Electron micrograph of muscle cell from a patient with Pompe disease. Glycogen-engorged lysosomes are seen throughout the cell, including the myofibrils. As the disease progresses, lysosomes may rupture, releasing large amounts of glycogen into the cytoplasm. Such accumulations of cytoplasmic glycogen are called glycogen lakes.

[Reproduced with permission of the author, from Thurberg, B. L. et. al. Characterization of pre- and post-treatment pathology after enyme replacement for Pompe disease. Lab. Invest. 86 (12):1208–1220, 2006.]