The results showed that the expression of the ER‐resident chaperone binding immunoglobulin protein (BiP) was significantly up‐regulated in D409H homozygous GBA1 mutant line and N370S GBA1 mutant PD line compared with wild‐type iPSC‐derived dopaminergic neurons under basal conditions (Figure 4a,b). This evidence concerns the gene GBA1 and Parkinson disease.