Why test for alpha-galactosidase A (α-Gal A)?
Deficient activity of the lysosomal enzyme alpha-galactosidase A (α-Gal A) leads to an accumulation of the glycosphingolipids globotriaosylceramide (Gb3) and globotriaosylsphingosine (lyso-Gb3) within almost all cell types and various organs in patients with Fabry disease.1-3 Some variants in the GLA gene encoding α-Gal A lead to these alterations in enzyme activity.4 Enzyme activity levels of <1% for α-Gal A are suggestive of classical Fabry disease.4,5 Patients with residual enzyme activity of levels of α-Gal A >3‒30% typically have late-onset Fabry disease.6
What is the α-Gal A enzyme activity assay?
Enzymatic activity of α-Gal A can be assessed in plasma, leukocytes, cultured fibroblasts or dried blood spots.7,8 Determination of α-Gal A activity using leukocyte and dried blood spot assays are performed using fluorometric methods; however, tandem mass spectrometry is also available for the evaluation of dried blood spots.9-13 In one study, the enzymatic activity of α-Gal A, evaluated using dried blood spots in male patients with Fabry disease, ranged from 0‒1.7 μmol/h/L, compared with 4.2‒17.3 μmol/h/L in unaffected individuals without Fabry disease.14 Therefore, the α-Gal A enzyme assay, in addition to genetic testing, can be used to confirm a diagnosis of Fabry disease in males.7,15-17 Female patients who are heterozygous for variants in the GLA gene had enzymatic activity levels of α-Gal A ranging from 0‒12.6 μmol/h/L in dried blood spots, which may be comparable with individuals without Fabry disease.14 Consequently, the α-Gal A enzyme assay is considered less reliable for diagnosing Fabry disease in females, because many patients exhibit enzyme activity levels within the normal range.15,16 Genetic testing is therefore used to confirm a diagnosis of Fabry disease in female patients.7,16,17
How sensitive is the α-Gal A enzyme activity assay in diagnosing Fabry disease?
The relative sensitivity of testing for α-Gal A enzyme activity in dried blood spots, analysing plasma lyso-Gb3, and GLA gene sequencing for diagnosing suspected Fabry disease in both males and females was assessed during a 2-year clinical diagnostics programme. In this study, enzymatic activity of α-Gal A was reported as pmol/punch/h, where activity ≤11 pmol/punch/h in males was considered low. In males, the sensitivity of the enzyme assay for α-Gal A for confirming a suspected diagnosis of Fabry disease was 100%; however, in females, the reported sensitivity was 49%. The findings from this study further indicate that testing for α-Gal A enzyme activity in males can be considered the first step in the diagnostic work-up. Whereas, a diagnosis of Fabry disease in females can instead be more efficiently made using concurrent analysis of plasma lyso-Gb3 and GLA gene sequencing.18
C-ANPROM/INT/FAB/0016; Date of preparation: March 2021
- Felis A, Whitlow M, Kraus A, et al. Current and investigational therapeutics for Fabry disease. Kidney Int Rep 2019; 5: 407-413.
- Schiffmann R, Hughes DA, Linthorst GE, et al. Screening, diagnosis, and management of patients with Fabry disease: conclusions from a "Kidney Disease: Improving Global Outcomes" (KDIGO) Controversies Conference. Kidney Int 2017; 91: 284-293.
- Brady RO, Gal AE, Bradley RM, et al. Enzymatic defect in Fabry's disease. Ceramidetrihexosidase deficiency. N Engl J Med 1967; 276: 1163-1167.
- Vardarli I, Rischpler C, Herrmann K, et al. Diagnosis and screening of patients with Fabry disease. Ther Clin Risk Manag 2020; 16: 551-558.
- Clarke JT. Narrative review: Fabry disease. Ann Intern Med 2007; 146: 425-433.
- Michaud M, Mauhin W, Belmatoug N, et al. When and how to diagnose Fabry disease in clinical pratice. Am J Med Sci 2020; 360: 641-649.
- Mehta A. Agalsidase alfa: specific treatment for Fabry disease. Hosp Med 2002; 63: 347-350.
- Chamoles NA, Blanco M, Gaggioli D. Fabry disease: enzymatic diagnosis in dried blood spots on filter paper. Clin Chim Acta 2001; 308: 195-196.
- Curiati M, Aranda C, Kyosen S, et al. The challenge of diagnosis and indication for treatment in Fabry disease. J Inborn Errors Metab Screen 2017; 5: 1-7.
- Müller KB, Rodrigues MD, Pereira VG, et al. Reference values for lysosomal enzymes activities using dried blood spots samples - a Brazilian experience. Diagn Pathol 2010; 5: 65.
- Li Y, Scott CR, Chamoles NA, et al. Direct multiplex assay of lysosomal enzymes in dried blood spots for newborn screening. Clin Chem 2004; 50: 1785-1796.
- Zhang XK, Elbin CS, Turecek F, et al. Multiplex lysosomal enzyme activity assay on dried blood spots using tandem mass spectrometry. Methods Mol Biol 2010; 603: 339-350.
- Sozmen EY, Sezer ED. Methods for determination of α-glycosidase, β-glycosidase, and α-galactosidase activities in dried blood spot samples. Methods Mol Biol 2017; 1594: 255-264.
- Caudron E, Prognon P, Germain DP. Enzymatic diagnosis of Fabry disease using a fluorometric assay on dried blood spots: an alternative methodology. Eur J Med Genet 2015; 58: 681-684.
- Gupta S, Ries M, Kotsopoulos S, et al. The relationship of vascular glycolipid storage to clinical manifestations of Fabry disease: a cross-sectional study of a large cohort of clinically affected heterozygous women. Medicine (Baltimore) 2005; 84: 261-268.
- Barbey F, Hayoz D, Widmer U, et al. Efficacy of enzyme replacement therapy in Fabry disease. Curr Med Chem Cardiovasc Hematol Agents 2004; 2: 277-286.
- German Society for Neurology (DGN). Interdisciplinary guidelines for the diagnosis and treatment of Fabry disease. September 2013.
- Stiles AR, Zhang H, Dai J, et al. A comprehensive testing algorithm for the diagnosis of Fabry disease in males and females. Mol Genet Metab 2020; 130: 209-214.