Pro-inflammatory cytokines, including IL-1β, TNF, IFNγ, IL-2, IL-6, and CXCL8, are associated with initiation and progression of IBD49, and many of these are the same cytokines found to be increased in the sera, cerebrospinal fluid (CSF), and brain of PD patients relative to age-matched healthy controls50–55. This evidence concerns the gene IFNG and Parkinson disease.