Morphological alterations in the inner ear of the arylsulfatase A-deficient mouse.

Metachromatic leukodystrophy of humans is an inherited sulfatide lipidosis due to deficiency of arylsulfatase A (ASA). As an animal model, ASA(-/-) mice have been generated. A previous study showed that the mice lose most of their spiral (acoustic) ganglion cells and develop deafness by the end of the first year of life. The present report describes the sulfatide histochemistry and ultrastructure of the inner ears of ASA(-/-) mice at 0.5-26 months of age. Lysosomal accumulation of sulfatides was observed in various cell types such as Schwann cells that maintain the myelin sheaths around the spiral and vestibular ganglion cells, periaxonal Schwann cells, macrophages, and spiral and vestibular ganglion cell perikarya. In the spiral ganglion, the only surviving neurons were those which are primarily non-myelinated (type 2 cells). However, the myelinated spiral neurons and their processes were rarely encountered within the process of dying, suggesting that this was a rather rapid process. Since the myelin sheaths around dying perikarya and axons appeared structurally normal, the primary cause of the neuronal cell death seems to reside in the neuron. In contrast to the spiral ganglion, the vestibular ganglion as a whole survived throughout the period of observation. The organ of Corti and the vestibular apparatus appeared preserved at the light microscopic level, despite massive sulfatide storage in the vestibular hair cells.