TNF and Parkinson disease: In PD, TNF-α is known to bind to TNF-α receptor, present on the surface of microglia, to produce more pro-inflammatory factors, such as inducible nitric oxide synthase (iNOS), COX2, and IL-6 (Goetz et al., 2004; Lefkowitz and Lefkowitz, 2008; Hernandes and Britto, 2012; Kang et al., 2020), which may be one of the reasons for the increased plasma FAM19A5 levels in PD patients.