Aspartylglycosaminuria: a generalized storage disease. Morphological and histochemical studies

Aspartylglycosaminuria (AGU) is a hereditary metabolic disorder characterized by slowly progressive mental deterioration from infancy, urinary excretion of large amounts of aspartylglycosamine, and decreased activity of the lysosomal enzyme aspartylglcosamine amido hydrolase in various body tissues and fluids. The nature and distribution of the morphological and histochemical alterations in AUG are described in the light of the first AGU patient investigated post mortem and brain and liver. Most nerve cells and hepatocytes contained large vacuoles without any histochemically demonstrable lipid or carbohydrate material. Ultrastructural studies revealed numerous electron-lucent vaculoles, limited by a single, membrane, in the cytoplasm of these cells. In addition to evenly disperesed finely granular or reticular material the vacuoles contained small electron-opaque "lipid" droplets and polymorphic membraneous or granular aggregates. Similar vacuoles were also seen in a number of other cell types, particularly in the kupffer cells and brain macrophages, as well as in the capillary pericytes. Biochemical studies suggest that the principal storage material consists of aspartylglycosamine itself; glycoasparagines of higher molecular weight are present as only minor components. Correlated morphological and biochemical studies thus definitely establish that AGU is a generalized storage disorder. The condition is apparently due to decreased activity of aspartylglycosamine amido hydrolase, with accumulation of products of flycoprotein carabolism in cytoplasmic vacuoles in both epithelial and mesenchymal cells.