Rho-GTPase Activating Protein myosin MYO9A identified as a novel candidate gene for monogenic focal segmental glomerulosclerosis.

Focal segmental glomerulosclerosis (FSGS) is a podocytopathy leading to kidney failure, whose molecular cause frequently remains unresolved. Here, we describe a rare MYO9A loss of function nonsense heterozygous mutation (p.Arg701∗) as a possible contributor to disease in a sibling pair with familial FSGS/proteinuria. MYO9A variants of uncertain significance were identified by whole exome sequencing in a cohort of 94 biopsy proven patients with FSGS. MYO9A is an unconventional myosin with a Rho-GAP domain that controls epithelial cell junction assembly, crosslinks and bundles actin and deactivates the small GTPase protein encoded by the RHOA gene. RhoA activity is associated with cytoskeleton regulation of actin stress fiber formation and actomyosin contractility. Myo9A was detected in mouse and human podocytes in vitro and in vivo. Knockin mice carrying the p.Arg701∗MYO9A (Myo9AR701X) generated by gene editing developed proteinuria, podocyte effacement and FSGS. Kidneys and podocytes from Myo9AR701X/+ mutant mice revealed Myo9A haploinsufficiency, increased RhoA activity, decreased Myo9A-actin-calmodulin interaction, impaired podocyte attachment and migration. Our results indicate that Myo9A is a novel component of the podocyte cytoskeletal apparatus that regulates RhoA activity and podocyte function. Thus, Myo9AR701X/+ knock-in mice recapitulate the proband FSGS phenotype, demonstrate that p.R701X Myo9A is an FSGS-causing mutation in mice and suggest that heterozygous loss-of-function MYO9A mutations may cause a novel form of human autosomal dominant FSGS. Hence, identification of MYO9A pathogenic variants in additional individuals with familial or sporadic FSGS is needed to ascertain the gene contribution to disease.

Inherited glomerular diseases in the gilded age of genomic advancements.

The synchronized advent of high-throughput next-generation sequencing technology and knowledge of the human genome has rendered exponential contributions to our understanding of the pathophysiology of glomerular kidney diseases. A genetic diagnosis can now be made or confirmed in about two-thirds of the suspected inherited glomerular diseases. Next-generation sequencing is adept at identifying single nucleotide variations and small insertions or deletions that constitute majority of the disease-causing mutations. Description of the complete mutation spectrum in syndromic glomerulopathies may require the use of both sequencing and cytogenetic methods to detect large structural DNA variation in addition to single nucleotide changes. The enthusiastic application of genetic and genomic knowledge to inherited glomerular diseases has uncovered anticipated and unforeseen challenges mainly related to the biological interpretation of variants of uncertain significance and the limited benefit on clinical management for the individual patient when a diagnosis is obtained. To attain the ultimate goal of transforming clinical decision-making based on accurate genetic diagnosis using genomic information, these challenges need to be addressed. Till then, the glory of genomic medicine stands the test of time in this gilded age of genomic advancements.

ALG9 Mutation Carriers Develop Kidney and Liver Cysts.

BACKGROUND: Mutations in PKD1 or PKD2 cause typical autosomal dominant polycystic kidney disease (ADPKD), the most common monogenic kidney disease. Dominantly inherited polycystic kidney and liver diseases on the ADPKD spectrum are also caused by mutations in at least six other genes required for protein biogenesis in the endoplasmic reticulum, the loss of which results in defective production of the PKD1 gene product, the membrane protein polycystin-1 (PC1). METHODS: We used whole-exome sequencing in a cohort of 122 patients with genetically unresolved clinical diagnosis of ADPKD or polycystic liver disease to identify a candidate gene, ALG9, and in vitro cell-based assays of PC1 protein maturation to functionally validate it. For further validation, we identified carriers of ALG9 loss-of-function mutations and noncarrier matched controls in a large exome-sequenced population-based cohort and evaluated the occurrence of polycystic phenotypes in both groups. RESULTS: Two patients in the clinically defined cohort had rare loss-of-function variants in ALG9, which encodes a protein required for addition of specific mannose molecules to the assembling N-glycan precursors in the endoplasmic reticulum lumen. In vitro assays showed that inactivation of Alg9 results in impaired maturation and defective glycosylation of PC1. Seven of the eight (88%) cases selected from the population-based cohort based on ALG9 mutation carrier state who had abdominal imaging after age 50; seven (88%) had at least four kidney cysts, compared with none in matched controls without ALG9 mutations. CONCLUSIONS: ALG9 is a novel disease gene in the genetically heterogeneous ADPKD spectrum. This study supports the utility of phenotype characterization in genetically-defined cohorts to validate novel disease genes, and provide much-needed genotype-phenotype correlations.

A randomized clinical trial indicates that levamisole increases the time to relapse in children with steroid-sensitive idiopathic nephrotic syndrome.

Levamisole has been considered the least toxic and least expensive steroid-sparing drug for preventing relapses of steroid-sensitive idiopathic nephrotic syndrome (SSINS). However, evidence for this is limited as previous randomized clinical trials were found to have methodological limitations. Therefore, we conducted an international multicenter, placebo-controlled, double-blind, randomized clinical trial to reassess its usefulness in prevention of relapses in children with SSINS. The efficacy and safety of one year of levamisole treatment in children with SSINS and frequent relapses were evaluated. The primary analysis cohort consisted of 99 patients from 6 countries. Between 100 days and 12 months after the start of study medication, the time to relapse (primary endpoint) was significantly increased in the levamisole compared to the placebo group (hazard ratio 0.22 [95% confidence interval 0.11-0.43]). Significantly, after 12 months of treatment, six percent of placebo patients versus 26 percent of levamisole patients were still in remission. During this period, the most frequent serious adverse event (four of 50 patients) possibly related to levamisole was asymptomatic moderate neutropenia, which was reversible spontaneously or after treatment discontinuation. Thus, in children with SSINS and frequent relapses, levamisole prolonged the time to relapse and also prevented recurrence during one year of treatment compared to prednisone alone. However, regular blood controls are necessary for safety issues.

TREX1 Mutation Causing Autosomal Dominant Thrombotic Microangiopathy and CKD-A Novel Presentation.

Renal thrombotic microangiopathy (TMA) involves diverse causes and clinical presentations. Genetic determinants causing alternate pathway complement dysregulation underlie a substantial proportion of cases. In a significant proportion of TMAs, no defect in complement regulation is identified. Mutations in the major mammalian 3' DNA repair exonuclease 1 (TREX1) have been associated with autoimmune and cerebroretinal vasculopathy syndromes. Carboxy-terminal TREX1 mutations that result in only altered localization of the exonuclease protein with preserved catalytic function cause microangiopathy of the brain and retina, termed retinal vasculopathy and cerebral leukodystrophy (RVCL). Kidney involvement reported with RVCL usually accompanies significant brain and retinal microangiopathy. We present a pedigree with autosomal dominant renal TMA and chronic kidney disease found to have a carboxy-terminal frameshift TREX1 variant. Although symptomatic brain and retinal microangiopathy is known to associate with carboxy-terminal TREX1 mutations, this report describes a carboxy-terminal TREX1 frameshift variant causing predominant renal TMA. These findings underscore the clinical importance of recognizing TREX1 mutations as a cause of renal TMA. This case demonstrates the value of whole-exome sequencing in unsolved TMA.

Whole exome sequencing: a state-of-the-art approach for defining (and exploring!) genetic landscapes in pediatric nephrology.

The genesis of whole exome sequencing as a powerful tool for detailing the protein coding sequence of the human genome was conceptualized based on the availability of next-generation sequencing technology and knowledge of the human reference genome. The field of pediatric nephrology enriched with molecularly unsolved phenotypes is allowing the clinical and research application of whole exome sequencing to enable novel gene discovery and provide amendment of phenotypic misclassification. Recent studies in the field have informed us that newer high-throughput sequencing techniques are likely to be of high yield when applied in conjunction with conventional genomic approaches such as linkage analysis and other strategies used to focus subsequent analysis. They have also emphasized the need for the validation of novel genetic findings in large collaborative cohorts and the production of robust corroborative biological data. The well-structured application of comprehensive genomic testing in clinical and research arenas will hopefully continue to advance patient care and precision medicine, but does call for attention to be paid to its integrated challenges.

Risk factors for loss of residual renal function in children treated with chronic peritoneal dialysis.

In dialyzed patients, preservation of residual renal function is associated with better survival, lower morbidity, and greater quality of life. To analyze the evolution of residual diuresis over time, we prospectively monitored urine output in 401 pediatric patients in the global IPPN registry who commenced peritoneal dialysis (PD) with significant residual renal function. Associations of patient characteristics and time-variant covariates with daily urine output and the risk of developing oligoanuria (under 100 ml/m(2)/day) were analyzed by mixed linear modeling and Cox regression analysis including time-varying covariates. With an average loss of daily urine volume of 130 ml/m(2) per year, median time to oligoanuria was 48 months. Residual diuresis significantly subsided more rapidly in children with glomerulopathies, lower diuresis at start of PD, high ultrafiltration volume, and icodextrin use. Administration of diuretics significantly reduced oligoanuria risk, whereas the prescription of renin-angiotensin system antagonists significantly increased the risk oligoanuria. Urine output on PD was significantly associated in a negative manner with glomerulopathies (-584 ml/m(2)) and marginally with the use of icodextrin (-179 ml/m(2)) but positively associated with the use of biocompatible PD fluid (+111 ml/m(2)). Children in both Asia and North America had consistently lower urine output compared with those in Europe perhaps due to regional variances in therapy. Thus, in children undergoing PD, residual renal function depends strongly on the cause of underlying kidney disease and may be modifiable by diuretic therapy, peritoneal ultrafiltration, and choice of PD fluid.

Efficacy and safety of rituximab in children with difficult-to-treat nephrotic syndrome.

BACKGROUND: Rituximab has emerged as an important medication for patients with steroid-dependent or steroid-resistant nephrotic syndrome. PATIENTS: We report the efficacy and safety of therapy with intravenous rituximab, administered once weekly for 2-4 doses, in 193 patients (mean age 10.9, range 2.2-18.7 years) with difficult-to-treat steroid dependence (n = 101), calcineurin inhibitor (CNI)-dependent steroid resistance (n = 34) and CNI-resistant nephrotic syndrome (n = 58) managed at this center during 2006-13. OUTCOMES: Therapy in patients with steroid dependence and CNI-dependent steroid resistance led to significantly reduced relapse rates (respective mean difference 2.7 relapses/year and 2.2 relapses/year, corresponding to a decrease in relapses by 81.8 and 71.0%; both P < 0.0001). This resulted in a significant reduction in steroid requirement (mean difference 104.5 and 113.6 mg/kg/year, respectively; both P < 0.0001) and a trend to improved standard deviation scores for height (P = 0.069) and body mass index (P = 0.029). Remission was longer in patients with steroid dependence compared with CNI-dependent steroid resistance (median 16 versus 10 months; P < 0.0001). Prior response to cyclophosphamide predicted a lower risk of relapse in the former (hazard ratio, HR 0.56; P = 0.045); patients with initial resistance and CNI-dependent steroid resistance had increased risk of relapse (HR 2.66; P = 0.042). B-cell recovery, noted in 62.5% patients at 6 months, was not related to occurrence of relapse; redosing (n = 42 patients) was safe and effective. Response to therapy was unsatisfactory in patients with steroid- and CNI-resistant nephrotic syndrome, with remission in 29.3%. Focal segmental glomerulosclerosis was associated with higher odds of non-response (odds ratio 11.1; P = 0.028) and lack of response was associated with progressive chronic kidney disease (HR 9.97; P = 0.035). Therapy with rituximab was safe; adverse effects or infections were noted in 19 (9.8%) patients. CONCLUSIONS: Therapy with rituximab is effective and safe in reducing relapse rates and need for immunosuppressive medications in patients with steroid-dependent and CNI-dependent steroid-resistant nephrotic syndrome.

Prompt plasma exchanges and immunosuppressive treatment improves the outcomes of anti-factor H autoantibody-associated hemolytic uremic syndrome in children.

Antibodies to complement factor H are an uncommon cause of hemolytic uremic syndrome (HUS). Information on clinical features and outcomes in children is limited. In order to explore this we studied a multicenter cohort of 138 Indian children with anti-complement factor H antibody associated HUS, constituting 56% of patients with HUS. Antibody titers were high (mean 7054 AU/ml) and correlated inversely with levels of complement C3, but not complement factor H. Homozygous deletion of the CFHR1 gene was found in 60 of 68 patients. Therapies included dialysis in 119 children, 105 receiving plasma exchanges and 26 intravenous immunoglobulin. Induction immunosuppression consisted of 87 children receiving prednisolone with or without intravenous cyclophosphamide or rituximab. Antibody titers fell significantly following plasma exchanges and increased during relapses. Adverse outcome (stage 4-5 CKD or death) was seen in 36 at 3 months and 41 by last follow up, with relapse in 14 of 122 available children. Significant independent risk factors for adverse outcome were an antibody titer over 8000 AU/ml, low C3 and delay in plasma exchange. Combined plasma exchanges and induction immunosuppression resulted in significantly improved renal survival: one adverse outcome prevented for every 2.6 patients treated. Maintenance immunosuppressive therapy, of prednisolone with either mycophenolate mofetil or azathioprine, significantly reduced the risk of relapses. Thus, prompt use of immunosuppressive agents and plasma exchanges are useful for improving outcomes in pediatric patients with anti-complement factor H-associated HUS.

Overall neutralization of complement factor H by autoantibodies in the acute phase of the autoimmune form of atypical hemolytic uremic syndrome.

Complement is a major innate immune surveillance system. One of its most important regulators is the plasma protein factor H (FH). FH inactivation by mutations or by autoantibodies is associated with a thrombotic microangiopathy disease, atypical hemolytic uremic syndrome. In this study, we report the characterization of blood samples from 19 anti-FH Ab-positive atypical hemolytic uremic syndrome patients collected at the acute phase of the disease. Analyses of the functional consequences and epitope mapping, using both fluid phase and solid phase approaches, were performed. The anti-FH Abs perturbed FH-mediated cell protection (100%), inhibited FH interaction with C3 (46%), and caused C3 consumption (47%). The Abs were directed against multiple FH epitopes located at the N and C termini. In all tested patients, high titers of FH-containing circulating immune complexes were detected. The circulating immune complex titers correlated with the disease stage better than did the Ab titers. Our results show that anti-FH autoantibodies induce neutralization of FH at acute phase of the disease, leading to an overall impairment of several functions of FH, extending the role of autoantibodies beyond the impairment of the direct cell surface protection.

The VUS Challenge in Cystic Kidney Disease: A Case-Based Review.

Genetic testing in nephrology is becoming increasingly important to diagnose patients and to provide appropriate care. This is especially true for autosomal dominant polycystic kidney disease (ADPKD) because this is a common cause of kidney failure and genetically complex. In addition to the major genes, PKD1 and PKD2 , there are at least six minor loci, and phenotypic, and in some cases, genetic overlap with other cystic disorders. Targeted next-generation sequencing, a low-cost, high-throughput technique, has made routine genetic testing viable in nephrology clinics. Appropriate pre- and post-testing genetic counseling is essential to the testing process. Carefully assessing variants is also critical, with the genetic report classifying variants in accordance with American College of Medical Genetics and Genomics guidelines. However, variant of uncertain significance (VUSs) may pose a significant challenge for the ordering clinician. In ADPKD, and particularly within PKD1 , there is high allelic heterogeneity; no single variant is present in more than 2% of families. The Mayo/Polycystic Kidney Disease Foundation variant database, a research tool, is the best current database of PKD1 and PKD2 variants containing over 2300 variants identified in individuals with polycystic kidney disease, but novel variants are often identified. In patients with a high pretest probability of ADPKD on the basis of clinical criteria, but no finding of a pathogenic (P) or likely pathogenic (LP) variant in a cystic kidney gene, additional evaluation of cystic gene VUS can be helpful. In this case-based review, we propose an algorithm for the assessment of such variants in a clinical setting and show how some can be reassigned to a diagnostic grouping. When assessing the relevance of a VUS, we consider both patient/family-specific and allele-related factors using population and variant databases and available prediction tools, as well as genetic expertise. This analysis plus further family studies can aid in making a genetic diagnosis.

Thrombotic microangiopathy and acute kidney injury following vivax malaria.

BACKGROUND: Infection with Plasmodium vivax, a common human parasite, is occasionally recognized to cause severe organ dysfunction similar to P. falciparum infection. Acute kidney injury (AKI) in malaria is attributed to acute tubular necrosis; thrombotic microangiopathy is not described. METHODS: This observational study includes patients referred to a tertiary care center in North India during June to September 2011 with severe AKI, anemia, and thrombocytopenia following vivax malaria. Renal biopsies were processed by light, immunofluorescence, and electron microscopy. RESULTS: Nine patients (including 5 children) had persistent AKI with thrombocytopenia and variable anemia following the diagnosis of malaria. Based on peripheral smear, eight patients were diagnosed with vivax malaria and had received antimalarial therapy prior to referral; a laboratory diagnosis of P. vivax infection was made for one patient at this center. Renal histology in all cases showed features of thrombotic microangiopathy, including fibrin thrombi, subendothelial widening, and mesangiolysis, along with variable tubulointerstitial nephritis and acute tubular or cortical necrosis. Ultrastructural examination confirmed endothelial injury and subendothelial widening. All patients required hemodialysis, and six were dialysis dependent at four weeks. Delayed presentation to the hospital (P = 0.019), hemolysis on peripheral smear (P = 0.083), and prolonged oligoanuria (P = 0.036) were associated with dialysis dependence. CONCLUSION: The association of anemia, thrombocytopenia, and renal histological evidence of thrombotic microangiopathy with vivax malaria is novel, and suggests the presence of severe endothelial injury. Further studies are necessary to confirm the association and examine the factors associated with its occurrence.

Vascular Complications in Autosomal Dominant Polycystic Kidney Disease: Perspectives, Paradigms, and Current State of Play.

Autosomal dominant polycystic kidney disease (ADPKD) is the leading cause of inherited kidney disease with significant contributions to CKD and end-stage kidney disease. The underlying polycystin proteins (PC1 and PC2) have widespread tissue expression and complex functional roles making ADPKD a systemic disease. Vascular complications, particularly intracranial aneurysms (ICA) are the most feared due to their potential for devastating neurological complications and sudden death. Intracranial aneurysms occur in 8-12% of all patients with ADPKD, but the risk is intensified 4-5-fold in those with a positive family history. The basis for this genetic risk is not well understood and could conceivably be due to features of the germline mutation with a significant contribution of other genetic modifiers and/or environmental factors. Here we review what is known about the natural history and genetics of unruptured ICA in ADPKD including the prevalence and risk factors for aneurysm formation and subarachnoid hemorrhage. We discuss two alternative screening strategies and recommend a practical algorithm that targets those at highest risk for ICA with a positive family history for screening.

Treatment with tacrolimus and prednisolone is preferable to intravenous cyclophosphamide as the initial therapy for children with steroid-resistant nephrotic syndrome.

There are limited data on the relative efficacy and safety of calcineurin inhibitors and alkylating agents for idiopathic steroid-resistant nephrotic syndrome in children. To clarify this, we compared tacrolimus and intravenous cyclophosphamide therapy in a multicenter, randomized, controlled trial of 131 consecutive pediatric patients with minimal change disease, focal segmental glomerulosclerosis, or mesangioproliferative glomerulonephritis, stratified for initial or late steroid resistance. Patients were randomized to receive tacrolimus for 12 months or 6-monthly infusions of intravenous cyclophosphamide with both arms receiving equal amounts of alternate-day prednisolone. The primary outcome of complete or partial remission at 6 months, based on spot urine protein to creatinine ratios, was significantly higher in children receiving tacrolimus compared to cyclophosphamide (hazard ratio 2.64). Complete remission was significantly higher with tacrolimus (52.4%) than with cyclophosphamide (14.8%). The secondary outcome of sustained remission or steroid-sensitive relapse of nephrotic syndrome at 12 months was significantly higher with tacrolimus than cyclophosphamide. Treatment withdrawal was higher with cyclophosphamide, chiefly due to systemic infections. Compared to cyclophosphamide, 3 patients required treatment with tacrolimus to achieve 1 additional remission. Thus, tacrolimus and prednisolone are effective, safe, and preferable to cyclophosphamide as the initial therapy for patients with steroid-resistant nephrotic syndrome.

Short-term efficacy of rituximab versus tacrolimus in steroid-dependent nephrotic syndrome.

Although therapy with intravenous (IV) rituximab and tacrolimus reduces the relapse rate in steroid-dependent nephrotic syndrome (SDNS), studies on comparative efficacy are lacking. We retrospectively reviewed the records of patients with difficult-to-treat SDNS who had previously received levamisole, cyclophosphamide and/or mycophenolate mofetil, then treated with either rituximab or tacrolimus and followed for 12 months. Between January 2009 and April 2010, ten patients received two to three doses of IV rituximab (375 mg/m(2)/week) and 13 received tacrolimus (0.1-0.2 mg/kg/day) for 12 months; none had previously received either agent. Patients received tapering doses of alternate-day prednisolone; other immunosuppressive agents were discontinued. The mean age of the patients at treatment initiation with rituximab and tacrolimus was 12.2 ± 2.3 and 12.3 ± 3.0 years, respectively. The respective pre-treatment relapse rates (3.1 ± 1.1 and 3.5 ± 1.6 relapses per year) and cumulative prednisolone dose (137.2 ± 69.4 and 140.5 ± 59.0 mg/kg/year) were similar. Therapy resulted in a decline in relapse rate in both groups (P < 0.001). The number of relapses in the rituximab and tacrolimus groups was similar at 6 months (0.3 ± 0.5 vs. 0.3 ± 0.6 episodes, respectively), 12 months (0.8 ± 1.0 vs. 0.9 ± 1.1 episodes) and last follow-up (1.2 ± 1.0 vs. 1.5 ± 1.3 episodes). There were no differences in relapse-free survival at 6, 12 and 18 months. Therapy resulted in a significant decline in the cumulative prednisolone dose (67.2% in the rituximab group and 43.6% in the tacrolimus group) and a reduced body mass index. These findings suggest that in our patients with difficult-to-treat SDNS, treatment with two to three doses of rituximab was as effective as 12 months of therapy with tacrolimus in terms of steroid sparing and reduction in the relapse rate.

Gitelman syndrome: novel mutation and long-term follow-up.

We report a case of Gitelman syndrome presenting with fatigue, paresthesias, weakness of limbs and neck muscles since 2.5 years of age. Investigations showed hypokalemia and hypomagnesemia with urinary magnesium wasting. Genetic analysis revealed the presence of a novel homozygous mutation in the SLC12A3 gene (c.2879_2883+9ins14bp, p.Val 960 Glu fsx12). Management with potassium and magnesium supplements and spironolactone resulted in a significant improvement in symptoms. Over a follow-up of 11 years, the patient showed satisfactory growth and physical development.

Pediatric renal transplantation: an overview and update.

PURPOSE OF REVIEW: Transplantation is the preferred method of treatment for end-stage renal disease in children. The rate of pediatric kidney transplantation has been steadily rising over the past decade. The use of increasingly potent immunosuppressive drugs has lessened the risk for acute rejection substantially and improved short-term outcomes; however, the long-term outcomes have remained inadequate. RECENT FINDINGS: The follow-up of pediatric cohorts and the encouraging results from data registries prompt us to revisit our practices in transplantation so as to devise additional strategies to improve long-term outcomes. SUMMARY: This review presents a comprehensive discussion of the major issues in pediatric renal transplantation, the newer immunosuppression approaches to limit toxicities of therapies in children and some critical issues that remain to be addressed, specific to the care of the transplanted child. The ultimate goal of designing optimum conditions for equating graft survival to patient survival still remains a major goal for pediatric organ transplantation.