AbstractBackgroundCSF concentration of neurogranin has been suggested as a biomarker for synapse dysfunction.ObjectivesTo investigate CSF neurogranin in parkinsonian disorders compared to controls and Alzheimer's disease and the possible correlations between neurogranin and cognitive and motor impairment.MethodsWe included 157 patients with PD, 29 with PD with dementia, 11 with dementia with Lewy bodies, 26 with MSA, 21 with PSP, 6 with corticobasal syndrome, 47 controls, and 124 with Alzheimer's disease. CSF neurogranin was measured using two enzyme‐linked immunosorbent assays; from EUROIMMUN and the University of Gothenburg.ResultsWe found a strong correlation between CSF neurogranin‐EI and CSF neurogranin–University of Gothenburg (Rs = 0.890; P < 0.001). Neurogranin was decreased in PD, PD with dementia, MSA, and PSP compared to controls and Alzheimer's disease. Neurogranin did not correlate with motor or cognitive impairment, longitudinal decline, or progression to dementia in PD.ConclusionsCSF neurogranin is decreased in parkinsonian disorders compared to controls, emphasizing the importance of synaptic dysfunction in these disorders. © 2019 International Parkinson and Movement Disorder Society