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EAST/SeSAME syndrome is a rare disease affecting the Central Nervous System (CNS), inner ear, and kidney. The syndrome is due to loss-of-function mutations in the KCNJ10 gene encoding the inward-rectifying potassium channel Kir4.1. EAST/SeSAME syndrome is mainly diagnosed during childhood with a tonic-clonic seizure being the usual first symptom. Due to a limited number of patients and recent identification of the disease, few data are available on the clinical progress of this disease in adulthood. In particular, neurologic and nephrological outcomes have not been reported. We present a case series of 4 adult patients harbouring homozygous missense mutation p.Ala167Val and homozygous frameshift mutations p.Asn232Glnfs*14 and p.Gly275Valfs*7. Effects of these mutations were predicted by in silico modelling and bioinformatic tools. Patients with truncating mutations were associated with more severe outcomes, both in tubulopathy severity and neurological symptomatology. Conversely, either missense or truncating mutations were correlated with similar severity of epilepsy, with a long free-of-event period up to 20 years old. No eGFR decline was documented. Modelling predicted that truncating mutations lead to complete Kir4.1 dysfunction. Finally, all patients had a mild increase in urinary protein excretion. Our study indicates that the prognosis of patients suffering from EAST/SeSAME syndrome is related to the severity of the mutation causing the disease. As predicted by in silico modelling, truncating mutations of KCNJ10 are associated with more severe disease, with recurrence of symptomatic hypokalemia and more severe neurological phenotype. The type of mutation should be considered for the therapy tailored to patients' phenotype.

Background: Hypertension is a complex disease and is the major cause of cardiovascular complications. In the vast majority of individuals, the aetiology of elevated blood pressure (BP) cannot be determined, thus impairing optimized therapies and prognosis for individual patients. A more precise understanding of the molecular pathogenesis of hypertension remains a pressing priority for both basic and translational research. Here we investigated the effect of salt on naive hypertensive patients in order to better understand the salt intake-blood pressure relationship. Methods: Patients underwent an acute saline infusion and were defined as salt-sensitive or salt-resistant according to mean blood pressure changes. Urinary proteome changes during the salt load test were analysed by a label-free quantitative proteomics approach. Results: Our data show that salt-sensitive patients display equal sodium reabsorption as salt-resistant patients, as major sodium transporters show the same behaviour during the salt load. However, salt-sensitive patients regulate the renin angiotensin system (RAS) differently from salt-resistant patients, and upregulate proteins, as epidermal growth factor (EGF) and plasminogen activator, urokinase (PLAU), involved in the regulation of epithelial sodium channel ENaC activity. Conclusions: Salt-sensitive and salt-resistant subjects have similar response to a saline/volume infusion as detected by urinary proteome. However, we identified glutamyl aminopeptidase (ENPEP), PLAU, EGF and Xaa-Pro aminopeptidase 2 precursor XPNPEP2 as key molecules of salt-sensitivity, through modulation of ENaC-dependent sodium reabsorption along the distal tubule. Graphic abstract: [Figure not available: see fulltext.].

Background: Diuretic resistance is among the most challenging problems that the cardio-nephrologist must address in daily clinical practice, with a considerable burden on hospital admissions and health care costs. Indeed, loop diuretics are the first-line therapy to overcome fluid overload in heart failure patients. The pathophysiological mechanisms of fluid and sodium retention are complex and depend on several neuro-hormonal signals mainly acting on sodium reabsorption along the renal tubule. Consequently, doses and administration modalities of diuretics must be carefully tailored to patients in order to overcome under- or overtreatment. The frequent and tricky development of diuretic resistance depends in part on post-diuretic sodium retention, reduced tubular secretion of the drug, and reduced sodium/chloride sensing. Sodium and chloride depletions have been recently shown to be major factors mediating these processes. Aquaretics and high-saline infusions have been recently suggested in cases of hyponatremic conditions. This review discusses the limitations and strengths of these approaches. Summary: Long-term diuretic use may lead to diuretic resistance in cardio-renal syndromes. To overcome this complication intravenous administration of loop diuretics and a combination of different diuretic classes have been proposed. In the presence of hyponatremia, high-saline solutions in addition to loop diuretics might be beneficial, whereas aquaretics require caution to avoid overcorrection. Key Messages: Diuretic resistance is a central theme for cardio-renal syndromes. Hyponatremia and hypochloremia may be part of the mechanisms for diuretic resistance. Aquaretics and high-saline solutions have been proposed as possible new therapeutic solutions.

Background and Aims Genetic testing has changed the clinical management of inherited kidney diseases patients, improving prognosis, surveillance and therapy. On the other hand, it has put geneticists and clinicians in front of new challenges, as the heterogeneity of these disorders and the high number of variants, with no clear genotype-phenotype correlation. Method 108 patients underwent genetic analysis through a kidney focused NGS panel, named Nephroplex, containing 119 genetic loci associated with inherited kidney disorders. The study aimed to addressed the genetic landscape of cystic individuals and to analyze PKD1 and PKD2 variants in non-cystic individuals. Results Following diagnostic criteria, patients were divided as cystic kidney diseases (n=36) and non-cystic kidney diseases (n=72). Among the group of cystic patients, a causative mutation was detected in 51% of cases. We found thirty-seven PKD1 and PKD2 variants in 26 out of 35 individuals. In particular, 12 variants were shown to be damaging and nine of that were reported in public database, as CLINVAR and Mayo Clinic databases. Among pathogenic variants, twelve were truncating and the remaining were missense variants. Of note, 7 out of 12 damaging PKD1 mutations were located in duplicated regions. Moreover, in three cystic patients, we found a (i) a frameshift hemizygote OFD1 mutation (ii) compound heterozygote PKHD1 variants and (iii) a frameshift MUC1 variant, framing the diagnosis of oro-facio-digital type 1, autosomal recessive polycystic kidney disease and autosomal dominant tubulointerstitial disease, respectively. Interestingly, we detected 28 PKD1-2 rare variants in 21 out of 75 adult non cystic patients (28%). The most were observed in PKD1 genes (82% vs 18% in PKD2). Eighteen of 28 variants were described in the literature as likely benign or as mutations of uncertain significance, while we found 10 novel variants. In silico analysis revealed as pathogenic a frameshift mutation located in exon 15. Of note, the great part of these variations reside into the duplicated PKD1 regions. Conclusion Our data showed that genetic analysis of ADPKD retains unique challenges, given the high degree of homology of PKD1 with his pseudogenes and the high allelic heterogeneity in non-cystic individuals.

Background and Aims Kidney plays a central role on the maintenance of water homeostasis, acid-base and electrolytes balances through the activity of different types of ion channels/transporters expressed along the nephron segments. Mutations in genes encoding these transporters could subsequently lead to aberrant transporter activities, resulting in abnormal renal handling of electrolytes, thus represent monogenic form of rare kidney diseases. Accumulating number of mutations identified in genes responsible for such monogenic disorders demonstrated that eventual disease phenotypes may vary according to the type and localization of the mutation within the gene. Thus, careful evaluation of gene variation would be crucial prior to designing the strategy for the therapy in each case. Here we present various mutations from our patients, identified in genes including kcnj10, SLC12A1, SLC26A4 and clcn7 which are associated with rare tubulopathies EAST/SeSAME syndrome, Bartter’s syndrome, Pendred syndrome and Fanconi syndrome, respectively. In order to explore molecular mechanisms underlying the observed disease conditions in our patients, we have performed computational modeling analyses of these mutations in comparison with wild-type models. Method Three-dimensional homology models of Kir4.1, NKCC2, Pendrin and CLC-7 proteins were generated by Swiss-Model protein structure homology-modelling server (http://swissmodel. expasy.org) and I-TASSER server (https://zhanglab.ccmb.med.umich.edu/I-TASSER/). Disease-related mutations including novel mutations identified from our patients were mapped onto the three-dimensional models and compared with wild-type models in terms of atomic interactions as well as secondary, tertiary and quaternary structures. Furthermore, we assessed possible effects of missense mutations on the function of ion channels/transporters using online bioinformatic prediction tools PolyPhen-2, Mutation taster, PROVEAN and SIFT. Results The three-dimensional model comparison between wild-type Kir4.1 and Ala167Val variant, which is related to EAST/SeSAME syndrome, revealed that Ala167Val located at the junction between transmembrane domain 2 (TM2) and C-terminus is predicted not to interrupt the sequence of the hydrogen bonds, thus not altering the TM2 alpha-helix structure. In addition, while PolyPhen-2 and Mutation taster evaluated Ala167Val as ‘probably damaging’, PROVEAN and SIFT predicted Ala167Val as ‘neutral’ and ‘tolerated’. These observations are in line with the clinical data demonstrating the milder phenotype in patients with Ala167Val mutation compared with the ones harboring frameshift mutations leading to truncated Kir4.1 channel (Figure. 1). Furthermore, computational modeling of wild-type NKCC2 and frameshift mutation Arg302Glyfs*3 variant clearly demonstrated that Arg302Glyfs*3 results in a loss of large part of the protein, indicating that NKCC2-Arg302Glyfs*3 is practically nonfunctional (Figure. 2). Conclusion Computational modeling of disease-related mutations in various ion channels/transporters represents a novel, powerful approach for comprehensive interpretation of the disease phenotypes observed in patients with rare tubulopathies. In addition, combination of in silico modeling and clinical data could provide us with further insight into molecular mechanisms underlying the renal transporter activities. Furthermore, this in silico computational modeling approach can be applicable and suggestive for novel pharmacological intervention as well as the visual disease severity assessment.

The recent Chandos House meeting of the Alport Variant Collaborative extended the indications for screening for pathogenic variants in the COL4A5, COL4A3 and COL4A4 genes beyond the classical Alport phenotype (haematuria, renal failure; family history of haematuria or renal failure) to include persistent proteinuria, steroid-resistant nephrotic syndrome, focal and segmental glomerulosclerosis (FSGS), familial IgA glomerulonephritis and end-stage kidney failure without an obvious cause. The meeting refined the ACMG criteria for variant assessment for the Alport genes (COL4A3–5). It identified ‘mutational hotspots’ (PM1) in the collagen IV α5, α3 and α4 chains including position 1 Glycine residues in the Gly-X-Y repeats in the intermediate collagenous domains; and Cysteine residues in the carboxy non-collagenous domain (PP3). It considered that ‘well-established’ functional assays (PS3, BS3) were still mainly research tools but sequencing and minigene assays were commonly used to confirm splicing variants. It was not possible to define the Minor Allele Frequency (MAF) threshold above which variants were considered Benign (BA1, BS1), because of the different modes of inheritances of Alport syndrome, and the occurrence of hypomorphic variants (often Glycine adjacent to a non-collagenous interruption) and local founder effects. Heterozygous COL4A3 and COL4A4 variants were common ‘incidental’ findings also present in normal reference databases. The recognition and interpretation of hypomorphic variants in the COL4A3–COL4A5 genes remains a challenge.

BackgroundUrine concentrating defect is a common dysfunction in ciliopathies, even though its underlying mechanism and its prognostic meaning are largely unknown. This study assesses renal function in a cohort of 54 Bardet–Biedl syndrome (BBS) individuals and analyses whether renal hyposthenuria is the result of specific tubule dysfunction and predicts renal disease progression.MethodsThe estimated glomerular filtration rate (eGFR), urine albumin:creatinine ratio (ACR) and maximum urine osmolality (max-Uosm) were measured in all patients. Genetic analysis was conducted in 43 patients. Annual eGFR decline (ΔeGFR) was measured in patients with a median follow-up period of 6.5 years. Urine aquaporin-2 (uAQP2) excretion was measured and the furosemide test was performed in patients and controls.ResultsAt baseline, 33 (61.1%), 12 (22.2%) and 9 (16.7%) patients showed an eGFR >90, 60–90 and 30 mg/g and 55.8% of patients showed urine concentrating defect in the absence of renal insufficiency. Baseline eGFR, but not max-Uosm, correlated negatively with age. Conversely, truncating mutations affected max-Uosm and showed a trend towards a reduction in eGFR. Max-Uosm correlated with ΔeGFR (P ConclusionsHyposthenuria is a warning sign predicting poor renal outcome in BBS. The pathophysiology of this defect is most likely beyond defective tubular function.

Kidney structural abnormalities are common features of Bardet-Biedl syndrome (BBS) patients that lead to a progressive decline in renal function. Magnetic resonance diffusion tensor imaging (DTI) provides useful information on renal microstructures but it has not been applied to these patients. This study investigated using DTI to detect renal abnormalities in BBS patients with no overt renal dysfunction. Ten BBS subjects with estimated glomerular filtration rates over 60 ml/min/1.73m2 and 14 individuals matched for age, gender, body mass index and renal function were subjected to high-field DTI. Fractional anisotropy (FA), and mean, radial and axial diffusivity were evaluated from renal cortex and medulla. Moreover, the corticomedullary differentiation of each DTI parameter was compared between groups. Only cortical FA statistically differed between BBS patients and controls (p = 0.033), but all the medullary DTI parameters discriminated between the two groups with lower FA (p

Background and Aims Bardet Biedl Syndrome (BBS) is a rare genetic disorder characterized by a wide range of organ dysfunction, including kidney disease. The severity of renal dysfunction is highly variable in this setting, ranging from tubular defects to the end stage renal disease, with poor genotype-phenotype correlation. Proteomics and metabolomics are powerful tools able to contribute to the better understanding of molecular basis of disease conditions. Our previous studies demonstrated that the urinary proteomic pattern of BBS patients differed from that of healthy subjects, with a set of deregulated proteins including cell adhesion and extracellular matrix organization proteins (1). The present study aims to characterize urine metabolomic profile of BBS patients, in order to identify both 1) potential disease biomarkers and 2) aberrant metabolic pathways underlying renal disease Method To this end, in the pilot study urine samples have been collected from 14 adult BBS patients and have been compared with healthy volunteers, using an untargeted strategy. In the confirmation study, 24 BBS patients with wide range of kidney dysfunction have been enrolled, and additional control groups, besides healthy subjects, were included: 1) age-gender-matched chronic kidney disease patients by other causes and 2) obese individuals. Results Several metabolites were de-regulated in BBS patients compared with normal subjects (lactic acid, glycolic acid,3-Hydroxypropionic acid, pyruvic acid, 3-hydroxyisobutyric acid, 2-ethyl-3-hydroxy-propionic acid, succinic acid, fumaric acid, erythropentonic acid, 2-hydroxyglutaric acid, 4-hydroxyphenyllactic acid, 3,4-pyridinedicarboxylic acid, retinoic acid, 4-hydroxyphenylacetic acid, palmitic acid, 9-Hexadecenoic acid, oleic acid and 9-Octadecenoic acid). The clusterization performed by MetaboAnalyst tool, revealed a possible deregulation of different metabolic pathways, including glycolysis, TCA cycle, pyruvate metabolism, lipids biosynthesis and glutamate metabolism (p-value Conclusion These findings suggest that urine metabolomic fingerprint of BBS patients is different from that of healthy subjects and indicate a possible deregulation of several metabolic pathways; some urinary molecules correlated with kidney dysfunction only in BBS patients, suggesting the specificity of these results.

Potassium (K+) is essential for cells functions and alterations of the normal plasmatic levels can be life-threatening. The kidney is crucial in maintaining K+ homeostasis, mainly by regulating its secretion in the urine. Hypokalemia is influenced by acid-base status and can be associated to both metabolic alkalosis or acidosis. In adults, drug-induced hypokalemia is the most common form, however, genetically undiagnosed conditions should always be investigated.

Bardet–Biedl syndrome (BBS) is a rare pleiotropic inherited disorder known as a ciliopathy. Kidney disease is a cardinal clinical feature; however, it is one of the less investigated traits. This study is a comprehensive analysis of the literature aiming to collect available information providing mechanistic insights into the pathogenesis of kidney disease by analyzing clinical and basic science studies focused on this issue. The analysis revealed that the syndrome is either clinically and genetically heterogenous, with 24 genes discovered to date, but with 3 genes (BBS1, BBS2, and BBS10) accounting for almost 50% of diagnoses; genotype–phenotype correlation studies showed that patients with BBS1 mutations have a less severe renal phenotype than the other 2 most common loci; in addition, truncating rather than missense mutations are more likely to cause kidney disease. However, significant intrafamilial clinical variability has been described, with no clear explanation to date. In mice kidneys, Bbs genes have relative low expression levels, in contrast with other common affected organs, like the retina; surprisingly, Bbs1 is the only locus with basal overexpression in the kidney. In vitro studies indicate that signalling pathways involved in embryonic kidney development and repair are affected in the context of BBS depletion; in mice, kidney disease does not have a full penetrance; when present, it resembles human phenotype and shows an age-dependent progression. Data on the exact contribution of local versus systemic consequences of Bbs dysfunction are scanty and further investigations are required to get firm conclusions.

The primary cilium (PC) was considered as a vestigial organelle with no significant physiological importance, until the discovery that PC perturbation disturbs several signalling pathways and results in the dysfunction of a variety of organs. Genetic studies have demonstrated that mutations affecting PC proteins or its anchoring structure, the basal body, underlie a class of human disorders (known as ciliopathies) characterized by a constellation of clinical signs. Further investigations have demonstrated that the PC is involved in a broad range of biological processes, in both developing and mature tissues. Kidney disease is a common clinical feature of cilia disorders, supporting the hypothesis of a crucial role of the PC in kidney homoeostasis. Clinical proteomics and metabolomics are an expanding research area. Interestingly, the application of these methodologies to the analysis of urine, a biological sample that can be collected in a non-invasive fashion and possibly in large amounts, makes these studies feasible also in patients. The present article describes the most recent proteomic and metabolomic studies exploring kidney dysfunction in the setting of ciliopathies, showing the potential of these methodologies in the elucidation of disease pathophysiology and in the discovery of biomarkers.

Introduction: Renal dysfunction is a frequent complication in patients suffering from β-thalassemia major (β-TM). The aim of this study was to analyze the renal function and urine metabolomic profile of β-TM patients undergoing transfusions and deferasirox (DFX) therapy, in order to better characterize and shed light on the pathogenesis of renal disease in this setting. Methods and Subjects: 40 patients affected by β-TM treated with DFX and 35 age- and gender-matched healthy controls were enrolled in the study. Renal function was assessed. Glomerular filtration rate (GFR) was estimated with CKD-EPI and Schwartz formula for adults and children, respectively. Renal tubular function and maximal urine concentration ability were tested. Urine specimens were analyzed by nuclear magnetic resonance spectroscopy to identify the urinary metabolite profiles. Results: The study of renal function in β-TM patients revealed normal estimated (e)GFR mean values and the albumin-to-creatinine ratio was Discussion: The major finding of this work is that β-TM patients and controls exhibit different concentrations of some metabolites in the urine. Early recognition of urinary abnormalities may be useful to detect and prevent kidney damage.

Background:/Aims: Renal disease is a common cause of morbidity in patients with Bardet-Biedl syndrome (BBS), however the severity of kidney dysfunction is highly variable. To date, there is little information on the pathogenesis, the risk and predictor factors for poor renal outcome in this setting. The present study aims to analyze the spectrum of urinary proteins in BBS patients, in order to potentially identify 1) disease-specific proteomic profiles that may differentiate the patients from normal subjects; 2) urinary markers of renal dysfunction. Methods: Fourteen individuals (7 males and 7 females) with a clinical diagnosis of BBS have been selected in this study. A pool of 10 aged-matched males and 10 aged-matched females have been used as controls for proteomic analysis. The glomerular filtration rate (eGFR) has been estimated using the CKD-EPI formula. Variability of eGFR has been retrospectively assessed calculating average annual eGFR decline (ΔeGFR) in a mean follow-up period of 4 years (3-7). Results: 42 proteins were significantly over- or under-represented in BBS patients compared with controls; the majority of these proteins are involved in fibrosis, cell adhesion and extracellular matrix organization. Statistic studies revealed a significant correlation between urine fibronectin (u-FN) (r2=0.28; p2 =0.35; p20.27; p2 =0.2389; pConclusion: The present study demonstrates that urine proteome of BBS patients differs from that of normal subjects; in addition, kidney dysfunction correlated with urine abundance of known markers of renal fibrosis.

Bardet Biedl syndrome (BBS) is a rare inherited syndromic condition characterized by renal and extra-renal disorders. Renal defect, at either structural or functional level, is one of the cardinal clinical features, and is a major cause of morbidity. However, the pathogenic mechanism underlying its dysfunction remains largely unknown, and to date only symptomatic treatment with no specific therapy is available for these patients. Elucidating aberrant cellular and/or systemic processes that impact kidney function is therefore a prerequisite to develop targeted innovative therapeutic strategies for the BBS patients. Given the proven role of BBS proteins in the function of the primary cilium (PC) and considering the clinical overlapping of BBS with other ciliopathies, BBS is considered the result of disruption of ciliary activities. The present review aims at giving an updated overview of the spectrum of renal abnormalities in BBS patients according to the existing scientific literature, and discusses the possible role of intrinsic PC dysfunction into the pathogenesis of renal defects based on the most recent findings demonstrating a possible role of systemic factors in favoring the progression of renal disease. (c) 2017 The Author(s) Published by S. Karger AG, Basel

Background: Inherited metabolic disorders or inborn errors of metabolism are caused by deficiency of enzymatic activities in the catabolism of amino acids, carbohydrates, or lipids. These disorders include aminoacidopathies, urea cycle defects, organic acidemias, defects of oxidation of fatty acids, and lysosomal storage diseases. Inborn errors of metabolism constitute a significant proportion of genetic diseases, particularly in children; however, they are individually rare. Clinical phenotypes are very variable, some of them remain asymptomatic, others manifest metabolic decompensation in neonatal age, and others encompass mental retardation at later age. The clinical manifestation of these disorders can involve different organs and/or systems. Some disorders are easily managed if promptly diagnosed and treated, whereas in other cases neither diet, vitamin therapy, nor transplantation appears to prevent multi-organ impairment. Summary: Here, we discuss the principal challenges of metabolomics and proteomics in inherited metabolic disorders. We review the recent developments in mass spectrometry-based proteomic and metabolomic strategies. Mass spectrometry has become the most widely used platform in proteomics and metabolomics because of its ability to analyze a wide range of molecules, its optimal dynamic range, and great sensitivity. The fast measurement of a broad spectrum of metabolites in various body fluids, also collected in small samples like dried blood spots, have been facilitated by the use of mass spectrometry-based techniques. These approaches have enabled the timely diagnosis of inherited metabolic disorders, thereby facilitating early therapeutic intervention. Due to its analytical features, proteomics is suited for the basic investigation of inborn errors of metabolism. Modern approaches enable detailed functional characterization of the pathogenic biochemical processes, as achieved by quantification of proteins and identification of their regulatory chemical modifications. Key Message: Mass spectrometry-based “omics” approaches most frequently used to study the molecular mechanisms underlying inherited metabolic disorders pathophysiology are described.

The gut microbiota is considered to be a novel important factor to take into account in the pathogenesis of chronic kidney disease and uremia. Much attention has been paid to specific uremic retention solutes of microbial origin, such as indoxyl sulfate, p-cresyl sulfate, and trimethylamine-N-oxide. However, other novel less well studied compounds, such as hydrogen sulfide and related sulfur metabolites (sulfane sulfur, lanthionine, etc.), should be included in a more comprehensive appraisal of this topic, in light of the potential therapeutic opportunities for the future.

The thick ascending limb (TAL) of Henle’s loop is a crucial segment for many tasks of the nephron. Indeed, the TAL is not only a mainstay for reabsorption of sodium (Na+), potassium (K+), and divalent cations such as calcium (Ca2+) and magnesium (Mg2+) from the luminal fluid, but also has an important role in urine concentration, overall acid–base homeostasis, and ammonia cycle. Transcellular Na+ transport along the TAL is a prerequisite for Na+, K+, Ca2+, Mg2+ homeostasis, and water reabsorption, the latter through its contribution in the generation of the cortico-medullar osmotic gradient. The role of this nephron site in acid–base balance, via bicarbonate reabsorption and acid secretion, is sometimes misunderstood by clinicians. This review describes in detail these functions, reporting in addition to the well-known molecular mechanisms, some novel findings from the current literature; moreover, the pathophysiology and the clinical relevance of primary or acquired conditions caused by TAL dysfunction are discussed. Knowing the physiology of the TAL is fundamental for clinicians, for a better understanding and management of rare and common conditions, such as tubulopathies, hypertension, and loop diuretics abuse.

In the last decades, proteomics has been largely applied to the Nephrology field, with the double aim to (1) elucidate the biological processes underlying renal diseases; (2) identify disease-specific biomarkers, predictor factors of therapeutic efficacy and prognostic factors of disease progression. Kidney stone disease, and in particular, inherited nephrolithiasis (INL) are not an exception. Given the multifactorial origin of these disorders, the combination of genomics and proteomics studies may complement each other, with the final objective to give a global and comprehensive mechanistic view. In this review, we summarize the results of recent proteomic studies which have expanded our knowledge about INL, focusing the attention on monogenic forms of nephrolithiasis (cystinuria, Dent’s disease, Bartter syndrome, distal renal tubular acidosis and primary hyperoxaluria), on polygenic hypercalciuria and on medullary sponge kidney disease.

Background: Emerging evidence suggests that chronic metabolic acidosis (CMA) may have significant implications in terms of worsening renal disease in CKD patients, but the effect of CMA on renal function and structure has not been fully elucidated. Method: We studied the acute and chronic consequences of an acid load (AL) on glomerular filtration rate (GFR) and renal histology in C57BL/6 mice. FITC-inulin clearance was performed at several time points; markers of renal fibrosis were studied at mRNA and protein levels; finally, kidney expression of candidate molecules triggering changes in renal function was studied. Results: Glomerular hyperfiltration occurred within 1–3 days from AL; after 1 week, the GFR returned to baseline and then declined progressively within 15–21 days. The GFR decline was accompanied by the onset of renal fibrosis, as shown by Masson trichrome staining. Markers of renal fibrosis, namely α-smooth muscle actin and collagen-1, increased after 1 day of acid loading in both mRNA and protein levels and remained higher than baseline for up to 21 days. Well-known mediators of renal fibrosis, including transforming growth factor (TGF)-β and the intrarenal renin–angiotensin system (RAS) axis, were increased even before the decline of the GFR. Conclusion: Acid load caused hyperfiltration acutely and a progressive decline of the GFR chronically; the evidence of renal fibrosis indicates that structural and not only functional renal changes occurred. The concomitant upregulation of TGF-β and intrarenal RAS axis indicates that those factors may be potentially involved in the progression of kidney disease in this setting.

The triad composed by α-Klotho, fibroblast growth factor-23, and its receptor are involved in the pathogenesis of chronic kidney disease–mineral and bone disorder. A disintegrin and metalloproteinase 17 (ADAM17) is a metalloproteinase causing the proteolytic shedding of α-Klotho from the cell membrane, and its role in chronic kidney disease–mineral and bone disorder is not yet known. We studied the circulating levels of the above-mentioned mediators in patients with secondary hyperparathyroidism due to uremia, compared to control subjects, as well as in patients with primary hyperparathyroidism. We also measured the immunofluorescence pattern of the relevant tissue proteins in specimens obtained from patients undergoing parathyroid surgery for secondary compared to primary hyperparathyroidism. Results showed that α-Klotho tissue levels are reduced, in the presence of increased ADAM17 tissue levels. In addition, we showed increased serum levels of the main product of ADAM17 proteolytic activity, tumor necrosis factor-α. Thus, we found a paradoxical situation, in secondary compared to primary hyperparathyroidism, that is, that in the face of increased tumor necrosis factor-α in circulation, both soluble and tissue α-Klotho are reduced significantly, despite increased tissue ADAM17. In conclusion, tissue and serum levels of α-Klotho seem to have become independent from the regulation induced by ADAM17, which constitutes therefore another tassel in the impaired α-Klotho–FGF23 receptor axis present in uremia.

Background: The ciliopathies are a growing number of disorders caused by mutations in genes involved in the function of the primary cilium. Bardet-Biedl syndrome (BBS) belongs to this group of disorders. In this setting, kidney dysfunction is highly variable, and urine concentrating defect, a common feature of multiple ciliopathies, has been described as the most frequent defect. Here we review the mechanism of urine concentration and describe the possible mechanism underling this defect in ciliopathies and especially BBS, based on the current body of literature. Summary: Active Na+ absorption along the thick ascending limb of the loop of Henle (TAL) is critical for generating the corticomedullary osmotic gradient, and the countercurrent anatomical arrangement of the 2 branches of the loop of Henle enhances this gradient. The vasa recta, paralleling the loop of Henle, operate into the countercurrent mechanism, minimizing washout of solutes from the interstitium. Final water reabsorption is mediated by the aquaporin 2 (AQP2) water channels along the distal nephron, and it is under hormonal control. Several studies demonstrated that hyposthenuria in BBS patients relies on kidney resistance to desmopressin, suggesting a renal origin. We recently showed that the majority of hyposthenuric BBS patients have also a defect regarding maximal urine dilution. Independent studies showed that BBS10 deficiency caused AQP2 mistrafficking in vitro; accordingly, we demonstrated impaired urinary AQP2 excretion in BBS patients with combined concentrating and diluting defect. Whether receptor signaling pathways or downstream events cause AQP2 deregulation is still unclear. In addition, reduced urinary uromodulin excretion in BBS patients opens the possibility that TAL dysfunction may also play a pathogenic role. Key Message: Impaired water handling in BBS is associated with AQP2 mistrafficking. The potential role of additional factors, such as the dissipation of the medullary osmotic gradient due to TAL dysfunction and/or structural anomalies, remains to be elucidated.

Background/Aims: Little information is available about the tubular functions and the renal adjustments that take place in obese subjects after a protein meal. How the excess fat may affect renal response to dietary proteins is currently only partially understood. This paper aims to address (i) whether severe obesity, in the absence of other comorbidities, is responsible of kidney dysfunction at either the glomerular or the tubular level and (ii) whether it compromises renal adaptations to a large protein meal. Methods: Twenty-eight obese subjects without albuminuria, along with 20 control subjects, age and gender matched, have been studied. The glomerular filtration rate (GFR; inulin clearance), renal plasma flow (p-aminohippurate clearance), the proximal tubular function (lithium clearance), the fractional excretion of sodium (FPRNa) have been measured at the basal level (steady state) and after a protein meal (perturbation). Results: Under steady state conditions, filtration fraction, proximal tubular sodium handling and the FPRNa were not significantly different in non proteinuric obese subjects compared with controls. However, a protein meal led to a delayed glomerular hyperfiltration in obese patients compared with controls. Conclusion: This study shows that obese patients, in the absence of significant comorbidities, have a normal proximal tubule Na+ absorption at basal; conversely, these subjects showed a different response to a protein meal compared with normal subjects in terms of changes of GFR. Overall, these results suggest that the modified hemodynamic response to a protein meal might be the earliest hallmark of future kidney dysfunction in obese subjects.

Background: The prevention and slowing of chronic kidney disease still represent major challenges in nephrology. To this end, a major contribution may come from the extensive knowledge on the molecular pathways involved in the pathogenesis of rare kidney diseases, since it is now possible to shed light on several aspects of these pathologies thanks to the introduction of new technologies, including next-generation sequencing. Summary: In steroid-resistant nephrotic patients, a genetic background has been demonstrated in both children and adults; individualized mutations have been correlated with glomerular filtration barrier alterations. In addition, studies on genetic tubulopathies expressing hypertensive phenotypes can provide useful information for a correct diagnostic and therapeutic approach in patients with essential hypertension and a poor responsiveness to therapy. Key Message: This review deals with the pathogenesis of rare glomerular diseases and tubulopathies associated with hypertension, highlighting the importance of the study of rare diseases to better understand the molecular basis of more common and complex disorders leading to end-stage renal disease.

Tuberous sclerosis complex (TCS) is a genetic disorder with a variable clinical presentation. It is commonly characterized by seizures, mental retardation and cutaneous angiofibromas. Renal manifestations frequently include angiomyolipomas and cysts which lead to chronic kidney disease. We report a case of valproic acid-induced acute pancreatitis in a dialysis patient affected by TCS. The case demonstrates the importance of assessing antiepileptic drug treatment in dialysis patients. © 2012 Società Italiana di Nefrologia.

Primary hypertension is one of the leading risk factors for cardiovascular disease. Although the pathogenesis is not completely understood, an imbalance of sodium and chloride homeostasis seems to be relevant both in the induction and in the maintenance of salt-sensitive hypertension. Besides individual renal phenotypes, salt intake is one of the most important environmental determinants of this condition. The Milan hypertensive strain (MHS) of rats is an interesting model to investigate the molecular mechanisms underling the development of salt-sensitive hypertension. In young MHS rats, hypertension is anticipated by a phase of increased salt reabsorption localized along the medullary thick ascending limb associated with the up-regulation of the apical sodium-potassium-chloride cotransporter (NKCC2). Later, the frank hypertensive status of adult MHS rats is accompanied by the activation of the luminal and basal lateral transporters of sodium chloride (NaCl) in the distal convoluted tubule (DCT). Several lines of evidence have proven the key role of DCT in the maintenance of hypertension in MHS rats; more importantly, hypertensive patients carrying a mutation of α-adducin (resembling the MHS model) have a high sensitivity to thiazides, suggesting that the Na(+)-Cl(-) cotransporter also plays a pivotal role in humans.

Renal cell carcinoma (RCC) is a frequent adult malignancy comprising different subtypes, with clear cell renal cell carcinoma (CCRCC) the most common. CCRCC is associated with the loss of function of the von Hippel-Lindau (VHL) gene. pVHL, the product of the VHL gene, is a component of an E3 ubiquitin ligase complex which targets proteins for degradation. In the absence of functional pVHL, a series of proteins accumulate in the cells, including hypoxic-inducible factor-1a (HIF-1a) and the products of the target genes of pVHL, such as vascular endothelial growth factor (VEGF). The activation of this pathway explains the use of both VEGF and VEGF-receptor inhibitors (bevacizumab, sunitinib and sorafenib) in the therapy of advanced CCRCC. In addition, mammalian target of rapamycin (mTOR), an intracellular serine/threonine kinase, is also implicated in HIF-1a regulation, thus reinforcing the rationale for using mTOR inhibitors (rapamycin) in CCRCC. Proteomic technologies have been applied to human renal cancer to detect biomarkers able to guide physicians for diagnostic and prognostic purposes. Among others, vimentin, heat shock protein 27 (Hsp27), annexin IV and serum amyloid alpha-1 (SAA-1) have been identified as reliable markers of RCC that are potentially useful in the clinical setting. Renal cell carcinoma (RCC) is a frequent adult malignancy comprising different subtypes, with clear cell renal cell carcinoma (CCRCC) the most common. CCRCC is associated with the loss of function of the von Hippel-Lindau (VHL) gene. pVHL, the product of the VHL gene, is a component of an E3 ubiquitin ligase complex which targets proteins for degradation. In the absence of functional pVHL, a series of proteins accumulate in the cells, including hypoxic-inducible factor-1α (HIF-1α) and the products of the target genes of pVHL, such as vascular endothelial growth factor (VEGF). The activation of this pathway explains the use of both VEGF and VEGF-receptor inhibitors (bevacizumab, sunitinib and sorafenib) in the therapy of advanced CCRCC. In addition, mammalian target of rapamycin (mTOR), an intracellular serine/threonine kinase, is also implicated in HIF-1α regulation, thus reinforcing the rationale for using mTOR inhibitors (rapamycin) in CCRCC. Proteomic technologies have been applied to human renal cancer to detect biomarkers able to guide physicians for diagnostic and prognostic purposes. Among others, vimentin, heat shock protein 27 (Hsp27), annexin IV and serum amyloid alpha-1 (SAA-1) have been identified as reliable markers of RCC that are potentially useful in the clinical setting. © 2011 Società Italiana di Nefrologia.

Uromodulin (UMOD), also named Tamm Horsfall protein, is the most abundant protein secreted in the urine under normal conditions. It was purified the first time in 1950 and since then considerable efforts have highlighted its importance in human pathophysiology. However, its precise biological functions still remain elusive. The clinical interest in UMOD derives from the evidence that UMOD genetic mutations result in tubulointerstitial nephropathies currently known as UMODassociated kidney disease (UAKD), rare genetic disorders characterized by hyperuricaemia, gout and a progressive decline of renal function [1]. In addition, UMOD has been proposed to modulate water and electrolyte homeostasis by acting on the main transporters expressed along the thick ascending limb (TAL) and the early distal convoluted tubule. The precursor undergoes extensive post-translational modifications through the endoplasmic reticulum (ER) and the Golgi apparatus, and ultimately it is targeted to the apical membrane [2]. From the luminal site, it is cleaved by an unknown protease and then released into the tubular fluid. The exact mechanism linking UMOD mutations to renal concentrating defect has not been fully characterized. It has been suggested that the filamentous gel-like structure of the extracellular domain may serve as a barrier to water permeability [3]. In vitro and in vivo studies have recently demonstrated that UMOD modulates the function of the Na-K-2Cl (NKCC2) co-transporter [4] and the renal outer medullary potassium (ROMK) channel [5] (Figure 1). UMOD-deficient mice showed normal electrolyte balance at basal and urine concentrating defect after water deprivation [6]. Impaired urine concentration was coupled with a compensatory up-regulation of distal Na transporters, including the Na-Cl co-transporter (NCC), suggesting indirectly an impaired function of the TAL. Immunostaining analysis revealed the absence of any difference in NKCC2 protein abundance on the apical membrane between knockout (KO) and wild-type (WT) mice, but an increased sub-apical immunoreactivity, with overall increased NKCC2 protein abundance compared with WT [4]. It is possible that an impaired protein degradation, in the absence of UMOD, resulted in NKCC2 accumulation. However, the same study demonstrated that phospho-NKCC2 levels, a marker of NKCC2 activity, were lower in KO than WT mice, and intraperitoneal injection of frusemide resulted in attenuated natriuretic and cloruretic responses, further supporting the hypothesis of reduced NKCC2 activity in the absence of UMOD. Consistent with these findings, in vitro NKCC2 phosphorylation was enhanced in the presence of UMOD, indicating that also in cultured cells UMOD promoted NKCC2 activity. This hypothesis has been further corroborated by recent observations linking salt-sensitive hypertension with a genetic UMOD variant leading to an increased UMOD synthesis and secretion in humans [7]. Transgenic mice expressing this genetic variant resembled human features, showing salt-sensitive hypertension. This finding correlated with the up-regulation of NKCC2, with increased protein phosphorylation via the STE20/SPS1-related proline/alanine-rich kinase (SPAK) and the down-regulation of the negative regulator kidney-specific KS-SPAK. Besides NKCC2, UMOD has been shown to modulate also the activity of ROMK. Renigunta et al. [5] have shown that UMOD co-localized with ROMK in a protein lysate from mice, while in oocytes, co-expression of UMOD and ROMK resulted in increased current amplitude, associated with an increased surface ROMK abundance. Patients suffering from UAKD commonly do manifest a defect in urine concentrating ability even before the decline of the GFR [8]. The mechanism by which UMOD mutations lead to urine concentrating defect in humans remains to be better elucidated. In this issue of NDT, Labriola et al. [9] show original data exploring the tubular function of a patient suffering UAKD during the early phase of the disease.

Potassium (K + ) deficiency is a common and eventually life-treating condition. Hypokalemia is defined as serum K+ level less than 3.5 mM. This chapter, together with cornerstone mechanisms, reviews the newest molecular regulators of the K + homeostasis, including the feedforward signals recently hypothesized in the gut. The renal and extra-renal diseases leading to hypokalemia are reported here. Newest findings in the mechanism underlying the renal inherited K + -losing syndrome, like Gitelman, Bartter and Liddle syndromes are described in details.

The cortical distalnephron is committed to the fine regulation of electrolytes and water balance. Several investigations have addressed the molecular mechanisms implicated in this process. The paper by Belge et al. [1] demonstrates the emerging role of parvalbumin (PV) on distal tubule NaCl reabsorption. PV is a divalent cation buffering protein, exclusively expressed in the early distal convoluted tubule (DCT1). The authors show solid data suggesting a functional relationship between PV and the thiazide-sensitive Na+-Cl− cotransporter (NCC), the main entry step for Na+ and Cl− through the apical membrane at this nephron site. PV−/− mice exhibit a salt-losing phenotype characterized by increased diuresis, kaliuresis and high aldosterone levels, a phenotype very similar, although not identical, to the NCC knock-out mice. Accordingly, PV−/− mice manifest decreased expression of NCC, paralleled by no significant diuretic response to hydrochlorothiazide. Furthermore, in vitro studies performed on DCT cells show that PV may regulate NCC expression by modulating the Ca2+-dependent signalling pathway.

You might find this additional info useful...This article cites 19 articles, 9 of which can be accessed free at:http://ajprenal.physiology.org/content/301/4/F743.full.html#ref-list-1 Updated information and services including high resolution figures, can be found at:http://ajprenal.physiology.org/content/301/4/F743.full.html Additional material and information about AJP - Renal Physiology can be found at:http://www.the-aps.org/publications/ajprenalThis infomation is current as of October 10, 2011.€

BackgroundGenetic testing of patients with inherited kidney diseases has emerged as a tool of clinical utility by improving the patients’ diagnosis, prognosis, surveillance and therapy.MethodsThe present study applied a Next Generation Sequencing (NGS)-based panel, named NephroPlex, testing 115 genes causing renal diseases, to 119 individuals, including 107 probands and 12 relatives. Thirty-five (poly)cystic and 72 non (poly)cystic individuals were enrolled. The latter subgroup of patients included Bardet-Biedl syndrome (BBS) patients, as major components.ResultsDisease-causing mutations were identified in 51.5 and 40% of polycystic and non-polycystic individuals, respectively. Autosomal dominant polycystic kidney disease (ADPKD) patients with truncatingPKD1variants showed a trend towards a greater slope of the age-estimated glomerular filtration rate (eGFR) regression line than patients with (i) missense variants, (ii) anyPKD2mutations and (iii) no detected mutations, according to previous findings. The analysis of BBS individuals showed a similar frequency ofBBS4,9,10and12mutations. Of note, allBBS4-mutated patients harbored the novel c.332+1G>GTT variant, which was absent in public databases, however, in our internal database, an additional heterozygote carrier was found. AllBBS4-mutated individuals originated from the same geographical area encompassing the coastal provinces of Naples.DiscussionIn conclusion, these findings indicate the potential for a genetic panel to provide useful information at both clinical and epidemiological levels.Graphic abstract