Importantly, aggregated α-synuclein is the most abundant component of Lewy bodies and dystrophic Lewy neurites in PD brain (Spillantini et al., 1998) and is also present in Dementia with Lewy bodies (DLB) brain and can sometimes be present in Alzheimer’s disease (AD) brain alongside AD pathology (Matej et al., 2019). This evidence concerns the gene SNCA and Alzheimer disease.