SNCA and Parkinson disease: Parkinson’s disease (PD) is the second most common neuronal degenerative disorder, with selective degeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta and the concomitant loss of nigrostriatal DAergic termini, along with the aggregation and accumulation of an intraneuronal protein complex called Lewy bodies, comprised of aggregated α-synuclein (α-syn) as the principal component.