CSF α-synuclein improves diagnostic and prognostic performance of CSF tau and Aβ in Alzheimer's disease

Alzheimer's disease (AD) and Lewy body diseases (LBD), e.g., Parkinson's disease (PD) dementia and dementia with Lewy bodies (DLB), are common causes of geriatric cognitive impairments. In addition, AD and LBD are often found in the same patients at autopsy; therefore, biomarkers that can detect the presence of both pathologies in living subjects are needed. In this investigation, we report the assessment of alpha-synuclein (alpha-syn) in cerebrospinal fluid (CSF) and its association with CSF total tau (t-tau), phosphorylated tau(181) (p-tau(181)), and amyloid beta(1-42) (A beta(1-42)) in subjects of the Alzheimer's Disease Neuroimaging Initiative (ADNI; n = 389), with longitudinal clinical assessments. A strong correlation was noted between alpha-syn and t-tau in controls, as well as in patients with AD and mild cognitive impairment (MCI). However, the correlation is not specific to subjects in the ADNI cohort, as it was also seen in PD patients and controls enrolled in the Parkinson's Progression Markers Initiative (PPMI; n = 102). A bimodal distribution of CSF alpha-syn levels was observed in the ADNI cohort, with high levels of alpha-syn in the subjects with abnormally increased t-tau values. Although a correlation was also noted between alpha-syn and p-tau(181), there was a mismatch (alpha-syn-p-tau(181)-Mis), i.e., higher p-tau(181) levels accompanied by lower alpha-syn levels in a subset of ADNI patients. We hypothesize that this alpha-syn-p-tau(181)-Mis is a CSF signature of concomitant LBD pathology in AD patients. Hence, we suggest that inclusion of measures of CSF alpha-syn and calculation of alpha-syn-p-tau(181)-Mis improves the diagnostic sensitivity/specificity of classic CSF AD biomarkers and better predicts longitudinal cognitive changes.