A decrease in expression of B3GALT4 and ST3GAL2 genes, as currently observed in residual dopaminergic neurons in the PD SN, is expected to have a major impact on both GM1 and GD1a levels (as well as GD1b and GQ1b levels), reducing expression of these gangliosides, and potentially putting the affected neurons at risk. Here, B3GALT4 is linked to Parkinson disease.