SNCG and Parkinson disease: Abnormal accumulation of α-synuclein (α-syn) is hypothesized to underlie the dopaminergic and non-dopaminergic neuronal cell death and synaptic dysfunction leading to motor and cognitive symptoms in Parkinson’s disease (PD), PD dementia (PDD) and Dementia with Lewy Bodies (DLB)1, 2, 3, 4.