Importantly, no up-regulation in Gpr75 protein levels (Fig. S5) or CHOP translocation (Fig. 8F) was detected in control GM1 gangliosidosis patient fibroblasts following lentivirus-mediated transduction with the GFP reporter gene (Fig. S5 and Fig. 8F). Here, GPR75 is linked to GM1 gangliosidosis.