GM₂ gangliosidosis in a Japanese Spaniel

A storage disease in a 2-year-old Japanese Spaniel resembled a GM₂ gangliosidosis previously identified in a now extinct line of German Shorthaired Pointers. Despite a later appearance of signs in the Japanese Spaniel, the distribution, staining, and ultrastructure of the stored material were similar in the two breeds. Golgi studies of cerebral cortical neurons revealed the formation of spiny and aspiny enlargements at the axon hillock region (meganeurites) and the growth of secondary neurites from this region. As in the German Shorthaired Pointer model, there was massive storage of GM₂ ganglioside as well as a seemingly paradoxical increase in total β-hexosaminidase activity measured in vitro.