Biopsy-proven alpha-glucosidase deficiency with normal lymphocyte enzyme activity

Alpha-glucosidase deficiency is a rare cause of muscle disease in adults. The diagnosis relies on recognition of the salient clinical features and determination of significantly reduced alpha-glucosidase (GAA) activity. Lymphocytes are the usual tissue for diagnostic enzymology; discrepant results from analyses of different tissues are unusual. We report a patient with clinical, electromyographic, and biopsy findings indicative of alpha-glucosidase deficiency whose muscle and lymphocyte enzyme results were markedly discrepant on multiple analyses. As a result, we conclude that all patients with suspected alpha-glucosidase deficiency and a normal lymphocyte GAA assay should also have a determination of GAA activity in muscle or skin fibroblasts.