NEU1 and sialidosis: None of the other three sialidases, which are distributed in the cytosol (NEU2 neuramidase 2), plasma membrane (NEU3 neuramidase 3), or mitochondrial/lysosomal/intracellular membranes (NEU4 neuramidase 4), appears to compensate for the deficiency of lysosomal sialidase in sialidosis patients [8].