SNCA and Parkinson disease: It has long been known, thanks to the pioneering observations of Polymeropoulos and co-workers first, Spillantini and colleagues later, that Lewy bodies in PD, initially localized in the substantia nigra pars compacta, are predominantly composed of alpha-synuclein (aS) protein (Polymeropoulos et al., 1997; Spillantini et al., 1997).