α-Synuclein propagation through a gut-to-brain pathway has been modeled experimentally through injections of PFFs or human PD brain lysate into the gastric and duodenal walls; this treatment resulted in a progressive accumulation of aggregated α-synuclein in a variety of brain regions, including the DMnX and substantia nigra [17, 65, 66]. This evidence concerns the gene SNCA and Parkinson disease.