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IgA nephropathy (IgAN) is the most common chronic primary glomerulonephritis in both children and adults, and 20–30% of patients with persistent hematuria/proteinuria progress to kidney failure within 20 years. In Japan, most cases of childhood IgAN are detected by school screening programs during the early onset of the disease when hematuria/proteinuria are asymptomatic and kidney function is normal. Therefore, it is possible to follow the detailed clinical course and appropriate therapeutic interventions from early onset of the disease. Data on non-immunosuppressive therapies for children with IgAN are highly limited. The Japanese Pediatric IgA Nephropathy Treatment Study Group was organized in 1989 to conduct clinical trials and accumulate data on treatments for childhood IgAN. In this review, we focus on non-immunosuppressive therapies, notably with renin-angiotensin-aldosterone system (RAAS) inhibitors for childhood IgAN and related clinical trials conducted primarily in Japan. We also describe the anti-inflammatory and antiproteinuric effects of RAAS inhibitors in IgAN, differences in treatment regimens because of the acute and active pathological features of childhood IgAN, adverse events of RAAS inhibitors, other non-immunosuppressive treatment options, and future directions.

Numerous disease-causing gene mutations have been identified in proteinuric diseases, such as nephrotic syndrome and glomerulosclerosis. This report describes the results of comprehensive genetic diagnosis of Japanese patients with severe proteinuria. In addition, the report describes the clinical characteristics of patients with monogenic disease-causing mutations. We conducted comprehensive gene screening of patients who had either congenital nephrotic syndrome, infantile nephrotic syndrome, steroid-resistant nephrotic syndrome, or focal segmental glomerular sclerosis. Using targeted next-generation sequencing, 60 podocyte-related genes were screened in 230 unrelated patients with proteinuria. A retrospective review of clinical data was conducted for these patients. We detected monogenic disease-causing mutations in 30% (69 of 230) of patients among 19 of the screened genes. Common genes with disease-causing mutations were WT1 (25%), NPHS1 (12%), INF2 (12%), TRPC6 (10%), and LAMB2 (9%). With various immunosuppressive or renoprotective therapies, remission of proteinuria in patients with unknown causative mutations was observed in 26% of patients, whereas only 5% of patients with monogenic disease-causing mutations exhibited complete remission. We assessed the genetic backgrounds of Japanese patients with severe proteinuria. The proportion of patients with gene defects was similar to that of other reports, but the disease-causing gene mutation frequency was considerably different.

Gitelman syndrome is an autosomal recessive inherited salt-losing tubulopathy. It has a prevalence of around 1 in 40,000 people, and heterozygous carriers are estimated at approximately 1%, although the exact prevalence is unknown. We estimated the predicted prevalence of Gitelman syndrome based on multiple genome databases, HGVD and jMorp for the Japanese population and gnomAD for other ethnicities, and included all 274 pathogenic missense or nonsense variants registered in HGMD Professional. The frequencies of all these alleles were summed to calculate the total variant allele frequency in SLC12A3 . The carrier frequency and the disease prevalence were assumed to be twice and the square of the total allele frequency, respectively, according to the Hardy–Weinberg principle. In the Japanese population, the total carrier frequencies were 0.0948 (9.5%) and 0.0868 (8.7%) and the calculated prevalence was 0.00225 (2.3 in 1000 people) and 0.00188 (1.9 in 1000 people) in HGVD and jMorp, respectively. Other ethnicities showed a prevalence varying from 0.000012 to 0.00083. These findings indicate that the prevalence of Gitelman syndrome in the Japanese population is higher than expected and that some other ethnicities also have a higher prevalence than has previously been considered.

BackgroundIgA nephropathy (IgAN) is characterized by predominant mesangial IgA deposition. Some patients with IgAN demonstrate IgA deposition in glomerular peripheral capillaries (cap-IgA). The clinicopathological significance of cap-IgA remains incompletely investigated in children.MethodsWe retrospectively analyzed 503 consecutive cases of biopsy-proven childhood IgAN between July 1976 and June 2013 to compare clinical and pathological features between IgAN patients with and without cap-IgA.ResultsAmong the 503 patients, 30 (6.0%) had cap-IgA. We found significant differences in proteinuria (2.0 vs. 0.5 g/day/m2, p < 0.0001), time from onset to kidney biopsy (2.2 vs. 8.3 months, p < 0.0001), and rate of proteinuria remission after treatment (23.3% vs. 48.0%, p = 0.007) between both groups. Pathological analysis revealed significant differences in M1 (83.3% vs. 56.0%, p = 0.002), ratio of subendothelial electron dense deposits (EDDs, 58.6% vs. 16.5%, p < 0.0001) and subepithelial EDDs (48.3% vs. 16.5%, p = 0.0001), and glomerular basement membrane (GBM) lysis (58.6% vs. 27.1%, p = 0.0006) between both groups. More than half of cap-IgA patients (17/30, 56.7%), whereas only 26.2% of non-cap-IgA patients (124/473), were treated with immunosuppressive treatments. Six of 30 cases (20%) with cap-IgA reached glomerular filtration rate (GFR) categories G3a–G5 (estimated GFR < 60 ml/min/1.73 m2) at most recent observation (mean observation period: 7.0 ± 4.0 years). According to Kaplan-Meier analysis, patients with cap-IgA had significantly lower kidney survival curves than non-cap-IgA patients (72.8% vs. 97.2% at 10 years, p < 0.0001).ConclusionsCap-IgA is associated with acute inflammation with GBM changes, resulting in refractory heavier proteinuria. Cap-IgA may represent a poor prognostic factor.

Background Proteinuria remission is the most significant predictive factor for kidney outcome in childhood IgA nephropathy (c-IgAN). Even if proteinuria remission can be obtained, some patients have recurrence of proteinuria in the long-term. Methods This is a retrospective analysis of 312 cases of proteinuria remission among 538 consecutive children with biopsy-proven IgAN from 1976 to 2013. To elucidate the incidence and factors related to recurrence of proteinuria in c-IgAN, we compare clinical and pathological findings between patients with and without recurrence of proteinuria. Results Among 312 patients with remission of proteinuria, 91 (29.2%) had recurrence of proteinuria within the observation period (median 8 years). Using a multivariate Cox regression analysis, significant factors associated with recurrence of proteinuria were onset age (HR 1.13 [95%CI: 1.05–1.22], P  = 0.002) and presence of hematuria after proteinuria remission (HR 2.11 [95%CI: 1.30–3.45], P  = 0.003). The Kaplan–Meier analysis showed significant differences in CKD G3a-G5-free survival between the patients with no-recurrence of proteinuria, recurrence of proteinuria and non-proteinuria remission ( P  < 0.0001, log-rank test). Kidney survival was 100% in no-recurrence of proteinuria, 92.2% in recurrence of proteinuria, and 65.6% in non-proteinuria remission at 15 years. Cox analyses adjusted by proteinuria remission showed that recurrence of proteinuria (HR 03.10e 9 [95%CI: NA], P  = 0.003) was a significant factor associated with progression to CKD G3a-G5 in all patients with c-IgAN. Conclusions Approximately 30% of patients with proteinuria remission had recurrence of proteinuria regardless of treatment. Both remission and recurrence of proteinuria are significant prognostic factors for kidney outcome. Graphical abstract A higher resolution version of the Graphical abstract is available as Supplementary information

Purpose: Phenotypic overlap exists among type III Bartter syndrome (BS), Gitelman syndrome (GS), and pseudo-BS/GS (p-BS/GS), which are clinically difficult to distinguish. We aimed to clarify the differences between these diseases, allowing accurate diagnosis based on their clinical features. Methods: A total of 163 patients with genetically defined type III BS ( n = 30), GS ( n = 90), and p-BS/GS ( n = 43) were included. Age at diagnosis, sex, body mass index, estimated glomerular filtration rate, and serum and urine electrolyte concentrations were determined. Results: Patients with p-BS/GS were significantly older at diagnosis than those with type III BS and GS. Patients with p-BS/GS included a significantly higher percentage of women and had a lower body mass index and estimated glomerular filtration rate than did patients with GS. Although hypomagnesemia and hypocalciuria were predominant biochemical findings in patients with GS, 17 and 23% of patients with type III BS and p-BS/GS, respectively, also showed these abnormalities. Of patients with type III BS, GS, and p-BS/GS, 40, 12, and 63%, respectively, presented with chronic kidney disease. Conclusions: This study clarified the clinical differences between BS, GS, and p-BS/GS for the first time, which will help clinicians establish differential diagnoses for these three conditions. Genet Med 18 2, 180–188.

ObjectivesCrescentic IgA nephropathy (C-IgAN) is defined as IgAN with more than 50% of glomeruli showing crescents. C-IgAN in children is rare; we investigate in detail for the first time.MethodsWe retrospectively analyzed the 515 consecutive children who were newly diagnosed with biopsy-proven IgAN between June 1976 and May 2010. We compared clinical and pathological findings between C-IgAN and non-C-IgAN.ResultsAmong 515 cases of childhood IgAN, 25 children (4.9%) had C-IgAN. Of these 25, 16 children (64%) were referred to hospitals by annual school screening. Clinical findings showed significant differences in gross hematuria (76 vs. 50%, p = .03), excretion of proteinuria (1.9 vs. 0.5 g/day/m2, p < .0001), eGFR (102 vs. 108 ml/min/1.73 m2, p = .03), and duration from onset to renal biopsy (4.0 vs. 8.0 months, p = .04) between groups. Pathological findings showed significant differences in M1 (88 vs. 55%, p = .02), E1 (83 vs. 53%, p = .008), and presence of tubular atrophy/interstitial fibrosis (88 vs. 53%, p < .0001) between groups. The 16 children with C-IgAN were treated with prednisolone and immunosuppressant. Four cases (16%) reached chronic renal failure (eGFR < 60) at the latest observation (mean observation period: 6.0 ± 3.6 years). Patients with C-IgAN had significantly lower renal survival curve than non-C-IgAN patients according to Kaplan-Meier analysis (77.1% vs. 92.6% at 13 years, p < .0001). Compared with previous reports, however, they had better renal outcome.ConclusionsWe confirmed the importance of school screening to find C-IgAN. Although most crescents (mean: 98.1%) of C-IgAN were cellular/fibrocellular, and acute lesions were well modified with combination therapy, the presence of tubular atrophy in C-IgAN may be the reason for poorer prognosis.

Galactose-deficient IgA1 (Gd-IgA1) is important in the pathogenesis of IgA nephropathy (IgAN). A Gd-IgA1-specific monoclonal antibody (KM55) has revealed glomerular Gd-IgA1 deposition solely in patients with IgAN and IgA vasculitis with nephritis (IgAV-N). However, this specificity is controversial and has not been demonstrated in pediatric patients. Here, we conducted double-immunofluorescence staining of IgA and Gd-IgA1 in 60 pediatric patients with various glomerular diseases. We divided patients into four groups: (1) patients with IgAN and IgAV-N (n = 23); (2) patients with immunocomplex-mediated glomerulonephritis accompanied by IgA deposition, including lupus nephritis, membranoproliferative glomerulonephritis, and membranous nephropathy (n = 14); (3) patients with other glomerular diseases involving IgA deposition, including idiopathic nephrotic syndrome (INS), oligomeganephronia, Alport syndrome, dense deposit disease, and crescentic glomerulonephritis (n = 11); and (4) patients with IgA-negative diseases including INS, membranoproliferative glomerulonephritis, membranous nephropathy, oligomeganephronia, Alport syndrome, C3 glomerulonephritis, poststreptococcal acute glomerulonephritis, and hemolytic uremic syndrome (n = 12). KM55 staining revealed Gd-IgA1-positive findings in 23/23 patients in Group 1 and 13/14 patients in Group 2, but not in patients in Groups 3 or 4. Therefore, KM55 may detect incidental IgA deposition in pediatric patients. Gd-IgA1 may be involved in the pathogenesis of these immune-related diseases; alternatively, KM55 may recognize IgA-related immunocomplexes in a non-specific manner.

BackgroundPersistent proteinuria seems to be a risk factor for progression of renal disease. Its reduction by angiotensin-converting inhibitors (ACEIs) or angiotensin II receptor blockers (ARBs) is renoprotective. Our previous pilot study showed that 2-year lisinopril therapy is effective and safe for children with mild IgA nephropathy. When combined with ACEI and ARB, reported results are of greater decrease in proteinuria than monotherapy in chronic glomerulonephritis, including IgA nephropathy. To date, however, there have been no randomized controlled trials in children.MethodsThis is an open-label, multicenter, prospective, and randomized phase II controlled trial of 63 children with biopsy-proven proteinuric mild IgA nephropathy. We compared efficacy and safety between patients undergoing lisinopril monotherapy and patients undergoing combination therapy of lisinopril and losartan to determine better treatment for childhood proteinuric mild IgA nephropathy.ResultsThere was no difference in proteinuria disappearance rate (primary endpoint) between the two groups (cumulative disappearance rate of proteinuria at 24 months: 89.3% vs 89% [combination vs monotherapy]). Moreover, there were no significant differences in side effects between the two groups.ConclusionsWe propose lisinopril monotherapy as treatment for childhood proteinuric mild IgA nephropathy as there are no advantages of combination therapy.Clinical trial registrationClinical trial registry, UMIN ID C000000006, https://www.umin.ac.jp.

Background Membranoproliferative glomerulonephritis (MPGN) can be divided into immune-complex MPGN (IC-MPGN) and C3 glomerulopathy (C3G), which includes dense deposit disease (DDD) and C3 glomerulonephritis (C3GN). These conditions result from abnormalities in different complement pathways and may lead to different prognoses. However, there are limited studies describing the respective clinical courses. Methods In this study, Japanese pediatric patients diagnosed with MPGN based on kidney biopsies conducted between February 2002 and December 2022 were reclassified as having IC-MPGN or C3G (DDD or C3GN). We retrospectively analyzed the clinical characteristics and outcomes of these patients. Results Out of 25 patients with MPGN, three (12.0%) were diagnosed with DDD, 20 (80.0%) with C3GN, and two (8.0%) with IC-MPGN. There were 13 (65.0%) patients and one (33.3%) patient in remission after treatment for C3GN and DDD, respectively, and no patients with IC-MPGN achieved remission. The median follow-up period was 5.3 (2.5–8.9) years, and none of the patients in either group progressed to an estimated glomerular filtration rate < 15 ml/min/1.73 m 2 . Patients with C3GN presenting mild to moderate proteinuria ( n  = 8) received a renin-angiotensin system inhibitor (RAS-I) alone, and these patients exhibited a significant decrease in the urinary protein creatinine ratio and a notable increase in serum C3 levels at the last follow-up. Conclusions Most patients with MPGN were diagnosed with C3GN. The remission rate for C3GN was high, and no patients developed kidney failure during the approximately 5-year follow-up. Additionally, patients with C3GN with mild to moderate proteinuria had good outcomes with RAS-I alone, but continued vigilance is necessary to determine long-term prognosis. Graphical abstract A higher resolution version of the Graphical abstract is available as Supplementary information