Beta-mannosidosis is an autosomal recessive lysosomal storage disease of glycoprotein catabolism caused by a deficiency of lysosomal beta-mannosidase activity. The most severely affected patients show developmental delay and mental retardation, but there are differing levels of severity and some patients may have comparatively mild disease. The disorder was first described in goats, who have a more severe neurodegenerative disorder than that seen in humans. [From OMIM]