Enzymatic diagnosis of Fabry disease using a fluorometric assay on dried blood spots: An alternative methodology

Screening for Fabry disease in patients with left ventricular hypertrophy in China: A multicentre and prospective study

AIMS

Left ventricular hypertrophy (LVH) is frequently detected via echocardiography in individuals with Fabry disease (FD), sometimes leading to confusion with hypertrophic cardiomyopathy (HCM) of other aetiologies. Considering this diagnosis challenge, FD should be included in the list of differential diagnosis for patients presenting with LVH. To address this concern, we conducted a prospective screening study in China, using dried blood spot (DBS) testing, to evaluate patients with unexplained LVH.

METHODS

Our study was designed as a nationwide, multicentre prospective investigation. A total of 1015 patients from 55 different centres who were diagnosed with LVH by echocardiography were screened in the study from September 2022 to December 2023. Demographic information, biochemistry data, echocardiography parameters and clinical observations were meticulously collected from all participants. The DBS method was used to assess α-galactosidase A (α-Gal A) activity in males and both α-Gal A and globotriaosylsphingosine (lyso-Gb3) levels in females.

RESULTS

The final screening population included 906 patients (589 males, 65%) with LVH, characterized by a mean maximal myocardial thickness of 14.8 ± 4.6 mm and an average age of 56.9 ± 17.2 years. In total, 43 patients (38 males, 5 females) exhibited low α-Gal A activity measurement (<2.2 μmol/L), while 21 patients (10 males, 11 females) presented low α-Gal A activity or elevated lyso-Gb3 levels (>1.1 ng/mL). Among these patients, eight individuals (7 males and 1 female) were genetically confirmed to harbour pathogenic GLA mutations, resulting in a total prevalence of 0.88%. Compared with patients without FD, patients with FD tended to have proteinuria (75% vs. 21.2%, P = 0.001), family history of HCM (37.5% vs. 2.3%, P < 0.01) and neuropathic pain (37.5% vs. 4.4%, P < 0.01) but lower systolic blood pressure (118.5 ± 12.5 vs. 143.3 ± 29.3 mmHg, P = 0.017). Five mutations were previously recognized as associated with FD while the remaining two, p.Asp313Val (c.938A>T) and c.547+3A>G, were deemed potentially pathogenic. Subsequent familial validation post-diagnosis identified an additional 14 confirmed cases.

CONCLUSIONS

This pioneering screening study for FD among Chinese patients with unexplained LVH using DBS measurement, revealed an FD detection rate of 0.88%. Our findings confirmed that the combined measurement of lyso-Gb3 and α-Gal A activity is beneficial for primary screening of FD in patients with LVH. Given the availability of efficacious therapies and the value of cascade screening in extended families, early detection of FD in LVH patients is clinically important.

Prevalence of Fabry disease in patients with chronic pain: Lessons from the DOUFAB and DOUFABIS studies

BACKGROUND

Fabry disease (FD) is a rare X-linked lysosomal disorder caused by alpha-galactosidase deficiency consecutive to a pathogenic variant in the GLA gene. Age at onset is highly variable, with a wide clinical spectrum including frequent renal, cardiac, skin and nervous system manifestations. Since pain can be an indicator of underlying FD, we wanted to estimate the prevalence of FD in a population of chronic pain patients.

METHODS

Two studies, DOUFAB and DOUFABIS, were carried out in expert centers for chronic pain to assess the prevalence of FD by measuring alpha galactosidase A activity in men and analysing the GLA gene in women.

RESULTS

Analysis of 893 patients, essentially adults, led to the diagnosis of FD in one female patient, now treated with enzyme replacement therapy.

CONCLUSIONS

The prevalence of FD is estimated about 1/1000 in our population of men and women suffering from various chronic pain. This is nearly the prevalence of FD observed in other previously screened high-risk populations with renal failure.

SIGNIFICANCE

Although a systematic search for FD does not seem relevant in the context of unexplained chronic pain in adults, a positive family history of FD or the presence of additional FD related organ features must lead to consider this rare disease diagnosis. Therefore, pain specialists need to be aware of main features of FD, including pain characteristics.

Genome-wide expression analysis in a Fabry disease human podocyte cell line

Fabry disease (FD) is an X-linked lysosomal disease caused by an enzyme deficiency of alpha-galactosidase A (α-gal A). This deficiency leads to the accumulation of glycosphingolipids in lysosomes, resulting in a range of clinical symptoms. The complex pathogenesis of FD involves lysosomal dysfunction, altered autophagy, and mitochondrial abnormalities. Omics sciences, particularly transcriptomic analysis, comprehensively understand molecular mechanisms underlying diseases. This study focuses on genome-wide expression analysis in an FD human podocyte model to gain insights into the underlying mechanisms of podocyte dysfunction. Human control and GLA-edited podocytes were used. Gene expression data was generated using RNA-seq analysis, and differentially expressed genes were identified using DESeq2. Principal component analysis and Spearman correlation have explored gene expression trends. Functional enrichment and Reporter metabolite analyses were conducted to identify significantly affected metabolites and metabolic pathways. Differential expression analysis revealed 247 genes with altered expression levels in GLA-edited podocytes compared to control podocytes. Among these genes, 136 were underexpressed, and 111 were overexpressed in GLA-edited cells. Functional analysis of differentially expressed genes showed their involvement in various pathways related to oxidative stress, inflammation, fatty acid metabolism, collagen and extracellular matrix homeostasis, kidney injury, apoptosis, autophagy, and cellular stress response. The study provides insights into molecular mechanisms underlying Fabry podocyte dysfunction. Integrating transcriptomics data with genome-scale metabolic modeling further unveiled metabolic alterations in GLA-edited podocytes. This comprehensive approach contributes to a better understanding of Fabry disease and may lead to identifying new biomarkers and therapeutic targets for this rare lysosomal disorder.

Screening for Fabry disease in patients on Hemodialysis

Background

Fabry disease is an under-recognized X-linked lysosomal storage disorder characterized by the accumulation of trihexosylceramides in multifarious tissues, leading to end-organ damage, including progressive renal failure. Antecedent screening studies worldwide have shown inconsistent prevalence in the hemodialysis population. We conducted this study to screen for Fabry disease in patients undergoing dialysis at a tertiary care hospital.

Materials and Methods

All patients undergoing dialysis were screened with a gal assay using dried blood spots (DBS) on filter paper using the fluorescence method. Patients with positive DBS test results were further tested for underlying mutations.

Results

A total of 112 patients (64.3% males and 35.7% females) on dialysis were screened. Nineteen patients (13 males and 6 females) were found to have low enzyme activity on DBS. Further mutation analysis confirmed that one female patient had Fabry disease. The mutation detected was a heterozygous missense variation in exon 7 of the GLA gene, which resulted in the amino acid substitution of histidine for arginine at codon 363 (p.Arg363His). Subsequent screening of the family members revealed that the son of the patient was asymptomatic and carried the same genotypic mutation. Genetic counseling was performed, and enzyme replacement therapy was offered to both patients.

Conclusions

Fabry disease remains underdiagnosed, especially in high-risk populations such as those undergoing dialysis. DBS is a convenient and effective screening tool for Fabry disease. Facilities should be augmented for similar screening studies in the dialysis population.

Low skeletal muscle mass as an early sign in children with fabry disease

BACKGROUND & AIMS

Fabry disease (FD) is a rare X-linked metabolic storage disorder due to the deficiency of lysosomal α-galactosidase A which causes the accumulation of glycosphingolipids throughout the body. Underweight and low BMI have been occasionally reported in FD patients previously. Whether underweight is common in the early stage of FD and body composition analysis to determine the cause have not been reported.

METHODS

Children who were diagnosed with FD in the Children's Hospital of Zhejiang University School of Medicine from July 2014 to December 2022 were enrolled. Clinical data were obtained from medical records. Whole body dual energy X-ray absorptiometry scans (DXA) were used to assess body composition (fat mass, FM; fat free mass, FFM and bone mass) according to the International Society of Clinical Densitometry's standard operating method. Whole body muscle mass was calculated as fat-free mass minus bone mass. Appendicular skeletal muscle mass (ASM) was calculated as the sum of the arm and the leg muscle mass. The FM, FFM, ULSM and LLSM indices were calculated by dividing the total FM, FFM, and upper and lower limb skeletal muscle mass (ULSM and LLSM) by the height squared.

RESULTS

A total of eighteen children (14 boys and 4 girls) were enrolled. Thirteen boys had the classical phenotype, and five children (1 boy with the N215S mutation and 4 girls) had the late-onset phenotype. Seven children with the classical phenotype (53.8%) and two of the five children (40%) with the late-onset phenotype had abnormal BMIs. Sixteen of the eighteen children (88.9%) had a height in the normal range, suggesting that low BMI was mainly due to underweight. By DXA body composition analysis, the FMI was abnormal in 3 children (2 boys and 1 girl), and the FFMI was abnormal in 12 children (9 boys and 3 girls). For the classical phenotype, 2 of the 13 children (15.4%) had abnormal FMI values, while 10 (76.9%) had abnormal FFMI values. Eight patients (61.5%) with the classical phenotype had a significant reduction in muscle mass index, ASM index and LLSM index values compared with age- and sex- matched Chinese controls. Late-onset patients also had mild low skeletal muscle mass compared to controls. The results suggested that low skeletal muscle mass is common in early FD.

CONCLUSIONS

This is the first study to examine body composition and muscle mass in early Fabry disease patients. Low skeletal muscle mass is a common early symptom in children with Fabry disease, suggesting that skeletal muscle is significantly affected in the early stages of FD.

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.

Screening for Fabry disease in male patients with end-stage renal disease in western France

CONTEXT

Fabry disease is a rare X-linked genetic disease due to pathogenic variants in the GLA gene. Classic Fabry disease is characterized by glycosphingolipids accumulation in all organs including the kidney, resulting in end-stage renal disease in a subset of male patients. Fabry disease should therefore be considered in the differential diagnosis of patients with unexplained end-stage renal disease.

OBJECTIVE

We performed a prospective screening study in Western France to determine the prevalence of Fabry disease in a large population of dialyzed and transplanted patients.

PATIENTS AND METHODS

Patients meeting the inclusion criteria (males, 18-70 years with end-stage renal disease of unknown or vascular origin) were selected from the REIN® registry and the CRISTAL® database. Screening on filter papers was performed after patient consent was obtained during either a dialysis session or a transplantation follow-up visit.

RESULTS

One thousand five hundred and sixty-one end-stage renal disease male patients were screened and 819 consented (dialysis: n=242; transplant: n=577). One single patient was found with decreased alpha-galactosidase levels <25%. GLA sequencing identified the p.Phe113Leu variant in favor of an unknown superimposed kidney disease responsible for end-stage renal disease since this GLA pathogenic variant is associated with a later-onset cardiac form of Fabry disease with minimal kidney involvement. Family cascade genotyping revealed a previously undiagnosed affected brother.

CONCLUSION

The prevalence of Fabry disease in end-stage renal disease patients was 0.12%, questioning the efficacy of this screening strategy with respect to the low prevalence. However, beside the benefit for the patient and his family, the increased awareness of Fabry disease among participating nephrologists may be of interest for future patients.

Fabry Disease With Concomitant Lewy Body Disease

Although Gaucher disease can be accompanied by Lewy pathology (LP) and extrapyramidal symptoms, it is unknown if LP exists in Fabry disease (FD), another progressive multisystem lysosomal storage disorder. We aimed to elucidate the distribution patterns of FD-related inclusions and LP in the brain of a 58-year-old cognitively unimpaired male FD patient suffering from predominant hypokinesia. Immunohistochemistry (CD77, α-synuclein, collagen IV) and neuropathological staging were performed on 100-µm sections. Tissue from the enteric or peripheral nervous system was unavailable. As controls, a second cognitively unimpaired 50-year-old male FD patient without LP or motor symptoms and 3 age-matched individuals were examined. Inclusion body pathology was semiquantitatively evaluated. Although Lewy neurites/bodies were not present in the 50-year-old individual or in controls, severe neuronal loss in the substantia nigra pars compacta and LP corresponding to neuropathological stage 4 of Parkinson disease was seen in the 58-year-old FD patient. Major cerebrovascular lesions and/or additional pathologies were absent in this individual. We conclude that Lewy body disease with parkinsonism can occur within the context of FD. Further studies determining the frequencies of both inclusion pathologies in large autopsy-controlled FD cohorts could help clarify the implications of both lesions for disease pathogenesis, potential spreading mechanisms, and therapeutic interventions.

Screening for Fabry Disease in patients with unexplained left ventricular hypertrophy

Fabry Disease (FD) is a systemic disorder that can result in cardiovascular, renal, and neurovascular disease leading to reduced life expectancy. FD should be considered in the differential of all patients with unexplained left ventricular hypertrophy (LVH). We therefore performed a prospective screening study in Edmonton and Hong Kong using Dried Blood Spot (DBS) testing on patients with undiagnosed LVH. Participants found to have unexplained LVH on echocardiography were invited to participate and subsequently subjected to DBS testing. DBS testing was used to measure α-galactosidase (α-GAL) enzyme activity and for mutation analysis of the α-galactosidase (GLA) gene, both of which are required to make a diagnosis of FD. DBS testing was performed as a screening tool on patients (n = 266) in Edmonton and Hong Kong, allowing for detection of five patients with FD (2% prevalence of FD) and one patient with hydroxychloroquine-induced phenocopy. Left ventricular mass index (LVMI) by GLA genotype showed a higher LVMI in patients with IVS4 + 919G > A mutations compared to those without the mutation. Two patients were initiated on ERT and hydroxychloroquine was discontinued in the patient with a phenocopy of FD. Overall, we detected FD in 2% of our screening cohort using DBS testing as an effective and easy to administer screening tool in patients with unexplained LVH. Utilizing DBS testing to screen for FD in patients with otherwise undiagnosed LVH is clinically important due to the availability of effective therapies and the value of cascade screening in extended families.

Correlation between GLA variants and alpha-Galactosidase A profile in dried blood spot: an observational study in Brazilian patients

BACKGROUND

Fabry disease is a rare X-linked inherited disorder caused by deficiency of α-Galactosidase A. Hundreds of mutations and non-coding haplotypes in the GLA gene have been described; however, many are variants of unknown significance, prompting doubts about the diagnosis and treatment. The α-Galactosidase A enzymatic activity in dried blood spot (DBS) samples are widely used for screening purposes; however, even when values below the normal are found, new tests are required to confirm the diagnosis. Here we describe an analysis of GLA variants and their correlation with DBS α-Galactosidase A enzymatic activity in a large Brazilian population with Fabry disease symptoms.

RESULTS

We analyzed GLA variants by DNA sequencing of 803 male patients with suspected Fabry disease or belonging to high-risk populations; in 179 individuals, 58 different exonic variants were detected. From these, 50 are variants described as pathogenic and eight described as variants of unknown significance. The other individuals presented complex non-coding haplotypes or had no variants. Interestingly, the enzymatic activity in DBS was different among pathogenic variants and the other genotypes, including variants of unknown significance; the first presented mean of 12% of residual activity, while the others presented levels above 70% of the activity found in healthy controls.

CONCLUSION

The activity of α-Galactosidase A in DBS was markedly reduced in males with known pathogenic variants when compared with subjects presenting variants of unknown significance, non-coding haplotypes, or without variants, indicating a possible non-pathogenic potential of these latter genotypes. These findings bring a better understanding about the biochemical results of α-Galactosidase A in DBS samples, as well as the possible non-pathogenic potential of non-coding haplotypes and variants of unknown significance in GLA gene. These results certainly will help clinicians to decide about the treatment of patients carrying variants in the gene causing this rare but life-threatening disease.

Inter-assay variability influences migalastat amenability assessments among Fabry disease variants

Fabry disease is a lysosomal storage disorder caused by mutations in the GLA gene that encodes for the lysosomal enzyme α-galactosidase A (α-Gal A). Reduced or absent α-Gal A activity leads to substrate accumulation and deleterious effects in multiple organs. Migalastat is a pharmacological chaperone that may stabilize the enzyme in specific GLA variants, considered amenable, assisting enzyme trafficking to lysosomes and thus increasing enzyme activity. Using a good laboratory practice (GLP)-validated human embryonic kidney cell (HEK)-based (GLP-HEK) amenability assay established during the clinical development of migalastat, approximately one-third of GLA variants are reported to be amenable to migalastat. On the basis of this biochemical amenability, migalastat is approved for use in patients with specific GLA variants. In this study, the reproducibility of the amenability assay was assessed by evaluation of 59 GLA variants for α-Gal A activity in the presence and absence of migalastat. As for the GLP-HEK assay, variants were considered amenable when there was both an absolute increase in enzyme activity of ≥3% wild-type and a relative increase in enzyme activity ≥1.2 fold over baseline following incubation with migalastat. Six of the 59 variants tested here did not match the classification of amenability reported using the GLP-HEK assay. Linear regression and Bland-Altman analyses, comparing data from all variants with and without migalastat, provided additional evidence for a lack of assay reproducibility. Data from the GLP-HEK assay (and the resulting classification of amenability) can determine treatment strategy and, ultimately, patient outcomes, so discrepancies between amenability assay data could be a cause for concern for physicians managing patients with Fabry disease.

Clinical impact of the alpha-galactosidase A gene single nucleotide polymorphism -10C>T: A single-center observational study

Single nucleotide polymorphisms (SNPs) in the alpha-galactosidase A gene region (GLA) have been discussed as potential cause of symptoms and organ manifestations similarly to those seen in Fabry disease (FD). However, due to scarce data, clinical implications remain limited. The aim of the present study was to investigate the clinical impact of -10C>T SNP in the GLA.Prospective single-center observational study to determine the natural history and outcome of FD.Subjects initially referred to the Fabry Center for Interdisciplinary Therapy Würzburg (FAZIT) for management of suspected FD (11 women, 2 men, mean age 42 ± 10 years) who were tested negative for coding GLA mutations but positive for the noncoding -10C>T SNP underwent comprehensive characterization for therapy recommendation.All subjects reported at least 1 neurological, but no cardiac or renal symptoms. In 7 patients, pain of unknown etiology was reported and 3 patients had a history of cryptogenic stroke. In all patients, α-GAL activity was at a lower limit, ranging between 0.27 and 0.45 nmol/min per mg protein (reference: 0.4-1.0), while plasma Lyso-Gb3 levels remained normal (range 0.39 ± 0.33; reference: ≤0.9 ng/mL). For both hemizygous subjects investigated, brain magnetic resonance imaging revealed unspecific white matter lesions. One of these subjects had suffered from severe early-onset stroke, the other showed mild hypertrophic cardiomyopathy.Presence of isolated heterozygous -10C >T SNP is not associated with clinically relevant symptoms or organ manifestations as seen in FD. Respective polymorphisms might, however, play a role in modifying disease severity in FD. Great care has to be taken in respective subjects suspected to suffer from nonclassical FD in order to prevent unnecessary Fabry-specific therapy.