BACKGROUND: Personalized disease models are crucial for evaluating how diseased cells respond to treatments, especially in case of innovative biological therapeutics. Extracellular vesicles (EVs), nanosized vesicles released by cells for intercellular communication, have gained therapeutic interest due to their ability to reprogram target cells. We here utilized urinary podocytes obtained from children affected by steroid-resistant nephrotic syndrome with characterized genetic mutations as a model to test the therapeutic potential of EVs derived from kidney progenitor cells (nKPCs).
METHODS: EVs were isolated from nKPCs derived from the urine of a preterm neonate. Three lines of urinary podocytes obtained from nephrotic patients\' urine and a line of Alport syndrome patient podocytes were characterized and used to assess albumin permeability in response to nKPC-EVs or various drugs. RNA sequencing was conducted to identify commonly modulated pathways after nKPC-EV treatment. siRNA transfection was used to demonstrate the involvement of SUMO1 and SENP2 in the modulation of permeability.
RESULTS: Treatment with the nKPC-EVs significantly reduced permeability across all the steroid-resistant patients-derived and Alport syndrome-derived podocytes. At variance, podocytes appeared unresponsive to standard pharmacological treatments, with the exception of one line, in alignment with the patient\'s clinical response at 48 months. By RNA sequencing, only two genes were commonly upregulated in nKPC-EV-treated genetically altered podocytes: small ubiquitin-related modifier 1 (SUMO1) and Sentrin-specific protease 2 (SENP2). SUMO1 and SENP2 downregulation increased podocyte permeability confirming the role of the SUMOylation pathway.
CONCLUSIONS: nKPCs emerge as a promising non-invasive source of EVs with potential therapeutic effects on podocytes with genetic dysfunction, through modulation of SUMOylation, an important pathway for the stability of podocyte slit diaphragm proteins. Our findings also suggest the feasibility of developing a non-invasive in vitro model for screening regenerative compounds on patient-derived podocytes.

BACKGROUND: In patients with steroid-resistant nephrotic syndrome (SRNS), the presence of monogenic variants influences therapeutic strategies. Large cohort studies reported the detection of monogenic variants in approximately 30% of patients with SRNS. However, these cohorts included many patients, such as those with symptomatic proteinuria, who did not meet the strict diagnostic criteria for pediatric nephrotic syndrome (NS). Therefore, we investigated the proportion of causative monogenic variants detected in patients who strictly met the diagnostic criteria of SRNS and explored their clinical characteristics.
METHODS: We examined pediatric SRNS cases with genetic analysis conducted in our hospital. Cases satisfying all of the following criteria were included: (1) age at onset 1-18 years, (2) serum albumin at onset ≤ 2.5 g/dl, (3) persistent heavy proteinuria, and (4) no complete remission after 4 weeks of steroid monotherapy.
RESULTS: The proportion of detected monogenic variants was 12% (22/185) among all patients. The proportion was only 7% (9/129) in patients with edema at disease onset compared with 38% (9/24) in those without (p < 0.0001). Monogenic variants were rare in patients with acute kidney injury associated with NS (1% (1/11)) or a history of complete remission (4% (2/51)).
CONCLUSIONS: Our study revealed a monogenic cause in 12% of individuals with strictly defined SRNS, a much smaller proportion than previously reported. The presence or absence of edema at the onset was an important factor to distinguish SRNS with monogenic cause from SRNS without. Our results provide further evidence of the SRNS types attributable to monogenic causes.

BACKGROUND: Recurrence of focal segmental glomerulosclerosis (FSGS) or steroid-resistant nephrotic syndrome (SRNS) after kidney transplant leads to significant morbidity and potentially earlier allograft loss. To date however, reported rates, risk factors and treatment outcomes have varied widely.
METHODS: We applied computational phenotypes to a multicenter aggregation of electronic health records data from 7 large pediatric health systems in the USA, to identify recurrence rates, risk factors, and treatment outcomes. We refined the data collection by chart review.
RESULTS: From > 7 million patients, we compared children with primary FSGS/SRNS who received a kidney transplant between 2009 and 2020 and who either developed recurrence (n = 67/165; 40.6%) or did not (n = 98/165). Serum albumin level at time of transplant was significantly lower and recipient HLA DR7 presence was significantly higher in the recurrence group. By 36 months post-transplant, complete remission occurred in 58.2% and partial remission in 17.9%. Through 6 years post-transplant, no remission after recurrence was associated with an increased risk of allograft loss over time (p < 0.0001), but any remission showed similar allograft survival and function decline to those with no recurrence. Since treatments were used in non-random fashion, using spline curves and multivariable non-linear analyses, complete + partial remission chance was significantly higher with greater plasmapheresis sessions, CTLA4-Ig doses or LDL-apheresis sessions. Only treatment with anti-CD20, CTLA4-Ig agents, or LDL-apheresis sessions were associated with complete remission. Excluding 25 patients with mutations did not significantly change our results.
CONCLUSIONS: Our contemporary high-risk cohort had higher favorable response rates than most prior reports, from combinations of agents.

BACKGROUND: Steroid-resistant nephrotic syndrome is the second leading cause of chronic kidney disease among patients < 25 years of age. Through exome sequencing, identification of > 65 monogenic causes has revealed insights into disease mechanisms of nephrotic syndrome (NS).
METHODS: To elucidate novel monogenic causes of NS, we combined homozygosity mapping with exome sequencing in a worldwide cohort of 1649 pediatric patients with NS.
RESULTS: We identified homozygous missense variants in MYO1C in two unrelated children with NS (c.292C > T, p.R98W; c.2273 A > T, p.K758M). We evaluated publicly available kidney single-cell RNA sequencing datasets and found MYO1C to be predominantly expressed in podocytes. We then performed structural modeling for the identified variants in PyMol using aligned shared regions from two available partial structures of MYO1C (4byf and 4r8g). In both structures, calmodulin, a common regulator of myosin activity, is shown to bind to the IQ motif. At both residue sites (K758; R98), there are ion-ion interactions stabilizing intradomain and ligand interactions: R98 binds to nearby D220 within the myosin motor domain and K758 binds to E14 on a calmodulin molecule. Variants of these charged residues to non-charged amino acids could ablate these ionic interactions, weakening protein structure and function establishing the impact of these variants.
CONCLUSIONS: We here identified recessive variants in MYO1C as a potential novel cause of NS in children.

BACKGROUND: The efficacy of rituximab in steroid-resistant nephrotic syndrome (SRNS) is controversial. We previously reported that rituximab in combination with methylprednisolone pulse therapy (MPT) and immunosuppressants was associated with favorable outcomes. We determined risk factors for poor response following rituximab treatment, which remains unknown.
METHODS: This retrospective study included 45 patients with childhood-onset SRNS treated with rituximab across four pediatric kidney facilities. Treatment effects were categorized as complete remission (CR), partial remission (PR), and no remission (NR) at one year after rituximab treatment. The primary outcome was the rate of CR, PR, and NR. Risk factors for non-CR were calculated with multivariate logistic regression. Adverse events and the relationship between disease status at one year and long-term prognosis were also evaluated.
RESULTS: The rates of CR, PR, and NR at one year were 69%, 24%, and 7%, respectively. The median time from rituximab administration to CR was 90 days. The median follow-up period after rituximab administration was 7.4 years. In multivariate analysis, significant risk factors for poor response were the pathologic finding of focal segmental glomerular sclerosis and a long interval between SRNS diagnosis and rituximab administration. The rates of CR were 90.3% and 21.4% in patients receiving rituximab within and after 6 months following SRNS diagnosis, respectively (p < 0.001). Five patients developed chronic kidney disease stage G5, including 2 of the 11 patients with PR and all 3 patients with NR, whereas none of the 31 patients with CR developed chronic kidney disease stage G5.
CONCLUSIONS: Early administration of rituximab in combination with MPT and immunosuppressants might achieve favorable outcomes in patients with SRNS.

Focal segmental glomerulosclerosis (FSGS) defines a distinct histologic pattern observed in kidney tissue that is linked to several distinct underlying causes, all converging on the common factor of podocyte injury. It presents a considerable challenge in terms of classification because of its varied underlying causes and the limited correlation between histopathology and clinical outcomes. Critically, precise nomenclature is key to describe and delineate the pathogenesis, subsequently guiding the selection of suitable and precision therapies. A proposed pathomechanism-based approach has been suggested for FSGS classification. This approach differentiates among primary, secondary, genetic, and undetermined causes, aiming to provide clarity. Genetic FSGS from monogenic mutations can emerge during childhood or adulthood, and it is advisable to conduct genetic testing in cases in which there is a family history of chronic kidney disease, nephrotic syndrome, or resistance to treatment. Genome-wide association studies have identified several genetic risk variants, such as those in apolipoprotein L1 (APOL1), that play a role in the development of FSGS. Currently, no specific treatments have been approved to treat genetic FSGS; however, interventions targeting underlying cofactor deficiencies have shown potential in some cases. Furthermore, encouraging results have emerged from a phase 2 trial investigating inaxaplin, a novel small molecule APOL1 channel inhibitor, in APOL1-associated FSGS.

UNASSIGNED: Unlike idiopathic nephrotic syndrome (NS), hereditary podocytopathies are not expected to recur after kidney transplantation. However, some reports of posttransplant recurrence of NS in patients carrying variants in the NPHS2 gene have been described, notably with the p.Arg138Gln variant, which is more prevalent in Europe. The objective of this study was to assess the risk of recurrence after kidney transplantation in a large cohort of patients with biallelic NPHS2 pathogenic variants.
UNASSIGNED: Since January 2010, 61 patients identified at Necker-Enfants Malades Hospital and 56 enrolled in the PodoNet Registry with biallelic variants in the NPHS2 gene were transplanted and were compared with 44 transplanted children with steroid-resistant NS (SRNS) without any identified pathogenic variant.
UNASSIGNED: Of the 117 patients, 23 carried the p.Arg138Gln variant in the homozygous state and 16 in the compound heterozygous state. The other 78 patients carried different variants in the homozygous (n = 44) or compound heterozygous state. Only 1 patient with NPHS2-related SRNS experienced posttransplant recurrence (median follow-up of cohort 8.5 years [2.5-15]). Conversely, 7 of 44 patients (16%) without any identified pathogenic variant recurred within a maximum of 7 days after transplantation (median follow-up 8.9 years [0.6-13.9]).
UNASSIGNED: In this large cohort, the risk of patients with causative variants in the NPHS2 gene to develop NS recurrence after kidney transplantation was extremely low. This is coherent with the pathophysiology of intrinsic slit-diaphragm disease. These data are reassuring and should be considered when counselling patients, making living kidney donation, whether related or not, a safe choice.

Idiopathic nephrotic syndrome is the most common chronic glomerular disease in children. Treatment with steroids is usually successful; however, in a small percentage of patients, steroid resistance is observed. The most frequent histologic kidney feature of steroid-resistant nephrotic syndrome (SRNS) is focal segmental glomerulosclerosis (FSGS). Genetic testing has become a valuable diagnostic tool in defining the etiology of SRNS, leading to the identification of a genetic cause. The TRIM8 gene is expressed in various tissues, including kidney cells and the central nervous system (CNS). An association between a mutation in the TRIM8 gene and an early onset of FSGS has been proposed but is not well described. We present a 17-year-old boy with epilepsy, early mild developmental delay, a low IgG serum level, and proteinuria, secondary to FSGS. A Next-Generation Sequencing (NGS)-based analysis revealed a heterozygous de novo pathogenic variant in the TRIM8 gene (c.1200C>G, p.Tyr400Ter). TRIM8 gene sequencing should be considered in individuals with early onset of FSGS, particularly accompanied by symptoms of cortical dysfunction, such as epilepsy and intellectual disability.

BACKGROUND: Steroid-resistant nephrotic syndrome (SRNS) are monogenic in some cases, however, there are still no clear guidelines on genetic testing in the clinical practice of SRNS in children.
METHODS: Three hundred thirty-two children were diagnosed with SRNS, and all children underwent genetic testing, including gene panels and/or whole-exome/genome sequencing (WES/WGS), during treatment. We analysed the relationship between clinical manifestation and genotype, and compared different genetic testing methods\' detection rates and prices.
RESULTS: In this study, 30.12% (100/332) of children diagnosed with SRNS had monogenic causes of the disease. With 33.7% (122/332) of children achieving complete remission, 88.5% (108/122) received steroids combined with tacrolimus (TAC). In detectability, WES increased by 8.69% (4/46) on gene panel testing, while WGS increased by 4.27% (5/117) on WES, and WES was approximately 1/7 of the price of WGS for every further 1% increase in pathogenicity.
CONCLUSIONS: We verified that steroids combined with TAC were the most effective option in paediatric SRNS. In detection efficiency, we found that WGS was the highest, followed by WES. The panel was the lowest, but the most cost-effective method when considering the economic-benefit ratio, and thus it should be recommended first in SRNS.

BACKGROUND: The variants of nucleoporins are extremely rare in hereditary steroid-resistant nephrotic syndrome (SRNS). Most of the patients carrying such variants progress to end stage kidney disease (ESKD) in their childhood. More clinical and genetic data from these patients are needed to characterize their genotype-phenotype relationships and elucidate the role of nucleoporins in SRNS.
METHODS: Four patients of SRNS carrying biallelic variants in the NUP93, NUP107 and NUP160 genes were presented. The clinical and molecular genetic characteristics of these patients were summarized, and relevant literature was reviewed.
RESULTS: All four patients in this study were female and initially presented with SRNS. The median age at the onset of the disease was 5.08 years, ranging from 1 to 10.5 years. Among the four patients, three progressed to ESKD at a median age of 7 years, ranging from 1.5 to 10.5 years, while one patient reached stage 3 chronic kidney disease (CKD3). Kidney biopsies revealed focal segmental glomerulosclerosis in three patients. Biallelic variants were detected in NUP93 in one patient, NUP107 in two patients, as well as NUP160 in one patient respectively. Among these variants, five yielded single amino acid substitutions, one led to nonsense mutation causing premature termination of NUP107 translation, one caused a single nucleotide deletion resulting in frameshift and truncation of NUP107. Furthermore, one splicing donor mutation was observed in NUP160. None of these variants had been reported previously.
CONCLUSIONS: This report indicates that biallelic variants in NUP93, NUP107 and NUP160 can cause severe early-onset SRNS, which rapidly progresses to ESKD. Moreover, these findings expand the spectrum of phenotypes and genotypes and highlight the importance of next-generation sequencing in elucidating the molecular basis of SRNS and allowing rational treatment for affected individuals.