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Background and Aims Monogenic causes of steroid-resistant nephrotic syndrome (SRNS) have been reported for up to one-third of children depending on age of the disease onset. Immunosuppressive treatment of genetic SRNS with calcineurin inhibitors (CNIs) is still controversial. The aim of the study was to investigate the efficacy of CNIs with focus on inducing remission and long-term kidney function in children with monogenic SRNS. Method Retrospective analysis of efficacy CNIs in five children (2M/3F) with monogenic SRNS was performed. Kidney biopsy prior CNIs revealed FSGS (n=4) and MCD (n=1). The initial cyclosporine (CsA) dose was 5 mg/kg/24h to keep a target level of 80-150 ng/ml and tacrolimus (TAC) - 0.1 mg/kg/24h to achieve a target level of 5-10 ng/ml. CsA took all 5 patients with subsequent switching to TAC in 2 children due to cosmetic side effects. The median follow-up period was 165.0 (IQR: 59.0; 185.5) months. Next generation sequencing (NGS) was used for identification of pathogenic variants in all patients. Results The median age at onset of monogenic SRNS was 33.0 (IQR: 16.5; 63.0) months. 2/5 (40%) patients presented with acute SRNS, 1/5 (20%) child with infantile NS, 1/5 (20%) - with isolated nephrotic range proteinuria with hypoalbuminemia and 1/5 (20%) - with NS and extrarenal features of Nail-Patella syndrome. NGS identified previously described pathogenic variants in all 5 children, including NPHS2 homozygous c.28dup (p.Glu87Ter) (n=1), NPHS2 compound heterozygous c.868G>A (p.Val290Met) in combination with c.686G>A (p.Arg229Gln) (n=1), LMX1B heterozygous c.788T>G (p.Val263Gly) (n=1), LMX1B heterozygous c.737G>A (p.Arg246Gln) (n=1), and COL4A3 heterozygous c.2962G>A (p.Gly988Arg) variant (n=1). The median time from diagnosis to initiation of CNIs treatment was 72.0 (IQR: 33.0; 93.0) months. CNIs induced complete remission in 2/5 (40%) patients, presented with acute SRNS, including one girl with MCD due to NPHS2 compound heterozygous variants with mutation-dependent pathogenicity of one (p.R229Q) of them and one boy with FSGS due to COL4A3 heterozygous variant (n=1). Partial remission was induced by CNIs in 2/5 (40%) girls with FSGS due to LMX1B heterozygous variants with isolated SRNS (n=1) and Nail-Patella syndrome (n=1). The median duration of CNIs treatment to obtain complete or partial remission was 13.5 (IQR: 6.8; 15.8) months. Acute CNIs-associated nephrotoxicity had 2 patients with LMX1B variants. At the last follow up full and partial responders to CNIs treatment aged of 16.5 (IQR: 11.8; 17.5) years had CKD-1 (n=3) and CKD-2 (n=1). 1/5 (20%) boy with NPHS2-associated infantile NS was CNI resistant and developed CKD-5 at the age of 6.5 years with subsequent living related kidney transplantation. Conclusion We found that 4/5 (80%) children with monogenic SRNS demonstrated partial or full response to CNIs treatment with stable long-term kidney function. We assume that CNIs might improve podocyte function by stabilization of their cytoskeleton disrupted in patients with monogenic SRNS.

Background and Aims Distal renal tubular acidosis (dRTA) is a rare disorder characterised by an inability of the distal tubule to secrete acid, leading to metabolic acidosis. Clinical consequences typically include hypokalaemia, hypercalciuria with nephrocalcinosis and/or urolithiasis, as well as bone disease. Treatment with adequate alkali supplementation corrects the acidosis and hypercalciuria, but there are few data on long-term outcome. In 2018, a registry for dRTA was established by the European Society for Paediatric Nephrology, hosted by the European Rare Kidney Disease Reference Network. Here, we present an initial analysis of data in the registry. Method Analysis of data entered into the registry by the cut-off data of 18/11/2020. Results A total of 135 patients had been entered, of which 106 had additional data from an annual follow-up visit. Median age at last visit was 10 years (range 0-54), including 16 adults (>17y). Genetic testing had been performed in 91 subjects and causative variants were reported in 74 (81%). Pertinent clinical details according to genetic group are listed in table 1. Treatment was provided with at least 15 different preparations, containing citrate or bicarbonate, given in 1-10 (median 3) daily doses. Adequate treatment at last follow-up, as judged by a plasma bicarbonate level >21 mmol/l and a urine calcium-creatinine ratio in the age-specific normal range was present in 46% of subjects. There was a trend for higher eGFR and height SDS in subjects with adequate treatment compared to those without, but this was not statistically significant. Conclusion Currently available data demonstrate the difficulties in treating dRTA, with less than half of subjects achieving adequate control of their acidosis. By collecting long-term data, the registry will provide important information on the prognosis and complications of dRTA and to what degree these can be prevented with treatment. Enrollment of further, especially adult patients will contribute to our understanding of this rare disorder.

Background and Aims Hereditary hypophosphatemic rickets with hypercalciuria (HHRH; MIM #241530) is an autosomal recessive renal phosphate-wasting disorder caused by mutations in the SLC34A3/NPT2c gene. HHRH characterized by increased urinary phosphate excretion leading to hypophosphatemic rickets, short stature and elevated serum 1,25(OH)2D levels which result in hypercalciuria leads to nephrocalcinosis/urolithiasis due to enhanced intestinal calcium absorption and reduced PTH-dependent calcium reabsorption in the distal renal tubules. Treatment of HHRH involves administration of oral phosphate supplements alone to normalize of serum phosphate, alkaline phosphatase activity (ALP), PTH levels, urine calcium excretion for prevention of renal calcifications and progression of rickets. Currently there is no consensus on the optimal dose of oral phosphate in patients with HHRH. The aim of the study was to evaluate the efficacy of oral phosphate supplements in Russian cohort of children with HHRH. Method 9 children (7M/2F) with homozygous (n=6) and compound heterozygous (n=3) SLC34A3 mutations from unrelated families were examined. Treatment with oral phosphate supplements was started at the median age of patients 12.0 (IQR: 9.0; 13.0) years. The median dosage of oral phosphate supplements was 14.1 (IQR: 13.8; 14.8) mg/kg/day based on elemental phosphorus. The duration of follow-up was 36.0 (IQR: 16; 49) months. Blood electrolytes levels, ALP, PTH and 24-hour-urine excretion of calcium were evaluated in all children. ALP Z-scores were calculated using age- and sex-specific mean/standard deviation (SD) lab reference data. Bone mineral density with Z-score were measured in lumbar spine and whole body for all patients using a dual energy X-ray absorptiometry device. Molecular genetic analysis was performed in all children using by next generation sequencing. Results The median SD score of height at the first and last follow-up was -1.35 (IQR: -1.8; -0.87) and -1.51 (IQR: -2.0; -0.66) (p=0.6), respectively, short stature had 33.3% (3/9) of patients at first and 44.4% (4/9) at last follow-up (p=0.7). Treatment with low doses of oral phosphate supplements did not led to normalization of serum phosphorus:1.05 (IQR: 0.97; 1.39) vs. 0.93 (IQR: 0.81; 1.27) mmol/l (p=0.13), PTH: 8.3 (IQR: 5.8; 13.8) vs. 12.9 (IQR: 12.0; 16.0) pg/ml (p=0.34), Z-score in lumbar spine: -1.2 (IQR: -2.7; -0.1) vs. -1.8 (IQR: -2.8; -1.1) (p=0.48) and Z-score in total body: -2.1 (IQR -2.6; -1.5) vs. -2.4 (IQR: -3.0; -2.0) (p=0.37). Hypercalciuria had 88.8% (8/9) of children (0.15 (IQR: 0.12; 0.19) mmol/kg/day) at first follow-up and 44.4% (4/9) (0.09 (IQR: 0.08; 0.16) mmol/kg/day) in last examination (p=0.13). ALP blood levels were elevated in all patients (9/9) at first and most recent visit, but ALP Z-score were significant lower at last follow-up: 3.9 (IQR: 1.2; 5.1) vs. 0.57 (IQR: -0.36; 2.1) (p=0.04). There were significant correlations between doses of oral phosphate supplements and ALP Z-score (r=-0.68; p=0.04) and total body Z-score (r=0.78; p=0.03). There was no significant correlations between ALP Z-score and total body Z-score (r=-0.3) or lumbar spine Z-score (r=-0.1). Conclusion The present study demonstrated that treatment of HHRH with low doses ( Lack of association between ALP Z-score and bone mineral density severity on radiographs limits the value of serum ALP as the indicator of rickets activity.

Autosomal recessive polycystic kidney disease (ARPKD) is a severe disease of early childhood that is clinically characterized by fibrocystic changes of the kidneys and the liver. The main cause of ARPKD are variants in the PKHD1 gene encoding the large transmembrane protein fibrocystin. The mechanisms underlying the observed clinical heterogeneity in ARPKD remain incompletely understood, partly due to the fact that genotype-phenotype correlations have been limited to the association of biallelic null variants in PKHD1 with the most severe phenotypes. In this observational study we analyzed a deep clinical dataset of 304 patients with ARPKD from two independent cohorts and identified novel genotype-phenotype correlations during childhood and adolescence. Biallelic null variants frequently show severe courses. Additionally, our data suggest that the affected region in PKHD1 is important in determining the phenotype. Patients with two missense variants affecting amino acids 709-1837 of fibrocystin or a missense variant in this region and a null variant less frequently developed chronic kidney failure, and patients with missense variants affecting amino acids 1838-2624 showed better hepatic outcome. Variants affecting amino acids 2625-4074 of fibrocystin were associated with poorer hepatic outcome. Thus, our data expand the understanding of genotype-phenotype correlations in pediatric ARPKD patients and can lay the foundation for more precise and personalized counselling and treatment approaches. German Society for Pediatric Nephrology (GPN); ESCAPE Network; European Society for Paediatric Nephrology (ESPN); German PKD foundation; Koeln Fortune program; GEROK program of the Medical Faculty of University of Cologne; Marga and Walter Boll-Foundation; German Federal Ministry of Research and Education (BMBF)Federal Ministry of Education & Research (BMBF) [01GM1515, 01GM1903]; working group CAKUT of the ESPN; working group Inherited Kidney Diseases of the ESPN We thank the German Society for Pediatric Nephrology (GPN) and the ESCAPE Network for their support. We thank Mr Mathias Burgmaier (Aachen) and Mr Samuel Kilian (Heidelberg) for support in conducting statistical analysis. ML was supported by grants of the GPN, the European Society for Paediatric Nephrology (ESPN), the German PKD foundation, the Koeln Fortune program, the GEROK program of the Medical Faculty of University of Cologne, and the Marga and Walter Boll-Foundation. FS, CB, and ML are supported by the German Federal Ministry of Research and Education (BMBF grant 01GM1515 and 01GM1903). KB was supported by the Koeln Fortune program and the GEROK program of the Medical Faculty of University of Cologne, as well as the Marga and Walter Boll-Foundation. This work was generated within the European Reference Network for Rare Kidney Disorders (ERKNet). The work was supported by the working groups CAKUT and Inherited Kidney Diseases of the ESPN.

Background and Aims Hepatocyte nuclear factor 1 gene (HNF1B) encodes for HNF-1ß, a transcription factor that is expressed early in embryonic development and plays a key role for tissue-specific regulations of gene expression in various organs such as the kidneys, urogenital tract, liver, biliary ducts and pancreas. HNF1B disease (MIM 137920) is recognized to represent an autosomal dominant syndromal disorder comprising variable phenotype with renal and extrarenal manifestations. Renal phenotype in HNF1B nephropathy is highly heterogeneous. The aim of the study was to evaluate the clinical characteristics of renal involvement in children with genetically proven HNF1B nephropathy. Method Five children (2M/3F) from unrelated families with heterozygous HNF1β mutations and kidney disorders were examined. We evaluated serum levels of electrolytes, magnesium (Mg), phosphorus (P), uric acid, acid-base composition; urinary excretion of Ca, P, creatinine (Cr); fractional excretion (FE) of Mg, urate (Ur), Na, K; tubular maximum phosphate reabsorption per GFR (TmP/GFR), and urinary β-2 microglobulin. Molecular genetic analysis was performed using by next generation sequencing. Results Cortical or medullary bilateral renal cysts were detected in all five children with HNF1B nephropathy. Kidney hypoplasia, medullary nephrocalcinosis, and low-grade proteinuria ( Conclusion The present study demonstrates that patients with HNF1B-associated disease had wide spectrum of renal involvement. The most prevalent features of HNF1B nephropathy in our children were bilateral renal cysts, defects of proximal tubular function with wasting of electrolytes and progression to CKD stage 2-3 at early age.

BackgroundCystinosis is an autosomal recessive lysosomal storage disorder characterized by accumulation of cystine in lysosomes throughout the body. Cystinosis is caused by mutations in theCTNSgene that encodes the lysosomal cystine carrier protein cystinosin.CTNSmutations result in either complete absence or reduced cystine transporting function of the protein. The diagnosis of nephropathic cystinosis is generally based on measuring leukocyte cystine level, demonstration of corneal cystine crystals by the slit lamp examination and confirmed by genetic analysis of theCTNSgene.Case presentationA boy born to consanguineous Caucasian parents had the characteristic clinical features of the infantile nephropathic cystinosis including renal Fanconi syndrome (polydipsia/polyuria, metabolic acidosis, hypokalemia, hypophosphatemia, low molecular weight proteinuria, glycosuria, cystine crystals in the cornea) and elevated WBC cystine levels. Initially we performed RFLP analysis of the common in the Northern European population 57-kb deletion of proband’s DNA, then a direct Sanger sequencing which revealed no mutations in the coding part of theCTNSgene. To confirm the diagnosis we performed RT-PCR analysis of total RNA obtained from patient-derived fibroblasts in combination with cDNA sequencing. This revealed the skipping of exon 4 and exon 5 in theCTNSin our patient. Therefore, we detected a novel 9-kb homozygous deletion in theCTNSgene at genomic DNA level, spanning region from intron 3 to intron 5. In order to identify the inheritance pattern of the deletion we analyzed DNA of proband’s mother and father. Both parents were found to be heterozygous carriers of theCTNSmutation.ConclusionsAnalysis ofCTNSgene transcript allowed to identify a large homozygous deletion in the patient with infantile nephropathic cystinosis. Mutational detection at RNA level may be an efficient tool to establish the genetic defect in some cystinosis patients.

BACKGROUND AND OBJECTIVES: Autosomal dominant polycystic kidney disease is the most common inheritable kidney disease, frequently thought to become symptomatic in adulthood. However, patients with autosomal dominant polycystic kidney disease may develop signs or symptoms during childhood, in particular hypertension. Although ambulatory BP monitoring is the preferred method to diagnose hypertension in pediatrics, data in children with autosomal dominant polycystic kidney disease are limited. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Our retrospective multicenter study was conducted to collect ambulatory BP monitoring recordings from patients with autosomal dominant polycystic kidney disease age 1 cm per kidney and daytime hypertension (odds ratio, 1.70; 95% confidence interval, 1.21 to 2.4; P=0.002), nighttime hypertension (odds ratio, 1.31; 95% confidence interval, 1.05 to 1.63; P=0.02), or 24-hour hypertension (odds ratio, 1.39; 95% confidence interval, 1.08 to 1.81; P=0.01). Kidney length, expressed as SD score, was also significantly associated with nighttime hypertension (odds ratio, 1.23; 95% confidence interval, 1.06 to 1.42; P=0.10). CONCLUSIONS: These data indicate high prevalence of hypertension in children with autosomal dominant polycystic kidney disease starting at young ages. ispartof: CLINICAL JOURNAL OF THE AMERICAN SOCIETY OF NEPHROLOGY vol:13 issue:6 pages:874-883 ispartof: location:United States status: published

OBJECTIVE: To identify prenatal, perinatal, and postnatal risk factors for dialysis within the first year of life in children with autosomal recessive polycystic kidney disease (ARPKD) as a basis for parental counseling after prenatal and perinatal diagnosis. STUDY DESIGN: A dataset comprising 385 patients from the ARegPKD international registry study was analyzed for potential risk markers for dialysis during the first year of life. RESULTS: Thirty-six out of 385 children (9.4%) commenced dialysis in the first year of life. According to multivariable Cox regression analysis, the presence of oligohydramnios or anhydramnios, prenatal kidney enlargement, a low Apgar score, and the need for postnatal breathing support were independently associated with an increased hazard ratio for requiring dialysis within the first year of life. The increased risk associated with Apgar score and perinatal assisted breathing was time-dependent and vanished after 5 and 8 months of life, respectively. The predicted probabilities for early dialysis varied from 1.5% (95% CI, 0.5%-4.1%) for patients with ARPKD with no prenatal sonographic abnormalities to 32.3% (95% CI, 22.2%-44.5%) in cases of documented oligohydramnios or anhydramnios, renal cysts, and enlarged kidneys. CONCLUSIONS: This study, which identified risk factors associated with onset of dialysis in ARPKD in the first year of life, may be helpful in prenatal parental counseling in cases of suspected ARPKD. ispartof: JOURNAL OF PEDIATRICS vol:199 pages:22-+ ispartof: location:United States status: published

Autosomal recessive polycystic kidney disease (ARPKD) is a rare monogenic disease with a severe phenotype often presenting prenatally or in early childhood. With its obligate renal and hepatic involvement, ARPKD is one of the most important indications for liver and/or kidney transplantation in childhood. Marked phenotypic variability is observed, the genetic basis of which is largely unknown. Treatment is symptomatic and largely empiric as evidence-based guidelines are lacking. Therapeutic initiatives for ARPKD face the problem of highly variable cohorts and lack of clinical or biochemical risk markers without clear-cut clinical end points. ARegPKD is an international, multicenter, retro- and prospective, observational study to deeply phenotype patients with the clinical diagnosis of ARPKD. Initiated in 2013 as a web-based registry (www.aregpkd.org), ARegPKD enrolls patients across large parts of Europe and neighboring countries. By January 2017, more than 400 patients from 17 mostly European countries have been registered in the ARPKD registry study with significant follow-up data. Due to comprehensive retro- and prospective data collection and associated biobanking, ARegPKD will generate a unique ARPKD cohort with detailed longitudinal clinical characterization providing a basis for future clinical trials as well as translational research. Hence, ARegPKD is hoped to contribute to the pathophysiological understanding of the disease and to the improvement of clinical management. ispartof: Frontiers in Pediatrics vol:5 pages:18- ispartof: location:Switzerland status: published