CD9 and Parkinson disease: To observe the differences between PD patients and controls, Western blot volume normalization was used where we loaded an equal sample volume (5 μl) from PD and healthy controls (similarly done in the NTA); and here, we observed a significant increase in CD9 (p = 0.0004) (Fig. 3A, Additional file 1: Fig. S2) in PD patients than healthy controls.