Other potential biomarkers for the prodromal period of Parkinson’s disease include inflammatory cytokines (such as tumour necrosis factor alpha (TNF-α), interleukin (IL)-1β, and IL-6,) and the non-motor symptoms of REM sleep behaviour disorder (RBD), anosmia and hyposmia, gastrointestinal disturbances and gut microbiome diversity [14]. Here, TNF is linked to Parkinson disease.