Hidden genetics behind glomerular scars: an opportunity to understand the heterogeneity of focal segmental glomerulosclerosis?

Endoplasmic reticulum stress as a driver and therapeutic target for kidney disease

The endoplasmic reticulum (ER) has crucial roles in metabolically active cells, including protein translation, protein folding and quality control, lipid biosynthesis, and calcium homeostasis. Adverse metabolic conditions or pathogenic genetic variants that cause misfolding and accumulation of proteins within the ER of kidney cells initiate an injurious process known as ER stress that contributes to kidney disease and its cardiovascular complications. Initiation of ER stress activates the unfolded protein response (UPR), a cellular defence mechanism that functions to restore ER homeostasis. However, severe or chronic ER stress rewires the UPR to activate deleterious pathways that exacerbate inflammation, apoptosis and fibrosis, resulting in kidney injury. This insidious crosstalk between ER stress, UPR activation, oxidative stress and inflammation forms a vicious cycle that drives kidney disease and vascular damage. Furthermore, genetic variants that disrupt protein-folding mechanisms trigger ER stress, as evidenced in autosomal-dominant tubulointerstitial kidney disease and Fabry disease. Emerging therapeutic strategies that enhance protein-folding capacity and reduce the burden of ER stress have shown promising results in kidney diseases. Thus, integrating knowledge of how genetic variants cause protein misfolding and ER stress into clinical practice will enhance treatment strategies and potentially improve outcomes for various kidney diseases and their vascular complications.

Advances in focal segmental glomerulosclerosis research: genetic causes to non-coding RNAs

Focal Segmental Glomerulosclerosis (FSGS) is a clinicopathological illness characterized by podocyte damage, impairing glomerular filtration, and substantial proteinuria, which often results in end-stage renal disease (ESRD). Divided into primary, secondary, genetic, and idiopathic categories, its diverse origin highlights the intricacy of its diagnosis and treatment. The existing dependence on immunosuppressive medicines highlights their side effects and inconsistent efficacy, underscoring the pressing necessity for innovative, focused treatments. Recent advancements in genomics and molecular biology have shown the significant involvement of genetic alterations, especially in podocyte-associated proteins, in the pathogenesis of FSGS. Identifying possible novel biomarkers for diagnosing FSGS and monitoring disease activity has revitalized interest in this condition. Recent data underscores the significance of non-coding RNAs, including microRNAs (miRNAs), circular RNAs (circRNAs), and long non-coding RNAs (lncRNAs), in the modulation of gene expression and podocyte functionality. Please check and confirm that the authors and their respective affiliations have been correctly identified and amend if necessary. Particular dysregulated miRNAs and circRNAs have demonstrated potential as biomarkers for early diagnosis and disease monitoring. Furthermore, understanding lncRNA-mediated pathways provides novel therapeutic targets. This review consolidates current progress in elucidating the genetic and molecular processes of FSGS, emphasizing biomarker identification and treatment innovation.

Indications for genetic testing in adults with focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a histological pattern of injury that derives from various pathological processes that affect podocytes, resulting in loss of selectivity of the glomerular filtration membrane, proteinuria and the development of renal failure that progresses to end-stage kidney disease in a significant number of patients. The classification proposed by the 2021 KDIGO guidelines divides FSGS into four categories: primary, secondary, genetic, and FSGS of undetermined cause, thus facilitating its diagnosis and management. Genetic causes of FSGS present significant clinical variability, complicating their identification. Genetic testing is crucial to identify FSGS of genetic cause. The prevalence of genetic FSGS is significant in children and considerable in adults, highlighting the importance of early diagnosis to avoid unnecessary treatments and facilitate genetic counselling. Massive sequencing techniques have revolutionized genetic diagnosis, allowing the identification of more than 60 genes responsible for podocyte damage. This document proposes clinical recommendations for carrying out genetic studies in adults with FSGS, highlighting the need for a correct classification for adequate therapeutic planning and improvement of results in clinical trials.

Frameshift Mutation in PAX2 Related to Focal Segmental Glomerular Sclerosis: A Case Report and Literature Review

BACKGROUND

Paired box gene 2 (PAX2) heterozygous mutations can cause renal coloboma syndrome, but its role in patients with focal segmental glomerular sclerosis (FSGS) has been rarely reported.

METHODS

Based on the clinical manifestations and renal pathological characteristics of the patient, as well as familial whole exome sequencing, the diagnosis of FSGS related to PAX2 mutation was confirmed. Treatment such as lowering urinary protein and blood pressure was given, and the patient was followed up and observed.

RESULTS

There is a familial heterozygous case presented with chronic kidney disease secondary to FSGS, which was related to PAX2 frameshift mutation due to the deletion of G at the position 76 (c.76delG). To our knowledge, this is the first report of PAX2 c.76delG variant related to adult-onset FSGS.

CONCLUSION

Here, we further expand the phenotypic spectrum of FSGS. Genetic screening especially PAX2 mutation is recommended in patients with adult-onset FSGS of unknown etiology.

What Is Hidden in Patients with Unknown Nephropathy? Genetic Screening Could Be the Missing Link in Kidney Transplantation Diagnosis and Management

Between 15-20% of patients with end stage renal disease (ESRD) do not know the cause of the primary kidney disease and can develop complications after kidney transplantation. We performed a genetic screening in 300 patients with kidney transplantation, or undiagnosed primary renal disease, in order to identify the primary disease cause and discriminate between overlapping phenotypes. We used a custom-made panel for next-generation sequencing (Agilent technology, Santa Clara, CA, USA), including genes associated with Fabry disease, podocytopaties, complement-mediated nephropathies and Alport syndrome-related diseases. We detected candidate diagnostic variants in genes associated with nephrotic syndrome and Focal Segmental Glomerulosclerosis (FSGS) in 29 out of 300 patients, solving about 10% of the probands. We also identified the same genetic cause of the disease (PAX2: c.1266dupC) in three family members with different clinical diagnoses. Interestingly we also found one female patient carrying a novel missense variant, c.1259C>A (p.Thr420Lys), in the GLA gene not previously associated with Fabry disease, which is in silico defined as a likely pathogenic and destabilizing, and associated with a mild alteration in GLA enzymatic activity. The identification of the specific genetic background may provide an opportunity to evaluate the risk of recurrence of the primary disease, especially among patient candidates living with a donor kidney transplant.

Developmental Causes of Focal Segmental Glomerulosclerosis

Background

Focal segmental glomerulosclerosis (FSGS) is a histological pattern of glomerular damage that includes idiopathic conditions as well as genetic and non-genetic forms. Among these various etiologies, different phenotypes within the spectrum of congenital anomalies of the kidney and urinary tract (CAKUT) have been associated with FSGS.

Summary

Until recently, the main pathomechanism of how congenital kidney and urinary tract defects lead to FSGS was attributed to a reduced number of nephrons, resulting in biomechanical stress on the remaining glomeruli, detachment of podocytes, and subsequent inability to maintain normal glomerular architecture. The discovery of deleterious single-nucleotide variants in PAX2, a transcription factor crucial in normal kidney development and a known cause of papillorenal syndrome, in individuals with adult-onset FSGS without congenital kidney defects has shed new light on developmental defects that become evident during podocyte injury.

Key Message

In this mini-review, we challenge the assumption that FSGS in CAKUT is caused by glomerular hyperfiltration alone and hypothesize a multifactorial pathogenesis that includes overlapping cellular mechanisms that are activated in both damaged podocytes as well as nephron progenitor cells.