We utilized Western blotting to demonstrate that chronic lentivirus-mediated, CMV promoter–driven GLB1 overexpression in GM1 gangliosidosis patient fibroblasts leads to accumulation of the precursor form of rhβ-gal in a prelysosomal compartment, where it activates an unfolded protein response and ER stress (Fig. 8). The gene discussed is GLB1; the disease is GM1 gangliosidosis.