NPTX2 and Parkinson disease: Notable single protein changes in PSP included downregulation of CD200, which plays a key role in protecting neurons from microglia-induced neurotoxicity [45], and of the synaptic protein neuronal pentraxin-2 (NPTX2), which has been found to be decreased in CSF of patients with PD, PSP, and MSA, and likely reflects synaptic dysfunction and loss in the prefrontal cortex [46].