Quantitative mass spectrometry (MS) analysis performed by parallel reaction monitoring (PRM) on the CSF of healthy subject (H-CSF, n = 13) and PD patients (PD-CSF, n = 10) confirmed that the deamidation of the endogenous ceruloplasmin 962NGR-motif was significantly higher (p = 0.0094) in PD patients compared to healthy subjects (Fig. 1b). Here, CP is linked to Parkinson disease.