SNCA and Parkinson disease: According to this theory, the dorsal nucleus of the vagus nerve and the olfactory bulb, as well as possibly the periphery from the myenteric plexus to the lower brainstem, are the sites of atypical or severe accumulation/aggregation of α-synuclein, which is a major constituent of the hallmark pathologic lesions (including Lewy bodies and Lewy neurites) and whose mutations and multiplication are interconnected to dominantly inherited PD (Rietdijk et al., 2017).