GAA and Glycogen storage disease due to acid maltase deficiency: Pompe disease, or glycogen storage disease type II (GSD II), is a rare autosomal recessive disorder caused by a deficiency in the lysosomal enzyme acid α-glucosidase (GAA).1 GAA deficiency leads to lysosomal glycogen accumulation in multiple tissues, including the CNS.1-5 Pompe disease presents as a clinical spectrum.