Colony stimulating factor-1 receptor drives glomerular parietal epithelial cell activation in focal segmental glomerulosclerosis.

Parietal epithelial cells (PECs) are kidney progenitor cells with similarities to a bone marrow stem cell niche. In focal segmental glomerulosclerosis (FSGS) PECs become activated and contribute to extracellular matrix deposition. Colony stimulating factor-1 (CSF-1), a hematopoietic growth factor, acts via its specific receptor, CSF-1R, and has been implicated in several glomerular diseases, although its role on PEC activation is unknown. Here, we found that CSF-1R was upregulated in PECs and podocytes in biopsies from patients with FSGS. Through in vitro studies, PECs were found to constitutively express CSF-1R. Incubation with CSF-1 induced CSF-1R upregulation and significant transcriptional regulation of genes involved in pathways associated with PEC activation. Specifically, CSF-1/CSF-1R activated the ERK1/2 signaling pathway and upregulated CD44 in PECs, while both ERK and CSF-1R inhibitors reduced CD44 expression. Functional studies showed that CSF-1 induced PEC proliferation and migration, while reducing the differentiation of PECs into podocytes. These results were validated in the Adriamycin-induced FSGS experimental mouse model. Importantly, treatment with either the CSF-1R-specific inhibitor GW2580 or Ki20227 provided a robust therapeutic effect. Thus, we provide evidence of the role of the CSF-1/CSF-1R pathway in PEC activation in FSGS, paving the way for future clinical studies investigating the therapeutic effect of CSF-1R inhibitors on patients with FSGS.

Overcoming limits: First ABO incompatible living donor paired kidney transplant in an hypersensitized pediatric recipient in Spain.

INTRODUCTION: HLA sensitization is a growing problem in children awaiting kidney transplantation. In some cases, finding an immunologically compatible donor entails contemplating the option of an ABO incompatible transplant or paired transplant. METHODS: Patient with genetic nephrotic syndrome and progressive chronic kidney disease, with a previous thrombosis of a first kidney transplant, resulting hypersensitized and remaining for a long-time on hemodialysis. Despite a desensitization strategy, family members were incompatible and deceased donation options must be ruled out due to the presentation of donor-specific antibodies (DSA). After 4 years, the possibility arises to perform a kidney paired transplant with a 62-year-old woman with an incompatible blood group. Although the current cytotoxicity- and cell-based crossmatches were negative, history of DSA were recorded. RESULTS: An intensive ABO and HLA desensitization protocol was performed in order to combat the isohemagglutinin antibodies and on the memory-HLA, based on rituximab, apheresis sessions, and immunoglobulins. Despite the donor being older in terms of pediatric transplantation, the donor-recipient weight difference, and immunological risk, the transplant was completed successfully. Maintenance of titration of up to 1/2 was confirmed after 3 weeks post-transplant (IgM and IgG). Kidney biopsy at 2 weeks and 6 months without signs of rejection. The patient is currently 12 months post-transplant and has not presented any signs of transplant rejection and has proper renal function. CONCLUSIONS: Kidney paired transplantation is an excellent solution for hypersensitized children, and ABO incompatibility can be considered to increase their options to find a good donor, without thereby obtaining worse results.

The Density of Renal Lymphatics Correlates With Clinical Outcomes in IgA Nephropathy.

Introduction: IgA nephropathy (IgAN) is the most common primary glomerulonephritis (GN) worldwide. The disease course fluctuates, and the most important challenge is the considerable variation in the time lag between diagnosis and the development of a hard clinical end point, such as end-stage kidney disease (ESKD). The reaction of renal tissue to damage resembles the common wound-healing response. One part of this repair in IgAN is the expansion of lymphatic vessels known as lymphangiogenesis. The aim of this work was to establish the prognostic value of the density of lymphatic vessels in the renal biopsy at the time of diagnosis, for predicting the risk of ESKD in a Spanish cohort of patients with IgAN. Methods: We performed a retrospective multicenter study of 76 patients with IgAN. The end point of the study was progression to ESKD. The morphometric analysis of lymphatic vessels was performed on tissue sections stained with antipodoplanin antibody. Results: Density of lymphatic vessels was significantly higher in patients with IgAN with mesangial hypercellularity >50%, segmental sclerosis, higher degrees of interstitial fibrosis, and tubular atrophy. Patients with more lymphatic vessels had significantly higher values of proteinuria and lower estimated glomerular filtration rate (eGFR). A density of lymphatic vessels ≥8 per mm2 was associated with a significantly higher rate of progression to ESKD at 3 years from biopsy. After adjustment for the International IgAN prediction score, at the multivariate logistic regression, high density of lymphatic vessels (≥8 per mm2) remained significantly associated with a higher rate of early progression to ESKD. Conclusion: This study contributes to the understanding of the natural history of the progression to ESKD in patients with IgAN revealing the density of lymphatics vessels may optimize the prognostic value of the International IgA predicting tool to calculate the risk of ESKD, favoring the evaluation of new targeted therapies.

CD44-negative parietal-epithelial cell staining in minimal change disease: association with clinical features, response to corticosteroids and kidney outcome.

BACKGROUND: Activation of parietal-epithelial cells (PECs) with neo-expression of CD44 has been found to play a relevant role in the development of focal and segmental glomerulosclerosis (FSGS). The aim of this study was to analyse whether the expression of CD44 by PECs in biopsies of minimal change disease (MCD) is associated with the response to corticosteroids, with kidney outcomes and/or can be considered an early sign of FSGS. METHODS: This multicentric, retrospective study included paediatric and adult patients with MCD. Demographic, clinical and biochemical data were recorded, and biopsies were stained with anti-CD44 antibodies. The association between PECs, CD44 expression and the response to corticosteroids, and kidney outcomes were analysed using logistic, Kaplan-Meier and Cox regression analyses. RESULTS: A total of 54 patients were included: 35 (65%) <18 years and 19 (35%) adults. Mean follow-up was 68.3 ± 37.9 months. A total of 19/54 patients (35.2%) showed CD44-positive staining. CD44-positive patients were younger (14.5 ± 5 versus 21.5 ± 13, P = 0.006), and showed a higher incidence of steroid-resistance [11/19 (57.8%) versus 7/35 (20%), P = 0.021; odds ratio: 5.5 (95% confidence interval 1.6-18), P = 0.007] and chronic kidney disease [9/19 (47.3%) versus 6/35 (17.1%), P = 0.021; relative risk: 3.01 (95% confidence interval 1.07-8.5), P = 0.037]. Follow-up re-biopsies of native kidneys (n = 18), identified FSGS lesions in 10/12 (83.3%) of first-biopsy CD44-positive patients versus 1/6 (16.7%) of first-biopsy CD44-negative patients (P = 0.026). CONCLUSIONS: In patients with a light microscopy pattern of MCD, CD44-positive staining of PECs is associated with a higher prevalence of steroid resistance and worse kidney outcomes, and can be considered an early sign of FSGS.

Charcoal Hemoperfusion for Methotrexate Toxicity: A Safe and Effective Life-Rescue Alternative When Glucarpidase Is Not Available.

Background: High dose methotrexate (HDMTX) is used for the treatment of pediatric hemato-oncological diseases. HDMTX can induce acute kidney injury in cases of delayed elimination. The use of leucovorin remains the most effective rescue action. Further treatment options are of difficult access in the rare cases where leucovorin fails to prevent renal failure from occurring. Glucarpidase is an effective treatment in cases of methotrexate (MTX) delayed elimination, but cost is high and availability is limited. Charcoal hemoperfusion (CHP) is a very efficient procedure to remove protein-bound drugs, promoting fast MTX elimination, but is rarely considered as a treatment option. Methods: We present three pediatric cases with prolonged exposure to MTX after HDMTX and delayed elimination in which hemoperfusion was performed as rescue treatment for methotrexate intoxication. Results: Charcoal hemoperfusion was performed with positive results and no complications as bridging until glucarpidase was available in two cases and in one case where two doses of glucarpidase led to insufficient reduction of MTX levels. Conclusions: CHP can be considered as a rescue treatment option in MTX intoxication, since it is an effective and safe extracorporeal method for removing MTX, in cases where rescue with leucovorin is insufficient and glucarpidase is not available or while waiting for delivery.

Multidimensional inflammatory and immunological endotypes of idiopathic focal segmental glomerulosclerosis and their association with treatment outcomes.

OBJECTIVES: Idiopathic focal segmental glomerulosclerosis (FSGS) has been linked to immunological and inflammatory response dysregulations. The aim of this study was to find endotypes of FSGS patients using a cluster (CL) analysis based on inflammatory and immunological variables, and to analyse whether a certain endotype is associated with response to treatment with corticosteroids. METHODS: This prospective observational study included patients with idiopathic FSGS diagnosed by kidney biopsy. Serum levels of soluble interleukin (IL)-1 receptor, tumoural necrosis factor alpha, Interferon gamma (IFNγ), IL-6, IL-17, IL-12, IL-23, IL-13, IL-4, IL-5, IL-6, haemopexin (Hx), haptoglobin (Hgl), soluble urokinase-type plasminogen activator receptor (suPAR) and urinary CD80 (uCD80) were measured with enzyme-linked immunosorbent assay or nephelometry. T-helper lymphocyte populations and T-regulatory lymphocytes were analysed by flow cytometry. A factorial analysis followed by a k-means CL analysis was performed. RESULTS: A total of 79 FSGS patients were included. Three CLs were identified. CL1 (27.8%) included IL-12, IL-17, IL-23 and a T helper 17 (Th17) pattern. CL2 (20.2%) included IL-4, IL-5, IL-13, immunoglobulin E and Th2 pattern. CL3 (51.8%) included IL-6, Hx, Hgl, suPAR and uCD80. There were no differences in age, gender, kidney function, albumin or proteinuria among CLs. About 42/79 patients (53.1%) showed cortico-resistance. The prevalence of cortico-resistance was significantly lower in CL2 (4/16, 25%) than in CL1 (16/26, 72.7%) and CL3 (22/41, 53.7%) (P = 0.018), with no significant differences between CLs 1 and 3 (P = 0.14). CONCLUSIONS: Patients with FSGS and indistinguishable clinical presentation at diagnosis were classified in three distinct CLs according to predominant Th17, Th2 and acute inflammatory responses that display differences in clinical response to treatment with corticosteroids.

Activation of the acute inflammatory phase response in idiopathic nephrotic syndrome: association with clinicopathological phenotypes and with response to corticosteroids.

BACKGROUND: Data on the activation of the acute inflammatory response and its clinicopathological associations in idiopathic nephrotic syndrome (INS) are scarce and discordant. OBJECTIVE: To analyse the associations between the activation of the inflammatory response, the clinicopathological characteristics of disease and the response to treatment with steroids in patients with INS. METHODS: A total of 101 patients with INS due to minimal change disease (MCD; n = 44), focal segmental glomerulosclerosis (FSGS; n = 33) and membranous nephropathy (MN; n = 24) and 50 healthy controls were included. At diagnosis, we measured the levels of haemopexin (Hx), haptoglobin (Hgl), interleukin-6 (IL-6), soluble urokinase-type plasminogen activator receptor (suPAR), tumour necrosis factor-α (TNF-α), soluble IL-1 receptor, interferon-γ and C-reactive protein. We analysed their clinicopathological associations. In MCD and FSGS patients, we determined the association between the levels of these variables and steroid resistance. RESULTS: The levels of Hx, Hgl, TNF-α, suPAR and IL-6 were higher in patients with INS than in healthy controls, and were not associated with proteinuria, estimated glomerular filtration rate or serum albumin. In MCD and FSGS patients, Hx, Hgl, IL-6 and TNF-α levels were similar and significantly higher than in MN patients. In patients with MCD and FSGS, multivariate analyses identified FSGS and the levels of Hx, Hgl or IL-6 as independent predictors of steroid resistance. CONCLUSIONS: The activation of the inflammatory response in patients with INS is heterogeneous and more prevalent in MCD or FSGS patients than in those with MN. In MCD and FSGS, elevated levels of Hx, Hgl or IL-6 are independently associated with steroid resistance.

Complement Genetic Variants and FH Desialylation in S. pneumoniae-Haemolytic Uraemic Syndrome.

Haemolytic Uraemic Syndrome associated with Streptococcus pneumoniae infections (SP-HUS) is a clinically well-known entity that generally affects infants, and could have a worse prognosis than HUS associated to E. coli infections. It has been assumed that complement genetic variants associated with primary atypical HUS cases (aHUS) do not contribute to SP-HUS, which is solely attributed to the action of the pneumococcal neuraminidase on the host cellular surfaces. We previously identified complement pathogenic variants and risk polymorphisms in a few Hungarian SP-HUS patients, and have now extended these studies to a cohort of 13 Spanish SP-HUS patients. Five patients presented rare complement variants of unknown significance, but the frequency of the risk haplotypes in the CFH-CFHR3-CFHR1 region was similar to the observed in aHUS. Moreover, we observed desialylation of Factor H (FH) and the FH-Related proteins in plasma samples from 2 Spanish and 4 Hungarian SP-HUS patients. To analyze the functional relevance of this finding, we compared the ability of native and "in vitro" desialylated FH in: (a) binding to C3b-coated microtiter plates; (b) proteolysis of fluid-phase and surface-bound C3b by Factor I; (c) dissociation of surface bound-C3bBb convertase; (d) haemolytic assays on sheep erythrocytes. We found that desialylated FH had reduced capacity to control complement activation on sheep erythrocytes, suggesting a role for FH sialic acids on binding to cellular surfaces. We conclude that aHUS-risk variants in the CFH-CFHR3-CFHR1 region could also contribute to disease-predisposition to SP-HUS, and that transient desialylation of complement FH by the pneumococcal neuraminidase may have a role in disease pathogenesis.

Single-cycle rituximab-induced immunologic changes in children: Enhanced in neuroimmunologic disease?

OBJECTIVE: To investigate the immunologic impact of a single cycle of rituximab (RTX) in children and adolescents with immune-mediated disorders, we evaluated B cells and immunoglobulin levels of 20 patients with neuroimmunologic, nephrologic, dermatologic, and rheumatologic disorders treated under recommended guidelines. METHODS: Retrospective study of immunologic changes in children (aged ≤18 years) diagnosed with immune-mediated disorders in which RTX was prescribed between June 2014 and February 2019. Patients were excluded if they had prior diagnosis of malignant disease or primary immunodeficiency. Patients were clinically and immunologically followed up every 3 months. Only patients having received a single cycle of RTX and with a follow-up greater than 12 months were included in the analysis of persistent dysgammaglobulinemia. RESULTS: Twenty children were included. Median age at RTX treatment was 12.8 years (interquartile range [IQR] 6.6-15.5 years). Median follow-up was 12.6 months (IQR 10.2-24 months). Of the 14 patients eligible for persistent dysgammaglobulinemia analysis (3 had received RTX retreatment, 2 had <12 months post-RTX follow-up, and in 1 data for this time point was missing), 2/14 (14%) remained with complete B-cell depletion, and 5/14 (36%) had dysgammaglobulinemia. Patients with dysgammaglobulinemia were younger (7.8 vs 15.6 years, p = 0.072), had more underlying neuroimmunologic diseases (5/5 vs 0/9, p < 0.001), and had received more frequently concentrated doses of RTX (3/5 vs 1/9, p = 0.05) than patients without dysgammaglobulinemia. Kinetics of immunoglobulins in the 20 patients revealed a decrease as early as 3 months after RTX in patients with neuroimmunologic disorders. CONCLUSION: In our cohort, single-cycle RTX-induced dysgammaglobulinemia was enhanced in patients with neuroimmunologic diseases. Further studies are needed to confirm this observation.

A kidney-disease gene panel allows a comprehensive genetic diagnosis of cystic and glomerular inherited kidney diseases.

Molecular diagnosis of inherited kidney diseases remains a challenge due to their expanding phenotypic spectra as well as the constantly growing list of disease-causing genes. Here we develop a comprehensive approach for genetic diagnosis of inherited cystic and glomerular nephropathies. Targeted next generation sequencing of 140 genes causative of or associated with cystic or glomerular nephropathies was performed in 421 patients, a validation cohort of 116 patients with previously known mutations, and a diagnostic cohort of 207 patients with suspected inherited cystic disease and 98 patients with glomerular disease. In the validation cohort, a sensitivity of 99% was achieved. In the diagnostic cohort, causative mutations were found in 78% of patients with cystic disease and 62% of patients with glomerular disease, mostly familial cases, including copy number variants. Results depict the distribution of different cystic and glomerular inherited diseases showing the most likely diagnosis according to perinatal, pediatric and adult disease onset. Of all the genetically diagnosed patients, 15% were referred with an unspecified clinical diagnosis and in 2% genetic testing changed the clinical diagnosis. Therefore, in 17% of cases our genetic analysis was crucial to establish the correct diagnosis. Complex inheritance patterns in autosomal dominant polycystic kidney disease and Alport syndrome were suspected in seven and six patients, respectively. Thus, our kidney-disease gene panel is a comprehensive, noninvasive, and cost-effective tool for genetic diagnosis of cystic and glomerular inherited kidney diseases. This allows etiologic diagnosis in three-quarters of patients and is especially valuable in patients with unspecific or atypical phenotypes.

Vascular thrombosis in pediatric kidney transplantation: Graft survival is possible with adequate management.

OBJECTIVE: Vascular thrombosis (VT) in pediatric kidney transplantation (KT) is a dreaded event that leads to graft loss in almost 100% of cases. In recent years, VT has become the most common cause of early graft loss. The aim of this study was to analyze our experience in diagnosis and treatment of VT and the impact of a new management protocol on patient outcome. METHODS: We conducted a retrospective study of 176 consecutive KT performed at our institution by the pediatric urology team between January 2000 and December 2015 and identified patients with VT. A protocol of prevention and early detection of VT was introduced in 2012. RESULTS: Out of 176 KT, nine cases of VT were identified (5.1%). The mean recipient age was 5.1 years (SD 4.9 years) and mean weight was 22.28 kg (SD 15.6 kg). Diagnosis was intraoperative in two cases and within the first 24 h after surgery in the remaining seven. Immediate surgical exploration was performed after diagnosis in all. Of the five episodes that occurred before 2012, all developed complete graft ischemia requiring transplantectomy. However, in the four cases diagnosed after 2012, graft perfusion could be restored in three, and abdominal wall closure with a mesh and delayed sequentially closure under ultrasound guidance was performed. With a follow-up of 30, 25, and 20 months, the three recovered grafts are still functioning normally. CONCLUSIONS: Increased awareness and the application of a protocol for prevention, detection and treatment of VT in pediatric KT can prevent graft loss. Immediate surgical intervention is mandatory after diagnosis. Avoiding compartment syndrome with delayed sequential closure may be useful to improve graft survival.

Primary distal renal tubular acidosis: novel findings in patients studied by next-generation sequencing.

This corrects the article DOI: 10.1038/pr.2015.243.

Mesangial C4d Deposits in Early IgA Nephropathy.

BACKGROUND AND OBJECTIVES: The prognostic value of mesangial C4d deposits in IgA nephropathy has been analyzed in patients with reduced GFR but has not been analyzed in those with normal kidney function. The main objective of the study was to analyze the prognostic value of C4d deposits and association with response to treatment in patients with IgA nephropathy and normal GFR. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: This retrospective cohort study included 190 patients with idiopathic IgA nephropathy diagnosed by kidney biopsy between 1988 and 2005. The patients had GFR≥80 ml/min per 1.73 m2 at the time of diagnosis, and they had a paraffin-embedded kidney biopsy with eight glomeruli available. RESULTS: In total, 170 (89%) and 20 (11%) patients were >18 and <18 years old, respectively; median (interquartile range) follow-up was 15 (12-22) years. Mesangial C4d deposit prevalence was 20% (38 of 190). At diagnosis, C4d-positive versus -negative patients had higher protein-to-creatinine ratio (median [interquartile range]: 1.94 g/g [0.9-3.1] versus 1.45 g/g [0.9-2.2]; P=0.04). During follow-up, C4d-positive patients showed a higher number of nephritic flares (median [range]: 1.4 [0-5] versus 0.9 [0-2]; P=0.04), had a higher protein-to-creatinine ratio (median [interquartile range]: 1.32 g/g [0.7-1.7] versus 0.89 g/g [0.1-1.3]; P<0.01), were more prone to receive repeated treatment with corticosteroids (45% versus 24%; P<0.01), and showed a larger reduction in eGFR (-1.6 versus -0.8 ml/min per 1.73 m2 per year; P=0.04). Furthermore, the presence of mesangial C4d deposits was an independent predictor of long-term kidney survival. CONCLUSIONS: C4d deposits may be one of the earliest poor prognostic variables available for patients with idiopathic IgA nephropathy and normal kidney function at the time of diagnosis. However, Cd4 deposits alone are not associated with the response to angiotensin blockers or corticosteroid treatment.

Poor phenotype-genotype association in a large series of patients with Type III Bartter syndrome.

INTRODUCTION: Type III Bartter syndrome (BS) is an autosomal recessive renal tubule disorder caused by loss-of-function mutations in the CLCNKB gene, which encodes the chloride channel protein ClC-Kb. In this study, we carried out a complete clinical and genetic characterization in a cohort of 30 patients, one of the largest series described. By comparing with other published populations, and considering that 80% of our patients presented the p.Ala204Thr Spanish founder mutation presumably associated with a common phenotype, we aimed to test the hypothesis that allelic differences could explain the wide phenotypic variability observed in patients with type III BS. METHODS: Clinical data were retrieved from the referral centers. The exon regions and flanking intronic sequences of the CLCNKB gene were screened for mutations by polymerase chain reaction (PCR) followed by direct Sanger sequencing. Presence of gross deletions or duplications in the region was checked for by MLPA and QMPSF analyses. RESULTS: Polyuria, polydipsia and dehydration were the main common symptoms. Metabolic alkalosis and hypokalemia of renal origin were detected in all patients at diagnosis. Calciuria levels were variable: hypercalciuria was detected in 31% of patients, while 23% had hypocalciuria. Nephrocalcinosis was diagnosed in 20% of the cohort. Two novel CLCNKB mutations were identified: a small homozygous deletion (c.753delG) in one patient and a small deletion (c.1026delC) in another. The latter was present in compound heterozygosis with the already previously described p.Glu442Gly mutation. No phenotypic association was obtained regarding the genotype. CONCLUSION: A poor correlation was found between a specific type of mutation in the CLCNKB gene and type III BS phenotype. Importantly, two CLCNKB mutations not previously described were found in our cohort.

Intracranial Hypertension in Cystinosis Is a Challenge: Experience in a Children's Hospital.

BACKGROUND: Cystinosis is a rare systemic lysosomal disease affecting mainly the kidney and eye. Ocular involvement in cystinosis is universal being the presence of cystine crystals in the cornea a diagnostic criterion and one of the earliest manifestations of the disease. Neuro-ophthalmologic manifestations are considered a rare and late complication in these patients. The aim of this article is to report the unexpectedly high incidence of intracranial hypertension in children with cystinosis at our centre. METHODS: This study included eight children (0-16 years of age) with cystinosis seen at the paediatric ophthalmology department, Hospital Universitari Vall d'Hebron (Barcelona, Spain), a tertiary hospital, over the last 5 years. RESULTS: Three girls and five boys, mean age: 9.6 years (range: 5-14 years), were studied. During follow-up, 4 out of 8 developed papilledema and confirmed high cerebrospinal fluid (CSF) pressure. The only symptomatic child presented an Arnold-Chiari anomaly with enlarged ventricles, whereas the other three, all asymptomatic, were diagnosed by scheduled fundoscopy and had normal neuroimaging studies. All four patients had at least one known risk factor for developing intracranial hypertension: initiation of growth hormone therapy, tapering of corticosteroids, acute renal failure and Arnold-Chiari malformation. Two of them required a ventriculoperitoneal shunt. CONCLUSIONS: Our results show that intracranial hypertension can occur more frequently than expected in patients with cystinosis. Furthermore, visual prognosis depends on early diagnosis and prompt treatment. A multidisciplinary approach is necessary, and we recommend fundoscopic examinations in all paediatric patients with cystinosis whether or not they present symptoms.

Primary distal renal tubular acidosis: novel findings in patients studied by next-generation sequencing.

BACKGROUND: Primary distal renal tubular acidosis (DRTA) is a rare disease caused by loss-of-function mutations in at least three genes (ATP6V0A4, ATP6V1B1, and SLC4A1) involved in urinary distal acidification. The next-generation sequencing (NGS) technique facilitates the search for mutations in DRTA patients and helps to characterize the genetic and clinical spectrum of the disease. METHODS: Ten DRTA patients were studied. They had normal serum anion gap (AG), metabolic acidosis with simultaneous positive urinary AG, and inability to maximally acidify the urine. The exons of the three genes were sequenced in two pools by ultrasequencing. Putative mutations were confirmed by corresponding Sanger sequencing of each exon. RESULTS: We found 13 mutations in nine patients. ATP6V0A4: Intron16+2insA; p.R807Q; p.Q276fs; p.P395fs; Intron7-2T>C. ATP6V1B1: p.I386fs; p.R394Q. SLC4A1: p.V245M; p.R589C; p.R589H; p.G609A. One case was a compound heterozygous with a known mutation in ATP6V1B1 (p.G609R) and a pathogenic variation at SLC4A1 (p.E508K). One patient was negative for mutations. CONCLUSION: This study evidences that NGS is labor and cost effective for the analysis of DRTA genes. Our results show for the first time SLC4A1 gene mutations in Spanish patients and disclose that compound heterozygosity at two different genes can be responsible for DRTA.

Novel mutations associated with nephrogenic diabetes insipidus. A clinical-genetic study.

UNLABELLED: Molecular diagnosis is a useful diagnostic tool in primary nephrogenic diabetes insipidus (NDI), an inherited disease characterized by renal inability to concentrate urine. The AVPR2 and AQP2 genes were screened for mutations in a cohort of 25 patients with clinical diagnosis of NDI. Patients presented with dehydration, polyuria-polydipsia, failure to thrive (mean ± SD; Z-height -1.9 ± 2.1 and Z-weight -2.4 ± 1.7), severe hypernatremia (mean ± SD; Na 150 ± 10 mEq/L), increased plasma osmolality (mean ± SD; 311 ± 18 mOsm/Kg), but normal glomerular filtration rate. Genetic diagnosis revealed that 24 male patients were hemizygous for 17 different putative disease-causing mutations in the AVPR2 gene (each one in a different family). Of those, nine had not been previously reported, and eight were recurrent. Moreover, we found those same AVPR2 changes in 12 relatives who were heterozygous carriers. Further, in one female patient, AVPR2 gene study turned out to be negative and she was found to be homozygous for the novel AQP2 p.Ala86Val alteration. CONCLUSION: Genetic analysis presumably confirmed the diagnosis of nephrogenic diabetes insipidus in every patient of the studied cohort. We emphasize that we detected a high presence (50 %) of heterozygous females with clinical NDI symptoms. WHAT IS KNOWN: • In most cases (90 %), inherited nephrogenic diabetes insipidus (NDI) is an X-linked disease, caused by mutations in the AVPR2 gene. • In rare occasions (10 %), it is caused by mutations in the AQP2 gene. What is new: • In this study, we report 10 novel mutations associated with NDI. • We have detected a high presence (50 %) of heterozygous carriers with clinical NDI symptoms.

Targeted next-generation sequencing in steroid-resistant nephrotic syndrome: mutations in multiple glomerular genes may influence disease severity.

Genetic diagnosis of steroid-resistant nephrotic syndrome (SRNS) using Sanger sequencing is complicated by the high genetic heterogeneity and phenotypic variability of this disease. We aimed to improve the genetic diagnosis of SRNS by simultaneously sequencing 26 glomerular genes using massive parallel sequencing and to study whether mutations in multiple genes increase disease severity. High-throughput mutation analysis was performed in 50 SRNS and/or focal segmental glomerulosclerosis (FSGS) patients, a validation cohort of 25 patients with known pathogenic mutations, and a discovery cohort of 25 uncharacterized patients with probable genetic etiology. In the validation cohort, we identified the 42 previously known pathogenic mutations across NPHS1, NPHS2, WT1, TRPC6, and INF2 genes. In the discovery cohort, disease-causing mutations in SRNS/FSGS genes were found in nine patients. We detected three patients with mutations in an SRNS/FSGS gene and COL4A3. Two of them were familial cases and presented a more severe phenotype than family members with mutation in only one gene. In conclusion, our results show that massive parallel sequencing is feasible and robust for genetic diagnosis of SRNS/FSGS. Our results indicate that patients carrying mutations in an SRNS/FSGS gene and also in COL4A3 gene have increased disease severity.

Genetics of type III Bartter syndrome in Spain, proposed diagnostic algorithm.

The p.Ala204Thr mutation (exon 7) of the CLCNKB gene is a "founder" mutation that causes most of type III Bartter syndrome cases in Spain. We performed genetic analysis of the CLCNKB gene, which encodes for the chloride channel protein ClC-Kb, in a cohort of 26 affected patients from 23 families. The diagnostic algorithm was: first, detection of the p.Ala204Thr mutation; second, detecting large deletions or duplications by Multiplex Ligation-dependent Probe Amplification and Quantitative Multiplex PCR of Short Fluorescent Fragments; and third, sequencing of the coding and flanking regions of the whole CLCNKB gene. In our genetic diagnosis, 20 families presented with the p.Ala204Thr mutation. Of those, 15 patients (15 families) were homozygous (57.7% of overall patients). Another 8 patients (5 families) were compound heterozygous for the founder mutation together with a second one. Thus, 3 patients (2 siblings) presented with the c. -19-?_2053+? del deletion (comprising the entire gene); one patient carried the p.Val170Met mutation (exon 6); and 4 patients (3 siblings) presented with the novel p.Glu442Gly mutation (exon 14). On the other hand, another two patients carried two novel mutations in compound heterozygosis: one presented the p.Ile398_Thr401del mutation (exon 12) associated with the c. -19-?_2053+? del deletion, and the other one carried the c.1756+1G>A splice-site mutation (exon 16) as well as the already described p.Ala210Val change (exon 7). One case turned out to be negative in our genetic screening. In addition, 51 relatives were found to be heterozygous carriers of the described CLCNKB mutations. In conclusion, different mutations cause type III Bartter syndrome in Spain. The high prevalence of the p.Ala204Thr in Spanish families thus justifies an initial screen for this mutation. However, should it not be detected further investigation of the CLCNKB gene is warranted in clinically diagnosed families.

Claudin-19 mutations and clinical phenotype in Spanish patients with familial hypomagnesemia with hypercalciuria and nephrocalcinosis.

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis is an autosomal recessive tubular disorder characterized by excessive renal magnesium and calcium excretion and chronic kidney failure. This rare disease is caused by mutations in the CLDN16 and CLDN19 genes. These genes encode the tight junction proteins claudin-16 and claudin-19, respectively, which regulate the paracellular ion reabsorption in the kidney. Patients with mutations in the CLDN19 gene also present severe visual impairment. Our goals in this study were to examine the clinical characteristics of a large cohort of Spanish patients with this disorder and to identify the disease causing mutations. We included a total of 31 patients belonging to 27 unrelated families and studied renal and ocular manifestations. We then analyzed by direct DNA sequencing the coding regions of CLDN16 and CLDN19 genes in these patients. Bioinformatic tools were used to predict the consequences of mutations. Clinical evaluation showed ocular defects in 87% of patients, including mainly myopia, nystagmus and macular colobomata. Twenty two percent of patients underwent renal transplantation and impaired renal function was observed in another 61% of patients. Results of the genetic analysis revealed CLDN19 mutations in all patients confirming the clinical diagnosis. The majority of patients exhibited the previously described p.G20D mutation. Haplotype analysis using three microsatellite markers showed a founder effect for this recurrent mutation in our cohort. We also identified four new pathogenic mutations in CLDN19, p.G122R, p.I41T, p.G75C and p.G75S. A strategy based on microsequencing was designed to facilitate the genetic diagnosis of this disease. Our data indicate that patients with CLDN19 mutations have a high risk of progression to chronic renal disease.