Pathology and pathogenic pathways in fabry nephropathy

Identification of a novel nonsense mutation in α-galactosidase A that causes Fabry disease in a Chinese family

Fabry disease, a lysosomal storage disease, is an uncommon X-linked recessive genetic disorder stemming from abnormalities in the alpha-galactosidase gene (GLA) that codes human alpha-Galactosidase A (α-Gal A). To date, over 800 GLA mutations have been found to cause Fabry disease (FD). Continued enhancement of the GLA mutation spectrum will contribute to a deeper recognition and underlying mechanisms of FD. In this study, a 27-year-old male proband exhibited a typical phenotype of Fabry disease. Subsequently, family screening for Fabry disease was conducted, and high-throughput sequencing was employed to identify the mutated gene. The three-level structure of the mutated protein was analyzed, and its subcellular localization and enzymatic activity were determined. Apoptosis was assessed in GLA mutant cell lines to confirm the functional effects. As a result, a new mutation, c.777_778del (p. Gly261Leufs*3), in the GLA gene was identified. The mutation caused a frameshift during translation and the premature appearance of a termination codon, which led to a partial deletion of the domain in C-terminal region and altered the protein's tertiary structure. In vitro experiments revealed a significant reduction of the enzymatic activity in mutant cells. The expression was noticeably decreased at the mRNA and protein levels in mutant cell lines. Additionally, the subcellular localization of α-Gal A changed from a homogeneous distribution to punctate aggregation in the cytoplasm. GLA mutant cells exhibited significantly higher levels of apoptosis compared to wild-type cells.

Developing gene therapy for mitigating multisystemic pathology in Fabry disease: proof of concept in an aggravated mouse model

Fabry disease (FD) is a multi-systemic lysosomal storage disorder caused by the loss of α-galactosidase A (α-Gal) function. The current standard of care, enzyme replacement therapies (ERTs), while effective in reducing kidney pathology when treated early, do not fully ameliorate cardiac issues, neuropathic manifestations, and risk of cerebrovascular events. AAV-based gene therapies (AAV-GT) can provide superior efficacy across multiple tissues owing to continuous, endogenous production of the therapeutic enzyme and lower treatment burden. We set out to develop a robust AAV-GT to achieve optimal efficacy with the lowest feasible dose to minimize any safety risks that are associated with high dose AAV-GTs. In this proof-of-concept study we evaluated the effectiveness of an rAAV9 vector expressing human GLA transgene under a strong ubiquitous promoter, combined with Woodchuck hepatitis virus Posttranscriptional Regulatory Element (WPRE) (rAAV9-hGLA). We tested our GT at three different doses, 5e10 vg/kg, 2.5e11 vg/kg, and 6.25e12 vg/kg in the G3Stg/GLAko Fabry mouse model that has tissue Gb3 substrate levels comparable to FD patients and develops several early FD pathologies. After intravenous injections of rAAV9-hGLA at 11 weeks of age, we observed dose-dependent increases in α-Gal activity in the key target tissues, reaching as high as 393-fold of WT in the kidneys and 6156-fold in the heart at the highest dose. Complete or near complete substrate clearance was observed in animals treated with the two higher dose levels tested in all tissues except for the brain. We also found dose-dependent improvements in several pathological biomarkers, as well as prevention of structural and functional organ pathology. Taken together, these results indicate that an AAV-GT under a strong ubiquitous promoter has the potential to address the unmet therapeutic needs in FD patients at relatively low doses.

Inflammation in Fabry disease: stages, molecular pathways, and therapeutic implications

Fabry disease, a multisystem X-linked disorder caused by mutations in the alpha-galactosidase gene. This leads to the accumulation of globotriaosylceramide (Gb3) and globotriaosylsphingosine (Lyso-Gb3), culminating in various clinical signs and symptoms that significantly impact quality of life. Although treatments such as enzyme replacement, oral chaperone, and emerging therapies like gene therapy exist; delayed diagnosis often curtails their effectiveness. Our review highlights the importance of delineating the stages of inflammation in Fabry disease to enhance the timing and efficacy of diagnosis and interventions, particularly before the progression to fibrosis, where treatment options are less effective. Inflammation is emerging as an important aspect of the pathogenesis of Fabry disease. This is thought to be predominantly mediated by the innate immune response, with growing evidence pointing towards the potential involvement of adaptive immune mechanisms that remain poorly understood. Highlighted by the fact that Fabry disease shares immune profiles with systemic autoinflammatory diseases, blurring the distinctions between these disorders and highlighting the need for a nuanced understanding of immune dynamics. This insight is crucial for developing targeted therapies and improving the administration of current treatments like enzyme replacement. Moreover, our review discusses the complex interplay between these inflammatory processes and current treatments, such as the challenges posed by anti-drug antibodies. These antibodies can attenuate the effectiveness of therapies, necessitating more refined approaches to mitigate their impact. By advancing our understanding of the molecular changes, inflammatory mediators and causative factors that drive inflammation in Fabry disease, we aim to clarify their role in the disease's progression. This improved understanding will help us see how these processes fit into the current landscape of Fabry disease. Additionally, it will guide the development of more effective diagnostic and therapeutic approaches, ultimately improving patient care.

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

Focal segmental glomerulosclerosis (FSGS) is a complex disease which describes different kinds of kidney defects, not exclusively linked with podocyte defects. Since nephrin mutation was first described in association with early-onset nephrotic syndrome (NS), many advancements have been made in understanding genetic patterns associated with FSGS. New genetic causes of FSGS have been discovered, displaying unexpected genotypes, and recognizing possible site of damage. Many recent large-scale sequencing analyses on patients affected by idiopathic chronic kidney disease (CKD), kidney failure (KF) of unknown origin, or classified as FSGS, have revealed collagen alpha IV genes, as one of the most frequent sites of pathogenic mutations. Also, recent interest in complex and systemic lysosomal storage diseases, such as Fabry disease, has highlighted GLA mutations as possible causes of FSGS. Tubulointerstitial disease, recently classified by KDIGO based on genetic subtypes, when associated with UMOD variants, may phenotypically gain FSGS features, as well as ciliopathy genes or others, otherwise leading to completely different phenotypes, but found carrying pathogenic variants with associated FSGS phenotype. Thus, glomerulosclerosis may conceal different heterogeneous conditions. When a kidney biopsy is performed, the principal objective is to provide an accurate diagnosis. The broad spectrum of phenotypic expression and genetic complexity is demonstrating that a combined path of management needs to be applied. Genetic investigation should not be reserved only to selected cases, but rather part of medical management, integrating with clinical and renal pathology records. FSGS heterogeneity should be interpreted as an interesting opportunity to discover new pathways of CKD, requiring prompt genotype-phenotype correlation. In this review, we aim to highlight how FSGS represents a peculiar kidney condition, demanding multidisciplinary management, and in which genetic analysis may solve some otherwise unrevealed idiopathic cases. Unfortunately there is not a uniform correlation between specific mutations and FSGS morphological classes, as the same variants may be identified in familial cases or sporadic FSGS/NS or manifest a variable spectrum of the same disease. These non-specific features make diagnosis challenging. The complexity of FSGS genotypes requires new directions. Old morphological classification does not provide much information about the responsible cause of disease and misdiagnoses may expose patients to immunosuppressive therapy side effects, mistaken genetic counseling, and misguided kidney transplant programs.

Fabry disease: a rare disorder calling for personalized medicine

Fabry Disease (FD) is a genetic disease caused by a deficiency in the activity of lysosomal galactosidase A (α-GalA), an enzyme responsible for the catabolism of globotriaosylceramide (Gb3). Since lysosomes are present throughout the body and play a crucial role in catabolism and recycling of cytosolic compounds, FD can affect multiple organs and result in various symptoms, including renal, cardiovascular, neurological, cutaneous, and ophthalmic manifestations. Due to the nonspecific symptoms and the rarity of FD, it is often diagnosed late in life. However, introducing targeted therapies such as enzyme replacement therapy (ERT) and chaperone therapy has significantly improved FD's natural history and prognosis by restoring α-GalA enzyme activity. Despite the advancements, there are limitations to the currently available therapies, which has prompted research into new potential treatments for FD, including alternative forms of enzyme replacement therapy, substrate reduction therapy, mRNA therapy, and genetic therapy. In this review, we analyze the epidemiology, pathophysiology, and treatment of FD, with particular emphasis on promising therapeutic opportunities that could shift the treatment of this rare disease from a standardized to a personalized approach soon.

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.

Updated Evaluation of Agalsidase Alfa Enzyme Replacement Therapy for Patients with Fabry Disease: Insights from Real-World Data

The clinical use of agalsidase alfa as enzyme replacement therapy (ERT) for Fabry disease (FD) has spread since 2001, and a large body of evidence of its effectiveness has been collected. This review presents the clinical and laboratory results achieved with agalsidase alfa, which has been published in the literature. Agalsidase alfa infusion slows down or stops the progression of renal damage, expressed by reduction or stabilization of the annual decline of the glomerular filtration rate; yearly decrease of glomerular filtration rate (slope) sometimes is reduced until its stabilization. ERT prevents or reduces the occurrence of hypertrophic cardiomyopathy or slows the increase over time if it is already present. Moreover, regarding neurological manifestations, ERT improves neuropathic pain and quality of life, and recent data indicated that it may also prevent the burden of cerebrovascular disease. In addition to ERT's clinical benefits, crucial topics like the most appropriate time to start therapy and the role of anti-drug antibodies (ADA) are analyzed. Treatment with agalsidase alfa in patients with FD substantially improves their outcomes and enhances their quality of life in patients with FD.

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.

Complement activation and cellular inflammation in Fabry disease patients despite enzyme replacement therapy

Defective α-galactosidase A (AGAL/GLA) due to missense or nonsense mutations in the GLA gene results in accumulation of the glycosphingolipids globotriaosylceramide (Gb3) and its deacylated derivate globotriaosylsphingosine (lyso-Gb3) in cells and body fluids. The aberrant glycosphingolipid metabolism leads to a progressive lysosomal storage disorder, i. e. Fabry disease (FD), characterized by chronic inflammation leading to multiorgan damage. Enzyme replacement therapy (ERT) with agalsidase-alfa or -beta is one of the main treatment options facilitating cellular Gb3 clearance. Proteome studies have shown changes in complement proteins during ERT. However, the direct activation of the complement system during FD has not been explored. Here, we demonstrate strong activation of the complement system in 17 classical male FD patients with either missense or nonsense mutations before and after ERT as evidenced by high C3a and C5a serum levels. In contrast to the strong reduction of lyso-Gb3 under ERT, C3a and C5a markedly increased in FD patients with nonsense mutations, most of whom developed anti-drug antibodies (ADA), whereas FD patients with missense mutations, which were ADA-negative, showed heterogenous C3a and C5a serum levels under treatment. In addition to the complement activation, we found increased IL-6, IL-10 and TGF-ß1 serum levels in FD patients. This increase was most prominent in patients with missense mutations under ERT, most of whom developed mild nephropathy with decreased estimated glomerular filtration rate. Together, our findings demonstrate strong complement activation in FD independent of ERT therapy, especially in males with nonsense mutations and the development of ADAs. In addition, our data suggest kidney cell-associated production of cytokines, which have a strong potential to drive renal damage. Thus, chronic inflammation as a driver of organ damage in FD seems to proceed despite ERT and may prove useful as a target to cope with progressive organ damage.

Interpretation of GFR slope in untreated and treated adult Fabry patients

Nephropathy is one of the main features of Fabry disease (FD) that leads, in untreated patients with classical mutations, to end-stage renal disease (ESRD) from the third to the fifth decade of life. The availability of a specific treatment modified the natural history of FD; in particular, it was widely reported that enzyme replacement therapy (ERT) is able to slow the progression of the disease. Regarding Fabry nephropathy, several reports have documented an elevated estimated glomerular filtration rate (eGFR) slope in untreated patients as expression of a rapid disease progression towards ESRD. Otherwise, the prompt start of treatment may be beneficial in stabilizing renal function or slowing its decline. Therefore, based on data in the literature about the effects of ERT on eGFR decline and on the evidence supporting the role of eGFR slope as a surrogate endpoint for chronic kidney disease progression, we suggest, in this 'Expert Opinion', that a treatment should be defined effective when eGFR decline is <1 ml/min/1.73 m2/year and not effective when eGFR loss remains ≥3 ml/min/1.73 m2/year (≥2.5 ml/min/1.73 m2/year in females). Moreover, practical clinical recommendations and guidance for Fabry patients suggests that a change in treatment may be appropriate if individualized therapeutic goals are not achieved. Since a dose-dependent efficacy has been demonstrated for ERT, we suggest considering a switch to a higher dose of ERT in symptomatic adult Fabry patients (ages 18-60 years) with an eGFR of 45-90 ml/min/1.73 m2 and treated with a stable dose of ERT for at least 1 year, in which a linear negative slope of eGFR of 3 ml/min/1.73 m2/year for males (2.5 ml/min/1.73 m2/year for females) was observed.

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.

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.

High-risk screening for Fabry disease in hemodialysis patients in Chiba Prefecture, Japan

BACKGROUND

High-risk screening for Fabry disease in dialysis patients is an effective means for reducing the number of undiagnosed cases. However, such screening has not been conducted in Chiba Prefecture, Japan. Herein, we aimed to estimate the prevalence of Fabry disease among patients undergoing hemodialysis in Chiba Prefecture by high-risk screening using α-galactosidase A (αGal A) activity measurement, and examine the hemodialysis effect on αGal A activity.

METHODS

Patients who underwent maintenance hemodialysis at 25 facilities in Chiba Prefecture were recruited. The αGal A activity was measured using the dried blood spot (DBS) test as the first screening. If the enzyme activity was lower than the cut-off, the second screening was performed with the same method before and after dialysis.

RESULTS

Overall, 2924 patients (2036 men and 888 women) were included from which 94 cases (45 men and 48 women) showed decreased αGAL activity in the first screening and 3 (two men and one women) in the second screening. Genetic testing was performed in 3 patients, and the c.1078G > A mutation in GLA gene was detected in one male patient (0.03%). There has been a statistically significant decrease in αGal A activity of DBS at post-dialysis compared to that at pre-dialysis (20.5 ± 10.4 pmol/h/disk and 22.7 ± 11.5 pmol/h/disk, p < 0.0001).

CONCLUSION

The prevalence of Fabry disease among patients undergoing hemodialysis in Chiba Prefecture was estimated as 0.03%. This is the first time that dialysis has been shown to affect the αGal A activity.

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.

Unexpectedly high renal pathological scores of two female siblings with Fabry disease presenting with urinary mulberry cells without microalbuminuria

We describe the cases of 47- and 45-year-old sisters who were diagnosed with Fabry disease by genomic analysis. Although the only abnormal finding was the presence of mulberry cells in their urinary sediment, the renal pathological scores, which were evaluated by light and electron microscopy, were unexpectedly very high due to severe accumulation of globotriaosylceramide in the glomerular podocytes and tubular epithelial cells. Nephrologists and laboratory technicians should recognize the importance of screening for mulberry cells during urinalysis as this is a simple, inexpensive, and non-invasive method for early diagnosis, leading to early treatment of Fabry disease.