs2746432, P = 2.79 × 10-8, OR = 1.37), which was also replicated in an independent South Asian cohort. AHI1 is implicated in ciliary protein transport and immune dysregulation, with rare variation in this gene contributing to Joubert syndrome type 3.

Conclusions

Common variation in AHI1 confers risk of the development of SSNS in both Sri Lankan and European populations. The association with common variation in AHI1 further supports the role of immune dysregulation in the pathogenesis of SSNS and demonstrates that variation across the allele frequency spectrum in a gene can contribute to disparate monogenic and polygenic diseases.

Metabolomic profiles in serum and urine uncover novel biomarkers in children with nephrotic syndrome

BACKGROUND

Nephrotic syndrome is common in children and adults worldwide, and steroid-sensitive nephrotic syndrome (SSNS) accounts for 80%. Aberrant metabolism involvement in early SSNS is sparsely studied, and its pathogenesis remains unclear. Therefore, the goal of this study was to investigate the changes in initiated SSNS patients-related metabolites through serum and urine metabolomics and discover the novel potential metabolites and metabolic pathways.

METHODS

Serum samples (27 SSNS and 56 controls) and urine samples (17 SSNS and 24 controls) were collected. Meanwhile, the non-targeted analyses were performed by ultra-high-performance liquid chromatography-quadrupole time of flight-mass spectrometry (UHPLC-QTOF-MS) to determine the changes in SSNS. We applied the causal inference model, the DoWhy model, to assess the causal effects of several selected metabolites. An ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used to validate hits (D-mannitol, dulcitol, D-sorbitol, XMP, NADPH, NAD, bilirubin, and α-KG-like) in 41 SSNS and 43 controls. In addition, the metabolic pathways were explored.

RESULTS

Compared to urine, the metabolism analysis of serum samples was more clearly discriminated at SSNS. 194 differential serum metabolites and five metabolic pathways were obtained in the SSNS group. Eight differential metabolites were identified by establishing the diagnostic model for SSNS, and four variables had a positive causal effect. After validation by targeted MS, except XMP, others have similar trends like the untargeted metabolic analysis.

CONCLUSION

With untargeted metabolomics analysis and further targeted quantitative analysis, we found seven metabolites may be new biomarkers for risk prediction and early diagnosis for SSNS.

Shared genetic risk across different presentations of gene test-negative idiopathic nephrotic syndrome

BACKGROUND

Idiop athic nephrotic syndrome (INS) is classified in children according to response to initial corticosteroid therapy into steroid-sensitive (SSNS) and steroid-resistant nephrotic syndrome (SRNS), and in adults according to histology into minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS). However, there is well-recognised phenotypic overlap between these entities. Genome-wide association studies (GWAS) have shown a strong association between SSNS and variation at HLA, suggesting an underlying immunological basis. We sought to determine whether a risk score generated from genetic variants associated with SSNS could be used to gain insight into the pathophysiology of INS presenting in other ways.

METHODS

We developed an SSNS genetic risk score (SSNS-GRS) from the five variants independently associated with childhood SSNS in a previous European GWAS. We quantified SSNS-GRS in independent cohorts of European individuals with childhood SSNS, non-monogenic SRNS, MCD, and FSGS, and contrasted them with SSNS-GRS quantified in individuals with monogenic SRNS, membranous nephropathy (a different immune-mediated disease-causing nephrotic syndrome), and healthy controls.

RESULTS

The SSNS-GRS was significantly elevated in cohorts with SSNS, non-monogenic SRNS, MCD, and FSGS compared to healthy participants and those with membranous nephropathy. The SSNS-GRS in all cohorts with non-monogenic INS were also significantly elevated compared to those with monogenic SRNS.

CONCLUSIONS

The shared genetic risk factors among patients with different presentations of INS strongly suggests a shared autoimmune pathogenesis when monogenic causes are excluded. Use of the SSNS-GRS, in addition to testing for monogenic causes, may help to classify patients presenting with INS. A higher resolution version of the Graphical abstract is available as Supplementary information.

Therapeutic trials in difficult to treat steroid sensitive nephrotic syndrome: challenges and future directions

Steroid sensitive nephrotic syndrome is a common condition in pediatric nephrology, and most children have excellent outcomes. Yet, 50% of children will require steroid-sparing agents due to frequently relapsing disease and may suffer consequences from steroid dependence or use of steroid-sparing agents. Several steroid-sparing therapeutic agents are available with few high quality randomized controlled trials to compare efficacy leading to reliance on observational data for clinical guidance. Reported trials focus on short-term outcomes such as time to first relapse, relapse rates up to 1-2 years of follow-up, and few have studied long-term remission. Trial designs often do not consider inter-individual variability, and differing response to treatments may occur due to heterogeneity in pathogenic mechanisms, and genetic and environmental influences. Strategies are proposed to improve the quantity and quality of trials in steroid sensitive nephrotic syndrome with integration of biomarkers, novel trial designs, and standardized outcomes, especially for long-term remission. Collaborative efforts among international trial networks will help move us toward a shared goal of finding a cure for children with nephrotic syndrome.

B-Cell Dysregulation in Idiopathic Nephrotic Syndrome: What We Know and What We Need to Discover

The therapeutic efficacy of B-cell depletion by anti-CD20 treatment in pediatric and, more recently, in adult idiopathic nephrotic syndrome patients suggests a key role of B cells in the pathogenesis of the disease. However, their exact role is still unclear. B cells are able to secrete a large variety of antibodies that can protect against infections. However, B-cell dysregulation is well-established in a variety of autoimmune diseases. In parallel with their ability to produce antibodies, pathogenic B cells display altered effector functions by expressing activating surface molecules, which can strongly modify the immune homeostasis, or by producing specific cytokines, which can directly affect either podocyte structure and functions or modulate T-cell homeostasis. Herein, we report the most relevant clinical and experimental evidences of a pathogenic role of B cells in idiopathic nephrotic syndrome. We further highlight similarities and differences between children and adults affected by non-genetic forms of the disease and discuss what needs to be investigated in order to define the exact mechanisms underlying the pathogenic role of B cells and to identify more tailored therapeutic approaches.

An updated view of the pathogenesis of steroid-sensitive nephrotic syndrome

Idiopathic nephrotic syndrome is the most common childhood glomerular disease. Most forms of this syndrome respond to corticosteroids at standard doses and are, therefore, defined as steroid-sensitive nephrotic syndrome (SSNS). Immunological mechanisms and subsequent podocyte disorders play a pivotal role in SSNS and have been studied for years; however, the precise pathogenesis remains unclear. With recent advances in genetic techniques, an exhaustive hypothesis-free approach called a genome-wide association study (GWAS) has been conducted in various populations. GWASs in pediatric SSNS peaked in the human leukocyte antigen class II region in various populations. Additionally, an association of immune-related CALHM6/FAM26F, PARM1, BTNL2, and TNFSF15 genes, as well as NPHS1, which encodes nephrin expressed in podocytes, has been identified as a locus that achieves genome-wide significance in pediatric SSNS. However, the specific mechanism of SSNS development requires elucidation. This review describes an updated view of SSNS pathogenesis from immunological and genetic aspects, including interactions with infections or allergies, production of circulating factors, and an autoantibody hypothesis.