The GM2 gangliosidoses are a group of severe, neurodegenerative conditions that include Tay-Sachs disease, Sandhoff disease, and the GM2 activator deficiency. Bone marrow transplantation (BMT) was examined as a potential treatment for these disorders using a Sandhoff disease mouse model. BMT extended the life span of these mice from approximately 4.5 mo to up to 8 mo and slowed their neurologic deterioration. BMT also corrected biochemical deficiencies in somatic tissues as indicated by decreased excretion of urinary oligosaccharides, and lower glycolipid storage and increased levels of beta-hexosaminidase activity in visceral organs. Even with neurologic improvement, neither clear reduction of brain glycolipid storage nor improvement in neuronal pathology could be detected, suggesting a complex pathogenic mechanism. Histological analysis revealed beta-hexosaminidase-positive cells in the central nervous system and visceral organs with a concomitant reduction of colloidal iron-positive macrophages. These results may be important for the design of treatment approaches for the GM2 gangliosidoses.

IntroductionThe G M2 gangliosidoses are progressive, neurodegenerative lysosomal storage diseases. 1 The hydrolysis of G M2 is catalyzed by ␤-hexosaminidase. The HEXA and HEXB genes encode the ␤-hexosaminidase ␣ and ␤ subunits, respectively. 1 Mutations in the ␣ and ␤ subunit genes result in Tay-Sachs and Sandhoff diseases, respectively. Potential therapeutic approaches include enzyme augmentation (enzyme replacement, bone marrow transplantation [BMT], or gene therapy) and substrate deprivation. 2,3 In BMT microglial cells of donor origin are thought to repopulate the brain, becoming perivascular macrophages and microglia, and to supply enzyme to neurones by secretion-recapture. 4-6 Substrate deprivation utilizes an inhibitor of GSL biosynthesis, such as N-butyldeoxynojirimycin (NB-DNJ). 7 By partially inhibiting GSL biosynthesis, the residual enzyme activity can hydrolyze the reduced influx of substrate into the lysosome, thus preventing storage. NB-DNJ inhibits the ceramide glucosyltransferase (glucosylceramide synthase, UDP-glucose-Nacylsphingosine D-glucosyltransferase, EC 2.4.1.80), which is the first enzyme in the GSL biosynthetic pathway. 3,8 In a mouse model of Tay-Sachs disease, NB-DNJ treatment reduced G M2 accumulation in the brain. 9 In the symptomatic mouse model of Sandhoff disease, NB-DNJtreated mice 10,11 survived 40% longer than untreated controls. 10 BMT of Sandhoff mice extended life expectancy up to 8 months. 12 Because the augmentation of enzyme through BMT and substrate deprivation may together show greater efficacy, we have treated Sandhoff mice with BMT and NB-DNJ and find that the 2 therapies act synergistically. Study designAnimals, treatment procedures, and behavioral tests Sandhoff mice were bone marrow transplanted at 10 to 16 days of age. 12 Drug treatment was carried out as previously described. 10,13 NB-DNJ was a gift from Searle/Monsanto (St Louis, MO) and Oxford GlycoSciences (Abingdon, United Kingdom). Mice were tested on the bar crossing or inverted screen as previously described. 10 The Open Field Test (box 45 ϫ 25 ϫ 12 cm with a 150 cm 2 floor grid) was conducted according to published methods. 14 Biochemical analysisWe used published methods to assay ␤-hexosaminidase. 10 BCA protein assay was used for protein determinations (Pierce, Chester, United Kingdom). GSL analysis was conducted as previously described. 9 Statistical analysisSurvival graphs were analyzed by the log-rank or the Mantel-Haenszel test. 15 Log-likelihood test was used for ␤-hexosaminidase enzyme level correlations. We used the Student t test to analyze ␤-hexosaminidase, GSL levels, and locomotion scores. Bar-crossing and inverted-screen test data were analyzed using a nonparametric regression model with a logistic link to the data set. P values were estimated using likelihood ratio. The statistical software used was S-PLUS version 3.4 (MathSoft, Seattle, WA). Results and discussion Survival of Sandhoff mice receiving combination therapyBone marrow-transplanted Sandhoff (SH) mice were treated with NB-DNJ (6...