GAA and glycogen storage disease II: Pompe disease (OMIM No. 232300, glycogen storage disease type II), an autosomal recessive, multisystemic neuromuscular disorder, is caused by biallelic mutations in the GAA gene encoding for the lysosomal enzyme acid alpha-glucosidase (GAA enzyme, EC 3.2.1.20) that degrades lysosomal glycogen [1].