This group of rare lysosomal disorders results from deficiencies of enzymes involved in glycoprotein degradation. Glycoproteins consist of oligosaccharide chains attached to a protein core. Defective degradation of glycoproteins leads to the neurovisceral storage of oli-gosaccharides, glycopeptides, and glycolipids, and the urinary excretion of abnormal oligosaccharides. The group encompasses the mannosidosis, the fucosidoses, aspartyl-glycosaminuria, and Schindler's disease. The diseases affect neonates, infants, and young children, but juvenile and adult forms also occur. The clinical expression, except for the Schindler's disease, resembles that of Hurler's disease: psychomotor retardation, facial and skeletal abnormalities, corneal opacity, deafness, angiokeratomas, and hepatosplenomegaly. Vacuolated lymphocytes in blood smear and foamy histiocytes in bone marrow occur in all diseases.

The brain may be atrophic or enlarged. The neurons, in paraffin sections, are vacuolated because the water-soluble stored material is extracted during processing. In frozen sections, the compound stains positively with PAS and lipid stains.

Schindler's disease presents with psychomotor retardation, visual impairment, various neurologic deficits, and myoclonus. The pathology is distinguished by the presence of neuroaxonal dystrophy in the cerebral white matter.

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