Moreover, intestinal inflammation and injury are strikingly pronounced prior to the onset of AD and PD, which, besides the additional inflammatory burden, induce the leakage of Aβ- and α-synuclein-like amyloids that may cross the enteric nervous system (ENS), enter the brain and stimulate cross-seeding (Ambrosini et al., 2019). Here, SNCA is linked to Alzheimer disease.