NRGN and Alzheimer disease: Recently, in a smaller cohort no overall differences were found in the levels of CSF neurogranin in PD, in contrast to increased levels in AD.26 Given the association with cognition in our study, it is possible that some of the synaptic proteins may be more related to amyloid pathology, which seems to be a driver of cognitive decline in PD.30 Whether the increase in neurogranin levels in AD, which has been previously reported,10,12,26 is specific only for AD or not needs to be further explored.