Pathomechanisms of renal Fabry disease

The role of podocyte injury in the pathogenesis of Fabry disease nephropathy

Renal involvement is one of the most severe morbidities of Fabry disease (FD), a multisystemic lysosomal storage disease with an X-linked inheritance pattern. It results from pathogenic variants in the GLA gene (Xq22.2), which encodes the production of alpha-galactosidase A (α-Gal), responsible for glycosphingolipid metabolism. Insufficient activity of this lysosomal enzyme generates deposits of unprocessed intermediate substrates, especially globotriaosylceramide (Gb3) and derivatives, triggering cellular injury and subsequently, multiple organ dysfunction, including chronic nephropathy. Kidney injury in FD is classically attributed to Gb3 deposits in renal cells, with podocytes being the main target of the pathological process, in which structural and functional alterations are established early and severely. This configures a typical hereditary metabolic podocytopathy, whose clinical manifestations are proteinuria and progressive renal failure. Although late clinical outcomes and morphological changes are well established in this nephropathy, the molecular mechanisms that trigger and accelerate podocyte injury have not yet been fully elucidated. Podocytes are highly specialized and differentiated cells that cover the outer surface of glomerular capillaries, playing a crucial role in preserving the structure and function of the glomerular filtration barrier. They are frequent targets of injury in many nephropathies. Furthermore, dysfunction and depletion of glomerular podocytes are essential events implicated in the pathogenesis of chronic kidney disease progression. We will review the biology of podocytes and their crucial role in regulating the glomerular filtration barrier, analyzing the main pathogenic pathways involved in podocyte injury, especially related to FD nephropathy.

The Effect of Fabry Disease Therapy on Bone Mineral Density

Fabry disease (FD) is an X-linked lysosomal storage disorder, characterised by the cellular accumulation of globotriaosylceramide due to impaired alpha-galactosidase A enzyme activity. FD may manifest with multisystem pathology, including reduced bone mineral density (BMD). Registry data suggest that the introduction of Fabry-specific therapies (enzyme replacement therapy or chaperone therapy) has led to significant improvements in overall patient outcomes; however, there are limited data on the impact on bone density. The aim of this study was to describe the effect of Fabry-specific therapies on longitudinal changes in bone mineral density (BMD) in FD. We performed a retrospective observational study analysing bone densitometry (DXA) in patients with genetically confirmed FD. Patients were grouped based on the use of Fabry-specific therapies. The between-group longitudinal change in BMD Z-score was analysed using linear mixed effects models. A total of 88 FD patients were analysed (50 untreated; 38 treated). The mean age at first DXA was 38.5 years in the untreated group (84% female) and 43.7 years in the treated group (34% female). There was no significant longitudinal between-group difference in the BMD Z-score at the lumbar spine. However, the Z-score per year at the total hip (β = -0.105, p < 0.001) and femoral neck (β = -0.081, p = 0.001) was significantly lower over time in the treated than the untreated group. This may reflect those receiving therapy having a more severe underlying disease. Nevertheless, this suggests that Fabry-specific therapies do not reverse all disease mechanisms and that the additional management of BMD may be required in this patient population.

Fabry Disease Nephropathy: Histological Changes With Nonclassical Mutations and Genetic Variants of Unknown Significance

RATIONALE & OBJECTIVE

Fabry disease (FD) is an X-linked genetic disorder that causes lysosomal storage of glycosphingolipids, primarily globotriaosylceramide (Gb3) and its derivative globotriaosylsphingosine (lyso-Gb3), with multiorgan dysfunction including chronic kidney disease. Affected individuals may be carriers of gene variants that are of uncertain significance (GVUS). We describe kidney pathology at the early stages of FD-related kidney disease to gain insights into its association with GVUS and sex.

STUDY DESIGN

Single-center, case series.

SETTING & PARTICIPANTS

Thirty-five consecutively biopsied patients (aged 48.1±15.4 years, 22 females) from among 64 patients with genetically diagnosed FD. Biopsies were retrospectively screened using the International Study Group of Fabry Nephropathy Scoring System.

OBSERVATIONS

Genetic mutation type, p.N215S and D313Y, sex, age, estimated glomerular filtration rate (eGFR), plasma lyso-Gb3 (pLyso-Gb3) levels, and histological parameters, including Gb3 deposits were recorded. Genetic analyses showed mostly missense mutations, p.N215S variant in 15, and the "benign polymorphism" D313Y in 4 of the biopsied patients. Morphological lesions were similar for men and women except for interstitial fibrosis and arteriolar hyalinosis being more common in men. Early in their clinical course, patients with normal/mild albuminuria had podocyte, tubular, and peritubular capillary vacuoles/inclusions, and evidence of chronicity, i.e., glomerulosclerosis, interstitial fibrosis, tubular atrophy. These findings appeared to be associated with pLyso-Gb3, eGFR, and age.

LIMITATIONS

Retrospective design and inclusion of outpatients partially based on family pedigree.

CONCLUSIONS

In early stages of kidney disease in the setting of FD, numerous histological abnormalities are present. These observations suggest that kidney biopsies early in FD may reveal activity of kidney involvement that may inform clinical management.

Systems analyses of the Fabry kidney transcriptome and its response to enzyme replacement therapy identified and cross-validated enzyme replacement therapy-resistant targets amenable to drug repurposing

Fabry disease is a rare disorder caused by variations in the alpha-galactosidase gene. To a degree, Fabry disease is manageable via enzyme replacement therapy (ERT). By understanding the molecular basis of Fabry nephropathy (FN) and ERT's long-term impact, here we aimed to provide a framework for selection of potential disease biomarkers and drug targets. We obtained biopsies from eight control individuals and two independent FN cohorts comprising 16 individuals taken prior to and after up to ten years of ERT, and performed RNAseq analysis. Combining pathway-centered analyses with network-science allowed computation of transcriptional landscapes from four nephron compartments and their integration with existing proteome and drug-target interactome data. Comparing these transcriptional landscapes revealed high inter-cohort heterogeneity. Kidney compartment transcriptional landscapes comprehensively reflected differences in FN cohort characteristics. With exception of a few aspects, in particular arteries, early ERT in patients with classical Fabry could lastingly revert FN gene expression patterns to closely match that of control individuals. Pathways nonetheless consistently altered in both FN cohorts pre-ERT were mostly in glomeruli and arteries and related to the same biological themes. While keratinization-related processes in glomeruli were sensitive to ERT, a majority of alterations, such as transporter activity and responses to stimuli, remained dysregulated or reemerged despite ERT. Inferring an ERT-resistant genetic module of expressed genes identified 69 drugs for potential repurposing matching the proteins encoded by 12 genes. Thus, we identified and cross-validated ERT-resistant gene product modules that, when leveraged with external data, allowed estimating their suitability as biomarkers to potentially track disease course or treatment efficacy and potential targets for adjunct pharmaceutical treatment.

Vitamin C Urinary Loss in Fabry Disease: Clinical and Genomic Characteristics of Vitamin C Renal Leak

BACKGROUND

Reduced plasma vitamin C concentrations in chronic diseases may result from abnormal urinary excretion of vitamin C: a renal leak. We hypothesized that vitamin C renal leak may be associated with disease-mediated renal dysregulation, resulting in aberrant vitamin C renal reabsorption and increased urinary loss.

OBJECTIVES

We investigated the prevalence, clinical characteristics, and genomic associations of vitamin C renal leak in Fabry disease, an X-linked lysosomal disease associated with renal tubular dysfunction and low plasma vitamin C concentrations.

METHODS

We conducted a non-randomized cross-sectional cohort study of men aged 24-42 y, with Fabry disease (n = 34) and controls without acute or chronic disease (n = 33). To match anticipated plasma vitamin C concentrations, controls were placed on a low-vitamin C diet 3 wk before inpatient admission. To determine the primary outcome of vitamin C renal leak prevalence, subjects were fasted overnight, and matched urine and fasting plasma vitamin C measurements were obtained the following morning. Vitamin C renal leak was defined as presence of urinary vitamin C at plasma concentrations below 38 μM. Exploratory outcomes assessed the association between renal leak and clinical parameters, and genomic associations with renal leak using single nucleotide polymorphisms (SNPs) in the vitamin C transporter SLC23A1.

RESULTS

Compared with controls, the Fabry cohort had 16-fold higher odds of renal leak (6% vs. 52%; OR: 16; 95% CI: 3.30, 162; P < 0.001). Renal leak was associated with higher protein creatinine ratio (P < 0.01) and lower hemoglobin (P = 0.002), but not estimated glomerular filtration rate (P = 0.54). Renal leak, but not plasma vitamin C, was associated with a nonsynonymous single nucleotide polymorphism in vitamin C transporter SLC23A1 (OR: 15; 95% CI: 1.6, 777; P = 0.01).

CONCLUSIONS

Increased prevalence of renal leak in adult men with Fabry disease may result from dysregulated vitamin C renal physiology and is associated with abnormal clinical outcomes and genomic variation.

Epidemiology of Fabry disease in patients in hemodialysis in the Madrid community

This study screened for Fabry disease (FD) in patients in hemodialysis (HD) in the region of Madrid (CAM) with a cross-sectional design to evaluate HD-prevalent patients, followed by a three-year period prospective design to analyze HD-incident patients.

INCLUSION CRITERIA

patients older than 18 years on HD in the CAM, excluding patients diagnosed with any other hereditary disease with renal involvement different from FD, that sign the Informed Consent (IC).

EXCLUSION CRITERIA

underaged patients or not agreeing or not being capable of signing the IC.

RESULTS

3470 patients were included, 63% males and with an average age of 67.9±9.7 years. 2357 were HD-prevalent patients and 1113 HD-incident patients. For HD-prevalent patients, average time in HD was 45.2 months (SD 51.3), in HD-incident patients proteinuria was present in 28.4%. There were no statistical differences in plasmatic alpha-galactosidase A (α-GAL-A) activity or Lyso-GL-3 values when comparing HD-prevalent and HD-incident populations and neither between males and females. A genetic study was performed in 87 patients (2.5% of patients): 60 male patients with decreased enzymatic activity and 27 female patients either with a decreased GLA activity, increased Lyso-Gl3 levels or both. The genetic variants identified were: p.Asp313Tyr (4 patients), p.Arg220Gln (3 patients) and M290I (1 patient). None of the identified variants is pathogenic.

CONCLUSIONS

76% of HD Centers of the CAM participated in the study. This is the first publication to describe the prevalence of FD in the HD-population of a region of Spain as well as its average α-GAL-A-activity and plasmatic Lyso-Gl3 levels. It is also the first study that combines a cross-sectional design with a prospective follow-up design. This study has not identified any FD patient.

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.

TRPML1-Induced Lysosomal Ca2+ Signals Activate AQP2 Translocation and Water Flux in Renal Collecting Duct Cells

Lysosomes are acidic Ca²⁺ storage organelles that actively generate local Ca²⁺ signaling events to regulate a plethora of cell functions. Here, we characterized lysosomal Ca²⁺ signals in mouse renal collecting duct (CD) cells and we assessed their putative role in aquaporin 2 (AQP2)-dependent water reabsorption. Bafilomycin A1 and ML-SA1 triggered similar Ca²⁺ oscillations, in the absence of extracellular Ca²⁺, by alkalizing the acidic lysosomal pH or activating the lysosomal cation channel mucolipin 1 (TRPML1), respectively. TRPML1-dependent Ca²⁺ signals were blocked either pharmacologically or by lysosomes' osmotic permeabilization, thus indicating these organelles as primary sources of Ca²⁺ release. Lysosome-induced Ca²⁺ oscillations were sustained by endoplasmic reticulum (ER) Ca²⁺ content, while bafilomycin A1 and ML-SA1 did not directly interfere with ER Ca²⁺ homeostasis per se. TRPML1 activation strongly increased AQP2 apical expression and depolymerized the actin cytoskeleton, thereby boosting water flux in response to an hypoosmotic stimulus. These effects were strictly dependent on the activation of the Ca²⁺/calcineurin pathway. Conversely, bafilomycin A1 led to perinuclear accumulation of AQP2 vesicles without affecting water permeability. Overall, lysosomal Ca²⁺ signaling events can be differently decoded to modulate Ca²⁺-dependent cellular functions related to the dock/fusion of AQP2-transporting vesicles in principal cells of the CD.

Early renal failure in childhood in a male with Fabry disease

Fabry disease is an X-linked lysosomal storage disorder caused by reduced activity or absence of the alpha-galactosidase A enzyme resulting in systemic accumulation of glycosphingolipids. End-stage renal disease (ESRD) is a late-stage manifestation of Fabry disease, typically presenting in the fifth decade of life, but is very rare in childhood. Here we present a case of an 11-year-old boy with classical Fabry disease presenting with ESRD requiring haemodialysis and transplant. Diagnosis was confirmed by renal biopsy, GLA mutation and low alpha-galactosidase A levels. He has an unusual genotype, hemizygous for the c.1000-11T>A intronic variant and positive for the pseudodeficiency allele D313Y. Due to the possibility of very early and accelerated disease progression, Fabry disease should be considered as a possible diagnosis in unexplained renal failure in males from a younger age.

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.

Multidisciplinary approach to screening and management of children with Fabry disease: practice at a Tertiary Children's Hospital in China

Background

Fabry disease (FD) remains poorly recognized, especially in children in China. Considering the diversity and nonspecific clinical manifestations accompanying with life-threatening aspect of this disease, methods to improve effective screening and management of the suspects are needed. This study aims to explore how it can be done effectively from a multidisciplinary perspective for children with FD at a tertiary children’s hospital in China.

Methods

A multidisciplinary team (MDT) of pediatric FD experts was launched at Children’s Hospital of Fudan University. Children with high-risk characteristics were referred by the MDT screening team using the dried blood spot (DBS) triple-test (α-galactosidase A, globotriaosylsphingosine, GLA gene). For newborns who were undergoing genetic testing in the hospital, the GLA gene was listed as a routine analysis gene. Evaluation, family screening, and genetic counselling were implemented after screening by the MDT management team.

Results

Before the establishment of the MDT, no case was diagnosed with FD in the hospital. However, twelve months following the MDT program's implementation, thirty-five children with high-risk profiles were referred for screening by DBS triple-test, with a yield of diagnosis of 14.3% (5/35). These 5 diagnosed children were referred due to a high-risk profile of pain accompanied by dermatological angiokeratoma and hypohidrosis (n = 2), pain accompanied by abnormal liver function (n = 1), pain only (n = 1), and unexplained renal tubular dysfunction (n = 1). Two neonates were detected early with GLA mutations in the hospital, with a yield of detection of 0.14% (2/1420). Furthermore, another 3 children diagnosed with FD were referred from other hospitals. Family screening of these 10 diagnosed children indicated that 9 boys inherited it from their mothers and 1 girl inherited it from her father. Four of them started to receive enzyme replacement therapy.

Conclusion

Screening and management of children with FD is effective based on a defined screening protocol and a multidisciplinary approach. We should pay more attention to the high-risk profiles of pain, angiokeratoma, decreased sweating, and unexplained chronic kidney disease in children.

Renal involvement in a patient with the chronic visceral subtype of acid sphingomyelinase deficiency resembles Fabry disease

Acid sphingomyelinase deficiency (ASMD) is a lysosomal storage disease (LSD) in which sphingomyelin accumulates due to deficient acid sphingomyelinase. In the chronic visceral subtype, organ manifestations are generally limited to the spleen, liver, and lungs. We report a male patient with the chronic visceral subtype who developed proteinuria and renal insufficiency at the age of 49. In renal tissue, foam cells were observed in the glomeruli as well as sphingomyelin accumulation within podocytes, mesangial cells, endothelial cells, and tubular epithelial cells. Although macrophages are the primary storage cells in both ASMD and Gaucher disease, comparison to the histopathological findings in Gaucher and Fabry disease revealed a diffuse storage pattern in multiple renal cell types, closer resembling the pattern found in Fabry disease.

Human kidney organoids reveal the role of glutathione in Fabry disease

Fabry disease is an X-linked lysosomal storage disease caused by a mutation in the galactosidase alpha (GLA) gene. Despite advances in therapeutic technologies, the lack of humanized experimental models of Fabry disease has limited the development of new therapies to cure the disease. Herein, we modeled Fabry disease using human inducible pluripotent stem cell (iPSC)-derived kidney organoids and the CRISPR-Cas9 genome-editing system. GLA-mutant human kidney organoids revealed deformed podocytes and tubular cells with accumulation of globotriaosylceramide (Gb3). Ultrastructural analysis showed abundant electron-dense granular deposits and electron-dense lamellate lipid-like deposits that formed concentric bodies (zebra bodies) in the cytoplasm of podocytes and tubules. The oxidative stress level was increased in GLA-mutant kidney organoids, and the increase was accompanied by apoptosis. Enzyme replacement treatment (ERT) with recombinant human α-Gal A decreased the Gb3 accumulation and oxidative stress, which resulted in amelioration of the deformed cellular structure of the GLA-mutant kidney organoids. Transcription profile analyses showed decreased glutathione (GSH) metabolism in GLA-mutant kidney organoids. GSH replacement treatment decreased oxidative stress and attenuated the structural deformity of the GLA-mutant kidney organoids. GSH treatment also increased the expression of podocyte and tubular markers and decreased apoptosis. In conclusion, GLA-mutant kidney organoids derived from human iPSCs are valuable tools for studying the mechanisms and developing novel therapeutic alternatives for Fabry disease.

Defective lysosomal storage in Fabry disease modifies mitochondrial structure, metabolism and turnover in renal epithelial cells

Fabry disease (FD) is an X-linked lysosomal storage disorder. Deficiency of the lysosomal enzyme alpha-galactosidase (GLA) leads to accumulation of potentially toxic globotriaosylceramide (Gb3) on a multisystem level. Cardiac and cerebrovascular abnormalities as well as progressive renal failure are severe, life-threatening long-term complications. The complete pathophysiology of chronic kidney disease (CKD) in FD and the role of tubular involvement for its progression are unclear. We established human renal tubular epithelial cell lines from the urine of male FD patients and male controls. The renal tubular system is rich in mitochondria and involved in transport processes at high-energy costs. Our studies revealed fragmented mitochondria with disrupted cristae structure in FD patient cells. Oxidative stress levels were elevated and oxidative phosphorylation was upregulated in FD pointing at enhanced energetic needs. Mitochondrial homeostasis and energy metabolism revealed major changes as evidenced by differences in mitochondrial number, energy production and fuel consumption. The changes were accompanied by activation of the autophagy machinery in FD. Sirtuin1, an important sensor of (renal) metabolic stress and modifier of different defense pathways, was highly expressed in FD. Our data show that lysosomal FD impairs mitochondrial function and results in severe disturbance of mitochondrial energy metabolism in renal cells. This insight on a tissue-specific level points to new therapeutic targets which might enhance treatment efficacy.

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.

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.

Stroke and Chronic Kidney Disease in Fabry Disease

Fabry disease is an X-linked lysosomal storage disorder caused by pathogenic variants in the GLA gene leading to a deficiency of the enzyme alpha-galactosidase A (α-Gal A). Multiple organ systems are implicated in Fabry disease, most severely the cardiac, kidney, and central nervous systems. In this brief review, we will focus on the kidney and central nervous system involvement.

Variables Associated with Glomerular Hyperfiltration in Fabry Disease Patients

Background: Fabry disease is a genetic disorder caused by the deficiency of the lysosomal α-galactosidase A enzyme. This failure generates the storage of globotriaosylceramide in different cells with a progressive multi-organ involvement. Objectives: To report the prevalence of glomerular hyperfiltration in Fabry disease patients and the association with clinical variables. Methods: Adult patients (≥ 18 years) at the moment of FD diagnosis were evaluated. The variables studied were: central and peripheral nervous system compromise, presence of arterial hypertension, cardiac arrhythmia, left ventricular hypertrophy, albuminuria/proteinuria, cornea verticillata, gastrointestinal involvement, treatment with inhibitors of the renin-angiotensin-aldosterone system, deafness, and presence of angiokeratomas. Results: Forty-eight adults with Fabry disease (35.9 ± 11.7 years), 28 women (58.3%), and 20 men (41.7%) were analyzed. Nine (18.8%) patients with glomerular hyperfiltration, including six females and three males (mean age: 28.8 years), were detected. A significant association between and central nervous system (P = 0.021) and peripheral nervous system (P = 0.001) compromise, cardiac arrhythmia (P = 0.001), cornea verticillata (P = 0.009), and gastrointestinal involvement (P = 0.009) was observed. However, no association was found between glomerular hyperfiltration and proteinuria or treatment with inhibitors of the renin-angiotensin-aldosterone system. Conclusions: This research showed a higher prevalence of glomerular hyperfiltration in the younger group and a significant association between glomerular hyperfiltration and some typical manifestations of classic Fabry patients. Although more studies are needed, it is concluded that other mechanisms than glomerular hyperfiltration, like injury by glycosphingolipids deposit into the filtration barrier, might influence the protein loss in Fabry nephropathy.

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

BACKGROUND

In males with classic Fabry disease, the processes leading to the frequent outcome of ESKD are poorly understood. Defects in the gene encoding α-galactosidase A lead to accumulation of globotriaosylceramide (GL3) in various cell types. In the glomerular podocytes, accumulation of GL3 progresses with age. Of concern, podocytes are relatively resistant to enzyme replacement therapy and are poorly replicating, with little ability to compensate for cell loss.

METHODS

In this study of 55 males (mean age 27 years) with classic Fabry disease genotype and/or phenotype, we performed unbiased quantitative morphometric electron microscopic studies of biopsied kidney samples from patients and seven living transplant donors (to serve as controls). We extracted clinical information from medical records and clinical trial databases.

RESULTS

Podocyte GL3 volume fraction (proportion of podocyte cytoplasm occupied by GL3) increased with age up to about age 27, suggesting that increasing podocyte GL3 volume fraction beyond a threshold may compromise survival of these cells. GL3 accumulation was associated with podocyte injury and loss, as evidenced by increased foot process width (a generally accepted structural marker of podocyte stress and injury) and with decreased podocyte number density per glomerular volume. Worsening podocyte structural parameters (increasing podocyte GL3 volume fraction and foot process width) was also associated with increasing urinary protein excretion-a strong prognosticator of adverse renal outcomes in Fabry disease-as well as with decreasing GFR.

CONCLUSIONS

Given the known association between podocyte loss and irreversible FSGS and global glomerulosclerosis, this study points to an important role for podocyte injury and loss in the progression of Fabry nephropathy and indicates a need for therapeutic intervention before critical podocyte loss occurs.

Multiple phenotypic domains of Fabry disease and their relevance for establishing genotype- phenotype correlations

Fabry disease (FD) is a rare X-linked glycosphingolipidosis resulting from deficient α-galactosidase A (AGAL) activity, caused by pathogenic mutations in the GLA gene. In males, the multisystemic involvement and the severity of tissue injury are critically dependent on the level of AGAL residual enzyme activity (REA) and on the metabolic load of the disease, but organ susceptibility to damage varies widely, with heart appearing as the most vulnerable to storage pathology, even with relatively high REA. The expression of FD can be conceived as a multidomain phenotype, where each of the component domains is the laboratory or clinical expression of the causative GLA mutation along a complex pathophysiologic cascade pathway. The AGAL enzyme activity is the most clinically useful marker of the protein phenotype. The metabolic phenotype and the pathologic phenotype are diverse expressions of the storage pathology, respectively, assessed by biochemical and histological/ultrastructural methods. The storage phenotypes are the direct consequences of enzyme deficiency and hence, together with the enzymatic phenotype, constitute the more specific diagnostic markers of FD. In the pathophysiology cascade, the clinical phenotypes are most distantly linked to the underlying genetic causation, being critically influenced by the patients’ gender and age, and modulated by the effects of variation in other genetic loci, of polygenic inheritance and of environmental risk factors. A major challenge in the clinical phenotyping of patients with FD is the differential diagnosis between its nonspecific, later-onset complications, particularly the cerebrovascular, cardiac and renal, and similar chronic illnesses that are common in the general population. Comprehensive phenotyping, whenever possible performed in hemizygous males, is therefore crucial for grading the severity of pathogenic GLA variants, to clarify the phenotypic correlations of hypomorphic alleles, to define benign polymorphisms, as well as to establish the pathogenicity of variants of uncertain significance.

Early decrease in the podocalyxin to synaptopodin ratio in urinary Fabry podocytes

Background

In Fabry nephropathy, podocyturia is an early event that may lead to glomerulosclerosis and chronic kidney disease. The glycocalyx is a potential podocyte damaged compartment in glomerulopathies. We investigated glycocalyx podocalyxin in urinary detached podocytes compared with cytoplasmic synaptopodin.

Methods

This was a cross-sectional study including 68 individuals: Controls (n = 20) and Fabry patients (n = 48), 15 untreated and 33 treated. Variables included age, gender, urinary protein/creatinine ratio (UPCR), estimated glomerular filtration rate (eGFR), lyso-triasocylsphingosine (lyso-Gb3) levels and enzyme replacement therapy (ERT). Podocyturia was assessed by immunofluorescence and podocyte subpopulations were analyzed.

Results

Fabry patients displayed higher podocyturia than controls. Fabry treated subjects (n = 33) presented significantly higher UPCR compared with untreated ones (n = 15); podocyturia, eGFR and lyso-Gb3 levels were not different. All control podocytes colocalized synaptopodin and podocalyxin; 13 Fabry patients (27%) colocalized these proteins, while 35 (73%) were only synaptopodin positive. No podocalyxin-positive/synaptopodin-negative cells were encountered. In Fabry patients, podocyturia was significantly higher and proteinuria lower in those that colocalized.

Conclusion

Fabry patients present higher podocyturia and a presumably more damaged glycocalyx assessed by podocalyxin. Treated patients had significant higher proteinuria suggesting ERT is initiated late, at advanced stages. The degree of podocalyxin-negative podocytes was similar in both groups, but colocalization was associated with lower proteinuria. Podocyturia assessed by podocalyxin alone may be underestimated. The implications of podocyte glycocalyx damage deserve further investigations.