SNCA and Parkinson disease: By facing the gut lumen and being directly connected with alpha-synuclein positive enteric neurons (Chandra et al., 2017), the EEC might be a key component of the neural circuit between the gut lumen and the brain for the bottom-up propagation of PD pathology as initially hypothesized by Braak et al. (2006) and more recently by Borghammer and Van Den Berge (2019).