Determination of acid α-glucosidase activity in blood spots as a diagnostic test for Pompe disease

Background: Pompe disease is an autosomal recessive disorder of glycogen metabolism that is characterized by a deficiency of the lysosomal acid α-glucosidase. Enzyme replacement therapy for the infantile and juvenile forms of Pompe disease currently is undergoing clinical trials. Early diagnosis before the onset of irreversible pathology is thought to be critical for maximum efficacy of current and proposed therapies. In the absence of a family history, the presymptomatic detection of these disorders ideally can be achieved through a newborn-screening program. Currently, the clinical diagnosis of Pompe disease is confirmed by the virtual absence, in infantile onset, or a marked reduction, in juvenile and adult onset, of acid α-glucosidase activity in muscle biopsies and cultured fibroblasts. These assays are invasive and not suited to large-scale screening. Methods: A sensitive immune-capture enzyme activity assay for the measurement of acid α-glucosidase protein was developed and used to determine the activity of this enzyme in dried-blood spots from newborn and adult controls, Pompe-affected individuals, and obligate heterozygotes. Results: Pompe-affected individuals showed an almost total absence of acid α-glucosidase activity in blood spots. The assay showed a sensitivity and specificity of 100% for the identification of Pompe-affected individuals. Conclusions: The determination of acid α-glucosidase activity in dried-blood spots is a useful, noninvasive diagnostic assay for the identification of Pompe disease. With further validation, this procedure could be adapted for use with blood spots collected in newborn-screening programs.