Phenotypical characterization of α-galactosidase A gene mutations identified in a large Fabry disease screening program in stroke in the young

In vitro characterization of cells derived from a patient with the GLA variant c.376A>G (p.S126G) highlights a non-pathogenic role in Fabry disease

Fabry disease (FD) is a life-limiting disorder characterized by intracellular globotriaosylceramide (Gb3) accumulations. The underlying α-galactosidase A (α-GAL A) deficiency is caused by variants in the gene GLA. Variants of unknown significance (VUS) are frequently found in GLA and challenge clinical management. Here, we investigated a 49-year old man with cryptogenic lacunar cerebral stroke and the chance finding of the VUS S126G, who was sent to our center for diagnosis and initiation of a costly and life-long FD-specific treatment. We combined clinical examination with in vitro investigations of dermal fibroblasts (HDF), induced pluripotent stem cells (iPSC), and iPSC-derived sensory neurons. We analyzed α-GAL A activity in iPSC, Gb3 accumulation in all three cell types, and action potential firing in sensory neurons. Neurological examination and small nerve fiber assessment was normal except for reduced distal skin innervation. S126G iPSC showed normal α-GAL A activity compared to controls and no Gb3 deposits were found in all three cell types. Baseline electrophysiological characteristics of S126G neurons showed no difference compared to healthy controls as investigated by patch-clamp recordings. We pioneer multi-level cellular characterization of the VUS S126G using three cell types derived from a patient and provide further evidence for the benign nature of S126G in GLA, which is of great importance in the management of such cases in clinical practice.

A new multiplex analysis of glucosylsphingosine and globotriaosylsphingosine in dried blood spots by tandem mass spectrometry

Background

Gaucher's and Fabry's disease are two of the most common treatable lysosomal storage diseases, and have a wide spectrum of clinical symptoms. Early detection is important, because timely initiation of treatments can improve the disease status and prevent complications. However disease manifestations develop in childhood, diagnosis is delayed until adulthood partly due to the limitations of the currently used diagnostic pathway. The aim of this research is to develop and validate a multiplex assay and defining reference ranges, which do not exist at this moment, to improve and facilitate the entire diagnostic work up and enable treatment in an earlier stage of disease.

Methods and findings

Biomarkers glucosylsphingosine (GlcSph) and globotriaosylsphingosine (Lyso-Gb3) were detected and quantified using LC-MS/MS on dried blood spots. We developed an improved and new extraction method that allowed to measure GlcSph and Lyso-Gb3 in a multiplex analytical platform. After validation of the method, samples of 1480 individuals with normal enzymatic activity were collected to determine age and gender-related reference ranges.Our combination method showed a good linearity, precision, accuracy and limit of quantification with lack of carry-over following the specific international CLSI guidelines. The suggested protocol is robust, efficient, sensitive, specific, comprehensive and relatively cheap in order to accelerate the diagnostic process for both lysosomal storage diseases. The samples, with normal enzymatic activity, defined statistical relevant and clinical correct reference ranges for each specific age group by gender.

Conclusion

We report a multiplex LC-MS/MS method and relevant reference ranges that are appropriate for the targeted screening, diagnosis and follow-up of Fabry and Gaucher disease.

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.

From Lysosomal Storage Disorders to Parkinson's Disease - Challenges and Opportunities

Lysosomes are specialized organelles with an acidic pH that act as recycling hubs for intracellular and extracellular components. They harbour numerous different hydrolytic enzymes to degrade substrates like proteins, peptides, and glycolipids. Reduced catalytic activity of lysosomal enzymes can cause the accumulation of these substrates and loss of lysosomal integrity, resulting in lysosomal dysfunction and lysosomal storage disorders (LSDs). Post-mitotic cells, such as neurons, seem to be highly sensitive to damages induced by lysosomal dysfunction, thus LSDs often manifest with neurological symptoms. Interestingly, some LSDs and Parkinson's disease (PD) share common cellular pathomechanisms, suggesting convergence of aetiology of the two disease types. This is further underlined by genetic associations of several lysosomal genes involved in LSDs with PD. The increasing number of lysosome-associated genetic risk factors for PD makes it necessary to understand functions and interactions of lysosomal proteins/enzymes both in health and disease, thereby holding the potential to identify new therapeutic targets. In this review, we highlight genetic and mechanistic interactions between the complex lysosomal network, LSDs and PD, and elaborate on methodical challenges in lysosomal research.

The Benefits of Family Screening in Rare Diseases: Genetic Testing Reveals 165 New Cases of Fabry Disease among At-Risk Family Members of 83 Index Patients

Background: Fabry disease (FD, OMIM #301500) is a rare, progressive, X-linked, inherited genetic disease caused by a functional deficiency of lysosomal α-galactosidase, leading to the accumulation of glycosphingolipids in virtually all of the body’s cell types and fluids. Patients with rare genetic diseases and non-specific symptoms often experience substantial diagnostic delays, which can negatively impact the prompt initiation of treatment. If FD is not treated specifically, end organ damage (such as chronic renal failure, hypertrophic cardiomyopathy with arrhythmia, and strokes) impairs quality of life and reduces life expectancy. Patients and Methods: For 83 consecutive patients with FD referred to the Russian reference center for lysosomal storage diseases, family trees were built and genetic testing (cascade genotyping) was offered to family members. Results: The pathogenic GLA variant associated with FD was identified for all 83 probands. Family testing using cascade genotyping enabled the identification of 165 additional cases of FD among the tested 331 at-risk family members. Discussion: This is the first study to have described family screening in a large Russian cohort of patients with FD and chronic kidney disease. Raising awareness of FD among clinicians is important for earlier diagnosis and specific treatment.

Newborn screening for Fabry disease in Oregon: Approaching the iceberg of A143T and variants of uncertain significance

Fabry disease newborn screening (NBS) has been ongoing in Oregon for over 41 months by first-tier enzyme quantitation and second-tier DNA testing. During that period the majority of abnormal referrals received (34/60) were for the presence of the controversial c.427G > A (p.Ala143Thr) aka A143T and the majority of non-A143T referrals were for other variants of uncertain significance (17/60) resulting in at least 32 infants with an inconclusive case outcome even after clinical evaluation and/or diagnostic testing. To date there has been no significant family history or onset of symptoms in individuals with an inconclusive outcome. Based on our experience, we have developed a framework for approaching A143T and other variants of uncertain clinical significance in an attempt to balance sensitivity with the unnecessary medicalization of healthy infants.

Fabry Disease: A Atypical Presentation

Fabry Disease (FD) is a rare X-linked recessive disease caused by mutations in the GLA gene that lead to a decrease or lack of activity of the enzyme alpha galactosyl A. This lysosomal storage disorder results in progressive damage and dysfunction of several organs and, depending on the type of mutation and gender of the patient, and it may have different manifestations. As FD is a multisystem disease with a progressive character and varying severity, the diagnosis can be challenging, especially when it comes to non-classical forms. As this is a hereditary disease, its diagnosis impacts not only the patient but also his family, making an accurate and timely diagnosis even more important.

We present the case of a 59-years-old man diagnosed with non-classical FD, with previous neurological and psychiatric complaints, who was admitted to the Emergency Department (ED) with a generalized tonic-clonic seizure that required orotracheal intubation for airway protection and transferred to an Intensive Care Unit (ICU).

Detailed Phenotype of GLA Variants Identified by the Nationwide Neurological Screening of Stroke Patients in the Czech Republic

Fabry disease (FD) is a rare X-linked disorder of glycosphingolipid metabolism caused by pathogenic variants within the alpha-galactosidase A (GLA) gene, often leading to neurological manifestations including stroke. Multiple screening programs seeking GLA variants among stroke survivors lacked detailed phenotype description, making the interpretation of the detected variant’s pathogenicity difficult. Here, we describe detailed clinical characteristics of GLA variant carriers identified by a nationwide stroke screening program in the Czech Republic. A total of 23 individuals with 8 different GLA variants were included in the study. A comprehensive diagnostic workup was performed by a team of FD specialists. The investigation led to the suggestion of phenotype reclassification for the G325S mutation from late-onset to classical. A novel variant R30K was found and was classified as a variant of unknown significance (VUS). The typical manifestation in our FD patients was a stroke occurring in the posterior circulation with an accompanying pathological finding in the cerebrospinal fluid. Moreover, we confirmed that cornea verticillata is typically associated with classical variants. Our findings underline the importance of detailed phenotype description and data sharing in the correct identification of pathogenicity of gene variants detected by high-risk-population screening programs.

Newborn Screening for Fabry Disease in Northeastern Italy: Results of Five Years of Experience

Fabry disease (FD) is a progressive multisystemic lysosomal storage disease. Early diagnosis by newborn screening (NBS) may allow for timely treatment, thus preventing future irreversible organ damage. We present the results of 5.5 years of NBS for FD by α-galactosidase A activity and globotriaosylsphingosine (lyso-Gb₃) assays in dried blood spot through a multiplexed MS/MS assay. Furthermore, we report our experience with long-term follow-up of positive subjects. We screened more than 170,000 newborns and 22 males were confirmed to have a GLA gene variant, with an incidence of 1:7879 newborns. All patients were diagnosed with a variant previously associated with the later-onset phenotype of FD or carried an unclassified variant (four patients) or the likely benign p.Ala143Thr variant. All were asymptomatic at the last visit. Although lyso-Gb₃ is not considered a reliable second tier test for newborn screening, it can simplify the screening algorithm when its levels are elevated at birth. After birth, plasma lyso-Gb₃ is a useful marker for non-invasive monitoring of all positive patients. Our study is the largest reported to date in Europe, and presents data from long-term NBS for FD that reveals the current incidence of FD in northeastern Italy. Our follow-up data describe the early disease course and the trend of plasma lyso-Gb₃ during early childhood.

Plasma Globotriaosylsphingosine and α-Galactosidase A Activity as a Combined Screening Biomarker for Fabry Disease in a Large Japanese Cohort

Fabry disease is an X-linked disorder of α-galactosidase A (GLA) deficiency. Our previous interim analysis (1 July 2014 to 31 December 2015) revealed plasma globotriaosylsphingosine as a promising primary screening biomarker for Fabry disease probands. Herein, we report the final results, including patients enrolled from 1 January to 31 December 2016 for evaluating the potential of plasma globotriaosylsphingosine and GLA activity as a combined screening marker. We screened 5691 patients (3439 males) referred from 237 Japanese specialty clinics based on clinical findings suggestive of Fabry disease using plasma globotriaosylsphingosine and GLA activity as primary screening markers, and GLA variant status as a secondary screening marker. Of the 14 males who tested positive in the globotriaosylsphingosine screen (≥2.0 ng/mL), 11 with low GLA activity (<4.0 nmol/h/mL) displayed GLA variants (four classic, seven late-onset) and one with normal GLA activity and no pathogenic variant displayed lamellar bodies in affected organs, indicating late-onset biopsy-proven Fabry disease. Of the 19 females who tested positive in the globotriaosylsphingosine screen, eight with low GLA activity displayed GLA variants (six classic, two late-onset) and five with normal GLA activity displayed a GLA variant (one classic) and no pathogenic variant (four late-onset biopsy-proven). The combination of plasma globotriaosylsphingosine and GLA activity can be a primary screening biomarker for classic, late-onset, and late-onset biopsy-proven Fabry disease probands.

The benefits and challenges of family genetic testing in rare genetic diseases-lessons from Fabry disease

Background

Family genetic testing of patients newly diagnosed with a rare genetic disease can improve early diagnosis of family members, allowing patients to receive disease‐specific therapies when available. Fabry disease, an X‐linked lysosomal storage disorder caused by pathogenic variants in GLA, can lead to end‐stage renal disease, cardiac arrhythmias, and stroke. Diagnostic delays are common due to the rarity of the disease and non‐specificity of early symptoms. Newborn screening and screening of at‐risk populations, (e.g., patients with hypertrophic cardiomyopathy or undiagnosed nephropathies) can identify individuals with Fabry disease. Subsequent cascade genotyping of family members may disclose a greater number of affected individuals, often at younger age than they would have been diagnosed otherwise.

Methods

We conducted a literature search to identify all published data on family genetic testing for Fabry disease, and discussed these data, experts’ own experiences with family genetic testing, and the barriers to this type of screening that are present in their respective countries.

Results

There are potential barriers that make implementation of family genetic testing challenging in some countries. These include associated costs and low awareness of its importance, and cultural and societal issues. Regionally, there are barriers associated with population educational levels, national geography and infrastructures, and a lack of medical geneticists.

Conclusion

In this review, the worldwide experience of an international group of experts of Fabry disease highlights the issues faced in the family genetic testing of patients affected with rare genetic diseases.

Assessment of Peripheral Nervous System Alterations in Patients with the Fabry Related GLA-Variant p.A143T

The purpose of this study is to examine alterations of the peripheral nervous system (PNS) in oligo-symptomatic patients carrying the Fabry related GLA-gene variant p.A143T by Magnetic Resonance Neurography (MRN) and skin biopsy. This prospective study assessed dorsal root ganglia (DRG) volume L3 to S2, vascular permeability of the DRG L5, S1, and the spinal nerve L5 in five patients carrying p.A143T in comparison to patients with classical Fabry mutations and healthy controls. Moreover, skin punch biopsies above the lateral malleolus of the right foot were obtained in four patients and intraepidermal nerve fiber density (IENFD) was counted individually. Compared to controls, DRG volumes of p.A143T patients were enlarged by 30% (L3, p < 0.05), 35% (L4, p < 0.05), 29% (L5, p = 0.15), 36% (S1, p < 0.01), and 18% (S2, p < 0.05), but less pronounced compared to patients carrying a classical Fabry mutation. Compared to healthy controls, vascular permeability was decreased by 40% (L5 right), 49% (L5 left), 48% (S1 right), and 49% (S1) (p < 0.01–p < 0.001), but non-significant less than patients carrying a classical Fabry mutation. Compared to sex-matched 5% lower normative reference values per decade, IENFD was decreased in three of four patients. MRN and determination of IENFD is able to detect early alteration of the PNS segment in oligo-symptomatic patients with the disease-modifying GLA-variant p.A143T on an individual basis. This procedure might also help in further GLA-variants of uncertain significance for early identification of patients with single major organ manifestation.

Is the alpha-galactosidase A variant p.Asp313Tyr (p.D313Y) pathogenic for Fabry disease? A systematic review

The identification of pathogenic GLA variants plays a central role in the establishment of a definite Fabry disease (FD) diagnosis. We aimed to review and interpret the published data on the p.Asp313Tyr (p.D313Y) variant pathogenicity and clinical relevance. We performed a systematic review of peer-reviewed publications and case-reports on individuals and populations harbouring the p.Asp313Tyr variant. Overall, 35 studies were included in this review. We collected data regarding the clinical manifestations, alpha-galactosidase A enzyme activity, levels of the biomarkers globotriaosylceramide (Gb₃ ) and sphingosine-globotriaosylceramide (lyso-Gb₃ ) and histological findings of p.Asp313Tyr carriers. The prevalence of p.Asp313Tyr in populations at risk for FD (kidney, heart, neurologic disorders, or symptomatic populations) was calculated. We found high residual enzyme activity, low frequency of clinical features specific for FD, non-elevated lysoGb₃ /Gb₃ concentrations and lack of intracellular Gb₃ accumulation in biopsies in the p.Asp313Tyr carriers. The prevalence of the variant in populations at risk for FD was comparable to the reported frequency in the general population. A possible higher frequency was only observed in neurologic disorders. p.Asp313Tyr can be classified as neutral or variant of unknown significance. Further investigations will be helpful to clarify a possible association between the variant and manifestations in the brain vessels.

Use of a rare disease registry for establishing phenotypic classification of previously unassigned GLA variants: a consensus classification system by a multispecialty Fabry disease genotype-phenotype workgroup

BACKGROUND

Fabry disease (α-galactosidase deficiency) is an X-linked genetic disease caused by a variety of pathogenic GLA variants. The phenotypic heterogeneity is considerable, with two major forms, classic and later-onset disease, but adjudication of clinical phenotype is currently lacking for many variants. We aimed to determine consensus phenotypic classification for previously unclassified GLA variants from the GLA-specific fabry-database.org database.

METHODS

A Fabry disease genotype-phenotype workgroup developed a five-stage iterative system based on expert clinical assessment, published literature and clinical evidence of pathogenicity using a 2-point scoring system based on clinical hallmarks of classic disease. Kaplan-Meier (KM) analysis of severe clinical event-free survival was used as final validation. Results were compared with those from web-based disease databases and in silico pathogenicity prediction programmes.

RESULTS

Final consensus on classifications of 'pathogenic' was achieved for 32 of 33 GLA variants (26 'classic' phenotype, 171 males; 6 'later-onset' phenotype, 57 males). One variant remained of uncertain significance. KM curves were similar for the known fabry-database.org database phenotypes and when workgroup consensus classifications were added, and the curves retained the same separation between 'classic' and 'later-onset' phenotypes.

CONCLUSION

The iterative system implemented by a Fabry disease genotype-phenotype workgroup achieved phenotypic classifications for variants that were previously unclassified. Clinical pathogenicity associated with a particular GLA variant defined in affected males appears to have predictive value and also generally correlates with risk for affected females. The newly established classifications can be of benefit to the clinical care of Fabry patients harbouring these variants.

Cardiomyopathy associated with the Ala143Thr variant of the α-galactosidase A gene

OBJECTIVE

To investigate whether the Ala143Thr variant of the α-galactosidase A gene (A143T/GLA), with conflicting interpretations of pathogenicity, is associated with Fabry cardiomyopathy.

METHODS

The index patient, a woman in her 60s with cardiomyopathy, was screened for variants in 59 cardiomyopathy-related genes. A143T/GLA, the only rare variant found, was screened in 10 relatives. GLA activity and lyso-Gb3 levels were measured and echocardiography was performed in 8 of 9 subjects carrying A143T/GLA. Cardiac magnetic resonance (CMR) imaging and ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/CT (PET/CT) were performed in four adult A143T/GLA carriers. Endomyocardial biopsy was obtained from two adult A143T/GLA carrying sons of the index patient.

RESULTS

The index patient and her elder son had a pacemaker implantation because of sick sinus syndrome and atrioventricular block. GLA activities were decreased to 25%-40% of normal in both sons and one granddaughter. Lyso-Gb3 levels were elevated in both sons. In CMR, the index patient and her two sons had left ventricular (LV) hypertrophy and/or dilatation. The elder son had late gadolinium enhancement, high CMR-derived T1 time and positive FDG signal in PET/CT in the basal inferolateral LV wall. The younger son had low T1 time and the mother had positive FDG signal in PET/CT in the basal inferolateral LV wall. Endomyocardial biopsy of both sons showed myocardial accumulation compatible with glycolipids in light and electron microscopy, staining with anti-Gb3 antibody available for the younger son. Five female relatives with A143T/GLA had no cardiomyopathy in cardiac imaging.

CONCLUSIONS

A143T/GLA is likely a late-onset Fabry cardiomyopathy causing variant with incomplete penetrance.

Higher rate of rheumatic manifestations and delay in diagnosis in Brazilian Fabry disease patients

BACKGROUND

Fabry disease (FD) is an X-linked lysosomal disorder due to mutations in the GLA gene resulting in defective enzyme alpha-galactosidase A. FD patients are frequently misdiagnosed, commonly for rheumatic diseases. Determining pathogenicity of a mutation depends of in silico predictions but mostly on available clinical information and interpretation may change in light of evolving knowledge. Similar signs and symptoms in carriers of GLA gene genetic variants of unknown significance or of benign variants may hamper diagnosis. This study reviews rheumatic and immune-mediated manifestations in a cohort of Brazilian FD patients with classic mutations and also in subjects with GLA gene A143T and R118C mutations. Misdiagnoses, time to correct diagnosis or determination of GLA gene status, time to treatment initiation and reasons for treatment prescription in A143T and R118C subjects are reviewed.

METHODS

Genotype confirmed classic FD patients (n = 37) and subjects with GLA gene mutations A143T and R118C (n = 19) were referred for assessment. Subjects with R118C and A143T mutations had been previously identified during screening procedures at hemodialysis units. All patients were interviewed and examined by a rheumatologist with previous knowledge of disease and/or mutation status. A structured tool developed by the authors was used to cover all aspects of FD and of common rheumatic conditions. All available laboratory and imaging data were reviewed.

RESULTS

Thirty-seven consecutive FD patients were interviewed - 16 male / 21 female (mean age: 43.1 years) and 19 consecutive subjects with GLA gene mutations R118C and A143T were evaluated - 8 male / 11 female (mean age: 39.6 years); 15 [R118C] / 4 [A143T]. Misdiagnosis in FD patients occurred in 11 males (68.8%) and 13 females (61.9%) of which 10 males and 9 females were previously diagnosed with one or more rheumatic conditions, most frequently rheumatic fever or "rheumatism" (unspecified rheumatic disorder). Median time for diagnosis after symptom onset was 16 years (range, 0-52 years). Twenty-two patients were treated with enzyme replacement therapy (ERT) - 13 male and 9 female. Median time to ERT initiation after FD diagnosis was 0.5 years (range, 0-15 years). Rheumatic manifestations occurred in 68.4% of R118C and A143T subjects. Two subjects had been prescribed ERT because of renal disease [R118C] and neuropsychiatric symptoms [A143T].

CONCLUSION

Misdiagnoses occurred in 64.8% of FD patients, most frequently for rheumatic conditions. Median time for correct diagnosis was 16 years. Rheumatic manifestations are also frequent in subjects with GLA gene R118C and A143T mutations. These results reinforce the need to raise awareness and increase knowledge about Fabry disease among physicians, notably rheumatologists, who definitely have a role in identifying patients and determining disease burden. Decision to start treatment should consider expert opinion and follow local guidelines.

Galactosidase Alpha p.A143T Variant Fabry Disease May Result in a Phenotype With Multifocal Microvascular Cerebral Involvement at a Young Age

Introduction

A 16-year-old male presented with episodic headaches and a brain magnetic resonance imaging (MRI) that showed multifocal punctate to patchy white matter lesions. The diagnosis of Fabry disease (FD) was suggested upon the finding of significantly reduced plasma alpha-galactosidase A activity (0.62 µmol/L or 13% of normal; normal range ≥ 1.65 μmol/L) and genetic investigation confirmed the presence of a hemizygous missense variant in the galactosidase alpha (GLA) gene (p.A143T). Baseline assessment of other systemic involvement showed only a discrete proteinuria.

Background

FD is a rare lysosomal storage disorder. Genetic screening studies have revealed over 600 variants in the GLA gene. The p.A143T variant is a genetic variant of unknown significance, with its associated phenotype ranging from classical FD to healthy unaffected patients. Some authors, however, deem this variant non-pathogenic. We describe the case of a 16-year-old male with multifocal white matter lesions on brain MRI, who was diagnosed with FD and carried this genetic variant.

Discussion

The causative p.A143T mutation can be associated with a more severe subclinical phenotype than has been reported to date. Furthermore, a diagnosis of FD should be considered when finding asymptomatic cerebral white matter lesions in a young patient.

Fabry Disease: prevalence of affected males and heterozygotes with pathogenic GLA mutations identified by screening renal, cardiac and stroke clinics, 1995-2017

BACKGROUND

Fabry Disease (FD), an X linked lysosomal storage disease due to pathogenic α-galactosidase A (GLA) mutations, results in two major subtypes, the early-onset Type 1 'Classic' and the Type 2 'Later-Onset' phenotypes. To identify previously unrecognised patients, investigators screened cardiac, renal and stroke clinics by enzyme assays. However, some screening studies did not perform confirmatory GLA mutation analyses, and many included recently recognised 'benign/likely-benign' variants, thereby inflating prevalence estimates.

METHODS

Online databases were searched for all FD screening studies in high-risk clinics (1995-2017). Studies reporting GLA mutations were re-analysed for pathogenic mutations, sex and phenotype. Phenotype-specific and sex-specific prevalence rates were determined.

RESULTS

Of 67 studies, 63 that screened 51363patients (33943M and 17420F) and provided GLA mutations were reanalysed for disease-causing mutations. Of reported GLA mutations, benign variants occurred in 47.9% of males and 74.1% of females. The following were the revised prevalence estimates: among 36820 (23954M and 12866F) haemodialysis screenees, 0.21% males and 0.15% females; among 3074 (2031M and 1043F) renal transplant screenees, 0.25% males and no females; among 5491 (4054M and 1437F) cardiac screenees, 0.94% males and 0.90% females; and among 5978 (3904M and 2074F) stroke screenees, 0.13% males and 0.14% females. Among male and female screenees with pathogenic mutations, the type 1 Classic phenotype was predominant (~60%), except more male cardiac patients (75%) had type 2 Later-Onset phenotype.

CONCLUSIONS

Compared with previous findings, reanalysis of 63 studies increased the screenee numbers (~3.4-fold), eliminated 20 benign/likely benign variants, and provided more accurate sex-specific and phenotype-specific prevalence estimates, ranging from ~0.13% of stroke to ~0.9% of cardiac male or female screenees.

Fabry disease and multiple sclerosis misdiagnosis: the role of family history and neurological signs

Fabry disease (FD) is an X-linked inherited lysosomal storage disorder caused by α galactosidase A (α-gal A) deficiency. Central nervous system involvement and chronic white matter lesions are observed in both FD and multiple sclerosis (MS), which can confound the differential diagnosis. We analyzed the GLA gene, which encodes α-gal A, in 86 patients with clinical and neuroradiological findings consistent with MS to determine whether they had FD. We identified four women initially diagnosed with MS who had GLA mutations associated with FD. Our results indicate that family history besides neurological findings should be evaluated in patients with an uncertain diagnosis of MS. Also the involvement of organs outside the central nervous system can support the FD diagnosis.

Fabry disease due to D313Y and novel GLA mutations

OBJECTIVES

Our aim is to report four novel α-gal A gene (GLA) mutations resulting in Fabry disease (FD) and provide evidence of pathogenicity of the D313Y mutation regarding which contradictory data have been presented in the literature.

SETTING AND PARTICIPANTS

Twenty-five family members of nine unrelated patients with definite FD diagnosis, 10 clinically suspected cases and 18 members of their families were included in this polycentric cohort study.

PRIMARY AND SECONDARY OUTCOME MEASURES

Genotyping and measurement of lyso-Gb₃ was performed in all individuals. The α-Gal A activity was measured in all men as well as plasma and urine Gb₃ concentration in selected cases. Optical and electron microscopy was performed in kidney biopsies of selected patients. All the above were evaluated in parallel with the clinical data of the patients.

RESULTS

Fourteen new cases of FD were recognised, four of which were carrying already described GLA mutations. Four novel GLA mutations, namely c.835C>T, c.280T>A, c.924A>C and c.511G>A, resulting in a classic FD phenotype were identified. Moreover, FD was definitely diagnosed in five patients carrying the D313Y mutation. Eight D313Y carriers were presenting signs of FD despite not fulfilling the criteria of the disease, two had no FD signs and two others were apparently healthy.

CONCLUSIONS

Four novel GLA pathogenic mutations are reported and evidence of pathogenicity of the D313Y mutation is provided. It seems that the D313Y mutation is related to a later-onset milder phenotype than the typical phenotype with normal lysoGb₃ concentration. Our study underlines the significance of family member genotyping and newborn screening to avoid misdiagnoses and crucial delays in diagnosis and treatment of the disease.

Alpha-Galactosidase A p.A143T, a non-Fabry disease-causing variant

BACKGROUND

Fabry disease (FD) is an X-linked multisystemic disorder with a heterogeneous phenotype. Especially atypical or late-onset type 2 phenotypes present a therapeutical dilemma.

METHODS

To determine the clinical impact of the alpha-Galactosidase A (GLA) p.A143T/ c.427G > A variation, we retrospectively analyzed 25 p.A143T patients in comparison to 58 FD patients with other missense mutations.

RESULTS

p.A143T patients suffering from stroke/ transient ischemic attacks had slightly decreased residual GLA activities, and/or increased lyso-Gb3 levels, suspecting FD. However, most male p.A143T patients presented with significant residual GLA activity (~50 % of reference), which was associated with normal lyso-Gb3 levels. Additionally, p.A143T patients showed less severe FD-typical symptoms and absent FD-typical renal and cardiac involvement in comparison to FD patients with other missense mutations. Two tested female p.A143T patients with stroke/TIA did not show skewed X chromosome inactivation. No accumulation of neurologic events in family members of p.A143T patients with stroke/transient ischemic attacks was observed.

CONCLUSIONS

We conclude that GLA p.A143T seems to be most likely a neutral variant or a possible modifier instead of a disease-causing mutation. Therefore, we suggest that p.A143T patients with stroke/transient ischemic attacks of unknown etiology should be further evaluated, since the diagnosis of FD is not probable and subsequent ERT or chaperone treatment should not be an unreflected option.

Pain management strategies for neuropathic pain in Fabry disease--a systematic review

Background

Neuropathic pain is one of the key features of (classical) Fabry disease (FD). No randomized clinical trials comparing effectiveness of different pain management strategies have been performed. This review aims to give an overview of existing pain management strategies.

Methods

PubMed and Embase were searched up to September 2014 for relevant articles on treatment of neuropathic pain in FD.

Results

Seven-hundred-thirty-one articles were identified of which 26 were included in the analysis. Studies reported on 55 individuals in total, with group-sizes ranging from 1 to 8. Carbamazepine appeared most beneficial: complete pain relief in 5/25, partial relief in 17/25, and no benefit in 3/25 patients. Phenytoin resulted in complete relief in 1/27, partial relief in 12/27 and no benefit in 6/27 patients. In 8 patients a significant reduction in the frequency of pain attacks was described. Gabapentin caused partial relief in 6/7 and no relief in 1/7 patients. Little evidence was reported for SSNRI’s or treatment combinations. Adverse-effects were reported in all treatment strategies.

Conclusions

Only for carbamazepine, phenytoin and gabapentin there is evidence of effectiveness in neuropathic pain due to FD, but comparison of effectiveness between these drugs is lacking. In routine clinical practice adverse-effects may discourage use of carbamazepine and phenytoin in favor of second-generation antiepileptic drugs, but this is currently not supported by clinical evidence. This review suffers greatly from incomplete outcome reports and a predominance of case reports, which emphasizes the need for robust clinical trials and observational cohort studies.

Diagnostic dilemmas in Fabry disease: a case series study on GLA mutations of unknown clinical significance

Fabry disease' (FD) phenotype is heterogeneous: alpha-galactosidase A gene mutations (GLA) can lead to classical or non-classical FD, or no FD. The aim of this study is to describe pitfalls in diagnosing non-classical FD and assess the diagnostic value of plasma globotriaosylsphingosine. This is a case series study. Family 1 (p.A143T) presented with hypertrophic cardiomyopathy (HCM), absent classical FD signs, high residual alpha-galactosidase A activity (AGAL-A) and normal plasma globotriaosylsphingosine. Co-segregating sarcomeric mutations were found. Cardiac biopsy excluded FD. In family 2 (p.P60L), FD was suspected after kidney biopsy in a female with chloroquine use. Males had residual AGAL-A, no classical FD signs and minimally increased plasma globotriaosylsphingosine, indicating that p.P60L is most likely non-pathogenic. Non-specific complications and histology can be explained by chloroquine and alternative causes. Males of two unrelated families (p.R112H) show AGAL-A <5%, but slightly elevated plasma globotriaosylsphingosine (1.2-2.0 classical males >50 nmol/l). Histological evidence suggests a variable penetrance of this mutation. Patients with GLA mutations and non-specific findings such as HCM may have non-classical FD or no FD. Other (genetic) causes of FD-like findings should be excluded, including medication inducing FD-like storage. Plasma globotriaosylsphingosine may serve as a diagnostic tool, but histology of an affected organ is often mandatory.

The implications of familial incidental findings from exome sequencing: the NIH Undiagnosed Diseases Program experience

PURPOSE

Using exome sequence data from 159 families participating in the National Institutes of Health Undiagnosed Diseases Program, we evaluated the number and inheritance mode of reportable incidental sequence variants.

METHODS

Following the American College of Medical Genetics and Genomics recommendations for reporting of incidental findings from next-generation sequencing, we extracted variants in 56 genes from the exome sequence data of 543 subjects and determined the reportable incidental findings for each participant. We also defined variant status as inherited or de novo for those with available parental sequence data.

RESULTS

We identified 14 independent reportable variants in 159 (8.8%) families. For nine families with parental sequence data in our cohort, a parent transmitted the variant to one or more children (nine minor children and four adult children). The remaining five variants occurred in adults for whom parental sequences were unavailable.

CONCLUSION

Our results are consistent with the expectation that a small percentage of exomes will result in identification of an incidental finding under the American College of Medical Genetics and Genomics recommendations. Additionally, our analysis of family sequence data highlights that genome and exome sequencing of families has unavoidable implications for immediate family members and therefore requires appropriate counseling for the family.

Case-finding in Fabry disease: experience from the North of England

The advent of effective therapy for Fabry disease (FD) creates two challenges: (1) how do we identify individuals with the condition early in its natural history, and (2) how many people have the condition and require expensive therapy? Between 1981 and 2011, 17 new FD families were referred to the Northern Genetics Service in the North of England, the majority between 2005 and 2001. Since 2009 we have employed biochemical screening in dried blood spots from individuals with high risk phenotypes, such as left ventricular hypertrophy and unexplained renal failure, to identify four of the new index cases; and we have offered comprehensive cascade genetic testing to identify pre-symptomatic and symptomatic cases of FD in their 233 'at risk' relatives. Overall, this combined approach identified a further 23 symptomatic cases of FD and 38 asymptomatic cases. The uptake of cascade genetic testing in this cohort was 48%, which is similar to other inherited disorders for which there is an effective intervention. The minimum prevalence of GLA mutation in the North of England population at the end of 2011 was 1 in 40,800 and the prevalence of symptomatic FD was 1 in 64,600. Improved uptake of cascade genetic testing would increase these estimates to a maximum of 1 in 21,800 and 1 in 49,000 respectively. We suggest that any protocol for case identification should consist of targeted biochemical screening and coordinated cascade genetic testing.