Pediatric kidney transplantation in patients with inherited disorders and associated congenital anomalies constitutes a true challenge, especially in low weight recipients (< 15–20 kg). Potential barriers for a successful transplant involve size-mismatch between donor organ and recipient as well as identification of suitable vascular anastomotic sites in case of vascular anomalies. We present a case of a 5-year-old girl with azygos continuation of the inferior vena cava (IVC), a condition generally precluding transplantation of an adult-sized kidney as adequate venous outflow from the transplant cannot be achieved. By interposing a prosthetic vascular graft, the donor renal vein was anastomosed to the suprahepatic IVC, thereby enabling transplantation of a live donor kidney to the pediatric recipient with the technical success being reflected in immediate graft function. Anatomical barriers such as azygos continuation of the IVC do not preclude kidney transplantation from a size-mismatched adult live donor a priori but demand a patient-tailored innovative surgical approach and a committed multidisciplinary perioperative management to potentially overcome this kind of vascular anomaly.

Children presenting with proliferative lupus nephritis (LN) are treated with intensified immunosuppressive protocols. Data on renal outcome and treatment toxicity is scare. Twelve-month renal outcome and comorbidity were assessed in 79 predominantly Caucasian children with proliferative LN reported to the Lupus Nephritis Registry of the German Society of Paediatric Nephrology diagnosed between 1997 and 2015. At the time of diagnosis, median age was 13.7 (interquartile range 11.8–15.8) years; 86% showed WHO histology class IV, nephrotic range proteinuria was noted in 55%, and median estimated glomerular filtration rate amounted to 75 ml/min/1.73 m2. At 12 months, the percentage of patients with complete and partial remission was 38% and 41%, respectively. Six percent of patients were non-responders and 15% presented with renal flare. Nephrotic range proteinuria at the time of diagnosis was associated with inferior renal outcome (odds ratio 5.34, 95% confidence interval 1.26–22.62, p = 0.02), whereas all other variables including mode of immune-suppressive treatment (e.g., induction treatment with cyclophosphamide (IVCYC) versus mycophenolate mofetil (MMF)) were not significant correlates. Complications were reported in 80% of patients including glucocorticoid toxicity in 42% (Cushingoid appearance, striae distensae, cataract, or osteonecrosis), leukopenia in 37%, infection in 23%, and menstrual disorder in 20%. Growth impairment, more pronounced in boys than girls, was noted in 78% of patients. In this cohort of juvenile proliferative LN, renal outcome at 12 months was good irrespectively if patients received induction treatment with MMF or IVCYC, but glucocorticoid toxicity was very high underscoring the need for corticoid sparing protocols.

A major obstacle in kidney transplantation for primary focal segmental glomerulosclerosis (FSGS) is the risk of disease recurrence. Recurrent FSGS affects up to 60% of first kidney grafts and exceeds 80% in patients who have lost their first graft due to recurrent FSGS. Clinical and experimental evidence support the hypothesis that a circulating permeability factor is the mediator in the pathogenesis of primary and recurrent disease. Despite all efforts, the causing agent has not yet been identified. Several treatment options for the management of recurrent FSGS have been proposed. In addition to plasma exchange, B-cell depleting antibodies are effective in recurrent FSGS. This indicates, that the secretion and/or activity of the postulated circulating permeability factor(s) may be B-cell related. This review summarizes the current knowledge on permeability factor(s) possibly related to the disease and discusses strategies for the management of recurrent FSGS. These include profound B-cell depletion prior to transplantation, as well as the salvage of an allograft affected by recurrent FSGS by transfer into a second recipient.

Aims & Objectives: Regional citrate anticoagulation (RCA) is the preferred method of anticoagulation for continuous renal replacement therapy (CRRT) as it prolonges circuit lifespan without increasing the risk of bleeding. However, as citrate binds to calcium and is reduced to bicarbonate, RCA may lead to electrolyt and acid-base disturbances. Methods A retrospective analyses were performed in all children treated with CRRT and RCA at a PICU in a academic children´s hospital over a three year period. RCA was performed using a pre-dilution citrate solution to achieve a circuit citrate concentration of 3mmol/l blood flow and aiming for an extracorporeal ionised calcium (iCa) of 0.25-0.35mmol/l. Calcium was re-infused to the patient aiming for a systemic iCa of 0.9–1.2mmol/l. Results Twenty five patients (mean age: 7.2 years, mean duration of CRRT: 154 hours) were analysed. Episodes of metabolic disturbances detected during CRRT were: Hyponatremia: mild (130-135mmol/l), n=271, severe (<130), n=5; Hypernatremia: mild (145–150), n=2, severe (>150), n=0; Hypokalemia: mild (2.5–3.5mmol/l), n=349, severe (<2.5l), n=1; Hyperkalemia: mild (5.5-7l), n=2, severe (>7), n=0; Hypomagnesaemia: mild (0.35-7mg/dl), n=148, severe (<0.35), n=1; Hypermagnesaemia: mild (1.0–1.6), n=147, severe (>1.6), n=15; Hypophosphataemia:, mild (0.65–1.05mg/dl), n=426, severe (<0.65), n=127; Hyperphosphataemia: mild (1.7–2.0), n=31, severe (>2.0), n=11; Hypocalcaemia: mild (1.75–2.2mmol/l), n=83, severe (<1.75); n=7; Hypercalcaemia: mild (2.7–3.1), n=98, severe (>3.1), n=22; metabolic acidosis: mild (7.25–7.35), n=127, severe (<7.25), n=52; metabolic alkalosis: mild (7.45–7.55), n=268, severe (>7.55), n=16. Conclusions Metabolic disturbances during CRRT with RCA are common and mostly mild in nature. A strict protocol with rigourous monitoring is mandatory to ensure patient safety during RCA.

Over the last decades, a growing spectrum of monogenic disorders of human magnesium homeostasis has been clinically characterized, and genetic studies in affected individuals have identified important molecular components of cellular and epithelial magnesium transport. Here, we describe three infants who are from non-consanguineous families and who presented with a disease phenotype consisting of generalized seizures in infancy, severe hypomagnesemia, and renal magnesium wasting. Seizures persisted despite magnesium supplementation and were associated with significant intellectual disability. Whole-exome sequencing and conventional Sanger sequencing identified heterozygous de novo mutations in the catalytic Na+, K+-ATPase alpha 1 subunit (ATP1A1). Functional characterization of mutant Na+, K+-ATPase alpha 1 subunits in heterologous expression systems revealed not only a loss of Na+, K+-ATPase function but also abnormal cation permeabilities, which led to membrane depolarization and possibly aggravated the effect of the loss of physiological pump activity. These findings underline the indispensable role of the alpha 1 isoform of the Na+, K+-ATPase for renal-tubular magnesium handling and cellular ion homeostasis, as well as maintenance of physiologic neuronal activity.

Primary focal segmental glomerulosclerosis (FSGS) recurs in up to 55% of patients after kidney transplantation. Herein we report the successful management of recurrent FSGS. A 5-year-old boy with primary FSGS received a deceased donor renal transplant. Immediate and fulminant recurrence of FSGS caused anuric graft failure that was resistant to plasmapheresis and rituximab. After exclusion of structural or immunologic damage to the kidney by repeated biopsies, the allograft was retrieved from the first recipient on day 27 and transplanted into a 52-year-old second recipient who had vascular nephropathy. Immediately after retransplantation, the allograft regained function with excellent graft function persistent now at 3 years after transplant. After 2 years on hemodialysis, the boy was listed for kidney retransplantation. To prevent FSGS recurrence, pretreatment with ofatumumab was performed. Nephrotic range proteinuria still occurred after the second transplantation, which responded, however, to daily plasma exchange in combination with ofatumumab. At 8 months after kidney retransplantation graft function is good. The clinical course supports the hypothesis of a circulating permeability factor in the pathogenesis of FSGS. Successful ofatumumab pretreatment implicates a key role of B cells. Herein we provide a description of successful management of kidney failure by FSGS, carefully avoiding waste of organs.

We identified two unrelated consanguineous families with three children affected by the rare association of congenital nephrotic syndrome (CNS) diagnosed in the first days of life, of hypogonadism, and of prenatally detected adrenal calcifications, associated with congenital adrenal insufficiency in one case. Using exome sequencing and targeted Sanger sequencing, two homozygous truncating mutations, c.1513C>T (p.Arg505*) and c.934delC (p.Leu312Phefs*30), were identified in SGPL1-encoding sphingosine-1-phosphate (S1P) lyase 1. SGPL1 catalyzes the irreversible degradation of endogenous and dietary S1P, the final step of sphingolipid catabolism, and of other phosphorylated long-chain bases. S1P is an intracellular and extracellular signaling molecule involved in angiogenesis, vascular maturation, and immunity. The levels of SGPL1 substrates, S1P, and sphingosine were markedly increased in the patients' blood and fibroblasts, as determined by liquid chromatography-tandem mass spectrometry. Vascular alterations were present in a patient's renal biopsy, in line with changes seen in Sgpl1 knockout mice that are compatible with a developmental defect in vascular maturation. In conclusion, loss of SGPL1 function is associated with CNS, adrenal calcifications, and hypogonadism.

BackgroundTherapeutic plasma exchange (TPE) has evolved to an accepted therapy for selected indications. However, it is technically challenging in children. Moreover, data on safety and efficacy are mainly derived from adult series. The aim of this study was to review the procedure in the context of clinical indications, effectiveness, and safety. Study Design and MethodsAll TPE procedures performed at a tertiary care hospital during a 12-year period (2005-2016) were retrospectively evaluated. ResultsEighteen patients with a median age of 8.5 (0.2-17) years underwent a total of 280 TPE sessions. Eleven (61%) patients were treated for renal diseases. Three (17%) patients were diagnosed with neurological diseases, two had liver failure, and one patient each had sepsis and stem cell transplant-associated thrombotic microangiopathy. Seven patients (39%) were classified as American Society for Apheresis Category I, four (22%) as Category II, two (13%) each as Category III and IV, and two (13%) were not classified. Two patients with atypical hemolytic-uremic syndrome received TPE as long-term therapy over 2 and 5 years. All procedures were performed using the filtration technique and heparin anticoagulation. Twelve (67%) patients showed full or partial recovery after TPE, six had no response or an uncertain response. Minor adverse events occurred in 30/280 (10.6%) procedures, and one major complication (0.4%) was reported. ConclusionTPE is a safe apheresis method in children, even when performed as a long-term therapy. Efficacy is high under selected conditions. A highly skilled and experienced staff is mandatory to ensure patient safety and efficacy.

BACKGROUND:Calcineurin inhibitor (CNI)-induced thrombotic microangiopathy (TMA) is a rare complication after renal transplantation. It may be difficult to distinguish from CNI toxicity and acute antibody-mediated rejection (AMR). Its clinical presentation may vary from isolated localised forms up to catastrophic systemic presentations.CASE:We report a case of tacrolimus-induced TMA soon after renal transplantation in an 11-year-old boy who received his second renal transplantation. His first graft was lost because of AMR. On day 12 after his second renal transplantation, his renal function started worsening and a kidney biopsy was performed, which showed histopathological signs of TMA. The diagnosis of tacrolimus-induced TMA was established after excluding AMR and other causes of de novo TMA. Genetic complement investigation disclosed two complement factor H risk polymorphisms as possible modifiers of TMA emergence. Treatment was based on replacing tacrolimus with everolimus, with a subsequent normalisation of renal function.CONCLUSION:A prompt diagnosis of de novo TMA by early allograft biopsy is essential for the allograft outcome and genetic investigations for possible complement abnormalities are reasonable, not only for patients with a systemic aspect of their post-transplant TMA. Replacing tacrolimus with everolimus effectively controlled the TMA and stabilised renal function in our patient.

Alloimmune antenatal membranous nephropathy (MN) during pregnancy results from antibodies produced by a neutral endopeptidase (NEP)-deficient mother. Here we report two recent cases that provide clues to the severity of renal disease. Mothers of the two children had circulating antibodies against NEP showing the characteristic species-dependent pattern by immunofluorescence on kidney slices. A German mother produced predominantly anti-NEP IgG4 accompanied by a low amount of IgG1. Her child recovered renal function within a few weeks. In sharp contrast, an Italian mother mainly produced complement-fixing anti-NEP IgG1, which also inhibits NEP enzymatic activity, whereas anti-NEP IgG4 has a weak inhibitory potency. Her child was dialyzed for several weeks. A kidney biopsy performed at 12 days of age showed MN, ischemic glomeruli, and arteriolar and tubular lesions. A second biopsy performed at 12 weeks of age showed aggravation with an increased number of collapsed capillary tufts. Both mothers were homozygous for the truncating deletion mutation 466delC and were thus NEP deficient. The 466delC mutation, identified in three previously described families, suggests a founder effect. Because of the potential severity of alloimmune antenatal MN, it is essential to identify families at risk by the detection of anti-NEP antibodies and NEP antigen in urine. On the basis of the five families identified to date, we propose an algorithm for the diagnosis of the disease and the prevention of complications.

TGF-β is a pathogenic factor in patients with acute respiratory distress syndrome (ARDS), a condition characterized by alveolar edema. A unique TGF-β pathway is described, which rapidly promoted internalization of the αβγ epithelial sodium channel (ENaC) complex from the alveolar epithelial cell surface, leading to persistence of pulmonary edema. TGF-β applied to the alveolar airspaces of live rabbits or isolated rabbit lungs blocked sodium transport and caused fluid retention, which--together with patch-clamp and flow cytometry studies--identified ENaC as the target of TGF-β. TGF-β rapidly and sequentially activated phospholipase D1, phosphatidylinositol-4-phosphate 5-kinase 1α, and NADPH oxidase 4 (NOX4) to produce reactive oxygen species, driving internalization of βENaC, the subunit responsible for cell-surface stability of the αβγENaC complex. ENaC internalization was dependent on oxidation of βENaC Cys(43). Treatment of alveolar epithelial cells with bronchoalveolar lavage fluids from ARDS patients drove βENaC internalization, which was inhibited by a TGF-β neutralizing antibody and a Tgfbr1 inhibitor. Pharmacological inhibition of TGF-β signaling in vivo in mice, and genetic ablation of the nox4 gene in mice, protected against perturbed lung fluid balance in a bleomycin model of lung injury, highlighting a role for both proximal and distal components of this unique ENaC regulatory pathway in lung fluid balance. These data describe a unique TGF-β-dependent mechanism that regulates ion and fluid transport in the lung, which is not only relevant to the pathological mechanisms of ARDS, but might also represent a physiological means of acutely regulating ENaC activity in the lung and other organs.

Störungen des Säure-Basen-Haushalts, die aus einer reduzierten Kapazität der renalen Säureelimination oder aus einem renalen Bikarbonatverlust resultieren, werden als renal-tubuläre Azidosen (RTA) bezeichnet. Gemeinsames Merkmal aller zugrunde liegenden Störungen ist die in der arteriellen Blutgasanalyse auffällige metabolische Azidose mit normaler Anionenlücke bei fast immer inadäquat hohem Urin-pH (>5,5). Das Spektrum der dazu führenden Störungen unterscheidet sich in begleitenden Auffälligkeiten wie Störungen des Kaliumhaushalts, Vorliegen einer Nephrokalzinose oder Nephrolithiasis, Auftreten von Schwerhörigkeit, Wachstumsverzögerung, Rachitis und Polyurie. Traditionell werden hereditäre RTA-Formen in 4 klinische Typen gegliedert: Typ-I-RTA mit gestörter Protonensekretion im distalen Nephron („distale“ dRTA), Typ-II-RTA mit beeinträchtigter Bikarbonatresorption im proximalen Nephron („proximale“ pRTA), Typ-III-RTA oder gemischte RTA mit verminderter Kapazität proximal tubulärer Bikarbonatresorption und distal tubulärer Protonensekretion, Typ-IV-RTA mit mangelhafter Aldosteronwirkung am distalen Nephron (RTA mit Hyperkaliämie).

Background/Aims: ROMK channels mediate potassium secretion and regulate NaCl reabsorption in the kidney. The aim was to study the functional implications of the interaction between ROMK2 (Kir1.1b) and two glycolytic enzymes, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and enolase-alpha, which were identified as potential regulatory subunits of the channel complex. Methods: We performed a membrane yeast-two-hybrid screen of a human kidney cDNA library with ROMK2 as a bait. Interaction of ROMK2 with GAPDH and enolase was verified using GST pull-down, co-immunoprecipitation, immunohistochemistry and co-expression in Xenopus oocytes. Results: Confocal imaging showed co-localisation of enolase and GAPDH with ROMK2 in the apical membrane of the renal epithelial cells of the thick ascending limb. Over-expression of GAPDH or enolase-in Xenopus oocytes markedly reduced the amplitude of ROMK2 currents but did not affect the surface expression of the channels. Co-expression of the glycolytically inactive GAPDH mutant C149G did not have any effect on ROMK2 current amplitude. Conclusion: Our results suggest that the glycolytic enzymes GAPDH and enolase are part of the ROMK2 channel supramolecular complex and may serve to couple salt reabsorption in the thick ascending limb of the loop of Henle to the metabolic status of the renal epithelial cells. Copyright (C) 2011 S. Karger AG, Basel

Tight junctions (TJs) play a key role in mediating paracellular ion reabsorption in the kidney. The paracellular pathway in the collecting duct of the kidney is a predominant route for transepithelial chloride reabsorption that determines the extracellular NaCl content and the blood pressure. However, the molecular mechanisms underlying the paracellular chloride reabsorption in the collecting duct are not understood. Here we showed that in mouse kidney collecting duct cells, claudin-4 functioned as a Cl– channel. A positively charged lysine residue at position 65 of claudin-4 was critical for its anion selectivity. Claudin-4 was observed to interact with claudin-8 using several criteria. In the collecting duct cells, the assembly of claudin-4 into TJ strands required its interaction with claudin-8. Depletion of claudin-8 resulted in the loss of paracellular chloride conductance, through a mechanism involving its recruitment of claudin-4 during TJ assembly. Together, our data show that claudin-4 interacts with claudin-8 and that their association is required for the anion-selective paracellular pathway in the collecting duct, suggesting a mechanism for coupling chloride reabsorption with sodium reabsorption in the collecting duct.

Tamm-Horsfall glycoprotein (THGP) or Uromodulin is a membrane protein exclusively expressed along the thick ascending limb (TAL) and early distal convoluted tubule (DCT) of the nephron. Mutations in the THGP encoding gene result in Familial Juvenile Hyperuricemic Nephropathy (FJHN), Medullary Cystic Kidney Disease type 2 (MCKD-2), and Glomerulocystic Kidney Disease (GCKD). The physicochemical and biological properties of THGP have been studied extensively, but its physiological function in the TAL remains obscure. We performed yeast two-hybrid screening employing a human kidney cDNA library and identified THGP as a potential interaction partner of the renal outer medullary potassium channel (ROMK2), a key player in the process of salt reabsorption along the TAL. Functional analysis by electrophysiological techniques in Xenopus oocytes showed a strong increase in ROMK current amplitudes when co-expressed with THGP. The effect of THGP was specific for ROMK2 and did not influence current amplitudes upon co-expression with Kir2.x, inward rectifier potassium channels related to ROMK. Single channel conductance and open probability of ROMK2 were not altered by co-expression of THGP, which instead increased surface expression of ROMK2 as determined by patch clamp analysis and luminometric surface quantification, respectively. Despite preserved interaction with ROMK2, disease-causing THGP mutants failed to increase its current amplitude and surface expression. THGP(-/-) mice exhibited increased ROMK accumulation in intracellular vesicular compartments when compared with WT animals. Therefore, THGP modulation of ROMK function confers a new role of THGP on renal ion transport and may contribute to salt wasting observed in FJHN/MCKD-2/GCKD patients.

Störungen des Phosphathaushaltes sind ein kleines, wegen der potenziell bedrohlichen Komplikationen aber ein wichtiges Thema der Intensivmedizin. Therapeutische Strategien setzen das Wissen um die Ätiologie des gestörten Phosphathaushaltes voraus. Sowohl bei der Hyper- als auch bei der Hypophosphatämie sind dabei die Zufuhr, die Verteilung über intra- und extrazelluläre Kompartimente sowie die renale Elimination zu berücksichtigen. Der vorliegende Beitrag erläutert die wesentlichen Komponenten des normalen Phosphathaushaltes, beschreibt die wichtigsten Störungen sowie die aktuell empfohlenen Therapien. In Zusammenhang mit der Hyperphosphatämie wird dabei die durch Verabreichung salinischer Laxanzien induzierte akute Phosphatnephropathie besonderes hervorgehoben. Bei den Ursachen von Hypophosphatämien hingegen dominieren Umverteilungsphänomene, die in erster Linie durch eine respiratorische Alkalose und durch Insulin hervorgerufen werden. Folgen der schweren Hypophosphatämie wie Rhabdomyolyse, Hämolyse und respiratorische Insuffizienz werden beschrieben und ihre Therapie dargestellt.