Biochemical and ultrastructural evidence suggests that aggregated/fibrillar alpha-synuclein (aSyn), encoded by SNCA, is a defining feature of Lewy pathology in PD and Dementia with Lewy bodies, as well as intraglial inclusions in Multiple System Atrophy, diseases referred to as alpha-synucleinopathies (Spillantini et al., 1997; Braak et al., 2003; Goedert et al., 2013; Lashuel, 2020). This evidence concerns the gene SNCA and dementia.