Accumulation of Globotriaosylceramide in Podocytes in Fabry Nephropathy Is Associated with Progressive Podocyte Loss

The role of tubular cells in the pathogenesis of Fabry nephropathy

The pathophysiology of Fabry nephropathy (FN) is induced by galactosidase A deficiency with a chronic exposure of glycolipids to every lineage of renal cells. Tissue damage is attributed to the activation of molecular pathways, resulting in tissue fibrosis and chronic kidney disease. Podocytes have been the primary focus in clinical pathophysiological research because of the striking accumulation of large glycolipid deposits observable in histology. Yet, the tubular interstitium makes up a large portion of the whole organ, and therefore, its role must be further considered in pathogenic processes. In this review, we would like to propose Fabry tubulopathy and its ensuing functional effects as the first pathological signs and contributing factors to the development of FN. We will summarize and discuss the current literature regarding the role of tubular cells in Fabry kidney pathophysiology. Starting from clinical and histological evidence, we will highlight the data from animal models and cell cultures outlining the pathophysiological pathways associated with tubular interstitial injury causing renal fibrosis in Fabry nephropathy.

Pathogenic pathways of renal damage in Fabry nephropathy: interplay between immune cell infiltration, apoptosis and fibrosis

BACKGROUND

Fabry nephropathy is a consequence of the deposition of globotriaosylceramide, caused by deficient GLA enzyme activity in all types of kidney cells. These deposits are perceived as damage signals leading to activation of inflammation resulting in renal fibrosis. There are few studies related to immunophenotype characterization of the renal infiltrate in kidneys in patients with Fabry disease and its relationship to mechanisms of fibrosis. This work aims to quantify TGF-β1 and active caspase 3 expression and to analyze the profile of cells in inflammatory infiltration in kidney biopsies from Fabry naïve-patients, and to investigate correlations with clinical parameters.

METHODS

Renal biopsies from 15 treatment-naïve Fabry patients were included in this study. Immunostaining was performed to analyze active caspase 3, TGF-β1, TNF-α, CD3, CD20, CD68 and CD163. Clinical data were retrospectively gathered at time of kidney biopsy.

RESULTS

Our results suggest the production of TNFα and TGFβ1 by tubular cells, in Fabry patients. Active caspase 3 staining revealed that tubular cells are in apoptosis, and apoptotic levels correlated with clinical signs of chronic kidney disease, proteinuria, and inversely with glomerular filtration rate. The cell infiltrates consisted of macrophages, T and B cells. CD163 macrophages were found in biopsy specimens and their number correlates with TGFβ1 and active caspase 3 tubular expression.

CONCLUSIONS

These results suggest that CD163+ cells could be relevant mediators of fibrosis in Fabry nephropathy, playing a role in the induction of TGFβ1 and apoptotic cell death by tubular cells. These cells may represent a new player in the pathogenic mechanisms of Fabry nephropathy.

GLA Mutations Suppress Autophagy and Stimulate Lysosome Generation in Fabry Disease

Fabry disease (FD) is an X-linked recessive inheritance lysosomal storage disorder caused by pathogenic mutations in the GLA gene leading to a deficiency of the enzyme alpha-galactosidase A (α-Gal A). Multiple organ systems are implicated in FD, most notably the kidney, heart, and central nervous system. In our previous study, we identified four GLA mutations from four independent Fabry disease families with kidney disease or neuropathic pain: c.119C>A (p.P40H), c.280T>C (C94R), c.680G>C (p.R227P) and c.801+1G>A (p.L268fsX3). To reveal the molecular mechanism underlying the predisposition to Fabry disease caused by GLA mutations, we analyzed the effects of these four GLA mutations on the protein structure of α-galactosidase A using bioinformatics methods. The results showed that these mutations have a significant impact on the internal dynamics and structures of GLA, and all these altered amino acids are close to the enzyme activity center and lead to significantly reduced enzyme activity. Furthermore, these mutations led to the accumulation of autophagosomes and impairment of autophagy in the cells, which may in turn negatively regulate autophagy by slightly increasing the phosphorylation of mTOR. Moreover, the overexpression of these GLA mutants promoted the expression of lysosome-associated membrane protein 2 (LAMP2), resulting in an increased number of lysosomes. Our study reveals the pathogenesis of these four GLA mutations in FD and provides a scientific foundation for accurate diagnosis and precise medical intervention for FD.

Development of an automated estimation of foot process width using deep learning in kidney biopsies from patients with Fabry, minimal change, and diabetic kidney diseases

Podocyte injury plays a key role in pathogenesis of many kidney diseases with increased podocyte foot process width (FPW), an important measure of podocyte injury. Unfortunately, there is no consensus on the best way to estimate FPW and unbiased stereology, the current gold standard, is time consuming and not widely available. To address this, we developed an automated FPW estimation technique using deep learning. A U-Net architecture variant model was trained to semantically segment the podocyte-glomerular basement membrane interface and filtration slits. Additionally, we employed a post-processing computer vision approach to accurately estimate FPW. A custom segmentation utility was also created to manually classify these structures on digital electron microscopy (EM) images and to prepare a training dataset. The model was applied to EM images of kidney biopsies from 56 patients with Fabry disease, 15 with type 2 diabetes, 10 with minimal change disease, and 17 normal individuals. The results were compared with unbiased stereology measurements performed by expert technicians unaware of the clinical information. FPW measured by deep learning and by the expert technicians were highly correlated and not statistically different in any of the studied groups. A Bland-Altman plot confirmed interchangeability of the methods. FPW measurement time per biopsy was substantially reduced by deep learning. Thus, we have developed a novel validated deep learning model for FPW measurement on EM images. The model is accessible through a cloud-based application making calculation of this important biomarker more widely accessible for research and clinical applications.

Cardiomyocyte Globotriaosylceramide Accumulation in Adult Male Patients with Fabry Disease and IVS4 + 919G>A GLA Mutation is Progressive with Age and Correlates with Left Ventricular Hypertrophy and Reduced Left Ventricular Ejection Fraction

Background

While cardiovascular complications are the most common cause of mortality in Fabry disease, the relationship between globotriaosylceramide (GL-3) accumulation, the hallmark of Fabry cardiomyopathy, and cardiac hypertrophy has not been fully elucidated.

Methods

We developed unbiased stereology protocols to quantify the ultrastrcture of Fabry cardiomyopathy. Endomyocardial biopsies from 10 adult male enzyme replacement therapy naïve Fabry patients with IVS4 + 919G>A GLA mutation were studied. The findings were correlated with cardiac MRI and clinical data.

Results

Ultrastructural parameters showed significant relationships with key imaging and clinical and functional variables. Average cardiomyocyte volume and GL-3 volume per cardiomyocyte were progressively increased with age. Eighty-four percent of left ventricular mass index (LVMI) variability was explained by cardiomyocyte nuclear volume, age and plasma globotriaosylsphingosine with cardiomyocyte nuclear volume being the only independent predictor of LVMI. Septal thickness was directly and left ventricular ejection fraction (LVEF) was inversely correlated with cardiomyocyte GL-3 accumulation. Sixty-five percent of left ventricular ejection fraction (LVEF) variability was explained by cardiomyocyte GL3 volume, serum α-galactosidase-A activity and age with cardiomyocyte GL3 volume being the only independent predictor of LVEF. Residual α-galactosidase-A activity was directly correlated with myocardial microvasculature density.

Conclusions

The unbiased stereological methods introduced in this study unraveled novel relationships between cardiomyocyte structure and important imaging and clinical parameters. These novel tools can help better understand Fabry cardiomyopathy pathophysiology.

Prevalence of Kidney and Urinary Tract Complications in Fabry Disease from 2000 to 2020: A Global Cohort Study Including 10,637 Patients

BACKGROUND/AIM

Fabry disease, an X-linked lysosomal storage disorder, causes progressive globotriaosylceramide accumulation in cells throughout the body. Characteristic multiorgan manifestations include renal dysfunction (Fabry nephropathy) and associated urinary tract complications. Enzyme replacement therapy (ERT) has been available since 2001, but contemporary real-world data are lacking regarding Fabry nephropathy risks and treatment outcomes.

PATIENTS AND METHODS

This retrospective cohort study analyzed electronic medical records data for 10,637 Fabry disease patients from the TriNetX research database. Kidney and urinary tract outcomes were evaluated over two decades, 2000-2010 and 2011-2020. Outcomes assessed included chronic kidney disease (CKD), urinary tract infections, urinary incontinence, obstruction, renal insufficiency, and end-stage renal disease (ESRD).

RESULTS

The prevalence of stage 4-5 CKD nearly doubled between 2000-2010 and 2011-2020, while ESRD prevalence rose over 4-fold. Incidence rates showed similar marked elevations across renal and urologic complications. Females and Black patients experienced disproportionate escalations in kidney and urinary tract morbidity.

CONCLUSION

This large cohort study revealed significantly increased Fabry nephropathy and associated urologic complications over the past two decades, contradicting expectations of reduced morbidity with ERT availability. The findings highlight needs to optimize screening, treatment strategies, monitoring practices, and address disparities to curb rising disease burden and improve patient outcomes.

Early Risk Stratification for Natural Disease Course in Fabry Patients Using Plasma Globotriaosylsphingosine Levels

BACKGROUND

Fabry disease is a very heterogeneous X-linked lysosomal storage disease. Disease manifestations in the kidneys, heart, and brain vary greatly, even between patients of the same sex and with the same disease classification (classical or nonclassical). A biomarker with a strong association with the development of disease manifestations is needed to determine the need for Fabry-specific treatment and appropriate frequency of follow-up because clinical manifestations of the disorder may take decennia to develop.

METHODS

We investigated the levels of plasma lysoGb3 levels over time and its association with disease manifestations and disease course in 237 untreated patients with Fabry disease (median age 42 years, 38% male) using linear mixed-effect models.

RESULTS

LysoGb3 levels are stable over time in plasma of untreated patients with Fabry disease. Higher levels of lysoGb3 were associated with steeper decline in eGFR ( P = 0.05) and a faster increase in albuminuria (measured as the urinary albumin-to-creatinine ratio, P < 0.001), left ventricular mass (measured on echocardiography, P < 0.001), left atrial volume index ( P = 0.003), and Fazekas score ( P = 0.003). In addition, regardless of age, higher lysoGb3 levels were associated with higher relative wall thickness ( P < 0.001) and unfavorable functional markers on echocardiography, including septal mitral annular early diastolic velocity (e', P < 0.001) and the ratio of early transmitral velocity (E) to e' (E/e', P = 0.001).

CONCLUSIONS

In an individual patient with Fabry disease, the plasma lysoGb3 level reached a specific level in early childhood which, in the absence of Fabry-specific treatment, remained stable throughout life. The level of lysoGb3 in untreated patients was associated with nearly all Fabry-specific disease manifestations, regardless of the sex of the patient.

Consensus recommendations for the treatment and management of patients with Fabry disease on migalastat: a modified Delphi study

Objective

Fabry disease is a progressive disorder caused by deficiency of the α-galactosidase A enzyme (α-Gal A), leading to multisystemic organ damage with heterogenous clinical presentation. The addition of the oral chaperone therapy migalastat to the available treatment options for Fabry disease is not yet universally reflected in all treatment guidelines. These consensus recommendations are intended to provide guidance for the treatment and monitoring of patients with Fabry disease receiving migalastat.

Methods

A modified Delphi process was conducted to determine consensus on treatment decisions and monitoring of patients with Fabry disease receiving migalastat. The multidisciplinary panel comprised 14 expert physicians across nine specialties and two patients with Fabry disease. Two rounds of Delphi surveys were completed and recommendations on the use of biomarkers, multidisciplinary monitoring, and treatment decisions were generated based on statements that reached consensus.

Results

The expert panel reached consensus agreement on 49 of 54 statements, including 16 that reached consensus in round 1. Statements that reached consensus agreement are summarized in recommendations for migalastat treatment and monitoring, including baseline and follow-up assessments and frequency. All patients with Fabry disease and an amenable mutation may initiate migalastat treatment if they have evidence of Fabry-related symptoms and/or organ involvement. Treatment decisions should include holistic assessment of the patient, considering clinical symptoms and organ involvement as well as patient-reported outcomes and patient preference. The reliability of α-Gal A and globotriaosylsphingosine as pharmacodynamic response biomarkers remains unclear.

Conclusion

These recommendations build on previously published guidelines to highlight the importance of holistic, multidisciplinary monitoring for patients with Fabry disease receiving migalastat, in addition to shared decision-making regarding treatments and monitoring throughout the patient journey. GRAPHICAL ABSTRACT.

An expert consensus on the recommendations for the use of biomarkers in Fabry disease

Fabry disease is an X-linked lysosomal storage disorder caused by the accumulation of glycosphingolipids in various tissues and body fluids, leading to progressive organ damage and life-threatening complications. Phenotypic classification is based on disease progression and severity and can be used to predict outcomes. Patients with a classic Fabry phenotype have little to no residual α-Gal A activity and have widespread organ involvement, whereas patients with a later-onset phenotype have residual α-Gal A activity and disease progression can be limited to a single organ, often the heart. Diagnosis and monitoring of patients with Fabry disease should therefore be individualized, and biomarkers are available to support with this. Disease-specific biomarkers are useful in the diagnosis of Fabry disease; non-disease-specific biomarkers may be useful to assess organ damage. For most biomarkers it can be challenging to prove they translate to differences in the risk of clinical events associated with Fabry disease. Therefore, careful monitoring of treatment outcomes and collection of prospective data in patients are needed. As we deepen our understanding of Fabry disease, it is important to regularly re-evaluate and appraise published evidence relating to biomarkers. In this article, we present the results of a literature review of evidence published between February 2017 and July 2020 on the impact of disease-specific treatment on biomarkers and provide an expert consensus on clinical recommendations for the use of those biomarkers.

Modeling of Fabry disease nephropathy using patient derived human induced pluripotent stem cells and kidney organoid system

OBJECTIVES

To explore the possibility of kidney organoids generated using patient derived human induced pluripotent stem cells (hiPSC) for modeling of Fabry disease nephropathy (FDN).

METHODS

First, we generated hiPSC line using peripheral blood mononuclear cells (PBMCs) from two male FD-patients with different types of GLA mutation: a classic type mutation (CMC-Fb-001) and a non-classic type (CMC-Fb-003) mutation. Second, we generated kidney organoids using wild-type (WT) hiPSC (WTC-11) and mutant hiPSCs (CMC-Fb-001 and CMC-Fb-003). We then compared alpha-galactosidase A (α-GalA) activity, deposition of globotriaosylceremide (Gb-3), and zebra body formation under electromicroscopy (EM).

RESULTS

Both FD patients derived hiPSCs had the same mutations as those detected in PBMCs of patients, showing typical pluripotency markers, normal karyotyping, and successful tri-lineage differentiation. Kidney organoids generated using WT-hiPSC and both FD patients derived hiPSCs expressed typical nephron markers without structural deformity. Activity of α-GalA was decreased and deposition of Gb-3 was increased in FD patients derived hiPSCs and kidney organoids in comparison with WT, with such changes being far more significant in CMC-Fb-001 than in CMC-Fb-003. In EM finding, multi-lammelated inclusion body was detected in both CMC-Fb-001 and CMC-Fb-003 kidney organoids, but not in WT.

CONCLUSIONS

Kidney organoids generated using hiPSCs from male FD patients might recapitulate the disease phenotype and represent the severity of FD according to the GLA mutation type.

CRISPR/Cas9-mediated A4GALT suppression rescues Fabry disease phenotypes in a kidney organoid model

The objective of this study was to investigate whether CRISPR/Cas9-mediated suppression of A4GALT could rescue phenotype of Fabry disease nephropathy (FDN) using human induced pluripotent stem cells (hiPSCs) derived kidney organoid system. We generated FDN patient-derived hiPSC (CMC-Fb-002) and FD-specific hiPSCs (GLA-KO) by knock-out (KO) of GLA in wild-type (WT) hiPSCs using CRISPR/Cas9. We then performed A4GALT KO in both CMC-Fb-002 and GLA-KO to make Fb-002-A4GALT-KO and GLA/A4GALT-KO, respectively. Using these hiPSCs, we generated kidney organoids and compared alpha-galactosidase-A enzyme (α-GalA) activity, globotriaosylceramide (Gb-3) deposition, and zebra body formation under electron microscopy (EM). We also compared mRNA expression levels using RNA-seq and qPCR. Generated hiPSCs showed typical pluripotency markers without chromosomal disruption. Expression levels of GLA in CMC-Fb-002 and GLA-KO and expression levels of A4GALT in Fb-002-A4GALT-KO and GLA/A4GALT-KO were successfully decreased compared to those in WT-hiPSCs, respectively. Generated kidney organoids using these hiPSCs expressed typical nephron markers. In CMC-Fb-002 and GLA-KO organoids, α-GalA activity was significantly decreased along with increased deposition of Gb-3 in comparison with WT organoids. Intralysosomal inclusion body was also detected under EM. However, these disease phenotypes were rescued by KO of A4GALT in both GLA/A4GALT-KO and Fb-002-A4GALT-KO kidney organoids. RNA-seq showed increased expression levels of genes related to FDN progression in both GLA-mutant organoids compared to those in WT. Such increases were rescued in GLA/A4GALT-KO or Fb-002-A4GALT-KO organoids. CRISPR/Cas9 mediated suppression of A4GALT could rescue FDN phenotype. Hence, it can be proposed as a therapeutic approach to treat FDN.

Mass Spectrometry Analysis of Globotriaosylsphingosine and Its Analogues in Dried Blood Spots

Fabry disease (FD) is an X-linked lysosomal storage disorder where impaired α-galactosidase A enzyme activity leads to the intracellular accumulation of undegraded glycosphingolipids, including globotriaosylsphingosine (lyso-Gb₃) and related analogues. Lyso-Gb₃ and related analogues are useful biomarkers for screening and should be routinely monitored for longitudinal patient evaluation. In recent years, a growing interest has emerged in the analysis of FD biomarkers in dried blood spots (DBSs), considering the several advantages compared to venipuncture as a technique for collecting whole-blood specimens. The focus of this study was to devise and validate a UHPLC-MS/MS method for the analysis of lyso-Gb₃ and related analogues in DBSs to facilitate sample collection and shipment to reference laboratories. The assay was devised in conventional DBS collection cards and in Capitainer^®B blood collection devices using both capillary and venous blood specimens from 12 healthy controls and 20 patients affected with FD. The measured biomarker concentrations were similar in capillary and venous blood specimens. The hematocrit (Hct) did not affect the correlation between plasma and DBS measurements in our cohort (Hct range: 34.3-52.2%). This UHPLC-MS/MS method using DBS would facilitate high-risk screening and the follow-up and monitoring of patients affected with FD.

Clinical outcomes among young patients with Fabry disease who initiated agalsidase beta treatment before 30 years of age: An analysis from the Fabry Registry

BACKGROUND

Clinical manifestations of classic Fabry disease (α-galactosidase A deficiency) usually occur in childhood, while complications involving major organs typically develop in adulthood. Outcomes of Fabry-specific treatment among young patients have not been extensively reported. Our aim was to analyze clinical outcomes among patients aged 5-30 years at initiation of treatment with agalsidase beta using data from the Fabry Registry (NCT00196742, sponsor: Sanofi).

METHODS

Reported GLA variants were predicted to be associated with the classic phenotype or not classified in fabry-database.org. Linear mixed models were conducted to assess changes over ≥2-year follow-up in the estimated glomerular filtration rate (eGFR) stratified by low (LRI) and high (HRI) renal involvement (defined by proteinuria/albuminuria levels), and changes in interventricular septal thickness (IVST) and left ventricular posterior wall thickness (LVPWT) Z-scores stratified by median age at first treatment. Self-reports ('yes'/'no') of abdominal pain, diarrhea, chronic peripheral pain (denoting neuropathic pain), and acute pain crises at baseline were compared with reports after ≥0.5-year and ≥2.5-year follow-up using McNemar's test.

RESULTS

Male (n = 117) and female patients (n = 59) with LRI initiated treatment at a median age of 19.9 and 23.6 years, respectively, and were followed for a median of 6.3 and 5.0 years, respectively. The eGFR slopes were -1.18 (P_{from 0} <0.001) and -0.92 mL/min/1.73 m²/year (P_{from 0} = 0.040), respectively. Males with HRI (n = 23, median UPCR 1.0 g/g), who started treatment at a median age of 26.7 years, had an eGFR slope of -2.39 mL/min/1.73 m²/year (P_{from 0} <0.001; P_difference = 0.055, as compared with the slope of -1.18 mL/min/1.73 m²/year for LRI males) during a median follow-up of 5.6 years. Echocardiographic variables were stable among males, regardless of age, and among young females (median follow-up >5.5 years and ≥4.5 years, respectively). Older females (treatment initiation at median age 27.5 years) had a slope of LVPWT Z-scores of 0.18/year (n = 12, P_{from 0} = 0.028), whereas IVST Z-scores remained stable (n = 13, 0.10/year, P_{from 0} = 0.304) during a median follow-up of ≥3.7 years. These slopes did not significantly differ from slopes of younger females. Reports of chronic peripheral pain and acute pain crises by males, and of diarrhea and acute pain crises by females, significantly reduced after a median follow-up of ≥4.0 years. After a median follow-up of ≥5.4 years, reports of all four symptoms significantly decreased among males, whereas among females only reports of abdominal pain significantly decreased.

CONCLUSIONS

During sustained treatment with agalsidase beta in young Fabry patients with a predicted classic phenotype or with unclassified GLA variants with similar characteristics, the decline in eGFR was modest among male and female patients with LRI. The greater decline in eGFR among older, proteinuric (i.e., HRI) males may suggest a benefit of earlier treatment. Overall, echocardiographic variables remained stable, particularly among males and younger females. Significant reductions in symptom reports occurred primarily among males after longer follow-up and were less noticeable among females. These observed trends are suggestive of an overall improvement after treatment in young patients, but warrant larger longitudinal studies.

A nationwide cross-sectional analysis of biopsy-proven Fabry nephropathy: the Japan Renal Biopsy Registry

BACKGROUND

Fabry disease (FD) is an X-linked inherited disease where renal complications are associated with a poor prognosis. However, little is known about the prevalence of Fabry nephropathy (FN) in patients with chronic kidney disease (CKD). We extracted FN data from the Japan Renal Biopsy Registry, analyzed the prevalence of FN, and examined the correlation between clinical characteristics and renal involvement according to sex differences and hemi- and heterozygosity in patients with FD.

METHODS

A total of 38,351 participants who underwent renal biopsy were retrospectively enrolled, and FN was determined. The clinical characteristics of FD patients were examined based on sex differences.

RESULTS

Twenty-nine patients (0.076%) (19 males and 10 females, mean age: 43.7 ± 15.5 years old) were diagnosed with FN. Median estimated urinary protein (UP) and mean eGFR levels were 0.9 [interquartile range (IQR) [0.7-1.6] g/gCr and 67.1 ± 36.8 mL/min/1.73 m², respectively. Mean systolic blood pressure (SBP) was 126.4 ± 17.1 mmHg and diastolic blood pressure was 76.1 ± 12.6 mmHg. An inverse correlation between eGFR and logarithm UP levels was observed (r² = 0.23, p = 0.02), SBP was positively associated with logarithm UP (r² = 0.34, p = 0.004) overall and inversely associated with eGFR (r² = 0.25, p = 0.007) regardless of sex, and SBP was an independent determinant of proteinuria (p = 0.004) and eGFR (p = 0.007).

CONCLUSIONS

The prevalence of biopsy-proven FN was 0.076%. Since SBP is associated with eGFR regardless of zygosity, strict SBP control might be necessary to prevent progression to end-stage kidney disease in both male and female patients with FN.

Gene Expression Analysis in gla-Mutant Zebrafish Reveals Enhanced Ca2+ Signaling Similar to Fabry Disease

Fabry disease (FD) is an X-linked inborn metabolic disorder due to partial or complete lysosomal α-galactosidase A deficiency. FD is characterized by progressive renal insufficiency and cardio- and cerebrovascular involvement. Restricted access on Gb3-independent tissue injury experimental models has limited the understanding of FD pathophysiology and delayed the development of new therapies. Accumulating glycosphingolipids, mainly Gb3 and lysoGb3, are Fabry specific markers used in clinical follow up. However, recent studies suggest there is a need for additional markers to monitor FD clinical course or response to treatment. We used a gla-knockout zebrafish (ZF) to investigate alternative biomarkers in Gb3-free-conditions. RNA sequencing was used to identify transcriptomic signatures in kidney tissues discriminating gla-mutant (M) from wild type (WT) ZF. Gene Ontology (GO) and KEGG pathways analysis showed upregulation of immune system activation and downregulation of oxidative phosphorylation pathways in kidneys from M ZF. In addition, upregulation of the Ca²⁺ signaling pathway was also detectable in M ZF kidneys. Importantly, disruption of mitochondrial and lysosome-related pathways observed in M ZF was validated by immunohistochemistry. Thus, this ZF model expands the pathophysiological understanding of FD, the Gb3-independent effects of gla mutations could be used to explore new therapeutic targets for FD.

Clinical relevance of globotriaosylceramide accumulation in Fabry disease and the effect of agalsidase beta in affected tissues

Fabry disease (FD) is a rare lysosomal storage disorder, characterized by a reduction in α-galactosidase A enzyme activity and the progressive accumulation of globotriaosylceramide (GL3) and its metabolites in the cells of various organs. Agalsidase beta, an enzyme replacement therapy (ERT), is approved for use in patients with FD in Europe, Canada, Australia, South America, and Asia, and is the only ERT approved for use in the United States. In this review, we discuss the clinical relevance of GL3 accumulation, the effect of agalsidase beta on GL3 in target tissues, and the association between treatment-related tissue GL3 clearance and long-term structure, function, or clinical outcomes. Accumulation of GL3 in the kidney, heart, vasculature, neurons, skin, gastrointestinal tract and auditory system correlates to cellular damage and irreversible organ damage, as a result of sclerosis, fibrosis, apoptosis, inflammation, and endothelial dysfunction. Damage leads to renal dysfunction and end-stage renal disease; myocardial hypertrophy with heart failure and arrhythmias; ischemic stroke; neuropathic pain; skin lesions; intestinal ischemia and dysmotility; and hearing loss. Treatment with agalsidase beta is effective in substantially clearing GL3 in a range of cells from the tissues affected by FD. Agalsidase beta has also been shown to slow renal decline and lower the overall risk of clinical progression, demonstrating an indirect link between treatment-related GL3 clearance and stabilization of FD.

Kidney and lipids: novel potential therapeutic targets for dyslipidemia in kidney disease?

INTRODUCTION

Altered lipid distribution and metabolism may lead to the development and/or progression of chronic kidney disease (CKD). Dyslipidemia is a major risk factor for CKD and increases the risk of cardiovascular events and mortality. Therefore, lipid-lowering treatments may decrease cardiovascular risk and prevent death.

AREAS COVERED

Key players involved in regulating lipid accumulation in the kidney; contribution of lipids to CKD progression, lipotoxicity, and mitochondrial dysfunction in kidney disease; recent therapeutic approaches for dyslipidemia.

EXPERT OPINION

The precise mechanisms for regulating lipid metabolism, particularly in kidney disease, are poorly understood. Guidelines for lipid-lowering therapy for CKD are controversial. Several hypolipemic therapies are available, but compared to others, statin therapy is the most common. No clinical trial has evaluated the efficacy of proprotein convertase subtilisin/kexin type 9 inhibitors (PCSK9i) in preventing cardiovascular events or improving kidney function among patients with CKD or kidney transplant recipients. Attractive alternatives, such as PCSK9-small interfering RNA (siRNA) molecules or evinacumab are available. Additionally, several promising agents, such as cyclodextrins and the FXR/TGR5 dual agonist, INT-767, can improve renal lipid metabolism disorders and delay CKD progression. Drugs targeting mitochondrial dysfunction could be an option for the treatment of dyslipidemia and lipotoxicity, particularly in renal diseases.

Improvement in Decline Rate of Estimated Glomerular Filtration Rate after Febuxostat Treatment in a Fabry Disease Patient with Enzyme Replacement Therapy-resistant Proteinuria

Fabry disease is an inherited lysosomal disorder caused by mutations in the alpha-galactosidase A gene. We herein report a Fabry disease patient with enzyme replacement therapy (ERT)-resistant proteinuria who showed improvement in the estimated glomerular filtration rate (eGFR) decline rate after uric acid (UA)-lowering therapy. The patient was diagnosed with Fabry disease at 36 years old. After that, even under ERT, proteinuria and eGFR decline persisted. During the clinical course, serum UA levels were elevated with increases in renal tubular damage markers. Febuxostat administration immediately improved tubular damage and prevented further eGFR decline. UA-mediated tubulopathy may become an additional therapeutic target for eGFR decline in Fabry disease.

Identification and functional characterization of the first deep intronic GLA mutation (IVS4+1326C>T) causing renal variant of Fabry disease

BACKGROUND

Fabry disease (FD, OMIM #301500) is an X-linked lysosomal disorder caused by the deficiency of α-galactosidase A (α-GalA), encoded by the GLA gene. Among more than 1100 reported GLA mutations, few were deep intronic mutations which have been linked to classic and cardiac variants of FD.

METHODS AND RESULTS

We report a novel hemizygous deep intronic GLA mutation (IVS4+1326C>T) in a 33-year-old Chinese man with a mild α-GalA deficiency phenotype involving isolated proteinuria and predominant globotriaosylceramide deposits in podocytes. IVS4+1326C>T, which appears to be the first deep intronic GLA mutation associated with renal variant of FD, was identified by Sanger sequencing the entire GLA genomic DNA sequence of the patient's peripheral mononuclear blood lymphocytes (PBMCs). Further sequencing of cDNA from PBMCs of the patient revealed a minor full-length GLA transcript accounting for about 25% of total GLA transcript, along with two major aberrantly spliced GLA transcripts encoding mutant forms of α-GalA with little enzyme activity characterized by in vitro α-GalA overexpression system in the HEK293T cells. Thus, the combined clinical phenotype, genetic analysis and functional studies verified the pathogenicity of IVS4+1326C>T.

CONCLUSIONS

The identification of IVS4+1326C>T establishes a link between deep intronic GLA mutation and the renal variant of FD, which extends the mutation spectrum in GLA gene and justifies further study of how IVS4+1326C>T and potentially other deep intronic GLA mutations contribute to Fabry podocytopathy through aberrant splicing. Future studies should also assess the true incidence of IVS4+1326C>T in patients with different variants of FD, which may improve early genetic diagnosis to allow timely treatment that can prevent disease progression and improve survival.

A novel unbiased method reveals progressive podocyte globotriaosylceramide accumulation and loss with age in females with Fabry Disease

While females can suffer serious complications of Fabry disease, most studies are limited to males to avoid confounding by mosaicism. Here, we developed a novel unbiased method for quantifying globotriaosylceramide (GL3) inclusion volume in affected podocytes (F+) in females with Fabry disease independent of mosaicism leading to important new observations. All podocytes in male patients with Fabry are F+. The probability of observing random profiles from F+ podocytes without GL3 inclusions (estimation error) was modeled from electron microscopic studies of 99 glomeruli from 40 treatment-naïve males and this model was applied to 28 treatment-naïve females. Also, podocyte structural parameters were compared in 16 age-matched treatment-naïve males and females with classic Fabry disease and 11 normal individuals. A 4^th degree polynomial equation best described the relationship between podocyte GL3 volume density and the estimation error (R² =0.94) and was confirmed by k-fold cross-validation. In females, this model showed that age related directly to F+ podocyte GL3 volume (correlation coefficient (r = 0.54) and podocyte volume (r = 0.48) and inversely to podocyte number density (r = -0.56), (all significant). F+ podocyte GL3 volume was significantly inversely related to podocyte number density (r = -0.79) and directly to proteinuria. There was no difference in F+ podocyte GL3 volume or volume fraction between age-matched males and females. Thus, in females with Fabry disease GL3 accumulation in F+ podocytes progresses with age in association with podocyte loss and proteinuria, and F+ podocyte GL3 accumulation in females with Fabry is similar to males, consistent with insignificant cross-correction between affected and non-affected podocytes. Hence, these findings have important pathophysiological and clinical implications.

Divergent Impact of Enzyme Replacement Therapy on Human Cardiomyocytes and Enterocytes Affected by Fabry Disease: Correlation with Mannose-6-phosphate Receptor Expression

Background: The impact of enzyme replacement therapy (ERT) on cardiomyocytes and intestinal cells, affected by Fabry disease (FD), is still unclear. Methods: Six patients with FD, including five family members with GLA mutation c.666delC and one with GLA mutation c.658C > T, manifesting cardiomyopathy and intestinal symptoms (abdominal pain, diarrhea and malabsorption) were included in the study. Clinical outcome, cardiac magnetic resonance (CMR), endomyocardial and gastro-intestinal biopsies were evaluated before and after 2 years of treatment with agalsidase-α (0.2 mg/kg every other week). Immunohistochemistry and Western blot assessments of mannose-6-phosphate receptors (IGF-II-R) on intestinal and myocardial frozen tissue were obtained at diagnosis and after 2 years of ERT. Results: After ERT left ventricular maximal wall thickness, ranging from pre (<10.5 mm) to mild (<15 mm) and moderate hypertrophy (16 mm), was not associated with significant changes at CMR. Degree of dyspnea, mean cardiomyocyte diameter and % vacuolated areas of cardiomyocytes, representing intracellular GL3, remained unmodified. In contrast, intestinal symptoms improved with disappearance of diarrhea, recovery of anemia and weight gain, correlating with near complete clearance of the enterocytes from GL3 inclusions. IGF-II-R expression was remarkably higher even at histochemistry in intestinal tissue compared with myocardium (p < 0.001) either at baseline and after ERT, thus justifying intestinal recovery. Conclusions: Human cells affected by FD may respond differently to ERT: while cardiomyocytes retain their GL3 content after 2 years of treatment, gastro-intestinal cells show GL3 removal with recovery of function. This divergent response may be related to differences in cellular turnover, as well as tissue IGF-II-R expression.

Brazilian consensus recommendations for the diagnosis, screening, and treatment of individuals with fabry disease: Committee for Rare Diseases - Brazilian Society of Nephrology/2021

Fabry disease (FD) is an X-linked inherited disorder caused by mutations in the GLA gene encoding enzyme alpha-galactosidase A (α-Gal A). The purpose of this study was to produce a consensus statement to standardize the recommendations concerning kidney involvement in FD and provide advice on the diagnosis, screening, and treatment of adult and pediatric patients. This consensus document was organized from an initiative led by the Committee for Rare Diseases (Comdora) of the Brazilian Society of Nephrology (SBN). The review considered randomized clinical trials, real-world data studies, and the expertise of its authors. The purpose of this consensus statement is to help manage patient and physician expectations concerning the outcomes of treatment. Our recommendations must be interpreted within the context of available evidence. The decisions pertaining to each individual case must be made with the involvement of patients and their families and take into account not only the potential cost of treatment, but also concurrent conditions and personal preferences. The Comdora intends to update these recommendations regularly so as to reflect recent literature evidence, real-world data, and appreciate the professional experience of those involved. This consensus document establishes clear criteria for the diagnosis of FD and for when to start or stop specific therapies or adjuvant measures, to thus advise the medical community and standardize clinical practice.

Podocyturia in Fabry disease: a 10-year follow-up

Background

Fabry disease (FD) is a rare X-linked disorder of sphingolipid metabolism that results in chronic proteinuric nephropathy. Podocytes are one of the most affected renal cells and play an important role in the development and progression of kidney disease. Detached podocytes found in urine (podocyturia) are considered as a non-invasive early marker of kidney injury; however, the dynamics of podocyte loss remains unknown.

Methods

In this 10-year follow-up study, podocyturia and other renal clinical data were evaluated in 39 patients with FD. From 2009 to 2019, podocyturia was assessed in 566 fresh urine samples from 13 male and 26 female FD patients using immunocytochemical detection of podocalyxin.

Results

Podocyturia (number of podocytes per 100 mL of urine) was found in 311/566 (54.9%) of the samples, more frequently (68.9 ± 21.9% versus 50.6 ± 25.9%; P = 0.035) and with higher values (364 ± 286 versus 182 ± 180 number of podocytes per gram of creatinine (Cr) in urine; P = 0.020) in males compared with females. The mean number of assessed samples for each patient was 14.5 (range 3–40) and the frequency of samples with podocyturia ranged from 0% to 100% (median 57%). Podocyturia was already present in 42.9% of patients <20 years of age and in 89.5% of normoalbuminuric patients. Podocyturia correlated with albuminuria (urine albumin:Cr ratio) (r = 0.20, P < 0.001) and a higher incidence and values of podocyturia were observed in patients with lower estimated glomerular filtration rate.

Conclusions

Our data demonstrated that podocyturia is an early clinical event in the development of nephropathy. In addition, we found podocyturia to be a discontinuous event with wide variability.

Early start of enzyme replacement therapy in pediatric male patients with classical Fabry disease is associated with attenuated disease progression

BACKGROUND

Enzyme replacement therapy (ERT) slows disease progression of Fabry disease (FD), especially when initiated before the onset of irreversible organ damage. However, with the clinically asymptomatic progression of renal, cardiac and cerebral disease manifestations spanning decades, optimal timing of ERT initiation remains unclear.

METHODS

In this cross-sectional retrospective study, seven male FD patients with a classical disease phenotype (cFD) who started treatment with agalsidase-beta in childhood were evaluated after 10 years of treatment (median age at evaluation 24 years, range 14-26). Cardiac imaging (echocardiography and MRI), electrophysiological and biochemical data of these patients were compared to those of untreated male cFD patients (n = 23, median age 22 years, range 13-27).

RESULTS

Albuminuria was less common and less severe in treated patients (albumin to creatinine ratio, ACR 0-8.8 mg/mmol, median 0.4) compared to untreated patients (ACR 0-248 mg/mmol, median 3.7, p = 0.02). The treated group had a lower left ventricular mass, measured using echocardiography (median 80 g/m² versus 94 g/m², p = 0.02) and MRI (median 53 g/m² versus 68 g/m², p = 0.02). Myocardial fibrosis was absent in all included patients. eGFR was normal in all treated patients whereas 7/23 (30%) of untreated patients had abnormal eGFR. Cerebral manifestations did not differ.

CONCLUSIONS

Start of treatment with ERT before age 16, in male cFD patients is associated with reduced occurrence of renal and cardiac manifestations of FD, as assessed by intermediate endpoints. Confirmation that this approach delays or even prevents renal failure and cardiac events requires another decade of follow-up.

Molecular Mechanisms of Kidney Injury and Repair

Chronic kidney disease (CKD) will become the fifth global cause of death by 2040, thus emphasizing the need to better understand the molecular mechanisms of damage and regeneration in the kidney. CKD predisposes to acute kidney injury (AKI) which, in turn, promotes CKD progression. This implies that CKD or the AKI-to-CKD transition are associated with dysfunctional kidney repair mechanisms. Current therapeutic options slow CKD progression but fail to treat or accelerate recovery from AKI and are unable to promote kidney regeneration. Unraveling the cellular and molecular mechanisms involved in kidney injury and repair, including the failure of this process, may provide novel biomarkers and therapeutic tools. We now review the contribution of different molecular and cellular events to the AKI-to-CKD transition, focusing on the role of macrophages in kidney injury, the different forms of regulated cell death and necroinflammation, cellular senescence and the senescence-associated secretory phenotype (SAPS), polyploidization, and podocyte injury and activation of parietal epithelial cells. Next, we discuss key contributors to repair of kidney injury and opportunities for their therapeutic manipulation, with a focus on resident renal progenitor cells, stem cells and their reparative secretome, certain macrophage subphenotypes within the M2 phenotype and senescent cell clearance.

Relapsing minimal change disease superimposed on late-onset p.N215S Fabry nephropathy

We present the case of a 76-year-old man with late-onset Fabry disease caused by the p.N215S missense mutation, with Fabry cardiomyopathy and nephropathy. In this case, the diagnosis of Fabry disease was incidental and followed minimal change disease (MCD) onset, with nephrotic syndrome and acute kidney injury requiring renal replacement therapy. Fabry nephropathy associated with the p.N215S mutation is becoming increasingly recognized among older patients. The importance of electron microscopy is herein highlighted and histological features common to Fabry nephropathy and MCD are discussed, along with the challenges associated with the diagnosis and clinical management.

Clinical Characteristics, Renal Involvement, and Therapeutic Options of Pediatric Patients With Fabry Disease

Inherited renal diseases represent 20% of the causes of end-stage renal diseases. Fabry disease, an X-linked lysosomal storage disorder, results from α-galactosidase A deficient or absent activity followed by globotriaosylceramide (Gb3) accumulation and multiorgan involvement. In Fabry disease, kidney involvement starts early, during intrauterine life by the Gb3 deposition. Even if chronic kidney disease (CKD) is discovered later in adult life in Fabry disease patients, a decline in glomerular filtration rate (GFR) can occur during adolescence. The first clinical sign of kidney involvement is represented by albuminuria. So, early and close monitoring of kidneys function is required: albuminuria and proteinuria, urinary albumin-to-creatinine ratio, serum creatinine, or cystatin C to estimate GFR, while urinary sediment with phase-contrast microscopy under polarized light may be useful in those cases where leucocyte α-Gal A activity and GLA genotyping are not available. Children with Fabry disease and kidney involvement should receive enzyme replacement therapy and nephroprotective drugs (angiotensin-converting enzyme inhibitors or angiotensin receptor blockers) to prevent or slow the progressive loss of kidney functions. Early diagnosis of Fabry disease is important as enzyme replacement therapy reduces symptoms, improves clinical features and biochemical markers, and the quality of life. More importantly, early treatment could slow or stop progressive organ damage in later life.

Fabry nephropathy before and after enzyme replacement therapy: important role of renal biopsy in patients with Fabry disease

Background

In Fabry disease, the presence of globotriaosylceramide (GL3) deposits in various kidney cells leads to progressive renal dysfunction. However, kidney biopsy studies in patients with Fabry disease are limited. In the present study, the pathologic findings of patients with Fabry nephropathy receiving enzyme replacement therapy (ERT) and untreated patients without albuminuria were investigated.

Methods

The present study included 15 patients with Fabry disease who underwent renal biopsy while receiving ERT (group 1: n = 9, age 19–58 years, two males and seven females) or before ERT initiation (group 2: n = 6, age 11–66 years, one male and five females). All patients in group 2 were normoalbuminuric.

Results

Group 1 showed improved clinical symptoms, such as acroparesthesia. The ERT duration was 1.2 to 8 years and seven of the nine patients showed GL3 deposits in various kidney cells and segmental foot process effacement (FPE) of podocytes. GL3 deposits and FPE were not observed in the two remaining patients in group 1. Group 2 showed segmental FPE and podocyte GL3 deposits. Most patients in group 2 also showed GL3 deposits in the mesangium, endothelium, or tubular epithelium.

Conclusion

The study results showed that segmental FPE and GL3 deposits can persist in Fabry nephropathy despite ERT. In addition, segmental FPE and GL3 deposits were observed in various kidney cells in normoalbuminuric patients with Fabry disease. These findings indicated that kidney biopsies at baseline and follow-up evaluation of Fabry nephropathy are essential for timely ERT initiation and ERT response assessment.

α-Galactosidase a Deficiency in Fabry Disease Leads to Extensive Dysregulated Cellular Signaling Pathways in Human Podocytes

Fabry disease (FD) is caused by mutations in the α-galactosidase A (GLA) gene encoding the lysosomal AGAL enzyme. Loss of enzymatic AGAL activity and cellular accumulation of sphingolipids (mainly globotriaosylcermide) may lead to podocyturia and renal loss of function with increased cardiovascular morbidity and mortality in affected patients. To identify dysregulated cellular pathways in FD, we established a stable AGAL-deficient podocyte cell line to perform a comprehensive proteome analysis. Imbalanced protein expression and function were analyzed in additional FD cell lines including endothelial, epithelial kidney, patient-derived urinary cells and kidney biopsies. AGAL-deficient podocytes showed dysregulated proteins involved in thermogenesis, lysosomal trafficking and function, metabolic activity, cell-cell interactions and cell cycle. Proteins associated with neurological diseases were upregulated in AGAL-deficient podocytes. Rescues with inducible AGAL expression only partially normalized protein expression. A disturbed protein expression was confirmed in endothelial, epithelial and patient-specific cells, pointing toward fundamental pathway disturbances rather than to cell type-specific alterations in FD. We conclude that a loss of AGAL function results in profound changes of cellular pathways, which are ubiquitously in different cell types. Due to these profound alterations, current approved FD-specific therapies may not be sufficient to completely reverse all dysregulated pathways.

Podocyte Foot Process Effacement Precedes Albuminuria and Glomerular Hypertrophy in CD2-Associated Protein Deficient Mice

Background: Podocyte foot process effacement is a key histologic finding in proteinuric kidney disease. We previously showed that 3-week old CD2AP-deficient mice have significant proteinuria, glomerular hypertrophy and mesangial expansion. The goal of this study is to use morphometry to establish the temporal sequence of podocyte foot process effacement, glomerular volume expansion and albuminuria in Cd2ap^−/− mice by measuring these parameters at the 2-week time point.

Methods: Wild-type mice age 14 ± 1 days with the Cd2ap gene (WT, N = 5) and mice deficient for Cd2ap (Cd2ap KO, N = 5) were generated. Kidneys were harvested and fixed in 2.5% glutaraldehyde and processed for examination by light and electron microscopy. An average of 415.2 (range 268–716) grid points were counted for all the glomeruli, and quantification of glomerular volume from each kidney. Urine was collected the day prior to sacrifice for urine albumin-to-creatinine ratio (ACR) measurements.

Results: There was no difference in albuminuria [median (range) mg/g] between WT [212.2 (177.6–388.4) mg/g] vs. Cd2ap KO mice [203.3 (164.7–910.2) mg/g], P = 0.89; or glomerular volume 68,307[10,931] vs. 66,844[13,022] μm³, p = 0.92. The volume densities of glomerular components of the podocyte, capillary lumen and mesangium were not different for the two groups, P = 0.14, 0.14 and 0.17 respectively. However, foot process width was increased in Cd2ap KO 1128[286] vs. WT [374 ± 42] nm, P = 0.02.

Conclusion: Here we show that while 2-week old WT and Cd2ap KO mice have similar levels of albuminuria, glomerular and mesangial volume, Cd2ap KO mice have more extensive podocyte foot process effacement. The data suggests that podocyte injury is the initiating event leading to mesangial expansion and albuminuria in this model.

Pathogenesis and Molecular Mechanisms of Anderson-Fabry Disease and Possible New Molecular Addressed Therapeutic Strategies

Anderson-Fabry disease (AFD) is a rare disease with an incidenceof approximately 1:117,000 male births. Lysosomal accumulation of globotriaosylceramide (Gb3) is the element characterizing Fabry disease due to a hereditary deficiency α-galactosidase A (GLA) enzyme. The accumulation of Gb3 causes lysosomal dysfunction that compromises cell signaling pathways. Deposition of sphingolipids occurs in the autonomic nervous system, dorsal root ganglia, kidney epithelial cells, vascular system cells, and myocardial cells, resulting in organ failure. This manuscript will review the molecular pathogenetic pathways involved in Anderson-Fabry disease and in its organ damage. Some studies reported that inhibition of mitochondrial function and energy metabolism plays a significant role in AFD cardiomyopathy and in kidney disease of AFD patients. Furthermore, mitochondrial dysfunction has been reported as linked to the dysregulation of the autophagy-lysosomal pathway which inhibits the mechanistic target of rapamycin kinase (mTOR) mediated control of mitochondrial metabolism in AFD cells. Cerebrovascular complications due to AFD are caused by cerebral micro vessel stenosis. These are caused by wall thickening resulting from the intramural accumulation of glycolipids, luminal occlusion or thrombosis. Other pathogenetic mechanisms involved in organ damage linked to Gb3 accumulation are endocytosis and lysosomal degradation of endothelial calcium-activated intermediate-conductance potassium ion channel 3.1 (KCa3.1) via a clathrin-dependent process. This process represents a crucial event in endothelial dysfunction. Several studies have identified the deacylated form of Gb3, globotriaosylsphingosine (Lyso-Gb3), as the main catabolite that increases in plasma and urine in patients with AFD. The mean concentrations of Gb3 in all organs and plasma of Galactosidase A knockout mice were significantly higher than those of wild-type mice. The distributions of Gb3 isoforms vary from organ to organ. Various Gb3 isoforms were observed mainly in the kidneys, and kidney-specific Gb3 isoforms were hydroxylated. Furthermore, the action of Gb3 on the KCa3.1 channel suggests a possible contribution of this interaction to the Fabry disease process, as this channel is expressed in various cells, including endothelial cells, fibroblasts, smooth muscle cells in proliferation, microglia, and lymphocytes. These molecular pathways could be considered a potential therapeutic target to correct the enzyme in addition to the traditional enzyme replacement therapies (ERT) or drug chaperone therapy.

A Case of a 49-Year-Old Man with Nonclassical Fabry Disease Diagnosed by Renal Biopsy

Fabry disease (FD) is a rare X-linked lysosomal storage disorder caused by mutations in the galactosidase A (GLA) gene that result in deficiency of α-GLA activity, leading to major organ failure and premature mortality. According to different disease courses, FD can be divided into classical and nonclassical phenotypes. The nonclassical FD phenotype is always absent of characteristic symptoms, which makes identifying it challenging. This article presents a 49-year-old man with a 10-year history of proteinuria and decreased glomerular filtration rate. An electrocardiogram showed a complete right bundle branch block and abnormal Q waves in high lateral, accompanied by dramatically elevated ST segment. Consequently, a renal biopsy was performed. Vacuolation was found in many podocytes in light microscopic examinations. Similarly, a myelin-like structure was detected by electron microscopy. Pathological findings were most consistent with FD. Consequently, genetic analysis, p.R301Q (c.902G>A [p.Arg301Gln]), confirmed the FD diagnosis. Angiotensin receptor blocker and traditional Chinese medicine, but not enzyme replacement therapy, were prescribed due to financial constraints. The patient had stabilization of kidney disease 6 months later. The case showed that renal biopsy should be performed in patients with cardiac and renal symptoms, which could contribute toward the correct diagnosis for nonclassical FD type.

Gene therapy for Fabry disease: Progress, challenges, and outlooks on gene-editing

Gene therapy is the delivery of a therapeutic gene for endogenous cellular expression with the goal of rescuing a disease phenotype. It has been used to treat an increasing number of human diseases with many strategies proving safe and efficacious in clinical trials. Gene delivery may be viral or non-viral, performed in vivo or ex vivo, and relies on gene integration or transient expression; all of these techniques have been applied to the treatment of Fabry disease. Fabry disease is a genetic disorder of the α-galactosidase A gene, GLA, that causes an accumulation of glycosphingolipids in cells leading to cardiac, renal and cerebrovascular damage and eventually death. Currently, there are no curative treatments available, and the therapies that are used have significant drawbacks. These treatment concerns have led to the advent of gene therapies for Fabry disease. The first Fabry patients to receive gene therapy were treated with recombinant lentivirus targeting their hematopoietic stem/progenitor cells. Adeno-associated virus treatments have also begun. Alternatively, the field of gene-editing is a new and rapidly growing field. Gene-editing has been used to repair disease-causing mutations or insert genes into cellular DNA. These techniques have the potential to be applied to the treatment of Fabry disease provided the concerns of gene-editing technology, such as safety and efficiency, were addressed. This review focuses on the current state of gene therapy as it is being developed for Fabry disease, including progresses and challenges as well as an overview of gene-editing and how it may be applied to correct Fabry disease-causing mutations in the future.

Long-term follow-up of renal function in patients treated with migalastat for Fabry disease

The effect of migalastat on long-term renal outcomes in enzyme replacement therapy (ERT)-naive and ERT-experienced patients with Fabry disease is not well defined. An integrated posthoc analysis of the phase 3 clinical trials and open-label extension studies was conducted to evaluate long-term changes in renal function in patients with Fabry disease and amenable GLA variants who were treated with migalastat for ≥2 years during these studies. The analysis included ERT-naive (n = 36 [23 females]; mean age 45 years; mean baseline estimated glomerular filtration rate (eGFR), 91.4 mL/min/mL/1.73 m²) and ERT-experienced (n = 42 [24 females]; mean age, 50 years; mean baseline eGFR, 89.2 mL/min/1.73m²) patients with amenable variants who received migalastat 123 mg every other day for ≥2 years. The annualized rate of change from baseline to last observation in estimated glomerular filtration rate using the Chronic Kidney Disease Epidemiology Collaboration equation (eGFR_CKD-EPI) was calculated by both simple linear regression and a random coefficient model. In ERT-naive patients, mean annualized rates of change from baseline in eGFR_CKD-EPI were - 1.6 mL/min/1.73 m² overall and - 1.8 mL/min/1.73 m² and - 1.4 mL/min/1.73 m² in male and female patients, respectively, as estimated by simple linear regression. In ERT-experienced patients, mean annualized rates of change from baseline in eGFR_CKD-EPI were - 1.6 mL/min/1.73 m² overall and - 2.6 mL/min/1.73 m² and - 0.8 mL/min/1.73 m² in male and female patients, respectively. Mean annualized rate of change in eGFR_CKD-EPI in ERT-naive patients with the classic phenotype (defined by white blood cell alpha galactosidase A [α-Gal A] activity of <3% of normal and multiorgan system involvement) was -1.7 mL/min/1.73 m². When calculated using the random coefficient model, which adjusted for sex, age, and baseline renal function, the annualized eGFR_CKD-EPI change was minimal (mean: -0.1 and 0.1 mL/min/1.73 m² in ERT-naive and ERT-experienced patients, respectively). In conclusion, patients with Fabry disease and amenable GLA variants receiving long-term migalastat treatment (≤8.6 years) maintained renal function irrespective of treatment status, sex, or phenotype.

Precision medicine in Fabry disease

Fabry disease (FD) is a rare X-linked lysosomal storage disorder caused by mutations in the α-galactosidase A (GLA) gene, leading to a deficiency in α-galactosidase A. The lysosomal accumulation of glycosphingolipids, primarily globotriaosylceramide (Gb3) and its deacylated form, globotriaosylsphingosine (lyso-Gb3), results in progressive renal failure, cardiomyopathy associated with cardiac arrhythmia and recurrent cerebrovascular events, significantly limiting life expectancy in affected patients. In male patients, a definitive diagnosis of FD involves demonstrating a GLA deficiency in leucocytes. In females, because of the potential high residual enzymatic activity, the diagnostic gold standard requires molecular genetic analyses. The current treatment options for FD include recombinant enzyme replacement therapies (ERTs) with intravenous agalsidase-α (0.2 mg/kg body weight) or agalsidase-β (1 mg/kg body weight) every 2 weeks as well as an oral pharmacological chaperone (migalastat 123 mg every other day) that selectively and reversibly binds to the active sites of amenable mutant forms of the GLA enzyme. These therapies facilitate cellular Gb3 clearance and an overall improvement of disease burden. However, ERT can lead to infusion-associated reactions, as well as the formation of neutralizing anti-drug antibodies in ∼40% of all ERT-treated males, leading to an attenuation of therapy efficacy. This article reviews the clinical presentation, diagnosis and interdisciplinary clinical management of FD and discusses the therapeutic options, with a special focus on precision medicine, accounting for individual variability in genetic mutations, Gb3 and lyso-Gb3 levels, allowing physicians to predict more accurately which prevention and treatment strategy is best for which patient.

Biomarkers in Fabry Disease. Implications for Clinical Diagnosis and Follow-up

Fabry disease (FD) is a lysosomal storage disorder caused by deficient alpha-galactosidase A activity in the lysosome due to mutations in the GLA gene, resulting in gradual accumulation of globotriaosylceramide and other derivatives in different tissues. Substrate accumulation promotes different pathogenic mechanisms in which several mediators could be implicated, inducing multiorgan lesions, mainly in the kidney, heart and nervous system, resulting in clinical manifestations of the disease. Enzyme replacement therapy was shown to delay disease progression, mainly if initiated early. However, a diagnosis in the early stages represents a clinical challenge, especially in patients with a non-classic phenotype, which prompts the search for biomarkers that help detect and predict the evolution of the disease. We have reviewed the mediators involved in different pathogenic mechanisms that were studied as potential biomarkers and can be easily incorporated into clinical practice. Some accumulation biomarkers seem to be useful to detect non-classic forms of the disease and could even improve diagnosis of female patients. The combination of such biomarkers with some response biomarkers, may be useful for early detection of organ injury. The incorporation of some biomarkers into clinical practice may increase the capacity of detection compared to that currently obtained with the established diagnostic markers and provide more information on the progression and prognosis of the disease.

Fabry disease-what cardiologists can learn from the nephrologist: a narrative review

Fabry disease (FD) is a rare, X-linked lysosomal storage disorder resulting in decreased or absent activity of the lysosomal enzyme alpha-galactosidase A. Subsequent accumulation of storage material can occur in virtually all cells of the body. Organs and structures affected by storage material deposition include the heart, the kidney, the central and peripheral nervous system and the cornea of the eyes. Progressive cardiac hypertrophy, arrhythmias, cardiac fibrosis, heart failure and cardiac death are common characteristics of cardiac involvement. Renal depositions of glycosphingolipids are already detectable in childhood. An early clinical sign of Fabry renal involvement is albuminuria, often preceding a detectable loss of kidney function. Later in life Fabry patients may exhibit a progressive decline of their kidney function leading to end-stage renal disease (ESRD). The clinical presentation of Fabry patients regarding renal involvement depends on the underlying mutation in the GLA gene. Classically affected males typically show a gradual decrease in kidney function, patients with mild or late onset mutations as well as a subgroup of females may exhibit only little or no renal abnormalities. This review summarizes the characteristics of renal involvement in FD, the diagnostics necessary to evaluate the degree of renal impairment and possible treatment options.

Pathology and pathogenic pathways in fabry nephropathy

BACKGROUND

The pathophysiology of renal damage in Fabry nephropathy involves a complex biological mechanism. The intracellular deposition globotriaosylceramide (Gb3) is just the first step of the mechanism. The glycolipid deposition occurs in all renal cells (endothelial, epithelial and mesangial cells). It stimulates many biological processes, including cytokine release, epithelial-mesenchymal transdifferentiation, oxidative stress and the remodelling of vascular walls, resulting in subtle initial inflammation and eventually tissue fibrosis. It has been hypothesized that the processes activated by Gb3 deposition can subsequently progress independently of cellular deposition and that even Gb3 clearance by specific therapy cannot retard or stop these pathways.

AIM

This review aims to gather the reported evidence of these cellular alterations and the resulting histological changes. Our approach is similar to a routine study of kidney biopsy.

RESULTS

In the first part of the review, "histology" section, we describe the structures involved (glomeruli, vessels, tubules and interstitium) from a histological point of view. While in the second part, "pathogenesis" section, we present some interpretations about the implicated pathways based on the up-to-date available evidence.

RIPK3 Contributes to Lyso-Gb3-Induced Podocyte Death

Fabry disease is a lysosomal storage disease with an X-linked heritage caused by absent or decreased activity of lysosomal enzymes named alpha-galactosidase A (α-gal A). Among the various manifestations of Fabry disease, Fabry nephropathy significantly affects patients' morbidity and mortality. The cellular mechanisms of kidney damage have not been elusively described. Necroptosis is one of the programmed necrotic cell death pathways and is known to play many important roles in kidney injury. We investigated whether RIPK3, a protein phosphokinase with an important role in necroptosis, played a crucial role in the pathogenesis of Fabry nephropathy both in vitro and in vivo. The cell viability of podocytes decreased after lyso-Gb3 treatment in a dose-dependent manner, with increasing RIPK3 expression. Increased reactive oxygen species (ROS) generation after lyso-Gb3 treatment, which was alleviated by GSK'872 (a RIPK3 inhibitor), suggested a role of oxidative stress via a RIPK3-dependent pathway. Cytoskeleton rearrangement induced by lyso-Gb3 was normalized by the RIPK3 inhibitor. When mice were injected with lyso-Gb3, increased urine albuminuria, decreased podocyte counts in the glomeruli, and effaced foot processes were observed. Our results showed that lyso-Gb3 initiated albuminuria, a clinical manifestation of Fabry nephropathy, by podocyte loss and subsequent foot process effacement. These findings suggest a novel pathway in Fabry nephropathy.

Renal Manifestations of Fabry Disease: A Narrative Review

Purpose of review

In this narrative review, we describe general aspects, histological alterations, treatment, and implications of Fabry disease (FD) nephropathy. This information should be used to guide physicians and patients in a shared decision-making process.

Source of information

Original peer-reviewed articles, review articles, and opinion pieces were identified from PubMed and Google Scholar databases. Only sources in English were accessed.

Methods

We performed a focused narrative review assessing the main aspects of FD nephropathy. The literature was critically analyzed from a theoretical and contextual perspective, and thematic analysis was performed.

Key findings

FD nephropathy is related to the progressive accumulation of GL3, which occurs in all types of renal cells. It is more prominent in podocytes, which seem to play an important role in the pathogenesis of this nephropathy. A precise detection of renal disorders is of fundamental importance because the specific treatment of FD is usually delayed, making reversibility unlikely and leading to a worse prognosis.

Limitations

As no formal tool was applied to assess the quality of the included studies, selection bias may have occurred. Nonetheless, we have attempted to provide a comprehensive review on the topic using current studies from experts in FD and extensive review of the literature.

Lysosome function in glomerular health and disease

The lysosome represents an important regulatory platform within numerous vesicle trafficking pathways including the endocytic, phagocytic, and autophagic pathways. Its ability to fuse with endosomes, phagosomes, and autophagosomes enables the lysosome to break down a wide range of both endogenous and exogenous cargo, including macromolecules, certain pathogens, and old or damaged organelles. Due to its center position in an intricate network of trafficking events, the lysosome has emerged as a central signaling node for sensing and orchestrating the cells metabolism and immune response, for inter-organelle and inter-cellular signaling and in membrane repair. This review highlights the current knowledge of general lysosome function and discusses these findings in their implication for renal glomerular cell types in health and disease including the involvement of glomerular cells in lysosomal storage diseases and the role of lysosomes in nongenetic glomerular injuries.

Biomarkers of Fabry Nephropathy: Review and Future Perspective

Progressive nephropathy is one of the main features of Fabry disease, which largely contributes to the overall morbidity and mortality burden of the disease. Due to the lack of specific biomarkers, the heterogeneity of the disease, and unspecific symptoms, diagnosis is often delayed. Clinical presentation in individual patients varies widely, even in patients from the same family carrying the same pathogenic GLA variant. Therefore, it is reasonable to anticipate that additional genomic, transcriptomic, proteomic, and metabolomics factors influence the manifestation and progression of the disease. The aim of this article is to provide an overview of nephropathy in Fabry patients and the biomarkers currently used in the diagnosis and follow-up. Current biomarkers are associated with late signs of kidney damage. Therefore, there is a need to identify biomarkers associated with early stages of kidney damage that would enable early diagnosis, which is crucial for effective treatment and prevention of severe irreversible complications. Recent advances in sequencing and -omics technologies have led to several studies investigating new biomarkers. We will provide an overview of the novel biomarkers, critically evaluate their clinical utility, and propose future perspectives, which we believe might be in their integration.

Parietal epithelial cell differentiation to a podocyte fate in the aged mouse kidney

Healthy aging is typified by a progressive and absolute loss of podocytes over the lifespan of animals and humans. To test the hypothesis that a subset of glomerular parietal epithelial cell (PEC) progenitors transition to a podocyte fate with aging, dual reporter PEC-rtTA|LC1|tdTomato|Nphs1-FLPo|FRT-EGFP mice were generated. PECs were inducibly labeled with a tdTomato reporter, and podocytes were constitutively labeled with an EGFP reporter. With advancing age (14 and 24 months) glomeruli in the juxta-medullary cortex (JMC) were more severely injured than those in the outer cortex (OC). In aged mice (24m), injured glomeruli with lower podocyte number (41% decrease), showed more PEC migration and differentiation to a podocyte fate than mildly injured or healthy glomeruli. PECs differentiated to a podocyte fate had ultrastructural features of podocytes and co-expressed the podocyte markers podocin, nephrin, p57 and VEGF164, but not markers of mesangial (Perlecan) or endothelial (ERG) cells. PECs differentiated to a podocyte fate did not express CD44, a marker of PEC activation. Taken together, we demonstrate that a subpopulation of PECs differentiate to a podocyte fate predominantly in injured glomeruli in mice of advanced age.

Podocytes: The Role of Lysosomes in the Development of Nephrotic Syndrome

This commentary highlights the article by Li et al that links ceramide accumulation in podocytes to cellular damage and nephrotic syndrome.