To determine if an additional copy of Cstb is sufficient to raise CSTB protein abundance or alter cathepsin B enzyme activity in the adult brain of a mouse model of DS, we measured CSTB protein level and cathepsin activity in the Dp(10)2Yey mouse model, which has an additional copy of 38 genes, carried on an internal duplication on Mmu10 of the region of homology with Hsa21. This evidence concerns the gene CTSS and Dravet syndrome.