Cerebrospinal α-synuclein in α-synuclein aggregation disorders: tau/α-synuclein ratio as potential biomarker for dementia with Lewy bodies.

Several studies have addressed the utility of cerebrospinal (CSF) α-synuclein levels as a potential biomarker of α-synuclein aggregation disorders. However, its relevance in the differential diagnostic context of neurodegenerative and movement disorders is still a contentious subject. Here, we report total CSF α-synuclein levels in a cohort of clinically diagnosed α-synuclein-related disorders encompassing Parkinson's disease, Parkinson's disease dementia, dementia with Lewy bodies and multiple system atrophy in comparison to essential tremor and neurological control cases. α-synuclein levels in α-synuclein-related disorders were significantly lower than in controls (p < 0.001). However, in the differential diagnostic context, only Parkinson's disease cases presented significant lower α-synuclein levels compared to essential tremor and neurological controls. In cases with clinically diagnosed α-synuclein pathology, CSF α-synuclein levels showed a moderate positive correlation with CSF tau and p-tau, but not with Aβ42 levels. Due to elevated CSF tau levels in dementia with Lewy bodies samples, tau/α-synuclein ratio showed a good clinical accuracy in discriminating controls from dementia with Lewy bodies cases (AUC = 0.8776) compared to single α-synuclein (AUC = 0.7192) and tau (AUC = 0.7739) levels. In conclusion, α-synuclein alone lacks of clinical value as a biomarker of α-synuclein-related disorders, but in combination with total tau, it may improve the diagnosis of dementia with Lewy bodies.