Precision medicine in Fabry disease

Abstract

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.

DEFINITION, EPIDEMIOLOGY AND PATHOGENESIS

Fabry disease (FD) is an X-linked lysosomal storage disorder based on a defect in α-galactosidase A (AGAL) activity, which causes a progressive, life-threatening multisystemic disease due to intracellular accumulation of globotriaosylceramide (Gb₃; GL3 and glycosphingolipid) [1]. The disease affects men and women of all ethnic groups with an incidence of 1:40 000–1:117 000. Newborn screenings point to higher incidences of 1:3100 [2] to 1:1250 in males [3]. Disease-causing mutations are detected in the GLA gene, which codes for AGAL. The gene is located on the long arm of the X chromosome (band q22), has a length of 12 kb and consists of seven exons and six introns. There are >1000 GLA mutations known, with most patients having ‘private’ (family-specific) mutations. In X-linked inheritance, family history is important. An affected father passes the mutation on to all daughters while his sons are unaffected. An affected mother passes the mutation on to 50% of all children. Hence genetic counselling should be recommended to all families with an FD patient.

Nearly all body cells can have a damaging Gb₃ accumulation, so numerous organs and tissues such as kidneys, heart, vessels and the central and peripheral nervous system are affected and show progressive functional impairment of varying degrees between individuals.

CLINICAL PICTURE

FD patients suffer from a progressive multisystemic disease in which the number of affected organ systems (especially kidney, heart, vasculature, central and peripheral nervous system) and the burden of disease increases with age (Table 1 and Figure 1) [1, 4]. The variability of the clinical picture is larger in women than in men. This is due to the random inactivation of one of the two X chromosomes of each cell in early embryogenesis, with a preference for stronger expression of the affected or unaffected X chromosome in individual tissues (Lyon hypothesis) [5].

DIAGNOSTICS FOR DIAGNOSIS CONFIRMATION

A suspicion of FD arises from the family history and/or from the evidence of the above-mentioned manifestations. In males, the determination of AGAL activity in blood leucocytes is the method of choice for confirmation of the diagnosis. A pathologically low AGAL activity indicates the presence of FD. In females, molecular genetic testing with detection of a disease-causing mutation in the GLA gene is necessary to confirm the diagnosis, since females with FD often have AGAL activities within the reference range. Determination of the genetic variant/mutation allows the classification of its pathogenetic significance into five categories (pathogenic, likely pathogenic, uncertain significance, likely benign and benign) [6] as well as classification regarding the response to chaperone therapy (see Chaperone therapy).

Special laboratories offer the determination of AGAL activity, genotyping and determination of globotriaosylsphingosine (lyso-Gb₃) by means of dry blood testing. As a biomarker (marker of disease burden), pathologically elevated lyso-Gb₃ in plasma or urine can contribute to improved diagnosis and monitoring. If biopsies are performed, electron microscopic multilamellar myelin bodies (so-called zebra bodies or paper roll phenomenon) can be detected, which are pathognomonic for FD. In many countries, prenatal diagnostics are not or only to a limited extent authorized. If authorized, prenatal diagnostics can be performed by measuring AGAL activity in chorionic villi or cultured amniotic cells and, in the case of a mutation known in the family, by molecular genetic methods.

DIAGNOSTICS FOR CONFIRMED FD

Once the diagnosis of FD has been confirmed, an initial examination of the typically affected organs and organ systems should be performed at a specialized FD centre, including analysis of the skin, gastrointestinal tract, eyes, ears, kidneys, heart and central and peripheral nervous systems. The diagnostic evaluation of a Fabry nephropathy should include measurement of creatinine and the estimated glomerular filtration rate (eGFR) using the Chronic Kidney Disease Epidemiology Collaboration formula [7] (for adults) or the Schwartz formula [8] (for children). In addition, determination of the albumin:creatinine and protein:creatinine ratios in spontaneous urine or albumin and protein in 24-h urine collection is pivotal. Morphologic analysis includes ultrasound (detection of cysts, vascular lesions and chronic parenchymatous changes). Depending on the cohort, elevated blood pressure can be detected in ~50% of FD patients [9, 10]. Since the presence of hypertension was shown to negatively impact disease progression and prognosis in FD [11], a 24-h blood pressure measurement is advisable [12].

The diagnostic evaluation of a Fabry cardiomyopathy comprises an electrocardiogram, 24-h electrocardiogram and cardiac magnetic resonance imaging (MRI; including late enhancement imaging). MRI is the preferred modality, but if this is unaavailable, an echocardiogram is warranted instead. Coronary angiography and myocardial biopsy are only necessary for special indications (e.g. myocardial biopsy for diagnostic confirmation of a cardiac manifestation).

Neurological manifestations should be evaluated by Doppler/duplex sonography and cranial MRI to detect an intima-media thickening, an ectasia of the arteria basilaris, white matter lesions and (clinically silent) cerebral infarctions. Pain intensity and quality of life should be assessed with corresponding questionnaires such as the Neuropathic Pain Symptom Inventory, Graded Chronic Pain Scale or the more FD specific Fabry Pain Questionnaire [13].

Fabry nephropathy

Untreated FD patients may have an annual GFR loss of up to 8–12 mL/min/1.73 m² [14, 15]. Known progression factors are male sex, presence of uncontrolled/poorly controlled hypertension, extent of proteinuria and an advanced CKD stage [16–18]. Cardiovascular morbidity is increased in FD patients with progressive renal failure [19]. The extent of renal insufficiency determines the disease course under enzyme replacement therapy (ERT) [20].

More recent studies suggest that podocyturia correlates with the clinical severity of Fabry nephropathy and is of prognostic importance [21, 22].

Renal biopsy for Fabry nephropathy

Fabry nephropathy is both a morphological and a clinical–functional term [23]. It can be characterized bioptically and by laboratory chemical parameters of renal function with regard to diagnosis and course. The insufficient metabolism of Gb₃ leads to deposits in various cells of the kidney tissue, which can result in glomerulosclerosis and interstitial fibrosis with proteinuria and renal insufficiency. The significance of a kidney biopsy finding with regard to therapeutic consequences has not yet been sufficiently investigated in adults. The electron microscopic detection of Gb₃ deposits in a kidney biopsy is recommended for diagnostic confirmation if the usual laboratory chemical and molecular genetic diagnostics appear unclear [24]. However, even if a biopsy is not the clinical standard procedure for an FD diagnosis previously established by laboratory chemistry, molecular genetics and/or clinical evidence of other typical manifestations, it can provide clinically relevant information in the case of disease progression despite treatment or uncertain diagnosis to assess histologically the severity of a Fabry nephropathy (extent of fibrosis, foot process effacement, etc.) and to exclude other renal diseases or comorbidities (hypertension and diabetes mellitus) [25]. Due to the sophisticated methodology of novel methods to quantify Gb₃ inclusions [26], we still suggest an easier standardized scoring system for renal pathology in patients with FD [25].

Fabry nephropathy is usually diagnosed by light microscopy, preferably by toluidine blue staining. An immunohistological or electron microscopic examination reveals the ceramide deposits (‘zebra bodies’), which are usually onion-shaped, but require special sample preparation. Advanced damage to the renal parenchyma and the associated functional deterioration leads to interstitial fibrosis and focal sclerosis of the glomerula with varying degrees of severity [18, 27].

DIFFERENTIAL DIAGNOSES OF FD

Due to the rarity of the disease, patients with FD are often misdiagnosed and treated incorrectly. Pain is misdiagnosed as rheumatoid arthritis, rheumatic fever, arthritis, erythromelalgia, Raynaud’s syndrome, fibromyalgia or panarteriitis nodosa. But often ‘growth pains’ or psychosomatic complaints are also assumed, especially in children and adolescents.

Abdominal complaints are considered to be irritable bowel syndrome or non-specific chronic inflammatory bowel disease. The clinical picture of a cerebral manifestation with visual disturbance, sensitivity disorders and hemiparesis, as well as MRI findings, often leads to the misdiagnosis of multiple sclerosis. On average, it takes ∼14 years for males and 16 years for females to obtain a correct diagnosis.

FABRY NEPHROPATHY AND RENAL REPLACEMENT THERAPY

Patients with terminal renal failure require renal replacement therapy (haemodialysis, peritoneal dialysis and kidney transplantation). Kidney transplantation is recommended as the therapy of choice, demonstrating excellent long-term outcomes [28]. Since the transplanted kidney has a normal function of AGAL, a clinically relevant Fabry nephropathy in the transplant has not been observed thus far [29]. FD patients after transplantation show a better disease course than dialysed patients. Due to the still existing pathological metabolic situation, ERT should be continued unchanged to prevent further extrarenal damage and to protect other organs. The tolerability and effectiveness of ERT in kidney transplant patients have been described repeatedly [30–33]. In dialysis patients, ERT treatment should also be continued and can be performed without loss of the enzyme during haemodialysis [34].

PRECISION MEDICINE

Precision medicine refers to the adaptation of medical treatment to the individual characteristics of each patient. It is based on the ability to divide individuals into subpopulations that reflect different risk groups. For example, male FD patients generally have a higher risk of a worse disease course compared with females. Thus treatment recommendations [24] suggest that males should generally be treated prophylactically and women only if incipient FD-typical organ damage becomes apparent. However, early treatment in females with a classical phenotype might be more effective before significant end-organ damage occurs. In addition, patients with a nonsense mutation (no residual AGAL activity) often show a severe disease course compared with those with a missense mutation, so that more frequent (at least annual) controls are recommended to be able to initiate therapy in time. Only patients with an amenable mutation can be treated with oral chaperone therapy, all others require intravenous ERT.

An early start of therapy is therefore particularly necessary in men with significantly reduced AGAL activity, increased lyso-Gb₃ (marker of disease burden) and organ manifestations typical for FD. In particular, women with so-called late onset mutations (e.g. p.N215S, ‘cardiac’ variant) may be without therapy for many years if regular, inconspicuous follow-up examinations are carried out, thus saving costs and avoiding side effects. Patients with ‘benign’ GLA variants should not be treated with FD-specific therapies.

FABRY-SPECIFIC THERAPY

Once the diagnosis has been confirmed, the patient should be referred to an interdisciplinary Fabry centre for initial examination and therapy planning and initiation. The following therapeutic goals should be reached in the context of multimodal care [35, 36]: reduction of complaints (especially pain reduction), delaying/preventing the progression of organ manifestations (especially the kidney, heart and central nervous system), improvement of quality of life and normalization of life expectancy.

Since 2001, ERT has been available as a causal treatment option to compensate for AGAL deficiency [1]. The AGAL enzyme, which is produced by genetic engineering and expression, is administered every 2 weeks as an intravenous infusion (Figure 2). Two preparations in different dosages are currently approved for lifelong therapy. Agalsidase-α (Replagal; Takeda Pharmaceutical, Tokyo, Japan) is produced in a human cell line (human fibrosarcoma cells HT-1080), with an approved dosage of 0.2 mg/kg body weight, leading to an infusion duration of ∼40 min. Agalsidase-β (Fabrazyme; Sanofi Genzyme, Cambridge, MA, USA) is produced in Chinese hamster ovary cells with a recommended dose of 1.0 mg/kg body weight and an infusion duration of ∼240 min, which may be progressively reduced to 90 min.

ERT shows overall good efficacy, with improvement or stabilization of disease progression and improvement of quality of life and extension of lifetime. Unfortunately, females with FD are often still untreated despite organ manifestations [37], although an early start of therapy is particularly important for the (long-term) success of the therapy [38]. Under ERT, the following therapeutic effects can be achieved: stabilization of kidney function, delay of progression to terminal kidney failure, reduction of left ventricular hypertrophy or stabilization of the thickness of the heart wall, relief of neuropathic burning pains in the extremities, improvement of gastrointestinal complaints and an improvement in the ability to perspire [39–42]. Especially in Fabry nephropathy with a significant Gb₃ accumulation in the podocytes, a dose-dependent clearance effect was demonstrated in children, suggesting a dose-dependent ERT efficacy with regard to the stabilization of renal function [43–47].

PITFALLS OF ERT

However, ERT also has limitations leading to challenges in everyday clinical practice. For example, allergic infusion reactions can occur, including cephalia, paraesthesia, drop in blood pressure, fever, chills, nausea and fatigue. By reducing the infusion rate or administration of non-steroidal anti-inflammatory drugs, antihistamines and/or glucocorticoids, the symptoms can usually be alleviated. Approximately 40% of all Fabry males under ERT produce immunoglobulin G antibodies (especially males with absent endogenous AGAL activity), which leads to ERT inhibition with worse disease course [48]. The so-called neutralizing anti-drug antibodies (ADAs) inhibit the infused enzyme during infusion [49], in addition to endothelial enzyme uptake and intracellular enzymatic activity [50]. Only higher ERT doses can compensate for these neutralizing antibodies [49, 51]. In a group of transplanted male Fabry patients, it could be shown that immunosuppressive therapy suppresses the antibody-mediated ERT inhibition. Higher immunosuppressive doses are associated with lower antibody titres and reduced ERT inhibition [52]. Future studies should develop ADA-specific immunosuppressive therapy protocols, leading to improved disease course in patients with ADAs.

CHAPERONE THERAPY

Since May 2016, the pharmacological chaperone migalastat (Galafold; 123 mg hard capsules, every other day; Amicus Therapeutics, Philadelphia, PA, USA) has been approved as the first oral therapy for FD [53]. In some AGAL protein mutants, the addition of migalastat under cell culture conditions (HEK293T cells) leads to a significant increase in enzymatic activity [54]. According to current understanding, this is based on a reversible binding of migalastat to the active centre of the AGAL, which, as a consequence of the resulting stabilization, promotes proper transport to the lysosomes. After uptake of the chaperone enzyme complex into the lysosomes, the small molecule dissociates. As a result of the more effective folding and transport, higher enzyme activity is achieved in the lysosomes, which leads to an improved catabolism of Gb₃ (Figure 2). AGAL mutants that show an increase in enzyme activity after migalastat administration are termed ‘amenable’ variants. The small molecule compound is available for the long-term treatment of adults and adolescents ≥16 years of age with a confirmed Fabry diagnosis and an amenable mutation. Specialists can find out which mutations respond to migalastat in vitro (status 05/2020: 1384 amenable and 754 non-amenable mutations) by going to www.galafoldamenabilitytable.com.

Two Phase 3 studies for therapy with migalastat have been conducted so far. The FACETS study is a placebo-controlled study with treatment-naïve patients [n = 50; 22 (placebo) versus 28 (migalastat)] [55]. In the ATTRACT study, the efficacy and safety of migalastat were assessed compared with ERT (agalsidase-β and agalsidase-α) in 57 [36 (migalastat) versus 21 (ERT)] male and female patients with FD [56].

The data are promising, as renal function remained stable under a maximum 18-month treatment with migalastat, a significant reduction of the left ventricular mass index was observed and plasma lyso-Gb₃, as a marker of disease burden, remained low and stable when switching from ERT to migalastat (ATTRACT) [56]. An analysis of clinical events related to kidney, heart and cerebrovascular events and death revealed a frequency of 29% in the migalastat group and 44% in the ERT group (P = 0.36) [56]. Overall, migalastat therapy shows good tolerability, with side effects (including ≥1/10 headache) not occurring more frequently than under ERT (ATTRACT study) [56]. Even though the study population is not large, and the study duration is limited, the data are of clinical relevance, as migalastat does not appear to be inferior to the previous gold standard of ERT. In the meantime, the first long-term data (FACETS + 041 Extension, average treatment duration 3.4 years; ATTRACT, 30 months) are available, which document a stabilization of renal function and a decrease in the left ventricular mass index under migalastat [53].

Treatment effects are currently analysed in terms of responsiveness (∼30% of all Fabry patients), safety and efficacy by a Germany-wide, multicentre, long-term study (n = 60). The 1-year real-world data confirmed that migalastat therapy appears to be safe and is associated with improvement of the left ventricular cardiac mass. Regarding impaired renal function, blood pressure control seems to be a neglected important goal, since patients with poorly adjusted blood pressure suffered from a loss of eGFR [10].

PITFALLS OF CHAPERONE THERAPY

For many patients, oral therapy with migalastat seems to be a good alternative to intravenous ERT. However, patients with different mutations show different responses, which may be partly due to the severity of the disease, possible comorbidities, therapy adherence and the mutation present. Recent studies have demonstrated that in vitro amenability does not necessarily correspond to clinical amenability [10, 57, 58]. Some amenable AGAL mutations with low residual activity within the Good Laboratory Practice Human Embryonic Kidney (GLP-HEK) assay failed to show a biochemical response in appropriate migalastat-treated patients [10, 58]. The establishment of CRISPR/Cas9 knockout HEK cells (without endogenous AGAL activity) and investigation of immortalized patient-specific cell models allowed a better understanding of the different clinical effectiveness of chaperone therapy for certain mutations [10, 58].

CONCOMITANT MEDICATION

In cases of FD-typical symptoms and organ manifestation, symptomatic concomitant medication can be therapeutically helpful (see Table 2).

Similar to other diseases with progressive loss of renal function, management of proteinuria is an important goal to preserve renal function in patients with FD. Antiproteinuric therapy with angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) was demonstrated to decrease progressive kidney disease in FD [59, 60]. Since a high-sodium diet might diminish the efficiency of ACE inhibitors and ARBs [61] and is also associated with an increased risk of progression to end-stage renal disease in patients with proteinuria [62], a low-sodium diet in FD patients with proteinuria is warranted [63]. In addition, the use of sodium–glucose cotransporter-2 (SGLT2) inhibitors might be of future interest, due to the general cardiovascular and kidney protection in non-diabetic patients [64].

Pain with high intensity often dominates the everyday life of many FD patients and significantly lowers quality of life. There is only limited data on the symptomatic treatment of neuropathic pain in FD. According to current knowledge, the combination of ERT and symptomatic analgesic drugs leads to the most effective pain relief. Even if established drugs are used for the treatment of neuropathic pain, some should not be used due to FD-typical manifestations. This applies in particular to tricyclic antidepressants, which, as a frequent and clinically relevant side effect, negatively influence the cardiac conduction system that is often affected in FD. The effect of non-steroidal anti-inflammatory drugs in neuropathic pain is low, so they should be used with caution, partly due to their nephrotoxicity.

In everyday clinical practice, therapy with pregabalin (e.g. 75 mg 1-0-1, target dose 150 mg 1-0-1, maximum dose 600 mg/day) in case of resistance to therapy in combination with a dual serotonin and norepinephrine reuptake inhibitor (e.g. duloxetine, starting with 30 mg 1-0-0) may be useful (personal opinion). For pain relevant to everyday life, this medication should be combined with ERT. The effect of chaperone therapy on neuropathic pain seems promising according to the study results but has yet to be proved in clinical practice.

COURSE AND PROGNOSIS

The course of FD is progressive, but the quality of life and life expectancy is significantly improved by the current treatment options. However, the prognosis is decisively influenced by a timely start of therapy. The indication for therapy is always when there are signs of organ manifestation (heart, kidney, brain and pain); in males, treatment is also prophylactically and is required lifelong. Due to the multisystem symptoms and manifestations, annual check-ups in a centre that has expertise in FD are recommended. In addition, contact with a local patient support group is also recommended.

FUTURE THERAPEUTIC APPROACHES

Next-generation ERT

Pegunigalsidase alfa (PRX-102, Protalix Biotherapeutics/Chiesi, Carmiel, Israel ; tobacco plant cell–based ProCellEx System), a novel PEGylated [polyethylene glycol (PEG)] covalently cross-linked form of AGAL developed as an ERT for FD, was designed to increase plasma half-life (80 h) and reduce immunogenicity, thereby enhancing efficacy compared with available products. The long half-life (80 h) due to PEGylation stabilizes the AGAL homodimer, possibly allowing the infusion interval (monthly intravenous administration) to be extended [65]. Three Phase 3 studies are currently under way [BALANCE (NCT02795676), BRIDGE (NCT03018730) and BRIGHT (NCT03180840)].

Moss-aGal [Eleva (formerly Greenovation), Frieburg, Germany] is a recombinant form of human AGAL developed as an ERT for patients with FD. Moss-aGal is expressed in Physcomitrella patens (genetically modified moss). Preclinical studies suggest an improved uptake of the protein (via mannose receptors instead of mannose-6-phosphate receptors) into target cells [66]. A Phase 1 study showed good safety and tolerability of Moss-aGal in six women after a single intravenous dose of 0.2 mg/kg [67]. Phase 2 and 3 studies are in preparation.

Substrate reduction therapy

While on ERT, the missing or defective AGAL is replaced by the infusion of a genetically engineered enzyme. The aim of substrate reduction therapy is reduction of the substrate and subsequent inhibition of Gb₃ accumulation in the cells (Figure 2). Lucerastat (Idorsia) is a low molecular weight iminosugar that inhibits glucosylceramide synthase and thus the biosynthesis of glycosphingolipids including upstream Gb₃, indicating a potential new oral treatment alternative [68, 69]. A pivotal Phase 3 study [MODIFY (NCT03425539)] was initiated in 2018.

Gene therapy

Gene therapy is a promising future therapeutic option. By therapeutically introducing DNA or RNA with the genetic code for the GLA gene into patients’ cells, the causal chain ‘mutated gene to defective enzyme to defective function to deposition of Gb₃ to Fabry disease’ would be reached one step earlier than with ERT (Figure 2). Currently, several clinical studies are evaluating the safety of gene therapy for FD, which differ in their therapeutic approaches.

The first announced interventional, multicentre and multinational open-label studies (NCT03454893 and NCT02800070; AvroBio, Cambridge, MA, USA) are based on the lentiviral transduction of haematopoietic stem cells ex vivo (Figure 3A).

Three further clinical studies (NCT04046224, NCT04040049 and NCT04519749) [70, 71] are based on the principle of adeno-associated virus (AAV) transduction of hepatocytes in vivo (Figure 3B). STAAR (NCT04046224; Sangamo Therapeutics, Brisbane, CA, USA) is a multicentre, open-label, single-dose, dose-finding study for the AAV2/6 vector-based drug ST-920. The second clinical study on AAV-based gene therapy (FLT-190) is also still in the recruitment phase (NCT04040049; Freeline Therapeutics, Stevenage, UK). FLT190 is a gene therapy in the test phase, based on a platform that will also be used for haemophilia A and B and Gaucher disease. FLT190 consists of a codon-optimized GLA transgene under the control of a liver-specific promoter. The construct is packaged in a novel synthetic capsid and shows improved transduction of human hepatocytes compared with wild-type AAV serotypes [71]. A third clinical study on AAV-based gene therapy is also in the recruitment phase, using an attenuated AAV (4D-310; 4D Molecular Therapeutics, Emeryville, CA, USA). Preclinical studies in mice demonstrated that the use of the novel capsid 4D-C102 was especially efficient to transduce human cardiomyocytes. Since myocardial cells are hard to reach by ERT, this novel approach is of interest especially for those patients with FD-specific cardiac manifestations and symptoms.

AUTHORS’ CONTRIBUTIONS

M.L. and E.B. wrote the manuscript.

FUNDING

This article is part of a supplement supported by a sponsorship from Amicus Therapeutics UK Limited, a research grant from Boehringer Ingelheim RCV GmbH & Co KG, an educational sponsorship agreement from Astellas Pharma, and a restricted research grant from Vifor Pharma Osterreich GmbH. This supplement is part of the project DC-ren that has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 848011.

CONFLICT OF INTEREST STATEMENT

M.L. received speaker honoraria, travel funding and research grants from Amicus Therapeutics, Sanofi Genzyme and Takeda. E.B. received speaker honoraria and research grants from Amicus Therapeutics, Sanofi Genzyme and Takeda.

REFERENCES