GAA and glycogen storage disease II: Glycogen storage disease (Pompe disease) is an autosomal recessive lysosomal storage disease caused by a deficiency of acid α-1,4-glucosidase encoded by the GAA gene (GAA [MIM: 606800] acid maltase, EC 3.2.1.20/3, 17q25.3), which is a key enzyme in hydrolyzation of lysosomal glycogen to glucose [1].