Summarizing the currently available studies, conducted between 2010 and 2022, and concerning the applicability of salivary biomarkers amyloid-β, tau, α-synuclein, and DJ-1 for the diagnosis of either AD or PD, the authors of the present investigation cautiously point to the potential of saliva as a non-invasive biomarker source. The gene discussed is MAPT; the disease is Parkinson disease.