GBA1 and Parkinson disease: Work with iPSC-derived dopamine neurons from PD patients carrying GBA (Fernandes et al., 2016, Schöndorf et al., 2014) or leucine-rich repeat kinase 2 (LRRK2) mutations (Sánchez-Danés et al., 2012) has revealed deficits in protein homeostasis via the endoplasmic reticulum (ER), autophagic, and lysosomal pathways.