SNCA and Parkinson disease: α-Synuclein (α-syn), a 140-amino-acid presynaptic neuronal protein, is critical for synaptic function but plays a central role in PD pathogenesis due to its propensity to aggregate and form Lewy bodies, the hallmark of PD and related α-synucleinopathies, such as multiple system atrophy (MSA) and dementia with Lewy bodies (DLB) [11,17].