Synaptosomal-Associated Protein 25 kDA (SNAP-25) Levels in Cerebrospinal Fluid: Implications for Alzheimer's Disease Diagnosis and Monitoring.

Synaptic degeneration has been linked to cognitive decline. The presynaptic protein, synaptosomal-associated protein 25 kDA (SNAP-25), is crucial for synaptic transmission and has been suggested as a biomarker in Alzheimer's disease (AD). In the current study, we investigated the ability of SNAP-25 to differentiate between heterogenous dementia etiologies and whether SNAP-25 could be a staging marker in AD. SNAP-25 in the cerebrospinal fluid (CSF) from a retrospective (n = 187) and a prospective (n = 134) cohort was investigated with immunoprecipitation mass spectrometry (IP-MS) and single-molecule array (Simoa), respectively. Both cohorts consisted of healthy controls (HC) and patients with cognitive decline of different etiologies. CSF SNAP-25 concentration was higher in AD and non-neurodegenerative diseases (i.e., vascular dementia) compared with controls but did not differ between AD and non-AD neurodegenerative diseases. We found a trend toward an association between SNAP-25 and disease burden when comparing HC, mild cognitive impairment due to AD, and AD. CSF SNAP-25 concentrations were strongly associated with CSF phosphorylated tau (p-tau) concentrations, thus strengthening the link between synaptic dysfunction and tau pathophysiology in AD. Our initial findings suggest that SNAP-25 may be a potential biomarker for differentiating AD from dementia due to other etiologies. However, due to the significant association between SNAP-25 and p-tau proteins, the clinical utility of SNAP-25 as a diagnostic biomarker for AD may be limited, while SNAP-25 may be useful for monitoring disease progression or treatment response.