SNCA and Alzheimer disease: The transmissibility of pathological proteins such as alpha-synuclein, beta-amyloid, tau and TDP-43 has been reported, and these proteins can be transmitted between cells in the central nervous system (CNS), propagate across species (e.g., transmitted PD-associated α-synuclein seeds could propagate in new mammal host) (119), and even spread between individuals (e.g., AD-associated pathological beta-amyloid) (122), like prions in prion diseases (122–126).