SNCA and Parkinson disease: A critical pathological hallmark of PD is the aggregation of misfolded α-synuclein into Lewy bodies, which occurs not only in the CNS but also in the ENS.14 Braak’s hypothesis postulates that α-synuclein pathology may originate in the gut and ascend via the vagus nerve to the brainstem, suggesting a gut-to-brain axis in PD pathogenesis.15 In support of this, α-synuclein aggregates have been identified in the enteric neurons of the myenteric and submucosal plexuses, even before the onset of classic motor symptoms.