Autosomal dominant tubulointerstitial kidney disease

A Novel Heterozygous and Pathogenic Variant of the HNF1B Gene Associated with Autosomal Dominant Tubulointerstitial Kidney Disease with a Broad Spectrum of Extrarenal Phenotypes: A Case Report

We encountered a family with hereditary renal failure, renal medullary cysts, pancreatic hypoplasia, hypomagnesemia, liver enzyme abnormalities, and diabetes mellitus (DM). We identified a novel heterozygous variant of HNF1B (NM_000458.4:c.791dup, p.L264Ffs*30) using whole-exome sequencing of genomic DNA samples from this family. This variant is located in the DNA-binding domain of the HNF1B protein and produces a truncated protein with a de novo sequence, suggesting that this variant changes HNF1B binding to genomic DNA or causes nonsense-mediated mRNA decay. Based on the phenotypes and identified gene variants, this family suffers from autosomal dominant tubulointerstitial kidney disease caused by this HNF1B variant.

Eight-fold increased COVID-19 mortality in autosomal dominant tubulointerstitial kidney disease due to MUC1 mutations: an observational study

BACKGROUND

MUC1 and UMOD pathogenic variants cause autosomal dominant tubulointerstitial kidney disease (ADTKD). MUC1 is expressed in kidney, nasal mucosa and respiratory tract, while UMOD is expressed only in kidney. Due to haplo-insufficiency ADTKD-MUC1 patients produce approximately 50% of normal mucin-1.

METHODS

To determine whether decreased mucin-1 production was associated with an increased COVID-19 risk, we sent a survey to members of an ADTKD registry in September 2021, after the initial, severe wave of COVID-19. We linked results to previously obtained ADTKD genotype and plasma CA15-3 (mucin-1) levels and created a longitudinal registry of COVID-19 related deaths.

RESULTS

Surveys were emailed to 637 individuals, with responses from 89 ADTKD-MUC1 and 132 ADTKD-UMOD individuals. 19/83 (23%) ADTKD-MUC1 survey respondents reported a prior COVID-19 infection vs. 14/125 (11%) ADTKD-UMOD respondents (odds ratio (OR) 2.35 (95%CI 1.60-3.11, P = 0.0260). Including additional familial cases reported from survey respondents, 10/41 (24%) ADTKD-MUC1 individuals died of COVID-19 vs. 1/30 (3%) with ADTKD-UMOD, with OR 9.21 (95%CI 1.22-69.32), P = 0.03. The mean plasma mucin-1 level prior to infection in 14 infected and 27 uninfected ADTKD-MUC1 individuals was 7.06 ± 4.12 vs. 10.21 ± 4.02 U/mL (P = 0.035). Over three years duration, our longitudinal registry identified 19 COVID-19 deaths in 360 ADTKD-MUC1 individuals (5%) vs. 3 deaths in 478 ADTKD-UMOD individuals (0.6%) (P = 0.0007). Multivariate logistic regression revealed the following odds ratios (95% confidence interval) for COVID-19 deaths: ADTKD-MUC1 8.4 (2.9-29.5), kidney transplant 5.5 (1.6-9.1), body mass index (kg/m2) 1.1 (1.0-1.2), age (y) 1.04 (1.0-1.1).

CONCLUSIONS

Individuals with ADTKD-MUC1 are at an eight-fold increased risk of COVID-19 mortality vs. ADTKD-UMOD individuals. Haplo-insufficient production of mucin-1 may be responsible.

The renin-angiotensin-aldosterone system in kidney diseases of cats and dogs

The renin-angiotensin-aldosterone system (RAAS) has a well-established key pathophysiologic role in kidney diseases, and pharmacotherapy targeting this system is a mainstay of treatment of affected human beings, cats, and dogs. Several studies have evaluated the circulating RAAS in animals with spontaneous or experimentally induced kidney diseases. Evidence supporting the activation of this system has been demonstrated in some - but not all - studies and individuals, and the interindividual variability in circulating RAAS markers is high. Advances over the last few decades have expanded our understanding of the system, which now includes the existence of a counterbalancing "alternative" RAAS and tissular renin-angiotensin systems (RASs), the latter regulated independently of the circulating endocrine RAAS. The local RAS in the kidney, termed the intrarenal RAS, is currently recognized as an important regulator of kidney function and mediator of kidney disease. In general, information on the intrarenal RAS is lacking in cats and dogs with kidney diseases; however, existing limited data suggest its activation. Despite the inconsistent evidence for circulating RAAS activation in chronic kidney diseases, RAAS inhibitors have proven effective for the treatment of its common comorbidities, systemic arterial hypertension and renal proteinuria, in both cats and dogs. Further research of the circulating RAAS, the intrarenal RAS, and the interplay between these systems in the context of kidney diseases in companion animals might contribute to the development or refinement of future treatment strategies.

Case Report: A potentially pathogenic new variant of the REN gene found in a family experiencing autosomal dominant tubulointerstitial kidney disease

Background

Autosomal dominant tubulointerstitial kidney disease (ADTKD) caused by REN-causing pathogenic variants (ADTKD-REN) is a rare group of heritable diseases. ADTKD-REN often manifests in childhood with symptoms such as mild hypotension, chronic kidney disease, hyperkalemia, anemia, and acidosis. The diagnosis of ADTKD-REN remains challenging.

Case presentation

We describe a 14-year-old boy with acute kidney injury who was found to have a heterozygous missense mutant c.1085G>A;p.Cys362Tyr (not previously reported in the literature) through Sanger sequencing genetic testing. This confirmed a genetic disorder with a probable autosomal dominant inheritance pattern. Notably, despite a family history of autosomal dominant polycystic kidney disease, he was diagnosed with ADTKD.

Conclusion

This case identified a new variant in the REN gene, expanding the known spectrum of REN pathogenic variants. In addition, the importance of family history and genetic testing in confirming the diagnosis is emphasized. Genetic sequencing should be pursued when there are indications for testing.

Advances in uromodulin biology and potential clinical applications

Uromodulin (also known as Tamm-Horsfall protein) is a kidney-specific glycoprotein secreted bidirectionally into urine and into the circulation, and it is the most abundant protein in normal urine. Although the discovery of uromodulin predates modern medicine, its significance in health and disease has been rather enigmatic. Research studies have gradually revealed that uromodulin exists in multiple forms and has important roles in urinary and systemic homeostasis. Most uromodulin in urine is polymerized into highly organized filaments, whereas non-polymeric uromodulin is detected both in urine and in the circulation, and can have distinct roles. The interactions of uromodulin with the immune system, which were initially reported to be a key role of this protein, are now better understood. Moreover, the discovery that uromodulin is associated with a spectrum of kidney diseases, including acute kidney injury, chronic kidney disease and autosomal-dominant tubulointerstitial kidney disease, has further accelerated investigations into the role of this protein. These discoveries have prompted new questions and ushered in a new era in uromodulin research. Here, we delineate the latest discoveries in uromodulin biology and its emerging roles in modulating kidney and systemic diseases, and consider future directions, including its potential clinical applications.

Genetic Characterization of Kidney Failure of Unknown Etiology in Spain: Findings From the GENSEN Study

RATIONALE & OBJECTIVE

Chronic kidney disease of unknown etiology (CKDUE) is one of the main global causes of kidney failure. Genetic studies may identify an etiology in these patients, but few studies have implemented genetic testing of CKDUE in a population-based series of patients, which was the focus of the GENSEN Study.

STUDY DESIGN

Case series.

SETTINGS & PARTICIPANTS

818 patients aged≤45 years at 51 Spanish centers with CKDUE, and either an estimated glomerular filtration rate of<15mL/min/1.73m2 or treatment with maintenance dialysis or transplantation.

OBSERVATIONS

Genetic testing for 529 genes associated with inherited nephropathies using high-throughput sequencing (HTS). Pathogenic and/or likely pathogenic (P/LP) gene variants concordant with the inheritance pattern were detected in 203 patients (24.8%). Variants in type IV collagen genes were the most frequent (COL4A5, COL4A4, COL4A3; 35% of total gene variants), followed by NPHP1, PAX2, UMOD, MUC1, and INF2 (7.3%, 5.9%, 2.5%, 2.5%, and 2.5%, respectively). Overall, 87 novel variants classified as P/LP were identified. The top 5 most common previously undiagnosed diseases were Alport syndrome spectrum (35% of total positive reports), genetic podocytopathies (19%), nephronophthisis (11%), autosomal dominant tubulointerstitial kidney disease (7%), and congenital anomalies of the kidney and urinary tract (CAKUT, 5%). A family history of kidney disease was reported by 191 participants (23.3%) and by 65 of 203 patients (32.0%) with P/LP variants.

LIMITATIONS

Missing data, and selection bias resulting from voluntary enrollment.

CONCLUSIONS

Genomic testing with HTS identified a genetic cause of kidney disease in approximately one quarter of young patients with CKDUE and advanced kidney disease. These findings suggest that genetic studies are a potentially useful tool for the evaluation of people with CKDUE.

PLAIN-LANGUAGE SUMMARY

The cause of kidney disease is unknown for 1 in 5 patients requiring kidney replacement therapy, reflecting possible prior missed treatment opportunities. We assessed the diagnostic utility of genetic testing in children and adults aged≤45 years with either an estimated glomerular filtration rate of<15mL/min/1.73m2 or treatment with maintenance dialysis or transplantation. Genetic testing identified the cause of kidney disease in approximately 1 in 4 patients without a previously known cause of kidney disease, suggesting that genetic studies are a potentially useful tool for the evaluation of these patients.

UMOD Genotype and Determinants of Urinary Uromodulin in African Populations

Introduction

Single-nucleotide polymorphisms (SNPs) in the UMOD -PDILT genetic locus are associated with chronic kidney disease (CKD) in European populations, through their effect on urinary uromodulin (uUMOD) levels. The genetic and nongenetic factors associated with uUMOD in African populations remain unknown.

Methods

Clinical parameters, 3 selected UMOD-PDILT SNPs and uUMOD levels were obtained in 1202 young Black and White adults from the African-PREDICT study and 1943 middle aged Black adults from the PURE-NWP-SA study, 2 cross-sectional, observational studies.

Results

Absolute uUMOD and uUMOD/creatinine levels were lower in Black participants compared to White participants. The prime CKD-risk allele at rs12917707 was more prevalent in Black individuals, with strikingly more risk allele homozygotes compared to White individuals. Haplotype analysis of the UMOD-PDILT locus predicted more recombination events and linkage disequilibrium (LD) fragmentation in Black individuals. Multivariate testing and sensitivity analysis showed that higher uUMOD/creatinine associated specifically with risk alleles at rs12917707 and rs12446492 in White participants and with higher serum renin and lower urine albumin-to-creatinine ratio in Black participants, with a significant interaction of ethnicity on the relationship between all 3 SNPs and uUMOD/creatinine. The multiple regression model explained a greater percentage of the variance of uUMOD/creatinine in White adults compared to Black adults (23% vs. 8%).

Conclusion

We evidenced ethnic differences in clinical and genetic determinants of uUMOD levels, in particular an interaction of ethnicity on the relationship between CKD-risk SNPs and uUMOD. These differences should be considered when analyzing the role of uromodulin in kidney function, interpreting genome-wide association studies (GWAS), and precision medicine recommendations.

Arab founder variants: Contributions to clinical genomics and precision medicine

BACKGROUND

Founder variants are ancestral variants shared by individuals who are not closely related. The large effect size of some of these variants in the context of Mendelian disorders offers numerous precision medicine opportunities.

METHODS

Using one of the largest datasets on Mendelian disorders in the Middle East, we identified 2,908 medically relevant founder variants derived from 18,360 exomes and genomes and investigated their contribution to the clinical annotation of the human genome.

FINDINGS

Strikingly, ∼34% of Arab founder variants are absent in gnomAD. We found a strong contribution of Arab founder variants to the identification of novel gene-disease links (n = 224) and the support/dispute (n = 81 support, n = 101 dispute) of previously reported candidate gene-disease links. The powerful segregation evidence generated by Arab founder variants allowed many ClinVar and Human Gene Mutation Database variants to be reclassified. Overall, 39.5% of diagnostic reports from our clinical lab are based on founder variants, and 19.41% of tested individuals carry at least one pathogenic founder variant. The presumptive loss-of-function mechanism that typically underlies autosomal recessive diseases means that Arab founder variants also offer unique opportunities in "druggable genome" research. Arab founder variants were also informative of migration patterns in the Middle East consistent with documented historical accounts.

CONCLUSIONS

We highlight the contribution of founder variants from an under-represented population group to precision medicine and inform future prevention programs. Our study also sheds light on the added value of these variants in supplementing other lines of research in tracing population history.

FUNDING

There is no funding for this work.

Systematic Screening of Autosomal Dominant Tubulointerstitial Kidney Disease- MUC1 27dupC Pathogenic Variant through Exome Sequencing

Key Points

Background

The MUC1 gene is associated with autosomal dominant tubulointerstitial kidney disease (ADTKD), leading to CKD. Current methods of sequencing, such as exome sequencing, rarely detect MUC1 pathogenic variants because of the variable number of tandem repeats (VNTR) in MUC1 exon2. We demonstrated that combining fast read filtering with a sensitive VNTR genotyping strategy enables systematic screening of 27dupC pathogenic MUC1 variant from exome data.

Methods

We initially validated our bioinformatics pipeline in a proof-of-concept cohort incorporating exome data from 33 participants with a known MUC1 pathogenic variant identified by Snapshot PCR and confirmed by 54 MUC1-negative individuals for negative control. We then retrospectively analyzed exome sequencing data from January 2019 to October 2023 from 3512 adult participants with nephropathy of unknown origin. Finally, we prospectively validated our pipeline in 825 additional participants enrolled from November 2023.

Results

SharkVNTyper accurately identified MUC1 variants in 32 of 33 participants and excluded its presence in all the 54 negative controls in the proof-of-concept cohort (sensitivity of 97%, specificity of 100%). Integration of the Shark tool with VNTyper significantly reduced running time from 6–12 hours to 5–10 minutes per sample, allowing both retrospective and prospective analyses. In the retrospective cohort, SharkVNTyper identified 23 additional positive participants who were not suspected clinically and had been missed in the initial exome analysis; 18 of these participants were confirmed as carrying the MUC1 27dupC mutation by low-throughput Snapshot PCR. In the prospective cohort of 825 participants with CKD, systematic screening discovered 13 positive participants, with 12 confirmed by PCR. Overall, of 63 participants (1.4% of 4653) with molecularly confirmed ADTKD-MUC1, comprehensive diagnoses and descriptions of the disease were available for 24 participants. The median age of kidney failure was 50 years, 38% exhibited bilateral multiple kidney cysts, 8% had early-onset gout, and 58% had arterial hypertension.

Conclusions

SharkVNTyper enabled the analysis of highly repeated regions, such as the MUC1 VNTR, and facilitated the systematic screening of ADTKD-MUC1 from exome data, fostering 27dupC variation identification.

Practical Approach to Congenital Anomalies of the Kidneys: Focus on Anomalies With Insufficient or Abnormal Nephron Development: Renal Dysplasia, Renal Hypoplasia, and Renal Tubular Dysgenesis

Congenital anomalies of the kidney and urinary tract (CAKUT) accounts for up to 30% of antenatal congenital anomalies and is the main cause of kidney failure in children worldwide. This review focuses on practical approaches to CAKUT, particularly those with insufficient or abnormal nephron development, such as renal dysplasia, renal hypoplasia, and renal tubular dysgenesis. The review provides insights into the histological features, pathogenesis, mechanisms, etiologies, antenatal and postnatal presentation, management, and prognosis of these anomalies. Differential diagnoses are discussed as several syndromes may include CAKUT as a phenotypic component and renal dysplasia may occur in some ciliopathies, tumor predisposition syndromes, and inborn errors of metabolism. Diagnosis and genetic counseling for CAKUT are challenging, due to the extensive variability in presentation, genetic and phenotypic heterogeneity, and difficulties to assess postnatal lung and renal function on prenatal imaging. The review highlights the importance of perinatal autopsy and pathological findings in surgical specimens to establish the diagnosis and prognosis of CAKUT. The indications and the type of genetic testing are discussed. The aim is to provide essential insights into the practical approaches, diagnostic processes, and genetic considerations offering valuable guidance for pediatric and perinatal pathologists.

Hypoaldosteronism due to a novel SEC61A1 variant successfully treated with fludrocortisone

Background

Genetic variants in SEC61A1 are associated with autosomal dominant tubulointerstitial kidney disease. SEC61A1 is a translocon in the endoplasmic reticulum membrane and variants affect biosynthesis of renin and uromodulin.

Methods

A patient is described that presented at 1 year of age with failure-to-thrive, kidney failure (glomerular filtration rate, GFR, 18 ml/min/1.73m2), hyperkalemia and acidosis. Genetic evaluation was performed by whole genome sequencing.

Results

The patient has a novel de novo heterozygous SEC61A1 variant, Phe458Val. Plasma renin was low or normal, aldosterone was low or undetectable and uromodulin was low. Kidney biopsy at 2 years exhibited subtle changes suggestive of tubular dysgenesis without tubulocystic or glomerulocystic lesions and with renin staining of the juxtaglomerular cells. The patient experienced extreme fatigue due to severe hypotension attributed to hypoaldosteronism and at 8 years of age fludrocortisone treatment was initiated with marked improvement in her well-being. Blood pressure and potassium normalized. Biopsy at 9 years showed extensive glomerulosclerosis and mild tubulointerstitial fibrosis, as well as tubular mitochondrial abnormalities, without specific diagnostic changes. Her GFR improved to 54 ml/min/1.73m2.

Conclusions

As the renin-angiotensin system promotes aldosterone release, and the patient had repeatedly undetectable aldosterone levels, the SEC61A1 variant presumably contributed to severe hypotension. Treatment with a mineralocorticoid had a beneficial effect and corrected the electrolyte and acid-base disorder. We suggest that the increased blood pressure hemodynamically improved the patient's kidney function.

Pathogenic heterozygous TRPM7 variants and hypomagnesemia with developmental delay

Background

Heterozygous variants in Transient receptor potential melastatin type 7 (TRPM7), encoding an essential and ubiquitously expressed cation channel, may cause hypomagnesemia, but current evidence is insufficient to draw definite conclusions and it is unclear whether any other phenotypes can occur.

Methods

Individuals with unexplained hypomagnesemia underwent whole-exome sequencing which identified TRPM7 variants. Pathogenicity of the identified variants was assessed by combining phenotypic, functional and in silico analyses.

Results

We report three new heterozygous missense variants in TRPM7 (p.Met1000Thr, p.Gly1046Arg, p.Leu1081Arg) in individuals with hypomagnesemia. Strikingly, autism spectrum disorder and developmental delay, mainly affecting speech and motor skills, was observed in all three individuals, while two out of three also presented with seizures. The three variants are predicted to be severely damaging by in silico prediction tools and structural modeling. Furthermore, these variants result in a clear loss-of-function of TRPM7-mediated magnesium uptake in vitro, while not affecting TRPM7 expression or insertion into the plasma membrane.

Conclusions

This study provides additional evidence for the association between heterozygous TRPM7 variants and hypomagnesemia and adds developmental delay to the phenotypic spectrum of TRPM7-related disorders. Considering that the TRPM7 gene is relatively tolerant to loss-of-function variants, future research should aim to unravel by what mechanisms specific heterozygous TRPM7 variants can cause disease.

Endoplasmic Reticulum Stress-Mediated Cell Death in Renal Fibrosis

The endoplasmic reticulum (ER) is indispensable for maintaining normal life activities. Dysregulation of the ER function results in the accumulation of harmful proteins and lipids and the disruption of intracellular signaling pathways, leading to cellular dysfunction and eventual death. Protein misfolding within the ER disrupts its delicate balance, resulting in the accumulation of misfolded or unfolded proteins, a condition known as endoplasmic reticulum stress (ERS). Renal fibrosis, characterized by the aberrant proliferation of fibrotic tissue in the renal interstitium, stands as a grave consequence of numerous kidney disorders, precipitating a gradual decline in renal function. Renal fibrosis is a serious complication of many kidney conditions and is characterized by the overgrowth of fibrotic tissue in the glomerular and tubular interstitium, leading to the progressive failure of renal function. Studies have shown that, during the onset and progression of kidney disease, ERS causes various problems in the kidneys, a process that can lead to kidney fibrosis. This article elucidates the underlying intracellular signaling pathways modulated by ERS, delineating its role in triggering diverse forms of cell death. Additionally, it comprehensively explores a spectrum of potential pharmacological agents and molecular interventions aimed at mitigating ERS, thereby charting novel research avenues and therapeutic advancements in the management of renal fibrosis.

Advancements in Research on Genetic Kidney Diseases Using Human-Induced Pluripotent Stem Cell-Derived Kidney Organoids

Genetic or hereditary kidney disease stands as a pivotal cause of chronic kidney disease (CKD). The proliferation and widespread utilization of DNA testing in clinical settings have notably eased the diagnosis of genetic kidney diseases, which were once elusive but are now increasingly identified in cases previously deemed CKD of unknown etiology. However, despite these diagnostic strides, research into disease pathogenesis and novel drug development faces significant hurdles, chiefly due to the dearth of appropriate animal models and the challenges posed by limited patient cohorts in clinical studies. Conversely, the advent and utilization of human-induced pluripotent stem cells (hiPSCs) offer a promising avenue for genetic kidney disease research. Particularly, the development of hiPSC-derived kidney organoid systems presents a novel platform for investigating various forms of genetic kidney diseases. Moreover, the integration of the CRISPR/Cas9 technique into this system holds immense potential for efficient research on genetic kidney diseases. This review aims to explore the applications of in vitro kidney organoids generated from hiPSCs in the study of diverse genetic kidney diseases. Additionally, it will delve into the limitations of this research platform and outline future perspectives for advancing research in this crucial area.

Eight-Fold Increased COVID-19 Mortality in Autosomal Dominant Tubulointerstitial Kidney Disease due to MUC1 Mutations: An Observational Study

Background

MUC1 and UMOD pathogenic variants cause autosomal dominant tubulointerstitial kidney disease (ADTKD). MUC1 is expressed in kidney, nasal mucosa and respiratory tract, while UMOD is expressed only in kidney. Due to haplo-insufficiency ADTKD- MUC1 patients produce approximately 50% of normal mucin-1.

Methods

To determine whether decreased mucin-1 production was associated with an increased COVID-19 risk, we sent a survey to members of an ADTKD registry in September 2021, after the initial, severe wave of COVID-19. We linked results to previously obtained ADTKD genotype and plasma CA15-3 (mucin-1) levels and created a longitudinal registry of COVID-19 related deaths.

Results

Surveys were emailed to 637 individuals, with responses from 89 ADTKD- MUC1 and 132 ADTKD- UMOD individuals. 19/83 (23%) ADTKD- MUC1 survey respondents reported a prior COVID-19 infection vs. 14/125 (11%) ADTKD- UMOD respondents (odds ratio (OR) 2.35 (95%CI 1.60-3.11, P = 0.0260). Including additional familial cases reported from survey respondents, 10/41 (24%) ADTKD- MUC1 individuals died of COVID-19 vs. 1/30 (3%) with ADTKD- UMOD , with OR 9.21 (95%CI 1.22-69.32), P = 0.03. The mean plasma mucin-1 level prior to infection in 14 infected and 27 uninfected ADTKD- MUC1 individuals was 7.06±4.12 vs. 10.21±4.02 U/mL ( P = 0.035). Over three years duration, our longitudinal registry identified 19 COVID-19 deaths in 360 ADTKD- MUC1 individuals (5%) vs. 3 deaths in 478 ADTKD- UMOD individuals (0.6%) ( P = 0.0007). Multivariate logistic regression revealed the following odds ratios (95% confidence interval) for COVID-19 deaths: ADTKD- MUC1 8.4 (2.9-29.5), kidney transplant 5.5 (1.6-9.1), body mass index (kg/m 2 ) 1.1 (1.0-1.2), age (y) 1.04 (1.0-1.1).

Conclusions

Individuals with ADTKD- MUC1 are at an eight-fold increased risk of COVID-19 mortality vs. ADTKD- UMOD individuals. Haplo-insufficient production of mucin-1 may be responsible.

Familial juvenile hyperuricemic nephropathy: Revisiting the SLC8A1 gene, in a family with a novel terminal gross deletion in the UMOD gene

Autosomal dominant tubulointerstitial kidney disease (ADTKD) comprises a heterogeneous group of rare hereditary kidney diseases characterized by family history of progressive chronic kidney disease (CKD) with bland urine sediment, absence of significant proteinuria and normal or small-sized kidneys. Current diagnostic criteria require identification of a pathogenic variant in one of five genes - UMOD, MUC1, REN, HNF1β, SEC61A1. The most prevalent form of ADTKD is uromodulin-associated kidney disease (ADTKD-UMOD). Genetic study of a Portuguese family diagnosed with familial juvenile hyperuricemic nephropathy (FJHN), one of the nosological entities in the spectrum of ADTKD, revealed a previously unreported large deletion in UMOD encompassing the entire terminal exon, which strictly cosegregated with CKD and hyperuricemia/gout, establishing the primary diagnosis of ADTKD-UMOD; as well as an ultra-rare nonsense SLC8A1 variant cosegregating with the UMOD deletion in patients that consistently exhibited an earlier onset of clinical manifestations. Since the terminal exon of UMOD does not encode for any of the critical structural domains or amino acid residues of mature uromodulin, the molecular mechanisms underlying the pathogenicity of its deletion are unclear and require further research. The association of the SLC8A1 locus with FJHN was first indicated by the results of a genome-wide linkage analysis in several multiplex families, but those data have not been subsequently confirmed. Our findings in this family revive that hypothesis.

Uromodulin biology

Uromodulin is a kidney-specific glycoprotein which is exclusively produced by the epithelial cells lining the thick ascending limb and early distal convoluted tubule. It is currently recognized as a multifaceted player in kidney physiology and disease, with discrete roles for intracellular, urinary, interstitial and serum uromodulin. Among these, uromodulin modulates renal sodium handling through the regulation of tubular sodium transporters that reabsorb sodium and are targeted by diuretics, such as the loop diuretic-sensitive Na+-K+-2Cl- cotransporter type 2 (NKCC2) and the thiazide-sensitive Na+/Cl- cotransporter (NCC). Given these roles, the contribution of uromodulin to sodium-sensitive hypertension has been proposed. However, recent studies in humans suggest a more complex interaction between dietary sodium intake, uromodulin and blood pressure. This review presents an updated overview of the uromodulin's biology and its various roles, and focuses on the interaction between uromodulin and sodium-sensitive hypertension.

Ocular manifestations of renal ciliopathies

Renal ciliopathies are a common cause of kidney failure in children and adults, and this study reviewed their ocular associations. Genes affected in renal ciliopathies were identified from the Genomics England Panels. Ocular associations were identified from Medline and OMIM, and the genes additionally examined for expression in the human retina ( https://www.proteinatlas.org/humanproteome/tissue ) and for an ocular phenotype in mouse models ( http://www.informatics.jax.org/ ). Eighty-two of the 86 pediatric-onset renal ciliopathies (95%) have an ocular phenotype, including inherited retinal degeneration, oculomotor disorders, and coloboma. Diseases associated with pathogenic variants in ANK6, MAPKBP1, NEK8, and TCTN1 have no reported ocular manifestations, as well as low retinal expression and no ocular features in mouse models. Ocular abnormalities are not associated with the most common adult-onset "cystic" kidney diseases, namely, autosomal dominant (AD) polycystic kidney disease and the AD tubulointerstitial kidney diseases (ADTKD). However, other kidney syndromes with cysts have ocular features including papillorenal syndrome (optic disc dysplasia), Hereditary Angiopathy Nephropathy, Aneurysms and muscle Cramps (HANAC) (tortuous retinal vessels), tuberous sclerosis (retinal hamartomas), von Hippel-Lindau syndrome (retinal hemangiomas), and Alport syndrome (lenticonus, fleck retinopathy). Ocular abnormalities are associated with many pediatric-onset renal ciliopathies but are uncommon in adult-onset cystic kidney disease. However the demonstration of ocular manifestations may be helpful diagnostically and the features may require monitoring or treatment.

Description of a New Simple and Cost-Effective Molecular Testing That Could Simplify MUC1 Variant Detection

Introduction

Patients with autosomal dominant tubulointerstitial kidney disease (ADTKD) usually present with nonspecific progressive chronic kidney disease (CKD) with mild to negative proteinuria and a family history. ADTKD-MUC1 leads to the formation of a frameshift protein that accumulates in the cytoplasm, leading to tubulointerstitial damage. ADTKD-MUC1 prevalence remains unclear because MUC1 variants are not routinely detected by standard next-generation sequencing (NGS) techniques.

Methods

We developed a bioinformatic counting script that can detect specific genetic sequences and count the number of occurrences. We used DNA samples from 27 patients for validation, 11 of them were patients from the Lille University Hospital in France and 16 were from the Wake Forest Hospital, NC. All patients from Lille were tested with an NGS gene panel with our script and all patients from Wake Forest Hospital were tested with the snapshot reference technique. Between January 2018 and February 2023, we collected data on all patients diagnosed with MUC1 variants with this script.

Results

A total of 27 samples were tested anonymously by the BROAD Institute reference technique for confirmation and we were able to get a 100% concordance for MUC1 diagnosis. Clinico-biologic characteristics in our cohort were similar to those previously described in ADTKD-MUC1.

Conclusion

We describe a new simple and cost-effective method for molecular testing of ADTKD-MUC1. Genetic analyses in our cohort suggest that MUC1 might be the first cause of ADTKD. Increasing the availability of MUC1 diagnosis tools will contribute to a better understanding of the disease and to the development of specific treatments.

Autosomal dominant chronic tubulointerstitial nephropathy: do not forget amyloidosis

Amyloidosis is a rare cause of inherited kidney disease, with most variants responsible for prominent glomerular involvement. In this issue, Kmochová et al. reported the first description of autosomal dominant medullary amyloidosis due to apolipoprotein A4 variants, resulting in slowly progressive chronic kidney disease with minimal proteinuria. Combining next-generation sequencing with histopathological studies incorporating Congo red staining and mass spectrometry should be considered in the diagnostic workup of hereditary tubulointerstitial disorders not identified after routine genetic testing.

From Rare Disorders of Kidney Tubules to Acute Renal Injury: Progress and Prospective

Background

Acute kidney injury (AKI) is a severe condition marked by rapid renal function deterioration and elevated mortality, with traditional biomarkers lacking sensitivity and specificity. Rare tubulointerstitial diseases encompass a spectrum of disorders, primarily including monogenic diseases, immune-related conditions, and drug-induced tubulointerstitial diseases. The clinical manifestations vary from electrolyte and acid-base imbalances to kidney function insufficiency, which is associated with AKI in up to 20% of cases. Evidence indicated that rare tubulointerstitial diseases might provide new conceptual insights and perspectives for novel biomarkers and potential therapeutic strategies for AKI.

Summary

Autosomal dominant tubulointerstitial kidney disease (ADTKD) and Fanconi syndrome (FS) are rare tubulointerstitial diseases. In ADTKD, UMOD and REN are closely related to AKI by affecting oxidative stress and tubuloglomerular feedback, which provide potential new biomarkers for AKI. Both rare tubulointerstitial diseases and AKI share etiologies and treatment responses. From the mechanism standpoint, rare tubulointerstitial diseases and AKI involve tubular transporter injury, initially manifesting as tubular dysfunction in tubulointerstitial disorder and progressing to AKI because of the programmed cell death with apoptosis, pyroptosis, or necroptosis of proximal tubule cells. Additionally, mitochondrial dysfunction has been identified as a common mechanism in both tubulointerstitial diseases and AKI induced by drugs, pSS, or monoclonal diseases. In the end, both AKI and FS patients and animal models responded well to the therapy of the primary diseases.

Key Messages

In this review, we describe an overview of ADTKD and FS to identify their associations with AKI. Mitochondrial dysfunction contributes to rare tubulointerstitial diseases and AKI, which might provide a potential therapeutic target.

Autosomal dominant ApoA4 mutations present as tubulointerstitial kidney disease with medullary amyloidosis

Sporadic cases of apolipoprotein A-IV medullary amyloidosis have been reported. Here we describe five families found to have autosomal dominant medullary amyloidosis due to two different pathogenic APOA4 variants. A large family with autosomal dominant chronic kidney disease (CKD) and bland urinary sediment underwent whole genome sequencing with identification of a chr11:116692578 G>C (hg19) variant encoding the missense mutation p.L66V of the ApoA4 protein. We identified two other distantly related families from our registry with the same variant and two other distantly related families with a chr11:116693454 C>T (hg19) variant encoding the missense mutation p.D33N. Both mutations are unique to affected families, evolutionarily conserved and predicted to expand the amyloidogenic hotspot in the ApoA4 structure. Clinically affected individuals suffered from CKD with a bland urinary sediment and a mean age for kidney failure of 64.5 years. Genotyping identified 48 genetically affected individuals; 44 individuals had an estimated glomerular filtration rate (eGFR) under 60 ml/min/1.73 m2, including all 25 individuals with kidney failure. Significantly, 11 of 14 genetically unaffected individuals had an eGFR over 60 ml/min/1.73 m2. Fifteen genetically affected individuals presented with higher plasma ApoA4 concentrations. Kidney pathologic specimens from four individuals revealed amyloid deposits limited to the medulla, with the mutated ApoA4 identified by mass-spectrometry as the predominant amyloid constituent in all three available biopsies. Thus, ApoA4 mutations can cause autosomal dominant medullary amyloidosis, with marked amyloid deposition limited to the kidney medulla and presenting with autosomal dominant CKD with a bland urinary sediment. Diagnosis relies on a careful family history, APOA4 sequencing and pathologic studies.

State of the Science and Ethical Considerations for Preimplantation Genetic Testing for Monogenic Cystic Kidney Diseases and Ciliopathies

There is a broad phenotypic spectrum of monogenic polycystic kidney diseases (PKDs). These disorders often involve cilia-related genes and lead to the development of fluid-filled cysts and eventual kidney function decline and failure. Preimplantation genetic testing for monogenic (PGT-M) disorders has moved into the clinical realm. It allows prospective parents to avoid passing on heritable diseases to their children, including monogenic PKD. The PGT-M process involves embryo generation through in vitro fertilization, with subsequent testing of embryos and selective transfer of those that do not harbor the specific disease-causing variant(s). There is a growing body of literature supporting the success of PGT-M for autosomal-dominant and autosomal-recessive PKD, although with important technical limitations in some cases. This technology can be applied to many other types of monogenic PKD and ciliopathies despite the lack of existing reports in the literature. PGT-M for monogenic PKD, like other forms of assisted reproductive technology, raises important ethical questions. When considering PGT-M for kidney diseases, as well as the potential to avoid disease in future generations, there are regulatory and ethical considerations. These include limited government regulation and unstandardized consent processes, potential technical errors, high cost and equity concerns, risks associated with pregnancy for mothers with kidney disease, and the impact on all involved in the process, including the children who were made possible with this technology.

The Pathophysiology of Inherited Renal Cystic Diseases

Renal cystic diseases (RCDs) can arise from utero to early adulthood and present with a variety of symptoms including renal, hepatic, and cardiovascular manifestations. It is well known that common RCDs such as autosomal polycystic kidney disease and autosomal recessive kidney disease are linked to genes such as PKD1 and PKHD1, respectively. However, it is important to investigate the genetic pathophysiology of how these gene mutations lead to clinical symptoms and include some of the less-studied RCDs, such as autosomal dominant tubulointerstitial kidney disease, multicystic dysplastic kidney, Zellweger syndrome, calyceal diverticula, and more. We plan to take a thorough look into the genetic involvement and clinical sequalae of a number of RCDs with the goal of helping to guide diagnosis, counseling, and treatment.

Knowledge mapping of UMOD of English published work from 1985 to 2022: a bibliometric analysis

BACKGROUND

UMOD is exclusively produced by renal epithelial cells. Recent genome-wide association studies (GWAS) suggested that common variants in UMOD gene are closely connected with the risk of CKD. However, a comprehensive and objective report on the current status of UMOD research is lacking. Therefore, we aim to conduct a bibliometric analysis to quantify and identify the status quo and trending issues of UMOD research in the past.

METHODS

We collected data from the Web of Science Core Collection database and used the Online Analysis Platform of Literature Metrology, the Online Analysis Platform of Literature Metrology and Microsoft Excel 2019 to perform bibliometricanalysis and visualization.

RESULTS

Based on the data from the WoSCC database from 1985 to 2022, a total of 353 UMOD articles were published in 193 academic journals by 2346 authors from 50 different countries/regions and 396 institutions. The United States published the most papers. Professor Devuyst O from University of Zurich not only published the greatest number of UMOD-related papers but also is among the top 10 co-cited authors. KIDNEY INTERNATIONAL published the most necroptosis studies, and it was also the most cited journal. High-frequency keywords mainly included 'chronic kidney disease', 'Tamm Horsfall protein' and 'mutation'.

CONCLUSIONS

The number of UMOD-related articles has steadily increased over the past decades Current UMOD studies focused on Biological relevance of the UMOD to kidney function and potential applications in the risk of CKD mechanisms, these might provide ideas for further research in the UMOD field.

Allelic effects on uromodulin aggregates drive autosomal dominant tubulointerstitial kidney disease

Missense mutations in the uromodulin (UMOD) gene cause autosomal dominant tubulointerstitial kidney disease (ADTKD), one of the most common monogenic kidney diseases. The unknown impact of the allelic and gene dosage effects and fate of mutant uromodulin leaves open the gap between postulated gain-of-function mutations, end-organ damage and disease progression in ADTKD. Based on two prevalent missense UMOD mutations with divergent disease progression, we generated UmodC171Y and UmodR186S knock-in mice that showed strong allelic and gene dosage effects on uromodulin aggregates and activation of ER stress and unfolded protein and immune responses, leading to variable kidney damage. Deletion of the wild-type Umod allele in heterozygous UmodR186S mice increased the formation of uromodulin aggregates and ER stress. Studies in kidney tubular cells confirmed differences in uromodulin aggregates, with activation of mutation-specific quality control and clearance mechanisms. Enhancement of autophagy by starvation and mTORC1 inhibition decreased uromodulin aggregates. These studies substantiate the role of toxic aggregates as driving progression of ADTKD-UMOD, relevant for therapeutic strategies to improve clearance of mutant uromodulin.

Two sides of the same coin: a complex presentation of autosomal dominant tubulointerstitial kidney diseases: a literature review and case reports

Introduction

Genetic kidney diseases are underdiagnosed; namely, from 7% to 40% of patients suffering from chronic kidney disease (CKD) can carry a pathogenic variant, depending on population characteristics. Hereditary tubulointerstitial kidney diseases, including autosomal dominant tubulointerstitial kidney diseases (ADTKD), are even more challenging to diagnose. ADTKD is a rare form of genetic kidney disease resulting from pathogenic variants in the MUC1, UMOD, HNF1B, REN, SEC61A1, and DNAJB11 genes. There is no typical clinical or histopathological sign of ADTKD, it is characterized by progressive CKD, an autosomal dominant inheritance pattern, and tubular atrophy with interstitial fibrosis on kidney biopsy. There is no significant proteinuria, and the urinary sediment is bland. The patients usually do not have severe arterial hypertension. There can be a history of early gout, especially when compared to the UMOD gene variants. Children can have enuresis due to a loss of renal concentration. On ultrasound, the kidneys can appear normal or small in size. Renal cysts are not pathognomonic for any of the named diseases. End-stage renal disease (ESRD) develops at the average age of 45, but this can be very variable. Family history that suggests autosomal dominant inheritance and CKD fulfilling the aforementioned characteristics of tubulointerstitial kidney disease should raise suspicion of ADTKD. In the setting of a negative family history for CKD, clinical suspicion should be raised based on clinical characteristics, including early onset of hyperuricemia or gout and compatible histology on the kidney biopsy. Contrary to the aforementioned characteristics of ADTKD, in the case of HNF1B-related disease, there is a more complex clinical presentation with extrarenal manifestations of the disease (diabetes mellitus, hypomagnesemia, neurologic and psychiatric disturbances, etc.). The diagnosis of ADTKD is based on a positive family history and a detection of the pathogenic variant in one of the genes in an affected individual.

Aim

The aim of our study is to present two case reports of ADTKD with different characteristics (slowly progressive CKD vs. complex clinical presentation with an extrarenal manifestation of the disease) with a literature review.

Methods

A 34-year-old patient with CKD and a positive family history of CKD in whom kidney biopsy showed nonspecific chronic changes, with only genetic analysis confirming the diagnosis of MUC1-related ADTKD. Our second case is of a 17-year-old patient with an unremarkable family history who was initially referred to genetic counseling due to cognitive and motor impairment with long-lasting epilepsy. Extensive workup revealed increased serum creatinine levels with no proteinuria and bland urinary sediment, along with hypomagnesemia. His genetic analysis revealed 17q12 deletion syndrome, causing the loss of one copy of the HNF1B gene, the AATF, and the LHX1 gene.

Conclusion

Autosomal dominant tubulointerstitial kidney diseases are challenging to diagnose due to a lack of typical clinical or histopathological signs as well as an uncharacteristic and versatile clinical presentation. Increased clinical awareness is crucial for the detection of these diseases.

Diagnostic Yield and Benefits of Whole Exome Sequencing in CAKUT Patients Diagnosed in the First Thousand Days of Life

Introduction

Congenital anomalies of the kidney and urinary tract (CAKUT) are the predominant cause of chronic kidney disease (CKD) and the need for kidney replacement therapy (KRT) in children. Although more than 60 genes are known to cause CAKUT if mutated, genetic etiology is detected, on average, in only 16% of unselected CAKUT cases, making genetic testing unproductive.

Methods

Whole exome sequencing (WES) was performed in 100 patients with CAKUT diagnosed in the first 1000 days of life with CKD stages 1 to 5D/T. Variants in 58 established CAKUT-associated genes were extracted, classified according to the American College of Medical Genetics and Genomics guidelines, and their translational value was assessed.

Results

In 25% of these mostly sporadic patients with CAKUT, a rare likely pathogenic or pathogenic variant was identified in 1 or 2 of 15 CAKUT-associated genes, including GATA3, HNF1B, LIFR, PAX2, SALL1, and TBC1D1. Of the 27 variants detected, 52% were loss-of-function and 18.5% de novo variants. The diagnostic yield was significantly higher in patients requiring KRT before 3 years of age (43%, odds ratio 2.95) and in patients with extrarenal features (41%, odds ratio 3.5) compared with patients lacking these criteria. Considering that all affected genes were previously associated with extrarenal complications, including treatable conditions, such as diabetes, hyperuricemia, hypomagnesemia, and hypoparathyroidism, the genetic diagnosis allowed preventive measures and/or early treatment in 25% of patients.

Conclusion

WES offers significant advantages for the diagnosis and management of patients with CAKUT diagnosed before 3 years of age, especially in patients who require KRT or have extrarenal anomalies.

Hypoxia and renal fibrosis

Renal fibrosis is the final stage of most progressive kidney diseases. Chronic kidney disease (CKD) is associated with high comorbidity and mortality. Thus, preventing fibrosis and thereby preserving kidney function increases the quality of life and prolongs the survival of patients with CKD. Many processes such as inflammation or metabolic stress modulate the progression of kidney fibrosis. Hypoxia has also been implicated in the pathogenesis of renal fibrosis, and oxygen sensing in the kidney is of outstanding importance for the body. The dysregulation of oxygen sensing in the diseased kidney is best exemplified by the loss of stimulation of erythropoietin production from interstitial cells in the fibrotic kidney despite anemia. Furthermore, hypoxia is present in acute or chronic kidney diseases and may affect all cell types present in the kidney including tubular and glomerular cells as well as resident immune cells. Pro- and antifibrotic effects of the transcription factors hypoxia-inducible factors 1 and 2 have been described in a plethora of animal models of acute and chronic kidney diseases, but recent advances in sequencing technologies now allow for novel and deeper insights into the role of hypoxia and its cell type-specific effects on the progression of renal fibrosis, especially in humans. Here, we review existing literature on how hypoxia impacts the development and progression of renal fibrosis.

Unveiling the Hidden Power of Uromodulin: A Promising Potential Biomarker for Kidney Diseases

Uromodulin, also known as Tamm-Horsfall protein, represents the predominant urinary protein in healthy individuals. Over the years, studies have revealed compelling associations between urinary and serum concentrations of uromodulin and various parameters, encompassing kidney function, graft survival, cardiovascular disease, glucose metabolism, and overall mortality. Consequently, there has been a growing interest in uromodulin as a novel and effective biomarker with potential applications in diverse clinical settings. Reduced urinary uromodulin levels have been linked to an elevated risk of acute kidney injury (AKI) following cardiac surgery. In the context of chronic kidney disease (CKD) of different etiologies, urinary uromodulin levels tend to decrease significantly and are strongly correlated with variations in estimated glomerular filtration rate. The presence of uromodulin in the serum, attributable to basolateral epithelial cell leakage in the thick ascending limb, has been observed. This serum uromodulin level is closely associated with kidney function and histological severity, suggesting its potential as a biomarker capable of reflecting disease severity across a spectrum of kidney disorders. The UMOD gene has emerged as a prominent locus linked to kidney function parameters and CKD risk within the general population. Extensive research in multiple disciplines has underscored the biological significance of the top UMOD gene variants, which have also been associated with hypertension and kidney stones, thus highlighting the diverse and significant impact of uromodulin on kidney-related conditions. UMOD gene mutations are implicated in uromodulin-associated kidney disease, while polymorphisms in the UMOD gene show a significant association with CKD. In conclusion, uromodulin holds great promise as an informative biomarker, providing valuable insights into kidney function and disease progression in various clinical scenarios. The identification of UMOD gene variants further strengthens its relevance as a potential target for better understanding kidney-related pathologies and devising novel therapeutic strategies. Future investigations into the roles of uromodulin and regulatory mechanisms are likely to yield even more profound implications for kidney disease diagnosis, risk assessment, and management.

Genetic Spectrum of Polycystic Kidney and Liver Diseases and the Resulting Phenotypes

Polycystic kidney diseases are a group of monogenically inherited disorders characterized by cyst development in the kidney with defects in primary cilia function central to pathogenesis. Autosomal dominant polycystic kidney disease (ADPKD) has progressive cystogenesis and accounts for 5-10% of kidney failure (KF) patients. There are two major ADPKD genes, PKD1 and PKD2, and seven minor loci. PKD1 accounts for ∼80% of patients and is associated with the most severe disease (KF is typically at 55-65 years); PKD2 accounts for ∼15% of families, with KF typically in the mid-70s. The minor genes are generally associated with milder kidney disease, but for DNAJB11 and ALG5, the age at KF is similar to PKD2. PKD1 and PKD2 have a high level of allelic heterogeneity, with no single pathogenic variant accounting for >2% of patients. Additional genetic complexity includes biallelic disease, sometimes causing very early-onset ADPKD, and mosaicism. Autosomal dominant polycystic liver disease is characterized by severe PLD but limited PKD. The two major genes are PRKCSH and SEC63, while GANAB, ALG8, and PKHD1 can present as ADPKD or autosomal dominant polycystic liver disease. Autosomal recessive polycystic kidney disease typically has an infantile onset, with PKHD1 being the major locus and DZIP1L and CYS1 being minor genes. In addition, there are a range of mainly recessive syndromic ciliopathies with PKD as part of the phenotype. Because of the phenotypic and genic overlap between the diseases, employing a next-generation sequencing panel containing all known PKD and ciliopathy genes is recommended for clinical testing.

Maternal health and pregnancy outcomes in autosomal dominant tubulointerstitial kidney disease

Introduction

Autosomal dominant tubulointerstitial kidney disease (ADTKD) is an increasingly recognized cause of chronic kidney disease. ADTKD pregnancy outcomes have not previously been described.

Methods

A cross-sectional survey was sent to women from ADTKD families.

Results

Information was obtained from 85 afffected women (164 term pregnancies) and 23 controls (50 pregnancies). Only 16.5% of genetically affected women knew they had ADTKD during pregnancy. Eighteen percent of ADTKD mothers had hypertension during pregnancy versus 12% in controls (p  =  0.54) and >40% in comparative studies of chronic kidney disease in pregnancy. Eleven percent of births of ADTKD mothers were <37 weeks versus 0 in controls (p < 0.0001). Cesarean section occurred in 19% of pregnancies in affected women versus 38% of unaffected individuals (p  =  0.06). Only 12% of babies required a neonatal intensive care unit stay.

Conclusions

ADTKD pregnancies had lower rates of hypertension during pregnancy versus other forms of chronic kidney disease, which may have contributed to good maternal and fetal outcomes.

Hypoxia controls expression of kidney-pathogenic MUC1 variants

The interplay between genetic and environmental factors influences the course of chronic kidney disease (CKD). In this context, genetic alterations in the kidney disease gene MUC1 (Mucin1) predispose to the development of CKD. These variations comprise the polymorphism rs4072037, which alters splicing of MUC1 mRNA, the length of a region with variable number of tandem repeats (VNTR), and rare autosomal-dominant inherited dominant-negative mutations in or 5' to the VNTR that causes autosomal dominant tubulointerstitial kidney disease (ADTKD-MUC1). As hypoxia plays a pivotal role in states of acute and chronic kidney injury, we explored the effects of hypoxia-inducible transcription factors (HIF) on the expression of MUC1 and its pathogenic variants in isolated primary human renal tubular cells. We defined a HIF-binding DNA regulatory element in the promoter-proximal region of MUC1 from which hypoxia or treatment with HIF stabilizers, which were recently approved for an anti-anemic therapy in CKD patients, increased levels of wild-type MUC1 and the disease-associated variants. Thus, application of these compounds might exert unfavorable effects in patients carrying MUC1 risk variants.

Dnajb11-Kidney Disease Develops from Reduced Polycystin-1 Dosage but not Unfolded Protein Response in Mice

SIGNIFICANCE STATEMENT

Heterozygous DNAJB11 mutation carriers manifest with small cystic kidneys and renal failure in adulthood. Recessive cases with prenatal cystic kidney dysplasia were recently described. Our in vitro and mouse model studies investigate the proposed disease mechanism as an overlap of autosomal-dominant polycystic kidney disease and autosomal-dominant tubulointerstitial kidney disease pathogenesis. We find that DNAJB11 loss impairs cleavage and maturation of the autosomal-dominant polycystic kidney disease protein polycystin-1 (PC1) and results in dosage-dependent cyst formation in mice. We find that Dnajb11 loss does not activate the unfolded protein response, drawing a fundamental contrast with the pathogenesis of autosomal-dominant tubulointerstitial kidney disease. We instead propose that fibrosis in DNAJB11 -kidney disease may represent an exaggerated response to polycystin-dependent cysts.

BACKGROUND

Patients with heterozygous inactivating mutations in DNAJB11 manifest with cystic but not enlarged kidneys and renal failure in adulthood. Pathogenesis is proposed to resemble an overlap of autosomal-dominant polycystic kidney disease (ADPKD) and autosomal-dominant tubulointerstitial kidney disease (ADTKD), but this phenotype has never been modeled in vivo . DNAJB11 encodes an Hsp40 cochaperone in the endoplasmic reticulum: the site of maturation of the ADPKD polycystin-1 (PC1) protein and of unfolded protein response (UPR) activation in ADTKD. We hypothesized that investigation of DNAJB11 would shed light on mechanisms for both diseases.

METHODS

We used germline and conditional alleles to model Dnajb11 -kidney disease in mice. In complementary experiments, we generated two novel Dnajb11-/- cell lines that allow assessment of PC1 C-terminal fragment and its ratio to the immature full-length protein.

RESULTS

Dnajb11 loss results in a profound defect in PC1 cleavage but with no effect on other cystoproteins assayed. Dnajb11-/- mice are live-born at below the expected Mendelian ratio and die at a weaning age with cystic kidneys. Conditional loss of Dnajb11 in renal tubular epithelium results in PC1 dosage-dependent kidney cysts, thus defining a shared mechanism with ADPKD. Dnajb11 mouse models show no evidence of UPR activation or cyst-independent fibrosis, which is a fundamental distinction from typical ADTKD pathogenesis.

CONCLUSIONS

DNAJB11 -kidney disease is on the spectrum of ADPKD phenotypes with a PC1-dependent pathomechanism. The absence of UPR across multiple models suggests that alternative mechanisms, which may be cyst-dependent, explain the renal failure in the absence of kidney enlargement.

VNtyper enables accurate alignment-free genotyping of MUC1 coding VNTR using short-read sequencing data in autosomal dominant tubulointerstitial kidney disease

The human genome comprises approximately 3% of tandem repeats with variable length (VNTR), a few of which have been linked to human rare diseases. Autosomal dominant tubulointerstitial kidney disease-MUC1 (ADTKD-MUC1) is caused by specific frameshift variants in the coding VNTR of the MUC1 gene. Calling variants from VNTR using short-read sequencing (SRS) is challenging due to poor read mappability. We developed a computational pipeline, VNtyper, for reliable detection of MUC1 VNTR pathogenic variants and demonstrated its clinical utility in two distinct cohorts: (1) a historical cohort including 108 families with ADTKD and (2) a replication naive cohort comprising 2,910 patients previously tested on a panel of genes involved in monogenic renal diseases. In the historical cohort all cases known to carry pathogenic MUC1 variants were re-identified, and a new 25bp-frameshift insertion in an additional mislaid family was detected. In the replication cohort, we discovered and validated 30 new patients.

Cystic Kidney Diseases in Children and Adults: Differences and Gaps in Clinical Management

Cystic kidney diseases, when broadly defined, have a wide differential diagnosis extending from recessive diseases with a prenatal or pediatric diagnosis, to the most common autosomal-dominant polycystic kidney disease primarily affecting adults, and several other genetic or acquired etiologies that can manifest with kidney cysts. The most likely diagnoses to consider when assessing a patient with cystic kidney disease differ depending on family history, age stratum, radiologic characteristics, and extrarenal features. Accurate identification of the underlying condition is crucial to estimate the prognosis and initiate the appropriate management, identification of extrarenal manifestations, and counseling on recurrence risk in future pregnancies. There are significant differences in the clinical approach to investigating and managing kidney cysts in children compared with adults. Next-generation sequencing has revolutionized the diagnosis of inherited disorders of the kidney, despite limitations in access and challenges in interpreting the data. Disease-modifying treatments are lacking in the majority of kidney cystic diseases. For adults with rapid progressive autosomal-dominant polycystic kidney disease, tolvaptan (V2-receptor antagonist) has been approved to slow the rate of decline in kidney function. In this article, we examine the differences in the differential diagnosis and clinical management of cystic kidney disease in children versus adults, and we highlight the progress in molecular diagnostics and therapeutics, as well as some of the gaps meriting further attention.

Interstitial Deletion of 3q21 in a Kuwaiti Child with Multiple Congenital Anomalies-Expanding the Phenotype

Interstitial deletions in the long arm of chromosome 3, although relatively rare, have previously been reported to be associated with several congenital anomalies and developmental delays. Around 11 individuals with interstitial deletion spanning the region 3q21 were reported to have overlapping phenotypes, including craniofacial dysmorphism, global developmental delay, skeletal manifestations, hypotonia, ophthalmological abnormalities, brain anomalies (mainly agenesis of corpus callosum), genitourinary tract anomalies, failure to thrive and microcephaly. We present a male individual from Kuwait with a 5.438 Mb interstitial deletion of the long arm of chromosome 3 (3q21.1q21.3) detected on the chromosomal microarray with previously unreported features, including feeding difficulties, gastroesophageal reflux, hypospadias, abdomino-scrotal hydrocele, chronic kidney disease, transaminitis, hypercalcemia, hypoglycemia, recurrent infections, inguinal hernia and cutis marmorata. Our report expands the phenotype associated with 3q21.1q21.3 while summarizing the cytogenetics and clinical data of the previously reported individuals with interstitial deletions involving 3q21, thus providing a comprehensive phenotypic summary.

Shen Qi Wan attenuates renal interstitial fibrosis through upregulating AQP1

Renal interstitial fibrosis (RIF) is the crucial pathway in chronic kidney disease (CKD) leading to the end-stage renal failure. However, the underlying mechanism of Shen Qi Wan (SQW) on RIF is not fully understood. In the current study, we investigated the role of Aquaporin 1 (AQP1) in SQW on tubular epithelial-to-mesenchymal transition (EMT). A RIF mouse model induced by adenine and a TGF-β1-stimulated HK-2 cell model were etablished to explore the involvement of AQP 1 in the protective effect of SQW on EMT in vitro and in vivo. Subsequently, the molecular mechanism of SQW on EMT was explored in HK-2 cells with AQP1 knockdown. The results indicated that SQW alleviated kidney injury and renal collagen deposition in the kidneys of mice induced by adenine, increased the protein expression of E-cadherin and AQP1 expression, and decreased the expression of vimentin and α-smooth muscle actin (α-SMA). Similarly, treatmement with SQW-containing serum significantly halted EMT process in TGF-β1 stimulated HK-2 cells. The expression of snail and slug was significantly upregulated in HK-2 cells after knockdown of AQP1. AQP1 knockdown also increased the mRNA expression of vimentin and α-SMA, and decreased the expression of E-cadherin. The protein expression of vimentin increased, while the expression of E-cadherin and CK-18 significantly decreased after AQP1 knockdown in HK-2 cells. These results revealed that AQP1 knockdown promoted EMT. Furthermore, AQP1 knockdown abolished the protective effect of SQW-containing serum on EMT in HK-2 cells. In sum, SQW attentuates EMT process in RIF through upregulation of the expression of AQP1.

Genetic evaluation of living kidney donor candidates: A review and recommendations for best practices

The growing accessibility and falling costs of genetic sequencing techniques has expanded the utilization of genetic testing in clinical practice. For living kidney donation, genetic evaluation has been increasingly used to identify genetic kidney disease in potential candidates, especially in those of younger ages. However, genetic testing on asymptomatic living kidney donors remains fraught with many challenges and uncertainties. Not all transplant practitioners are aware of the limitations of genetic testing, are comfortable with selecting testing methods, comprehending test results, or providing counsel, and many do not have access to a renal genetic counselor or a clinical geneticist. Although genetic testing can be a valuable tool in living kidney donor evaluation, its overall benefit in donor evaluation has not been demonstrated and it can also lead to confusion, inappropriate donor exclusion, or misleading reassurance. Until more published data become available, this practice resource should provide guidance for centers and transplant practitioners on the responsible use of genetic testing in the evaluation of living kidney donor candidates.

Cystic Diseases of the Kidneys: From Bench to Bedside

Exploration into the causes of hereditary renal cystic diseases demonstrates a deep-rooted connection with the proteomic components of the cellular organelle cilia. Cilia are essential to the signaling cascades, and their dysfunction has been tied to a range of renal cystic diseases initiating with studies on the oak ridge polycystic kidney (ORPK) mouse model. Here, we delve into renal cystic pathologies that have been tied with ciliary proteosome and highlight the genetics associated with each. The pathologies are grouped based on the mode of inheritance, where inherited causes that result in cystic kidney disease phenotypes include autosomal dominant and autosomal recessive polycystic kidney disease, nephronophthisis (Bardet-Biedl syndrome and Joubert Syndrome), and autosomal dominant tubulointerstitial kidney disease. Alternatively, phakomatoses-, also known as neurocutaneous syndromes, associated cystic kidney diseases include tuberous sclerosis (TS) and Von Hippel-Lindau (VHL) disease. Additionally, we group the pathologies by the mode of inheritance to discuss variations in recommendations for genetic testing for biological relatives of a diagnosed individual.

An m6A-Driven Prognostic Marker Panel for Renal Cell Carcinoma Based on the First Transcriptome-Wide m6A-seq

To date, only a single transcriptome-wide m6A sequencing study of clear cell renal cell carcinoma (ccRCC) has been reported, with no validation so far. Herein, by TCGA analysis of the KIRC cohort (n = 530 ccRCC; n = 72 normal), an external expression validation of 35 preidentified m6A targets was performed. Further in-depth expression stratification enabled assessment of m6A-driven key targets. Overall survival (OS) analysis and gene set enrichment analyses (GSEA) were conducted to assess their clinical and functional impact on ccRCC. In the hyper-up cluster significant upregulation was confirmed for NDUFA4L2, NXPH4, SAA1, and PLOD2 (40%) and in the hypo-up cluster for FCHSD1 (10%). Significant downregulation was observed for UMOD, ANK3, and CNTFR (27.3%) in the hypo-down cluster and for CHDH (25%) in the hyper-down cluster. In-depth expression stratification showed consistent dysregulation in ccRCC only for 11.67%: NDUFA4L2, NXPH4, and UMOD (NNU-panel). Patients with strong NNU panel dysregulation had significantly poorer OS (p = 0.0075). GSEA identified 13 associated and significantly upregulated gene sets (all p-values < 0.5; FDR < 0.25). External validation of the only available m6A sequencing in ccRCC consistently reduced dysregulated m6A-driven targets on the NNU panel with highly significant effects on OS. Epitranscriptomics are a promising target for developing novel therapies and for identifying prognostic markers for daily clinical practice.

Mechanisms of Protein Trafficking and Quality Control in the Kidney and Beyond

Numerous trafficking and quality control pathways evolved to handle the diversity of proteins made by eukaryotic cells. However, at every step along the biosynthetic pathway, there is the potential for quality control system failure. This review focuses on the mechanisms of disrupted proteostasis. Inspired by diseases caused by misfolded proteins in the kidney (mucin 1 and uromodulin), we outline the general principles of protein biosynthesis, delineate the recognition and degradation pathways targeting misfolded proteins, and discuss the role of cargo receptors in protein trafficking and lipid homeostasis. We also discuss technical approaches including live-cell fluorescent microscopy, chemical screens to elucidate trafficking mechanisms, multiplexed single-cell CRISPR screening platforms to systematically delineate mechanisms of proteostasis, and the advancement of novel tools to degrade secretory and membrane-associated proteins. By focusing on components of trafficking that go awry, we highlight ongoing efforts to understand fundamental mechanisms of disrupted proteostasis and implications for the treatment of human proteinopathies.

Mutation Analysis of Autosomal-Dominant Polycystic Kidney Disease Patients

Autosomal-dominant polycystic kidney disease (ADPKD) is characterized by bilateral kidney cysts that ultimately lead to end-stage kidney disease. While the major causative genes of ADPKD are PKD1 and PKD2, other genes are also thought to be involved. Fifty ADPKD patients were analyzed by exome sequencing or multiplex ligation-dependent probe amplification (MLPA), followed by long polymerase chain reaction and Sanger sequencing. Variants in PKD1 or PKD2 or GANAB were detected in 35 patients (70%). Exome sequencing identified 24, 7, and 1 variants in PKD1, PKD2, and GANAB, respectively, in 30 patients. MLPA analyses identified large deletions in PKD1 in three patients and PKD2 in two patients. We searched 90 cyst-associated genes in 15 patients who were negative by exome sequencing and MLPA analyses, and identified 17 rare variants. Four of them were considered "likely pathogenic" or "pathogenic" variants according to the American College of Medical Genetics and Genomics guidelines. Of the 11 patients without a family history, four, two, and four variants were found in PKD1, PKD2, and other genes, respectively, while no causative gene was identified in one patient. While the pathogenicity of each variant in these genes should be carefully assessed, a comprehensive genetic analysis may be useful in cases of atypical ADPKD.

Brown-Norway chromosome 1 mitigates the upregulation of proinflammatory pathways in mTAL cells and subsequent age-related CKD in Dahl SS/JrHsdMcwi rats

Chronic kidney disease (CKD) has a strong genetic component; however, the underlying pathways are not well understood. Dahl salt-sensitive (SS)/Jr rats spontaneously develop CKD with age and are used to investigate the genetic determinants of CKD. However, there are currently several genetically diverse Dahl SS rats maintained at various institutions and the extent to which some exhibit age-related CKD is unclear. We assessed glomerulosclerosis (GS) and tubulointerstitial fibrosis (TIF) in 3- and 6-mo-old male and female SS/JrHsdMcwi, BN/NHsd/Mcwi [Brown-Norway (BN)], and consomic SS-Chr 1BN/Mcwi (SS.BN1) rats, in which chromosome 1 from the BN rat was introgressed into the genome of the SS/JrHsdMcwi rat. Rats were fed a 0.4% NaCl diet. GS (31 ± 3% vs. 7 ± 1%) and TIF (2.3 ± 0.2 vs. 0.5 ± 0.1) were significantly greater in 6-mo-old compared with 3-mo-old SS/JrHsdMcwi rats, and CKD was exacerbated in males. GS was minimal in 6- and 3-mo-old BN (3.9 ± 0.6% vs. 1.2 ± 0.4%) and SS.BN1 (2.4 ± 0.5% vs. 1.0 ± 0.3%) rats, and neither exhibited TIF. In SS/JrHsdMcwi and SS.BN1 rats, mean arterial blood pressure was significantly greater in 6-mo-old compared with 3-mo-old SS/JrHsdMcwi (162 ± 4 vs. 131 ± 2 mmHg) but not SS.BN1 (115 ± 2 vs. 116 ± 1 mmHg) rats. In 6-mo-old SS/JrHsdMcwi rats, blood pressure was significantly greater in females. RNA-sequencing analysis revealed that inflammatory pathways were upregulated in isolated medullary thick ascending tubules in 7-wk-old SS/JrHsdMcwi rats, before the development of tubule pathology, compared with SS.BN1 rats. In summary, SS/JrHsdMcwi rats exhibit robust age-related progression of medullary thick ascending limb abnormalities, CKD, and hypertension, and gene(s) on chromosome 1 have a major pathogenic role in such changes.NEW & NOTEWORTHY This study shows that the robust age-related progression of kidney disease in Dahl SS/JrHsdMcw rats maintained on a normal-salt diet is abolished in consomic SS.BN1 rats. Evidence that medullary thick ascending limb segments of SS/JrHsdMcw rats are structurally abnormal and enriched in proinflammatory pathways before the development of protein casts provides new insights into the pathogenesis of kidney disease in this model.

Kidney Histology Findings in a Patient with Autosomal Dominant Tubulointerstitial Kidney Disease Subtype Hepatocyte Nuclear Factor 1β

We evaluated kidney histology in a 43-year-old woman with autosomal dominant tubulointerstitial kidney disease subtype hepatocyte nuclear factor 1β. Magnetic resonance imaging showed multiple cysts in the renal medullary area, and computed tomography showed hypoplasia of the pancreatic body and tail. A kidney biopsy showed thinning of the cortex, size reduction of glomerular tuft area, proximal tubule clustering, fibrosis around the tubules, loss of peritubular capillaries, and multilayered epithelial cells of cortical collecting ducts; this last finding was consistent with so-called medullary dysplasia specific to congenital disease, in which the renal pelvic epithelial cells enter the collecting duct.