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

Coenzyme Q10 supplementation in adult-onset focal segmental glomerulosclerosis caused by the Chinese common pathogenic variant c.737G > A (p.Ser246Asn) in the COQ8B gene

COQ8B nephropathy, a mitochondrial disorder caused by mutations in the COQ8B gene, is a major pediatric genetic focal segmental glomerulosclerosis (GFSGS) etiology and stands out as one of the few treatable forms with good response to coenzyme Q10 (CoQ10) supplementation. As the diagnosis and clinical experience of COQ8B nephropathy were predominantly in the pediatric population, the long-term efficacy of CoQ10 supplementation and its application in the adult-onset patients remains largely unknown. Here, we report three cases of adult-onset FSGS from unrelated families, all carrying the Chinese common COQ8B mutation (c.737G > A; p.Ser246Asn) with divergent trajectories of renal function following CoQ10 supplementation initiated in different stages of renal dysfunction, providing valuable evidence on the implication of early disease diagnosis and prompt CoQ10 supplementation for the prognosis of adult patients affected with COQ8B nephropathy.

A 15-year experience highlighting the spectrum of Alport kidney disease in the pediatric population and novel genetic variants in COL4A3-5

BACKGROUND

Alport kidney disease (AKD) presents one of the most prevalent genetic kidney disorders, characterized by a complex genetic background and diverse clinical manifestations. This study aimed to review the clinical and genetic features of pediatric patients with COL4A3-5 variants and identify novel genetic variants.

METHODS

Data were collected retrospectively at a national level from pediatric patients up to 19 years old, who underwent genetic testing between 2008 and 2023. Patients with pathogenic and likely pathogenic COL4A3-5 variants were included. Their clinical, laboratory, and genetic characteristics were presented.

RESULTS

Over 15 years, 85 children and adolescents tested positive for pathogenic or likely pathogenic COL4A3-5 variants. Increasing incidence was noted as genetic testing became more prevalent. One patient (1.2%) progressed to kidney failure and six (7%) had extrarenal involvement. Pathogenic or likely pathogenic variants in COL4A3, COL4A4, and COL4A5 genes were found in 14 (16.4%), 34 (40.0%), and 37 (43.6%) patients, respectively. Patients were diagnosed with autosomal, X-linked, and digenic AKD in 55.2%, 43.6%, and 1.2%, respectively. Eight novel variants were recorded, and their associated phenotype presented.

CONCLUSIONS

This study expands the genetic and clinical background of pediatric patients with AKD, presenting on a spectrum from mild hematuria to progressive chronic kidney disease. Genetic confirmation and risk stratification in the pediatric population are critical to ensure timely care and potentially slow down the progression of kidney disease.

Novel Truncating Variants in PODXL Represent a New Entity to Be Explored Among Podocytopathies

BACKGROUND/OBJECTIVES

Podocalyxin is a sialoprotein mainly expressed in the kidney cortex and lung tissue, which has been described as a component of the podocyte glycocalyx. This protein promotes the reorganization of the podocyte cytoskeleton, as well as the morphogenesis and differentiation of nascent podocytes, actively participating in glomerular filtration. Previous research has suggested that PODXL haploinsufficiency leads to podocytopathy with development of focal segmental glomerulosclerosis, a disorder that has been demonstrated in Podxl-deficient animal models and proposed as a primary cause in human families affected by this condition. However, only a few families have been reported, which limits the understanding about the spectrum of phenotype and prognosis of the disease.

METHODS

We performed high-throughput sequencing in a cohort of young adults with CKD, describing the clinical scenario of those who harbored truncating variants in the PODXL gene and testing the families for detected variants.

RESULTS

The PODXL gene exhibited a slight deviation in loss intolerance probability and moderate deviation in the observed/expected ratio of variation, which is typically observed in dominant genes with age-dependent incomplete penetrance or variable expression. We reported four novel truncating variants in the PODXL gene, along with a collection of previously published monoallelic truncating variants.

CONCLUSIONS

These findings further support evidence about genetic defects in the PODXL gene associated with a new molecular entity of podocytopathy with adult onset. Additionally, the nucleotide sequence of PODXL contains particularities that require careful analysis to interpret the effect of the variants detected in this gene.

When should the nephrologist think about genetics in patients with glomerular diseases?

This review discusses the significance of genetics in diagnosing glomerular diseases. Advances in genetic testing, particularly next-generation sequencing, have improved the accessibility and accuracy of diagnosing monogenic diseases, allowing for targeted gene panels and whole-exome/genome sequencing to identify genetic variants associated with glomerular diseases. Key indicators for considering a genetic cause include the age of onset, extrarenal features, family history, and inconclusive kidney biopsy results. Early-onset diseases, for instance, have a higher likelihood of being genetically caused, while extrarenal manifestations can also suggest an underlying genetic condition. A thorough family history can reveal patterns of inheritance that point to monogenic causes, although complexities like incomplete penetrance, skewed X inactivation and mosaicism can complicate the assessment. Also, autosomal recessive conditions imply asymptomatic parents, making genetic suspicion less likely, while de novo mutations can occur without any family history, further obscuring genetic assessment. Focal segmental glomerulosclerosis (FSGS) is characterized by podocyte injury and depletion, presenting in various forms, including primary, genetic, and secondary FSGS. Accurate classification of FSGS patients based on clinical and histological features is essential for guiding treatment decisions, optimizing therapeutic plans, avoiding unnecessary immunosuppression, and predicting relapse risk after kidney transplantation. Overall, a clinicopathological approach, enriched by genetic testing, offers a precise framework for diagnosis and management in glomerular diseases. Future directions for research and clinical practice include potential advancements in genetic testing and personalized medicine, which could further improve diagnostic precision and individualized treatment strategies.

Candidate Genetic Modifiers in Alport Syndrome: A Case Series

BACKGROUND

Alport syndrome (AS) is one of the most common monogenic kidney disorders. Recent studies have highlighted the modifier effect of variants involving podocyte and non-collagenous extracellular matrix (ECM) proteins in AS.

METHODS

We report a case series of eight patients with genetically proven AS and simultaneous variants involving podocyte and non-collagenous ECM proteins. Our aim is to describe the influence of such variants on the phenotype of patients with AS.

RESULTS

We identified 10 different type IV collagen variants. Patients were diagnosed with autosomal dominant (3/8), autosomal recessive (2/8), digenic (2/8) and X-linked AS (1/8). There were eight different variants involving podocyte and non-collagenous ECM proteins. The genes involved were CRB2, LAMA5, LAMB2, NUP107, MYO1E and PLCE1. Four patients (LAMB2, LAMA5 and PLCE1 variants) presented with nephrotic syndrome or nephrotic range proteinuria. Two patients had hearing loss. Most patients (7/8) had a family history of kidney disease. Two patients (LAMB2 and LAMA5 variants) were diagnosed with focal segmental glomerulosclerosis. Two patients developed end-stage kidney disease (LAMA5, MYO1E and NUP107 variants).

CONCLUSIONS

Although mutations of podocyte and ECM proteins do not have phenotypic expression in monoallelic form, the presence of such variants could explain the phenotypic variability of AS.

KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease in Children and Adults: a commentary from the European Renal Best Practice (ERBP)

The Kidney Disease: Improving Global Outcomes (KDIGO) 2024 Guideline for Identification and Management of Chronic Kidney Disease (CKD) is a welcome development, coming 12 years after the paradigm-changing 2012 guidelines. We are living in an unprecedented era in nephrology with novel therapies, including sodium-glucose cotransporter-2 inhibitors, glucagon-like peptide-1 receptor agonists and non-steroidal mineralocorticoid receptor antagonists, now being proven in multiple randomized controlled clinical trials to reduce both the progression of CKD and cardiovascular morbidity and mortality. The KDIGO 2024 CKD Guideline is aimed at a broad audience looking after children and adults with CKD and provide practical and actionable steps to improve care. This commentary reviews the guideline sections pertaining to the evaluation and risk assessment of individuals with CKD from a European perspective. We feel that despite the last guideline being published 12 years ago, and the fact that the assessment of CKD has been emphasized by many other national/international nephrology, cardiology and diabetology guidelines and societies, the diagnosis and treatment of CKD remains poor across Europe. As such, the KDIGO 2024 CKD Guideline should be seen as an urgent call to action to improve diagnosis and care of children and adults with CKD across Europe. We know what we need to do. We now need to get on and do it.

The Diagnostic Yield of Genomic Sequencing-Based Genetic Kidney Disease Testing in Kidney Transplant Candidates: Experience at an Urban US Transplant Center

BACKGROUND

Recent studies suggest that approximately 10% of patients with chronic kidney disease (CKD) have disease-causing genetic variants, an observation relevant to evaluation of kidney transplant candidates.

METHODS

We retrospectively investigated the diagnostic yield of genetic testing in kidney transplant candidates evaluated at our program (January 1, 2021-December 8, 2022). Inclusion criteria were as follows: first-degree relative(s) with CKD/end-stage kidney disease (ESKD), early-onset CKD, focal segmental glomerulosclerosis, cystic kidney disease, alternative complement pathway-associated diseases, or ESKD of unknown cause.

RESULTS

One hundred eleven patients underwent genetic kidney disease testing. The most common indication for testing was early-onset CKD (34.2%), followed by a family history of CKD (23.4%), focal segmental glomerulosclerosis (18.0%), cystic kidney disease (9.0%), alternative complement pathway diseases (3.6%), and ESKD of unknown cause (11.7%). Overall diagnostic yield was 46.9% (52/111), and yield was highest among candidates with a family history of CKD (61.5%; 16/26). Among cases with positive testing, the most common diagnostic variant was APOL1, with 2 renal risk variants identified in 57.7% (30/52), while monogenic causes of CKD were identified in 42.3% (22/52). Genetic testing led to further evaluation or to a different diagnosis than the initial clinical diagnosis in 8.1% (9/111) of the cohort. For 24 transplant candidates, their identified diagnostic variants indicated the need for genetic testing of related living donor candidates; of these, 6 living donor candidates were evaluated and underwent testing, of whom donation was excluded in 1 candidate.

CONCLUSIONS

Pretransplant genetic testing increases understanding of CKD cause, and provides information for living donor evaluation and risk assessment of posttransplant disease recurrence.

MUC1-associated autosomal dominant tubulointerstitial kidney disease: prevalence in kidney failure of undetermined aetiology and clinical insights from Danish families

Background

Frameshift variants in the variable number tandem repeat region of mucin-1 (MUC1) cause autosomal dominant tubulointerstitial kidney disease (ADTKD-MUC1) but are challenging to detect. We investigated the prevalence in patients with kidney failure of undetermined aetiology and compared Danish families with ADTKD-MUC1.

Methods

We recruited patients with suspected kidney failure of undetermined aetiology at ≤50 years and excluded those with a clear-cut clinical or histopathological kidney diagnoses or established genetic kidney diseases identified thorough medical record review. MUC1 genotyping was performed by SNaPshot analysis, detecting the most common pathogenic cytosine duplication, followed by bioinformatics pipeline VNtyper analysis of short-read sequencing data.

Results

Of 172 recruited patients, 123 underwent SNaPshot analyses, which were abnormal in 5/123 patients (4%). Next, VNtyper genotyping was performed in all patients, including the five with abnormal SNaPshot analysis. VNtyper re-identified the common cytosine duplication in all five patients and revealed novel frameshift variants in two additional patients, while the analyses were normal in the remaining 116 patients. All patients carrying frameshift variants in MUC1 fulfilled ADTKD criteria and had a family history of kidney failure. A considerable inter- and intrafamilial variability of chronic kidney disease stage relative to age was observed in families with ADTKD-MUC1.

Conclusions

ADTKD-MUC1 was identified in 7/123 patients (6%) in a selected cohort of kidney failure of undetermined aetiology ≤50 years, and VNtyper effectively identified all pathogenic MUC1 variants.

In Silico Modeling of Fabry Disease Pathophysiology for the Identification of Early Cellular Damage Biomarker Candidates

Fabry disease (FD) is an X-linked lysosomal disease whose ultimate consequences are the accumulation of sphingolipids and subsequent inflammatory events, mainly at the endothelial level. The outcomes include different nervous system manifestations as well as multiple organ damage. Despite the availability of known biomarkers, early detection of FD remains a medical need. This study aimed to develop an in silico model based on machine learning to identify candidate vascular and nervous system proteins for early FD damage detection at the cellular level. A combined systems biology and machine learning approach was carried out considering molecular characteristics of FD to create a computational model of vascular and nervous system disease. A data science strategy was applied to identify risk classifiers by using 10 K-fold cross-validation. Further biological and clinical criteria were used to prioritize the most promising candidates, resulting in the identification of 36 biomarker candidates with classifier abilities, which are easily measurable in body fluids. Among them, we propose four candidates, CAMK2A, ILK, LMNA, and KHSRP, which have high classification capabilities according to our models (cross-validated accuracy ≥ 90%) and are related to the vascular and nervous systems. These biomarkers show promise as high-risk cellular and tissue damage indicators that are potentially applicable in clinical settings, although in vivo validation is still needed.