ST3GAL2 and Parkinson disease: On the other hand, in situ hybridization histochemistry demonstrated a significant decrease in B3galt4 (GM1 synthase) and ST3gal2 (GD1a synthase) gene expression in residual neuromelanin-containing cells in the substantia nigra of PD patients; these decreases in GM1-synthesizing enzymes were cell-type specific and were not observed in non-neuromelanin containing neurons outside the substantia nigra in sPD brain [27].