Albertien M. van Eerde

Introduction: Nephronophthisis (NPHP) is an autosomal recessive kidney disease resulting mainly from primary cilium defects, with unspecific and variable symptoms that can progress to kidney failure needing replacement therapy at a young age. Currently, up to 64% of likely NPHP cases can be diagnosed by assessing known genes. Therefore, there is a need to gain more insight in what genes can cause this disease. Methods: In a diagnostic setting, we performed broad genetic testing in patients with advanced kidney disease. We carried out in silico and in vitro analyses for TMEM72, including immunohistochemistry and affinity proteomics, and in vivo experiments to further interpret our findings. Results: We identified biallelic TMEM72 variants in 9 patients from six families with a phenotype suggestive for NPHP. Five families presented with kidney failure at a (young) adult age. One family had a different phenotype with prenatal onset of kidney failure and neurological symptoms. The phenotypes of the patients correspond to TMEM72 expression mainly in the kidney. In silico analyses indicate that homozygous loss-of-function variants are likely not tolerated in TMEM72. Immunohistochemistry staining of kidney biopsies revealed altered localization and expression of TMEM72 in cases compared to controls. In human-derived tubuloids, we showed that TMEM72 localizes to the cilium. Furthermore, using an affinity proteomics approach, we found an association of TMEM72 and ciliary function, more specifically in selective ciliary cholesterol transport. Conclusion: We present the first genetic evidence, underlined by immunohistochemistry and protein binding assays, linking TMEM72 variants to kidney disease and ciliary function. We conclude that TMEM72 is a candidate gene for NPHP. Future work is needed to further characterize TMEM72 variants and unravel its disease mechanism.

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.

Glomerular nephropathy resulting from the genetic defects in COL4A3/4/5 genes including the classical Alport syndrome is the second most common hereditary kidney disease characterized by persistent haematuria progressing to the need for kidney replacement therapy, frequently associated with sensorineural deafness, and occasionally with ocular anomalies. Diagnosis and management of COL4A3/4/5 glomerulopathy is a great challenge due to its phenotypic heterogeneity, multiple modes of inheritance, variable expressivity, and disease penetrance of individual variants as well as imperfect prognostic and progression factors and scarce and limited clinical trials, especially in children. As a joint initiative of the European Rare Kidney disease reference Network (ERKNet), European Renal Association (ERA Genes&Kidney), and European Society for Paediatric Nephrology (ESPN) Inherited renal disorders working group, a team of experts including adult and paediatric nephrologists, kidney geneticists, audiologists, ophthalmologists, and a kidney pathologist were selected to perform a systematic literature review on 21 clinically relevant PICO (Patient or Population covered, Intervention, Comparator, Outcome) questions. The experts formulated recommendations and formally graded them at a consensus meeting with input from patient representatives and a voting panel of nephrologists representing all regions of the world. Genetic diagnostics comprising joint analysis of COL4A3/4/5 genes is already the key diagnostic test during the initial evaluation of an individual presenting with persistent haematuria, proteinuria, kidney failure of unknown origin, focal segmental sclerosis of unknown origin, and possibly cystic kidney disease. Early renin-angiotensin system blockade is the standard of care therapy; sodium-glucose cotransporter-2 inhibitors may be added in adults with proteinuria and chronic kidney disease. Relatives with heterozygous COL4A3/4/5 variants should only be considered as the last possible resource for living kidney donation. This guideline provides guidance for the diagnosis and management of individuals with pathogenic variants in COL4A3/4/5 genes.

While up to 50% of children requiring kidney replacement therapy have congenital anomalies of the kidney and urinary tract (CAKUT), they represent only a fraction of the total patient population with CAKUT. The extreme variability in clinical outcome underlines the fundamental need to devise personalized clinical management strategies for individuals with CAKUT. Better understanding of the pathophysiology of abnormal kidney and urinary tract development provides a framework for precise diagnoses and prognostication of patients, the identification of biomarkers and disease modifiers, and, thus, the development of personalized strategies for treatment. In this review, we provide a state-of-the-art overview of the currently known genetic causes, including rare variants in kidney and urinary tract development genes, genomic disorders, and common variants that have been attributed to CAKUT. Furthermore, we discuss the impact of environmental factors and their interactions with developmental genes in kidney and urinary tract malformations. Finally, we present multi-angle translational modalities to validate candidate genes and environmental factors and shed light on future strategies to better understand the molecular underpinnings of CAKUT. Graphical abstract

Four European Reference Networks (ERN-EYE, ERKNet, Endo-ERN, ERN-ITHACA) have teamed up to establish a consensus statement and recommendations for Bardet-Biedl syndrome (BBS). BBS is an autosomal recessive ciliopathy with at least 26 genes identified to date. The clinical manifestations are pleiotropic, can be observed in utero and will progress with age. Genetic testing has progressively improved in the last years prompting for a revision of the diagnostic criteria taking into account clinical Primary and Secondary features, as well as positive or negative molecular diagnosis. This consensus statement also emphasizes on initial diagnosis, monitoring and lifelong follow-up, and symptomatic care that can be provided to patients and family members according to the involved care professionals. For paediatricians, developmental anomalies can be at the forefront for diagnosis (such as polydactyly) but can require specific care, such as for associated neuro developmental disorders. For ophthalmology, the early onset retinal degeneration requires ad hoc functional and imaging technologies and specific care for severe visual impairment. For endocrinology, among other manifestations, early onset obesity and its complications has benefited from better evaluation of eating behaviour problems, improved lifestyle programs, and from novel pharmacological therapies. Kidney and urinary track involvements warrants lifespan attention, as chronic kidney failure can occur and early management might improve outcome. This consensus recommends revised diagnostic criteria for BBS that will ensure certainty of diagnosis, giving robust grounds for genetic counselling as well as in the perspective of future trials for innovative therapies.

Mounting evidence indicates that monogenic disorders are the underlying cause in a significant proportion of patients with CKD. In recent years, the diagnostic yield of genetic testing in these patients has increased significantly as a result of revolutionary developments in genetic sequencing techniques and sequencing data analysis. Identification of disease-causing genetic variant(s) in patients with CKD may facilitate prognostication and personalized management, including nephroprotection and decisions around kidney transplantation, and is crucial for genetic counseling and reproductive family planning. A genetic diagnosis in a patient with CKD allows for screening of at-risk family members, which is also important for determining their eligibility as kidney transplant donors. Despite evidence for clinical utility, increased availability, and data supporting the cost-effectiveness of genetic testing in CKD, especially when applied early in the diagnostic process, many nephrologists do not use genetic testing to its full potential because of multiple perceived barriers. Our aim in this article was to empower nephrologists to (further) implement genetic testing as a diagnostic means in their clinical practice, on the basis of the most recent insights and exemplified by patient vignettes. We stress why genetic testing is of significant clinical benefit to many patients with CKD, provide recommendations for which patients to test and which test(s) to order, give guidance about interpretation of genetic testing results, and highlight the necessity for and essential components of pretest and post-test genetic counseling.

Background Clinical research on genetic kidney disease is thriving and the need for large cohorts, prospective data collection and biobanking is increasing. We aim to create a sustainable large genetic kidney disease biobank with a vast amount of uniformly collected high-quality data that is readily available for future research, with an infrastructure that allows for recontacting participants.Methods The GeNepher data- and biobank is an ongoing data- and sample collection that includes patients and family members with known and/or suspected genetic kidney disease. With a tiered approach participants can give broad consent for including their 1) available medical data (including genetic testing results), 2) inclusion of massively parallel sequencing data for add-on analysis, and 3) additional biobank sampling (e.g. urine for tubuloids, skin biopsy for fibroblasts). Recontacting is possible for additional data collection, novel research opportunities and return of relevant findings.Discussion The GeNepher data- and biobank collects prospective and retrospective data from kidney disease patients and their relatives. The broad consent allows for research that extends beyond one specific research question. Herewith, this biobank aims to 1) increase the scientific knowledge based on disease mechanisms including (novel) monogenic causes, 2) study modifiers, 3) improve care, including reproduction related research questions. Furthermore, it facilitates recontacting for opportunities in treatment development or when diagnose specific trials are started or specific treatment is approved.Conclusion The GeNepher biobank is designed to support a wide range of research projects by providing access to a diverse population of patients with (suspected) genetic kidney disease and has the potential to make a significant contribution to the field of rare kidney disease research.