Impact of immunosuppressive therapy on therapy-neutralizing antibodies in transplanted patients with Fabry disease

Anderson-Fabry disease management: role of the cardiologist

Anderson-Fabry disease (AFD) is a lysosomal storage disorder characterized by glycolipid accumulation in cardiac cells, associated with a peculiar form of hypertrophic cardiomyopathy (HCM). Up to 1% of patients with a diagnosis of HCM indeed have AFD. With the availability of targeted therapies for sarcomeric HCM and its genocopies, a timely differential diagnosis is essential. Specifically, the therapeutic landscape for AFD is rapidly evolving and offers increasingly effective, disease-modifying treatment options. However, diagnosing AFD may be difficult, particularly in the non-classic phenotype with prominent or isolated cardiac involvement and no systemic red flags. For many AFD patients, the clinical journey from initial clinical manifestations to diagnosis and appropriate treatment remains challenging, due to late recognition or utter neglect. Consequently, late initiation of treatment results in an exacerbation of cardiac involvement, representing the main cause of morbidity and mortality, irrespective of gender. Optimal management of AFD patients requires a dedicated multidisciplinary team, in which the cardiologist plays a decisive role, ranging from the differential diagnosis to the prevention of complications and the evaluation of timing for disease-specific therapies. The present review aims to redefine the role of cardiologists across the main decision nodes in contemporary AFD clinical care and drug discovery.

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.

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.

Outcomes and management of kidney transplant recipients with Fabry disease: a review

Fabry disease is an X-linked inheritable lysosomal storage disease caused by various mutations of the galactosidase α gene resulting in α-galactosidase deficiency. Chronic kidney disease (CKD) is one of the most significant consequences of Fabry disease, with risk of end-stage kidney disease (ESKD) in this population. Like for other patients with ESKD, kidney transplant is the optimal treatment for Fabry disease patients with ESKD. However, enzyme replacement therapy and newer Fabry disease treatments remain important to mitigate other end organ damage such as cardiomyopathy post transplantation. This review is a primer on Fabry disease, which examines the outcomes of disease in the context of kidney transplant prior to, and during, the enzyme replacement treatment era, medical treatment of kidney transplant recipients with Fabry disease, and progress in screening studies.

High-Dose ERT, Rituximab, and Early HSCT in an Infant with Wolman's Disease

Wolman's disease, a severe form of lysosomal acid lipase deficiency, leads to pathologic lipid accumulation in the liver and gut that, without treatment, is fatal in infancy. Although continued enzyme-replacement therapy (ERT) in combination with dietary fat restriction prolongs life, its therapeutic effect may wane over time. Allogeneic hematopoietic stem-cell transplantation (HSCT) offers a more definitive solution but carries a high risk of death. Here we describe an infant with Wolman's disease who received high-dose ERT, together with dietary fat restriction and rituximab-based B-cell depletion, as a bridge to early HSCT. At 32 months, the infant was independent of ERT and disease-free, with 100% donor chimerism in the peripheral blood.

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.

Fabry Disease: Current and Novel Therapeutic Strategies. A Narrative Review

BACKGROUND

Fabry disease (FD) is an inherited lysosomal storage disorder, leading to multisystemic manifestations and causing significant morbidity and mortality.

OBJECTIVE

The aim of this narrative review is to present the current and novel therapeutic strategies in FD, including symptomatic and specific treatment options.

METHODS

A systematic literature search was conducted to identify relevant studies, including completed and ongoing randomized-controlled clinical trials (RCTs), prospective or retrospective cohort studies, case series and case reports that provided clinical data regarding FD treatment.

RESULTS

A multidisciplinary symptomatic treatment is recommended for FD patients, personalized according to disease manifestations and their severity. During the last two decades, FD-specific treatments, including two enzyme-replacement-therapies (agalsidase alfa and agalsidase beta) and chaperone treatment with migalastat have been approved for use and allowed for symptoms' stabilization or even disease burden reduction. More therapeutic agents are currently under investigation. Substrate reduction therapies, including lucerastat and venglustat, have shown promising results in RCTs and may be used either as monotherapy or as complementary therapy to established enzymereplacement- therapies. More stable enzyme-replacement-therapy molecules that are associated with less adverse events and lower likelihood of neutralizing antibodies formation have also been developed. Ex-vivo and in-vivo gene therapy is being tested in animal models and pilot human clinical trials, with preliminary results showing a favorable safety and efficacy profile.

CONCLUSION

The therapeutic landscape in FD appears to be actively expanding with more treatment options expected to become available in the near future, allowing for a more personalized approach in FD patients.

Assessment and impact of dose escalation on anti-drug antibodies in Fabry disease

Enzyme replacement therapy (ERT) with recombinant α-galactosidase A (AGAL) can lead to the formation of neutralizing anti-drug antibodies (ADA), which significantly limit treatment efficacy in patients with Fabry disease (FD). The effects of dose escalation on ADA titer and plasma globotriaosylsphingosine (lyso-Gb₃) level are unknown. We screened 250 FD patients (200 males, 50 females) under ERT for ADAs and assessed the impact of an approved dose escalation in affected patients, focusing on ADA titers and plasma lyso-Gb₃. ADA-positive patients were identified by serum-mediated inhibition assays, followed by titration assays to determine the individual inhibitory capacities of ADAs against agalsidase-alfa and agalsidase-beta. 70 (35%) of the male patients were ADA-positive, with a mean inhibitory capacity of 83.5 ± 113.7mg AGAL. Although patients receiving agalsidase-beta showed higher inhibitory capacities (84.7 ± 34.7mg) than patients under agalsidase-alfa (60.3 ± 126.7mg, p<0.001), the "theoretical deficit" to the infused dose was lower in patients receiving agalsidase-beta. In seven patients receiving agalsidase-alfa (0.2 mg/kg) ADAs were saturable by switching patients to agalsidase-beta (1.0 mg/kg). The switch resulted in increasing ADA titers within the first months. In 2 out of 7 (28.6%) therapy switchers, dose escalation could lead to durable ADA saturation. Independent of an increase in ADA titers, lyso-Gb₃ levels decrease and cardiac and renal parameters remained stable after dose escalation. Dose escalation results in a heterogeneous, unpredictable ADA response, with more than a quarter of all treatment switchers succeeding in ADA saturation. Longitudinal ADA measurements are required to assess the individual risk of affected patients.

Mechanisms of Neutralizing Anti-drug Antibody Formation and Clinical Relevance on Therapeutic Efficacy of Enzyme Replacement Therapies in Fabry Disease

Fabry disease (FD) is a rare X-linked lysosomal storage disorder caused by mutations in the α-galactosidase A (AGAL/GLA) gene. The lysosomal accumulation of the substrates globotriaosylceramide (Gb₃) and globotriaosylsphingosine (lyso-Gb₃) results in progressive renal failure, cardiomyopathy associated with cardiac arrhythmia, and recurrent strokes, significantly limiting life expectancy in affected patients. 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, facilitating 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 (ADAs) in ERT-treated males, leading to an attenuation of therapy efficacy and thus disease progression. In this narrative review, we provide a brief overview of the clinical picture of FD and diagnostic confirmation. The focus is on the biochemical and clinical significance of neutralizing ADAs as a humoral response to ERT. In addition, we provide an overview of different methods for ADA measurement and characterization, as well as potential therapeutic approaches to prevent or eliminate ADAs in affected patients, which is representative for other ERT-treated lysosomal storage diseases.

Immunogenicity of Botulinum Toxin Formulations: Potential Therapeutic Implications

Botulinum neurotoxins (BoNTs) are proteins produced by bacteria of the Clostridium family. Upon oral ingestion, BoNT causes the neuroparalytic syndrome botulism. There are seven serotypes of BoNT (serotypes A-G); BoNT-A and BoNT-B are the botulinum toxin serotypes utilized for therapeutic applications. Treatment with BoNT injections is used to manage chronic medical conditions across multiple indications. As with other biologic drugs, immunogenicity after long-term treatment with BoNT formulations may occur, and repeated use can elicit antibody formation leading to clinical nonresponsiveness. Thus, approaching BoNT treatment of chronic conditions with therapeutic formulations that minimize stimulating the host immune response while balancing patient responsiveness to therapy is ideal. Immunogenicity is a clinical limitation in many settings that use biologic drugs for treatment, and clinically relevant immunogenicity reduction has been achieved through engineering smaller protein constructs and reducing unnecessary formulation components. A similar approach has influenced the evolution of BoNT formulations. Three BoNT-A products and one BoNT-B product have been approved by the Food and Drug Administration (FDA) for therapeutic use: onabotulinumtoxinA, abobotulinumtoxinA, incobotulinumtoxinA, and rimabotulinumtoxinB; a fourth BoNT-A product, daxibotulinumtoxinA, is currently under regulatory review. Additionally, prabotulinumtoxinA is a BoNT-A product that has been approved for aesthetic indications but not therapeutic use. Here, we discuss the preclinical and clinical immunogenicity data that exist within the scientific literature and provide a perspective for considering immunogenicity as a key factor in choice of BoNT formulation.

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.

Contemporary therapeutics and new drug developments for treatment of Fabry disease: a narrative review

Fabry disease (OMIM 301500) is an X-linked (Xq22.1) lysosomal storage disorder leading to a progressive multisystem disease with high variability in both genotype and phenotype expression. The pathophysiological origin is found in an enzyme deficiency of the α-galactosidase A (enzyme commission no. 3.2.1.22) leading to accumulation of globotriaosylceramides in all lysosome carrying tissue. Especially organ manifestations of the heart, kidneys and nervous system are of significant prognostic value and might complicate with Fabry-associated pain, young aged cryptogenic stroke, proteinuria, kidney failure, hypertrophic cardiomyopathy, heart failure, malign cardiac rhythm disturbances and eventually sudden cardiac death. Up to the introduction of the first enzyme replacement agent in 2001, patients faced the disease's natural course with no disease-specific therapies available. Today, two recombinant enzyme replacement agents (Fabrazyme^®, Sanofi Genzyme, Cambridge, MA, USA; Replagal^®, Takeda Pharmaceutical, Tokio, Japan) and one oral chaperone therapy (Migalastat^®, Amicus Therapeutics, USA) are available and well-established in daily clinical practice. Substrate reduction therapy, second-generation enzyme replacement agents and different gene therapy approaches are currently undergoing preclinical and clinical trial phases and aim to improve therapeutic success and long-term outcome of patients with Fabry disease. This narrative review summarizes the currently available therapeutic options and future perspectives in Fabry disease.

Fabry Disease: The Current Treatment Landscape

Fabry disease (FD) is a rare X-linked lysosomal storage disease based on a deficiency of α-galactosidase A (AGAL) caused by mutations in the α-galactosidase A gene (GLA). The lysosomal accumulation of glycosphingolipids, especially globotriaosylceramide (Gb₃) and globotriaosylsphingosine (lyso-Gb₃, deacylated form), leads to a multisystemic disease with progressive renal failure, cardiomyopathy with potentially malignant cardiac arrhythmias, and strokes, which considerably limits the life expectancy of affected patients. Diagnostic confirmation in male patients is based on the detection of AGAL deficiency in blood leukocytes, whereas in women, due to the potentially high residual enzymatic activity, molecular genetic detection of a causal mutation is required. Current treatment options for FD include recombinant enzyme replacement therapy (ERT) with intravenous agalsidase-alfa (0.2 mg/kg body weight) or agalsidase-beta (1 mg/kg body weight) every 2 weeks and oral chaperone therapy with migalastat (123 mg every other day), which selectively and reversibly binds to the active site of AGAL, thereby correcting the misfolding of the enzyme and allowing it to traffic to the lysosome. These therapies enable cellular Gb₃ clearance and improve the burden of disease. However, in about 40% of all ERT-treated men, ERT can lead to infusion-associated reactions and the formation of neutralizing antidrug antibodies, which reduces the efficacy of therapy. In chaperone therapy, there are carriers of amenable mutations that show limited clinical success. This article provides a brief overview of the clinical picture in FD patients, diagnostic confirmation, and interdisciplinary clinical management of FD. The focus is on current and future therapeutic options.

Outcomes of Kidney Transplantation in Fabry Disease: A Meta-Analysis

Background: Fabry disease (FD) is a rare X-linked lysosomal storage disorder with progressive systemic deposition of globotriaosylceramide, leading to life-threatening cardiac, central nervous system, and kidney disease. Current therapy involves symptomatic medical management, enzyme replacement therapy (ERT), dialysis, kidney transplantation, and, more recently, gene therapy. The aim of this systematic review was to assess outcomes of kidney transplantation among patients with FD. Methods: A comprehensive literature review was conducted utilizing MEDLINE, EMBASE, and Cochrane Database, from inception through to 28 February 2020, to identify studies that evaluate outcomes of kidney transplantation including patient and allograft survival among kidney transplant patients with FD. Effect estimates from each study were extracted and combined using the random-effects generic inverse variance method of DerSimonian and Laird. Results: In total, 11 studies, including 424 kidney transplant recipients with FD, were enrolled. The post-transplant median follow-up time ranged from 3 to 11.5 years. Overall, the pooled estimated rates of all-cause graft failure, graft failure before death, and allograft rejection were 32.5% (95%CI: 23.9%–42.5%), 14.5% (95%CI: 8.4%–23.7%), and 20.2% (95%CI: 15.4%–25.9%), respectively. In the sensitivity analysis, limited only to the recent studies (year 2001 or newer when ERT became available), the pooled estimated rates of all-cause graft failure, graft failure before death, and allograft rejection were 28.1% (95%CI: 20.5%–37.3%), 11.7% (95%CI: 8.4%–16.0%), and 20.2% (95%CI: 15.5%–26.0%), respectively. The pooled estimated rate of biopsy proven FD recurrence was 11.1% (95%CI: 3.6%–29.4%), respectively. There are no significant differences in the risks of all-cause graft failure (p = 0.10) or mortality (0.48) among recipients with vs. without FD. Conclusions: Despite possible FD recurrence after transplantation of 11.1%, allograft and patient survival are comparable among kidney transplant recipients with vs. without FD.

Anti-drug antibody formation in Japanese Fabry patients following enzyme replacement therapy

Enzyme replacement therapy (ERT) for Fabry disease (deficiency of α-galactosidase A, α-Gal) with recombinant α-Gals (agalsidase alfa and agalsidase beta) is widely available and improves some of the clinical manifestations and biochemical findings. However, recent reports suggest that recurrent administration of recombinant enzymes often induces the formation of anti-drug antibodies, which may have a negative impact on the outcome of the therapy. We examined the formation of anti-drug antibodies using blood samples from 97 Japanese Fabry patients following ERT and tried to characterize them by means of enzyme-linked immunosorbent assay (ELISA), serum-mediated α-Gal inhibition, and immunochromatographic (IC) assay, followed by GLA gene analysis and measurement of plasma globotriaosylsphingosine (lyso-Gb3). ELISA revealed that 20/35 (57%) classic Fabry males were antibody (Immunoglobulin G, IgG) -positive (Ab+) at 6 months after the initiation of ERT, although only two of the seventeen (12%) later-onset Fabry males and none of the 45 Fabry females were. The Ab+ state was maintained at least until 24 months after the initiation of ERT in most of the cases, the exceptions being two patients who acquired immune tolerance during ERT. As many Ab+ patients have nonsense mutations, attention should be paid to the formation of anti-drug antibodies in Fabry patients harboring such gene mutations, who hardly produce α-Gal protein. Serum-mediated α-Gal inhibition was seen in most of the Ab+ patients and the antibodies affected the reduction of the plasma lyso-Gb3 level following ERT, suggesting that the antibodies inhibit the enzyme activity. There was a correlation between the results of the IC test and those of the ELISA. As the former is easy and rapid, it should be useful as a bed-side test.

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The anti-drug antibodies formed in Fabry patients during ERT were characterized.

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Serum-mediated α-Gal inhibition was seen in most of the antibody-positive patients.

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The immunochromatographic test is easy, rapid, and useful as a bed-side test.

Developments in the treatment of Fabry disease

Enzyme replacement therapy (ERT) with recombinant α-galactosidase A (r-αGAL A) for the treatment of Fabry disease has been available for over 15 years. Long-term treatment may slow down disease progression, but cardiac, renal, and cerebral complications still develop in most patients. In addition, lifelong intravenous treatment is burdensome. Therefore, several new treatment approaches have been explored over the past decade. Chaperone therapy (Migalastat; 1-deoxygalactonojirimycin) is the only other currently approved therapy for Fabry disease. This oral small molecule aims to improve enzyme activity of mutated α-galactosidase A and can only be used in patients with specific mutations. Treatments currently under evaluation in (pre)clinical trials are second generation enzyme replacement therapies (Pegunigalsidase-alfa, Moss-aGal), substrate reduction therapies (Venglustat and Lucerastat), mRNA- and gene-based therapy. This review summarises the knowledge on currently available and potential future options for the treatment of Fabry disease.

Predicting the Development of Anti-Drug Antibodies against Recombinant alpha-Galactosidase A in Male Patients with Classical Fabry Disease

Fabry Disease (FD) is a rare, X-linked, lysosomal storage disease that mainly causes renal, cardiac and cerebral complications. Enzyme replacement therapy (ERT) with recombinant alpha-galactosidase A is available, but approximately 50% of male patients with classical FD develop inhibiting anti-drug antibodies (iADAs) that lead to reduced biochemical responses and an accelerated loss of renal function. Once immunization has occurred, iADAs tend to persist and tolerization is hard to achieve. Here we developed a pre-treatment prediction model for iADA development in FD using existing data from 120 classical male FD patients from three European centers, treated with ERT. We found that nonsense and frameshift mutations in the α-galactosidase A gene (p = 0.05), higher plasma lysoGb3 at baseline (p < 0.001) and agalsidase beta as first treatment (p = 0.006) were significantly associated with iADA development. Prediction performance of a Random Forest model, using multiple variables (AUC-ROC: 0.77) was compared to a logistic regression (LR) model using the three significantly associated variables (AUC-ROC: 0.77). The LR model can be used to determine iADA risk in individual FD patients prior to treatment initiation. This helps to determine in which patients adjusted treatment and/or immunomodulatory regimes may be considered to minimize iADA development risk.

Therapeutic challenges in two adolescent male patients with Fabry disease and high antibody titres

Enzyme replacement therapy (ERT) has been shown to stabilize certain aspects of Fabry disease (FD). However, in some patients on ERT, high antibody titres have been documented, with limited clinical improvement in systemic manifestations and often with significant adverse drug reactions. We present two related adolescent males with a 4.5 kb GLA deletion, not amenable to chaperone therapy, leading to profound reduction in α-galactosidase A (α-gal A) enzyme activity. Over a 3-year period of ERT, increasing IgG antibody titres against α-gal A were noted. After starting ERT serial urine globotriaosylceramide (Gb₃) measurements showed an upward trend from 333 to 2260 μg/mmol creatinine for patient 1 and 1165 to 2260 μg/mmol creatinine for patient 2. Markedly increased levels of urine and plasma globotriaosylsphingosine (Lyso-Gb₃₎ analogues were also found. The patients experienced recurrent infusion-associated reactions necessitating premedication and prolonged infusion times. Over the 3-year period of ERT, the patients experienced continued malaise, gastrointestinal symptoms and neuropathic pain. In addition, they had increasing anxiety related to their disease and apparent lack of response to ERT which led to a decision to ultimately stop ERT. No other approved treatment options are currently available for these patients. It is possible that the rapid development of the high antidrug neutralizing antibody (ADA) titres is related to the large GLA deletion leading to virtually absent enzyme activity. It remains unclear if their symptomatology during the period of receiving ERT is related to lack of its efficacy, the rising ADA titres, or both. These two patients highlight the need for further research into the management of antidrug antibodies and additional therapeutic approaches for FD.

Synopsis

The development of very high antidrug antibody titres in response to ERT in two related adolescent males with FD highlight the need for other therapeutic options for patients in whom ERT or other currently approved therapies does not meet their treatment needs.

Kidney Transplant in Fabry Disease: A Revision of the Literature

Fabry disease is classified as a rare X-linked disease caused by a complete or partial defect of enzyme alpha-galactosidase, due to GLA gene mutations. This disorder leads to intracellular globotriaosylceramide (Gb3) deposition associated with increased Gb3 plasma levels. Most of the symptoms of the disease, involving kidneys, heart and nervous system, result from this progressive Gb3 deposition. The incidence is estimated in 1/50,000 to 1/117,000 in males. Fabry nephropathy begins with microalbuminuria and/or proteinuria, which, in the classic form, appear from childhood. Thus, a progressive decline of renal function can start at a young age, and evolve to kidney failure, requiring dialysis or renal transplantation. Enzyme replacement therapy (ERT), available since 2001 for Fabry disease, has been increasingly introduced into the clinical practice, with overall positive short-term and long-term effects in terms of ventricular hypertrophy and renal function. Kidney transplantation represents a relevant therapeutic option for Fabry nephropathy management, for patients reaching end-stage renal disease, but little is known about long-term outcomes, overall patient survival or the possible role of ERT after transplant. The purpose of this review is to analyze the literature on every aspect related to kidney transplantation in patients with Fabry nephropathy: from the analysis of transplant outcomes, to the likelihood of disease recurrence, up to the effects of ERT and its possible interference with immunosuppression.

Current and Investigational Therapeutics for Fabry Disease

Fabry disease (FD) is an X-linked lysosomal storage disease caused by a deficiency in the lysosomal enzyme α-galactosidase (α-GAL). This in turn leads to the buildup of globotriaosylceramide, resulting classically in progressive kidney disease, peripheral neuropathy, early-onset cerebrovascular disease, gastrointestinal symptoms, hypertrophic cardiomyopathy, arrhythmias, corneal whorls, and angiokeratomas. The diagnosis of FD relies on identification of a low α-GAL enzyme activity, identification of a genetic mutation, or histologic evidence of disease. With more than 900 mutations identified, there is phenotypic variability deriving from both mutational effects as well as the effect of skewed X-inactivation in females. Treatment of this disease has relied on intravenous replacement of the deficient enzyme with agalsidase α or agalsidase β. However, treatment options for some patients with FD have recently expanded, with the approval of migalastat, an oral molecular chaperone. In addition to chaperone-based therapies, there are several additional therapies under development that could substantially reshape treatment options for patients with FD. Four approaches to gene therapy, through both ex vivo and in vivo methods, are under development. Another approach is through the administration of α-GAL mRNA to help stimulate production of α-GAL, which is another unique form of therapy. Finally, substrate reduction therapies act as inhibitors of glucosylceramide synthase, thus inhibiting the production of GB-3, promise another oral option to treat FD. This article will review the literature around current therapies as well as these newer therapeutics agents in the pipeline for FD.

Antibodies against recombinant alpha-galactosidase A in Fabry disease: Subclass analysis and impact on response to treatment

BACKGROUND

Treatment of Fabry disease (FD) with recombinant alpha-galactosidase A (r-αGAL A) is complicated by the formation of anti-drug antibodies in the majority of male patients with the classical disease phenotype. Detailed information regarding antibody subtypes, onset and persistence of antibody development and their effect on treatment efficacy is sparse.

METHODS

A retrospective study was carried out in 39 male patients with classical FD, treated with either agalsidase-alfa or agalsidase-beta (mean follow up of 10 years). With six to twelve months intervals plasma-induced in vitro inhibition of enzyme activity, lysoglobotriaosylsphingosine (lysoGb3) levels and renal function were assessed. In a subset of 12 patients, additionally anti- r-αGAL A IgM, IgA and IgG1, 2, 3 and 4 levels were analyzed.

RESULTS

In 23 out of 39 patients, plasma-induced in vitro inhibition of r-αGAL A activity was observed (inhibition-positive). The inhibition titer was strongly negatively correlated to the decrease in lysoGb3: agalsidase-alfa (FE_{log10(inhibition)} = -10.3, P ≤.001), agalsidase-beta (FE_{log10(inhibition)} = -4.7, P ≤.001). Inhibition-positive patients had an accelerated decline in renal function (FE = 1.21, p = .042). During treatment IgG1 anti-r-αGAL A levels increased only in inhibition-positive patients (p = .0045). IgG4 anti-r-αGAL A antibodies developed in 7 out of 9 inhibition-positive patients. Other antibody subclasses were either not present or too low to quantify.

CONCLUSION

Development of inhibiting antibodies against r-αGAL A negatively affects the biochemical response to ERT and resulted in an accelerated decline in renal function. The presence of IgG1 and IgG4 anti-r-αGAL A antibodies is associated with in vitro αGAL A activity inhibition.

Oral Chaperone Therapy Migalastat for Treating Fabry Disease: Enzymatic Response and Serum Biomarker Changes After 1 Year

Long‐term effects of migalastat therapy in clinical practice are currently unknown. We evaluated migalastat efficacy and biomarker changes in a prospective, single‐center study on 14 patients with Fabry disease (55 ± 14 years; 11 men). After 1 year of open‐label migalastat therapy, patients showed significant changes in alpha‐galactosidase‐A activity (0.06–0.2 nmol/minute/mg protein; P = 0.001), left ventricular myocardial mass index (137–130 g/m²; P = 0.037), and serum creatinine (0.94–1.0 mg/dL; P = 0.021), accounting for deterioration in estimated glomerular filtration rate (87–78 mL/minute/1.73 m²; P = 0.012). The enzymatic increase correlated with myocardial mass reduction (r = −0.546; P = 0.044) but not with renal function (r = −0.086; P = 0.770). Plasma globotriaosylsphingosine was reduced in therapy‐naive patients (10.9–6.0 ng/mL; P = 0.021) and stable (9.6–12.1 ng/mL; P = 0.607) in patients switched from prior enzyme‐replacement therapy. These first real‐world data show that migalastat substantially increases alpha‐galactosidase‐A activity, stabilizes related serum biomarkers, and improves cardiac integrity in male and female patients with amenable Fabry disease mutations.

Hot topics in Fabry disease

Fabry disease is a rare inborn error of the enzyme α-galactosidase (α-Gal) and results in lysosomal substrate accumulation in tissues with a wide range of clinical presentations. The disease has attracted a lot of interest over the last years, in particular since enzyme replacement therapy (ERT) has become widely available in 2001. With rising awareness and rising numbers of (diagnosed) patients, physicians encounter new challenges. Over 900 α-Gal gene mutations are currently known, some with doubtful clinical significance, posing diagnostic and prognostic difficulties for the clinician and a lot of uncertainty for patients. Another challenge are patients who develop neutralising antibodies to ERT, which possibly leads to reduced therapy effectiveness. In this article, we summarise the latest developments in the science community regarding diagnostics and management of this rare lysosomal storage disorder and offer an outlook to future treatments.

Dose-Dependent Effect of Enzyme Replacement Therapy on Neutralizing Antidrug Antibody Titers and Clinical Outcome in Patients with Fabry Disease

BACKGROUND

Use of enzyme replacement therapy (ERT) to treat Fabry disease, caused by deficient lysosomal α-galactosidase A activity, can lead to formation of neutralizing antidrug antibodies (ADAs). These antibodies are associated with increased accumulation of plasma globotriaosylceramide (Gb3) and disease progression. Because agalsidase ERT can saturate ADA-binding sites during infusions (achieving agalsidase/antibody equilibrium), we investigated in this open cohort study whether saturated patients (who have excess agalsidase after infusions) experience better clinical outcomes compared with not saturated patients (who have excess ADAs after infusions).

METHODS

We isolated ADAs from sera of 26 men with Fabry disease receiving ERT (for a median of 94 months) and determined the amount of agalsidase necessary for antibody saturation. Clinical and biochemical outcomes included measurements of eGFR, interventricular septum thickness, and lyso-Gb3.

RESULTS

ADA titers decreased significantly in all patients during infusion. Agalsidase-α and agalsidase-β had similar ADA-binding capacity and comparable ADA saturation frequency. Fourteen patients with saturated ADAs presented with mild (but significant) loss of eGFR, stable septum thickness, and significantly decreased lyso-Gb3 levels. The 12 not saturated patients had a more pronounced and significant loss of eGFR, increased septum thickness, and a smaller, nonsignificant reduction in lyso-Gb3, over time. In three patients, dose escalation resulted in partially elevated ADA titers, but importantly, also in reduced lyso-Gb3 levels.

CONCLUSIONS

A not saturated ADA status during infusion is associated with progressive loss of eGFR and ongoing cardiac hypertrophy. Dose escalation can result in saturation of ADAs and decreasing lyso-Gb3 levels, but may lead to increased ADA titers.

Deep characterization of the anti-drug antibodies developed in Fabry disease patients, a prospective analysis from the French multicenter cohort FFABRY

BACKGROUND

Fabry disease (OMIM #301500) is an X-linked disorder caused by alpha-galactosidase A deficiency with two major clinical phenotypes: classic and non-classic of different prognosis. From 2001, enzyme replacement therapies (ERT) have been available. We aimed to determine the epidemiology and the functional characteristics of anti-drug antibodies. Patients from the French multicenter cohort FFABRY (n = 103 patients, 53 males) were prospectively screened for total anti-agalsidase IgG and IgG subclasses with a home-made enzyme-linked immunosorbent assay (ELISA), enzyme-inhibition assessed with neutralization assays and lysoGb3 plasma levels, and compared for clinical outcomes.

RESULTS

Among the patients exposed to agalsidase, 40% of men (n = 18/45) and 8% of women (n = 2/25) had antibodies with a complete cross-reactivity towards both ERTs. Antibodies developed preferentially in men with non-missense GLA mutations (relative risk 2.88, p = 0.006) and classic phenotype (58.6% (17/29) vs 6.7% (1/16), p = 0.0005). Specific anti-agalsidase IgG1 were the most frequently observed (16/18 men), but the highest concentrations were observed for IgG4 (median 1.89 μg/ml, interquartile range (IQR) [0.41-12.24]). In the men exposed to agalsidase, inhibition was correlated with the total IgG titer (r = 0.67, p < 0.0001), especially IgG4 (r = 0.75, p = 0.0005) and IgG2 (r = 0.72, p = 0.001). Inhibition was confirmed intracellularly in Fabry patient leucocytes cultured with IgG-positive versus negative serum (median: 42.0 vs 75.6%, p = 0.04), which was correlated with IgG2 (r = 0.67, p = 0.017, n = 12) and IgG4 levels (r = 0.59, p = 0.041, n = 12). Plasma LysoGb3 levels were correlated with total IgG (r = 0.66, p = 0.001), IgG2 (r = 0.72, p = 0.004), IgG4 (r = 0.58, p = 0.03) and IgG1 (r = 0.55, p = 0.04) titers. Within the classic group, no clinical difference was observed but lysoGb3 levels were higher in antibody-positive patients (median 33.2 ng/ml [IQR 20.6-55.6] vs 12.5 [10.1-24.0], p = 0.005).

CONCLUSION

Anti-agalsidase antibodies preferentially develop in the severe classic Fabry phenotype. They are frequently associated with enzyme inhibition and higher lysoGb3 levels. As such, they could be considered as a hallmark of severity associated with the classic phenotype. The distinction of the clinical phenotypes should now be mandatory in studies dealing with Fabry disease and its current and future therapies.

Ten-year-long enzyme replacement therapy shows a poor effect in alleviating giant leg ulcers in a male with Fabry disease

Fabry disease is an X-linked lysosomal storage disorder caused by a deficiency of α-galactosidase A (α-gal A), leading to the progressive accumulation of glycosphingolipids. Classical hemizygous males usually present symptoms, including pain and paresthesia in the extremities, angiokeratoma, hypo- or anhidrosis, abdominal pain, cornea verticillata, early stroke, tinnitus, and/or hearing loss, during early childhood or adolescence. Moreover, proteinuria, renal impairment, and cardiac hypertrophy can appear with age. Enzyme replacement is the most common therapy for Fabry disease at present which has been approved in Japan since 2004. We report a case involving a 27-year-old male with extreme terminal pain, anhidrosis, abdominal pain, tinnitus, hearing impairment, cornea verticillata, and recurrent huge ulcers in the lower extremities. At the age of 16 years, he was diagnosed with Fabry disease with a positive family history and very low α-gal A activity. He then received enzyme replacement therapy (ERT) with recombinant human agalsidase beta at 1 mg/kg every 2 weeks for 10 years. Throughout the course of ERT, his leg ulcers recurred, and massive excretion of urinary globotriaosylceramide and plasma globotriaosylsphingosine was observed. Electron microscopy of the venous tissue in the regions of the ulcer showed massive typical zebra bodies in the vascular wall smooth muscle cells.

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A classical hemizygous male with Fabry disease presented with massive intractable leg ulcer.

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10 years' enzyme replacement therapy showed huge excretion of urinary Gb3 and plasma lyso-Gb3.

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Excessive zebra bodies in vascular wall smooth muscle cells caused venous reflux and varices on saphenous veins.