GLB1 and GM1 gangliosidosis: In our hands, we observed a dose-dependent (Fig. 8) and time-dependent (Fig. S5) up-regulation of an unfolded protein response in patient cells overexpressing β-gal, suggesting that careful tuning of GLB1 expression levels will help to avoid ER stress and can lead to a potentially safe and effective gene therapy for GM1 gangliosidosis.