A critical view on autoantibodies in lupus nephritis: Concrete knowledge based on evidence

Deposition of autoantibodies in glomeruli is a key factor in the development of lupus nephritis (LN). For a long time, anti-dsDNA and anti-C1q antibodies were thought to be the main cause of the kidney damage. However, recent studies have shown that the list of autoantibidies that have renal tropism and deposit in the kidney in LN is increasing and the link between anti-dsDNA and renal pathology is weak due to potential confounders. Aspecific bindings of dsDNA with cationic antibodies and of anti-dsDNA with several renal antigens such as actinin, laminin, entactin, and annexinA2 raised doubts about the specific target of these antibodies in the kidney. Moreover, the isotype of anti-dsDNA in SLE and LN has never received adequate interest until the recent observation that IgG2 are preponderant over IgG1, IgG3 and IgG4. Based on the above background, recent studies investigated the involvement of anti-dsDNA IgG2 and of other antibodies in LN. It was concluded that circulating anti-dsDNA IgG2 levels do not distinguish between LN versus non-renal SLE, and, in patients with LN, their levels do not change over time. Circulating levels of other antibodies such as anti-ENO1 and anti-H2 IgG2 were, instead, higher in LN vs non-renal SLE at the time of diagnosis and decreased following therapies. Finally, new classes of renal antibodies that potentially modify the anti-inflammatory response in the kidney are emerging as new co-actors in the pathogenetic scenario. They have been defined as 'second wave antibodies' for the link with detoxifying mechanisms limiting the oxidative stress in glomeruli that are classically stimulated in a second phase of inflammation. These findings have important clinical implications that may modify the laboratory approach to LN. Serum levels of anti-ENO1 and anti-H2 IgG2 should be measured in the follow up of patients for designing the length of therapies and identify those patients who respond to treatments. Anti-SOD2 could help to monitor and potentiate the anti-inflammatory response in the kidney.

Novel biomarkers and pathophysiology of membranous nephropathy: PLA2R and beyond

Research on membranous nephropathy truly exploded in the last 15 years. This happened because of the application of new techniques (laser capture microdissection, mass spectrometry, protein G immunoprecipitation, arrays) to the study of its pathogenesis. After the discovery of PLA2R as the major target antigen, many other antigens were identified and others are probably ongoing. Clinical and pathophysiology rebounds of new discoveries are relevant in terms of diagnosis and prognosis and it is time to make a first assessment of the innovative issues. In terms of classification, target antigens can be divided into: 'membrane antigens' and 'second wave' antigens. The first group consists of antigens constitutionally expressed on the podocyte membrane (as PLA2R) that may become a target of an autoimmune process because of perturbation of immune-tolerance. 'Second wave' antigens are antigens neo-expressed by the podocyte or by infiltrating cells after a stressing event: this allows the immune system to produce antibodies against them that intensify and maintain glomerular damage. With this abundance of target antigens it is not possible, at the moment, to test all antibodies at the bedside. In the absence of this possibility, the role of histological evaluation is still irreplaceable.

Microplastics and Kidneys: An Update on the Evidence for Deposition of Plastic Microparticles in Human Organs, Tissues and Fluids and Renal Toxicity Concern

Plastic pollution became a main challenge for human beings as demonstrated by the increasing dispersion of plastic waste into the environment. Microplastics (MPs) have become ubiquitous and humans are exposed daily to inhalation or ingestion of plastic microparticles. Recent studies performed using mainly spectroscopy or spectrometry-based techniques have shown astounding evidence for the presence of MPs in human tissues, organs and fluids. The placenta, meconium, breast milk, lung, intestine, liver, heart and cardiovascular system, blood, urine and cerebrovascular liquid are afflicted by MPs' presence and deposition. On the whole, obtained data underline a great heterogeneity among different tissue and organs of the polymers characterized and the microparticles' dimension, even if most of them seem to be below 50-100 µm. Evidence for the possible contribution of MPs in human diseases is still limited and this field of study in medicine is in an initial state. However, increasing studies on their toxicity in vitro and in vivo suggest worrying effects on human cells mainly mediated by oxidative stress, inflammation and fibrosis. Nephrological studies are insufficient and evidence for the presence of MPs in human kidneys is still lacking, but the little evidence present in the literature has demonstrated histological and functional alteration of kidneys in animal models and cytotoxicity through apoptosis, autophagy, oxidative stress and inflammation in kidney cells. Overall, the manuscript we report in this review recommends urgent further study to analyze potential correlations between kidney disease and MPs' exposure in human.

Vaccines and nephrotic syndrome: efficacy and safety

Vaccines represent the most important medical evolution in the last two centuries allowing prevention and formally eradication of a wide number of infectious diseases. Safety and effectiveness are main issues that still require an open discussion. A few clinical reports described a critical temporal relationship between vaccination and acute nephrotic syndrome, indirectly suggesting an association. For this review, the literature was reviewed to identify articles reporting associations of nephrotic syndrome with vaccines against a vast array of infectious diseases (including bacteria, virus and Sars-Cov-2). As specific aims, we evaluated effectiveness and safety in terms of occurrence of either "de novo" nephrotic syndrome in health subjects or "relapse" in those already affected by the disease. In total, 377 articles were found; 166 duplicates and 71 non-full text, animal studies or non-English language were removed. After excluding another 50 articles not containing relevant data on generic side effects or on relapses or new onset nephrotic syndrome, 90 articles met the search criteria. Overall, studies reported the effect of vaccines in 1015 patients, plus 4 nationwide epidemiologic investigations. Limited experience on vaccination of NS patients with measles, mumps, and rubella live attenuated vaccines does not allow any definitive conclusion on their safeness. VZV has been administered more frequently without side effects. Vaccines utilizing virus inactivated, recombinant, and toxoid can be utilized without risks in NS. Vaccines for influenza reduce the risk of infections during the pandemic and are associated with reduced risk of relapse of NS typically induced by the infection. Vaccines for SARS-CoV-2 (all kinds) offer a concrete approach to reduce the pandemic. "De novo" NS or recurrence are very rare and respond to common therapies.

Biologics in steroid resistant nephrotic syndrome in childhood: review and new hypothesis-driven treatment

Nephrotic syndrome affects about 2-7 per 100,000 children yearly and accounts for less than 15% of end stage kidney disease. Steroids still represent the cornerstone of therapy achieving remission in 75-90% of the cases The remaining part result as steroid resistant nephrotic syndrome, characterized by the elevated risk of developing end stage kidney disease and frequently presenting disease recurrence in case of kidney transplant. The pathogenesis of nephrotic syndrome is still far to be elucidated, however, efficacy of immune treatments provided the basis to suggest the involvement of the immune system in the pathogenesis of the disease. Based on these substrates, more immune drugs, further than steroids, were administered in steroid resistant nephrotic syndrome, such as antiproliferative and alkylating agents or calcineurin inhibitors. However, such treatments failed in inducing a sustained remission. In last two decades, the developments of monoclonal antibodies, including the anti-CD20 rituximab and inhibitor of B7-1 abatacept, represented a valid opportunity of treatment. However, also the effectiveness of biologics resulted limited. We here propose a new hypothesis-driven treatment based on the combining administration of rituximab with the anti-CD38 monoclonal antibody daratumumab (NCT05704400), sustained by the hypothesis to target the entire B-cells subtypes pool, including the long-lived plasmacells.

Genome-wide association analyses define pathogenic signaling pathways and prioritize drug targets for IgA nephropathy

IgA nephropathy (IgAN) is a progressive form of kidney disease defined by glomerular deposition of IgA. Here we performed a genome-wide association study of 10,146 kidney-biopsy-diagnosed IgAN cases and 28,751 controls across 17 international cohorts. We defined 30 genome-wide significant risk loci explaining 11% of disease risk. A total of 16 loci were new, including TNFSF4/TNFSF18, REL, CD28, PF4V1, LY86, LYN, ANXA3, TNFSF8/TNFSF15, REEP3, ZMIZ1, OVOL1/RELA, ETS1, IGH, IRF8, TNFRSF13B and FCAR. The risk loci were enriched in gene orthologs causing abnormal IgA levels when genetically manipulated in mice. We also observed a positive genetic correlation between IgAN and serum IgA levels. High polygenic score for IgAN was associated with earlier onset of kidney failure. In a comprehensive functional annotation analysis of candidate causal genes, we observed convergence of biological candidates on a common set of inflammatory signaling pathways and cytokine ligand-receptor pairs, prioritizing potential new drug targets.

Rare Single Nucleotide and Copy Number Variants and the Etiology of Congenital Obstructive Uropathy: Implications for Genetic Diagnosis

SIGNIFICANCE STATEMENT

Congenital obstructive uropathy (COU) is a prevalent human developmental defect with highly heterogeneous clinical presentations and outcomes. Genetics may refine diagnosis, prognosis, and treatment, but the genomic architecture of COU is largely unknown. Comprehensive genomic screening study of 733 cases with three distinct COU subphenotypes revealed disease etiology in 10.0% of them. We detected no significant differences in the overall diagnostic yield among COU subphenotypes, with characteristic variable expressivity of several mutant genes. Our findings therefore may legitimize a genetic first diagnostic approach for COU, especially when burdening clinical and imaging characterization is not complete or available.

BACKGROUND

Congenital obstructive uropathy (COU) is a common cause of developmental defects of the urinary tract, with heterogeneous clinical presentation and outcome. Genetic analysis has the potential to elucidate the underlying diagnosis and help risk stratification.

METHODS

We performed a comprehensive genomic screen of 733 independent COU cases, which consisted of individuals with ureteropelvic junction obstruction ( n =321), ureterovesical junction obstruction/congenital megaureter ( n =178), and COU not otherwise specified (COU-NOS; n =234).

RESULTS

We identified pathogenic single nucleotide variants (SNVs) in 53 (7.2%) cases and genomic disorders (GDs) in 23 (3.1%) cases. We detected no significant differences in the overall diagnostic yield between COU sub-phenotypes, and pathogenic SNVs in several genes were associated to any of the three categories. Hence, although COU may appear phenotypically heterogeneous, COU phenotypes are likely to share common molecular bases. On the other hand, mutations in TNXB were more often identified in COU-NOS cases, demonstrating the diagnostic challenge in discriminating COU from hydronephrosis secondary to vesicoureteral reflux, particularly when diagnostic imaging is incomplete. Pathogenic SNVs in only six genes were found in more than one individual, supporting high genetic heterogeneity. Finally, convergence between data on SNVs and GDs suggest MYH11 as a dosage-sensitive gene possibly correlating with severity of COU.

CONCLUSIONS

We established a genomic diagnosis in 10.0% of COU individuals. The findings underscore the urgent need to identify novel genetic susceptibility factors to COU to better define the natural history of the remaining 90% of cases without a molecular diagnosis.

Multi-population genome-wide association study implicates immune and non-immune factors in pediatric steroid-sensitive nephrotic syndrome

Pediatric steroid-sensitive nephrotic syndrome (pSSNS) is the most common childhood glomerular disease. Previous genome-wide association studies (GWAS) identified a risk locus in the HLA Class II region and three additional independent risk loci. But the genetic architecture of pSSNS, and its genetically driven pathobiology, is largely unknown. Here, we conduct a multi-population GWAS meta-analysis in 38,463 participants (2440 cases). We then conduct conditional analyses and population specific GWAS. We discover twelve significant associations-eight from the multi-population meta-analysis (four novel), two from the multi-population conditional analysis (one novel), and two additional novel loci from the European meta-analysis. Fine-mapping implicates specific amino acid haplotypes in HLA-DQA1 and HLA-DQB1 driving the HLA Class II risk locus. Non-HLA loci colocalize with eQTLs of monocytes and numerous T-cell subsets in independent datasets. Colocalization with kidney eQTLs is lacking but overlap with kidney cell open chromatin suggests an uncharacterized disease mechanism in kidney cells. A polygenic risk score (PRS) associates with earlier disease onset. Altogether, these discoveries expand our knowledge of pSSNS genetic architecture across populations and provide cell-specific insights into its molecular drivers. Evaluating these associations in additional cohorts will refine our understanding of population specificity, heterogeneity, and clinical and molecular associations.

CO-OCCURRENCE OF NEPHRONOPHTHISIS TYPE 1 AND ALSTRÖM SYNDROME: A CASE REPORT

We describe the unique case of a patient in whom two ciliopathies with autosomal recessive transmission were clinically and molecularly diagnosed: Nephronophthisis type1 (NPHP1) and Alström Syndrome (AS). NPHP1 is one of the main genetic causes of terminal kidney failure in childhood. AS is an ultra-rare multi-systemic disease, characterized by progressive kidney disease, hepatic failure, dystrophy of the rods and cones to blindness, slowly progressive neuro-sensory deafness, dilated cardiomyopathy, obesity, insulin resistance / type 2 diabetes mellitus. The coexistence in the same patient of two rare syndromes with overlapping clinical manifestations but genetically different is an eventuality to be considered. This case report would describe the onset and progression of the multi-organ manifestations of both syndromes to highlight that ciliopathies present a strong phenotype overlap but also specific peculiarities. Therefore, to make a correct diagnosis, that is essential to achieve the best clinical management, could be challenging.

Anti-glutathione S-transferase theta 1 antibodies correlate with graft loss in non-sensitized pediatric kidney recipients

Introduction

Immunity to Human leukocyte antigen (HLA) cannot explain all cases of ABMR, nor the differences observed in the outcome of kidney recipients with circulating DSAs endowed with similar biologic characteristics. Thus, increasing attention has recently been focused on the role of immunity to non-HLA antigenic targets.

Methods

We analyzed humoral auto- and alloimmune responses to the non-HLA antigen glutathione S-transferase theta 1 (GSTT1), along with development of de novo (dn)HLA-DSAs, in a cohort of 146 pediatric non-sensitized recipients of first kidney allograft, to analyze its role in ABMR and graft loss. A multiplex bead assay was employed to assess GSTT1 antibodies (Abs).

Results

We observed development of GSTT1 Abs in 71 recipients after transplantation, 16 with MFI > 8031 (4th quartile: Q4 group). In univariate analyses, we found an association between Q4-GSTT1Abs and ABMR and graft loss, suggesting a potential role in inducing graft damage, as GSTT1 Abs were identified within ABMR biopsies of patients with graft function deterioration in the absence of concomitant intragraft HLA-DSAs. HLA-DSAs and GSTT1 Abs were independent predictors of graft loss in our cohort. As GSTT1 Ab development preceded or coincided with the appearance of dnHLA-DSAs, we tested and found that a model with the two combined parameters proved more fit to classify patients at risk of graft loss.

Discussion

Our observations on the harmful effects of GSTT1Abs, alone or in combination with HLA-DSAs, add to the evidence pointing to a negative role of allo- and auto-non-HLA Abs on kidney graft outcome.

Multicentric Carpotarsal Osteolysis Syndrome Associated Nephropathy: Novel Variants of MAFB Gene and Literature Review

Multicentric carpo-tarsal osteolysis (MCTO) is a rare osteolysis syndrome mainly involving carpal and tarsal bones usually presenting in early childhood. MCTO has autosomal dominant inheritance with heterozygous mutation in the MAFB gene. The skeletal disorder is often associated with chronic kidney disease. Data on clinical characterization and best treatment option of MCTO-associated nephropathy are scarce and mostly limited to case reports. With the aim to better define the phenotype and long-term outcomes of MCTO-associated nephropathy, we launched an online survey through the Workgroup for hereditary glomerulopathies of the European Rare Kidney Disease Network (ERKNet). Overall, we collected clinical and genetic data of 54 MCTO patients, of which 42 previously described and 12 new patients. We observed a high rate of kidney involvement (70%), early age of kidney disease onset, nephrotic-range proteinuria, and a kidney survival around of 40% at long-term follow-up. Our finding confirmed the heterogeneity of clinical manifestations and widen the spectrum of phenotypes resulting from MCTO-associated nephropathy. Furthermore, we report the first case of complete remission after treatment with cyclosporine A. We demonstrated that multidisciplinary care is essential for MCTO patients and early referral to nephrologists is therefore warranted to facilitate prompt treatment.

FC066: Circulating Anti-Rituximab Antibodies Do Not Affect Response to Rituximab in Steroid-Dependent Nephrotic Syndrome

BACKGROUND AND AIMS

Previous studies reported that the chimeric anti-CD20 monoclonal rituximab may lead to the production of anti-rituximab antibodies (Anti-RTX-Abs), due to the chimeric nature, impairing the efficacy of further infusions. In the context of glomerulonephritis, recent findings have described that the incidence of anti-RTX-Abs development may affect the efficacy of rituximab in paediatric steroid dependent nephrotic syndrome (SDNS) [Fujinaga et al. Pediatr Nephrol. 2020 Oct; 35(10): 2003–2008] and in membranous nephropathy [Boyer-Suavet et al. Front Immunol. 2020 Jan 13; 10: 3069]. The improved patient outcomes and cost-effectiveness have led to the development of a new generation of fully human anti-B cell agents in haematological and autoimmune diseases [Klomjit et al. Am J Kidney Dis. 2020 Dec; 76(6): 883–888]. Therefore, elucidating the role of Anti-RTX-Abs with the aim to develop personalized therapies is mandatory. In a randomized clinical trial, we compared the efficacy of fully humanized anti-CD20 antibody ofatumumab versus rituximab in children and young adults with SDNS [Ravani et al. JASN Oct 2021, 32 (10) 2652–2663].

METHOD

We randomized 140 subjects to single infusion of rituximab or ofatumumab. Follow-up was of 24 months. We measured anti-rituximab IgG antibodies (LISA- TRACKER, Theradiag© Croissy Beaubourg, France) at the enrollment in 64/140 (46%) patients who previously received rituximab, regardless of the randomization arm, and at 6 months in 54/70 of the patients in the rituximab arm. (Fig. 1) Median time of last rituximab treatment was 36 months (13–54) before enrollment.

RESULTS

Anti-RTX-Abs were detected in none of the patients receiving more than or equal to one rituximab infusion before enrollment. At 6 months, Anti-RTX-Abs are detected in 14/54 patients (26%) who received rituximab (Fig. 2A). Patients developing anti-RTX-Abs or not had similar characteristics at enrollment. At T6, anti-RTX-Abs was not statistically different comparing who received rituximab before enrollment and who did not (Fig. 2B).

Of the 54 patients treated with rituximab, 35 (65%) relapsed in 12 months of follow-up. Incidence of patients with anti-RTX-Abs at T6 was not statistically different comparing who experienced relapse with who did not (Fig. 2C). Time to relapse is reported in Fig. 2D. According to the protocol study, the 35 relapsing received a further infusion of rituximab. In this subgroup, incidence of patients with anti-RTX-Abs at T6 was not statistically different comparing who experienced further relapses with who did not (Fig. 2E).

Both patients with and without anti-RTX-Abs had similar levels of total B-cell counts before rituximab therapy and at month 6 and 12 thereafter, showing similar B-cell reconstitution (Fig. 2F). We found similar percentages for memory B-cells comparing patients with and without Anti-RTX-Abs at enrollment, at month 6 and at month 12 of follow-up (Fig. 2G).

CONCLUSION

 We evaluated the impact of Anti-RTX-Abs in a prospective study considering a large cohort of SDNS patients who received additional rituximab in case of relapse after a single infusion (375 mg/m2). According to the literature, we reported the development of Anti-RTX-Abs after a single infusion, which seems to persist for limited time. However, in contrast to previous findings, the development of Anti-RTX-Abs does not represent an unfavourable factor, which may limit the efficacy and the safety of further infusions. The prospective design of our study, in contrast to previous ones, represents one of the major strength of the present work. Moreover, Anti-RTX-Abs did not affect total and memory B-cell reconstitution following rituximab treatment.

MO1033: Kidney and Bone Marrow Involvement in Ipex Syndrome with Atypical Presentation: the ‘Fil Rouge’ of Treg Between Ipex Features and Other Clinical Entities

BACKGROUND AND AIMS

The transcription factor Forkhead box protein P3 (FOXP3) is central to the function of regulatory T cells (Treg). Mutations in the FOXP3 gene lead to a systemic disease called immune dysregulation, polyendocrinopathy and enteropathy, X-linked syndrome (IPEX). Some FOXP3 mutations were associated with atypical presentation including rare diseases such as IgG4 related disease (IgG4 RD) and autoimmune lymphoproliferative syndrome (ALPS). IgG4 RD is characterized by fibro-inflammatory tissue damage and often by elevated serum IgG4, whereas ALPS is presented by early-onset, chronic, nonmalignant lymphoproliferation, splenomegaly and autoimmune manifestations due to defective lymphocyte apoptosis, due mainly to mutation of genes involved in the apoptosis pathway. Kidney involvement in ALPS is uncommon, whereas in IPEX and IgG4 RD is more frequent, with different renal manifestations.

METHOD

We reported two atypical cases of IPEX characterized by the kidney and haematologic involvement. These cases are anecdotal for the wide spectrum of possible phenotypes associated with FOXP3 mutations.

RESULTS

Case 1. A 16-year male with clinical diagnosis of ALPS was treated with an mTOR inhibitor. Due to the onset of proteinuria until 650 mg/day and estimated glomerular filtration rate (eGFR) 66 mL/min, a kidney biopsy was performed and light microscopy showed a membranous pattern. The M-type phospholipase A2 receptor (PLA2R) on serum was negative as well as immunofluorescence (IF) on tissue. IgG-IgG4 immunohistochemical (IHC) staining was negative. We decided to re-evaluate the genetics of the patient, implementing the HPO (Human Phenotype Ontology) code. We found a mutation of the FOXP3 gene (NM_014009.3): c.779T > A (p.L260Q), never reported before on the GnomAD database and predicted to be ‘Likely Pathogenic’ by the suite of variant annotation. The patient does not present the classical triad of IPEX and Treg resulted normal. He was treated with steroids and continues mTOR inhibitor with good control of proteinuria and stable kidney function. Case 2. A 2-year boy was diagnosed with a trilinear bone marrow failure, genetic investigations were negative. He presented elevated serum levels of IgG4 subclass and kidney failure with tubular acidosis. A renal biopsy showed MGP associated with TIN. IF and IHC for PLA2R resulted positive. IHC staining for IgG4 showed overlapping positivity for IgG and IgG4. After the diagnosis of IgG4 RD, steroid therapy was started, without clinical response. Thereafter the patient underwent a bone marrow transplant from his brother (HLA-identical). In consideration of the rarity of IgG4 RD in children, we decided to perform a new genetic exam. A whole-exome sequencing on the proband and relatives was done. A hemizygous mutation of the FOXP3 gene (NM_014009.3), c.1087A > G (p.I363V), was found. This variant, inherited by the mother and found also in the proband's brother, was already described in the literature, thus a diagnosis of IPEX was done. Therefore, Treg resulted normal for brother and mother but not in our patient (0.3%). The patient underwent kidney transplantation, and after 1 year he presents normal kidney function.

CONCLUSION

MGP and IgG4 RD are rare in paediatrics, and they encouraged us to perform further investigations and reconsider the previous diagnosis. MGP pathogenesis in IPEX is consistent with recent evidence of unbalance of Th17/Treg in idiopathic MGP, with a significant reduction of Treg cell and FOXP3 expression. Th17/Treg may be implicated also in the pathogenesis of IgG4 RD as sources of cytokines production responsible for fibrosis and IgG4-producing B cells. FOXP3 + Treg and FAS-ligand are crucial for autoimmunity and self-tolerance. In ALPS patients a reduced expression of FOXP3 + Treg subsets but with the normal suppressive function was found. IPEX poses a diagnostic challenge considering the spectrum of different phenotypes, but to recognize kidney involvement, together with the growing use of wide genomic analysis, could play a central role.

Case Report: Atypical Manifestations Associated With FOXP3 Mutations. The “Fil Rouge” of Treg Between IPEX Features and Other Clinical Entities?

Introduction

The Forkhead box protein P3 (FOXP3) is a transcription factor central to the function of regulatory T cells (Treg). Mutations in the FOXP3 gene lead to a systemic disease called immune dysregulation, polyendocrinopathy, and enteropathy, an X-linked syndrome (IPEX) characterized by the triad of early-onset intractable diarrhea, type 1 diabetes, and eczema. An atypical presentation of IPEX has been reported.

Method

We report rare cases with equivocal clinical associations that included inflammatory, kidney, and hematologic involvements screened with massively parallel sequencing techniques.

Results

Two patients with hemizygous mutations of FOXP3 [c.779T>A (p.L260Q)] and [c.1087A>G (p.I363V)] presented clinical manifestations not included in typical cases of IPEX: one was a 16-year-old male patient with an initial clinical diagnosis of autoimmune lymphoproliferative syndrome (ALPS) and who developed proteinuria and decreased kidney function due to membranous nephropathy, an autoimmune renal condition characterized by glomerular sub-epithelial antibodies. The second patient was a 2-year-old child with bone marrow failure who developed the same glomerular lesions of membranous nephropathy and received a bone marrow transplantation. High levels of IgG4 in serum, bone marrow, and kidney led to the definition of IgG4-related kidney disease (IgG4 RKD) in this young boy. The circulating Treg levels were normal in the former case and very low in the second.

Conclusion

Two atypical associations of functional mutations of FOXP3 that include ALPS and IgG4 RKD are described. Membranous nephropathy leading to renal failure completed in both cases the clinical phenotypes that should be included in the clinical panorama of FOXP3 failure.

New-Onset Anemia and Associated Risk of ESKD and Death in Non-Dialysis CKD Patients: A Multi-Cohort Observational Study

Background

Anemia is a common complication of chronic kidney disease (CKD), but its incidence in nephrology settings is poorly investigated. Similarly, the risks of adverse outcomes associated with new-onset anemia are not known.

Methods

We performed a pooled analysis of three observational cohort studies including 1031 non-anemic CKD patients with eGFR <60 mL/min/1.73 m² regularly followed in renal clinics. We estimated the incidence of mild anemia (hemoglobin 11–12 g/dL in women and 11–13 g/dL in men) and severe anemia (hemoglobin <11 g/dL or use of erythropoiesis-stimulating agents) during a 3-year follow-up period. Thereafter we estimated the risk of end-stage kidney disease (ESKD) and all-cause death associated with new-onset mild and severe anemia.

Results

The mean age was 63 ± 14 years, 60% were men and 20% had diabetes. The mean estimated glomerular filtration rate (eGFR) was 37 ± 13 mL/min/1.73 m² and the median proteinuria was 0.4 g/day [interquartile range (IQR) 0.1–1.1]. The incidence of mild and severe anemia was 13.7/100 patients-year and 6.2/100 patients-year, respectively. Basal predictors of either mild or severe anemia were diabetes, lower hemoglobin, higher serum phosphate, eGFR <30 mL/min/1.73 m² and proteinuria >0.50 g/day. Male sex, moderate CKD (eGFR 30–44 mL/min/1.73 m²) and moderate proteinuria (0.15–0.50 g/day) predicted only mild anemia. The incidence of anemia increased progressively with CKD stages (from 8.77 to 76.59/100 patients-year) and the proteinuria category (from 13.99 to 25.02/100 patients-year). During a median follow-up of 3.1 years, 232 patients reached ESKD and 135 died. Compared with non-anemic patients, mild anemia was associated with a higher adjusted risk of ESKD {hazard ratio [HR] 1.42 [95% confidence interval (CI) 1.02–1.98]} and all-cause death [HR 1.55 (95% CI 1.04–2.32)]. Severe anemia was associated with an even higher risk of ESKD [HR 1.73 (95% CI 1.20–2.51)] and death [HR 1.83 (95% CI 1.05–3.19)].

Conclusions

New-onset anemia is frequent, particularly in patients with more severe renal damage and in those with diabetes mellitus. The occurrence of anemia, even of a mild degree, is associated with mortality risk and faster progression towards ESKD.

Randomised controlled trial comparing rituximab to mycophenolate mofetil in children and young adults with steroid-dependent idiopathic nephrotic syndrome: study protocol

INTRODUCTION

Glucocorticoids induce remission in 90% of children with idiopathic nephrotic syndrome (INS). Some become steroid-dependent (SD) and require the addition of steroid sparing drugs such as calcineurin-inhibitors (CNI) or cyclophosphamide, to maintain remission. Considering the toxicity of these drugs, alternative interventions are needed for long-term treatment. The anti-CD20 antibody rituximab has shown promising steroid-sparing properties, with conflicting results in complicated forms of SD-INS. Mycophenolate mofetil (MMF) resulted effective in maintaining free-steroid remission, however, studies are limited to few uncontrolled trials with reported different dose of MMF.

METHODS AND ANALYSIS

This open-label, two-parallel-arm, superiority controlled randomised clinical trial will enrol children with SD-INS maintained in remission with oral glucocorticoids or CNI. Children and young adults will be randomised to either MMF (1.200 mg/m²) or rituximab (375 mg/m²) infusion. After enrolment, glucocorticoids will be tapered until complete withdrawal. We will enrol 160 children and young adults to detect as significant at the two-sided p value of 0.01 with a power >0.8 a reduction in the risk of 1-year relapse (primary end-point). As secondary endpoints, we will compare the amount of glucocorticoids required to maintain complete remission at 6 and 24 months.

ETHICS AND DISSEMINATION

The trial was approved by the local ethics boards (Comitato Etico Regione Liguria CER Liguria https://www.portalericerca-liguria.it/). We will publish the study results at international scientific meetings.

TRIAL REGISTRATION NUMBERS

NCT004585152.

Rituximab vs Low-Dose Mycophenolate Mofetil in Recurrence of Steroid-Dependent Nephrotic Syndrome in Children and Young Adults: A Randomized Clinical Trial

This randomized clinical trial examines the superiority of a single dose of rituximab vs low-dose mycophenolate mofetil in preventing the recurrence of steroid-dependent nephrotic syndrome in children and young adults.

De novo TRIM8 variants impair its protein localization to nuclear bodies and cause developmental delay, epilepsy, and focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is the main pathology underlying steroid-resistant nephrotic syndrome (SRNS) and a leading cause of chronic kidney disease. Monogenic forms of pediatric SRNS are predominantly caused by recessive mutations, while the contribution of de novo variants (DNVs) to this trait is poorly understood. Using exome sequencing (ES) in a proband with FSGS/SRNS, developmental delay, and epilepsy, we discovered a nonsense DNV in TRIM8, which encodes the E3 ubiquitin ligase tripartite motif containing 8. To establish whether TRIM8 variants represent a cause of FSGS, we aggregated exome/genome-sequencing data for 2,501 pediatric FSGS/SRNS-affected individuals and 48,556 control subjects, detecting eight heterozygous TRIM8 truncating variants in affected subjects but none in control subjects (p = 3.28 × 10-11). In all six cases with available parental DNA, we demonstrated de novo inheritance (p = 2.21 × 10-15). Reverse phenotyping revealed neurodevelopmental disease in all eight families. We next analyzed ES from 9,067 individuals with epilepsy, yielding three additional families with truncating TRIM8 variants. Clinical review revealed FSGS in all. All TRIM8 variants cause protein truncation clustering within the last exon between residues 390 and 487 of the 551 amino acid protein, indicating a correlation between this syndrome and loss of the TRIM8 C-terminal region. Wild-type TRIM8 overexpressed in immortalized human podocytes and neuronal cells localized to nuclear bodies, while constructs harboring patient-specific variants mislocalized diffusely to the nucleoplasm. Co-localization studies demonstrated that Gemini and Cajal bodies frequently abut a TRIM8 nuclear body. Truncating TRIM8 DNVs cause a neuro-renal syndrome via aberrant TRIM8 localization, implicating nuclear bodies in FSGS and developmental brain disease.

Impaired urinary concentration ability is a sensitive predictor of renal disease progression in Joubert syndrome

Background

Joubert syndrome (JS) is an inherited ciliopathy characterized by a complex midbrain–hindbrain malformation and multiorgan involvement. Renal disease, mainly juvenile nephronophthisis (NPH), was reported in 25–30% patients although only ∼18% had a confirmed diagnosis of chronic kidney disease (CKD). NPH often remains asymptomatic for many years, resulting in delayed diagnosis. The aim of the study was to identify a biomarker able to quantify the risk of progressive CKD in young children with JS.

Methods

Renal features were investigated in 93 Italian patients, including biochemical tests, ultrasound and 1-deamino-8D-arginine vasopressin test in children with reduced basal urine osmolality. A subset of patients was followed-up over time.

Results

At last examination, 27 of 93 subjects (29%) presented with CKD, ranging from isolated urinary concentration defect (UCD) to end-stage renal disease. Both normal and pathological urine osmolality levels remained stable over time, even when obtained at very early ages. Follow-up data showed that the probability of developing CKD can be modelled as a function of the urine osmolality value, exceeding 75% for levels <600 mOsm/kg H₂O, and significantly increased in patients with an early diagnosis of isolated UCD.

Conclusions

We conclude that the frequency of CKD in JS increases with age and is higher than previously reported. Urine osmolality represents an early sensitive quantitative biomarker of the risk of CKD progression.

Genetic and Clinical Predictors of Age of ESKD in Individuals With Autosomal Dominant Tubulointerstitial Kidney Disease Due to UMOD Mutations

INTRODUCTION

Autosomal dominant tubulo-interstitial kidney disease due to UMOD mutations (ADTKD-UMOD) is a rare condition associated with high variability in the age of end-stage kidney disease (ESKD). The minor allele of rs4293393, located in the promoter of the UMOD gene, is present in 19% of the population and downregulates uromodulin production by approximately 50% and might affect the age of ESKD. The goal of this study was to better understand the genetic and clinical characteristics of ADTKD-UMOD and to perform a Mendelian randomization study to determine if the minor allele of rs4293393 was associated with better kidney survival.

METHODS

An international group of collaborators collected clinical and genetic data on 722 affected individuals from 249 families with 125 mutations, including 28 new mutations. The median age of ESKD was 47 years. Men were at a much higher risk of progression to ESKD (hazard ratio 1.78, P < 0.001).

RESULTS

The allele frequency of the minor rs4293393 allele was only 11.6% versus the 19% expected (P < 0.01), resulting in Hardy-Weinberg disequilibrium and precluding a Mendelian randomization experiment. An in vitro score reflecting the severity of the trafficking defect of uromodulin mutants was found to be a promising predictor of the age of ESKD.

CONCLUSION

We report the clinical characteristics associated with 125 UMOD mutations. Male gender and a new in vitro score predict age of ESKD.

Schimke immuno-osseous dysplasia, two new cases with peculiar EEG pattern

Schimke Immuno-Osseous Dysplasia (SIOD) is an autosomal recessive multisystem disorder caused by pathogenic variants in the gene SMARCAL1. The clinical picture is characterized by spondyloepiphyseal dysplasia resulting in growth failure, nephropathy and T-cell deficiency. Neurologic manifestations include microcephaly, cognitive impairment, migraine-like headaches and cerebrovascular manifestations such as cerebral atherosclerotic vascular disease and reversible cerebral vasoconstriction. The role of SMARCAL1 deficiency in non-vascular neurological complications is still under debate. Epilepsy has been reported in a few patients, even in the absence of brain abnormalities. Data regarding electroencephalographic (EEG) patterns in SIOD are scarce METHODS: We describe the clinical, neuroradiological and EEG findings in two unrelated patients with SIOD showing a peculiar pseudo-periodic EEG pattern apparently not related to the cerebrovascular complications, since it was recognized both before and after cerebrovascular events CONCLUSION: Our observations support the hypothesis that SMARCAL1plays an important role in neurodevelopment and brain function and expand the spectrum of neurological abnormalities related to SIOD.

Renal involvement and Strømme syndrome

Strømme syndrome is a rare autosomal recessive congenital disorder involving multiple systems. Centromeric protein F (CENPF) is the causative gene of the disease, and variants are usually linked to lethal outcomes either during the foetal stage or in early life. We present a young adult with a genetic diagnosis of Strømme syndrome who—in addition to classic microcephalia, microphthalmia and intestinal atresia (apple peel-type)—experienced slow and unexpected evolution to end-stage renal disease (ESRD). In conclusion, Strømme syndrome is a complex multiorgan disease that needs multidisciplinary clinical management, and potential evolution to ESRD should be taken into account.

Post-transplant recurrence of steroid resistant nephrotic syndrome in children: the Italian experience

Background

Steroid resistant nephrotic syndrome (SRNS) is a frequent cause of end stage renal disease in children and post-transplant disease recurrence is a major cause of graft loss.

Methods

We identified all children with SRNS who underwent renal transplantation in Italy, between 2005 and 2017. Data were retrospectively collected for the presence of a causative gene mutation, sex, histology, duration of pre-transplant dialysis, age at onset and transplant, HLA matching, recurrence, therapy for recurrence, and graft survival.

Results

101 patients underwent a first and 22 a second renal transplant. After a median follow-up of 58.5 months, the disease recurred on the first renal transplant in 53.3% of patients with a non-genetic and none with a genetic SRNS. Age at transplant > 9 years and the presence of at least one HLA-AB match were independent risk factors for recurrence. Duration of dialysis was longer in children with relapse, but did not reach statistical significance. Overall, 24% of patients lost the first graft, with recurrence representing the commonest cause. Among 22 patients who underwent a second transplant, 5 suffered of SRNS recurrence. SRNS relapsed in 5/9 (55%) patients with disease recurrence in their first transplant and 2 of them lost the second graft.

Conclusions

Absence of a causative mutation represents the major risk factor for post-transplant recurrence in children with SRNS, while transplant can be curative in genetic SRNS. A prolonged time spent on dialysis before transplantation has no protective effect on the risk of relapse and should not be encouraged. Retransplantation represents a second chance after graft loss for recurrence.

Autosomal Dominant Tubulointerstitial Kidney Disease with Adult Onset due to a Novel Renin Mutation Mapping in the Mature Protein

Autosomal dominant tubulointerstitial kidney disease (ADTKD) is a genetically heterogeneous renal disorder leading to progressive loss of renal function. ADTKD-REN is due to rare mutations in renin, all localized in the protein leader peptide and affecting its co-translational insertion in the endoplasmic reticulum (ER). Through exome sequencing in an adult-onset ADTKD family we identified a new renin variant, p.L381P, mapping in the mature protein. To assess its pathogenicity, we combined genetic data, computational and predictive analysis and functional studies. The L381P substitution affects an evolutionary conserved residue, co-segregates with renal disease, is not found in population databases and is predicted to be deleterious by in silico tools and by structural modelling. Expression of the L381P variant leads to its ER retention and induction of the Unfolded Protein Response in cell models and to defective pronephros development in zebrafish. Our work shows that REN mutations outside of renin leader peptide can cause ADTKD and delineates an adult form of ADTKD-REN, a condition which has usually its onset in childhood. This has implications for the molecular diagnosis and the estimated prevalence of the disease and points at ER homeostasis as a common pathway affected in ADTKD-REN, and possibly more generally in ADTKD.

Diagnosis, Phenotype, and Molecular Genetics of Congenital Analbuminemia

Congenital analbuminemia (CAA) is an inherited, autosomal recessive disorder with an incidence of 1:1,000,000 live birth. Affected individuals have a strongly decreased concentration, or complete absence, of serum albumin. The trait is usually detected by serum protein electrophoresis and immunochemistry techniques. However, due to the existence of other conditions in which the albumin concentrations are very low or null, analysis of the albumin (ALB) gene is necessary for the molecular diagnosis. CAA can lead to serious consequences in the prenatal period, because it can cause miscarriages and preterm birth, which often is due to oligohydramnios and placental abnormalities. Neonatally and in early childhood the trait is a risk factor that can lead to death, mainly from fluid retention and infections in the lower respiratory tract. By contrast, CAA is better tolerated in adulthood. Clinically, in addition to the low level of albumin, the patients almost always have hyperlipidemia, but they usually also have mild oedema, reduced blood pressure and fatigue. The fairly mild symptoms in adulthood are due to compensatory increment of other plasma proteins. The condition is rare; clinically, only about 90 cases have been detected worldwide. Among these, 53 have been studied by sequence analysis of the ALB gene, allowing the identification of 27 different loss of function (LoF) pathogenic variants. These include a variant in the start codon, frame-shift/insertions, frame-shift/deletions, nonsense variants, and variants affecting splicing. Most are unique, peculiar for each affected family, but one, a frame-shift deletion called Kayseri, has been found to cause about one third of the known cases allowing to presume a founder effect. This review provides an overview of the literature about CAA, about supportive and additional physiological and pharmacological information obtained from albumin-deficient mouse and rat models and a complete and up-to-date dataset of the pathogenic variants identified in the ALB gene.

A novel insertion (c.1098dupT) in the albumin gene causes analbuminemia in a consanguineous family

Congenital analbuminemia (OMIM # 616000) is an extremely rare autosomal recessive disorder, caused by variations in the albumin gene (ALB), which is generally thought to be a relatively benign condition in adulthood, but seems to be potentially life threatening in the pre- and peri-natal period. The subject of our study was a consanguineous family, in which we identified two analbuminemic individuals. Mutation analysis of ALB revealed that both are homozygous for a previously unreported insertion in exon 9 (c.1098dupT), causing a subsequent frame-shift with the generation of a premature stop codon, and an aberrant truncated putative protein product, p.Val367fsTer12. This variation is present in heterozygous condition in several other members of the family. The phenotype and the molecular genetics of CAA are discussed.

Molecular and Cellular Mechanisms for Proteinuria in Minimal Change Disease

Minimal Change Disease (MCD) is a clinical condition characterized by acute nephrotic syndrome, no evident renal lesions at histology and good response to steroids. However, frequent recurrence of the disease requires additional therapies associated with steroids. Such multi-drug dependence and frequent relapses may cause disease evolution to focal and segmental glomerulosclerosis (FSGS) over time. The differences between the two conditions are not well defined, since molecular mechanisms may be shared by the two diseases. In some cases, genetic analysis can make it possible to distinguish MCD from FSGS; however, there are cases of overlap. Several hypotheses on mechanisms underlying MCD and potential molecular triggers have been proposed. Most studies were conducted on animal models of proteinuria that partially mimic MCD and may be useful to study glomerulosclerosis evolution; however, they do not demonstrate a clear-cut separation between MCD and FSGS. Puromycin Aminonucleoside and Adriamycin nephrosis are models of glomerular oxidative damage, characterized by loss of glomerular basement membrane polyanions resembling MCD at the onset and, at more advanced stages, by glomerulosclerosis resembling FSGS. Also Buffalo/Mna rats present initial lesions of MCD, subsequently evolving to FSGS; this mechanism of renal damage is clearer since this rat strain inherits the unique characteristic of overexpressing Th2 cytokines. In Lipopolysaccharide nephropathy, an immunological condition of renal toxicity linked to B7-1(CD80), mice develop transient proteinuria that lasts a few days. Overall, animal models are useful and necessary considering that they reproduce the evolution from MCD to FSGS that is, in part, due to persistence of proteinuria. The role of T/Treg/Bcells on human MCD has been discussed. Many cytokines, immunomodulatory mechanisms, and several molecules have been defined as a specific cause of proteinuria. However, the hypothesis of a single cell subset or molecule as cause of MCD is not supported by research and an interactive process seems more logical. The implication or interactive role of oxidants, Th2 cytokines, Th17, Tregs, B7-1(CD80), CD40/CD40L, c-Mip, TNF, uPA/suPAR, Angiopoietin-like 4 still awaits a definitive confirmation. Whole genome sequencing studies could help to define specific genetic features that justify a definition of MCD as a “clinical-pathology-genetic entity.”

Adverse events linked with the use of chimeric and humanized anti-CD20 antibodies in children with idiopathic nephrotic syndrome

AIMS

Anti-CD20 antibodies are increasingly being used to treat idiopathic nephrotic syndrome (INS) in children. While they may allow steroid and calcineurin inhibitor withdrawal, repeated infusions of anti-CD20 antibodies are often required to maintain remission. Data on their potential toxicity in INS are needed, to consider repeated infusions.

METHODS

We investigated the side effects associated with the use of rituximab (a chimeric antibody; 130 patients) and ofatumumab (a humanized antibody; 37 patients) in children with INS (steroid-dependent and steroid/calcineurin inhibitor-dependent disease) treated at a national referral centre over a 9-year period (400 treatments; follow-up 1-9 years).

RESULTS

Infusion reactions were mainly absent in children with steroid-dependent disease. Rash, dyspnoea, fever, cough and itchy throat (5% and 18% following rituximab and ofatumumab infusion, respectively) were resolved by using premedication with salbutamol. Other short-term reactions (up to 3 months), including arthritis (2%) and lung injury (1%), were more common with rituximab. Infections were observed 3-9 months following infusion, were similarly common in the two groups and resolved with targeted therapies [antibiotic, fluconazole, immunoglobulins (Igs), etc.]. The number of circulating CD19/20 cells fell to 0 at month 1 and were reconstituted at month 3; circulating IgG antibodies remained within the normal range for 1 year. Tetanus and hepatitis B virus immunization was not modified by either treatment; Epstein-Barr virus and John Cunningham virus activation markers were occasionally observed.

CONCLUSION

Overall, the toxicity of anti-CD20 monoclonal antibodies was limited to post-infusion side effects in children with more complex disease. The relatively safe profile of anti-CD20 antibodies supports their use as steroid-sparing agents in children with INS.

Whole-Exome Sequencing in Adults With Chronic Kidney Disease: A Pilot Study

BACKGROUND

The utility of whole-exome sequencing (WES) for the diagnosis and management of adult-onset constitutional disorders has not been adequately studied. Genetic diagnostics may be advantageous in adults with chronic kidney disease (CKD), in whom the cause of kidney failure often remains unknown.

OBJECTIVE

To study the diagnostic utility of WES in a selected referral population of adults with CKD.

DESIGN

Observational cohort.

SETTING

A major academic medical center.

PATIENTS

92 adults with CKD of unknown cause or familial nephropathy or hypertension.

MEASUREMENTS

The diagnostic yield of WES and its potential effect on clinical management.

RESULTS

Whole-exome sequencing provided a diagnosis in 22 of 92 patients (24%), including 9 probands with CKD of unknown cause and encompassing 13 distinct genetic disorders. Among these, loss-of-function mutations were identified in PARN in 2 probands with tubulointerstitial fibrosis. PARN mutations have been implicated in a short telomere syndrome characterized by lung, bone marrow, and liver fibrosis; these findings extend the phenotype of PARN mutations to renal fibrosis. In addition, review of the American College of Medical Genetics actionable genes identified a pathogenic BRCA2 mutation in a proband who was diagnosed with breast cancer on follow-up. The results affected clinical management in most identified cases, including initiation of targeted surveillance, familial screening to guide donor selection for transplantation, and changes in therapy.

LIMITATION

The small sample size and recruitment at a tertiary care academic center limit generalizability of findings among the broader CKD population.

CONCLUSION

Whole-exome sequencing identified diagnostic mutations in a substantial number of adults with CKD of many causes. Further study of the utility of WES in the evaluation and care of patients with CKD in additional settings is warranted.

PRIMARY FUNDING SOURCE

New York State Empire Clinical Research Investigator Program, Renal Research Institute, and National Human Genome Research Institute of the National Institutes of Health.

A nucleotide deletion and frame-shift cause analbuminemia in a Turkish family

Congenital analbuminemia is an autosomal recessive disorder, in which albumin, the major blood protein, is present only in a minute amount. The condition is a rare allelic heterogeneous defect, only about seventy cases have been reported worldwide. To date, more than twenty different mutations within the albumin gene have been found to cause the trait. In our continuing study of the molecular genetics of congenital analbuminemia, we report here the clinical and biochemical findings and the mutation analysis of the gene in two Turkish infants. For the molecular analysis, we used our strategy, based on the screening of the gene by single-strand conformation polymorphism, heteroduplex analysis and direct DNA sequencing. The results showed that both patients are homozygous for the deletion of a cytosine residue in exon 5, in a stretch of four cytosines starting from nucleotide position 524 and ending at position 527 (NM_000477.5(ALB):c.527delC). The subsequent frame-shift inserts a stop codon in position 215, markedly reducing the size of the predicted protein product. The parents are both heterozygous for the same mutation, for which we propose the name Erzurum from the city of origin of the family. In conclusion, our results show that in this family congenital analbuminemia is caused by a novel frame-shift/deletion defect, confirm the inheritance of the trait, and contribute to advance our understanding of the molecular basis underlying this condition.

Mutational Spectrum of CYP24A1 Gene in a Cohort of Italian Patients with Idiopathic Infantile Hypercalcemia

BACKGROUND/AIMS

Loss-of-function mutations in the CYP24A1 gene, which encodes the vitamin D-24 hydroxylase, have been recognized as a cause of elevated 1,25-dihydroxyvitamin D concentrations, hypercalcemia, hypercalciuria, nephrocalcinosis and nephrolithiasis in infants and adults. As only a case report describing 2 adult patients has been reported in Italian population, we report here the mutation analysis of CYP24A1 gene in an Italian cohort of 12 pediatric and adult patients with idiopathic infantile hypercalcemia (IIH).

METHODS

We performed mutational screening of CYP24A1 gene in a cohort of 12 Italian patients: 8 children with nephrocalcinosis, hypercalcemia and PTH levels <10 pg/ml and 4 adult patients with nephrolithiasis, mild hypercalcemia and PTH levels <10 pg/ml from 11 unrelated Italian families. Clinical and biochemical data were collected. Genomic DNA was extracted from peripheral blood leucocytes using standard methods, and whole coding sequence of CYP24A1 gene was analysed in all patients and family members by polymerase chain reaction and direct sequencing. The potential pathogenicity of the newly identified missense mutations was evaluated by 3 different in silico approaches (Sorting Intolerant from Tolerant, Polyphen and Mutation Taster) and by comparative analysis in 14 different species using ClustalW software.

RESULTS

CYP24A1 bi-allelic mutations were found in 8 individuals from 7 Italian families (7/11; 64%). Overall, 6 different CYP24A1 mutations, including one small deletion (p.Glu143del), 4 missense mutations (p.Leu148Pro; p.Arg396Trp; p.Pro503Leu; p.Glu383Gln) and one nonsense mutation (p.Tyr220*) were identified. Two out of 6 mutations (p.Tyr220* and p.Pro503Leu) were not previously described. Moreover, a new CYP24A1 variant was identified by genetic screening of asymptomatic controls.

CONCLUSION

To the best of our knowledge, this is the first report of a CYP24A1 molecular analysis performed in an Italian cohort of adult and pediatric Italian patients. This study (1) confirms that CYP24A1 plays a causal role in some but not all cases of IIH (64%); (2) expands the spectrum of known CYP24A1 pathogenic mutations; (3) describes 2 hotspots detected in 50% of all Italian cases; and (4) emphasizes the importance of recognition and genetic diagnosis of CYP24A1 defects in infantile as well as adult hypercalcemia.

Anti-CD20 Antibodies for Idiopathic Nephrotic Syndrome in Children

Rituximab, a chimeric anti-CD20 monoclonal antibody originally licensed for lymphoma, is emerging as a novel steroid-sparing agent for idiopathic nephrotic syndrome in children. The potential use of anti-CD20 monoclonal antibodies in idiopathic nephrotic syndrome has contributed to shifting the view of podocytopathies from T cell-mediated to more complex immunomediated disorders that can benefit from targeting B cells and other mediators of the early immune response. Clinical data on the use of rituximab also have implications on disease management and classification. In this review, we present results of clinical studies that support rituximab as an effective steroid-sparing agent in steroid-dependent idiopathic nephrotic syndrome. Recent randomized controlled trials suggest that potential benefits of rituximab therapy in steroid-dependent forms of idiopathic nephrotic syndrome vary depending on whether children are dependent on steroids alone or on both steroids and calcineurin inhibitors, with greater probabilities to achieve drug-free remission in the former group. Multiple-drug dependence may identify a different disease state with different prognosis and treatment options. Insufficient data are available on optimal use of rituximab as a maintenance steroid-sparing agent in these steroid-sensitive forms of the disease, including how often and for how long rituximab infusions should be repeated to maximize expected benefits and minimize potential harms. Finally, one randomized controlled trial in children with steroid-resistant idiopathic nephrotic syndrome yielded negative results. New anti-CD20 antibodies are under study in this patient population.

A novel splicing mutation in the albumin gene (c.270+1G>T) causes analbuminaemia in a German infant

Congenital analbuminaemia is a rare autosomal recessive disorder manifested by the presence of a very low amount of circulating serum albumin. The clinical diagnosis may be challenging because of the absence of unambiguous symptoms and because hypoalbuminemia may have many causes different from a genetic lack of the protein. We describe the clinical and molecular characterization of a new case of congenital analbuminaemia in an infant of apparently non-consanguineous parents from Treves, Germany. For molecular diagnosis, we used our strategy, based on the screening of the albumin gene by single-strand conformation polymorphism, heteroduplex analysis and direct DNA sequencing, which revealed that the proband is homozygous and both parents are heterozygous, for a novel G > T transversion at nucleotide c.270+ 1, the first base of intron 3. The mutation inactivates the strongly conserved GT dinucleotide at the 5' splice site consensus sequence of this intron. In conclusion, we report the clinical findings and the molecular defect of this case, which contributes to a better understanding of the biological mechanism of congenital analbuminaemia.

[Familial Focal Segmental Glomerulosclerosis, a vademecum for clinical nephrologist]

The new genomic technologies (Next Generation Sequencing, NGS) are opening a new era in Genomic Medicine. This simple guide gives a state-of-the-art description of the genes that cause Focal Segmental Glomerulosclerosis and nephrotic syndrome.

Novel INF2 mutations in an Italian cohort of patients with focal segmental glomerulosclerosis, renal failure and Charcot-Marie-Tooth neuropathy

BACKGROUND

Mutations of INF2 represent the major cause of familial autosomal dominant (AD) focal segmental glomerulosclerosis (FSGS). A few patients present neurological symptoms of Charcot-Marie-Tooth (CMT) disease but the prevalence of the association has not been assessed yet.

METHODS

We screened 28 families with AD FSGS and identified 8 INF2 mutations in 9 families (32 patients overall), 3 of which were new. Mutations were in all cases localized in the diaphanous-inhibitory domain (DID) of the protein.

RESULTS

Clinical features associated with INF2 mutations in our patient cohort included mild proteinuria (1.55 g/L; range 1-2.5) and haematuria as a unique symptom that was recognized at a median age of 21.75 years (range 8-30). Eighteen patients developed end-stage renal disease during their third decade of life; 12 patients presented a creatinine range between 1.2 and 1.5 mg/dL and 2 were healthy at 45 and 54 years of age. CMT was diagnosed in four cases (12.5%); one of these patients presented an already known mutation on exon 2 of INF2, whereas the other patients presented the same mutation on exon 4, a region that was not previously associated with CMT.

CONCLUSIONS

We confirmed the high incidence of INF2 mutations in families with AD FSGS. The clinical phenotype was mild at the onset of the disease, but evolution to ESRD was frequent. The incidence of CMT has, for the first time, been calculated here to be 12.5% of mutation carriers. Our findings support INF2 gene analysis in families in which renal failure and/or neuro-sensorial defects are inherited following an AD model.

mRNA sequencing of a novel NPHS2 intronic mutation in a child with focal and segmental glomerulosclerosis

The NPHS2 gene encodes podocin, a membrane protein that acts as the structural scaffold in podocyte foot processes. NPHS2 mutations are associated with steroid-resistant nephrotic syndrome (SRNS), with the pathologic variant being focal and segmental glomerulosclerosis (FSGS), an emerging cause of end-stage renal disease in children. We describe a novel NPHS2 sequence variant in a girl with SRNS. Onset occurred at the age of seven years, with edema, hypo-proteinemia, hypoalbuminemia, hypercholesterolemia, hypertriglyceridemia and nephrotic proteinuria. Renal function was normal and autoimmunity markers were negative. Proteinuria failed to decrease after standard steroid therapy. Renal biopsy showed FSGS. Cyclosporine therapy was instituted, but no remission of proteinuria was achieved and chronic renal failure developed. Molecular analysis of the NPHS2 gene revealed a homozygous nucleotide substitution in position c.451+3A>T in intron 3-4. This nucleotide substitution has not been reported in the literature till date. The effect of the detected substitution on podocin protein was demonstrated by renal biopsy RNA extraction and cDNA amplification analysis. This technique had never been applied to a NPHS2 mutation. Based on these results, immunosuppressive drugs were discontinued and conservative therapy was undertaken.

Genotype-phenotype associations in WT1 glomerulopathy

WT1 mutations cause a wide spectrum of renal and extrarenal manifestations. Here we evaluated disease prevalence, phenotype spectrum, and genotype-phenotype correlations of 61 patients with WT1-related steroid-resistant nephrotic syndrome relative to 700 WT1-negative patients, all with steroid-resistant nephrotic syndrome. WT1 patients more frequently presented with chronic kidney disease and hypertension at diagnosis and exhibited more rapid disease progression. Focal segmental glomerulosclerosis was equally prevalent in both cohorts, but diffuse mesangial sclerosis was largely specific for WT1 disease and was present in 34% of cases. Sex reversal and/or urogenital abnormalities (52%), Wilms tumor (38%), and gonadoblastoma (5%) were almost exclusive to WT1 disease. Missense substitutions affecting DNA-binding residues were associated with diffuse mesangial sclerosis (74%), early steroid-resistant nephrotic syndrome onset, and rapid progression to ESRD. Truncating mutations conferred the highest Wilms tumor risk (78%) but typically late-onset steroid-resistant nephrotic syndrome. Intronic (KTS) mutations were most likely to present as isolated steroid-resistant nephrotic syndrome (37%) with a median onset at an age of 4.5 years, focal segmental glomerulosclerosis on biopsy, and slow progression (median ESRD age 13.6 years). Thus, there is a wide range of expressivity, solid genotype-phenotype associations, and a high risk and significance of extrarenal complications in WT1-associated nephropathy. We suggest that all children with steroid-resistant nephrotic syndrome undergo WT1 gene screening.