Sandhoff disease is a lysosomal storage disorder characterized by G_M2 ganglioside accumulation in the central nervous system (CNS) and periphery. It results from mutations in the HEXB gene, causing a deficiency in β-hexosaminidase. Bone marrow transplantation (BMT), which augments enzyme levels, and substrate deprivation (using the glycosphingolipid biosynthesis inhibitor N-butyldeoxynojirimycin [NB-DNJ]) independently have been shown to extend life expectancy in a mouse model of Sandhoff disease. The efficacy of combining these 2 therapies was evaluated. Sandhoff disease mice treated with BMT and NB-DNJ survived significantly longer than those treated with BMT or NB-DNJ alone. When the mice were subdivided into 2 groups on the basis of their donor bone marrow–derived CNS enzyme levels, the high enzyme group exhibited a greater degree of synergy (25%) than the group as a whole (13%). Combination therapy may therefore be the strategy of choice for treating the infantile onset disease variants.