GAD1 and Parkinson disease: Among the differentially abundant proteins with prior evidence for PD involvement were SNCA (Synuclein, Alpha (Non A4 Component Of Amyloid Precursor); increased in PD) [34, 35], GAD1 (glutamate decarboxylase 1 (brain, 67 kDa); decreased in PD) [36], and NPTX2 (neuronal pentraxin II; decreased in PD) [37].