XBP1 and Parkinson disease: Concerning the interplay between ER stress and changes in N-glycosylation, it has been reported that the increase in spliced XBP1 due to the activation of the inositol requiring kinase 1 (IRE-1) branch of the UPR leads to a decrease in bisecting glycans and sialylation, and increases oligomannose structures (43), which corresponds to the nigral PD N-glycomic signature.