GAA and glycogen storage disease due to acid maltase deficiency, late-onset: Pompe disease (acid maltase deficiency disease) is a rare and progressive neuromuscular disorder caused by the absence or deficiency of acid alpha-glucosidase (GAA), the enzyme required for the breakdown of glycogen.1 Glycogen accumulation in muscle cell lysosomes results in a variety of symptoms due to potentially fatal myopathy.1 While the clinical presentation of Pompe disease is heterogeneous, it is generally classified as either infantile-onset Pompe disease (IOPD) or late-onset Pompe disease (LOPD).