autosomal recessively inherited glycogen storage disease caused by glucan 1,4-alpha-glucosidase deficiency; large amounts of glycogen accumulate in the lysosomes of skeletal muscle, heart, liver, spinal cord, and brain; three forms have been described: the infantile form is fatal in infancy and presents with hypotonia and a hypertrophic cardiomyopathy; the childhood form usually presents in the second year of life with proximal weakness and respiratory symptoms; the adult form consists of a slowly progressive proximal myopathy.