Multifocal white matter lesions associated with the D313Y mutation of the α-galactosidase A gene

Clinical study of left ventricular structure and function in patients with Anderson-Fabry disease before and after enzyme replacement therapy

AIMS

Cardiac left ventricular hypertrophy (LVH) is the most common manifestation of heart involvement in Anderson-Fabry disease (AFD). Conventional cardiac imaging is not sensitive enough to detect early signs of LVH in AFD. It remains uncertain whether enzyme replacement therapy (ERT) can prevent LVH progression and improve myocardial function. This study aimed to assess the effectiveness of two-dimensional speckle tracking echocardiography (2D-STE) in early detection of cardiac involvement in AFD and monitoring the efficacy of agalsidase alfa and agalsidase beta therapy.

METHODS AND RESULTS

Thirteen consecutive AFD patients and 12 healthy controls underwent standard transthoracic 2D, color Doppler, tissue Doppler echocardiography, and 2D strain analysis. Global longitudinal strain (GLS) and global circumferential strain (GCS) were measured. Diastolic strain rate (SR) was extracted. Compared to healthy subjects, AFD patients without LVH showed lower levels of GLS (p < 0.001) and SR (p = 0.01), while there was no difference in GCS (p = 0.82). Following treatment, apical circumferential strain (ACS) showed improvement (p = 0.01).

CONCLUSION

In AFD patients without LVH, there was a decrease in global and segmental LS. Higher plasma Lyso-GL-3 concentrations were associated with elevated ACS values after ERT, indicating that ACS in AFD patients without LVH, albeit normal, is involved in early LV dysfunction.

Genotype-Phenotype Correlations in 293 Russian Patients with Causal Fabry Disease Variants

BACKGROUND

Fabry disease (FD) is a rare hereditary multisystem disease caused by variants of the GLA gene. Determination of GLA gene variants and identification of genotype-phenotype correlations allow us to explain the features of FD associated with predominant damage of one or another system, both in the classical and atypical forms of FD, as well as in cases with late manifestation and involvement of one of the systems.

METHODS

The study included 293 Russian patients with pathogenic variants of the GLA gene, which were identified as a result of various selective screening programs. Screening was carried out for 48,428 high-risk patients using a two-step diagnostic algorithm, including the determination of the concentration of the biomarker lyso-Gb3 as a first-tier test. Screening of atypical FD among patients with HCM was carried out via high-throughput sequencing in another 2427 patients.

RESULTS

102 (0.20%) cases of FD were identified among unrelated patients as a result of the study of 50,855 patients. Molecular genetic testing allowed us to reveal the spectrum and frequencies of 104 different pathogenic variants of the GLA gene in 293 examined patients from 133 families. The spectrum and frequencies of clinical manifestations in patients with FD, including 20 pediatric patients, were described. Correlations between the concentration of the lyso-Gb3 biomarker and the type of pathogenic variants of the GLA gene have been established. Variants identified in patients with early stroke were described, and the association of certain variants with the development of stroke was established.

CONCLUSIONS

The results of a large-scale selective FD screening, as well as clinical and molecular genetic features, in a cohort of 293 Russian patients with FD are described.

D313Y variant in two related end-stage renal disease patients - Pathogenic or not yet?

Fabry disease is a multisystem lysosomal storage disorder caused by mutations in the GLA gene that result in a deficient or absent activity of alpha-galactosidase A. There is a wide spectrum of GLA gene variants, some of which are described as non-pathogenic. The clinical importance of the D313Y variant is still under debate, although in recent years it has been considered as a variant of unknown significance or a benign variant. Despite this prevailing notion, there are multiple case reports of patients with D313Y variant that presented signs and symptoms consistent with FD without any other etiological explanation. In this article, we present two family members with an important renal phenotype and other typical manifestations of FD (white matter lesions and left ventricular hypertrophy) that only had the D313Y variant. These cases suggest that this variant of unknown significance may contribute to the development of common features of FD and should not be undervalued.

Phenotyping of a novel COL4A4 and novel GLA variant in a patient presenting with microhematuria and mildly impaired kidney function: a case report

We describe the case of a 44-year-old male patient with a longstanding history of microhematuria and mildly impaired kidney function (CKD G2A1). The family history disclosed three females who also had microhematuria. Genetic testing by whole exome sequencing revealed two novel variants in COL4A4 (NM_000092.5: c.1181G>T, NP_000083.3: p.Gly394Val, heterozygous, likely pathogenic; Alport syndrome, OMIM# 141200, 203780) and GLA (NM_000169.3: c.460A>G, NP_000160.1: p.Ile154Val, hemizygous, variant of uncertain significance; Fabry disease, OMIM# 301500), respectively. Extensive phenotyping revealed no biochemical or clinical evidence for the presence of Fabry disease. Thus, the GLA c.460A>G, p.Ile154Val, is to be classified as a benign variant, whereas the COL4A4 c.1181G>T, p.Gly394Val confirms the diagnosis of autosomal dominant Alport syndrome in this patient.

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.

Expert opinion on the recognition, diagnosis and management of children and adults with Fabry disease: a multidisciplinary Turkey perspective

This consensus statement by a panel of Fabry experts aimed to identify areas of consensus on conceptual, clinical and therapeutic aspects of Fabry disease (FD) and to provide guidance to healthcare providers on best practice in the management of pediatric and adult patients with FD. This consensus statement indicated the clinical heterogeneity of FD as well as a large number of pathogenic variants in the GLA gene, emphasizing a need for an individualized approach to patient care. The experts reached consensus on the critical role of a high index of suspicion in symptomatic patients and screening of certain at-risk groups to reveal timely and accurate diagnosis of FD along with an increased awareness of the treating physician about the different kinds of pathogenic variants and their clinical implications. The experts emphasized the crucial role of timely recognition of FD with minimal delay from symptom onset to definite diagnosis in better management of FD patients, given the likelihood of changing the disease's natural history, improving the patients' quality of life and the prognosis after enzyme replacement therapy (ERT) administered through a coordinated, multidisciplinary care approach. In this regard, this consensus document is expected to increase awareness among physicians about unique characteristics of FD to assist clinicians in recognizing FD with a well-established clinical suspicion consistent with pathogenic variants and gender-based heterogeneous clinical manifestations of FD and in translating this information into their clinical practice for best practice in the management of patients with FD.

Assessment of small fiber neuropathy in patients carrying the non-classical Fabry variant p.D313Y

INTRODUCTION

The pathophysiological significance of the Fabry-related, non-classical variant p.D313Y still remains to be solved. This study assesses the involvement of the peripheral nervous system with respect to small fiber neuropathy and neuropathic pain in female patients carrying p.D313Y.

METHODS

This study examined nine females carrying the Fabry-related p.D313Y variant by obtaining skin punch biopsies above the right lateral malleolus. Intraepidermal nerve fiber density was determined for each patient and compared to reference values matched for the patient's decade of life and sex. Moreover, each patient was characterized by a detailed neurological examination and by pain assessment via questionnaire.

RESULTS

Compared to sex-matched lower fifth percentile reference values per decade, intraepidermal nerve fiber density was decreased in seven out of nine patients. Four patients reported acral paresthesias and neuropathic pain with an average visual analogue scale score of 7 out of 10 points. Two patients experienced acute pain crises. Six out of seven patients diagnosed with small fiber neuropathy had a their medical history of hypo- and/or hyperhidrosis.

DISCUSSION

The diagnosis of small fiber neuropathy was made in seven out of nine females carrying the non-classical variant p.D313Y. Moreover, neuropathic pain and symptoms indicative of autonomic nervous system dysfunction seem to be common findings that may be of clinical significance and may warrant therapeutic intervention.

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.

Screening for Fabry Disease in Kidney Transplant Recipients: Experience of a Multidisciplinary Team

Fabry disease (FD) is a rare cause of end-stage renal disease requiring kidney transplantation. Data on the incidence of unrecognized FD in kidney transplant recipients are scarce and probably underestimated. This study evaluated the incidence of FD in a population of kidney recipients, with a particular focus of the multidisciplinary approach for an early clinical assessment and therapeutic approach. Two hundred sixty-five kidney transplant recipients were screened with a genetic analysis for α-galactosidase A (GLA) mutation, with measurement of α-Gal A enzyme activity and Lyso Gb3 levels. Screening was also extended to relatives of affected patients. Seven patients (2.6%) had a GLA mutation. Two patients had a classic form of FD with Fabry nephropathy. Among the relatives, 15 subjects had a GLA mutation, and two had a Fabry nephropathy. The clinical and diagnostic assessment was completed after a median of 3.2 months, and mean time from diagnosis to treatment was 4.6 months. This study reported a high incidence of unrecognized GLA mutations in kidney transplant recipients. Evaluation and management by a multidisciplinary team allowed for an early diagnosis and treatment, and this would result in a delay in the progression of the disease and, finally, in better long-term outcomes.

Screening for Fabry Disease in Kidney Transplant Recipients: Experience of a Multidisciplinary Team

Fabry disease (FD) is a rare cause of end-stage renal disease requiring kidney transplantation. Data on the incidence of unrecognized FD in kidney transplant recipients are scarce and probably underestimated. This study evaluated the incidence of FD in a population of kidney recipients, with a particular focus of the multidisciplinary approach for an early clinical assessment and therapeutic approach. Two hundred sixty-five kidney transplant recipients were screened with a genetic analysis for α-galactosidase A (GLA) mutation, with measurement of α-Gal A enzyme activity and Lyso Gb3 levels. Screening was also extended to relatives of affected patients. Seven patients (2.6%) had a GLA mutation. Two patients had a classic form of FD with Fabry nephropathy. Among the relatives, 15 subjects had a GLA mutation, and two had a Fabry nephropathy. The clinical and diagnostic assessment was completed after a median of 3.2 months, and mean time from diagnosis to treatment was 4.6 months. This study reported a high incidence of unrecognized GLA mutations in kidney transplant recipients. Evaluation and management by a multidisciplinary team allowed for an early diagnosis and treatment, and this would result in a delay in the progression of the disease and, finally, in better long-term outcomes.

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.

Cerebral Hemodynamic Changes to Transcranial Doppler in Asymptomatic Patients with Fabry's Disease

BACKGROUND

Patients with Fabry's disease (FD) may be asymptomatic or show a spectrum of clinical manifestations, including cerebrovascular disease, mainly affecting posterior circulation. Few and conflicting studies on cerebral blood flow (CBF) velocity by transcranial Doppler sonography (TCD) in asymptomatic FD (aFD) subjects have been published. Our study aims to assess TCD in aFD subjects to identify any preclinical CBF change.

METHODS

A total of 30 aFD subjects were consecutively recruited and compared to 28 healthy controls. Brain magnetic resonance imaging was normal in all participants. TCD was used to study blood flow velocity and indices of resistance of intracranial arteries from the middle cerebral artery (MCA), bilaterally, and from the basilar artery (BA). Cerebral vasomotor reactivity (CVR) was also evaluated from MCA.

RESULTS

No difference was found between groups for MCA parameters of CBF velocity and CVR. Compared to controls, a higher mean blood flow velocity and a lower resistance index from BA were observed in FD subjects. No correlation was found between any BA-derived TCD parameter and the level of lyso-globotriaosylceramide.

CONCLUSIONS

aFD subjects show evidence of altered CBF velocity in posterior circulation. Preclinical detection of neurovascular involvement in FD might allow appropriate management and prevention of future cerebrovascular complications and disability.

Cerebral Hemodynamic Changes to Transcranial Doppler in Asymptomatic Patients with Fabry's Disease

BACKGROUND

Patients with Fabry's disease (FD) may be asymptomatic or show a spectrum of clinical manifestations, including cerebrovascular disease, mainly affecting posterior circulation. Few and conflicting studies on cerebral blood flow (CBF) velocity by transcranial Doppler sonography (TCD) in asymptomatic FD (aFD) subjects have been published. Our study aims to assess TCD in aFD subjects to identify any preclinical CBF change.

METHODS

A total of 30 aFD subjects were consecutively recruited and compared to 28 healthy controls. Brain magnetic resonance imaging was normal in all participants. TCD was used to study blood flow velocity and indices of resistance of intracranial arteries from the middle cerebral artery (MCA), bilaterally, and from the basilar artery (BA). Cerebral vasomotor reactivity (CVR) was also evaluated from MCA.

RESULTS

No difference was found between groups for MCA parameters of CBF velocity and CVR. Compared to controls, a higher mean blood flow velocity and a lower resistance index from BA were observed in FD subjects. No correlation was found between any BA-derived TCD parameter and the level of lyso-globotriaosylceramide.

CONCLUSIONS

aFD subjects show evidence of altered CBF velocity in posterior circulation. Preclinical detection of neurovascular involvement in FD might allow appropriate management and prevention of future cerebrovascular complications and disability.

Genetic Management Algorithm in High-Risk Fabry Disease Cases; Especially in Female Indexes with Mutations

BACKGROUND

Fabry Disease (FD, OMIM#301500) is a progressive, life-threatening, multisystemic, rare lysosomal storage disease. Today, approximately 1000 mutations are recorded in the Human Gene Mutation Database (www.hgmd.org) for GLA. Among the identified mutations, genetic variants of unknown significance (GVUS) and novel mutations cause problems in terms of diagnosis and treatment approach.

METHODS

In our study, 510 high-risk patients were enrolled. 229 out of 510 were Male (45%) (Mean age was 40.8 ±15.0) and 281 of were Female (55%) (Mean age was 39, 7±15.5). The definite diagnosis of the FD was confirmed by GLA gene sequence analysis. GLA mutation was found in 15 cases (3.4%). Family members of the relevant indexes were included in the screening programs according to the X-linked inheritance pattern. And then we conducted family screening on 74 family members of 15 index cases. Of those 74 cases, 39 had mutations (53%). In males, α-GalA activity and in both gender Lyso-Gb3 levels were measured and multisystem evaluation was performed in all cases with the mutation.

RESULTS

We found six different familial mutation types; two of them pathogenic; p.D170N (1), p.P205S (13), one of them GVUS; p.Q330R (1), three of them likely benign; p.D313Y (12), p.S126G (25), c.-30G>A (2) mutations were detected.

CONCLUSION

The purpose of this retrospective study is to approach Fabry disease on a genetic basis and to improve its management and to draw attention to the importance of early diagnosis. We also aimed to evaluate the appropriate algorithms to determine whether the mutation is the FD-causing mutation or not.

Fabry Disease Screening in Patients With Kidney Transplant: A Single-Center Study in Turkey

OBJECTIVES

Fabry disease is a rare X-linked multisystemic lysosomal storage disorder of the glycosphingolipid metabolic pathway. Nephropathy is one of the most important complications of Fabry disease, and patients with classical phenotype are at risk of developing endstage kidney disease. In this study, we investigated the use of screening for Fabry disease in kidney transplant recipients at our center.

MATERIALS AND METHODS

We screened 301 kidney transplant recipients with functioning grafts. Analyses for α-galactosidase A gene mutation were performed in all female and male kidney transplant recipients. We also measured leukocyte α-galactosidase A enzyme activity in patients with identified GLA mutation.

RESULTS

In 301 kidney transplant recipients, mean age was 42.9 ± 12.5 years, and the number of male patients was 180 (60%). Mean time after transplant was 79 ± 56 months, and estimated glomerular filtration rate was 66.8 ± 21 mL/min/1.73 m². One male patient who was diagnosed with Fabry disease before kidney transplant was also evaluated (mutation in the α-galactosidase A gene, c.1093_1101dup [p.Tyr365_lle367dup]). In 2 female patients, p.A143T (c.427G>A) mutation of unknown significance and p.D313Y (c.937G>T) heterozygous mutation were identified; however, leukocyte ?-galactosidase A enzyme activity was normal in these patients (63.7 and 67.3 nmol/h/mg protein). In the patient diagnosed with Fabry disease, family screening revealed 4 additional affected family members.

DISCUSSIONS

Although prevalence was shown to be low in our center (1/301 patients; 0.33%), screening studies in kidney transplant recipients may help to detect new patients before they develop life-threatening complications such as renal involvement.

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.

GLA Gene Mutation in Hypertrophic Cardiomyopathy with a New Variant Description: Is it Fabry's Disease?

BACKGROUND

Fabry disease (FD) is an X-linked lysosomal storage disorder caused by mutations in the alpha galactosidase A gene (GLA) that lead to the enzymatic deficiency of alpha galactosidase (α-Gal A), resulting in the accumulation of globotriaosylceramide (Gb3) and globotriaosylsphingosine (lyso-Gb3), causing multiple organ dysfunctions.

OBJECTIVE

To perform GLA gene screening in a group of patients with echocardiographic diagnosis of hypertrophic cardiomyopathy (HCM).

METHODS

a cross-sectional study was conducted with HCM patients from a university hospital. Patients with coronary artery disease and valvulopathies were excluded. Mutation analysis of the GLA gene was performed. In male subjects, the analysis was performed after evidence of low α-Gal A activity.

RESULTS

60 patients with echocardiographic diagnosis of HCM were included. Age ranged from 12 to 85 years and 60% were women. Mean myocardial fibrosis percentage on MRI was 10.7 ± 13.1% and mean ventricular thickness was18.7 ± 6.7 mm. Four patients had the following GLA gene mutations: c.967C>A (p.Pro323Thr), not yet described in the literature; c.937G>T (p.Asp313Tyr); and c.352C>T (p.Arg118Cys). All patients had normal levels of lyso-Gb3 and non-ischemic myocardial fibrosis on magnetic resonance imaging; one patient had proteinuria and one patient had ventricular tachycardia.

CONCLUSION

in this study, the frequency of mutation in the GLA gene in patients with HCM was 6.7%. A novel mutation in exon 6 of the GLA gene, c.967C>A (p.Pro323Thr), was identified. Patients with HCM may have GLA mutations and FD should be ruled out. Plasma (lyso-Gb3) levels do not seem to be sufficient to attain a diagnosis and organ biopsy should be considered.

Detection of blood Gb3 deposits as a new tool for diagnosis and therapy monitoring in patients with classic Fabry disease

BACKGROUND

The X-linked Fabry disease (FD) is a multiorgan disorder due to alpha-galactosidase A (α-GAL) deficiency with consequent lysosomal accumulation of globotriaosylceramide (Gb3). We established the immunocytochemical detection of Gb3 in blood cells of FD patients as a new method for FD diagnostics, follow-up and treatment control.

METHODS

We enrolled 67 FD patients (37 men, 30 women) and 52 healthy controls (26 men, 26 women). PBMC were isolated from whole venous blood and 3x10⁵ cells were immunoreacted with antibodies against CD77 as a marker for Gb3. Using fluorescence microscopy, the mean percentage of Gb3 positive PBMC was determined by an investigator blinded to subject allocation. As a second method, we qualitatively assessed Gb3 positive cells in blood smears.

RESULTS

Gb3 deposits were unequivocally visible in PBMC and in blood smears. Men (P < 0.001) and women (P < 0.01) with classical FD had more Gb3-positive PBMC than healthy controls, whose samples only occasionally showed positive cells. The number of Gb3 positive PBMC was negatively correlated with α-GAL activity and positively correlated with plasma lyso-Gb3 levels. Only the PBMC Gb3 load but not plasma lyso-Gb3 reflected short- and long-term effects of enzyme replacement therapy (P < 0.01).

CONCLUSIONS

Gb3 can be visualized in PBMC and blood smears and can be used as a novel marker for diagnostics, follow-up and treatment control in FD.

Altered Gene Expression in Prefrontal Cortex of a Fabry Disease Mouse Model

Fabry disease is an X-chromosome linked hereditary disease that is caused by loss of function mutations in the α-galactosidase A (α-Gal A) gene, resulting in defective glycolipid degradation and subsequent accumulation of globotriaosylceramide (Gb3) in different tissues, including vascular endothelial cells and neurons in the peripheral and central nervous system. We recently reported a differential gene expression profile of α-Gal A^(−/0) mouse dorsal root ganglia, an established animal model of Fabry disease, thereby providing new gene targets that might underlie the neuropathic pain related symptoms. To investigate the cognitive symptoms experienced by Fabry patients, we performed one-color based hybridization microarray expression profiling of prefrontal cortex samples from adult α-Gal A^(−/0) mice and age-matched wildtype controls, followed by protein-protein interaction and pathway analyses for the differentially regulated mRNAs. We found that from a total of 381 differentially expressed genes, 135 genes were significantly upregulated, whereas 246 genes were significantly downregulated between α-Gal A^(−/0) mice and wildtype controls. Enrichment analysis for downregulated genes revealed mainly immune related pathways, including immune/defense responses, regulation of cytokine production, as well as signaling and transport regulation pathways. Further analysis of the regulated genes revealed a large number of genes involved in neurodegeneration. The current analysis for the first time presents a differential gene expression profile of central nervous system tissue from α-Gal A^(−/0) mice, thereby providing novel knowledge on the deregulation and a possible contribution of gene expression to Fabry disease related brain pathologies.

Diagnostic Clues for the Diagnosis of Nonsarcomeric Hypertrophic Cardiomyopathy (Phenocopies): Amyloidosis, Fabry Disease, and Mitochondrial Disease

Hypertrophic cardiomyopathy (HCM) is the most common known inherited heart disorder, with a prevalence of 1:500 of the adult population. Etiology of HCM can be heterogeneous, with sarcomeric gene disease as the leading cause in up to 60% of the patients, and with a number of possible different diseases (phenocopies) in about 10%–15% of the patients. Early diagnosis of storage and infiltrative disorders, particularly those with specific treatments (i.e., Fabry disease and/or amyloidosis), means early management and treatment, with a significant impact on patients prognosis. Here, we report on four different cases of HCM, highlighting difficulties to make differential diagnosis of different forms of cardiomyopathies, and their potential impact on the management.

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.

Prevalence of Fabry Disease and Outcomes in Young Canadian Patients With Cryptogenic Ischemic Cerebrovascular Events

Background and Purpose—

Previous studies reported Fabry disease in 0% to 4% of young patients with cryptogenic ischemic stroke (IS). We sought to determine the prevalence of Fabry and outcomes among young Canadians with cryptogenic IS or transient ischemic attack (TIA).

Methods—

We prospectively enrolled individuals aged 18 to 55 with IS or speech or motor TIA, and no cause identified despite predetermined investigation. α-galactosidase-A gene was sequenced for Fabry diagnosis. National Institutes of Health Stroke Scale score was measured at presentation to quantify stroke severity. Modified Rankin Scale determined functional outcomes ≤7 days after presentation and 6 months later.

Results—

We enrolled 365 patients with IS and 32 with TIA. α-galactosidase-A sequencing identified a single carrier of a genetic variant of unknown significance (p.R118C) and no well-recognized pathogenic variants. Mean National Institutes of Health Stroke Scale score was 3.1. Proportion of patients with modified Rankin Scale of 0 to 2 was 70.7% at ≤7 days and 87.4% at 6 months. National Institutes of Health Stroke Scale score at presentation and diabetes mellitus predicted 6-month modified Rankin Scale. Thirteen patients experienced 5 recurrent IS and 9 TIA during follow-up. No patient died. Most patients (98.7%) returned home. Among previous workers, 43% had residual working limitations.

Conclusions—

In this Canadian cohort of patients with cryptogenic IS or TIA, the prevalence of Fabry was 0.3% if p.R118C variant is considered as pathogenic. This suggests that more cost-effective methods should be applied for diagnosis of Fabry rather than systematic genetic screening in this population. Overall, cryptogenic IS in young adults is associated with favorable outcomes.

The mutation p.D313Y is associated with organ manifestation in Fabry disease

Fabry disease (FD) is a multisystem lysosomal storage disorder caused by mutations in the GLA gene. The clinical significance of the mutation p.D313Y is still under debate. Retrospective chart analysis of clinical (neurological, cardiac, renal, and ophthalmological), genetic, and biochemical (lyso-globotriaosylsphingosine, lyso-Gb3; enzyme activity) data was performed in all our patients carrying the p.D313Y mutation. Fourteen patients from 5 families (10 female, 4 male; age range 10-51) were included. Symptoms and organ manifestations compatible with FD could be identified in 10 patients. Cerebrovascular events occurred in 4 females. Seven patients reported pain or acroparaesthesia. Cornea verticillata was found in 1 patient, mild retinal vascular tortuosity in 5 patients. Lyso-Gb3 was elevated in 2 females with cerebrovascular involvement. Classical cardiac, renal or skin manifestations could not be identified. The mutation p.D313Y in the GLA gene may lead to organ manifestations and elevation of the Fabry-specific biomarker lyso-Gb3. Neurological symptoms (stroke and pain) and ocular manifestations seem to be the leading findings. Annual routine visits are recommended for patients carrying the p.D313Y mutation. Enzyme replacement therapy might be considered in symptomatic patients.

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.

Organ manifestations and long-term outcome of Fabry disease in patients with the GLA haplotype D313Y

OBJECTIVES

The severity of Fabry disease is dependent on the type of mutation in the α-galactosidase A (AgalA) encoding gene (GLA). This study focused on the impact of the GLA haplotype D313Y on long-term organ involvement and function.

SETTING AND PARTICIPANTS

In this monocentric study, all participants presenting with the D313Y haplotype between 2001 and 2015 were comprehensively clinically investigated at baseline and during a 4-year follow-up if available. Five females and one male were included.

PRIMARY AND SECONDARY OUTCOME MEASURES

Cardiac, nephrological, neurological, laboratory and quality of life data.

RESULTS

AgalA enzyme activity in leucocytes (0.3±0.9 nmol/min/mg protein (mean±SD)) and serum lyso-Gb3 (0.6±0.3 ng/mL at baseline) were in normal range in all patients. Cardiac morphology and function were normal (left-ventricular (LV) ejection fraction 66±8%; interventricular septum 7.7±1.4 mm; LV posterior wall 7.5±1.4 mm; normalised LV mass in MRI 52±9 g/m(2); LV global longitudinal strain -21.6±1.9%) and there were no signs of myocardial fibrosis in cardiac MRI. Cardiospecific biomarkers were also in normal range. Renal function was not impaired (estimated glomerular filtration rate MDRD 103±15 mL/min; serum-creatinine 0.75±0.07 mg/dL; cystatin-c 0.71±0.12 mg/L). One female patient (also carrying a Factor V Leiden mutation) had a transitory ischaemic attack. One patient showed white matter lesions in brain MRI, but none had Fabry-associated pain attacks, pain crises, evoked pain or permanent pain. Health-related quality of life analysis revealed a reduction in individual well-being. At long-term follow-up after 4 years, no significant change was seen in any parameter.

CONCLUSIONS

The results of the current study suggest that the D313Y genotype does not lead to severe organ manifestations as seen in genotypes known to be causal for classical FD.

D313Y mutation in the differential diagnosis of white matter lesions: Experiences from a multiple sclerosis outpatient clinic

White matter lesions (WML) in younger patients might be due to a variety of neurological disorders. Fabry disease (FD), an x-linked inherited lysosomal storage disorder, happens to be misdiagnosed as multiple sclerosis (MS). In two middle-aged female patients, presenting bilateral WML, diagnosis of MS turned out to be doubtful. Human genetic analysis presented the Fabry mutation D313Y, in which clinical impact is still unclear. Disease manifestations outside the central nervous system were not detected. Our findings support the suspicion that Fabry mutation D313Y may be involved in neural damage resulting in WML.

Exploratory screening for Fabry's disease in young adults with cerebrovascular disorders in northern Sardinia

BACKGROUND

The etiologic determinants of stroke in young adults remain a diagnostic challenge in up to one-fourth of cases. Increasing evidences led to consider Fabry's disease (FD) as a possible cause to check up. We aimed at evaluating the prevalence of unrecognized FD in a cohort of patients with juvenile stroke in northern Sardinia.

METHODS

For this study, we enrolled 178 patients consecutively admitted to our Neurological Ward for ischemic stroke, transient ischemic attack, intracerebral haemorrhage, neuroradiological evidence of silent infarcts, or white matter lesions possibly related to cerebral vasculopathy at brain MRI, and cerebral venous thrombosis. The qualifying events have to occur between 18 and 55 years of age.

RESULTS

We identified two patients with an α-galactosidase A gene variant, with a prevalence of 0.9 %. According to recent diagnostic criteria, one patient, included for the occurrence of multiple white matter lesions at brain MRI, had a diagnosis of definite FD, the other, included for ischemic stroke, had a diagnosis of uncertain FD.

CONCLUSIONS

Our study places in a middle position among studies that found a prevalence of FD up to 4 % and others that did not find any FD patients. Our findings confirm that FD should be considered in the differential diagnosis of patients with juvenile stroke, particularly those with a personal or familial history positive for cerebrovascular events, or evidence of combined cardiologic and/or renal impairment. All types of cerebrovascular disorders should be screened for FD, including patients with white matter lesions possibly related to cerebral vasculopathy at brain MRI.

Functional and Clinical Consequences of Novel α-Galactosidase A Mutations in Fabry Disease

Fabry disease (FD) is a rare metabolic disorder of glycosphingolipid storage caused by mutations in the GLA gene encoding lysosomal hydrolase α-galactosidase A (α-gal A). Recently, the diagnostic procedure for FD has advanced in several ways, through the development of a specific biomarker (lyso-Gb3) and the implementation of newborn screenings, which acted as a catalyst to augment general awareness of the disease. Heterologous over-expression of α-gal A variants and subsequent in vitro measurement of enzyme activity provided molecular data to elucidate the relationship between mutation, enzyme damage, lyso-Gb3 biomarker levels, and clinical phenotype. This knowledge is the foundation for improved counseling with regard to prognosis and therapeutic decisions. Herein, we resume the approach of in vitro characterization, with a further 73 mainly novel GLA gene mutations. Patient lyso-Gb3 data were available for most of the mutations. All mutations were tested for responsiveness to pharmacological chaperone treatment and phenotypic data for 61 hemizygous male and 116 heterozygous female patients carrying a mutation associated with ≥ 20% residual activity, formerly classified as "mild" variant, were collected in order to evaluate the pathogenicity. We conclude that a mild GLA variant is typically characterized by high residual enzyme activity and normal biomarker levels. We found evidence that these variants can still be classified as a distinctive, but milder, sub-type of FD.

Cryptogenic stroke and small fiber neuropathy of unknown etiology in patients with alpha-galactosidase A -10T genotype

BACKGROUND

Fabry disease (FD) is a multisystemic disorder with typical neurological manifestations such as stroke and small fiber neuropathy (SFN), caused by mutations of the alpha-galactosidase A (GLA) gene. We analyzed 15 patients carrying the GLA haplotype -10C>T [rs2071225], IVS2-81_-77delCAGCC [rs5903184], IVS4-16A>G [rs2071397], and IVS6-22C>T [rs2071228] for potential neurological manifestations.

METHODS AND RESULTS

Patients were retrospectively analyzed for stroke, transient ischemic attack (TIA), white matter lesions (WML) and SFN with neuropathic pain. Functional impact of the haplotype was determined by molecular genetic methods including real-time PCR, exon trapping, promoter deletion constructs and electrophoretic mobility shift assays. Symptomatic -10T allele carriers suffered from stroke, TIA, WML, and SFN with neuropathic pain. Patients' mean GLA mRNA expression level was reduced to ~70% (p < 0.0001) and a dose-dependent effect of the -10T allele on GLA mRNA expression was observed in hemi/homozygous compared to heterozygous patients (p < 0.0001). Molecular analyzes revealed that the -10T allele resulted in a reduced promoter activity and an altered transcription factor binding, while a functional relevance of the co-segregated intronic variants was excluded by exon trapping.

CONCLUSIONS

Based on this complementary approach of clinical observation and functional testing, we conclude that the GLA -10T allele could be causal for the observed neurological manifestations. Future studies are needed to clarify whether affected patients benefit from GLA enzyme replacement therapy for end-organ damage prevention.

A novel method for detecting uniparental disomy from trio genotypes identifies a significant excess in children with developmental disorders

Exome sequencing of parent-offspring trios is a popular strategy for identifying causative genetic variants in children with rare diseases. This method owes its strength to the leveraging of inheritance information, which facilitates de novo variant calling, inference of compound heterozygosity, and the identification of inheritance anomalies. Uniparental disomy describes the inheritance of a homologous chromosome pair from only one parent. This aberration is important to detect in genetic disease studies because it can result in imprinting disorders and recessive diseases. We have developed a software tool to detect uniparental disomy from child-mother-father genotype data that uses a binomial test to identify chromosomes with a significant burden of uniparentally inherited genotypes. This tool is the first to read VCF-formatted genotypes, to perform integrated copy number filtering, and to use a statistical test inherently robust for use in platforms of varying genotyping density and noise characteristics. Simulations demonstrated superior accuracy compared with previously developed approaches. We implemented the method on 1057 trios from the Deciphering Developmental Disorders project, a trio-based rare disease study, and detected six validated events, a significant enrichment compared with the population prevalence of UPD (1 in 3500), suggesting that most of these events are pathogenic. One of these events represents a known imprinting disorder, and exome analyses have identified rare homozygous candidate variants, mainly in the isodisomic regions of UPD chromosomes, which, among other variants, provide targets for further genetic and functional evaluation.