SNCA and viral infectious disease: From all the available evidence, we conclude that sporadic PD is based on different triggers with a variety of mechanisms to release the disorder: (1) multiple genetic alterations with low penetrance, (2) triggers causing either rapid onset of PD, such as MPTP, which disturbs respiratory activity and interacts with α-synuclein but does not show LB formation (3), triggers such as influenza A viral infection, which causes postencephalitic parkinsonism only years after viral infection and is without LB formation.