SNCA and synucleinopathy: As olfactory dysfunction appears to be more closely associated with the body-first type of alpha-synuclein propagation, the pathology primarily affecting the dorsal motor nucleus of the vagus or brainstem may impact olfactory function through the development of alpha-synucleinopathy in the bilateral olfactory bulbs or other brainstem nuclei that project to the olfactory system (Borghammer, 2021).