Germline C1GALT1C1 mutation causes a multisystem chaperonopathy.

Mutations in genes encoding molecular chaperones can lead to chaperonopathies, but none have so far been identified causing congenital disorders of glycosylation. Here we identified two maternal half-brothers with a novel chaperonopathy, causing impaired protein O-glycosylation. The patients have a decreased activity of T-synthase (C1GALT1), an enzyme that exclusively synthesizes the T-antigen, a ubiquitous O-glycan core structure and precursor for all extended O-glycans. The T-synthase function is dependent on its specific molecular chaperone Cosmc, which is encoded by X-chromosomal C1GALT1C1. Both patients carry the hemizygous variant c.59C>A (p.Ala20Asp; A20D-Cosmc) in C1GALT1C1. They exhibit developmental delay, immunodeficiency, short stature, thrombocytopenia, and acute kidney injury (AKI) resembling atypical hemolytic uremic syndrome. Their heterozygous mother and maternal grandmother show an attenuated phenotype with skewed X-inactivation in blood. AKI in the male patients proved fully responsive to treatment with the complement inhibitor Eculizumab. This germline variant occurs within the transmembrane domain of Cosmc, resulting in dramatically reduced expression of the Cosmc protein. Although A20D-Cosmc is functional, its decreased expression, though in a cell or tissue-specific manner, causes a large reduction of T-synthase protein and activity, which accordingly leads to expression of varied amounts of pathological Tn-antigen (GalNAcα1-O-Ser/Thr/Tyr) on multiple glycoproteins. Transient transfection of patient lymphoblastoid cells with wild-type C1GALT1C1 partially rescued the T-synthase and glycosylation defect. Interestingly, all four affected individuals have high levels of galactose-deficient IgA1 in sera. These results demonstrate that the A20D-Cosmc mutation defines a novel O-glycan chaperonopathy and causes the altered O-glycosylation status in these patients.

The role of the FSGS disease gene product and nuclear pore protein NUP205 in regulating nuclear localization and activity of transcriptional regulators YAP and TAZ.

Mutations in genes encoding nuclear pore proteins (NUPs) lead to the development of steroid-resistant nephrotic syndrome and focal segmental glomerulosclerosis (FSGS). However, the precise molecular mechanisms by which NUP dysfunction contributes to podocyte injury preceding FSGS remain unclear. The tightly regulated activity of Yes-associated protein (YAP) and WW-domain-containing transcription regulator 1 (TAZ), the transcriptional effectors of the Hippo pathway, is crucial for podocytes and the maintenance of the glomerular filter. In this study, we investigate the impact of NUPs on the regulation of YAP/TAZ nuclear import and activity in podocytes. In unbiased interactome studies using quantitative label-free mass spectrometry, we identify the FSGS disease gene products NUP107, NUP133, NUP205, and Exportin-5 (XPO5) as components of YAP and TAZ protein complexes in podocytes. Moreover, we demonstrate that NUP205 is essential for YAP/TAZ nuclear import. Consistently, both the nuclear interaction of YAP/TAZ with TEA domain transcription factor 1 and their transcriptional activity were dependent on NUP205 expression. Additionally, we elucidate a regulatory feedback mechanism whereby YAP activity is modulated in response to TAZ-mediated NUP205 expression. In conclusion, this study establishes a connection between the FSGS disease protein NUP205 and the activity of the transcriptional regulators and Hippo effectors YAP and TAZ and it proposes a potential pathological role of YAP/TAZ dysregulation in podocytes of patients with pathogenic NUP205 variants.

Low incidence of acute kidney injury in VLBW infants with restrictive use of mechanical ventilation.

BACKGROUND: We assessed the incidence of and risk factors for acute kidney injury (AKI) in very low birthweight infants (VLBW) in a center with a specific neonatal management protocol focusing on avoidance of early mechanical ventilation (MV). METHODS: This retrospective single center analysis includes 128 infants born in 2020 with a gestational age ≥ 22 weeks who were screened for AKI using the nKDIGO criteria. RESULTS: AKI was identified in 25/128 patients (19.5%) with eight of them (6.3%) presenting with severe AKI. Low gestational age, birthweight and 10-minute Apgar score as well as high CRIB-1 score were all associated with incidence of AKI. Forty-five percent of the infants with MV developed AKI vs. 8.9% of those without MV (p < 0.001). Early onset of MV and administration of more than 3 dosages of NSAIDs for patent duct were identified as independent risk factors for AKI in a logistic regression analysis. CONCLUSIONS: We report a substantially lower frequency of AKI in VLBW infants as compared to previous studies, along with a very low rate of MV. A neonatal protocol focusing on avoidance of MV within the first days of life may be a key factor to decrease the risk of AKI in immature infants.

Development of a tool for predicting HNF1B mutations in children and young adults with congenital anomalies of the kidneys and urinary tract.

BACKGROUND: We aimed to develop a tool for predicting HNF1B mutations in children with congenital abnormalities of the kidneys and urinary tract (CAKUT). METHODS: The clinical and laboratory data from 234 children and young adults with known HNF1B mutation status were collected and analyzed retrospectively. All subjects were randomly divided into a training (70%) and a validation set (30%). A random forest model was constructed to predict HNF1B mutations. The recursive feature elimination algorithm was used for feature selection for the model, and receiver operating characteristic curve statistics was used to verify its predictive effect. RESULTS: A total of 213 patients were analyzed, including HNF1B-positive (mut + , n = 109) and HNF1B-negative (mut - , n = 104) subjects. The majority of patients had mild chronic kidney disease. Kidney phenotype was similar between groups, but bilateral kidney anomalies were more frequent in the mut + group. Hypomagnesemia and hypermagnesuria were the most common abnormalities in mut + patients and were highly selective of HNF1B. Hypomagnesemia based on age-appropriate norms had a better discriminatory value than the age-independent cutoff of 0.7 mmol/l. Pancreatic anomalies were almost exclusively found in mut + patients. No subjects had hypokalemia; the mean serum potassium level was lower in the HNF1B cohort. The abovementioned, discriminative parameters were selected for the model, which showed a good performance (area under the curve: 0.85; sensitivity of 93.67%, specificity of 73.57%). A corresponding calculator was developed for use and validation. CONCLUSIONS: This study developed a simple tool for predicting HNF1B mutations in children and young adults with CAKUT.

Humoral immune response and live-virus neutralization of the SARS-CoV-2 omicron (BA.1) variant after COVID-19 mRNA vaccination in children and young adults with chronic kidney disease.

BACKGROUND: Data on humoral immune response to standard COVID-19 vaccination are scarce in adolescent patients and lacking for children below 12 years of age with chronic kidney disease including kidney transplant recipients. METHODS: We therefore investigated in this retrospective two-center study (DRKS00024668; registered 23.03.2021) the humoral immune response to a standard two-dose mRNA vaccine regimen in 123 CKD patients aged 5-30 years. A live-virus assay was used to assess the serum neutralizing activity against the SARS-CoV-2 omicron (BA.1) variant. RESULTS: Children aged 5-11 years had a comparable rate and degree of immune response to adolescents despite lower vaccine doses (10 µg vs. 30 µg BNT162b2). Treatment with two (odds ratio 9.24) or three or more (odds ratio 17.07) immunosuppressants was an independent risk factor for nonresponse. The immune response differed significantly among three patient cohorts: 48 of 77 (62.3%) kidney transplant recipients, 21 of 26 (80.8%) patients on immunosuppressive therapy, and 19 of 20 (95.0%) patients with chronic kidney disease without immunosuppressive therapy responded. In the kidney transplant recipients, immunosuppressive regimens comprising mycophenolate mofetil, an eGFR of < 60 mL/min/1.73 m2, and female sex were independent risk factors for nonresponse. Two of 18 (11.1%) and 8 of 16 (50.0%) patients with an anti-S1-RBD IgG of 100-1411 and > 1411 BAU/mL, respectively, showed a neutralization activity against the omicron variant. CONCLUSION: A standard mRNA vaccine regimen in immunosuppressed children and adolescents with kidney disease elicits an attenuated humoral immune response with effective live virus neutralization against the omicron variant in approximately 10% of the patients, underlying the need for omicron-adapted vaccination. A higher resolution version of the Graphical abstract is available as Supplementary information.

Nutritional and Anthropometric Indices in Children Receiving Haemodiafiltration vs Conventional Haemodialysis - The HDF, Heart and Height (3H) Study.

BACKGROUND: The "HDF-Heart-Height" study showed that haemodiafiltration (HDF) is associated with improved growth compared to conventional haemodialysis (HD). We report a post-hoc analysis of this study assessing the effect of extracorporeal dialysis therapies on nutritional indices. METHODS: 107 children were included in the baseline cross-sectional analysis, of whom 79 (43 HD, 36 HDF) completed the 12-month follow-up. Height (Ht), optimal 'dry' weight (Wt), and body mass index (BMI) standard deviations scores (SDS), waist-to-hip ratio, des-acyl ghrelin (DAG), adiponectin, leptin, insulin-like growth factor-1 (IGF-1)-SDS and insulin were measured. RESULTS: The levels of nutritional indices were comparable between HDF and HD patients at baseline and 12-month. On univariable analyses Wt-SDS positively correlated with leptin and IGF-1-SDS, and negatively with DAG, while Ht-SDS of the overall cohort positively correlated with IGF1-SDS and inversely with DAG and adiponectin. On multivariable analyses, higher 12-month Ht-SDS was inversely associated with baseline DAG (beta = -0.13 per 500 higher; 95%CI -0.22, -0.04; P = .004). Higher Wt-SDS at 12-month was positively associated with HDF modality (beta = 0.47 vs HD; 95%CI 0.12-0.83; P = .01) and inversely with baseline DAG (beta = -0.18 per 500 higher; 95%CI -0.32, -0.05; P = .006). Growth Hormone (GH) treated patients receiving HDF had higher annualized increase in Ht SDS compared to those on HD. CONCLUSIONS: In children on HD and HDF both Wt- and Ht-SDS independently correlated with lower baseline levels of the anorexygenic hormone DAG. HDF may attenuate the resistance to GH, but further studies are required to examine the mechanisms linking HDF to improved growth.

Prevalence and potential relevance of hyperuricemia in pediatric kidney transplant recipients-a CERTAIN registry analysis.

BACKGROUND: Asymptomatic hyperuricemia is frequently observed in pediatric kidney transplant recipients; symptomatic hyperuricemia, however, is a rare complication. Only few data are available in this patient population. We, therefore, investigated the prevalence of hyperuricemia and its association with kidney transplant function and blood pressure in a multicenter cohort of pediatric kidney transplant recipients. METHODS: This is a retrospective, observational multicenter registry study. All pediatric kidney transplant recipients in the CERTAIN database with at least one documented serum uric acid level and a follow-up of 5 years posttransplant were eligible. We identified 151 patients with 395 measurements of serum uric acid. We calculated the prevalence of hyperuricemia, analyzed potential risk factors and clinical consequences such as elevated blood pressure and reduced estimated glomerular filtration rate (eGFR). Statistical analysis was performed using IBM SPSS Statistics 26. RESULTS: One hundred and ten of 395 (27.8%) serum uric acid levels were above 416 µmol/L (7.0 mg/dL), defined as the upper limit of normal. Univariate analysis showed a significant (p = .026) inverse association of serum uric acid with eGFR overtime. There was no significant association of serum uric acid concentrations with body mass index (z-score), blood pressure (z-score), or sex. No episodes of gout were documented. CONCLUSION: This study shows that hyperuricemia is present in a considerable number of patients sometime after pediatric kidney transplantation and is associated with lower eGFR. Whether hyperuricemia contributes to faster decline of graft function or to the overall cardiovascular risk of these patients remains to be elucidated.

NPHP1 gene-associated nephronophthisis is associated with an occult retinopathy.

Biallelic deletions in the NPHP1 gene are the most frequent molecular defect of nephronophthisis, a kidney ciliopathy and leading cause of hereditary end-stage kidney disease. Nephrocystin 1, the gene product of NPHP1, is also expressed in photoreceptors where it plays an important role in intra-flagellar transport between the inner and outer segments. However, the human retinal phenotype has never been investigated in detail. Here, we characterized retinal features of 16 patients with homozygous deletions of the entire NPHP1 gene. Retinal assessment included multimodal imaging (optical coherence tomography, fundus autofluorescence) and visual function testing (visual acuity, full-field electroretinography, color vision, visual field). Fifteen patients had a mild retinal phenotype that predominantly affected cones, but with relative sparing of the fovea. Despite a predominant cone dysfunction, night vision problems were an early symptom in some cases. The consistent retinal phenotype on optical coherence tomography images included reduced reflectivity and often a granular appearance of the ellipsoid zone, fading or loss of the interdigitation zone, and mild outer retinal thinning. However, there were usually no obvious structural changes visible upon clinical examination and fundus autofluorescence imaging (occult retinopathy). More advanced retinal degeneration might occur with ageing. An identified additional CEP290 variant in one patient with a more severe retinal degeneration may indicate a potential role for genetic modifiers, although this requires further investigation. Thus, diagnostic awareness about this distinct retinal phenotype has implications for the differential diagnosis of nephronophthisis and for individual prognosis of visual function.

Complement activation in children with Streptococcus pneumoniae associated hemolytic uremic syndrome.

BACKGROUND: Hemolytic uremic syndrome caused by invasive pneumococcal disease (P-HUS) is rare in children and adolescents, but accompanied by high mortality in the acute phase and complicated by long-term renal sequelae. Abnormalities in the alternative complement pathway may additionally be contributing to the course of the disease but also to putative treatment options. METHODS: Retrospective study to assess clinical course and laboratory data of the acute phase and outcome of children with P-HUS. RESULTS: We report on seven children (median age 12 months, range 3-28 months) diagnosed with P-HUS. Primary organ manifestation was meningitis in four and pneumonia in three patients. All patients required dialysis which could be discontinued in five of them after a median of 25 days. In two patients, broad functional and genetic complement analysis was performed and revealed alternative pathway activation and risk haplotypes in both. Three patients were treated with the complement C5 inhibitor eculizumab. During a median follow-up time of 11.3 years, one patient died due to infectious complications after transplantation. Two patients showed no signs of renal sequelae. CONCLUSIONS: Although pathophysiology in P-HUS remains as yet incompletely understood, disordered complement regulation seems to provide a clue to additional insights for pathology, diagnosis, and even targeted treatment.

Differential assessment of fluid compartments by bioimpedance in pediatric patients with kidney diseases.

BACKGROUND: The kidney is central for maintaining water balance. As a corollary, patients with impaired kidney function are prone to pathological fluid volumes. Total body water (TBW) is distributed between the extracellular (ECW) and intracellular fluid compartments (ICW). In clinical practice, the judgment of hydration status does not allow to distinguish between ECW and ICW. Here, we evaluate the hydration status in children with chronic kidney disease by analyzing TBW, ECW, and ICW. METHODS: Hydration was quantified using whole-body bioimpedance spectroscopy (BCM) in 128 outpatients (1-25 years, 52 girls). Forty-two were transplanted (TPL), 43 suffered from chronic kidney disease without kidney replacement therapy (CKD), 21 were on peritoneal dialysis (PD), and 22 on hemodialysis (HD). HD patients were investigated before, after, and sequentially during dialysis. RESULTS: The ECW and ICW values obtained by BCM were of the same magnitude as those from the literature using isotope dilution. When compared with a healthy control group, TBW was increased in 9 TPL, 9 CKD, 1 PD, and 11 HD patients before but in none after dialysis. The decline of overhydration during dialysis (p < 0.001, n = 22) correlated with the change in body weight (R2 = 0.62). The kinetics of fluid compartment changes assessed twice in six HD patients revealed a reproducible linear decay of the ECW/ICW ratio due to an increase of ICW and a decrease of ECW. CONCLUSION: BCM quantifies TBW and acute changes of ECW and ICW in children with chronic kidney failure. The clinical utility of measuring TBW, ECW, and ICW should be defined in the future.

Hemodiafiltration maintains a sustained improvement in blood pressure compared to conventional hemodialysis in children-the HDF, heart and height (3H) study.

BACKGROUND: Hypertension is prevalent in children on dialysis and associated with cardiovascular disease. We studied the blood pressure (BP) trends and the evolution of BP over 1 year in children on conventional hemodialysis (HD) vs. hemodiafiltration (HDF). METHODS: This is a post hoc analysis of the "3H - HDF-Hearts-Height" dataset, a multicenter, parallel-arm observational study. Seventy-eight children on HD and 55 on HDF who had three 24-h ambulatory BP monitoring (ABPM) measures over 1 year were included. Mean arterial pressure (MAP) was calculated and hypertension defined as 24-h MAP standard deviation score (SDS) ≥95th percentile. RESULTS: Poor agreement between pre-dialysis systolic BP-SDS and 24-h MAP was found (mean difference - 0.6; 95% limits of agreement -4.9-3.8). At baseline, 82% on HD and 44% on HDF were hypertensive, with uncontrolled hypertension in 88% vs. 25% respectively; p < 0.001. At 12 months, children on HDF had consistently lower MAP-SDS compared to those on HD (p < 0.001). Over 1-year follow-up, the HD group had mean MAP-SDS increase of +0.98 (95%CI 0.77-1.20; p < 0.0001), whereas the HDF group had a non-significant increase of +0.15 (95%CI -0.10-0.40; p = 0.23). Significant predictors of MAP-SDS were dialysis modality (ß = +0.83 [95%CI +0.51 - +1.15] HD vs. HDF, p < 0.0001) and higher inter-dialytic-weight-gain (IDWG)% (ß = 0.13 [95%CI 0.06-0.19]; p = 0.0003). CONCLUSIONS: Children on HD had a significant and sustained increase in BP over 1 year compared to a stable BP in those on HDF, despite an equivalent dialysis dose. Higher IDWG% was associated with higher 24-h MAP-SDS in both groups.

Long-term data on two sisters with C3GN due to an identical, homozygous CFH mutation and autoantibodies.

C3 glomerulonephritis (C3GN) is a rare but severe form of kidney disease caused by fluid-phase dysregulation of the alternative complement pathway. Causative mutations in complement regulating genes as well as auto-immune forms of C3GN have been described. However, therapy and prognosis in individual patients remain a matter of debate and long-term data are scarce. This also applies for the management of transplant patients as disease recurrence post-transplant is frequent. Here, we depict the clinical courses of two sisters with the unique combination of an identical, homozygous mutation in the complement factor H (CFH) gene as well as autoantibodies with a clinical follow-up of more than 20 years. Interestingly, the sisters presented with discordant clinical courses of C3GN with normal kidney function in one (patient A) and end-stage kidney disease in the other sister (patient B). In patient B, eculizumab was administered immediately prior to and in the course after kidney transplantation, with the result of a stable graft function without any signs of disease recurrence. Comprehensive genetic work-up revealed no further disease-causing mutation in both sisters. Intriguingly, the auto-antibody profile substantially differed in both sisters: autoantibodies in patient A reduced the C3b deposition, while the antibodies identified in patient B increased complement activation and deposition of split products. This study underlines the concept of a personalized-medicine approach in complement-associated diseases after thorough evaluation of the individual risk profile in each patient.

Effects of Hemodiafiltration versus Conventional Hemodialysis in Children with ESKD: The HDF, Heart and Height Study.

BACKGROUND: Hypertension and cardiovascular disease are common in children undergoing dialysis. Studies suggest that hemodiafiltration (HDF) may reduce cardiovascular mortality in adults, but data for children are scarce. METHODS: The HDF, Heart and Height study is a nonrandomized observational study comparing outcomes on conventional hemodialysis (HD) versus postdilution online HDF in children. Primary outcome measures were annualized changes in carotid intima-media thickness (cIMT) SD score and height SD score. RESULTS: We enrolled 190 children from 28 centers; 78 on HD and 55 on HDF completed 1-year follow-up. The groups were comparable for age, dialysis vintage, access type, dialysis frequency, blood flow, and residual renal function. At 1 year, cIMT SD score increased significantly in children on HD but remained static in the HDF cohort. On propensity score analysis, HD was associated with a +0.47 higher annualized cIMT SD score compared with HDF. Height SD score increased in HDF but remained static in HD. Mean arterial pressure SD score increased with HD only. Factors associated with higher cIMT and mean arterial pressure SD-scores were HD group, higher ultrafiltration rate, and higher ß2-microglobulin. The HDF cohort had lower ß2-microglobulin, parathyroid hormone, and high-sensitivity C-reactive protein at 1 year; fewer headaches, dizziness, or cramps; and shorter postdialysis recovery time. CONCLUSIONS: HDF is associated with a lack of progression in vascular measures versus progression with HD, as well as an increase in height not seen in the HD cohort. Patient-related outcomes improved among children on HDF correlating with improved BP control and clearances. Confirmation through randomized trials is required.

Inactivation of Apoptosis Antagonizing Transcription Factor in tubular epithelial cells induces accumulation of DNA damage and nephronophthisis.

Recent human genetic studies have suggested an intriguing link between ciliary signaling defects and altered DNA damage responses in nephronophthisis (NPH) and related ciliopathies. However, the molecular mechanism and the role of altered DNA damage response in kidney degeneration and fibrosis have remained elusive. We recently identified the kinase-regulated DNA damage response target Apoptosis Antagonizing Transcription Factor (AATF) as a master regulator of the p53 response. Here, we characterized the phenotype of mice with genetic deletion of Aatf in tubular epithelial cells. Mice were born without an overt phenotype, but gradually developed progressive kidney disease. Histology was notable for severe tubular atrophy and interstitial fibrosis as well as cysts at the corticomedullary junction, hallmarks of human nephronophthisis. Aatf deficiency caused ciliary defects as well as an accumulation of DNA double strand breaks. In addition to its role as a p53 effector, we found that AATF suppressed RNA:DNA hybrid (R loop) formation, a known cause of DNA double strand breaks, and enabled DNA double strand break repair in vitro. Genome-wide transcriptomic analysis of Aatf deficient tubular epithelial cells revealed several deregulated pathways that could contribute to the nephronophthisis phenotype, including alterations in the inflammatory response and anion transport. These results suggest that AATF is a regulator of primary cilia and a modulator of the DNA damage response, connecting two pathogenetic mechanisms in nephronophthisis and related ciliopathies.

HNF1B nephropathy has a slow-progressive phenotype in childhood-with the exception of very early onset cases: results of the German Multicenter HNF1B Childhood Registry.

BACKGROUND: HNF1B gene mutations are an important cause of bilateral (cystic) dysplasia in children, complicated by chronic renal insufficiency. The clinical variability, the absence of genotype-phenotype correlations, and limited long-term data render counseling of affected families difficult. METHODS: Longitudinal data of 62 children probands with genetically proven HNF1B nephropathy was obtained in a multicenter approach. Genetic family cascade screening was performed in 30/62 cases. RESULTS: Eighty-seven percent of patients had bilateral dysplasia, 74% visible bilateral, and 16% unilateral renal cysts at the end of observation. Cyst development was non-progressive in 72% with a mean glomerular filtration rate (GFR) loss of - 0.33 ml/min/1.73m2 per year (± 8.9). In patients with an increase in cyst number, the annual GFR reduction was - 2.8 ml/min/1.73m2 (± 13.2), in the total cohort - 1.0 ml/min/1.73m2 (±10.3). A subset of HNF1B patients differs from this group and develops end stage renal disease (ESRD) at very early ages < 2 years. Hyperuricemia (37%) was a frequent finding at young age (median 1 year), whereas hypomagnesemia (24%), elevated liver enzymes (21%), and hyperglycemia (8%) showed an increased incidence in the teenaged child. Genetic analysis revealed no genotype-phenotype correlations but a significant parent-of-origin effect with a preponderance of 81% of maternal inheritance in dominant cases. CONCLUSIONS: In most children, HNF1B nephropathy has a non-progressive course of cyst development and a slow-progressive course of kidney function. A subgroup of patients developed ESRD at very young age < 2 years requiring special medical attention. The parent-of-origin effect suggests an influence of epigenetic modifiers in HNF1B disease.

Indoxyl sulfate associates with cardiovascular phenotype in children with chronic kidney disease.

BACKGROUND: Cardiovascular disease is the leading cause of death in children with chronic kidney disease (CKD). Serum levels of gut-derived uremic toxins increase with deterioration of kidney function and are associated with cardiac comorbidities in adult CKD patients. METHODS: Indoxyl sulfate (IS) and p-cresyl sulfate (pCS) were measured by high-performance liquid chromatography in serum of children participating in the Cardiovascular Comorbidity in Children with CKD (4C) Study. Results were correlated with measurements of the carotid intima-media thickness (cIMT), central pulse wave velocity (PWV), and left ventricular mass index (LVMI) in children aged 6-17 years with initial eGFR of 10-60 ml/min per 1.73 m2. RESULTS: The median serum levels of total IS and of pCS, measured in 609 patients, were 5.3 µmol/l (8.7) and 17.0 µmol/l (21.6), respectively. In a multivariable regression model, IS and pCS showed significant positive associations with urea and negative associations with eGFR and uric acid. Furthermore, positive associations of pCS with age, serum albumin, and non-Mediterranean residency and a negative association with glomerular disease were observed. By multivariable regression analysis, only IS was significantly associated with a higher cIMT SDS at baseline and progression of PWV SDS within 12 months, independent of other risk factors. CONCLUSIONS: Serum levels of gut-derived uremic toxins IS and pCS correlated inversely with eGFR in children. Only IS was significantly associated with surrogate markers of cardiovascular disease in this large pediatric CKD cohort.

Discontinuation of maintenance therapy in frequently relapsing nephrotic syndrome
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Childhood steroid-dependent (SDNS) and frequently relapsing (FRNS) nephrotic syndromes often require long-term immunosuppressive therapy to maintain remission. Successful discontinuation of maintenance therapy remains to be a challenge with these children. In the following article, we report our experience on patients after discontinuation of steroid-sparing immunosuppressive maintenance therapy (IT). Thereby, we retrospectively reviewed all patients between 2006 and 2016 with a relapsing course of steroid-sensitive nephrotic syndrome (SDNS or FRNS) treated with steroid-sparing maintenance immunosuppressive medication. Patient data of a total of 24 patients were recorded for a median time of 53.5 (11.2 - 112) months. In 11 patients, therapy was discontinued at physician's discretion. Thereafter, 8 of 11 patients (group A) relapsed after a median time of 2.21 (0.23 - 9.17) months, and IT was restarted. The remaining 3 patients (group B) maintained in long-term remission for a median time of 26.9 (17.7 - 32.1) months until the end of observation. Neither age, at initial episode nor at discontinuation or duration of IT, differed significantly between the groups of patients with relapse after discontinuation of IT, compared to those without. There was a trend towards a shorter relapse-free interval before discontinuation in group A than in group B (35.7 vs. 44.1 months). All patients who restarted IT again attained a stable remission until the last follow-up and did not show any further relapse. These results demonstrate that a failed discontinuation attempt does not put the patient's future remission at risk.
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Three-layered proteomic characterization of a novel ACTN4 mutation unravels its pathogenic potential in FSGS.

Genetic diseases constitute the most important cause for end-stage renal disease in children and adolescents. Mutations in the ACTN4 gene, encoding the actin-binding protein α-actinin-4, are a rare cause of autosomal dominant familial focal segmental glomerulosclerosis (FSGS). Here, we report the identification of a novel, disease-causing ACTN4 mutation (p.G195D, de novo) in a sporadic case of childhood FSGS using next generation sequencing. Proteome analysis by quantitative mass spectrometry (MS) of patient-derived urinary epithelial cells indicated that ACTN4 levels were significantly decreased when compared with healthy controls. By resolving the peptide bearing the mutated residue, we could proof that the mutant protein is less abundant when compared with the wild-type protein. Further analyses revealed that the decreased stability of p.G195D is associated with increased ubiquitylation in the vicinity of the mutation site. We next defined the ACTN4 interactome, which was predominantly composed of cytoskeletal modulators and LIM domain-containing proteins. Interestingly, this entire group of proteins, including several highly specific ACTN4 interactors, was globally decreased in the patient-derived cells. Taken together, these data suggest a mechanistic link between ACTN4 instability and proteome perturbations of the ACTN4 interactome. Our findings advance the understanding of dominant effects exerted by ACTN4 mutations in FSGS. This study illustrates the potential of genomics and complementary, high-resolution proteomics analyses to study the pathogenicity of rare gene variants.

Effects of nutritional vitamin D supplementation on markers of bone and mineral metabolism in children with chronic kidney disease.

Background: We investigated the effects of nutritional vitamin D supplementation on markers of bone and mineral metabolism, i.e. serum levels of fibroblast growth factor 23 (FGF23), Klotho, bone alkaline phosphatase (BAP) and sclerostin, in two cohorts with chronic kidney disease (CKD). Methods: In all, 80 vitamin D-deficient children were selected: 40 with mild to moderate CKD from the ERGO study, a randomized trial of ergocalciferol supplementation [estimated glomerular filtration rate (eGFR) 55 mL/min/1.73 m2], and 40 with advanced CKD from the observational Cardiovascular Comorbidity in Children with Chronic Kidney Disease (4C) study (eGFR 24 mL/min/1.73 m2). In each study, vitamin D supplementation was started in 20 children and 20 matched children not receiving vitamin D served as controls. Measures were taken at baseline and after a median period of 8 months. Age- and gender-related standard deviation scores (SDSs) were calculated. Results: Before vitamin D supplementation, children in the ERGO study had normal FGF23 (median 0.31 SDS) and BAP (-0.10 SDS) but decreased Klotho and sclerostin (-0.77 and -1.04 SDS, respectively), whereas 4C patients had increased FGF23 (3.87 SDS), BAP (0.78 SDS) and sclerostin (0.76 SDS) but normal Klotho (-0.27 SDS) levels. Vitamin D supplementation further increased FGF23 in 4C but not in ERGO patients. Serum Klotho and sclerostin normalized with vitamin D supplementation in ERGO but remained unchanged in 4C patients. BAP levels were unchanged in all patients. In the total cohort, significant effects of vitamin D supplementation were noted for Klotho at eGFR 40-70 mL/min/1.73 m2. Conclusions: Vitamin D supplementation normalized Klotho and sclerostin in children with mild to moderate CKD but further increased FGF23 in advanced CKD.

Mycophenolate mofetil following glucocorticoid treatment in Henoch-Schönlein purpura nephritis: the role of early initiation and therapeutic drug monitoring.

BACKGROUND: Henoch-Schönlein purpura (HSP) is the most common vasculitis in childhood and traditionally considered as a self-limiting disease. However, renal involvement can unfavorably determine long-term prognosis. The reported regimens to treat HSP nephritis (HSPN) are diverse, indicating that the most effective treatment remains controversial. METHODS: This retrospective, single-center study involved 18 patients presenting with HSPN and nephrotic-range proteinuria. We aimed to investigate the efficacy and safety of mycophenolate mofetil (MMF) and identify a cut-off level for estimated mycophenolic acid area under the curve (eMPA-AUC0-12h) values, which can predict complete remission with high sensitivity. RESULTS: Despite prior insufficient therapeutic response to corticosteroids, 89% of patients showed a significant decrease in proteinuria after 1 month of MMF treatment. None of them relapsed during treatment; however, two children relapsed after discontinuation. Based on results of a receiver operating characteristic (ROC) analysis, an eMPA-AUC0-12h >56.4 mg*h/l was a predictor for complete remission within 3 months (80% sensitivity, 83.3% specificity, p = 0.035). During MMF administration, we encountered no adverse event requiring discontinuation of treatment. CONCLUSION: Our study demonstrates that MMF is a safe and potentially effective secondary treatment option for children with HSPN to achieve and maintain long-term remission without serious side effects. To achieve complete remission within 3 months, resolve severe inflammatory glomerular lesions, and avoid progression to chronic kidney disease, we propose timely diagnosis and early initiation of MMF with an eMPA-AUC0-12h value of 56.4 mg*h/l.