TNF and Parkinson disease: Additionally, for the preclinical stage of PD, TNF-α is seen as a potential risk biomarker (Majbour et al., 2020), with plasma levels closely linked to elevated phosphorylated α-synuclein (p-α-syn), which is significantly connected to fatigue symptoms in PD patients, implying its possible involvement in distinguishing fatigued from non-fatigued PD patients (Wang et al., 2023).