SNCA and Parkinson disease: The presence of alpha-synuclein protein (α-SYN) in pathological Lewy bodies, coupled with SNCA-associated familial forms of PD, has led to the foregone conclusion that the risk for sporadic PD at this locus is driven by a SNCA-associated mechanisms (Polymeropoulos et al., 1997; Spillantini et al., 1997; Grenn et al., 2020).