Introduction Alport syndrome (AS) is a genetically heterogenous kidney disease characterised by microhaematuria, proteinuria, and progressive chronic kidney disease (CKD). Although early renin-angiotensin system inhibitors (RASi) are standard of care, evidence on sodium-glucose cotransporter-2 inhibitors (SGLT2i) in AS is limited. Thus, this study evaluated SGLT2i effects in adult AS patients. Methods We conducted a retrospective, observational study including genetically confirmed AS patients with significant proteinuria treated with combined RASi+SGLT2i. Clinical-laboratory data were collected longitudinally and compared with the preceding decade on stable RASi alone. Chronic estimated glomerular filtration rate (eGFR) and proteinuria slopes, changes in time-averaged proteinuria, subgroups responses, and secondary SGLT2i effects were assessed. Results Eighteen adult AS patients (mean age 54.3±15.4 years; baseline eGFR 61.9±26.5 mL/min/1.73m2; median proteinuria 1010.0 [521.8;1662.5] mg/g) initiated RASi+SGLT2i therapy. Over 24.5±13.5 months, the chronic eGFR slope improved significantly (from -3.48 to +0.72 mL/min/1.73m2/year, P<0.001). Time-averaged proteinuria decreased by 24.1% (P=0.005), and longitudinal proteinuria slope also improved (P=0.038). Subgroup analyses confirmed consistent responses among patients with heterozygous COL4A3/COL4A4 carriers, normal Body Mass Index (BMI), and preserved renal function. Secondary effects included increases in haemoglobin and bicarbonate, alongside reduction in serum uric acid and weight loss. Three non-serious adverse events occurred, and no patient progressed to kidney failure. Conclusion This real-world study suggests a potential nephroprotective role of SGLT2i in adult AS patients, including heterozygous COL4A3/COL4A4 carriers. Benefits appeared independent of baseline BMI and renal function, supporting consideration of earlier initiation. Prospective studies are required to validate these findings and refine treatment timing.

Introduction:Alport syndrome (AS) is a genetically heterogenous kidney disease characterized by microhematuria, proteinuria, and progressive chronic kidney disease (CKD). Although early renin-angiotensin system inhibitors (RASi) are standard of care, evidence on sodium-glucose cotransporter-2 inhibitors (SGLT2i) in AS is limited. Thus, this study evaluated SGLT2i effects in adult patients with AS. Methods:We conducted a retrospective, observational study, including patients with genetically confirmed AS with significant proteinuria treated with combined RASi + SGLT2i. Clinico-laboratory data were collected longitudinally and compared with the preceding decade on stable RASi alone. Chronic estimated glomerular filtration rate (eGFR) and proteinuria slopes, changes in time-averaged proteinuria, subgroups responses, and secondary SGLT2i effects were assessed. Results:Eighteen adult patients with AS (mean age: 54.3 ± 15.4 years; baseline eGFR: 61.9 ± 26.5 ml/min per 1.73 m2; median proteinuria: 1010.0 [521.8-1662.5] mg/g) initiated RASi + SGLT2i therapy. Over 24.5 ± 13.5 months, the chronic eGFR slope improved significantly (-3.48 to +0.72 ml/min per 1.73 m2/yr, P < 0.001). Time-averaged proteinuria decreased by 24.1% (P = 0.005), and longitudinal proteinuria slope improved (P = 0.038). Subgroup analyses confirmed consistent responses among patients with heterozygous COL4A3/COL4A4 carriers, normal body mass index (BMI), and preserved renal function. Secondary effects included increases in hemoglobin and bicarbonate, alongside reduction in serum uric acid and weight loss. Three nonserious adverse events occurred, and no patient progressed to kidney failure (KF). Conclusion:This real-world study suggests a potential nephroprotective role of SGLT2i in adult patients with AS, including heterozygous COL4A3/COL4A4 carriers. Benefits appeared independent of baseline BMI and renal function, supporting consideration of earlier initiation. Prospective studies are required to validate these findings and refine treatment timing.

Background and aim Systemic Lupus Erythematosus (SLE) and Lupus Nephritis (LN) are prototypes of autoimmune diseases. Mechanisms determining the renal evolution in SLE patients and the identification of predictive biomarkers remain an open issue. Methods We reviwed data on serum levels of potential factors involved in SLE pathogenesis (i.e., NETs and dsDNA degradation) and autoantibodies associated with renal pathology (anti-dsDNA, anti-Histone 2 A and 3, anti-C1q, anti-ENO1, anti-ANXA1, anti-SOD2 IgG2) in patients recruited within the Italian collaborative Zeus study at the onset of renal symptoms (T0) and after 12 months (T12). Results Clustering analysis based on a few serum parameters allowed the stratification of LN/SLE/controls into well-separated groups. High dsDNA degradation and high anti-ENO1 antibody levels contributed to stratifying SLE and LN, respectively. Anti-ENO1, anti-SOD2, and anti-H2 A/-H3 antibodies paralleled proteinuria levels during the follow up (high at T0 and normalized after 12 months), whereas anti-dsDNA and anti-C1q IgG2 remained high for the whole observation period. Hazard Risk regression analysis indicated that anti-ENO1 and anti-H2 A IgG2 were associated with proteinuria (>1 g) and renal failure (eGFR <60 mL/min) (HRs and 95% CI highly significant). Conclusions Anti-ENO1 and anti-Histones 2A serum levels identify LN patients at the onset of renal symptoms and decrease following response to therapies. Both antibodies are associated with proteinuria and renal function loss. Our data support their use as predictive biomarkers for LN follow-up.

Congenital anomalies of the kidneys and urinary tract (CAKUT) are developmental disorders that commonly cause pediatric chronic kidney disease and mortality. We examine here rare coding variants in 248 CAKUT trios and 1742 singleton CAKUT cases and compare them to 22,258 controls. Diagnostic and candidate diagnostic variants are detected in 14.1% of cases. We find a significant enrichment of rare damaging variants in constrained genes expressed during kidney development and in genes associated with other developmental disorders, suggesting phenotype expansion. Consistent with these data, 18% of CAKUT patients with diagnostic variants have neurodevelopmental or cardiac phenotypes. We identify 40 candidate genes, including CELSR1, SSBP2, XPO1, NR6A1, and ARID3A. Two are confirmed as CAKUT genes: ARID3A and NR6A1. This study suggests that many yet-unidentified syndromes would be discoverable with larger cohorts and cross-phenotype analysis, leading to clarification of the genetic and phenotypic spectrum of developmental disorders.

Background:Tolvaptan is the only disease-modifying treatment approved to slow kidney disease progression in autosomal dominant polycystic kidney disease (ADPKD). Data on tolvaptan in ADPKD outside of clinical trials are limited, usually deal with short-term observations and are characterized by a drop-out rate of 21%-56%. Methods:In this retrospective, observational, multicenter study enrolling 122 Italian patients with ADPKD and rapid progressive renal disease, we evaluated the tolerability and side effects of tolvaptan treatment in a real-life setting. A personalized treatment strategy, based on an accurate patient selection and a strict clinical and laboratory monitoring, was applied. Results:During a median follow-up of 34.0 (interquartile range 17.3; -46.5) months the overall adherence on tolvaptan was 82.0%. Permanent withdrawal was reported in 22/122 patients (18.0%) after a mean of 34.4 ± 18.0 months; the main reasons for drug permanent withdrawal were onset of kidney failure in 7/122 (5.7%), poor tolerance to aquaresis in 4/122 (3.3%), family planning in 3/122 (2.5%) and liver function test elevation in 2/122 patients (1.6%). Temporary discontinuation was observed in 35/122 patients (28.7%) and in most cases it was not related to drug side effects. In order to evaluate tolvaptan eligibility, historic estimated glomerular filtration rate decline was the most inclusive criteria (92.9%) when compared with Mayo Imaging Classification (89.7%) and Predicting Renal Outcome in Polycystic Kidney Disease (PROPKD) Score (22.6%). Conclusion:This real-life study confirms the feasibility, safety, and tolerability of tolvaptan treatment. In order to overcome the challenges of tolvaptan treatment, our experience suggests that a dedicated PKD team may play a key role in implementing strategies focused to reduce drop-out and achieve treatment success.

Background Tolvaptan is the only disease-modifying treatment approved to slow kidney disease progression in ADPKD. Data on Tolvaptan in ADPKD outside of clinical trials are limited and usually deal with short-term observations and are characterized by a drop-out rate of 21-56%. Methods In this retrospective, observational, multicenter study enrolling 122 Italian patients with ADPKD and rapid progressive renal disease, we evaluated the tolerability and side effects of Tolvaptan treatment in a real-life setting. A personalized treatment strategy, based on an accurate patient selection and a strict clinical and laboratory monitoring, was applied. Results During a median follow-up of 34.0 (IQR 17.3;-46.5) months the overall adherence on Tolvaptan was 82.0%. Permanent withdrawal was reported in 22/122 patients (18.0%) after a mean of 34.4±18.0 months; the main reasons for drug permanent withdrawal were onset of kidney failure (KF) 7/122 (5.7%), poor tolerance to aquaresis 4/122 (3.3%), family planning in 3/122 (2.5%) and liver function test elevation 2/122 patients (1.6%). Temporary discontinuation was observed in 35/122 patients (28.7%) and in most cases it was not related to drug side effects. In order to evaluate Tolvaptan eligibility, historic eGFR decline was the most inclusive criteria (92.9%) when compared to Mayo Imaging Classification MIC (89.7%) and PROPKD score (22.6%). Conclusion This real-life study confirms the feasibility, safety, and tolerability of Tolvaptan treatment. In order to overcome the challenges of Tolvaptan treatment, our experience suggests that a dedicated PKD team may play a key role in implementing strategies focused to reduce drop-out and achieve treatment success.

ABSTRACT Background Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disorder, characterized by development and enlargement of kidney cysts, eventually leading to end-stage kidney disease (ESKD). Pathogenic variants in the PKD1 and PKD2 genes are the major cause of ADPKD; additional rare variants in the GANAB, DNAJB11, ALG5 and ALG9 genes have been found in a minority of ADPKD patients. More recently, a significant number of ADPKD families have been linked to monoallelic variants in the IFT140 gene. Methods In this retrospective study, we tested the prevalence of the known causative genes of ADPKD-spectrum phenotype, including the PKD1, PKD2, GANAB, DNAJB11, ALG5, ALG and IFT140 genes, in a cohort of 129 ADPKD patients who consecutively underwent genetic testing in a single centre in Italy. Genetic testing utilized a combination of targeted next-generation sequencing, long-range polymerase chain reaction, Sanger sequencing and multiplex ligation-dependent probe amplification. Clinical evaluation was conducted through renal function testing and imaging features, including ultrasonography, computer tomography and magnetic resonance imaging. Results Of the 129 enrolled patients, 86 (66.7%) had pathogenic variants in PKD1 and 28 (21.7%) in PKD2, loss of function pathogenic variants in the IFT140 gene were found in 3 unrelated patients (2.3%), no pathogenic variants were found in other ADPKD genes and 12 patients (9.3%) remained genetically unresolved (ADPKD-GUR). Familial clinical and genetic screening of the index patients with ADPKD due to an IFT140 pathogenic variant (ADPKD-IFT140) allowed identification of eight additional affected relatives. In the 11 ADPKD-IFT140 patients, the renal phenotype was characterized by mild and late-onset PKD, with large renal cysts and limited kidney insufficiency. Extrarenal manifestations, including liver cysts, were rarely seen. Conclusion Our data suggest the monoallelic pathogenic IFT140 variants are the third most common cause of the ADPKD-spectrum phenotype in Italy, usually associated with a mild and atypical renal cystic disease.

Rationale & ObjectiveAlport Syndrome (AS) is the most common genetic glomerular disease caused by mutations that affect Type IV collagen. However, the clinical characteristics and significance of AS with kidney cysts are not well defined. This study investigated the prevalence and clinical significance of cystic kidney phenotype in AS.Study DesignRetrospective cohort study.Setting& Participants: One hundred-eight patients with AS and a comparison cohort of 79 patients with IgA Nephropathy (IgAN). Clinical, genetic, and imaging data were collected from medical records.ExposuresCystic kidney phenotype evaluated by ultrasonography and defined as the presence of ≥3 cysts in each kidney. Demographic characteristics and eGFR at disease onset.OutcomesCystic kidney phenotype in the AS and IgAN cohorts. Time to CKD stage 3b and longitudinal changes in eGFR in the AS cohort.Analytical ApproachLogistic regression analysis to test independent strengths of associations of clinical/demographic features with the binary outcome of cystic phenotype. Survival analysis for the outcome of reaching CKD stage 3b and linear mixed models for changes in eGFR over time in the AS cohort.ResultsWe studied 108 patients with AS; 76 (70%) had genetic diagnosis. Autosomal dominant AS was prevalent, accounting for 68% of patients with genetic diagnosis. Cystic kidney phenotype was observed in 38% of patients with AS and was associated with normal sized kidneys in all but 3 patients, who showed increased total kidney volume, mimicking autosomal dominant polycystic kidney disease (ADPKD). The prevalence of cystic kidney phenotype was significantly higher in patients with AS when compared to comparison group of patients with IgAN (42% vs 19%; p=0.002). Patients with cystic kidney phenotype were older and had more marked reductions in eGFR than patients without cystic changes. Among patients with AS, the cystic phenotype was associated with older age and a faster decline eGFR.LimitationsRetrospective, single-center study.ConclusionsCystic kidney phenotype is a common finding in AS. The cystic kidney phenotype is a common finding in AS suggesting a possible role in cystogenesis for the genetic variants that cause this disease.

Kidney anomalies (KA) are developmental disorders that commonly cause pediatric chronic kidney disease and mortality. We examined rare coding variants in 248 KA trios and 1,742 singleton KA cases and compared them to 22,258 controls. Diagnostic and candidate diagnostic variants were detected in 14.1% of cases. We detected a significant enrichment of rare damaging variants in constrained genes expressed during kidney development and in genes associated with other developmental disorders, suggesting phenotype expansion. Consistent with these data, 18% of KA patients with diagnostic variants had neurodevelopmental or cardiac phenotypes. Extrarenal developmental phenotypes were associated with a higher burden of rare variants. Statistical analyses identified 40 novel candidate genes, 2 of which were confirmed as new KA genes: ARID3A and NR6A1. This study suggests that many yet-unidentified syndromes would be discoverable with larger cohorts and cross-phenotype analysis, leading to clarification the genetic and phenotypic spectrum of developmental disorders. ### Competing Interest Statement A.G. Gharavi receives a research grant from Natera and has served on advisory boards for Natera through a service agreement with Columbia University. A.G. Gharavi has served on advisory boards for Actio Biosciences, Alnylam, Novartis, Calliditas and Travere and has stock options for Actio Biosciences. H.M. Rasouly reports Research Funding: Natera. ### Funding Statement This study was funded by: HMR: the Donald E Wesson Research Fellowship from the ASN Foundation for Kidney Research Three NDDK grants AGG: Genetics of Human Renal HypoDysplasia 5R01DK080099-13 AGG: George M OBrien Center 5U54DK104309-10 HMR: Advancing equitable implementation of genomic medicine in nephrology 5K01DK132495-02 The DDD study presents independent research commissioned by the Health Innovation Challenge Fund (grant number HICF-1009-003) This study makes use of DECIPHER funded by Wellcome (grant number WT223718/Z/21/Z) ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: the Institutional Review Board of Columbia University Medical Center, as well as other relevant Ethics Review Boards at collaborating institutions gave ethical approval for this work I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors

ABSTRACTObjectiveDespite the increasing use of rituximab in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV), it remains unclear what the optimal dosing is, especially for maintenance of remission. A deeper understanding of post-rituximab B-cell repopulation patterns may aid better-tailored treatment.MethodsThis is a monocentric, retrospective study including ANCA-positive AAV patients receiving a single course of rituximab induction. CD19+ B cells were longitudinally monitored with flow cytometry. B-cell repopulation was defined as CD19+ >10 cells/μL.ResultsSeventy-one patients were included, the majority with microscopic polyangiitis (75%), myeloperoxidase-ANCA positivity (75%) and with renal involvement (79%). During a median follow-up of 54 months since the first rituximab infusion, 44 patients (62%) repopulated B cells, with a median time to repopulation of 39 months (range 7–102). Patients experiencing B-cell depletion lasting longer than the overall median time to repopulation (39 months) exhibited a lower risk of flare and higher risk of serious infection. In multivariate Cox regression, higher estimated glomerular filtration rate (eGFR) [hazard ratio (HR) 1.84, 95% confidence interval (CI) 1.13–2.98 per 30 mL/min/1.73 m2 eGFR] and female sex (HR 2.70, 95% CI 1.37–5.31) were independent predictors of increased rate of B-cell repopulation.ConclusionA subset of AAV patients develop sustained post-rituximab B-cell depletion, which associates with reduced risk of flare and increased risk of serious infection in the long term. Preserved renal function and female sex are associated with faster B-cell repopulation. These observations further highlight the need to personalize immunosuppression to improve clinical outcomes.

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.

IgA vasculitis (IgAV) is a pediatric disease with skin and systemic manifestations. Here, we conducted genome, transcriptome, and proteome-wide association studies in 2,170 IgAV cases and 5,928 controls, generated IgAV-specific maps of gene expression and splicing from blood of 255 pediatric cases, and reconstructed myeloid-specific regulatory networks to define disease master regulators modulated by the newly identified disease driver genes. We observed significant association at the HLA-DRB1 (OR=1.55, P=1.1×10-25) and fine-mapped specific amino-acid risk substitutions in DRβ1. We discovered two novel non-HLA loci: FCAR (OR=1.51, P=1.0×10-20) encoding a myeloid IgA receptor FcαR, and INPP5D (OR=1.34, P=2.2×10-9) encoding a known inhibitor of FcαR signaling. The FCAR risk locus co-localized with a cis-eQTL increasing FCAR expression; the risk alleles disrupted a PRDM1 binding motif within a myeloid enhancer of FCAR. Another risk locus was associated with a higher genetically predicted levels of plasma IL6R. The IL6R risk haplotype carried a missense variant contributing to accelerated cleavage of IL6R into a soluble form. Using systems biology approaches, we prioritized IgAV master regulators co-modulated by FCAR, INPP5D and IL6R in myeloid cells. We additionally identified 21 shared loci in a cross-phenotype analysis of IgAV with IgA nephropathy, including novel loci PAID4, WLS, and ANKRD55.

Abstract Background and Aims Autosomal-dominant polycystic kidney disease (ADPKD) is the most common inherited renal disorder characterized by progressive bilateral renal cysts development and extrarenal phenotype, i.e. liver and/or pancreatic cysts, intracranial aneurism, hernias, mitral valve prolapse and diverticulosis. More than 90% of patients harbour heterozygous pathogenic variant in PKD1 or PKD2 genes, rarely in other cystogenes (e.g. GANAB, DNAJB11, ALG8, ALG9). Recently Senum et al. demonstrated that monoallelic loss of function (LoF) IFT140 variants are an important cause of ADPKD-like disease distinguished by large renal cysts, few liver cysts and mostly mild renal failure. The aim of our study was to define prevalence and phenotype of IFT140-ADPKD in an Italian ADPKD cohort. Methods The study included ADPKD patients, evaluated in 2021 and 2022, at Outpatient Clinic of Genetic Kidney Diseases of Brescia, Italy, that underwent in-depth clinical, laboratory, and instrumental assessments. ADPKD was clinically diagnosed according to Pei modified criteria, in patients with age-specific ultrasound criteria and family history consistent with autosomal dominant inheritance. From January 2022, NGS genetic testing protocol for ADPKD has been updated with IFT140 gene, thus the ADPKD gene panel included: ALG8, ALG9, ANKS6, DNAJB11, GANAB, IFT140, LRP5, PARN, PKD1, PKD2, PRKCSH, SEC61A1, SEC63. The new protocol has been offered to patients evaluated since January 2022 and to all genetically unresolved patients evaluated in 2021. All patients performed also multiple ligation probe amplification (MPLA) analysis of PKD1 or PKD2. Results In 2021 and 2022 ADPKD genes testing has been performed in 129 patients. Pathogenic variants in PKD1 or PKD2 genes were detected in 110/129 patients (85%); among the negative cases (19/129, 15%), 3 patients (P1,P2,P3) resulted heterozygous carrier of LoF variants in IFT140 gene: p.Arg307*, p.Lys1275Argfs*23 and p.Arg834* respectively. Overall 2,3% of ADPKD patients harboured IFT140 pathogenic variant; considering unresolved cases only, the prevalence was 15.7% (3/19). Segregation analysis identified the LoF variant in 3 daughters of P1 and in a son of P2. The 3 probands were diagnosed with renal disease in adulthood from fourth to sixth decade. In P1 eGFR (CKD-EPI formula) slowly declined from 104 ml/min/1.73 at onset (43 year-old) to 74.6 ml/min/1.73 at age 55. In P2 eGFR at first evaluation was 38 ml/min/1.73 (68 year-old); at last follow-up 32.9 ml/min/1.73 (73 year-old). In P3 eGFR declined from 51.7 ml/min/1.73 (55 year-old) to 42 ml/min/1.73 at age 67. Renal imaging in P1 at and P2 disclosed increased total kidney volume (TKV 1042 and 5520 cc respectively), large cysts and absence of cystic liver disease. P3 had slightly increased kidneys (TKV 447cc) with large renal cysts and few liver cysts. Hypertension was present in 4 patients, all with adult-onset (46-60 years). Two patients had an early diagnosis of kidney stones (age 24 and 18). No macroscopic hematuria or cyst infections were reported. In accordance with an ADPKD-like disease form, P1 presented inguinal hernia. Imaging data are summarized in Figure 1. Conclusion In this Italian cohort, heterozygous LoF variants in IFT140 gene is confirmed to be the third most common genetic cause of ADPKD-spectrum disease, the prevalence being 2,3%. The major features are late onset hypertension, increased kidney volume due to large cysts and slow progressive renal failure. IFT140 gene must be included in diagnostic protocol of ADPKD patients to better define renal prognosis, therapy and familial screening.

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.

Autosomal Dominant Tubulointerstitial Kidney Disease, a rare genetic disorder characterised by progressive chronic kidney disease, is caused by mutations in different genes including REN, encoding renin. Renin is a secreted protease composed of 3 domains: the leader peptide allowing insertion in the endoplasmic reticulum (ER), a pro-segment regulating its activity, and the mature part. Mutations in mature renin lead to ER retention of mutant protein and to late onset disease, while mutations in the leader peptide, associated with defective ER translocation, and mutations in the pro-segment, accumulating in the ER-to-Golgi compartment, lead to a more severe, early-onset disease. In this study we demonstrate a common, unprecedented effect of mutations in the leader peptide and pro-segment as they lead to full or partial mistargeting of mutated protein to mitochondria. The mutated pre-pro sequence of renin is necessary and sufficient to drive mitochondrial rerouting, mitochondrial import defect and fragmentation. Mitochondrial localisation and fragmentation are also observed for wild type renin when affecting ER translocation. These results expand the spectrum of cellular phenotypes associated with ADTKD-REN mutations providing new insight into the disease molecular pathogenesis.

Abstract Background and Aims ADPKD is the most common form of inherited renal disease worldwide. ADPKD care has advanced over the past decade by the identification of several clinical/genetic risk factors of progression and approval of first disease-modifying drug. Further clinical outcomes research is needed to improve patient-centered clinical care; in addition new disease-modifying therapies are in pipeline, requiring a growing need for patient enrolment in clinical trials. To advance these goals, the Italian Society of Nephrology, supported by the Italian PKD Foundation (AIRP) established in 2020 the creation of a National web-based ADPKD Registry. Here we present the design of this Registry and the preliminary results. Method Adult patients with clinical or genetically confirmed diagnosis of ADPKD have been enrolled in the Registry, hosted by a secure online platform including both a clinical and genetic database. Databases have modular design collecting clinical features, including demographic data, type of diagnosis, e-GFR at onset and at time of first and last nephrological referral, age at onset of hypertension (HTN) and major urological complications (UC), Total Kidney Volume (hTKV) and Mayo Imaging Classification of ADPKD, age at ESRD, use of aspecific renal-protective and disease-modifying drugs, additional risk factors for CKD progression (smoke, diabetes, NSAID), extra-renal manifestations. Genetic data collected include type of PKD1/2 variant with ACMG classification and pathogenic prediction tools, testing method, results of segregation analysis. Statistics included estimation of eGFR slope using linear-mixed modelling. Results By January 2023, the Registry had recruited 985 ADPKD patients across 21 Italian Nephrology Unit; 513 (52,1%) were females; 967 (98,2%) Caucasians. Familiar history of ADPKD was reported in 738 patients (79%). All CKD stages were represented and 105 (14,1%) patients reached ESRD (median age 57y ± 11,5). hTKV was available for 353 (35,9%) patients, with a median value of 1100 ± 996 ml/m; a Mayo class of 1C or higher was found in 221 (70,4%). PROPKD score was evaluated in 162 patients, and in 50% of them it was associated with low risk of progression. A total of 191 (21,6%) were receiving Tolvaptan. Demographic and clinical characteristics are summarized in Table 1. Genetic testing was performed in 288 patients; 111 (38,5%) had PKD1 truncating (T) variants; 67 (23,3%) PKD1 non truncating variants; 69 (24%) PKD2 variants. In 41 patients (14,2%) no pathogenic variants were detected. In our cohort deterioration of renal function over time, estimated using eGFR slope was significantly associated with Mayo Imaging classes, high-medium PROPKD score, PKD1-T variant, HTN onset before 35 yo (Figure) and early UC (−2,3 vs. −1,9 ml/min/1.73m2/y, p = 0.014). Conclusion The Italian ADPKD National Registry is an important research tool collecting clinical and genetic information. Our preliminary data confirm that in the Italian population genotype, early onset HTN or UC, Mayo Imaging classification and PROPKD score are able to predict deterioration of GFR in ADPKD. The future empowerment of the Registry will provide a comprehensive description of clinical features and genetic variants related to ADPKD in a large cohort of Italian patients, enabling us to better understand genotype-phenotype correlation. Furthermore, the Registry could be an opportunity to identify patients suitable for future clinical trials or observational studies concerning specific aspects of the disease.