ST3GAL2 and Parkinson disease: Due to the fact that glycosyltransferases work in sequence, reduced expression of the B3galt and St3gal2 genes leads to a partial reduction of GM1 in PD, and lack of expression of the B4galnt1 gene, which controls the synthesis of GM1 from GM2 in an experimental mouse model of PD, results in the absence of GM1 and an increase in GM3, GD3, and GM2 gangliosides.