APP and Parkinson disease: In our approach, longitudinal samples of prodromal and de novo PD (NSD-ISS Stage 4 at baseline) subjects were assessed, identifying nine markers that were significantly decreased in CSF samples of PD subjects compared to healthy controls (VGF, APP, NPTX1/2 and NPTXR, neurogranin, secretogranin-2, syntaxin-7 and AP2B1).