One other protein, i.e., α-synuclein (α-syn), has been initially associated with another well-known neurodegenerative disease, i.e., PD, along with specific neurodegenerative diseases, such as dementia with Lewy bodies (DLB); α-syn is the main component of Lewy bodies, i.e., the most evident histopathological characteristic of PD and all of the aforementioned diseases [15,16]. This evidence concerns the gene SNCA and Lewy body dementia.