Beta-mannosidosis is a glycoprotein storage disorder caused by a deficiency of the beta-mannosidase enzyme. Individuals with beta-mannosidosis do not usually display the typical characteristics of lysosomal storage diseases such as coarse facial features, corneal changes, skeletal changes or hepatosplenomegaly. The most consistent features of beta mannosidosis are mental retardation, history of recurrent respiratory infections and hearing loss. Some individuals may present with angiokeratomas. Individuals with beta-mannosidosis may have an abnormal pattern of urine oligosaccharide excretion. Confirmation of diagnosis is made by measurement of beta-mannosidase enzyme activity directly.