Diagnostic efficacy of the fluorometric determination of enzyme activity for Pompe disease from dried blood specimens compared with lymphocytes—possibility for newborn screening
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Pompe disease is a rare, autosomal-recessive disorder which results from a defect in the lysosomal enzyme acid α-glucosidase (GAA). The onset of this disease is highly variable, with infantile types being the most severe. Traditionally, lymphocytes, fibroblasts or muscle biopsies were necessary for enzyme activity measurement, because these materials do not express maltase-glucoamylase (MGA) that interferes with the assay. Recently, acarbose was found to inhibit MGA activity selectively, so that dried blood became accessible for GAA assessment.
To evaluate the diagnostic efficacy of GAA measurement in dried blood specimens (DBSs) in comparison with lymphocytes. If DBSs provided reliable results, the diagnosis of Pompe disease could be facilitated, and high-throughput screening would become possible.
Methods and results
GAA activity was measured in DBSs of known patients at pH 3.8 (with and without acarbose) and at pH 7.0. Additionally, lymphocytes were obtained from the same patients, and the enzyme activity was determined at pH 4 to pH 7. In total, seven infantile patients and 29 patients with late-onset variants were investigated. All patients were reliably identified by both methods. Furthermore, a simplified protocol was established for neonatal screening.
The fluorometric technique for the assessment of GAA activity in DBS provides a reliable diagnosis for all variants of Pompe disease. The assay protocol could be simplified for neonatal screening, without increasing the false positive rate significantly or burdening the laboratory with time-consuming procedures.
KeywordsEnzyme Replacement Therapy Acarbose Pompe Disease Neonatal Screening Pompe Patient
The study was supported by the Genzyme Corp., USA. We also wish to express our gratitude to Dr. Joan Keutzer for her continuous help and support and to Dr. Gläser (Neu-Ulm) for assisting in the molecular genetic characterization of some patients.