The application of a targeted mass spectrometry biomarker panel (Table 2) showed nine markers that were differentially expressed between PD and healthy controls: neurosecretory protein VGF, amyloid-beta precursor protein (APP), the neuronal pentraxins and its corresponding receptor (NPTX1, NPTX2, NPTXR), secretogranin-2, neurogranin, syntaxin-7 and AP-2 complex subunit beta (AP2B1). Here, NRGN is linked to Parkinson disease.