SNCA and Parkinson disease: Although Lewy body formation is not entirely understood, as well as the exact mechanisms of PD progression, they found that the dorsal motor nucleus of the vagus nerve (cholinergic neurons), raphe nuclei (RNs—serotonergic neurons), and coeruleus–subcoeruleus complex (noradrenergic neurons) were previously affected (stages 1 and 2) by a α-synuclein pathology of the midbrain area (dopaminergic neurons) (stage 3) [3].