SNCA and Alzheimer disease: The aggregation of senile plaques containing extracellular amyloid-beta (Aβ) peptide and the formation of intraneuronal tau containing neurofibrillary tangles (NFTs) in AD and the accumulation of misfolded α-synuclein (α-syn) in PD are major pathogenic features of these diseases (Bourdenx et al., 2017).