The Simoa SNAP-25 assay targets the soluble N-terminal fragment of SNAP-25 (aa 2-47) which has been shown to distinguish between AD patients and nondemented controls. SNAP-25 (Synaptosomal- associated protein, 25kDa) is one of the major proteins involved in the formation of the SNARE (Soluble N-ethylmaleimidesensitive factor attachment protein receptors) protein complex. The complex formation is an important step in the exocytotic release of neurotransmitters during synaptic transmission. SNAP-25 is also involved in neurite extension, neuron repair and synaptogenesis and in LTP and formation of long-term memory. Cognitive decline in Alzheimer’s disease can be predicted by synaptic dysfunction and degeneration. Synaptic damage can be detected at the earliest stages of AD. MCI patients show loss of presynaptic proteins like synaptophysin and SNAP-25 and PSM like PSD-95 and Shank. Synaptic loss is closely related to severity of clinical disease and therefore SNAP-25 may be a good biomarker for early diagnosis and as a disease progression predictor. SNAP25 levels correlate with levels of T-tau and P-tau in control groups and patients with dementia due to AD. Therefore, SNAP-25 may be an important alternate marker in future clinical treatment studies with taubased-modifying drugs.