GAA and metabolic disease: Pompe disease (PD), which is also referred to as acid maltase deficiency or glycogen storage disease type II, is a metabolic disorder triggered by biallelic gene mutations in chromosome 17q25, which encodes for acid α-glucosidase (GAA), a lysosomal hydrolase, leading to a deficiency of the enzyme and, hence, lysosomal accumulation of glycogen, particularly in skeletal and cardiac muscle as well as the nervous system.