Potential CSF biomarkers for PD include α-synuclein and DJ-1, with Aβ42 potentially correlating with cognitive impairment, and various forms of tau protein and neurofilament light-chain differentiating PD from atypical parkinsonian disorders.50 Separately, observed biomarker changes in saliva have included reduction in α-synuclein levels and elevation of DJ-1 in the saliva (see online supplementary material for examples of individual studies of CSF and salivary biomarkers). Here, MAPT is linked to Parkinson disease.