Comparative study of the intracytoplasmic inclusions in Lafora disease and type IV glycogenosis by electron microscopy.

We compared the ultrastructure of the intracytoplasmic inclusion substance present in Lafora bodies and the myocardium of patients with Lafora disease, with that in the hepatocytes and myocardium of patients with type IV glycogenosis. Fibril-like structures and associated electron-dense clumps (crumpled plates) are the main components of the deposits in these two diseases. Ultrastructurally, the inclusions in both diseases appeared quite similar. In Lafora bodies, the electron-dense materials formed their central cores, but were also scattered in their peripheral areas. In type IV glycogenosis, the materials tended to be localized in the centers of large storage masses. The fibril-like structures in Lafora bodies were somewhat thicker and more electron-dense than those in type IV glycogenosis. The fibril-like structures and the crumpled plates in the intracytoplasmic inclusions of both Lafora disease and type IV glycogenosis were intensely stained in sections subjected to Thiéry staining. Despite previous considerations to the contrary, the findings of the present study suggested that the fibril-like structures are not true fibrils, but in fact plates.