Led by observations that PD patients can experience several gastrointestinal dysfunctions, in addition to studies reporting the presence of LBs and LNs in the enteric nervous system (ENS) as well as in the vagus nucleus, Braak and colleagues put forward the hypothesis that α-synuclein can behave and propagate in a prion-like manner, spreading from the ENS to the DMVN via vagal pathways; the so-called gut-brain hypothesis [146, 148–150]. This evidence concerns the gene SNCA and Parkinson disease.