SNCA and Parkinson disease: The concept of ascending development of lesions of the nervous system and frequent impairment of intestinal motility in the preclinical stage of PD have drawn attention to the important role of the gastrointestinal tract as a site of occurrence of the first inclusions of alpha-synuclein (Edwards et al., 1992; Braak et al., 2006; Sánchez-Ferro et al., 2015; Ambrosini et al., 2019).