Intriguingly, higher levels of normal non-mutated α-synuclein protein also increases α-synuclein protein aggregation and LB formation in PD patients (Singleton et al., 2003), suggesting that slight changes in SNCA gene expression or α-synuclein protein level will trigger PD progression regardless of the mutational status of SNCA gene or α-synuclein protein. Here, SNCA is linked to Parkinson disease.