Studies have also demonstrated that PD patients exhibit elevated serum levels of pro-inflammatory cytokines, such as TNF, IFNγ, IL-1β, IL-6, IL-2, CXC-chemokine ligand 8 (CXCL 8), and CCL 2, which correlate with disease severity and disability (Wang et al., 2015). Here, IFNG is linked to Parkinson disease.