SNCA and Parkinson disease: Although most PD cases are sporadic, resulting from a complex interaction of environmental and genetic factors, rare familial forms of the disease also exist and are caused by mutations in genes such as leucine-rich repeat kinase 2 (LRRK2), α-synuclein (SNCA), PARK2 (also known as PRKN), PARK7 or PTEN-induced kinase 1 (PINK1) (Kalia and Lang, 2015; Martin et al., 2011).