The discovery that alpha-synuclein is expressed during acute and chronic gastrointestinal infection (Stolzenberg et al., 2017) along with alpha-synuclein being repeatedly shown to directly activate immune cells (Erny et al., 2015; Sampson et al., 2016; Stolzenberg et al., 2017; Sun and Shen, 2018), not only provides strong support for the theory that alpha-synuclein is involved in activating inflammation in the gut but it also offers a plausible explanation for how the presence of alpha-synuclein in the gut may contribute to PD. This evidence concerns the gene SNCA and digestive system infectious disorder.