ST3GAL2 and Parkinson disease: 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.