SNCA and Parkinson disease: While the principal pathology of PD involves the loss of nigrostriatal dopaminergic neurons and their efferent termini, another pathological hallmark of PD is the misfolding, oligomerization, and accumulation of alpha-synuclein (α-syn) and other proteins within nigrostriatal neurons (Fig. 1A) (Goedert et al., 2013).