Distribution and Severity of Neuropathology in β-Mannosidase-Deficient Mice is Strain Dependent

Neurological dysfunction is common in humans and animals with lysosomal storage diseases. β-Mannosidosis, an autosomal recessive inherited disorder of glycoprotein catabolism caused by deficiency of the lysosomal enzyme β-mannosidase, is characterized by intracellular accumulation of small oligosaccharides in selected cell types. In ruminants, clinical manifestation is severe, and neuropathology includes extensive intracellular vacuolation and dysmyelination. In human cases of β-mannosidosis, the clinical symptoms, including intellectual disability, are variable and can be relatively mild. A β-mannosidosis knockout mouse was previously characterized and showed normal growth, appearance, and lifespan. Neuropathology between 1 and 9 months of age included selective, variable neuronal vacuolation with no hypomyelination. This study characterized distribution of brain pathology in older mutant mice, investigating the effects of two strain backgrounds. Morphological analysis indicated a severe consistent pattern of neuronal vacuolation and disintegrative degeneration in all five 129X1/SvJ mice. However, the mice with a mixed genetic background showed substantial variability in the severity of pathology. In the severely affected animals, neuronal vacuolation was prominent in specific layers of piriform area, retrosplenial area, anterior cingulate area, selected regions of isocortex, and in hippocampus CA3. Silver degeneration reaction product was prominent in regions including specific cortical layers and cerebellar molecular layer. The very consistent pattern of neuropathology suggests metabolic differences among neuronal populations that are not yet understood and will serve as a basis for future comparison with human neuropathological analysis. The variation in severity of pathology in different mouse strains implicates genetic modifiers in the variable phenotypic expression in humans.