Essential for the degradation of glycogen in lysosomes (PubMed:10723725). Has highest activity on alpha-1,4-linked glycosidic linkages, but can also hydrolyze alpha-1,6-linked glucans. Hydrolysis of terminal, non-reducing (1->4)-linked alpha-D-glucose residues with release of alpha-D-glucose. Defects in GAA are the cause of generalized glycogenosis. It is characterized by a accumulation of glycogen within lysosomes. This disease has been reported in Brahman and Shorthorn breeds. Its most common clinical representation is a failure to thrive, progressive muscular weakness and an un-coordinated gait. Belongs to the glycosyl hydrolase 31 family.