CSF cathepsins have been poorly studied in general in neurodegenerative diseases with few studies investigating their concentrations, e.g., a previous study reported a decrease in cathepsin B and cathepsin F in Parkinson’s disease (PD) when compared to controls and prodromal AD [16]; while in another study, cathepsin D was increased in AD [20]. Here, CTSS is linked to neurodegenerative disease.