Introduction: Cognitive impairment in early Parkinson's disease (PD) is common and distinct from early Alzheimer's disease. Predictors and mechanisms are only partially known, but a-synuclein, amyloid-b and tau dysmetabolism may be involved. Our aim was to study associations between cerebrospinal fluid biomarkers (CSF) and cognition in non-dementia PD compared to normal controls (NC) and non-PD patients with mild cognitive impairment (MCI non-PD). Methods: Patients were classified as having normal, subjective or mild cognitive impairment after cognitive screening. CSF levels of total a-synuclein (t-a-syn), amyloid-b (Ab) 38, 40 and 42, total tau (Ttau) and phosphorylated tau (P-tau) were measured in 34 NC, 31 early, non-dementia PD and 28 MCI non-PD patients. A well validated neuropsychological test battery was administered. Results: In the PD group,13 had normal cognition, 4 had subjective and 14 mild cognitive impairment. PD patients had significantly lower CSF biomarker levels of t-a-syn, Ab38, 40 and 42, T-tau and P-tau compared to NC. Compared to MCI non-PD, t-a-syn, Ab38 and 40, T-tau and P-tau were also lower, while Ab42 was significantly higher in the PD group. Ab38 and 40 correlated strongly with t-a-syn levels in PD. Lower Ab42 was associated with decreased verbal learning, delayed verbal recall and response inhibition in PD. Conclusion: While Ab38, 40 and t-a-syn levels are strongly correlated, only lower Ab42 was associated with reduced cognitive functions in early PD, mainly connected to medial temporal lobe-based cognitive functions.
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