SNCA and Parkinson disease: The high occurrence of gastrointestinal dysfunction in the early stages of PD [7], coupled with increased recognition of PD gut microbiome dysbiosis [8] and repeated observations of α-synuclein pathology in the enteric nervous system (ENS) of PD patients [9,10,11,12,13,14,15,16,17,18,19,20,21,22,23], have collectively inspired great interest in the possibility that the disorder may originate in the gut.