GAA and glycogen storage disease II: Pompe disease, also known as glycogen storage disease type II (OMIM 232300), is an autosomal recessive inherited metabolic disorder caused by a deficiency of the enzyme known as acid α-glucosidase (GAA, EC 3.2.1.20/3) that breaks down glycogen in the lysosome, leading to the accumulation of lysosomal glycogen in skeletal and heart muscles [1].