SNCA and Parkinson disease: PD usually has two main features: 1) the death of dopaminergic (DA) neurons in the pars compacta of substantia nigra, and 2) misfolded α-synuclein (α-syn) accumulates in neuronal cell bodies or dendrites and axons to form Lewy bodies (LBs) or Lewy neurites (LNs) (Goedert et al., 2013).