The present study was conducted to investigate our primary hypothesis that the CSF level of synaptosomal-associated protein 25 (SNAP-25), a presynaptic protein responsible for vesicle fusion as part of the soluble N-ethylmaleimide-sensitive-factor attachment receptor (SNARE) complex and a promising biomarker of synaptic function in neurodegenerative diseases,7 8 is of diagnostic utility for MDD. Here, SNAP25 is linked to neurodegenerative disease.