As a consequence of these alterations, impaired SCFA balance and/or the induction of oxidative stress are considered key factors triggering α-synuclein aggregation within the ENS and its subsequent vagal translocation to the CNS, leading to the characteristic neurological alterations of PD [29,58,117,153,168,169,170,171,172] (Figure 2). The gene discussed is SNCA; the disease is Parkinson disease.