Bone marrow transplantation corrects the enzyme defect in neurons of the central nervous system in a lysosomal

Neuronal storage disorders are fatal neuro- degenerative diseases of humans and animals that are caused by inherited deficiencies of lysosomal hydrolase activity. Affected individuals often appear normal at birth but eventually develop progressive neurologic symptoms including sensory and motor deficits, mental retardation, and seizures. We have examined efficacy of bone marrow transplantation as a means of enzyme replacement, using cats with the lysosomal storage disease a-mannosidosis. Treated animals showed little or no progres- sion of neurologic signs 1-2 years after transplant, whereas untreated cats became severely impaired and reached end- stage disease by 6 months of age. Increased lysosomal a-man- nosidase activity was found in brain tissue of the treated animals, and electron microscopy revealed no evidence of lysosomal storage within most neurons. Histochemical local- ization of acidic a-D-mannoside mannohydrolase (EC 3.2. 1.24), using 5-bromo-4-chloro-3-indolyl a-D-mannopyrano- side, showed that functional enzyme was present in neurons, glial cells, and cells associated with blood vessels. This study provides direct evidence that bone marrow transplantation as treatment for a neuronal storage disease can lead to significant levels of a missing lysosomal hydrolase within neurons of the central nervous system and to compensation for the genetic metabolic defect.