Electron microscopy of skeletal muscle and arrector pili smooth muscle of Pompe disease patients and controls. A: Granular glycogen accumulation disrupting the myofibrilar structure in skeletal muscle of a Pompe patient. Scale bar: 0,5 μm. B: Intramyofibrilar glycogenosome accumulation with varying density of the glycogen deposits, associated with autophagic vacuoles in the skeletal muscle of a Pompe disease patient. Scale bar: 1 μm. C: Large glycogenosomes containing tightly packed glycogen granules (arrows) in a smooth muscle cell of an intramuscular blood vessel from a patients muscle biopsy. Scale bar: 2 μm. D-E: Smooth muscle cells of arrector pili muscle from a skin biopsy of a healthy control. Many cells contain granular, non-membrane bound glycogen deposits (arrows) which are frequently associated loosely with the cellular membrane or mitochondria (arrowheads). Scale bar D: 2 μm; E: 1 μm. F-G: Glycogen appears in membrane bound (arrows) and also in granular form (arrowhead) in the arrector pili smooth muscle cells of Pompe patients. Scale bar F: 0,5 μm; G: 5 μm. H: Smooth muscle cells from arrector pili muscle of Pompe patients contain similar vacuoles that we can observe in skeletal muscle of such patients, containing diverse forms of glycogen and autophagic material. Scale bar: 1 μm. I: The glycogenosomes and autophagic vacuoles fill the entire cytoplasm of the arrector pili smooth muscle cells in some cases, severely disrupting their structure. Scale bar: 2 μm.