Diagnosis of Fabry Disease Using Alpha-Galactosidase A Activity or LysoGb3 in Blood Fails to Identify Up to Two Thirds of Female Patients.

Anderson-Fabry disease is a lysosomal storage disorder caused by mutations in the GLA gene, which encodes the enzyme α-galactosidase A. The GLA gene is located on the X-chromosome, causing an X-linked pathology: due to lyonization, female patients usually manifest a variable symptomatology, ranging from asymptomatic to severe phenotypes. The confirmation of the clinical diagnosis of Fabry disease, achieved by measuring α-galactosidase A activity, which is usually the first test used, shows differences between male and female patients. This assay is reliable in male patients with causative mutations in the GLA gene, in whom the enzymatic activity is lower than normal values; on the other hand, in female Fabry patients, the enzymatic activity is extremely variable between normal and pathological values. These fluctuations are also found in female patients' blood levels of globotriaosylsphingosine (LysoGb3) for the same reason. In this paper, we present a retrospective study conducted in our laboratories on 827 Fabry patients with causative mutations in the GLA gene. Our results show that 100% of male patients had α-galactosidase A activity below the reference value, while more than 70% of female patients had normal values. It can also be observed that almost half of the female patients with pathogenic mutations in the GLA gene showed normal values of LysoGb3 in blood. Furthermore, in women, blood LysoGb3 values can vary over time, as we show in a clinical case presented in this paper. Both these tests could lead to missed diagnoses of Fabry disease in female patients, so the analysis of the GLA gene represents the main diagnostic test for Fabry disease in women to date.

Genetic and phenotypic profile of Fabry disease in the population of Vale do Paraiba and Eastern São Paulo / Perfil genético e fenotípico da doença de Fabry na população do Vale do Paraíba e Zona Leste de São Paulo

ABSTRACT Introduction: Fabry disease (FD) is an inborn error of metabolism characterized by α-galactosidase A deficiency. The primary objective was to evaluate the genetic and phenotypic profile of Fabry disease in hemodialysis. Methods: Observational cohort study to determine the incidence of genetic variations and phenotypic changes for FD in hemodialysis patients in the Paraiba Valley and Eastern São Paulo. Genetic testing for the GLA gene was performed for men and women over 12 years of age at the hemodialysis clinics between January 2016 and December 2019 as a screening protocol. Results: The cases came from screening exams of the index case among patients with chronic kidney disease, resulting in 17 families and totaling 82 patients under study. The classification of the most prevalent variant was that of uncertain significance (54%), followed by the pathogenic variant (46%). Five patients in two families were described with two types of variants not previously described in the literature, with pathogenic behavior. Comparing the types of variants, the presence of a pathogenic variant was associated with higher levels of lysoGB3, lower values for alpha-GAL activity and higher frequency of symptoms related to FD. Conclusion: We characterized an extensive population of patients with FD variants with rich genetic, clinical and biomarker details. We believe that this study can help to better characterize the Brazilian population with FD and the most frequent types of variants.

RESUMO Introdução: A doença de Fabry (DF) é um erro inato do metabolismo caracterizado pela deficiência da enzima α-galactosidase A. O objetivo primário foi avaliar o perfil genético e fenotípico da doença de Fabry em hemodiálise. Métodos: Estudo de coorte observacional para determinar a incidência de variações genéticas e alterações fenotípicas para DF em pacientes em hemodiálise no Vale do Paraíba e Zona Leste de São Paulo. O teste genético para o gene GLA foi realizado para homens e mulheres em todos os pacientes das clínicas de hemodiálise maiores de 12 anos entre janeiro de 2016 a dezembro de 2019 como protocolo de rastreio. Resultados: Os casos foram provenientes de exames de triagem do caso índice entre pacientes portadores de doença renal crônica, resultando em 17 famílias e totalizando 82 pacientes em estudo. A classificação da variante mais prevalente foi a de significado incerto (54%), seguida da variante patogênica (46%). Foram descritos 5 pacientes em duas famílias com dois tipos de variantes ainda não previamente descritos na literatura com comportamento patogênico. Na comparação entre os tipos de variantes, a presença de variante patogênica foi associada a maiores níveis de lysoGB3, menores valores da atividade da alfa-GAL e maior frequência de sintomas relativos à DF. Conclusão: Caracterizamos uma extensa população de pacientes com variantes para DF com riqueza de detalhes de genética, clínica e de biomarcadores. Acreditamos que este estudo possa auxiliar na melhor caracterização da população brasileira com DF e nos tipos mais frequentes de variantes.

Newborn Screening for Fabry Disease: Current Status of Knowledge.

Fabry disease is an X-linked progressive lysosomal disorder, due to α-galactosidase A deficiency. Patients with a classic phenotype usually present in childhood as a multisystemic disease. Patients presenting with the later onset subtypes have cardiac, renal and neurological involvements in adulthood. Unfortunately, the diagnosis is often delayed until the organ damage is already irreversibly severe, making specific treatments less efficacious. For this reason, in the last two decades, newborn screening has been implemented to allow early diagnosis and treatment. This became possible with the application of the standard enzymology fluorometric method to dried blood spots. Then, high-throughput multiplexable assays, such as digital microfluidics and tandem mass spectrometry, were developed. Recently DNA-based methods have been applied to newborn screening in some countries. Using these methods, several newborn screening pilot studies and programs have been implemented worldwide. However, several concerns persist, and newborn screening for Fabry disease is still not universally accepted. In particular, enzyme-based methods miss a relevant number of affected females. Moreover, ethical issues are due to the large number of infants with later onset forms or variants of uncertain significance. Long term follow-up of individuals detected by newborn screening will improve our knowledge about the natural history of the disease, the phenotype prediction and the patients' management, allowing a better evaluation of risks and benefits of the newborn screening for Fabry disease.

How relevant are cerebral white matter lesions in the D313Y variant of the α-galactosidase A gene? Neurological, cardiological, laboratory, and MRI data of 21 patients within a follow-up of 3 years.

BACKGROUND: Fabry disease is an inherited metabolic disorder with various symptoms. Neurological manifestations are small fiber neuropathy, cerebral white matter lesions (WML), megadolicho basilar artery, and stroke. The relevance of the D313Y variant in the galactosidase alpha gene is controversially discussed. OBJECTIVES: We aimed at elucidating the implications of this differential diagnosis of multiple sclerosis (MS), focussing on the analysis of WML over time and correlations with other markers. METHODS: We reviewed retrospectively the clinical, laboratory, and magnetic resonance imaging data of 21 carriers of the D313Y variant at a single German outpatient clinic for MS between 2004 and 2021. RESULTS: In our cohort (15 females, 6 males), mean age at diagnosis was 44.1 ± 16.3 years, and mean follow-up duration was 3.1 ± 3.9 years. WML were rated on both, the Fazekas scale and the age-related white matter changes rating scale, and were of variable interindividual extent. Follow-up imaging showed virtually no progress. WML did not correlate with the severity of clinical findings or lysoGb3 levels. Symptomatic carriers of the variant are characterized by an almost complete lack of internal organ manifestations and laboratory findings, usually associated with Fabry disease. CONCLUSION: WML in carriers of the D313Y variant do not seem to be suitable for assessing or predicting the (para-) clinical status. Concerning MS patients, the variant and its clinical signs can be a differential diagnosis, but also a co-factor. Imaging and cerebrospinal fluid findings facilitate the distinction between both entities.

Potential Role of Sphingolipidoses-Associated Lysosphingolipids in Cancer.

Sphingolipids play a key structural role in cellular membranes and/or act as signaling molecules. Inherited defects of their catabolism lead to lysosomal storage diseases called sphingolipidoses. Although progress has been made toward a better understanding of their pathophysiology, several issues still remain unsolved. In particular, whether lysosphingolipids, the deacylated form of sphingolipids, both of which accumulate in these diseases, are simple biomarkers or play an instrumental role is unclear. In the meanwhile, evidence has been provided for a high risk of developing malignancies in patients affected with Gaucher disease, the most common sphingolipidosis. This article aims at analyzing the potential involvement of lysosphingolipids in cancer. Knowledge about lysosphingolipids in the context of lysosomal storage diseases is summarized. Available data on the nature and prevalence of cancers in patients affected with sphingolipidoses are also reviewed. Then, studies investigating the biological effects of lysosphingolipids toward pro or antitumor pathways are discussed. Finally, original findings exploring the role of glucosylsphingosine in the development of melanoma are presented. While this lysosphingolipid may behave like a protumorigenic agent, further investigations in appropriate models are needed to elucidate the role of these peculiar lipids, not only in sphingolipidoses but also in malignant diseases in general.

Metabolic Fingerprinting of Fabry Disease: Diagnostic and Prognostic Aspects.

Fabry disease (FD) is an X-linked lysosomal disease due to a deficiency in the activity of the lysosomal-galactosidase A (GalA), a key enzyme in the glycosphingolipid degradation pathway. FD is a complex disease with a poor genotype-phenotype correlation. In the early stages, FD could involve the peripheral nervous system (acroparesthesias and dysautonomia) and the ski (angiokeratoma), but later kidney, heart or central nervous system impairment may significantly decrease life expectancy. The advent of omics technologies offers the possibility of a global, integrated and systemic approach well-suited for the exploration of this complex disease. In this narrative review, we will focus on the main metabolomic studies, which have underscored the importance of detecting biomarkers for a diagnostic and prognostic purpose in FD. These investigations are potentially useful to explain the wide clinical, biochemical and molecular heterogeneity found in FD patients. Moreover, the quantitative mass spectrometry methods developed to evaluate concentrations of these biomarkers in urine and plasma will be described. Finally, the complex metabolic biomarker profile depicted in FD patients will be reported, which varies according to gender, types of mutations, and therapeutic treatment.

Plasma neurofilament light, glial fibrillary acidic protein and lysosphingolipid biomarkers for pharmacodynamics and disease monitoring of GM2 and GM1 gangliosidoses patients.

GM2 and GM1 gangliosidoses are genetic, neurodegenerative lysosomal sphingolipid storage disorders. The earlier the age of onset, the more severe the clinical presentation and progression, with infantile, juvenile and late-onset presentations broadly delineated into separate phenotypic subtypes. Gene and substrate reduction therapies, both of which act directly on sphingolipidosis are entering clinical trials for treatment of these disorders. Simple to use biomarkers for disease monitoring are urgently required to support and expedite these clinical trials. Here, lysosphingolipid and protein biomarkers of sphingolipidosis and neuropathology respectively, were assessed in plasma samples from 33 GM2 gangliosidosis patients, 13 GM1 gangliosidosis patients, and compared to 66 controls. LysoGM2 and lysoGM1 were detectable in 31/33 GM2 gangliosidosis and 12/13 GM1 gangliosidosis patient samples respectively, but not in any controls. Levels of the axonal damage marker Neurofilament light (NF-L) were highly elevated in both GM2 and GM1 gangliosidosis patient plasma samples, with no overlap with controls. Levels of the astrocytosis biomarker Glial fibrillary acidic protein (GFAP) were also elevated in samples from both patient populations, albeit with some overlap with controls. In GM2 gangliosidosis patient plasma NF-L, Tau, GFAP and lysoGM2 were all most highly elevated in infantile onset patients, indicating a relationship to severity and phenotype. Plasma NF-L and liver lysoGM2 were also elevated in a GM2 gangliosidosis mouse model, and were lowered by treatment with a drug that slowed disease progression. These results indicate that lysosphingolipids and NF-L/GFAP have potential to monitor pharmacodynamics and pathogenic processes respectively in GM2 and GM1 gangliosidoses patients.

Multicenter evaluation of use of dried blood spot compared to conventional plasma in measurements of globotriaosylsphingosine (LysoGb3) concentration in 104 Fabry patients.

OBJECTIVES: Fabry disease (FD) is an X-linked lysosomal storage disorder, resulting from a deficiency of the enzyme α-galactosidase A, responsible for breaking down glycolipids such as globotriaosylceramide and its deacylated derivative, globotriaosylsphingosine (LysoGb3). Here, we compare the levels of LysoGb3 in dried blood spots (DBS) and plasma in patients with classic and late-onset phenotypes. METHODS: LysoGb3 measurements were performed in 104 FD patients, 39 males and 65 females. Venous blood was collected. A portion was spotted onto filter paper and another portion separated to obtain plasma. The LysoGb3 concentrations in DBS and plasma were determined by highly sensitive electrospray ionization liquid chromatography tandem mass spectrometry. Agreement between different matrices was assessed using linear regression and Bland Altman analysis. RESULTS: The method on DBS was validated by evaluating its precision, accuracy, matrix effect, recovery, and stability. The analytical performances were verified by comparison of a total of 104 paired DBS and plasma samples from as many FD patients (representing 46 GLA variants). There was a strong correlation between plasma and the corresponding DBS LysoGb3 concentrations, with few exceptions. Discrepancies were observed in anemic patients with typically low hematocrit levels compared to the normal range. CONCLUSIONS: The method proved to be efficient for the rapid analysis of LysoGb3. DBS provides a convenient, sensitive, and reproducible method for measuring LysoGb3 levels for diagnosis, initial phenotypic assignment, and therapeutic monitoring in patients with FD.

Pathology and pathogenic pathways in fabry nephropathy.

BACKGROUND: The pathophysiology of renal damage in Fabry nephropathy involves a complex biological mechanism. The intracellular deposition globotriaosylceramide (Gb3) is just the first step of the mechanism. The glycolipid deposition occurs in all renal cells (endothelial, epithelial and mesangial cells). It stimulates many biological processes, including cytokine release, epithelial-mesenchymal transdifferentiation, oxidative stress and the remodelling of vascular walls, resulting in subtle initial inflammation and eventually tissue fibrosis. It has been hypothesized that the processes activated by Gb3 deposition can subsequently progress independently of cellular deposition and that even Gb3 clearance by specific therapy cannot retard or stop these pathways. AIM: This review aims to gather the reported evidence of these cellular alterations and the resulting histological changes. Our approach is similar to a routine study of kidney biopsy. RESULTS: In the first part of the review, "histology" section, we describe the structures involved (glomeruli, vessels, tubules and interstitium) from a histological point of view. While in the second part, "pathogenesis" section, we present some interpretations about the implicated pathways based on the up-to-date available evidence.

Fabry Disease: Molecular Basis, Pathophysiology, Diagnostics and Potential Therapeutic Directions.

Fabry disease (FD) is a lysosomal storage disorder (LSD) characterized by the deficiency of α-galactosidase A (α-GalA) and the consequent accumulation of toxic metabolites such as globotriaosylceramide (Gb3) and globotriaosylsphingosine (lysoGb3). Early diagnosis and appropriate timely treatment of FD patients are crucial to prevent tissue damage and organ failure which no treatment can reverse. LSDs might profit from four main therapeutic strategies, but hitherto there is no cure. Among the therapeutic possibilities are intravenous administered enzyme replacement therapy (ERT), oral pharmacological chaperone therapy (PCT) or enzyme stabilizers, substrate reduction therapy (SRT) and the more recent gene/RNA therapy. Unfortunately, FD patients can only benefit from ERT and, since 2016, PCT, both always combined with supportive adjunctive and preventive therapies to clinically manage FD-related chronic renal, cardiac and neurological complications. Gene therapy for FD is currently studied and further strategies such as substrate reduction therapy (SRT) and novel PCTs are under investigation. In this review, we discuss the molecular basis of FD, the pathophysiology and diagnostic procedures, together with the current treatments and potential therapeutic avenues that FD patients could benefit from in the future.

Oxidative stress biomarkers in Fabry disease: is there a room for them?

BACKGROUND: Fabry disease (FD) is an X-linked lysosomal storage disorder, caused by deficient activity of the alpha-galactosidase A enzyme leading to progressive and multisystemic accumulation of globotriaosylceramide. Recent data point toward oxidative stress signalling which could play an important role in both pathophysiology and disease progression. METHODS: We have examined oxidative stress biomarkers [Advanced Oxidation Protein Products (AOPP), Ferric Reducing Antioxidant Power (FRAP), thiolic groups] in blood samples from 60 patients and 77 healthy controls. RESULTS: AOPP levels were higher in patients than in controls (p < 0.00001) and patients presented decreased levels of antioxidant defences (FRAP and thiols) with respect to controls (p < 0.00001). In a small group of eight treatment-naïve subjects with FD-related mutations, we found altered levels of oxidative stress parameters and incipient signs of organ damage despite normal lyso-Gb3 levels. CONCLUSIONS: Oxidative stress occurs in FD in both treated and naïve patients, highlighting the need of further research in oxidative stress-targeted therapies. Furthermore, we found that oxidative stress biomarkers may represent early markers of disease in treatment-naïve patients with a potential role in helping interpretation of FD-related mutations and time to treatment decision.

First phenotypic description of a female patient with c.610 T > C variant of GLA: a renal-predominant presentation of Fabry disease.

BACKGROUND: Fabry disease (FD) is an X-linked lysosomal storage disorder due to deficient alpha-galactosidase activity leading to intracellular glycosphingolipid accumulation. Multiple variants have been reported in the GLA gene coding for alpha-galactosidase, and the question of the pathogenicity of rare variants needs to be addressed, especially in patients with mild phenotypes. CASE PRESENTATION: The patient, a 37-year-old female, presented with a persistent proteinuria after an otherwise uncomplicated first pregnancy. Renal biopsy showed both mild mesangial IgA deposits, and a striking vacuolization of podocytes and tubular cells consistent with Fabry disease. On electron microscopy, discrete but characteristic pseudo-myelinic lamellar inclusions were observed in the podocytes' lysosomes. A more detailed physical examination revealed an angiokeratoma, and medical history ancient acroparesthesia. There was no cardiac or cerebral involvement of Fabry disease on magnetic resonance imaging. While blood enzymatic activity of alpha-ga lactosidase was normal in this patient, lysoGb3 was elevated (3 N), and a rare heterozygous variant called c.610 T > C was documented in GLA gene. The patient was treated with an ACE inhibitor, with a rapid decrease in proteinuria. After a 5-year follow-up, her renal function has remained normal, with mild proteinuria, and normal cardiac echography. CONCLUSIONS: We report and phenotypically describe the first case of a Fabry disease female patient carrying the GLA c.610 T > C variant associated with a renal-predominant clinical presentation.

Unexpectedly High Prevalence of Low Alpha-Galactosidase A Enzyme Activity in Patients with Focal Segmental Glomerulosclerosis

OBJECTIVES: Fabry disease (FD) is a rare disease associated with sphingolipid accumulation. Sphingolipids are components of plasma membranes that are important in podocyte function and accumulate in various glomerular diseases such as focal segmental glomerulosclerosis (FSGS). Both FD and FSGS can cause podocyte damage and are classified as podocytopathies. In this respect, FD and FSGS share the same pathophysiologic pathways. Previous screening studies have shown that a significant proportion of end-stage renal disease (ESRD) patients receiving hemodialysis (HD) have unsuspected FD, and the prevalence of low alpha-galactosidase A (αGLA) enzyme activity in these patients is higher than that in the normal population. We aimed to compare αGLA enzyme activity in patients with biopsy-proven FSGS and ESRD receiving HD. METHODS: The records of 232 patients [62 FSGS (F/M: 33/29); 170 HD (M/F: 93/79)] were evaluated retrospectively. The screening was performed based on the αGLA enzyme activity on a dried blood spot, with the confirmation of plasma LysoGb3 levels, and the known GLA mutations were tested in patients with low enzyme activities. The two groups were compared using these parameters. RESULTS: The mean level of αGLA enzyme activity was found to be lower in FSGS patients than in the HD group (2.88±1.2 μmol/L/h versus 3.79±1.9 μmol/L/h, p<0.001). There was no significant relationship between the two groups with regard to the plasma LysoGb3 levels (2.2±1.22 ng/ml versus 1.7±0.66 ng/ml, p: 0.4). In the analysis of GLA mutations, a D313Y mutation [C(937G>T) in exon p] was found in one patient from the FSGS group. CONCLUSIONS: We found that αGAL activity in patients with FSGS is lower than that in patients undergoing HD. The low enzyme activity in patients with FSGS may be explained by considering the similar pathogenesis of FSGS and FD, which may also lead to sphingolipid deposition and podocyte injury.

Will the FAbry STabilization indEX make its way to everyday clinical practice?

Despite several attempts at setting up a standardized disease severity score for Fabry disease in the past, none have been established in routine clinical practice due to the multisystem nature and complexity of this inherited enzyme deficiency disorder. In this issue, Mignani et al. report a large multicentre application of the FASTEX, an online tool to assess disease progress over time that offers simple data inputting and graphic illustration of disease progression or stabilization. Mignani et al. succeeded in validating the tool in a large cohort of Fabry patients, including females and non-classical phenotypes, building on the first FASTEX introduction in 2016. We report on our own practical experience with the tool and comment on some limiting factors in its use as well as possible future prospects.

Implementation of Second-Tier Tests in Newborn Screening for Lysosomal Disorders in North Eastern Italy.

The increasing availability of treatments and the importance of early intervention have stimulated interest in newborn screening for lysosomal storage diseases. Since 2015, 112,446 newborns in North Eastern Italy have been screened for four lysosomal disorders-mucopolysaccharidosis type I and Pompe, Fabry and Gaucher diseases-using a multiplexed tandem mass spectrometry (MS/MS) assay system. We recalled 138 neonates (0.12%) for collection of a second dried blood spot. Low activity was confirmed in 62 (0.06%), who underwent confirmatory testing. Twenty-five neonates (0.02%) were true positive: eight with Pompe disease; seven with Gaucher disease; eight with Fabry disease; and two with Mucopolysaccharidosis type I. The combined incidence of the four disorders was 1 in 4497 births. Except for Pompe disease, a second-tier test was implemented. We conclude that newborn screening for multiple lysosomal storage diseases combined with a second-tier test can largely eliminate false-positives and achieve rapid diagnosis.

Mutations in the GLA Gene and LysoGb3: Is It Really Anderson-Fabry Disease?

Anderson-Fabry disease (FD) is a rare, progressive, multisystem storage disorder caused by the partial or total deficit of the lysosomal enzyme α-galactosidase A (α-Gal A). It is an X-linked, lysosomal enzymopathy due to mutations in the galactosidase alpha gene (GLA), encoding the α-Gal A. To date, more than 900 mutations in this gene have been described. In our laboratories, the study of genetic and enzymatic alterations related to FD was performed in about 17,000 subjects with a symptomatology referable to this disorder. The accumulation of globotriaosylsphingosine (LysoGb3) was determined in blood of positives. Exonic mutations in the GLA gene were detected in 471 patients (207 Probands and 264 relatives): 71.6% of mutations were associated with the classic phenotype, 19.8% were associated with the late-onset phenotype, and 8.6% of genetic variants were of unknown significance (GVUS). The accumulation of LysoGb3 was found in all male patients with a mutation responsible for classic or late-onset FD. LysoGb3 levels were consistent with the type of mutations and the symptomatology of patients. α-Gal A activity in these patients is absent or dramatically reduced. In recent years, confusion about the pathogenicity of some mutations led to an association between non-causative mutations and FD. Our study shows that the identification of FD patients is possible by associating clinical history, GLA gene analysis, α-Gal A assay, and blood accumulation of LysoGB3. In our experience, LysoGB3 can be considered a reliable marker, which is very useful to confirm the diagnosis of Fabry disease.

Genotype, phenotype and disease severity reflected by serum LysoGb3 levels in patients with Fabry disease.

BACKGROUND: Fabry disease (FD) is a rare X-linked lysosomal storage disease caused by mutations in the α-galactosidase A (GLA) gene causing deficiency of α-galactosidase A which results in progressive glycosphingolipid accumulation, especially globotriaosylceramide (Gb3), in body liquids and lysosomes. In a large cohort of FD patients, we aimed to establish genotype/phenotype relations as indicated by serum LysoGb3 (deacylated Gb3). METHODS: In 69 consecutive adult FD patients (males: n=28 (41%)) with a GLA-mutation confirmed diagnosis, we conducted a multidisciplinary clinical characterization during their routine annual examinations, and measured serum LysoGb3 levels by high-sensitive electrospray ionization liquid chromatography tandem mass spectrometry. RESULTS: Serum levels of LysoGb3 were significantly higher in Classic compared with Later-Onset phenotype and higher in the latter compared with controls, both in males (52 [40-83] vs 9.5 [4.5-20] vs 0.47 [0.41-0.61] ng/ml, P<0.001) and in females (9.9 [7.9-14] vs 4.9 [1.6-4.9] vs 0.41 [0.33-0.48] ng/ml, P<0.001), respectively. Multivariate linear regression analysis showed that LysoGb3 levels were independently associated with, serum creatinine (ß=0.09, 95%CI 0.04-0.13, P<0.001) and the presence of cardiomyopathy (ß=25, 95%CI 9.8-41, P=0.002). LysoGb3 levels were higher in males with frame-shift and nonsense mutations than in males with missense mutations (84 [72-109] vs 41 [37-52] ng/ml, P=0.002). CONCLUSION: LysoGb3 relates to disease severity, enzyme replacement response, and to the genotype severity in males. LysoGb3 supports identifying patients at risk who require intensive monitoring and treatment. LysoGb3 appears to be one marker of metabolic phenotyping of FD.

Favourable effect of early versus late start of enzyme replacement therapy on plasma globotriaosylsphingosine levels in men with classical Fabry disease.

BACKGROUND: The level of plasma globotriaosylsphingosine (lysoGb3) is an indication of disease severity in Fabry disease (FD) and its decrease during enzyme replacement therapy could be a reflection of treatment efficacy. Early treatment of FD may improve clinical outcome, but data to support this hypothesis are scarce. In this study we compared lysoGb3 decrease after ERT initiation in men with classical FD who started ERT before the age of 25 (early-treatment) with those who started later in life (late-treatment). METHODS: Treatment naïve men with classical FD from three centers of excellence in Europe were included. Measurements of lysoGb3 levels by tandem mass spectroscopy and antibodies by an inhibitory assay were performed in a single laboratory. Results were adjusted for lysoGb3 at baseline, first ERT (i.e. agalsidase alfa or beta) and the average ERT dose. RESULTS: 85 patients were included, 21 in the early-treatment and 64 in the late-treatment group. LysoGb3 level at baseline was not different between the two groups (112 vs 114nmol/L, p=0.92). The adjusted odds ratio for reaching a lysoGb3 level<20nmol/L was 7.38 for the early-treatment versus late-treatment group (95% CI: 1.91-34.04, p=0.006). The adjusted lysoGb3 levels one year after ERT initiation was 12.9nmol/L lower in the early-treatment (95% CI: -20.1--5.8, p<0.001) compared to the late-treatment group. CONCLUSION: The current retrospective cohort study shows that initiation of ERT at younger age in men with classical Fabry disease results in a better biochemical response.

Plasma LysoGb3: A useful biomarker for the diagnosis and treatment of Fabry disease heterozygotes.

BACKGROUND: Fabry disease (FD) is a rare X-linked lysosomal storage disorder due to mutations in the α-galactosidase A gene (GLA) that result in absent or markedly reduce α-galactosidase A (α-GalA) enzymatic activity. As a result, the major glycosphingolipid substrates, globotriaosylceramide (Gb3) and globotriaosylsphingosine (LysoGb3) accumulate in plasma, urine and tissue lysosomes. In females, the diagnosis can be complicated by the fact that 40-50% of GLA-mutation confirmed heterozygotes have normal or only slightly decreased leukocyte α-GalA activities. Recently, LysoGb3 has been appreciated as a novel FD biomarker, especially for therapeutic monitoring. METHODS: Among our GLA-mutation proven FD patients, we screened 18 heterozygotes whose leukocyte α-GalA activity was determined at initial diagnosis. For these females, we measured their serum LysoGb3 levels using highly-sensitive electrospray ionization liquid chromatography tandem mass spectrometry. RESULTS: We identified three unrelated females in whom the accumulating LysoGb3 was increased, whereas their leukocyte α-GalA activities were in the normal range. CONCLUSION: LysoGb3 serves as an useful biomarker to improve the diagnosis of FD heterozygotes and for therapeutic evaluation and monitoring.

Plasma globotriaosylsphingosine (lysoGb3) could be a biomarker for Fabry disease with a Chinese hotspot late-onset mutation (IVS4+919G>A).

BACKGROUND: Previous studies revealed a high incidence of late-onset Fabry disease mutation, IVS4+919G>A, in Taiwan. However, the natural course is largely unclear and suitable biomarkers for monitoring disease progress are unavailable. METHODS AND RESULTS: Patients carrying IVS4+919G>A or classical Fabry mutations were enrolled in this study. The subjects ranged from newborn to eighty year old adults. Plasma globotriaosylceramide (Gb3) and globotriaosylsphingosine (lysoGb3) were measured by LC-MS/MS in subjects to evaluate the sensitivity of these two biomarkers. All adult males and symptomatic females could be distinguished from healthy controls by an elevated plasma lysoGb3 level. The lysoGb3 level was also related to the left ventricular mass considering gender and age (p<0.01). Moreover, approximately 70% of male and 45% of female newborns already had an elevated plasma lysoGb3 level which increased gradually as the subjects got older (p<0.01). CONCLUSIONS: Plasma lysoGb3 is a more sensitive and reliable biomarker than plasma Gb3. LysoGb3 also correlated with age and left ventricular mass index in Fabry patients with IVS4+919G>A mutation. Because lots of infants with the IVS4+919G>A mutation already had elevated lysoGb3 levels at birth, that indicates that the development of hypertrophic cardiomyopathy may require a long and insidious course after lysoGb3 accumulation.