First, principal component analysis (PCA) on all or most proteins detected in each region (OCC, 4411 proteins; MTG, 5002 proteins; STR, 4714 proteins; CG, 5082 proteins; SN, 4534 proteins), revealed that samples did not cluster according to age, gender or GBA1 mutation (in the case of PD-GBA samples) (Fig. 2a and Supplementary Figs 2 and 3), demonstrating that none of these factors influence the data. Here, GBA1 is linked to Parkinson disease.