B3GALT4 and Parkinson disease: Since the variation was similar in both cell types, this might reflect transcriptional changes, and the lower GM1 levels could be explained either by increased degradation of GM1 in N2aGPR37-eGFP or decreased enzyme levels upstream of B3GALT4, such as B4GALNT1, which has been used as a model of GM1-induced parkinsonism.